A New Method for the Measurement of the Optical Volume Scattering Function in the Upper Ocean

Abstract

A new method to measure the optical volume scattering function (VSF) of seawater is presented. The VSF is a fundamental property used in the calculation of radiative transfer for applications as diverse as upper-ocean heating by solar radiation to laser ranging of the sea bottom. The approach differs from traditional ones and involves use of a special periscope prism that allows the direct determination of the VSF over a wide range of angles (0.6°?177.3°) with an angular resolution of 0.3°. Measurements taken in the laboratory using Barnstead International, Inc., Nanopure water, cleaned seawater, and known additions of defined scatterers indicate close correspondence between experimental data and theoretical simulations based on Mie theory over the angle range from 12° to 170°. Field deployments in the Atlantic Ocean continental shelf water are shown to produce high quality measurements of the VSF in the angle range from 0.6° to 177.3°; such observations have not been available before. The new data show that there is significant environmental variance in the VSF for small angles (from less than 1° to several degrees) in the forward direction and from 170° to 177.3° in the backward direction. The resulting observations are of profound and fundamental importance to the accurate modeling of the propagation of radiation in the ocean.