Use of beam spreading measurements to estimate volume-scattering properties in sea ice

Beam spread measurements have been made on sea ice samples and used to develop estimates of the volume scattering function at small scattering angles. In this technique Gaussian-like modelled beam spread functions (BSF) are used to derive the modulation transfer function (MTF) and Well's theory is applied to estimate the volume scattering function for the sea ice medium. A Monte Carlo model for beam propagation through homogeneous sea ice layers was used to estimate beam spreading and the surface distributions of irradiance and radiance. Light scattering was assumed to occur from the presence of spherical bubbles trapped within the ice. Volume scattering functions used in the model were calculated with Mie theory or derived from measured BSFs. The BSFs generated by the model, using estimated optical properties, were found to be comparable to those derived from the transforms over a range of ice thicknesses. The scattering transform technique was applied to beam spread data collected during Arctic and laboratory experiments for samples of young, first year, and multiyear ice to derive estimated MTF values. Requirements and limitations for applying this technique to sea ice are discussed.