The traditional method for validating calculated values of chlorophyll concentration in the sea is based on comparisons within situpoint measurements made from ships. In this paper we present an alternative approach based on a two-look method involving data from successive orbits of the NIMBUS-7 satellite. We present the results of some calculations based on the use of Coastal Zone Colour Scanner (CZCS) data for the Irish Sea viewed from two successive orbits of the NIMBUS-7 satellite. The method used involves a first attempt at a self-consistent approach to calculating the aerosol path radiance. Results are presented for two pairs of scenes from 6 April 1980 and 4 May 1980.