Optical properties of multiyear and first year sea ice

During LEADEX, beam spreading and beam transmission measurements were made on complete ice sheets, and on slabs of ice removed from the ice column with depth below the ice surface using a laser source beneath the ice sheet. The beam spread measurements are reported along with estimates of ice layer extinction and scattering optical properties. The scattering properties were derived from the beam spread function (BSF), using a Fourier-Bessel transform technique which establishes the forward small-angle portion of the volume scattering function. The stability and validity of this small-angle scattering theory are examined for the very inhomogeneous sea ice medium. The largest values of extinction and spreading were observed for bubbly near surface low density ice (LDI) layers, and also for the desalinated freeboard layer of first-year ice. These ice layers have also been shown to impact microwave volume backscatter. Data collected on physical ice properties included bubble size and were used to independently estimate the scattering function using Mie theory. These calculations support the observed beam spread observations. Modeling studies were conducted for these surface ice layers in combination with a dry snow layer of variable thickness. Radiative transfer model results demonstrate the impact of the LDI layers on albedo.