Instruments and methods for measuring the backward-scattering coefficient of ocean waters

The backward-scattering coefficient b(b) is an important optical property that plays a central role in studies of ocean-color remote sensing, suspended particle distributions, water clarity, and underwater visibility. We investigate the fixed-angle backscattering sensor approach for the application of measuring b(b). Analysis shows that the sensor response to volume scattering can be expressed as the integral of the volume scattering function (VSF) over the backward angles (90-180 degrees) weighted by the sensor-response function. We present a procedure for determining the sensor-response function that contains all the information necessary to calibrate the sensor fully to measure the VSF at a nominal backscattering angle. It is shown that, for fixed-angle backscattering sensors, b(b) is most accurately estimated when the sensor-response function covers the middle range of backscattering angles, roughly 110-160 degrees, where the shape of the VSF has the least variability. Backscattering at and near the end angles, namely, 90 degrees and 180 degrees, are least correlated with b(b). We describe a variety of spectral backscattering sensors that we have developed, and we present their sensor-response functions. (C) 1997 Optical Society of America.