Accuracy of Ocean Color Data Derived from the Coastal Zone Color Scanner (CZCS)

Abstract : The U.S. Navy is interested in investigating the use of ocean color data for naval applications, as they apply within the Air Defense Initiative. The major source of available data for assessment is the Coastal Zone Color Scanner (CZCS) data base. These data were collected during 1979-1986. Although the CZCS is no longer operational, much information has been published on the analysis of the data. This technical note reviews that literature, which deals primarily with the measured and estimated errors associated with using the CZCS data to derive either chlorophyll concentrations (C) or the diffuse attenuation coefficient (K) of oceanic waters. The recognized uncertainties in the absolute values of the quantities of C and K must be taken into account when addressing the potential use of CZCS data for certain naval applications. The literature generally agrees that on a global basis, K or C can be determined from CZCS data to only within a factor of 2, as compared with in situ measurements. In addition, the water-leaving radiance for one spectral band can probably be obtained from the CZCS data, but in a more regional or smaller geographical area, after corrections to within 15%. This percentage relates to an error approximately 30% in K or C, both of which use a ratio of at least two spectral bands. Extreme care must be taken in applying the appropriate corrections on a pixel-to-pixel basis if the error is to be reduced to this value. If the concern is with only spatial trends of water clarity at a particular point in time or with temporal trends at each point in space, the CZCS images can probably be used; however, the conditions under which they apply must be indicated.