Abstract
Improved remote sensing retrievals of the chlorophyll fluorescence component in coastal water reflectance can
significantly help environmental impact assessments. While retrieval of chlorophyll fluorescence from satellite
observations of open ocean reflectance using Fluorescence Line Height (FLH) algorithms is now routine, it is much
more complicated in coastal waters where the fluorescence overlaps with a NIR elastic scattering peak arising from the
combination of photosynthetic pigment and particulate scattering and absorption, and rapidly increasing water
absorption. To examine retrieval accuracies attainable in coastal waters by MODIS and other FLH algorithms, we
compared the results of extensive numerical simulations with those of our field measurements in the Chesapeake Bay.
The relationship between the contribution of fluorescence in the reflectance spectra and [Chl] and other water
constituents was analyzed by simulations of more than 1000 reflectances using the HYDROLIGHT radiative transfer
program. For these, IOP were related to parameterized microphysical models, following the same procedures used to
generate the IOCCG dataset, but with higher (1 nm) spectral resolution, and wider range of parameters including
chlorophyll specific absorption more typical of coastal waters. Results of simulations and field measurements show that
the variability of retrieved fluorescence can be attributed largely to its attenuation in the water by algae, CDOM and
mineral particles, and much less to the variation of the fluorescence quantum yield. Our systematic parametric study of
fluorescence as a function of the other water components is then used to define the range of water parameters where
fluorescence contributes significantly to the NIR peak reflectance, and where it is almost undetectable.
