Sensitivity of MODIS Retrievals of Chl, IOP and FLH to Coastal Water Characteristics and Atmospheric Correction Models

Sam Ahmed, CUNY/NASA URC, ahmed@ccny.cuny.edu (Presenting)
Alex Gilerson, CUNY/NASA URC, gilerson@ee.ccny.cuny.edu (Presenting)
Jing Zhou, CUNY/NASA URC, jzhou@ccny.cuny.edu
Barry Gross, CUNY/NASA URC, gross@ccny.cuny.edu
Fred Moshary, CUNY/NASA URC, moshary@ccny.cuny.edu

Ocean color algorithms for retrieval of chlorophyll [Chl] and mineral concentrations as well as water IOPs from satellite reflectance spectra usually fail in coastal waters because of their complexity and errors/inadequacies of atmospheric correction. Recent advances in the understanding of coastal water IOPs and in atmospheric correction procedures over coastal zones open possibilities for more detailed studies using satellite imagery which includes analysis of spatial and temporal trends in [Chl] and other water parameters.

We report on studies of MODIS time series data of [Chl], CDOM, absorption, backscattering coefficient and FLH for several years for Long Island Sound as well as for other coastal areas, using SeaDAS processing software with both NIR and SWIR atmospheric correction algorithms. Correlations between parameters retrieved using different procedures were calculated and analyzed to determine the sensitivity of retrievals to atmospheric correction procedures and coastal water characteristics.. Reflectance data and results of retrievals are complemented by our field measurements of reflectance spectra, IOPs and water samples.

Results of FLH retrieval are compared with the fluorescence algorithms in our recent published work where we parameterized the Chl fluorescence component of the reflectance spectra for coastal waters as a function of [Chl], CDOM and mineral concentrations. This was based on findings from both simulations and field measurements, showing that variations in fluorescence magnitude are attributed primarily to variability in the absorption/scattering of water components, rather than to variations in Chl fluorescence quantum yield, and which establishes relatively strict limitations on possible ranges of Chl and mineral concentrations where FLH algorithms can be applied in coastal zones.