OBSERVATIONAL SYSTEMS

OPTICAL OBSERVATIONS OF LARGE DIATOMS AND SINKING PARTICLES DURING THE NORTH ATLANTIC SPRING BLOOM MADE FROM SEAGLIDERS, FLOATS, AND A SHIP

Perry, Mary Jane¹; Briggs, Nathan¹; Gray, Amanda²; Lee, Craig M²; Rehm, Eric²; D'Asaro, Eric A²; Gudmundsson, Kristinn³; Kallin, Emily¹; Lampitt, Richard ⁴; Poulton, Nicole ⁵; Rynearson, Tatiana⁶; Sieracki, Michael E<sup>5

1</sup>University of Maine Darling Marine Center, 193 Clark's Cove Road, Walpole, ME, 04573-3307, United States; ²University of Washington, Seattle, Washington, 98105, United States; ³Hafrannsoknastofnunin, Reykjavick, Reykjavik, 121 , Iceland; ⁴National Oceanography Centre, Southampton, Southampton, Southampton, SO14 3ZH, United Kingdom; ⁵Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine, 04575, United States; ⁶University of Rhode Island, Narragansett, Rhode Island, 02882-1197, United States

Using optically-instrumented autonomous platforms, NAB08 provided continuous observation of the North Atlantic spring bloom – from pre-bloom to post-bloom. In early April when chlorophyll concentrations were still low (<0.3 mg m^-3), four Seagliders and two Lagrangian floats were deployed around 59ºN, 20ºW. In May, the R/V Knorr rendezvoused with the autonomous platforms, that by then had moved several degrees northeast. The three-week process cruise had two major goals: (1) to collect optical, biological, and chemical measurements to validate autonomous sensors, and (2) to enable more comprehensive interpretation of optical data. The Knorr arrived just as the bloom began. By mid-May, mixed layer depths shoaled and the bloom was maximal: chlorophyll concentrations were high (to 5 mg m^-3) and the phytoplankton assemblage was dominated by large and chain-forming diatoms, as documented by FlowCAM and microscopy. The large cells resulted in high-frequency variability in measurements of chlorophyll fluorescence, optical backscatter, and beam transmission due to movement of large particles in and out of the optical-sensing volume. Later, discrete spikes in chlorophyll fluorescence, optical backscatter, and beam transmission began to appear below the mixed layer, first extending to 250 m and then progressively deeper (deepest depth sampled was 900 m, by Seaglider). These optical spikes were associated with sinking organic particles; the largest catch of sinking cells, based on visual observations by PELAGRA floating sediments traps, coincided with a horizontally and vertically wide-spread distribution of optical spikes observed both by ship and Seagliders. Throughout the experiment, mapping of bloom optical signatures by Seagliders, floats and ships revealed km-scale patchiness with an amplitude (O(factor of two)), as well as larger scale patchiness and eddies. These observations show the power of coordinated autonomous and ship-based sampling, using complementary bio-optical and biogeochemical measurements to measure coupled biophysical processes controlling ocean carbon fluxes.

ASSIMILATION OF REMOTELY SENSED OBSERVATIONS IN A SEDIMENT TRANSPORT MODEL

Eleveld, Marieke A.¹; van der Woerd, Hans ¹; El Serafy, Ghada²; Blaas, Meinte¹; van Kessel, Thijs ¹; de Boer, Gerben<sup>1

1</sup>VU-IVM De Boelelaan 1087, Amsterdam, --, NL-!081 HV, Netherlands; ²Deltares (former Delft Hydualics), Rotterdamseweg 185, Delft, (Zuid-Holland), NL-2629 HD , Netherlands

Since 2003, VU-IVM has been developing HYDROPT, a case-2 algorithm based on HYDROLIGHT solutions, which allows derivation of amongst others SPM and CHL concentrations and their associated error products, and also generates KD output. MERIS-derived suspended particulate matter concentrations and their associated error products were assimilated into the Delft3D-WAQ numerical transport model of the southern North Sea. In this dynamic region, a case study was carried out aiming at a better understanding of the Dutch coastal sediment transport system and characterising the baseline SPM situation before extension of Rotterdam Harbour. Independent in situ data were used for validation. The results show that assimilation of SPM remote sensing products into the model is feasible, and that Ensemble Kalman filtering indeed improved the skill of the sediment model. Time-series showing remote sensing observations, original model output and the assimilation results provide insight into the behaviour of the SPM retrieval under different hydrodynamic conditions. We will demonstrate effects of tide, wind, and freshwater inflow and stratification. Interestingly, the hydro-optical algorithm HYDROPT works well even close to the coast (1-2 km offshore) where high sediment fluxes occur. The methods developed in this test case are promising for application to other sensors, water bodies, and parameters. The HYDROPT algorithm is physically based and was recently also adapted for MODIS. The hydrodynamic and sediment transport model also contains various components that are not North Sea specific, and the tools developed for the Ensemble Kalman filtering are also generic. For the North Sea, we would like to better characterize SPM (particle size, organic / inorganic) and associate the optics with settling velocities in the hydrodynamic and sediment transport models. Finally, assimilation in ecological models, using also KD, CHL and our first case-2 primary production estimates is foreseen.

GLOBCOLOUR: A EUROPEAN SERVICE FOR OCEAN COLOUR SUPPORTING GLOBAL CARBON-CYCLE RESEARCH AND OPERATIONAL OCEANOGRAPHY.

Lavender, Samantha Jane¹; Fanton d'Andon, Odile²; Mangin, Antoine²; Pinock, Simon<sup>3

1</sup>University of Plymouth / ARGANS Ltd Portland Square A403, Drake Circus, Plymouth, --, PL4 8AA, United Kingdom; ²ACRI-ST, Sophia Antipolis, Alpes Côte d’Azur , 06904, France; ³ESA, Frascati, Rome, 00044, Italy

The aim of the GlobColour ESA Data User Element project (www.globcolour.info) is to develop and demonstrate an Earth Observation (EO)-based service supporting global ocean carbon-cycle research by providing scientists with a long time-series of consistently calibrated global ocean colour information according to requirements as specified by the global ocean colour user community (represented by the user groups; International Ocean Colour Coordinating Group (IOCCG), International Ocean Carbon Coordination Project (IOCCP) and the UK Met Office. GlobColour will also put in place the capacity to continue the ocean colour service in the future by running a near-real time service in its third phase.The project started in November 2005 and will have its third user workshop (end of year three) in November 2008, so this presentation will give an overview of the whole project and outline the progress that has been made towards the final goals. A critical component of GlobColour is ocean colour data merging, as it provides a method for the rationalisation of space missions and data distribution. However, it requires critical preliminary steps and a demonstration of feasibility/usefulness of the merged data; therefore its acceptance depends very much on the quality of the first steps and overall process.To achieve this, GlobColour performed a comparative characterisation of the included ocean colour sensors (MERIS, MODIS-Aqua and SeaWiFS) including an analysis of the available retrieval algorithms and their compatibility between missions using Level-2 product match-ups. This characterisation provided a deep understanding of the different input data streams, and led to the prototyping of three different merging methods: simple averaging, error-weighted averaging and an advanced retrieval based on fitting an in-water bio-optical model to the merged set of observed normalised water-leaving radiances (nLw’s). This third technique is also being utilised by the NASA Ocean Color Time-Series Project, and is termed GSM because it originates from the Garver et al. (1997) bio-optical model (Maritorena & Siegel, 2005). Error statistics from the initial sensor characterisation are also used as an input to both the weighted averaging and GSM merging methods, and propagate through the merging process to provide error estimates on the output merged products.These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into their ocean simulations. The project has produced the 10 year global merged ocean colour dataset at various temporal scales. The dataset includes chlorophyll-a concentration, normalised water-leaving radiances, diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. An overview of the GlobColour dataset, the comparative characterisation and full dataset validation results will be presented.

REMOTE SENSING OF INHERENT OPTICAL PROPERTIES: UNCERTAINTIES AND SATELLITE APPLICATIONS (RESULTS FROM A WORKSHOP, 3-4 OCT 2008, BARGA, ITALY)

Werdell, Jeremy¹; Participants, IOP Algorithm Workshop<sup>1

1</sup>NASA Goddard Space Flight Center NASA-GSFC Mail Code 614.8, Greenbelt, MD, 20771, United States

Semi-analytical (SA) ocean color algorithms provide a mechanism for estimating marine inherent optical properties (IOP), such as spectral absorption and backscattering coefficients, from satellite radiometric measurements. While SA algorithms include empirical components, they improve upon purely statistical approaches through their foundation in radiative transfer theory and their ability to simultaneously retrieve multiple, often uncorrelated, optical parameters. Recently, the U.S. and international ocean color communities have shown considerable interest and invested significant effort in improving the regional and global quality of satellite-derived SA data products (see, e.g., IOCCG Report 5). As such, we hosted an international IOP algorithm workshop to extend the recent IOCCG IOP effort by explicitly defining the state-of-the-art with regards to the application of these algorithms to satellite radiometry. In particular, we reviewed algorithm: (a) parameterization, inversion, and optimization; (2) associated uncertainties; (3) spectral requirements; (4) applicable spatial and geophysical ranges; and (5) satellite inversion failure conditions (and their remediation). The workshop, held the weekend prior to Ocean Optics XIX, was the culmination of shared analyses conducted from June to September 2008 by the 25 workshop participants. Here, we present results from the workshop, specifically highlighting progress towards our underlying goal of achieving community consensus on an effective algorithmic approach for producing global-scale, remotely sensed IOP products.