DETERMINATION OF VOLUME AND SURFACE SCATTERING FROM SALINE ICE USING ICE SHEETS WITH PRECISELY CONTROLLED ROUGHNESS PARAMETERS

Experiments were performed at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH, to precisely determine the relative contributions of surface and volume scattering from salin e ice that has well-known surface roughness characteristics. The ice g rowth phase of the experiment made use of two 6-ft diameter tanks and a 6-ft diameter mold with known roughness statistical parameters of rm s height = 0.25 cm and Gaussian correlation (correlation length = 2.0 cm). One tank was used for growing a moderately thick saline ice sheet with very smooth surface, and the other was used for growing a thin l ayer of freshwater ice over the surface mold. The latter resulted in a layer with one statistically known rough boundary and one smooth boun dary. Wide-bandwidth, multiple incidence angle backscattering measurem ents were performed, first on the bare saline ice sheet and then on th e same sheet after the thin freshwater ice sheet was placed on top of it. Results indicate that the surface scattering dominates over saline ice volume scattering at all frequencies for low incidence angles for both the very smooth and Gaussian rough surfaces. The significance of volume scattering depends strongly on angle of incidence, frequency, volume scattering albedo, surface roughness, and surface correlation f unction.