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

The backward-scattering coefficient bb 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 bb . 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,bb 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 bb . We describe a variety of spectral backscattering sensors that we have developed, and we present their sensor-response functions.