The Coastal Zone Color Scanner (CZCS) Algorithm. A Critical Review of Residual Problems

Abstract

Computation of phytoplankton pigment concentrations from radiances received by the Coastal Zone Color Scanner (CZCS) is a complex process. Water-leaving radiances, a small portion of the total signal, control the value of pigment computed, but fully 80 to 90% of the total radiance is due to Rayleigh and aerosol scattering. These latter effects must be accurately modeled if reliable pigment concentrations are to be retrieved from CZCS data. In addition, prior to pigment retrieval a series of pre-processing steps must be performed to: (1) correct for instrumentation problems (e.g. drop-outs, zero counts, electronic overshoot); and (2) eliminate clouds from the scene. This paper critically reviews all of the aforementioned factors involved in the valid extraction of phytoplankton pigment concentrations from CZCS data. Also, several possible new approaches for improving the basic closure of the radiative transfer model used in CZCS pigment extraction algorithms (i.e., more robust approaches to the aerosol radiance terms) are introduced. Finally, based upon the community-wide CZCS experience, a few guidelines are suggested for the calibration and timely distribution of ocean color data from future generation sensors.