SURFACE CORRECTIONS FOR REMOTE SENSING REFLECTANCE IN CASE 2 WATERS OF LAKE SUPERIOR*

摘要

We establish the average wavelength dependence for rough-surface reflectance Srs(λ) in Lake Superior and determine its magnitude at any individual site by extrapolating the total reflectance RrsT(λ) at the site to the asymptotic limit of zero scattering where Srs≌RrsT. The results show that Srs(λ) differs from the flat-surface Fresnel reflectance used in standard calculations of the remote sensing reflectance Rrs(λ) attributed to scattering by particles and molecules in bulk water. Finding Srs(λ) is essential in accurate estimates of Rrs(λ) at ground truth stations used in calibration of satellite data for waters where the presence of colored dissolved organic matter (CDOM) often leads to negative values for Rrs if we assume Fresnel reflectance. We examine the differences between Fresnel reflectance and Srs and estimate the threshold concentration of CDOM that could produce negative values of Rrs if those differences are not taken into account in the calculation of Rrs.