Laboratory measurements of radar backscatter from bare and snow-covered saline ice sheets

Abstract

Abstraet. We performed experiments to collect radar backscatter data at K. (13-4GHz) and C bands (5'3GHz) over simulated sea ice at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) during the 1990 and 1992 winter seasons. These experiments were conducted over bare saline ice grown in an indoor tank and an outdoor pond facility. The radar data were calibrated using a complex vector calibration scheme to reduce systematic efTects. In conjunction with the radar measurements we measured ice physical properties.These measurements demonstrate that the dominant backscatter mechanism for bare saline ice is surface scattering. Both the copolarizcd and cross-polarized measurements compare favourably with the predictions of surface scattering models at two frequencies.During the 1992 indoor tank experiment we applied four successive layers of snow (about 2·5 ern each) to the saline ice sheet after the ice thickness had reached about 12cm. The backscatter at normal incidence dropped by 15dB and the backscatter at 45' increased by II dB with the introduction of the first snow layer. The application of three more layers, each of approximately 2·5 cm depth. did not alter the radar signature significantly. By modelling and direct observation we found that the initial change in the signature was caused by a roughening of the surface at the snow-ice interface and the change in dielectric contrast at the snow-icc interface.

Simulation of the CryoSat-2 satellite radar altimeter sea ice thickness retrieval uncertainty

“…However, the total altimeter backscatter is dominated by surface (or interface) scattering, and in our altimeter simulations volume scattering is insignificant as a backscatter source. This is in agreement with laboratory experiments showing that volume scattering at nadir incidence is insignificant as a backscatter source for snow-covered sea ice (Beaven et al, 1995). Though volume scattering is not a backscatter source, it does increase extinction and to some extent the distribution of backscatter between the snow and the ice surface.…”

Evaluation of CryoSat-2 derived sea-ice freeboard over fast ice in McMurdo Sound, Antarctica

“…For example, no single dominant backscattering surface was found for stratified snow during in situ investigations using a 10-16 GHz band instrument, but returns from the snow/ice interface dominated when layering in the snow cover was absent (Willatt and others, 2010). Surface roughness also influences the freeboard retrieval as it directly affects the shape of the returning radar waveform (Drinkwater, 1991;Beaven and others, 1995;Hendricks and others, 2010). Surface roughness may be separated into radar and geometric roughness: the former is associated with small-scale features at length scales comparable to the radar wavelength (in this case 0.02 m), and the latter is concerned with large-scale surface undulations (e.g.…”

Multiscale Surface Roughness and Backscattering

“…In conclusion, IEM is not yet applicable to large pixels of very rough surfaces with low permittivity values like Baltic sea ice. Small laboratory samples with salinity resembling that of Arctic sea ice (which is roughly 10 times larger than that of Baltic sea ice) have been successfully modelled using IEM [12,18]. The multiscale surface roughness of natural sea ice can be taken into account using the autocorrelation functions presented here, but further research of estimation of the field coefficients and of the effect of large rms height values is required.…”