Modeling of ice thickness effect and its application to data interpretation

A dense medium scattering model based on the standard radiative transfer formulation but with a scattering phase function for a group of scatterers as opposed to the conventional single scatterer phase function is developed to account for volume scattering from saline ice. Surface scattering due to air-ice and ice-water boundary is accounted for using the IEM surface scattering model. To avoid the coherent scattering effect only off nadir measurements are considered. Experimental measurements at CRREL during ice growth indicates that due possibly to some roughness of the bottom ice surface at the ice-water interface, backscattering from thin ice (less than 2 cm) is above -17 dB at 20 degrees incidence and 5.3 GHz. As ice grows in thickness towards 8 cm, backscattering between 20 to 40 degrees decreases with thickness to about -26 dB to -32 dB respectively. The purpose of this study is to investigate the cause of this decrease by examining the relative contributions from the ice volume and the two boundary surfaces. Preliminary study indicates that for thin ice the contribution of water under the ice sheet in the form of producing an effective impedance at the air-ice interface is the dominating factor. Reflectivity measurements confirm this idea. When the effective dielectric constant is used in the computation of backscattering from the air-ice agreement is obtained between model backscattering measurements. Results indicate that volume scattering is not a factor in this study