COASTAL AND OCEANIC OPTICAL MEASUREMENTS I

IMPROVED FLUORESCENCE MODELING AND RETRIEVAL IN COASTAL ZONES

Gilerson, Alexander¹; Zhou, Jing¹; Hlaing, Soe¹; Ioannou, Ioannis¹; Gross, Barry¹; Moshary, Fred¹; Ahmed, Sam<sup>1

1</sup>City College of the City University of New York 140 St @ Convent Ave, New York, NY, 10031, United States

Results of simulations and field measurements on the contribution of chlorophyll fluorescence to the reflectance spectra in coastal waters with a wide variety of water components are presented. This includes parameterization of fluorescence amplitude as a function of concentrations of water constituents, performance of fluorescence height (FLH) algorithms, their sensitivity to types of phytoplankton species and atmospheric correction models, dependence on illumination and viewing angles. Based on this parameterized model, near surface fluorescence quantum yield was indirectly estimated through a statistical analysis of the relationship between the chlorophyll concentration [Chl] and the shift of the total NIR peak from the fluorescence peak at 685 nm on reflectance spectra. On the other hand, a more direct measurement approach for the quantum yield was obtained by direct comparison of measured spectra with simulated spectra constructed from underwater attenuation and absorption spectral data (measured by WET Labs ac-s) together with fluorescence amplitude models based on insitu [Chl] measurements. Both approaches point to a smaller than expected quantum efficiency (0.3% – 0.5%) with less variability than normally believed. In addition, our modified FLH model applied to both MODIS and MERIS sensor bands are used to explore retrieval performance over a wide range of conditions. Performance based on actual MODIS and MERIS satellite imagery will also be presented.

RETRIEVE SIZE AND OPTICAL PROPERTIES OF INDIVIDUAL PARTICLE POPULATIONS FROM THE VOLUME SCATTERING FUNCTION

Zhang, Xiaodong¹; Twardowski, Michael¹; Hu, Chuanmin¹; Lewis, Marlon<sup>1

1</sup>University of North Dakota 4149 University Ave Stop 9011, Grand Forks, ND, 58202-9011, United States

Phytoplankton, suspended particles, and detritus are major particulate components in a coastal environment and knowledge of the spatial and temporal variations of their size distributions will provides important insight into understanding coastal dynamics of physical, chemical and biological processes. Traditional particle sizing and counting devices, such as Coulter Counter or an imaging system, while each has their own limitations, can not differentiate among different particles and can only provide a bulk estimate of the overall size distribution. Volume scattering function measures the angular variation of light scattered by a water volume, within which each component contributes additively. The contribution by each component, in turn, is a function of their size distribution, concentration, and refractive index. Here we report an inverse modeling approach using the measured volume scattering functions to derive the number densities and size distributions of major optically important water constituents simultaneously. The method will be evaluated by comparing the results with the estimated by other instruments.

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, John<sup>1

1</sup>Dalhousie 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.

MASS NORMALIZED OPTICAL PROPERTIES. WHY ARE THEY SO CONSTANT?

Boss, Emmanuel¹; Slade, Wayne Homer¹; Hill, Paul<sup>2

1</sup>University 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.

DETERMINING THE ROLE OF MEASUREMENT UNCERTAINTIES IN OBSERVED VARIABILITY IN THE BACKSCATTERING RATIO

McKee, David¹; Chami, Malik²; Cunningham, Alex ¹; Sanjuan-Calzado, Violeta³; Doxaran, David²; Brown, Ian<sup>1

1</sup>University of Strathclyde 107 Rottenrow, Glasgow, --, G4 0NG, United Kingdom; ²Laboratoire d'Oceanographie de Villefranche, Villefranche sur Mer, UMR 7093, BP 28, 06234, France; ³National Oceanography Centre Southampton, Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom

The backscattering ratio is a useful indicator of the angular scattering characteristics of natural waters. Its spectral variability is poorly documented. Recent studies in various marine waters have shown evidence both for and against significant spectral variability. However, most observations show significant variability in the magnitude of the backscattering signal. We present results from a study where both backscattering and scattering coefficients were measured at nine wavelengths in a region of UK coastal waters covering a wide range of turbidities. Measurement uncertainties are analysed for each parameter and it is shown that the majority of apparent variability in the magnitude of backscattering ratio signals can be attributed to measurement uncertainty effects. Regression analysis is used to demonstrate conclusively that the backscattering ratio is indeed wavelength dependent for the waters sampled. These results are important for radiative transfer simulation applications where the backscattering ratio has often been assumed to be spectrally flat. There are also profound implications for our understanding of particle size distributions in coastal waters since the commonly assumed Junge distribution is associated with a spectrally flat backscattering ratio.