On the feasibility of space-based radar ice sounding of the Antarctic ice sheet at P-band

Space-based radio echo sounding (RES) of the continental ice sheets can potentially offer full coverage, uniform data quality and sampling. Ice sounding radars must operate at low frequencies in order to ensure low attenuation of the signal as it propagates down through the ice and back from base of the ice sheet. Typical frequencies of airborne radar ice sounders are between 60 MHz and 150 MHz. However, the lowest possible frequency for space-based radar ice sounders is 435 MHz. In 2004 the International Telecommunication Union (ITU) radio regulations allocated a 6 MHz band at 435 MHz (P-band) enabling space-based Earth observation radar missions at a frequency that might be applicable for ice sounding. The payload of ESA's Earth Explorer 7 mission, Biomass, is a P-band radar.
At P-band the attenuation and scattering properties of the ice sheets are not as well known as they are at the lower frequencies commonly used from aircraft, but in 2005 ESA commissioned development of a P-band polarimetric airborne radar ice sounder (POLARIS) [1], and encouraging results were obtained with data acquired in Greenland. In February 2011 POLARIS data were acquired in Antarctica as part of a close scientific collaboration between seven organizations in Europe and North and South America [2]. The primary objective of this IceGrav campaign was to measure gravity in Queen Maud Land, but a secondary objective was to acquire P-band sounder data, benefitting from the large coverage offered by the Basler DC3 aircraft used.
In this study the feasibility of space-based radar ice sounding is assessed. A two-step approach is applied:
(1) Key ice sheet parameters are estimated from the airborne POLARIS data acquired in Antarctica.
(2) The performance of potential space-based ice sounding radars is simulated based on the estimated ice parameters and system parameters envisioned for a space-based radar.
The first step is accomplished by establishing empirical models of the attenuation coefficients and backscatter coefficients for the surface, volume and base of glaciers, ice shelves, central ice sheets etc.. The models are used in combination with the POLARIS system parameters and the data acquisition geometry to iteratively simulate return waveforms, compare them with the measured waveforms, and adjust the ice parameters until the simulated waveforms and the measured waveforms match.
This iterative approach is supplemented by a direct data analysis estimating the scattering patterns via the Doppler spectra of the POLARIS data. The scattering patterns of the ice surfaces are relevant because the geometry of a space-based radar increases the risk that off-nadir surface clutter masks the nadir depth-signal of interest.
Currently the ice sheet model is being established and validated. At the symposium measured and simulated satellite waveforms will be compared, and the feasibility of space-based ice sounding will be addressed.