Ocean Optics 2008

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FIELD CHARACTERIZATION OF WAVE-INDUCED UNDERWATER LIGHT FIELD FLUCTUATIONS

ANTOINE, David¹; GERNEZ, Pierre¹

¹CNRS LOV, Villefranche sur mer, --, 06230, France

An extensive characterization of the amplitude and periods of the underwater light field fluctuations is presented, based on field measurements of the downward and upward irradiances taken from a mooring at a deep (>2400 m) ocean site in the north western Mediterranean Sea (BOUSSOLE site). The optical time series at this site includes multi-spectral irradiance measurements at 2 fixed depths (about 4 and 9m) as well as irradiance profiles taken from free-fall radiometers. It is already several-years long, and is paralleled by a time series of environmental parameters (wind and waves) at the same location. When pooled together, both data sets provide an opportunity to complement previous field experiments dedicated to the understanding of underwater light fluctuations, which were mostly carried out in coastal waters and essentially for the downward irradiance, by exploring more systematically the e.m. spectrum and the range of environmental parameters, such as wave heights and periods, water clarity and diffuseness of the incoming irradiance. In addition, the characteristics of the upward flux are also investigated. The behavior of the amplitude and period of the Edfluctuations is generally coherent with previous findings, although a more global picture is provided here. The most favorable conditions for focusing are for wave heights of ~ 0.5 m or for wind speeds between ~1 and 5 m s^-1. The most unfavorable conditions are for wave heights > ~1.5 m or for wind speed > 7 m s^-1. The dominant periods of the fluctuations in the upward flux are changing in parallel to those in the downward flux. The amplitude of the fluctuations in the upward flux is, however, surprisingly evolving in the opposite direction as compared to the downward flux, e.g., decreasing when the water becomes clearer.

STRUCTURE OF POLARIZATION IN AN ATMOSPHERE-OCEAN SYSTEM

Adams, James¹; Gray, Deric²

¹ISPA Technology 6495 Tayack Pl. #301, Alexandria, VA, 22312, United States; ²Naval Research Laboratory, Code 7333, Stennis Space Center, Mississippi, 39529, United States

The scattering of sunlight in the atmosphere and ocean creates light fields with complex angular structures. We can describe the light field at any point in the atmosphere-ocean system by using Stokes Vectors to express the full radiance in any direction. We have simulated the light field at multiple locations in this system for observers above and beneath the ocean surface under a variety of conditions that include the presence of continental and marine hazes above the ocean, and the presence of hydrosols in the ocean. The results of these simulations are given by displaying the structure of the individual Stokes Vectors for all observation angles as well as the appearance of secondary quantities including the degree of linear polarization, degree of circular polarization, and ellipticity of the scattered light. We further relate key indicators such as the position of points of maximum and minimum linear polarization to scattering conditions and show how they may be used as a tool in remote sensing.

LISST-BACK OBSERVATIONS OF NEAR-PI SCATTERING: STUDIES ON CONTRAST BETWEEN MONO-DISPERSE SPHERES AND RANDOM SHAPED GRAINS

Agrawal, Yogi¹; Boss, Emmanuel²; Mikkelsen, Ole³

¹Sequoia Scientific, Inc. 2700 Richards Road, Suite 107, Bellevue, WA, 98005, United States; ²School of Marine Sciences, Orono, Maine, 04469, United States; ³2700 Richards Road, Suite 107, Bellevue, WA, 98005, United States

Backscattering near-pi is an important input to radiative transfer models used to study and interpret LIDAR data. A new instrument, the LISST-BACK, has been developed for the measurement of near-pi scattering of laser light. The instrument employs a 532 nm doubled-YAG laser, a CMOS array detector and optics similar to those used by Maffione and Honey (SPIE v.1750; 1992) and earlier by Kuga and Ishimaru (App. Opt. 1989). A key difference is that the present instrument incorporates a finite beam path of 20 cm so that studies of vertical variability of near-pi scattering may be observed. Further, the instrument measures beam attenuation, so that indirect estimates of c (Maffione and Honey, 1992) are not necessary. Here we describe the instrument and calibration tests performed with polystyrene beads, including measurements that reveal azimuthal variations consistent with the model of Pal and Carswell (App.Opt. 1985) and others. The instrument was deployed in a bottom boundary layer (BBL) experiment off the coast of Martha’s Vineyard, Massachusetts. Near-pi backscattering data from the BBL are compared with very sparse prior results. The observations reveal very little angular structure in the backscattering near pi. In contrast, Mie theory prediction using particle size distribution data from a nearby LISST-100X instrument suggests that a highly oscillatory structure in angular scattering should exist. It is suggested that this difference between observed near-pi scattering and prediction based on Mie theory is due to shape effects. Experiments with random shaped grains from an ISO standard dust sorted in a stratified settling column were conducted and their near-pi scattering is contrasted with equal size glass beads to illustrate shape effects. This study constitutes an effort toward replacing Mie theory to predict backscattering from measured size distributions, for LIDAR or remote sensing.

USE OF MODIS OCEAN COLOR IMAGERY FOR IMPROVED DETECTION AND MONITORING OF KARENIA BREVIS BLOOMS IN THE GULF OF MEXICO

Amin, Ruhul¹; Zhou, Jing¹; Gilerson, Alex ¹; Gross, Barry¹; Moshary, Fred¹; Ahmed, Sam¹

¹140 St @ Convent Ave, New York, NY, 10031, United States

Karenia brevis (K. brevis) blooms are of great interest and have been commonly reported throughout the Gulf of Mexico. However, detection still remains a challenge from space with standard bio-optical algorithms due to the uncertainty of atmospheric correction, and interference from high concentrations of organic and inorganic materials in optically complex coastal waters. We propose a simple normalized difference technique, which for convenience we call the K. brevis bloom index KBBI = (Rrs(678)-Rrs(667))/ (Rrs(678)+Rrs(667)), capable of detecting potential areas of K. brevis blooms from MODIS ocean color measurements. This index takes advantage of low backscattering efficiency of K. brevis. Remote sensing reflectance has a local minimum around 667nm (MODIS band 13) which is less than the signal at 678nm (MODIS band 14) when chlorophyll fluorescence is a significant fraction of water leaving radiance in the red bands; this increases the KBBI numerator. At the same time, lower reflectance values reduce the index denominator. As a result, the KBBI as a function of chlorophyll concentration for K. brevis differs from the similar function for the non- K. brevis blooms allowing K. brevis bloom detection to be more accurate and reliable. To assess the index, simulations including chlorophyll fluorescence based on the non-K. brevis bloom and K. brevis bloom were performed to determine the threshold of the detection conditions for possible K. brevis bloom using this technique. The approach was successfully applied to well documented blooms of K. brevis in the Gulf of Mexico and compared to other detection techniques, including FLH. Initial comparison indicates that this technique is generally capable of defining the area of K. brevis blooms more precisely and with fewer false alarms in the highly scattering and/or CDOM rich waters.

GOCI DATA PRE-PROCESSING METHODS

Ahn, Yu-Hwan¹; Shanmugam, Palanisamy ¹; Jeong, Han-Hee¹; Cho, Seongick-Raymond ¹

¹Korea Ocean Research and Development Institute Ansan P.O. Box. 29, Seoul, --, Seoul 425-600, Korea, Republic of

Korea’s Geostationary Ocean Color Imager (GOCI), designed to be operated in a staring-frame capture mode on board its Communication Ocean and Meteorological Satellite (COMS), is tentatively scheduled for launch in 2008. To provide an important new capability for imagining the coastal zone where the phenomena varying on shorter space and time scales demand a simultaneous increase in spatial and temporal resolution, the GOCI mission concept includes eight visible-to-near-infrared bands, a 500m×500m pixel resolution, and a coverage region of 2500m×2500 km centered at 36N and 130E. GOCI will provide multiple views of many locations within the fixed region during a single day (i.e. 8 images during the daytime and 2 images during the nighttime). The data from GOCI will therefore address various research areas in coastal, oceanographic and atmospheric sciences. In this paper, we present the GOCI data pre-processing methods for radiometric calibration, atmospheric correction and removing bidirectional effects. The GOCI radiometric calibration consists of three parts; on-ground calibration, in-orbit calibration, and ground processing. The radiometric response of the GOCI is characterized through on-ground calibration. The change of radiometric response is corrected by in-orbit calibration using the on-board calibration devices (solar diffusers). The radiometric models include the linear gain, non-linear gain, offset terms and integration time for calibration. Atmospheric correction is the key procedure as it removes about 80-90% of the top-of-atmospheric signal recorded by GOCI. Here we use the standard and regional atmospheric correction schemes to process GOCI data. Since the radiance observed from the ocean depends on the illumination and viewing geometry along with the water properties (this variation is called the bidirectional effect), we use a practical method developed by Morel et al. (1996), which quantifies systematically the variations of spectral radiances emerging from an ocean with varying chlorophyll, to remove the bidirectional effect from GOCI data. The results of these GOCI data pre-processing methods are presented and the errors are analyzed in this study.

EXTENDING THE SATELLITE SURFACE OPTICS TO DERIVE THE 3D OPTICAL FIELD BY DEFINING THE UNCERTAINTY OF PHYSICAL – OPTICAL RELATIONSHIPS

Arnone , Robert ¹; Casey , Branndon ²; Ko, Dong S³; Ladner, Sherwin ²; Flynn, Peter ¹; Rowley, Clark ³; Gould , Richard ¹

¹NRL NRL, Code 7330 - Ocean Sciences Branch , SSC, MS, 39529, United States; ²PSI, SSC, MS, 39529, United States; ³NRL Code 7320, SSC, MS, 39529, United States

Subsurface optical properties can be substantially different from the surface optical properties that are traditionally defined using satellite ocean color. We developed a method to vertically extend the satellite optical properties though relationships of physical and optical properties. Circulation models provide hindcast and forecast of the physical ocean properties, such as the temperature, salinity and current properties using advanced data assimilation. These physical properties such as the mixed layer depth (MLD) and the degree of stratification (IMLD) are many times coupled to the optical layers such as the chlorophyll maximum and the subsurface light field (1% light field).

The subsurface optical layers can be parameterized using a Gaussian profile shape which is constrained by 1) surface satellite optics at the surface 2) physical characteristics MLD and IMLD and 3) 1% light level. Using these constraints, we optimize the vertical profile shape based on insitu observations (gliders, profiles etc.) to determine optimal coefficients to define these physical – optical relationships for a Gaussian profile shape.

The optimized coefficients are used to derive the regional 3d optical field for satellite optical imagery combined with physical properties from circulation models. The uncertainty of the 3d optical field is defined by the variability of the optimized coefficients which represent the physical – optical relationships. We characterize the uncertainty of the 3d structure by creating ensembles of 3d profiles using variations in the optimized coefficients.

The results provide a unique method to combine satellite optical properties, insitu optical and physical measurements and ocean circulation models to represent the 3d bio-optical properties with some estimate of the uncertainty.

INFLUENCE OF PHYTOPLANKTON BLOOMS ON THE SPECTRAL SLOPE OF CDOM IN BELGIAN AND ADJACENT WATERS (SOUTHERN NORTH SEA).

Astoreca, Rosa¹; Rousseau, Véronique¹; Lancelot, Christiane¹

¹Université Libre de Bruxelles, Ecologie des Systèmes Aquatiques Campus Plaine - CP 221, Boulevard du Triomphe, Brussels, --, B-1050, Belgium

Analysis of a large dataset of Coloured Dissolved Organic Matter (CDOM) measurements performed in estuarine (Scheldt) and coastal (Belgian and adjacent) waters during different seasons revealed a larger variability of the slope of the CDOM absorption curve (S) in marine waters than in the estuarine area. The comparison between the CDOM absorption at 442 nm and S shows different relationships for offshore, coastal marine and estuarine waters. In order to explore the possible role of phytoplankton and derived matter in this variability, we compared S values obtained for different periods of the phytoplanktonbloom development (growth and post-bloom). Significant differences in S are found in years with intense blooms only, suggesting the post-bloom production of autochthonous CDOM. In addition we show that the interannual variability of S varies yearly according to intensity of the bloom.

SOLAR IRRADIANCE IN CORAL REEFS: CDOM AS A PHOTOPROTECTIVE BARRIER FROM UVR

Ayoub, Lore Michele¹; Coble, Paula G¹; Hallock, Pamela¹

¹University of South Florida 140 Seventh Avenue South, Saint Petersburg, FL, 33701, United States

Experiments have demonstrated that corals and reef-dwelling foraminifera bleach more readily when exposed to short wavelength, high energy solar radiation (blue, violet and ultraviolet; λ ~ 280 - 490 nm). In seawater, colored dissolved organic matter (CDOM), also called gelbstoff, preferentially absorbs these shorter wavelengths, which consequently bleach and degrade the CDOM. Alteration and destruction of watershed and coastal wetlands have reduced natural sources of CDOM that are tidally flushed into reefal waters. We have measured incident and in situ ultraviolet radiation (UVR) and absorption of UVR at various reefs in the Florida Keys that differ in distance from shore and in the degree of anthropogenic development, intact mangrove hammock, and CDOM-rich Everglades-sourced Florida Bay water of the adjacent shoreline. Onshore-offshore transects from a mangrove-lined canal, across a patch reef and reef margin to deep (blue) water, showed a steady decrease in absorption due to CDOM. Absorption due to CDOM at 320 nm (a_g320) was significantly higher and less variable, and spectral slope of CDOM absorption in the UVB range, S_{(280-312 nm)}, was significantly lower and less variable at reefs associated with intact shorelines and at reefs with consistent CDOM sources. Attenuation coefficient for downwelling irradiance, K_d, was calculated from in situ downwelling irradiance (E_d) (BIC Biospherical Instruments^©) at 3 wavelengths in the UV range (305, 330 and 380 nm) and PAR (400-700 nm). K_{d 305} and K_{d 330} were significantly higher at inshore reefs than offshore reefs. These results can provide guidance to resource managers regarding management of CDOM sources to reefal waters, including preservation of tidal wetlands, ground-truthing inherent optical properties, and basis for developing a new algorithm for UVR and for a_{g UV} based on satellite-derived measurements of a_{g PAR}.

ABSORPTION SIGNATURES OF PRIMARY PRODUCTION AND PHYTOPLANKTON PIGMENTS IN THE AGULHAS AND BENGUELA ECOSYSTEMS

BARLOW, RAY¹; Lamont, Tarron¹; Kyewalyanga, Margareth²; Sessions, Heather¹

¹Bayworld Centre for Research & Education 5 Riesling Road, Constantia, Cape Town, --, 7806, South Africa; ²Institute of Marine Sciences, Stone Town, Zanzibar, ------, Tanzania, United Republic of

Investigations of primary production, phytoplankton pigments and absorption properties were conducted during four research cruises on the continental shelf around southern Africa. The Benguela ecosystem is characterized by wind-driven upwelling processes across a broad shelf, while the Agulhas ecosystem is driven by shelf-edge current and eddy flow entraining nutrients onto a narrow shelf. Chlorophyll a concentrations ranged from 1-30 mg m^-3 and photosynthetic rates from 3.2-105.3 mg C m^-3 h^-1 on the Benguela shelf. For the Agulhas system, chlorophyll a concentrations ranged from 0.5-4 mg m^-3 and photosynthetic rates from 0.9 to 20.3 mg C m^-3 h^-1. Daily integrated production varied from 0.8-8.7 g C m^-2 d^-1 and 0.3-3.7 g C m^-2 d^-1 for the Benguela and Agulhas systems respectively. Data from within the upper 10 m were synthesized to examine the relationships between absorption, pigments and productivity, and assess the utility of absorption-based measurements for environmental monitoring. The slope of the linear regression of photosynthesis versus chlorophyll a yielded an assimilation number of 4.23 mg C (mg Chl)^-1 h^-1. The spectrally averaged (400-700 nm) phytoplankton absorption coefficient (a_ph) varied between 0.02 and 0.34 m^-1 and the regression of photosynthesis versus a_ph yielded a positive slope with 63% of the variance being explained. The power relationships between absorption and chlorophyll a for the blue and red maxima (a440; a676) displayed positive functions similar to those reported for other oceanic areas. Trends between a_ph and chlorophyll a, photosynthetic pigments and total pigments were also examined and found to yield positive power functions where 86-90% of the variance was explained. The results suggested that phytoplankton absorption maybe very useful for predicting primary production and phytoplankton pigments in the Agulhas and Benguela ecosystems, with potential application for remote sensing and in situ monitoring.

ARE THE NORTHERN BALTIC SEA WATERS EVEN BLACKER ?

BERTHON, Jean-François¹; Zibordi, Giuseppe¹; Canuti, Elisabetta¹; Kaitala, Seppo²; Seppälä, Jukka²; Ylöstalo, Pasi²

¹Joint Research Centre Via Fermi, Ispra, --, 21027, Italy; ²Finnish Institute of Marine Research, Helsinki, Helsinki, 00561, Finland

The Baltic Sea is well known for the strong light absorption by coloured dissolved organic matter (“CDOM”) in the blue part of the visible spectrum, which leads to an important decrease of the surface reflectance from the green to the blue. This classical definition of the optical properties of the Baltic Sea mainly refers to the well sampled southern Baltic Proper. Typically, in those waters the amount of CDOM is also associated with a relevant amount of particles and a positive correlation between them can be observed. Based on a unique bio-optical data set recently acquired, this study aims at presenting very peculiar optical properties observed in the northern Baltic Sea (from the Baltic Proper to the “almost fresh” waters of the northern Gulf of Bothnia, including the Gulf of Finland and Gulf of Riga). In particular, variations of the b/a ratio at 412nm from >1.5 in the Baltic Proper to less than 0.3 in the northern Gulf of Bothnia are reported. The latter value corresponds to relatively high absorption by CDOM (>1 m^-1) inversely correlated with the concentration of particles and scattering (TSM≈0.5 gm^-3, bp(412)<0.5 and bbp(442)<0.007 m^-1). This allows for a very good representation of the beam attenuation spectral dependency through a decreasing exponential fit. Surface irradiance reflectances at 412nm of these “black waters” are close to 0.001 and the reflectance ratio R(555)/R(412) reaches the value of 9 (against 3 in the Baltic Proper).

These peculiar optical properties are discussed with reference to a large and consistent bio-optical data set previously collected in the southern Baltic Proper (including Gdansk Bay and Pomeranian Bay). The study suggests that the northern Baltic Sea (in particular the northern Gulf of Bothnia) could constitute a separated bio-optical province for remote sensing applications. Further investigations should help confirming such a statement.

A LIGHT ABSORPTION BUDGET FOR SOUTH PACIFIC WATERS

BRICAUD, Annick¹; BABIN, Marcel¹; CLAUSTRE, Hervé¹; RAS, Joséphine¹; TIECHE, Fanny¹

¹Laboratoire d'Océanographie de Villefranche BP 08, Villefranche-sur-Mer, --, 06238, France

The relative contributions of phytoplankton, non-algal particles and colored dissolved organic matter (CDOM) to total light absorption, and their variability, are essential information for bio-optical and biogeochemical models. They remain, however, poorly documented in the open ocean, particularly in clear waters because of the difficulty in measuring very low absorption coefficients. The BIOSOPE cruise (October-December 2004), from Marquesas Islands to Concepcion (Chile), investigated a large range of oceanic regimes from hyper-oligotrophic waters in the sub-tropical gyre, to eutrophic waters in the upwelling area off Chile. The spectral absorption coefficients of phytoplankton and non-algal particles were determined using the classical filter technique, while the CDOM absorption coefficients were measured using a spectrophotometer equipped with a 2-m capillary waveguide (UltraPath, WPI Inc.). Over the whole transect, the absorption coefficients of both dissolved and particulate components covered approximately two orders of magnitude, and in the gyre, they were among the lowest ever reported for open ocean waters. In the oligotrophic and mesotrophic waters, absorption coefficients of phytoplankton were notably lower than those measured in other oceanic areas with similar chlorophyll contents, indicating some deviation from the standard chlorophyll-absorption relationships. The contribution of absorption by non-algal particles to total particulate absorption showed large variations, not only along the vertical but also horizontally, ranging in the surface layer from 10-15% (at 440 nm) in the upwelling area to around 50% in the clearest waters. The slopes of absorption spectra of non-algal particles revealed structured spatial variability. The contribution of CDOM to total absorption showed also structured variations both along the vertical and along the transect, ranging within the surface layer from 25-40% (at 440 nm) in the upwelling area to more than 70% in the gyre. Finally, some features on absorption spectra of phytoplankton and CDOM were observed and will be discussed.

LIGHT-DRIVEN CARBON FLUXES IN THE ARCTIC OCEAN: THE BALANCE BETWEEN PHOTO-OXIDATION AND PHOTOSYNTHESIS IN THE CONTEXT OF CLIMATE CHANGE

Simon, Bélanger¹; Babin, Marcel²

¹Département de biologie, chimie et géographie, Université du Québec à Rimouski, Rimouski, Québec, G5L 3A1, Canada; ²CNRS - Villefranche LOV, BP 8, Villefranche-sur-Mer Cedex, --, 06238, France

Primary production and CDOM photo-oxidation have opposing impacts on carbon fluxes in the ocean. The balance between the two processes may be significantly affected in the near future by climate change. This is especially true for the Arctic Ocean, which is increasingly exposed to light as perennial ice recedes, and which receives increasing amounts of terrigenous dissolved organic matter (tDOM) as the permafrost thaws and river discharges increase. In this study, we used remote sensing data to estimate the pan-Arctic distributions of primary production and CDOM photo-oxidation, and how they evolved from 1998 to now. Ocean color (merged data from SeaWiFS, MERIS and MODIS), ozone, cloud (ISCCP) and ice (SSMI) data are combined to run a UV-visible atmospheric radiative transfer code, and primary production and photo-oxidation models. We used state-of-the-art optical models for Case 2 waters, some being specific to the Arctic Ocean. A sensitivity analysis is conducted to assess the impact of chosen ocean color algorithms and of various model parameters on results. Our results provide the first pan-Arctic combined estimates of primary production and CDOM photo-oxidation based on remote sensing, and allow determining how these two processes compare. They indicate that CDOM photo-oxidation accounts for a major fraction of allochthonous organic carbon mineralization in the Arctic Ocean, and is comparable in magnitude to the fraction of gross primary production that ends up sequestered within the ocean bottom sediments. The ratio between photo-oxidation and primary production turns out being highly variable, which indicates significant competition for light between CDOM and phytoplankton. As a response to sea ice decline, both photo-oxidation and primary production showed increasing trends from 1998 to 2007. We speculate that the increasing photomineralization of tDOM is boosting the productivity of whole microbial communities and the food-web dynamics of the Arctic Ocean coastal.

ON THE MECHANISMS OF THIN LAYER FORMATION: EVIDENCE FROM CHALK-EX

Balch, William M.¹; Plueddemann, Albert J.²; Bowler, Bruce C.¹; Drapeau, David T.¹

¹Bigelow Laboratory for Ocean Sciences 180 McKown Point Road, W. Boothbay Harbor, ME, 04575, United States; ²Woods Hole Oceanographic Inst., Woods Hole, MA, 02543, United States

The fate of particles in the mixed layer is of great relevance to the global carbon cycle as well as to the propagation of light in the sea. We conducted four manipulative field experiments called “Chalk-ex” in which known quantities of uniform, calcium carbonate particles were injected into the surface mixed layer. Since the production term for these patches was known to high precision, the experimental design allowed us to focus on terms associated with particle loss. The mass of chalk in the patches was evaluated using the well-calibrated light scattering properties of the chalk plus measurements from a variety of optical measurements and platforms. Patches were surveyed with a temporal resolution of hours, over spatial scales of tens of kilometers. Our results demonstrated exponential loss of the chalk particles with time from the patches. There was little optical evidence for rapid sinking of the chalk. Instead, horizontal eddy diffusion appeared to be the major factor affecting the dispersion of the chalk to concentrations below the limits of detection. There was unequivocal evidence of subduction of the chalk along isopycnals and subsequent formation of thin layers. Shear dispersion is the most likely mechanism to explain these results. Calculations of horizontal eddy diffusivity were consistent with other mixed layer patch experiments. Our results provide insight into the importance of physics in the formation of sub-surface particle maxima in the sea, as well as the importance of rapid coccolith production and critical patch size for maintenance of natural coccolithophore blooms in nature.

MONITORING THE PARTICULATE AND DISSOLVED MATERIALS IN THE PENOBSCOT ESTUARY

Barnard, Andrew H¹; Roesler, Collin²; Orrico, Cristina M¹; Aiken, George³; Huntington, Tom⁴; Franklin, Heidi²

¹WET Labs PO Box 518, Philomath, OR, 97370, United States; ²University of Maine, Walpole, ME, 04573, United States; ³US Geological Survey, Boulder, CO, 83303, United States; ⁴US Geological Survey, August, ME, 04330, United States

High resolution temporal and spatial hydrographic and optical observations from moored, surface underway and undulating platforms have been used to identify and quantify specific optical and chemical characteristics of the colored particulate and dissolved fractions transported through the Penobscot River system to the coastal regions of the Gulf of Maine. We examined the relationship between the dissolved matter fluorescence as a function of salinity, and found that it is not conserved during any time of the year, regardless of total concentration. Data suggest that a specific geographic location, as opposed to an isohaline, appears to be a source of fluorescent DOM or that there is in situ transformation of nonfluorescent DOM to fluorescent DOM. This particular location in the estuary as a site of very high particle concentration suggesting there may also be some interplay between the particulate and dissolved fractions at work. In order to resolve the dynamics of DOC and POC transformations, we recently installed a small mooring system within the upper Penobscot Bay. This mooring is providing real-time observations of the surface water physical (temperature, conductivity, pressure, dissolved oxygen), chemical (nitrate) and optical (chlorophyll, cDOM fluorescence and backscattering) properties. We present initial data from this mooring, as well as initial modeling results of estimating DOC flux using this data.

COMPREHENSIVE OPTICAL MERGE PROCESSING AND ACQUISITION SOFTWARE SYSTEM (COMPASS) FOR COMPREHENSIVE USER CORRECTION OF WET LABS ABSORPTION AND ATTENUATION DATA.

Bell, Jethro¹; Twardowski, Michael²; Moore, Casey¹; Barnard, Andrew H¹

¹WET Labs PO Box 518, Philomath, OR, 97370, United States; ²WET Labs, Narragansett, RI, 02882, United States

The Comprehensive Optical Merge Processing and Acquisition Software System (COMPASS) is designed to provide an integrated and comprehensive software utility for providing optically corrected absorption and attenuation (AC) data from either the WET Labs AC-9 and AC-S spectral and hyperspectral absorption and attenuation meters. COMPASS operates both in real-time data acquisition mode and as a post processing software program. In real-time mode AC data can be viewed as a function of wavelength, depth profile, or both simultaneously. The post processing component of COMPASS accepts various file formats such as text or binary, collected using a serial communications program and other data logging tools. Default settings provide the user data correction capabilities based on the methods specified by Zaneveld et al. 1994. For temperature and salinity correction, COMPASS will import and merge conductivity, temperature and depth (CTD) data if available. Default temperature salinity corrections are defined by values contained in the factory device file. The user can track and correct for the effect of a clean water blank, collected in the laboratory. Data is output from COMPASS as merged text files, with a history of corrections, applied to the data, contained as part of the header information file for correction tracking. Additional features of the post-processing mode, include the ability of the user to zoom or mine AC data for features of interest, modification of the graph settings to produce and export publication-quality figures.

OCEAN COLOUR, BIO-OPTICS AND HARMFUL ALGAL BLOOMS: A GEOHAB PERSPECTIVE

Bernard, Stewart¹; Babin, Marcel²; Kudela, Raphael³; Allen, Icarus⁴

¹GEOHAB SSC and CSIR 11 Jan Cilliers Street, Stellenbosch, --, 7599, South Africa; ²GEOHAB SSC & Laboratoire d'Océanographie de Villefranche, CNRS & Univ. Pierre et Marie Curie (Paris VI), Villefranche-sur-Mer, Provence-Alpes-Cote d'Azur, 06238, France; ³GEOHAB SSC & Ocean Sciences & Institute for Marine Science, University of California Santa Cruz, 1156 High Street, Santa Cruz , CA, 95064, United States; ⁴GEOHAB SSC & Plymouth Marine Laboratory, Prospect Place, Plymouth, Devon, PL1 3DH, United Kingdom

The GEOHAB programme seeks to address the development of improved remote observation systems for harmful algae: identifying gaps in knowledge, and stimulating development and improved application of relevant techniques. Ocean colour remote sensing has demonstrated considerable potential for the observation of harmful algal blooms (HABs). However, there are still fundamental problems with the application of rigorous ocean colour techniques in optically complex coastal waters. The high levels of uncertainty currently associated with coastal products compromise many HAB applications seeking to make use of remotely sensed data e.g. bloom detection and tracking, empirical ecological studies, and coupled ecological-hydrodynamic models. The challenges facing ocean colour based harmful algal applications are reviewed here, using studies from a variety of coastal ecosystems. Atmospheric correction schemes considered suitable for the open ocean often perform poorly in turbid, atmospherically complex coastal waters, where a lack of suitable validation data hampers improvement. In addition, the often high biomass associated with many HAB events, and Case-2 water problems, lead to the failure of standard ocean colour products. Better coastal data and new specific products are needed, and some new approaches are discussed - fluorescence line height, and analytical and red wavelength based algorithms. HAB detection places rigorous demands on our understanding of causal processes; radiative transfer and empirical studies examining the potential and problems for the detection of algal community change in different systems are discussed. In situ bio-optical instrumentation similarly has considerable potential in harmful algal focused observations systems, and HAB applications are often used as development and marketing motivators. However, there is a need for robust, inexpensive instrumentation that can be easily implemented by coastal groups globally, and potential approaches for achieving this are discussed.

PHYTOPLANKTON BIO-OPTICAL MODELS USING POPULATIONS OF TWO-LAYERED SPHERES

Bernard, Stewart¹; Probyn, Trevor ²; Shillington, Frank³

¹Council for Scientific and Industrial Research 11 Jan Cilliers Street, Stellenbosch, --, 7599, South Africa; ²Marine and Coastal Management, Bag X1, Roggebaai, Cape Town, Western Cape, 8001, South Africa; ³University of Cape Town, Private Bag, Rondebosch, Cape Town, Western Cape, 7701, South Africa

Inherent optical property and reflectance inversion models are presented, using a two-layered spherical geometry and equivalent size distribution scheme to simulate the optical properties of phytoplankton populations. The two-layered geometry is chosen as the simplest heterogeneous structure potentially capable of simulating algal angular scattering properties. Simple, single cell models are used to demonstrate the optical effects of varying cellular geometry, chloroplast volume and complex refractive index. The approach is expanded to polydispersed populations using equivalent size distribution models to demonstrate variability in simulated inherent optical properties for phytoplankton assemblages of changing dominant cell size and functional type. This algal population model is then used as a component of a forward reflectance model to compare modeled and measured reflectance data from high biomass blooms in the Benguela system. The approach is expanded to construct reflectance inversion algorithms for use with data from hyper-spectral in water reflectance, and multi-spectral satellite derived ocean colour. Preliminary validation, with an independent bio-optical data set from the southern Benguela, shows the algorithm capable of deriving Chl a concentrations through several orders of magnitude and an algal size descriptor under high biomass conditions. Algorithm performance is used to to briefly discuss returned phytoplankton backscattering characteristics. Finally, the algorithm is used with data from the MERIS sensor during several high biomass algal bloom events in the Benguela system to demonstrate potential utility for monitoring algal dynamics and detecting harmful algal blooms.

DYNAMICAL INTERPOLATION OF THE OCEAN COLOR IMAGES USING COUPLED PHYSICAL, BIOLOGICAL AND OPTICAL MODEL

Besiktepe, Sukru Turan¹

¹NATO Undersea Research Centre Viale S. Bartolomeo 400, La Spezia, --, 19126, Italy

Collocated physical and biogeochemical observations at near

synoptic resolution during the Spring of 2001 in a region of

the South West Black Sea overlapping coastal and deep waters

across the Rim current are combined with remotely sensed

data (AVHRR, MODIS, T/P), and historical data to generate

four dimensional physical and ecological fields via a

coupled physical and biogeochemical models of the Harvard

Ocean Prediction System with sequential data assimilation.

The dynamical model employed here is the Harvard Primitive

Equation Model. The bio-chemical model coupled to physical

model includes phyto-plankton, zoo-plankton, detritus, nitrate,

ammonium and Chlorophyll. The propagation of light in the water

column as well as the utilization of that light by the phytoplankton

are linked with a full spectral irradiance model coupled

with a spectral absorption-based photosynthesis model.

The model calibrated and validated for the Southwetern Black Sea and

then used for data driven simulations. MODIS derived chlorophyll-a

data assimilated into the model together with in-situ chlorophyll-a

measurements which allows dynamical interpolation of the satellite derived

chlorophyll-a in which regions with missing data due to the cloud

covers was filled. Furthermore, 3-d daynamical model also allows

extensions of the surface values obtained by satellites to subsurface.

Therefore accurate and realistic four dimensional chlrophyll fields based

upon satellite and near synoptic observations constructed.

SUBTROPICAL OCEAN ECOSYSTEM STRUCTURE CHANGES FORCED BY NORTH PACIFIC CLIMATE VARIATIONS

Bidigare, Robert Richard¹

¹University of Hawaii 1680 East-West Road, POST 105, Honolulu, HI, 86822, United States

Potential biological responses to basin-scale climate forcing in the subtropical North Pacific Ocean are assessed based on temporal variations in plankton community structure observed at Station ALOHA and results of a coupled physical-biogeochemical model. Observational data and model simulations for the period 1990-2004 reveal distinct temporal patterns, with significant increases in net primary productivity, modeled nitrate flux and measured particulate nitrogen flux during 1999-2004. Concurrent increases in microalgae, cyanobacteria and modeled zooplankton biomass were also observed during this period, with a 2-year lag in the measured mesozooplankton biomass response. We provide evidence that these responses were a consequence of climate forcing that destratified the upper ocean, making it more susceptible to mixing events and nutrient entrainment. These findings underscore the importance of plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time-scales.

TURBULENT OCEANIC FLOW – AN OPTICALLY ACTIVE MEDIUM

Bogucki, Darek¹; Woods, Sarah¹; Freda, Wlodzimierz²

¹RSMAS, University of Miami 4600 Rickenbacker Causeway, Miami, FL, 33149, United States; ²Gdynia Maritime University/Physics Department/Gdynia, Gdynia, Pomorskie, 81-225 , Poland

Turbulent inhomogeneities of fluid flow have the effect of scattering light into near-forward angles.

In laboratory and in situ experiments we have examined the value and angular dependent contribution of the turbulent scattering coefficient b_turb as a function of turbulence strength. The b_turb can attain values as high as 10 [1/m] for some oceanic conditions such as near the ocean surface and values as low as 0.1 [1/m] at depth.

This ubiquitous presence of turbulent scattering has implications for oceanic measurements as well as for remote sensing applications.

MASS NORMALIZED OPTICAL PROPERTIES. WHY ARE THEY SO CONSTANT?

Boss, Emmanuel¹; Slade, Wayne Homer¹; Hill, Paul²

¹University of Maine 5706 Aubert Hall, Orono, ME, 04469-5706, United States; ²Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada

Recent analysis of scattering and beam attenuation normalized to particulate mass (PM) suggest they are much more constant than Mie theory would predict. We build upon the pioneering studies of Baker and Lavelle, 1984, JGR, who investigated the effect of particle size on mass normalized beam attenuation and Babin et al, 2003, L&O, who investigated the effect of composition on mass normalized scattering coefficient, by adding the effects of shape and aggregation. We find that adding shape and aggregation significantly reduce the variability in PM normalized optical properties. We also showcase a relatively novel data set collected by the Alliance of Coastal Technology, to assess which current commercially available optical method (beam attenuation, side scattering and backscattering) is superior in predicting PM. Results suggest, surprisingly, that backscattering is a superior method to predict PM. We attempt to explain these results with respect to both theory and biogeochemistry.

SEASONAL VARIATIONS IN THE OPTICAL AND PHOTOSYNTHETIC CHARACTERISTICS OF A COASTAL INLET

Bouman, Heather¹; Platt, Trevor²; Sathyendranath, Shubha³

¹Oxford University Dept of Earth Sciences, Oxford University, Parks Rd, Oxford, --, OX1 3PR, United Kingdom; ²Bedford Institute of Oceanography, Dartmouth, Nova Scotia, B2Y 4A2, Canada; ³Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, United Kingdom

Coastal ecosystems are subject to high levels of anthropogenic activity and therefore play an important role in issues of resource management. Continual monitoring of these waters is necessary to assess how human activity impacts the structure and function of these ecosystems and to estimate year-to-year fluctuations in their productivity. In situ optical sensors provide scientists with the potential of continual monitoring of changes in the ecological status of coastal waters over a range of spatial scales. By virtue of their close proximity to land, coastal waters are heavily influenced by optical components that are terrestrial in origin, which make the task of estimating the spectral quality and quality of irradiance available for photosynthesis difficult.

In this study, optical and photosynthetic characteristics of a coastal embayment (Bedford Basin, Nova Scotia) were measured with a nominal sampling frequency of once per week. Variability in the spectral shapes and magnitudes of absorption by CDOM, detritus and phytoplankton are assessed and their relationships with the physico-chemical and biological properties of the water column are examined. The influence of CDOM and phytoplankton absorption on the diffuse attenuation coefficients of spectral downwelling irradiance is discussed. In addition, changes in the photosynthetic properties of the phytoplankton community as they relate to variation in the optical and physical characteristics of the basin are explored. The implications of these findings for modelling primary production in coastal environments will also be addressed.

PHYTOPLANKTON LIGHT ABSORPTION PROPERTIES IN THE ARCTIC REGIONS: A GLOBAL VIEW

Bourgault Brunelle, Corinne¹

¹Institut Maurice Lamontage (IML) 845 Beauregard app.4, Québec, --, G1V 4P4, Canada

Corinne-Bourgault-Brunelle (presenter), ISMER, 310 allée des Ursulines, Rimouski, Québec, Canada G5L 3A1

Pierre Larouche, Institut Maurice-Lamontagne, Pêches et Océans Canada, BP 1000, Mont-Joli, Québec, Canada G5H 3Z4

David Doxaran and Marcel Babin, Laboratoire d’Océanographie de Villefranche, UMR 7093-CNRS/UPMC, BP 8, 06238 Villefranche-sur-Mer Cedex, France

ABSTRACT

The Arctic Ocean is currently experiencing major ecosystem changes due to the accelerated decline of its summer sea ice cover. This is virtually opening a whole new ocean for phytoplankton to grow. Due to its remoteness, this region is however hard to sample using traditional ship-based approaches. Remote sensing appears as a promising way to monitor the ecosystem changes that are likely to occur with the shrinking sea ice cover.

Remote sensing of phytoplankton biomass and of derived products such as primary production are fundamentally determined by the inherent optical properties of phytoplankton, dissolved matter and non algal particles. Previous studies conducted in arctic coastal waters showed that current operational algorithms were generally overestimating chlorophyll concentrations due to the presence of dissolved and suspended matter and because of significant pigment packaging in the arctic phytoplankton species.

The light absorption capacity of phytoplankton (a_ph) is thus the key to the accurate monitoring of possible climate change effects in the Arctic Ocean. To evaluate this parameter for arctic waters, we thus gathered a new set of measurements of a_ph as part of a series of expeditions: the Canadian Arctic Shelf Exchanges Study (CASES) field program conducted in 2003 and 2004; the Circumpolar Flaw Lead study in 2007-08, the 2005 and 2007 Arcticnet cruises, and finally the Nansen Amundsen Basin Observing System cruise in 2007.

These cruises sampled the major coastal regions surrounding the Arctic central basin: the eastern Beaufort Sea, the northern Baffin Bay, the Canadian archipelago, and the Laptev Sea. The presentation will describe the spatial and temporal variability of a_ph and evaluate its similitude with the database covering the southern waters.

PHYTOPLANKTON LIGHT ABSORPTION PROPERTIES IN THE ARCTIC REGIONS: A GLOBAL VIEW

Bourgeault-Brunelle, Corinne¹; Larouche, Pierre²; Doxaran, David³; Babin, Marcel³

¹ISMER 310 allée des Ursulines, Rimouski, QC, G5L 3A1, Canada; ²Institut Maurice-Lamontagne, Mont-Joli, Quebec, G5H 3Z4, Canada; ³Laboratoire d'Océanographie de Villefranche, UMR 7093-CNRS/UPMC, BP 8, 06238 Villefranche-sur-mer Cedex, France

The Arctic Ocean is currently experiencing major ecosystem changes due to the accelerated decline of its summer sea ice cover that is virtually opening a whole new ocean for phytoplankton to grow. Due to its remoteness, this region is however hard to sample using traditional ship-based approaches. Remote sensing appears as a promising way to monitor the ecosystem changes that are likely to occur with the shrinking sea ice cover. Remote sensing of phytoplankton biomass and of derived products such as primary production are fundamentally determined by the inherent optical properties of phytoplankton, dissolved matter and non algal particles. Previous studies conducted in arctic coastal waters showed that current operational algorithms were not performing well generally overestimating chlorophyll concentrations due to the presence of dissolved and suspended matter and because of significant pigment packaging in the arctic phytoplankton species. The light absorption capacity of phytoplankton (a_ph) is thus key to the accurate monitoring of possible climate change effects in the arctic ocean. To evaluate this parameter for arctic waters, we thus gathered a new set of measurements of aph as part of a series of expeditions: the Canadian Arctic Shelf Exchanges Study (CASES) field program conducted in 2003 and 2004; the Circumpolar Flaw Lead study in 2007-08, the 2005 and 2007 Arcticnet cruises, and finally the Nansen Amundsen Basin Observing System cruise in 2007. Together, these five cruises sampled the major coastal regions surrounding the Arctic central basin: the eastern Beaufort Sea, the northern Baffin Bay, the canadian archipelago, and the Laptev Sea. The presentation will describe the spatial and temporal variability of a_ph and evaluate its similitudes with the database covering the southern waters.

THE MERIS WATER PRODUCTS: PERFORMANCE, CURRENT ISSUES AND POTENTIAL FUTURE IMPROVEMENTS

Bouvet, Marc¹; Huot, Jean-Paul¹; Goryl, Philippe²; Antoine, David³; Barker, Kathryn⁴; Bourg, Ludovic⁵; Doerffer, Roland ⁶; Mazeran, Constant ⁵; Santer, Richard⁷; Zagolski, Francis⁸; Zibordi, Giuseppe⁹

¹European Space Agency ESA/ESTEC, Keplerlaan, 1, Noordwijk, --, 2200 AG, Netherlands; ² ESA/ESRIN, Frascati, N/A, 00044 , Italy; ³Laboratoire d’Oceanographie de Villefranche-sur-mer, Villefranche-sur-mer, N/A, 06234 , France; ⁴ARGANS, 49 The Drive, Rickmansworth, N/A, WD3 4EA, United Kingdom; ⁵ACRI, 260 Route du Pin Montard, BP 234, Sophia Antipolis, N/A, 06904 , France; ⁶GKSS Research Centre, Max-Planck.Str. 1,, Geesthacht, N/A, 21502 , Germany; ⁷ Université du Littoral (ULCO)/ Laboratoire LISE, MREN, 32 Avenue Foch, Wimereux, N/A, 62930 , France; ⁸PARBLEU, Saint-Jean-sur-Richelieu, Saint-Jean-sur-Richelieu, Quebec, J3B 3W7, Canada; ⁹Joint Research Center, Ispra, N/A, 21020 , Italy

The MEdium Resolution Imaging Spectrometer, onboard ENVISAT, has been delivering global ocean colour products since 2002. We present an assessment of the performance of the instrument and its operational processing chain based on the comparison of MERIS data with the MERIS Matchup In-situ Data (MERMAID) currently populated with AAOT, BOUSSOLE and MOBY matchups. The current understanding of the origin of the differences between L2 water leaving reflectances and the in-situ corresponding values is discussed. A vicarious calibration strategy to absorb residual biases is also discussed. Possible improvements under evaluation in the MERIS Quality Working Group and considered for implementation in the MERIS 3rd reprocessing, are presented.

GLOBAL OBSERVATION OF DIFFERENT PHYTOPLANKTON GROUPS USING PHYTODOAS WITH SCIAMACHY DATA

Bracher, Astrid ¹; Schmitt, Bettina¹; Vountas, Marco ²; Dinter, Tilman ²; Burrows, John Phillip²; Röttgers, Rüdiger ³; Gehnke, Steffen³; Ilka, Peeken⁴

¹Alfred-Wegener-Institut Bussestr. 24, Bremerhaven, --, 27570, Germany; ²Institute of Environmental Physics, University of Bremen, Bremen, --, 28334 , Germany; ³Institute of Coastal Research, GKSS, Geesthacht Research Center, Geesthacht, --, 21502, Germany; ⁴IFM Geomar, Kiel, --, 24105, Germany

In order to understand the marine phytoplankton’s role in the global marine ecosystem and biogeochemical cycles it is necessary to derive global information on the distribution of major functional phytoplankton types (PFT) in the world oceans. We use the PhytoDOAS method, the Differential Optical Absorption Spectroscopy used with input of phytoplankton differential absorption spectra, on hyperspectral satellite sensor’s SCIAMACHY ( Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) to retrieve information on the distribution and absorption of different phytoplankton groups, in particular cyanobacteria. SCIAMACHY measures back scattered solar radiation in the UV-Vis-NIR spectral region with a high spectral resolution (0.2 to 1.5 nm). We used in-situ measured phytoplankton absorption spectra taken on five meridional transects across the Atlantic Ocean where different phytoplankton groups were representing or dominating the phytoplankton composition in order to identify these characteristic absorption spectra in SCIAMACHY data in the range of 430 to 500 nm. In addition also SCIAMACHY data were analysed with DOAS in the range of 530 to 590 where absorption from cyanobacterial photosynthetic pigment phycoerythrin was identified. Our results show clearly these phytoplankton assemblage absorptions in the SCIAMACHY data. Phytoplankton concentrations have been determined for three monthly periods (Feb-March 2004, Oct-Nov 2005 and Oct-Nov 2007). The information retrieved by DOAS from SCIAMACHY on phytoplankton groups is compared to collocated in-situ measurements and to the global model analysis with the NASA Ocean Biogeochemical Model (NOBM from http://reason.gsfc.nasa.gov/OPS/Giovanni/) according to Gregg and Casey 2006 and Gregg 2006. Results are of great importance for global modelling of marine ecosystem and climate change studies regarding changes in the ocean.

ATMOSPHERIC CORRECTION OF MERIS DATA OVER CASE 2 WATERS

Brajard, Julien¹; Santer, Richard²; Thiria, Sylvie³

¹ULCO LOCEAN, BC 100, place Jussieu, Paris, --, 75005, France; ²ULCO, MREN, av. Foch, Wimereux, --, 62930, France; ³LOCEAN, BC 100, place Jussieu, Paris, --, 75005, France

Radiometers on board satellite measure the solar radiation reflected by both ocean and atmosphere. One difficulty is that the signal is strongly polluted by the contribution of the atmosphere. Standard algorithms make the hypothesis that the contribution of the ocean is null in the near infrared bands. But, for case 2 waters, the contribution of the sediments is no more neglictible, and standards algorithms failed.

We propose here a new methodology, called NeuroVaria, based on a spectral optimization in the near infrared to estimate simultaneously the particles and the atmospheric contribution on the “top of atmosphere” signal. The aerosols are supposed to be non absorbing and to follow a Junge size distribution law. The water contribution of the water in the near infrared is determined by the spectral signature of the particles that is characterized by intensity and a shape parameter. This methodology combines a neural network for modelling the radiative transfer and a variational algorithm for the inversion of the spectra.

NeuroVaria was applied to MERIS data of the Adriatic Sea off the Venice bay from August 2003 to September 2005 where in-situ measurements of the water-leaving reflectance and the aerosol optical thickness are available. We present the comparison between NeuroVaria, the standard MERIS algorithm and in-situ measurements. We show that NeuroVaria performed a better estimation of the inherent optical water properties and improved the atmospheric correction of case 2 waters.

ATMOSPHERIC CORRECTION OF MERIS DATA OVER CASE 2 WATERS

Brajard, Julien¹; Santer, Richard²; Thiria, Sylvie³

¹ULCO LOCEAN, BC100, T45-55, pl. Jussieu, Paris, --, 75 005, France; ²ULCO, MREN av. Foch, Wimereux, --, 62930, France; ³LOCEAN, BC100, T45-55, pl. Jussieu, Paris, --, 75005, France

SATELLITE RETRIEVAL OF CHLOROPHYLL CDOM AND NAP IN OPTICALLY COMPLEX WATERS USING A SEMI-ANALYTICAL INVERSION BASED ON SPECIFIC INHERENT OPTICAL PROPERTIES. A CASE STUDY FOR GREAT BARRIER REEF COASTAL WATERS

Brando, Vittorio E¹; Dekker, Arnold G¹; Schroeder, Thomas ¹; Park, Young Je ¹; Clementson, Lesley ²; Steven, Andy ³; Blondeau-Patissier, David¹

¹CSIRO Land & Water GPO Box 1666, Canberra, --, 2601, Australia; ²CSIRO Marine & Atmospheric Research, Hobart, --, 7001, Australia; ³CSIRO Land & Water, Brisbane, --, 4068, Australia

Valid and accurate satellite-derived information on water quality of the Great Barrier Reef (GBR) waters is required to effectively manage this world heritage listed area. Previous studies have shown that for this region the variability in optical properties leads to poor performance of standard algorithms.

To account for the seasonal and spatial variability of the spectral shapes and the magnitude of the Specific Inherent Optical Properties (SIOP), a generic remote sensing algorithm was developed based on the inversion of a semi-analytical model with a variable SIOP parameterisation.

In this study we present the regional SIOP parameterization and application of this algorithm to the coastal waters between Cairns (~16.8 ºS) and Townsville (~18.8 ºS). To characterise the variability in optical properties in these coastal waters and to estimate the key SIOP parameters for the model, two field campaigns were conducted during the austral dry (October 2007) and wet (April 2008) seasons. Wet season sampling followed monsoonal activity that resulted in significant riverine discharge to the GBR coastal waters.

Light absorption, scattering, backscattering, as well as particulate, pigment and dissolved matter concentrations were measured at 44 stations, spread over 28 different locations. Sixteen of these locations were visited both in the dry and wet season enabling a direct comparison. In both seasons we observed highest values (in concentration or IOP) of most optical properties at sites close to river mouths, decreasing with distance from the coast. Particulate and dissolved concentrations were higher during the wet season. Sites close to the rivers showed the greatest differences between seasons for several SIOP parameters.

The inversion algorithm was applied with the regional SIOP parameterization to MODIS data for the retrieval of the inherent optical properties and the concentrations of the optically active constituents. Our results show that the MODIS based retrieval accurately depicts the observed seasonal and spatial variability of the key optical properties for these complex coastal waters.

AN INTERCOMPARISON OF BIO-OPTICAL TECHNIQUES FOR DETECTING PHYTOPLANKTON FUNCTIONAL TYPES FROM SPACE

Brewin, Robert John William¹; Lavender, Samantha²; Hardman-Mountford, Nick³; Barciela, Rosa⁴

¹University of Plymouth A504 Portland Square, University of Plymouth, Drake Circus, Plymouth, --, PL4 8AA, United Kingdom; ²University of Plymouth / ARGANS Limited, A403 Portland Square, University of Plymouth, Drake Circus, Plymouth, Devon, PL4 8AA, United Kingdom; ³Plymouth Marine Laboratory, Prospect Place , Plymouth, Devon, PL1 3DH , United Kingdom; ⁴Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, United Kingdom

The process of photosynthesis is a fundamental part of the carbon cycle, and improving models of the flux of atmospheric carbon dioxide to the oceans depends on the accurate depiction of phytoplankton community abundance, distributions and physiology, which ultimately dictates the drawdown of CO₂. Developing and enhancing this understanding on a regional and global scale is, therefore, an essential step towards improving estimates of the atmospheric flux of CO₂ to the oceans. Satellite remote sensing of ocean colour is currently the only way of measuring synoptically wide-area ocean properties such as phytoplankton abundance, and recent bio-optical and ecological methods have been established that use satellite data to differentiate between certain phytoplankton functional groups (PFTs) e.g. Alvain et al. (2005); Uitz et al. (2006); Devred et al. (2006); Hirata et al. (accepted); Raitsos et al. (2008). These techniques have been developed using either inherent optical properties (IOPs) or apparent optical properties (AOPs), and thus vary significantly in their approach. These techniques have been applied to a long-term ocean colour merged data set from the GlobColour project and validated using a composite in situ dataset in order to establish a verified approach. Future work will compare CO₂ flux variation hindcasts, produced by the FOAM-HadOCC 3D physical model with coupled biology, in order to better understand the contribution of different PFTs to global CO₂ flux variability. The ultimate aim being a better understanding of how the oceans influence CO₂ fluxes and how it’s likely to change in the future.

ESTIMATING SHELF SEAWATER COMPOSITION BY INVERSION OF AC9 INHERENT OPTICAL PROPERTY MEASUREMENTS

Brown, Ian Christopher¹; Cunningham, Alex¹; McKee, David¹

¹University of Strathclyde 107 Rottenrow, Glasgow, --, G4 0NG, United Kingdom

Shelf seas are complex, dynamical systems, within which important physical and biological processes occur. Water composition information may be used to quantify and map these processes both spatially and temporally. This information is routinely obtained through laboratory sample analyses which have poor spatial and temporal resolution compared with those of other physical variables such as temperature and salinity. Hence, there is a requirement for the development of supplementary methods of determining water composition providing comparable coverage to that of other physical variables. The high sampling rate and relative ease of deployment suggest that in situ optics would provide a suitable basis for such procedures. As in situ absorption and scattering coefficient measurements are routinely made using WETLabs AC-9 (or AC-S) dual-beam spectrophotometers and the magnitude and spectral variation of these inherent optical properties (IOPs) are determined by the concentration and composition of seawater constituents, IOP inversion is a prime candidate. Such inversion techniques, applied to in situ optical data obtained from moorings or towed-bodies, may provide useful insights into variability in water composition and shelf sea processes.

Proposed strategies for partitioning in situ absorption coefficient measurements between optically significant constituents include matrix inversion (Gallegos & Neale, 2002) and constrained, non-linear regression methods (Schofield et al, 2004). As an extension of these ideas, we have developed a sequential, mechanistic, specific IOP based approach to partition both in situ absorption and scattering coefficient measurements between constituents and subsequently retrieve constituent concentrations. A comparison of these inversion procedures is presented, demonstrating that our specific IOP based procedure performs comparably with the previously published matrix inversion algorithm, appropriately constrained. Both procedures were validated using synthetic IOPs and field IOP measurements. Our procedure was used to interpret vertical water column structure and identify complex patterns of phytoplankton and suspended sediment distribution in Scottish fjords.

SECOND ORDER VARIABILITY IN SATELLITE OCEAN COLOR: THE ROLE OF NON-ALGAL MATTER AND BACKSCATTERING

Brown, Catherine A.¹; Huot, Yannick¹; Werdell, P. Jeremy²; Gentili, Bernard¹; Claustre, Hervé¹

¹Laboratoire d'Océanographie de Villefranche Quai de la darse, Villefranche sur Mer, --, 06230, France; ²NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771, United States

Empirical algorithms that describe (global) first order relationships between spectral water-leaving radiances and near-surface chlorophyll concentrations, [Chl], are widely applied to satellite ocean color imagery, but do not explain dispersion or anomalies around their mean statistical trends. We develop an empirical approach that removes the first order effect of [Chl] from satellite ocean color imagery, allowing us to observe the influence of other optically significant water-column constituents (those other than [Chl]) and their distributions. We present statistical and modeling analyses to interpret the observed anomalies in terms of their optical sources (i.e. absorption and backscattering). With this information, we examine the global distributions of anomalies in colored detrital and dissolved organic matter (CDM) and backscattering by particles, both of which display significant regional and seasonal trends. We then use the anomalies to develop alternative remote sensing algorithms to estimate the backscattering coefficient of particles and, more tentatively, the absorption of CDM, and compare our results with other published studies. We further show how these anomalies explain dispersion in standard empirical chlorophyll algorithms and how they could be used to correct such approaches.

MATHEMATICAL MODEL FOR POLARIZED RADIATION REFLECTION BY ATMOSPHERE-OCEAN SYSTEM

Budak, Vladimir Pavlovitch¹; Korkin, Sergey Vladimirovitch¹

¹Moscow Power Engineering Institute (TU) Krasnikazarmennaya, 14, Moscow, --, 111250, Russian Federation

The paper deals with mathematical model for polarized radiation transfer in the atmosphere-ocean turbid optical system. The vertical heterogeneity is approximated by a number of homogeneous slabs. The ocean is assumed to be a semi-infinite media in particular case with the analytic solution. The angle of the slab irradiance by infinitely wide collimated beam is assumed to be arbitrary. Polarization properties of the scattering media are described by Mie-scattering with particle size distribution (Deirmendjian) and Rayleigh scattering as well. The essential problem is the consideration of mathematical specialties of the vectorial radiative transfer boundary problem (VRTE BP) solution caused by ray approximation in the multiple scattering descriptions. We depart from the classical (Wick, Chandrasekhar) method and evaluate the solution singular part together with the most anisotropic one upon the vectorial modification of the spherical harmonics method (VMSH, Budak et al., JQSRT, V.109 (2008), p.1347). The BP for the smooth regular part which enlarges the VMSH to the complete VRTE solution was solved by the discrete ordinates method. The boundary air-water ordinates’ reflection was considered by the known procedure (Nakajima, Stamnes). Scaling transformation (Shettle-Green, Karp) preserves the solution from ill-conditionality. In particular case of semi-infinite media inverse exponential depth-depended elements are converted to zero in analytical evaluations. This gives the exact solution for Ambartsumian’s problem but for arbitrary phase function and including polarization. It is convenient to describe the vertical heterogeneity in matrix form after ordering the streams by the scattering angle to downward and upward parts. Each of them describes reflected and transmitted fluxes produced by every slab (Stokes, Gurevich, Plass-Kattawar) respectively. The proposed model of the direct VRTE BP solution serves as the basis for the inverse problem solution of satellite optical remote sensing of the ocean.

IMPROVING LIGHT PROPAGATION IN COASTAL BIOGEOCHEMICAL MODELS: A CASE STUDY IN TROPICAL COASTAL WATERS OF AUSTRALIA.

CHERUKURU, RAGHU CHANDRA NAGUR¹; Robson, Barbara¹; Brando, Vittorio¹; Dekker, Arnold¹

¹CSIRO GPO BOX 1666, BLACK MOUNTAIN lAB., CLUNIES ROSS STREET, CANBERRA, ACT, --, 2602, Australia

Estimating the light propagation across the air-water interface and under water accurately is critical in biogeochemical models, as this parameter controls processes such as photosynthesis, heat flux and biological growth, in the ecosystem. Better estimates of under water light propagation in coastal waters can be achieved when the influence of Chromophoric Dissolved Organic Matter and non-algal particulate matter are included along with phytoplankton. Further improvements to above water light environment can be made by representing diurnal variations, and cloud cover through the introduction of remote sensing derived estimates.

A biogeochemical model for Fitzroy Estuary and Keppel Bay (FEKB) which is based on the concepts of Model for Estuaries and Coastal Oceans (MECO) was used in this research. The FEKB biogeochemical model is built on a 3D hydrodynamic and sediment dynamic model and is capable of simulating various biological parameters.

Here we present an inherent optical property based underwater light propagation model for FEKB and the coupling of this IOP model with the biogeochemical model. We will then discuss the influence of MODIS derived PAR data on under water light intensity and chlorophyll a distribution. This modelling activity forms part of the wider research objective of data assimilation of remote sensing data into ecosystem models for coastal systems.

VARIABILITY IN THE SPECTRAL RESPONSE OF SEA SURFACE DURING A TRICHODESMIUM ERYTHRAEUM BLOOM IN THE CONTINENTAL SHELF OFF SANTOS, SOUTHEAST BRAZIL

Carvalho, Melissa¹; Gianesella, Sônia Maria Flores¹; Saldanha-Corrêa, Flávia Marisa Prado ¹; Ciotti, Áurea M.²

¹Instituto Oceanográfico - Universidade de São Paulo Praça do Oceanográfico, 191, São Paulo, --, 05508-900, Brazil; ²UNESP - Campus do Litoral Paulista, São Vicente, São Paulo, 11330-900, Brazil

A Trichodesmium erythraeum bloom was observed during an oceanographic cruise from March 23-26, 2006 in the continental shelf off Santos, Brazil. In this work, we report the variability in the radiometric response of sea surface during the occurrence of the bloom. Samplings were performed in 20 oceanographic stations, distributed over eight transects.Surface water samples for chlorophyll-a (Chl-a), phaeopigments and carotenoids determination were collected using a Niskin bottle and filtered through AP-40 Millipore filters. Radiometric measures of sea surface were carried with a spectroradiometer Spectrom SE590^®. Chl-a, carotenoids and phaeopigments concentration were determined by spectrophotometry. The relative abundance of T. erythraeum and other groups was performed in hemocytometer chambers (Nageotte, sample volume of 0,625 mm³) under a light optical microscope (Zeiss, 400x magnification). The cells were counted individually except for T. erythraeum, to which the number of filaments was considered. The cells were grouped in T. erythraeum, diatoms, dinoflagellates and other cyanophyceas. When T. erythraeum bundles were observed an estimative of the number of filaments per bundle was done. Bands with same intervals that MODIS bands (bands 8 to 14) were calculated for radiometric data acquired in situ. Thus, in a preliminary analyze it was observed higher reflectance values for all bands in the stations with higher T. erythraeum abundance. The stations that presented higher abundance of other groups like diatoms and dinoflagellates, showed lower reflectance values. Correlations were observed between the reflectance in the 412 and 443 nm bands and T. erythraeum abundance, while blue/green ratios band (412/551, 443/551, 488/551 and 531/551 nm) showed correlation with dinoflagellates abundance. Negative correlation was observed between diatoms abundance and reflectance in 412 nm.

PARTICLE DISTRIBUTION OVER SAN PEDRO SHELF

Cetinic, Ivona¹; Jones, Burton H¹; Moline, Mark²; Schoefield, Oscar ³

¹University of Southern California 3616 Trousdale Pkwy., Los Angeles, CA, 90089-0371, United States; ²California Polytechnic State University,, San Luis Obispo, CA, 93407, United States; ³Rutgers University, New Brunswick, NJ, 08903-0231, United States

Slocum glider was deployed over San Pedro Shelf during the summer of 2006 as a part of the SCCOOS conducted Huntington Beach 06 experiment. Glider was measuring temperature, salinity, density, optical backscattering coefficient on three wavelengths and chlorophyll, colored dissolved organic matter and rhodamine fluorescence. Three different particulate groups were detected. Two distinct chlorophyll maxima were resolved, one with high backscattering coefficients located over the shelf and one with low specific backscattering signal in the open ocean. Near-bottom suspended particles had high backscattering coefficients and high CDOM concentrations. Third detected particulate group coincided with high CDOM and low salinity signal, and found to be highly specific of the effluent plume coming from the outfall diffuser located on the shclf. High optical backscattering within the effluent plume allowed us to calculate distribution of the suspended particulate material concentration associated with the plume.

PARTICLES, THE BACKSCATTERING RATIO AND THEIR EFFECTS ON REMOTE SENSING: TOWARD SOLVING THE INVERSE PROBLEM IN OCEAN OPTICS

Chang, Grace¹; Whitmire, Amanda L.²

¹University of California Santa Barbara 6487 Calle Real Suite A, Goleta, CA, 93117, United States; ²Oregon State University, Corvallis, OR, 97331, United States

Mie scattering theory and the radiative transfer model, Hydrolight, are used to compute the IOPs and AOPs for a set of hypothetical water masses with variable indices of refraction and particle size distributions. The influence of particles and their properties (e.g., index of refraction and particle size distribution slope, n and x, respectively) on inversion algorithms to derive the IOPs from modeled AOPs is investigated using a semi-analytical remote sensing inversion algorithm.

Results indicate that successful derivation of the IOPs (absorption and backscattering) from remote sensing reflectance is highly dependent on proper parameterization of the shape of the backscattering spectrum. We find that b_bp(\lambda) does not follow the widely used expression: b_bp(\lambda) = b_bw(\lambda) + b_bp(\lambda₀) (\lambda₀/\lambda)^\eta. Additionally, our results show that the backscattering ratio, b_bp(\lambda)/b_p(\lambda), varies spectrally with increasing n and \xi. Contrary to assumptions made in the past, b_bp(\lambda)/b_p(\lambda) is not spectrally flat. We show that the best results for derived backscattering coefficients are found for n = 1.10 and \xi = 3.50 (b_bp^QAA/b_bp within 25% of b_bp) and worst for n = 1.01 and \xi = 3.00 (b_bp^QAA/b_bp > 200% of b_bp) for all wavelengths. For derivations of the absorption coefficient, the inversion algorithm performs best at high n-values (n > 1.15) and moderate \xi-values (\xi = 3.50). Derivations of a_t(\lambda) are highly wavelength, n, and \xi dependent.

MATCHING THE TOTAL AND POLARIZED WATERLEAVING RADIANCE CONTRIBUTIONS TO THE MULTIANGLE AND MULTISPECTRAL REMOTE SENSING MEASUREMENT CAPABILITIES OF THE 2009 NASA/GLORY MISSION

Chowdhary, Jacek¹; Cairns, Brian¹; Travis, Larry¹; Mishchenko, Michael¹

¹NASA/GISS & Columbia University 2880 Broadway, New York, NY, 10025, United States

The polarization intensity of light scattered by particles exhibits features as a function of wavelength and of scattering angle that are distinctively different from the features for the total intensity of this light. The polarized and total intensity features exhibit also very different sensitivities to particle properties such as size, shape, and composition. Finally, these sensitivities vary themselves with particle properties. For example, the polarization of light scattered by low-refractive particles (relative to the surrounding medium) such as marine particulates shows less features with scattering angle, and less variation with shape and size, than the corresponding features for light scattered by high-refractive particles such as atmospheric aerosols. This suggests that for observations over the ocean, one can use the different variations of polarized and total intensity features with observation angle and wavelength to separate aerosol signatures from changes in the ocean color and retrieve both these atmosphere-ocean system properties simultaneously.

However, the success of such retrievals depends strongly on the ability to measure total and polarized intensity features accurately, and on the numerical tools to match such features for observations over the ocean. This sets the stage for his talk as follows. First, we introduce the multi-angle, multi-spectral measuring capabilities of the polarimeter onboard the NASA/Glory mission scheduled for launch in 2009. Secondly, we present the Case-1 water hydrosol model developed for this mission to compute realistic underwater light scattering contributions of total and polarized light to observations from space. Thirdly, we describe simulations of such contributions as a function of viewing angle, wavelength, and Chlorophyll a concentration, and illustrate the underlying potential for separating aerosol and ocean color retrievals. And fourthly, we discuss actual measurements and analyses of such contributions with an airborne version of the NASA/Glory polarimeter deployed at low (65 m) and high (4 km) altitudes.

BIO-OPTICAL SPECTRAL MODELLING OF UNDERWATER IRRADIANCE AND PRIMARY PRODUCTION IN THE BLACK SEA

Churilova, Tatyana¹; Suslin, Vyacheslav²

¹Institute of Biology of the Southern Seas, National Academy of Sciences 2 Nakhimov Ave., Sevastopol, --, 99011, Ukraine; ²Marine Hydrophysical Institute, National Academy of Sciences, 2 Kapitanskay str., Sevastopol, Crimea, 99000, Ukraine

Light absorption by all suspended particles, phytoplankton, non-algal particles and coloured dissolved organic matter measured during last ten years in various regions of the Black Sea and in different seasons has been parameterized. Modelling of photosynthetic available radiance (PAR) has taken into account seasonal and regional peculiarities in light absorption features of all in-waters optically active components. The PAR modelling has been based on SeaWiFS and MODIS information about incident on sea surface PAR, subsurface temperature, subsurface chlorophyll a concentration based on which chlorophyll profile was retrieved. Analysis of sensitivity of the PAR model to variability of each variable has shown dissolved organic matter is the main optically active in-water component, which effects relatively stronger the spectral feature of under water irradiance. The spectral model of primary production (PP) is based on physiological parameters of phytoplankton – on light absorption coefficient and quantum yield of photosynthesis, which depend on environmental factors namely temperature, quantity and quality of available radiance and nutrient availability. The effect of seasonal variability in environmental factors and in species composition of phytoplankton community on efficiency of absorption of ambient light and finally on PP has been analyzed.

SPATIAL VARIABILITY OF THE OPTICAL BACKSCATTER FROM THIN LAYERS

Churnside, James¹; Donaghay, Percy²

¹NOAA Earth System Research Laboratory 325 Broadway, Boulder, CO, 80305, United States; ²University of Rhode Island, Narragansett, Rhode Island, 02874, United States

The open ocean waters off the Oregon coast can support thin plankton layers. The depolarized volume backscatter coefficient of layers in this region has been measured with an airborne lidar operating at a wavelength of 532 nm. This instrument has a depth resolution of about 1 m and a horizontal resolution of about 5 m. Surveys were made at a speed of 90 m s^-1, so we did not alias spatial and temporal variability. The lidar backscatter at a fixed depth was very patchy; the spatial power spectrum was very nearly a power law with an exponent of -1.5 over almost 4 decades of spatial frequency. The peak lidar signal within a layer was used to measure the spatial variability of individual layers. As an example, one of these layers was about 3 km long with an average depth of 7 m and an average thickness of 3 m. The horizontal correlation scale of the depth was only about 22 m. That of thickness was about 56 m. The volume backscatter coefficient had a correlation scale of about 180 m. The effects of internal waves were clearly seen in many layers. Small waves displaced the layers without significantly affecting the other properties. Larger, presumably nonlinear, waves could also affect layer thickness and scattering strength.

SEASONAL VARIABILITY OF REMOTE SENSING FLUORESCENCE OVER THE SOUTHEAST BRAZILIAN CONTINENTAL SHELF

Ciotti, Aurea Maria¹; Barbosa, Fabiana Pestana¹

¹UNESP- CLP Praça Infante Dom Henrique S/N, Parque Bitaru, São Vicente, --, 01223-000, Brazil

Remote sensing natural fluorescence is a potential tool to estimate phytoplankton biomass over optical complex waters. Here we present a winter/summer analysis MODIS FLH (Fluorescence Line Height) variability over the continental shelf area between Cabo de São Tomé (RJ) and Cananéia (SP), were several sources of non-algal material exist. Biological production is moderate and nutrient input include continental outflow in the south and both costal and eddy-induced upwelling in the north. Previous studies show that CDOM is the major component for in situ light absorption. Global, weekly, level 3 MODIS-aqua and SeaWIFS images, with 4 km and 9 km spatial resolution respectively, were acquired from March 2005 to July 2007. Using SEADAS, maps of FLH, Chlorophyll-a, Sea Surface Temperature (SST), Normalized water-leaving radiance at 551 nm (nLw551) and Photosynthetically Active Radiation (PAR) were generated, and the interest area was divided into four main sub areas based on hydrographic features reported in the literature. For each sub area, the FLH was statistically related to all other estimated products, to identify the respective degrees of optical complexity. Results confirm an expected non-linear relationship between FLH and Chlorophyll-a in all sub areas and seasons, with smaller ratio values over the continental shelf during winter. However, FLH over the shelf decreased with the decrease of both SST and PAR, suggesting additional factors regulating FLH.

VARIABILITY IN THE LIGHT ABSORPTION CHARACTERISTICS OF TWO CONTRASTING AUSTRALIAN COASTAL REGIONS.

Clementson, Lesley Ann¹; Stramski, Dariusz²

¹CSIRO Marine and Atmospheric Research PO Box 1538, Hobart, Tasmania, --, 7001, Australia; ²Scripps Institution of Oceanography, San Diego, California, 92093-0238, United States

Spectral absorption coefficients and pigment concentration and composition from two diverse coastal marine environments in Australia have been analysed to determine the variability in absorption and its sources. Of the two regions, one is the west coast of Tasmania (41-43ºS) where the surface waters are dominated by high values of CDOM associated primarily with terrestrial sources. The other region is the coastal waters off south-west Western Australia (31-33ºS) where the absorption coefficients for all in-water components (phytoplankton, detritus, and CDOM) are low to the point that these waters are optically similar to many open ocean environments. Our analysis is focused on the green-to-blue ratio of the total absorption coefficient and its relationship to chlorophyll-a concentration. This absorption band ratio usually plays a dominant role in driving the variability in the blue-to-green ratio of remote sensing reflectance, R_^rs, with the variability in the blue-to-green ratio of backscatter playing a minor role. The reflectance band ratio is commonly used to retrieve bio-optical data products such as the chlorophyll concentration from ocean colour satellite imagery. Our results thus provide insights into potential performance of band-ratio algorithms for retrieving chlorophyll in these two coastal regions. We demonstrate the extent to which the total absorption band ratio (i.e., a proxy for the reflectance band ratio) varies at given chlorophyll concentrations within the investigated regions. We also discuss the sources of this variability in terms of phytoplankton, detritus, and CDOM absorption components as well as the composition of phytoplankton pigments. Our results can aid in the determination of regional bio-optical algorithms for the investigated coastal waters.

SPATIAL AND TEMPORAL EFFECTS OF FORWARD SCATTERING ON AN INTENSITY MODULATED SOURCE FOR LASER COMMUNICATIONS UNDERWATER

Cochenour, Brandon¹; Mullen, Linda¹; Laux, Alan¹; Zege, Eleonora²

¹NAVAIR 22347 Cedar Point Rd Bldg 2185 Ste. 1100, Lexington Park, MD, 20670, United States; ²Belarus Academy of Sciences, Minsk, Minsk, 2200072, Belarus

A growing number of military, commercial, and scientific applications suggest that horizontal short range (<100m) wireless links are of great utility.Current acoustic links, even at short range, are fundamentally bandwidth limited to sub-Mbps rates.The maturity of fiber optic links, free space optical links, and all of their associated components, suggest that optics are well poised to provide a solution for high bandwidth communications (>10’s Mbps) undersea.

The underwater environment however is a challenging one, and accurate characterization is imperative in determining the performance of the link. Exponential losses from absorption and scattering will vary with water clarity and impose strict requirements on link range.Additionally the spatial profile of the transmitted beam is altered due to scattering from particulates in the underwater channel.Furthermore, photon path length differences that arise from these multiple scattering events may cause inter-symbol interference (ISI), which will ultimately decrease channel bandwidth.

Currently, most work in underwater lasercom examines channel effects on optical pulses.In this study however, we examine an optical link employing intensity modulation of the optical carrier at frequencies exceeding 10MHz. This type of encoding can be used to employ digital schemes such as phase shift keying (PSK) or quadrature amplitude modulation (QAM), which are commonly used in free-space RF links. Through experiment and modeling, we aim to determine how the underwater environment affects this modulated optical signal. For example, multiple scattering may result in a loss of modulation depth, limiting the maximum modulation frequency that can be used.Also investigated are factors such as water clarity, link range, transmitter/receiver pointing accuracy, receiver FOV, and others that will affect the transmission and detection of the encoded optical carrier.We attempt to quantify the impact that these tightly connected variables will ultimately have on the integrity of an underwater optical communications link.

EVALUATION OF REMOTE SENSING CHLOROPHYLL ALGORITHMS (SEAWIFS, MODIS AND MERIS) IN THE ADRIATIC SEA COASTAL WATERS

Colella, Simone¹; Veropalumbo, Fabiana¹; Marullo, Salvatore²; Santoleri, Rosalia¹

¹ISAC-CNR Via del Fosso del Cavaliere 100, Rome, --, 00128, Italy; ²ENEA - Centro Ricerche Frascati Via E. Fermi 45, Frascati, Rome, 00044, Italy

Shelf seas operational oceanography applications require an improvement of the chlorophyll products retrieved from ocean colour satellite data. In the framework of ECOOP (European Coastal Operational Oceanography Project) and ADRICOSM-Star projects, the Adriatic coastal areas were used to test standard and not-standard algorithms for the various ocean colour sensors (SeaWiFS, MODIS and Meris). In fact, due to the composition and optical properties of these case 2 waters a high quality estimation of ocean colour derived parameters is a very difficult issue. In order to perform an evaluation of the satellite chlorophyll estimates, an in situ data base has been built from available data acquired in different oceanographic cruises carried out in this area in the last years. After the standardization of the in situ data base and the processing of the satellite data with various chlorophyll algorithms, a match-up file for each sensor has obtained. From the analysis of the scatter plots (in situ-satellite data), it results that all the standard and not-standard algorithms investigated show low performances in case2 waters. The best results have been achieved with the Carder algorithm for the SeaWiFS and MODIS sensors and with Algal_2 algorithm for Meris. New specific algorithms have been developed and tested with in situ data. This new ocean colour algorithms will be implemented in the CNR operational chain for the Adriatic during the test phase of the ECOOP project.

VARIATIONS OF PHOTOACCLIMATION RELATED TO ENVIRONMENTAL CONDITIONS

Comeau, Adam Joseph¹; Craig, Susanne¹; Babin, Marcel²; Lewis, Marlon¹; Bruyant, Flavienne¹; Cullen, John¹

¹Dalhousie University 1355 Oxford street, Department of Oceanography, Dalhousie University, Halifax, NS, B3H4J1, Canada; ²Laboratoire d’Océanographie de Villefranche, Villefranche-sur-Mer, France, 06238, France

By understanding factors that influence parameters related to photosynthesis, better estimates of primary productivity and particle dynamics can be obtained. We describe a new method to estimate photoacclimation, a physiological process that influences both photosynthesis vs. irradiance (P vs. E) parameters and chemical composition of phytoplankton, based on profiles of in situ fluorescence and irradiance and apply it to a variety of datasets collected all over the world, to examine its variability in relation to environmental variables. Profiles of in situ chlorophyll fluorescence have been routinely measured during oceanographic surveys for several decades. Near surface decreases of fluorescence yield, chlorophyll fluorescence normalized to some measure of phytoplankton biomass, are commonly observed during daytime profiles. This decrease in fluorescence is due to physiological processes, activated in high irradiance, which act to dissipate light energy absorbed by phytoplankton. Lab studies show that the irradiance at which this quenching of fluorescence yield begins is related to the light saturation parameter, of P vs E curves. With the simple requirements of irradiance and fluorescence yield profiles, this method can be applied to many existing datasets. Examining variations of the light level where fluorescence quenching begins in response to environmental variables such as average light in the mixed layer, will provide new information on how phytoplankton acclimate to their environment.

DEVELOPMENT OF THE HYPERSPECTRAL IMAGER FOR THE COASTAL OCEAN (HICO) FOR THE INTERNATIONAL SPACE STATION

Corson, Michael¹; Korwan, Daniel R.¹; Lucke, Robert L.¹; Snyder, William A.¹; Davis, Curtis O.²

¹Naval Research Laboratory 4555 Overlook Ave. SW, Washington, DC, 20375, United States; ²Oregon State University, Corvallis, OR, 97331, United States

The Hyperspectral Imager for the Coastal Ocean (HICO) is the first spaceborne hyperspectral imager designed for environmental product retrievals in the littoral zone.HICO, sponsored by the Office of Naval Research, will be launched to the International Space Station in July 2009 for a one-year mission with a three year goal.From orbit, HICO will demonstrate shallow water bathymetry, water clarity, suspended and dissolved matter, bottom type, and classification of on-shore vegetation, and offers the opportunity to build time series of images at selected coastal sites globally.HICO is integrated and flown under the direction of DoD’s Space Test Program. Hyperspectral imaging of the littoral environment involves specific challenges that are understood from airborne hyperspectral programs.The ocean surface presents a dark scene, and is viewed through an atmosphere which is significantly brighter than the underlying water over most of the visible spectrum.This leads to performance requirements including high signal-to-noise ratio and accurate spectral and radiometric calibration.Water surface reflections of direct sunlight and sky background are also significant and must be accounted for.HICO has a signal-to-noise ratio greater than 200 to 1 for water-penetrating wavelengths for a five percent reflectance scene, and a ground sample distance of 100 meters over a 50 km wide by 200 km long scene. The maintenance of HICO’s radiometric and spectral calibration, and the accurate removal of the effects of the atmosphere, present new challenges from the Space Station orbit.On-orbit maintenance of calibration by imaging well-characterized ground sites is well developed for imagers in Sun-synchronous orbits, where the illumination and viewing conditions are essentially constant.This will not be true for the Space Station orbit, and existing methods will have to be extended and validated for HICO. This presentation will discuss the development and planned operation of the HICO imager.

THE EFFECTS OF PHYSICAL FORCING ON STIMULATED CHLOROPHYLL FLUORESCENCE REVEALS THE INFLUENCE OF OCEAN INTERIOR PROCESSES ON THE QUANTUM YIELD OF SUN-INDUCED CHLOROPHYLL FLUORESCENCE

Craig, Susanne Elizabeth¹; Comeau, Adam¹; Cullen, John¹

¹Dalhousie University 1355 Oxford Street, Halifax, NS, B3H 4J1, Canada

For over thirty years it has been recognised that the relative quantum yield of in vivo stimulated chlorophyll fluorescence, phi_rel, varies by a factor of ten or more, and is a function of phytoplankton physiology and taxonomic status, and controlled by incident irradiance and nutritional status. For almost as long, the same has been known of the quantum yield of sun induced chlorophyll fluorescence (SICF), phi_f, observed in situ and from satellites. Given the new capability for autonomous surveys of the ocean interior offered by gliders equipped with fluorometers, it should be useful to relate synoptic surveys of SICF phi_f from satellites to continuous measurements of fluorescence and other oceanographic properties from the ocean interior. We expect variability in SICF phi_f to be directly related to variability in phi_rel calculated from stimulated fluorescence at the surface. But, surprisingly, systematic studies examining this seemingly obvious relationship are, to our knowledge, at best few and far between. We present an analysis of fluorescence data from the Bering Sea showing that changes in SICF phi_f at the surface are also evident in phi_rel calculated from stimulated fluorescence measured with a simple chlorophyll fluorometer. By establishing this most fundamental relationship, we can ultimately apply knowledge gained from ocean interior studies of how phi_f is affected by physical forcing to examinations of how the same ocean interior processes manifest themselves in satellite SICF phi_f variability, potentially providing synoptic and continuous metrics of phytoplankton physiology.

ON THE USE OF OPTICAL MEASUREMENTS TO CONSTRAIN MODELS OF MARINE PRIMARY PRODUCTIVITY AND PARTICLE DYNAMICS

Cullen, John¹; Comeau, Adam¹; Craig, Susanne E.¹; Davis, Richard F.¹; Fennel, Katja¹

¹Dalhousie University Department of Oceanography, Halifax, NS, B3H 4J1, Canada

Just over 50 years ago, models were developed to describe photosynthesis in the water column as a function of chlorophyll concentration, irradiance at the surface, the penetration of photosynthetically available radiation (PAR), and parameters of the relationship between photosynthesis and PAR. At the time there was not much interest in relating estimated primary production normalized to chlorophyll directly to growth rates of phytoplankton -- the two are linked through the ratio of cellular carbon to chlorophyll (C:Chl). Estimation of growth rates is central to most models of marine ecosystem dynamics, and comparison with observations (e.g., fields of chlorophyll concentration estimated from remote sensing) is necessary for validation. Consequently, specification of C:Chl has become increasingly important in marine ecosystem modelling. To support this, optical assessment of phytoplankton carbon has recently been incorporated into remote-sensing models of primary production and growth rates of phytoplankton. Meanwhile, a number of optically-based approaches have been developed for assessing physiological properties of phytoplankton. Most use measurements of chlorophyll fluorescence: either sun-induced or stimulated by in situ fluorometers. We describe an approach to estimate the saturation parameter for photosynthesis from surveys using conventional fluorometers. We also examine possible links between sun-induced fluorescence yield and variability in the maximum rate of photosynthesis, where photosynthesis is normalized to light absorption rather than to chlorophyll, which we argue is an outdated variable in bio-optics. We are now in a position to consider a new class of phytoplankton model, in which most, if not all terms -- available and absorbed spectral radiation, photosynthetic parameters, biomass of phytoplankton -- can be directly constrained by optical measurements, which in turn can be incorporated into assimilative models of primary productivity and particle dynamics. Development and validation of such models will require old-fashioned measurements from ships to complement advanced optical sampling, laboratory studies and new approaches to modelling.

SENSORY ECOLOGY OF KELP FOREST FISHES

Cummings, Molly Elizabeth¹

¹University of Texas 2400 Speedway, University of Texas, Austin, TX, 78712, United States

A spectrally variable environment can tell us much about the ideal design for visual detection and visual communication. It is under such constrained environments that selection acts directionally on traits. I examine the evolutionary solutions to the problem of target detection and signal design in an optically variable environment by studying a group of closely related fish (surfperch: Embiotocidae) that inhabit the California kelp forest. Using species-specific measurements of habitat spectral irradiances collected over 3 years, visual pigment absorptances, and foraging target and color pattern reflectances along with simple visual detection models, I evaluate the direction of visual evolution in this system. The results show that photoreceptor peak sensitivity covaries with changes in optical habitat and that this divergence produces detectional biases. The evolutionary divergence in visual detection performance across this group of dichromats suggest that some species favor luminance contrast detection while others favor chromatic contrast. Divergence in sensory biases follows divergence in habitat optical properties—specifically the variation in signal:to:noise in particular detection channels. Signal design properties and display behaviors also show parallel divergence to exploit receiver biases, with signal design divergence observed across three different chromatophore types favoring species-specific biases.

OPTICAL EFFECTS OF TIDAL STIRRING IN A SEASONALLY STRATIFIED SHELF SEA.

Cunningham, Alex¹; McKee, David¹; Brown, Ian¹; Ramage, Leanne¹; Neil, Claire¹; Creanor, Danielle¹

¹University of Strathclyde 107 Rottenrow, Glasgow, --, G40NG, United Kingdom

The Irish and Celtic Seas constitute a semi-enclosed, relatively shallow region (maximum depth 175 m) between Ireland and the UK mainland. In spring and summer, these seas exhibit classical examples of shelf fronts separating regions where the water column is thermally stratified from those where it is tidally mixed. The mixed regions carry relatively low (< 5 mg m^-3) concentrations of suspended minerals throughout the year, and so particle loads are low compared to estuaries and major river plumes. However the fine mineral particles in these seas are efficient sources of scattering and backscattering, and they have a marked effect on the underwater light field and on the water-leaving radiance spectra. One consequence is that patterns of mixing and stratification predicted by hydrodynamic models (using the Simpson-Hunter parameter) are highly correlated with regions of enhanced reflectance and distinctive spectral signatures are observed in ocean colour images. A second consequence is that the depth of penetration of photosynthetically active radiation is greatly reduced, with important implications for primary production modelling.

This talk will review the results of 5 cruises in the Irish and Celtic Seas, during which extensive measurements were made of both inherent optical properties and in situ radiometric profiles. Specific inherent optical properties for the main optically significant seawater constituents have been derived and validated, and the results incorporated in Hydrolight radiative transfer models of both stratified and mixed water columns. The results, which confirm the significance of low concentrations of suspended minerals in degrading the performance of standard remote sensing algorithms for chlorophyll concentration and reducing water transparency, may be transferable to other shelf-sea regions. They also suggest that strategies for inverting ocean colour observations in optically complex (Case 2) waters can be targeted for different water types by relating spectral features to regional models of water column mixing.

SEASONALITY OF SURFACE CHLOROPHYLL CONCENTRATION: A PROXY TO CHARACTERIZE PHYTOPLANKTON TROPHIC REGIMES

D'Ortenzio, Fabrizio¹; Antoine, David¹; Martinez, Elodie ¹; Ribera d'Alcala, Maurizio²

¹CNRS Quai de la Darse, Villefranche sur mer, --, 06230, France; ²Stazione Zoologica Napoli “A. Dohrn”, Villa Comunale, Naples, NA, 80121, Italy

A primary goal of biological oceanography is the determination of the relative importance of the environmental (i.e. physical, chemical) and biological (i.e. species composition, grazing, nutrients uptake) forcing factors on the phytoplankton evolution. The separation of the impact of the different forcing factors is however not trivial, as they act on the biomass at different temporal and spatial scales. The main consequence is that the seasonal evolution of the phytoplankton shows a large spectrum of trends. In this sense, it could be interpreted as an indicator of a specific trophic regime.

Ocean color satellites offer more than 10 years of continuous and high-resolution observations of the surface oceanic chlorophyll concentration. In addition, CZCS data, recently reprocessed to be coherent with more modern sensors, allow estimating chlorophyll concentration for the period 1979-1983. We used these data to determine oceanic regions showing similar seasonal trends in the surface chlorophyll concentration. The main hypothesis here is that similarity in the seasonal trend indicates similarity in the forcing factors.

To generalize the approach, we produced a climatological weekly data set from ocean color data, we normalized, on a pixel-by pixel basis, each curve with his absolute maximum, and finally we applied a K-means cluster analysis. Each pixel was then classified on the basis of his seasonal courses of chlorophyll concentration and pixels exhibiting similar characteristics have been grouped together.

The method has been applied to the Mediterranean Sea ocean color observations from both the SeaWiFS and the CZCS sensors (using the Antoine et al., JGR, 2005, coherent data set). A first attempt at global scale and on an interannual scale has been also performed.

CDOM OPTICAL VARIABILITY AND DISTRIBUTION IN THE NORTHERN GULF OF MEXICO FROM FIELD AND OCEAN COLOR DATA

D'Sa, Eurico J.¹

¹Louisiana State University Coastal Studies Institute, Baton Rouge, LA, 70803, United States

The optical properties of colored dissolved organic matter (CDOM) were studied for the northern Gulf of Mexico coastal and oceanic waters influenced by the Mississippi-Atchafalaya river system. CDOM absorption determined from field measurements in the spring and summer of 2005 indicated a strong riverine influence with an inverse well-correlated relationship between CDOM absorption at 412 nm and salinity. Deviations from the conservative CDOM-salinity relationship and increases in the spectral slope S during summer suggested both losses and gains in CDOM with effects of photobleaching apparent during late summer. A previously derived empirical CDOM algorithm using the reflectance band ratios of R_rs(510)/R_rs(555) were used to derive estimates of surface CDOM absorption distribution at 412 nm from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery. Spatial and temporal CDOM absorption distribution from SeaWiFS for the northern Gulf of Mexico in the year 2005 indicated strong seasonal influences associated with discharge from the Mississippi-Atchafalaya river system. A seasonal increase in hurricanes allowed for an assessment of their effects on CDOM distribution. SeaWiFS estimates of CDOM following hurricane Rita in September 2005 revealed a decrease in nearshore CDOM absorption due to the transport of low CDOM offshore waters towards the coast. Using conservative CDOM-salinity relationship for the region, SeaWiFS surface salinity also indicated an increase in nearshore salinity east of the hurricane track. However, an increase in CDOM and a decrease in salinity were observed in coastal waters near the hurricane landfall likely associated with coastal runoff following extensive coastal flooding.

SPECTRAL VARIATIONS IN THE NEAR-INFRARED OCEAN REFLECTANCE

DORON, Maéva¹; BELANGER, Simon²; DOXARAN, David³; BABIN, Marcel³

¹LEGI - CNRS (formerly at LOV and ACRI-ST) LEGI - MEOM - BP53, Grenoble cedex 9, --, 38041, France; ²Université du Québec à Rimouski, Département de biologie, chimie et géographie, 300 allée des Ursulines , Rimouski, Québec, G5L 3A1, Canada; ³Laboratoire d'Océanographie de Villefranche, CNRS, Université Pierre et Marie Curie-Paris 6, Villefranche-sur-Mer, BP8, 06230, France

The optical properties of natural waters beyond the visible range, in the near-infrared (NIR, 700-900 nm), have received little attention because they are often assumed to be mostly determined by the large absorption coefficient of pure water, and because of methodological difficulties. It has recently been proposed that the variability in the shape of the surface ocean reflectance spectrum in the NIR is negligible in turbid waters. In the present study, we show, based on both in situ and remote sensing data, that the shape of the ocean reflectance spectrum in the NIR does vary in turbid to extremely turbid waters. Remotely sensed ocean reflectance data were collected using 3 different sensors (SeaWiFS, MODIS and MERIS) over the Amazon and Mackenzie turbid river plumes during extremely clear atmospheric conditions so that reliable removal of gases and aerosols effects on reflectance could be achieved. In situ NIR reflectance data were collected in different European estuaries where extremely turbid waters were found. In both data sets, a flattening of the NIR reflectance spectrum with increasing turbidity was observed. The ratio of reflectances at 765 and 865, for instance, varied from ca. 2 down to 1 in our in situ data set, while a constant value of 1.61 had been proposed based on theory in a previous study. Radiative transfer calculations were performed using a range of realistic values for the seawater inherent optical properties, to determine the possible causes of variations in the shape of the NIR reflectance spectrum. The most significant one was the gradual increase in the contribution of suspended sediments to the color of surface waters, which often leads to the flattening of the reflectance spectrum. Changes in the scattering and absorption properties of particles also contributed to variations in the shape of the NIR surface ocean reflectance spectrum. The impact of such variations on the interpretation of ocean color data is discussed.

EXPERIMENTAL COMPARISON OF PULSED-GATED AND CONTINUOUS WAVE LLS UNDERWATER IMAGERS

Dalgleish, Fraser R¹; Caimi, Frank M¹; Britton, Walter B¹; Andren, Carl F¹; Wan, Yueting¹

¹Harbor Branch Oceanographic Institute / FAU 5600 US 1 North, Fort Pierce, FL, 34946, United States

Laser Line Scan (LLS) underwater imaging is a serial imaging technique which involves the optical scanning of a narrow instantaneous field of view (IFOV) receiver in a synchronous fashion with a highly collimated laser source over a wide swath. It is widely regarded as the optimal technology for extended range underwater optical imaging, with up to 6 attenuation lengths achievable in turbid sea water. These imagers, which typically utilize high power green continuous wave (CW) lasers, require an adequate source-receiver separation to reduce near field backscattering events. They have been successfully deployed onboard towed bodies, and have potential as AUV-deployed imagers except their large size precludes them from this use. At the range limit of operation for these systems, the detection of CW laser return signals is convoluted by temporal overlap between the target return and that of the scatteringvolume from both laser and solar illumination. To increase their operational range, detection methods ideally must separate these two signals and estimate the energy returning from the target alone.Over-sampling techniques, which average many samples for each image pixel, are used to increase signal to noise ratio and hence improve image contrast, albeit with a reduction of image resolution due to intra-pixel scan and platform motion.

Another technique used for extended range underwater imaging system is that of range-gating, where the temporal aspects of the source and receiver are precisely controlled using a pulsed laser, a gated receiver, and knowledge of both the speed of light in water and the distance to the target. These methods, which also have the potential to determine bathymetry from the travel time of the light pulses, can offer increased backscatter rejection and in shallow water during daylight, increased ambient light rejection. Importantly, from a system packaging perspective, pulsed-gated imager architectures are amenable to a more compact implementation with a reduced source-receiver separation being possible, as the near-field scatter can be gated out temporally. Utilizing a gate-able receiver with sufficiently high temporal resolution, these techniques can allow separation of the target and scattering volume return signals, thereby increasing the imaging range possible under certain conditions.

Indeed, recent simulation work [1][2] has suggested that in scattering dominant waters, the pulsed-gated LLS will significantly improve the achievable image contrast over the CW LLS. To support this study, including the validation of image performance prediction simulation software, a prototype LLS system has been demonstrated in the Florida Atlantic University/Harbor Branch Oceanographic Institute full-scale laser imaging tank under highly controlled conditions of particle turbidity and ambient light. Two distinct design alternatives were tested and compared: i) the use of a CW laser and a non-gated photomultiplier tube (PMT); ii) the use of a high repetition rate (357 kHz) pulsed green laser and a custom gated-PMT. A series of experiments were conducted in the imaging test facility at realistic stand-off distances in a variety of turbidity conditions ranging from very clear conditions to greater than 7 attenuation lengths. Scattering was varied by the addition of Maalox and optical properties were measured with an ac-9 meter. The acquired images were analyzed using a variety of image quality metrics to compare the relative contrast and signal-noise ratios versus attenuation coefficient and stand-off distance. This workwas conducted undera grant monitoredby the US Office of Naval Research.

References

[1] Caimi, F.M., Dalgleish, F. R., Giddings, T.E. Shirron, J.J., Mazel, C.H., Chiang, K. “Pulse versus CW laser line scan imaging detection methods: simulation results” To appear at Oceans Europe 2007, June 18-21, 2007, Aberdeen, Scotland.

[2] Dalgleish, F. R., Caimi, F.M., Mazel, C.H., Glynn, J.M., Chiang, K., Giddings, T.E. and Shirron, J.J. “Model-based evaluation of pulsed lasers for an underwater laser line scan imager”. Ocean Optics XVIII. October 9-11, 2006, Montreal, Canada.

PARTICULATE BACKSCATTERING AND BEAM-ATTENUATION COEFFICIENTS IN THE EQUATORIAL PACIFIC

Dall'Olmo, Giorgio¹; Westberry, Toby K.¹; Behrenfeld, Michael J.¹; Boss, Emmanuel²; Slade, Wayne H.²

¹Oregon State University 2082 Cordley Hall, Corvallis, OR, OR, 97331, United States; ²University of Maine, Orono, ME, 04469, United States

Light scattering properties of the open ocean have been suggested as a superior index of phytoplankton biomass than chlorophyll-a concentration (chla), because they are insensitive to physiological forcing, such as light and nutrients, that alter the intracellular concentration of pigments. The drawback of particulate scattering is that it is not unique to phytoplankton. Nevertheless, field studies have demonstrated that variations in the beam-attenuation coeffcient (cp) closely track variations in phytoplankton abundance. The relationship between cp and the particulate backscattering coeffcient (bbp), the property retrievable from space, has not been fully evaluated, largely due to a lack of open-ocean field observations. Here, we present extensive data on inherent optical properties from the surface Equatorial Pacific and demonstrate a remarkable coherence in bbp and cp. Coincident measurements of particle size distribution (PSD) indicate that this covariance may be due to the conserved nature of the PSD.

SPATIAL AND SPECTRAL RESOLUTION CONSIDERATIONS FOR IMAGING COASTAL WATERS

Davis, Curtiss O.¹; Kavanaugh, Maria¹; Letelier, Ricardo ¹

¹Oregon State University College of Oceanic and Atmospheric Sciences, Corvallis, OR, 97331, United States

Current ocean color sensors, for example SeaWiFS and MODIS, are well suited for sampling the open ocean. However, coastal environments are spatially and optically more complex and their characterization require higher spatial resolution sensors equipped with additional spectral channels. In an earlier study (Davis, et al. Proc. SPIE vol. 6680 66800P:1-12, 2007) we analyzed the spectral characteristics and spatial scales of variability in airborne hyperspectral data of a harmful algal bloom in Monterey Bay, CA using semivariogram analysis. The results indicated the need for a channel near 709 nm (as found on MERIS) for the detection of these large surface blooms. Also, we found a continuum of spatial scales with the dominant scales being 150 to 300 m depending on the image analyzed. In this study we test the generality of those results by expanding the analysis to two very different coastal environments; coastal waters at the LEO-15 site offshore of Tuckerton, NJ and the Bahamas Bank near Lee Stocking Island.

IN-WATER REFLECTANCE SPECTRA MEASURED ON BOARD A JET-SKI ACROSS A COMPLEX NEARSHORE ZONE OF CASE-2 WATERS DURING THE ECORS EXPERIMENT

Dehouck, Aurélie¹; Martiny, Nadège¹; Froidefond, Jean-Marie¹; Sénéchal, Nadia¹

¹OASU-EPOC, UMR5805 CNRS, Université Bordeaux 1 avenue des facultés, Talence, --, 33400, France

In situ reflectance spectra have been measured during the international field experiment ECORS-Truc Vert 2008 (SW France) in the nearshore zone over a complex bathymetry and in moderately turbid waters (SPM <10 mg/l). The field site is a wide and high-energy sandy beach characterized by a double sand bar system which morphodynamics is driven by wave-induced flow motions and feedbacks between the topography and hydrodynamics.

Measurements of the atmospheric downwelling irradiance (E_d) and in-water upwelling radiance (L_u) were realized on board a jet-ski with TRIOS RAMSES sensors together with water samples to assess the optically significant seawater constituents (SPM, CDOM, Chl-a). Marine reflectance spectra were collected under low-energy swell conditions (H_s=0.5 m) in water depths of 3-25 m and after a long period of very energetic swells (H_s> 7 m). The jet-ski provides a valuable mean to gather optical data in shallow waters and in environments hard to sample with traditional coastal ships. Main results show reflectance spectra are typical of the presence of mineral particles with light absorption at short wavelengths. The shape and magnitude of the spectra are also very representative of the type of waters and bottom depth : the maximum of reflectance is reached around 500 nm in low turbidity waters (SPM<1 mg/l) while moving to the yellow spectral band (570-580 nm) in moderately turbid shallow waters (SPM=4 mg/l) where rip currents drive sediments outside the surf zone.

A very original dataset has been obtained considering the synchronization of optical data, bathymetric surveys and Formosat-2 high resolution satellite image all collected the same day (5 April 2008). In the present study, this dataset is tested to inverse optical models for bathymetry retrieval in order to compute diachronic bathymetric maps as the coastline is changing very fast and need frequent updates of the bathymetry.

MEASURING ORGANIC CARBON TRANSPORT BY THE MISSISSIPPI RIVER USING OCEAN COLOR REMOTE SENSING

Del Castillo, Carlos E¹; Spiering, Bruce A²; Miller, Richard L³

¹Johns Hopkins University-APL 11100 Johns Hopkins Rd, Laurel, MD, 20723, United States; ²NASA - Applications, Technology Development, and Transfer Office, Stennis Space Center, Mississippi, 39529, United States; ³Department of Geological Science East Carolina University, Greenvi