ATMOSPHERIC CORRECTION OF OCEAN-COLOR SENSORS - EFFECTS OF THE EARTHS CURVATURE

We investigate the influence of the curvature of the Earth on a proposed atmospheric-correction scheme for the Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) by simulating the radiance exiting the top of a spherical-shell atmosphere and inserting the result into the proposed correction algorithm. The error in the derived water-leaving reflectance suggests that the effects of the curvature are negligible for solar zenith angles (theta0) less-than-or-equal-to 70-degrees. Furthermore, for theta0 > 70-degrees the error in atmospheric correction can ususally be reduced if the molecular-scattering component of the top of the atmosphere reflectance (rho(r)) is computed with a spherical-shell atmosphere radiative transfer code. Also, for theta0 > 70-degrees the error in atmospheric correction in a spherical-shell atmosphere, when rho(r) is computed with a spherical-shell model, can be predicted reasonably well from computations made with plane-parallel atmosphere radiative transfer codes. This implies that studies aimed at improving atmospheric correction can be made assuming plane-parallel geometry and that the investigator can be confident when theta0 > 70-degrees that any improvements will still be valid for a spherical-shell atmosphere as long as rho(r) is computed in spherical-shell geometry. Finally, a scheme for computing rho(r) in a spherical-shell atmosphere in a relatively simple manner is developed.