The impact of cosine collector geometry on aquatic spectroradiometer performance

The design of underwater instruments is often a compromise between instrument optical performance features, ruggedness of design, and communications bandwidth. Further, the increased number of spectral bands reported by newer sensing systems and the wide dynamic range observed in optical signals in situ places special challenges on the design of next generation instrumentation. Error introduced into irradiance measurements by departures from a true cosine response is one important characteristic of spectroradiometer performance. Using laboratory data acquired using a newly developed nineteen wavelength PRR-800/810 Profiling Reflectance Radiometer, this paper illustrates the impact of cosine collector geometry on measurements of spectral irradiance. Typical departures from true cosine response for the PRR-800 are less than ±2% over the visible region of the spectrum over zenith angles ±65°, with ±10% out to +/- 88°. Using a uniformly diffuse light field, estimates of the inaccuracy from geometric errors integrated over all zenith and azimuthal angles are less than 2.5% total error throughout the visible region