The impending launch of a number of remote sensing platforms such as the NASA SeaWiFS (sea-viewing wide field-of-view sensor) has generated renewed interest in instrumentation for measuring ocean color in situ. The increased number of spectral bands desired and the large dynamic range of the measurements place special challenges on the design of these instruments. Of particular interest in measurements of spectral irradiance and in the calculation of irradiance reflectance are errors introduced by the departure of the instrument response from a true cosine at increasing angles of incident irradiance. Using field data as well as a modelled radiance distribution, this paper presents an evaluation of a commercial cosine collector for measurements of spectral irradiance. Preliminary results form a new program sampling the variability in immersion coefficient are also presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.