Measurement of the spectral absorption coefficient in the ocean with an isotropic source

Closed-form equations that describe the vector irradiance from an isotropic source embedded in the oceanare rigorously derived from the steady-state radiative transfer equation. The equations are exact for a homogeneous medium and are believed to be an excellent approximation along the vertical axis for a plane-parallel ocean. The equations are solved for the absorption coefficient as a function of distance from the source. For clear ocean water, it is shown that vector irradiance measurements alone provide sufficient information for an accurate calculation of the absorption coefficient. Measurements in Pacificwater of the vector irradiance from an isotropic source are presented, and the absorption coefficient is computed. The estimated value of the absorption coefficient from a linear least-squares fit to the data has a standard error of ~ 1%.