Abstract
Atmospheric correction of ocean color imagery is commonly based on the assumption that
water-leaving radiances (Lw) at near-infrared (NIR) wavelengths are negligible.To investigate
the validity of this assumption, we carry out radiative transfer simulations using a model appro
priate for the coupled atmosphere-ocean system. In this model both reflection (including total
reflection) and refraction at the atmosphere-ocean interface as well as light scattering both in the
atmosphere and the ocean are taken into account.Weassume that the atmosphere-ocean system is
vertically stratified, and that the effects of wave-slopeshave been removed so as to leave behind a
flat atmosphere-ocean interface. Simulated results show that for common open-ocean aerosol
loadings (aerosol optical depths in the range 0.08-0.11) water-leaving radiances at NIR wave
lengths (e.g., 865 nm) are usually not negligible.
The impact of the non-negligible values of water-leaving radiances at NIR wavelengths on
atmospheric correction depends on (i) the ocean particle concentration; (ii) the scattering charac
teristics of particles in the near-surface ocean water, described by their shape, size, and refractiveindex
distributions, which in turn determine the scattering phase function; (iii) the aerosol optical
depth; and (iv) the sun-satellite geometry. Our simulations demonstrate that a new approach to
atmospheric correction of ocean color imagery is needed to obtain reliable and accurate results
for open-ocean waters when particle concentrations are high. This is particularly important when
the aerosol loading is low because then the contribution from the water-leaving radiance to the
total radiance received by the satellite sensor is relatively larger, and will if ignored introduce
significant errors in atmospheric correction.
