Spaceborne GNSS-R Signal Coherence Dependence on Elevation Angles Over Sea Ice and Ice Sheets in Greenland and Antarctica

This paper presents a quantitative analysis of spaceborne GNSS-R signal coherence dependence on satellite elevation angles at specular reflection points over sea ice and ice sheets in Greenland and Antarctica using TechDemoSat-1 delay Doppler maps. Over sea ice and ice sheets, the probability of coherent reflections is high at low elevation angles and decreases with increasing elevation angles, as expected. For sea ice, the coherence rate is ~96% at elevation angles of
$20-43^{\circ}$
, then drops to a minimum of ~25% near nadir. Over the Greenland ice sheet, the maximum coherence rate is 86% at the elevation angle of
$47^{\circ}$
, and the minimum is 21% at
$73^{\circ}$
. In Antarctica, the coherence rate reaches a maximum of 90% at
$48^{\mathrm{o}}$
and a minimum of 36% at
$72^{\circ}$
. The findings provide a quantitative characterization of the GNSS-R coherency over sea ice and ice sheets and are useful for future GNSS-R mission designs.