Considerations for Ku-Band Scatterometer Calibration Using the Dry-Snow Zone of the Greenland Ice Sheet

Postlaunch calibration of satellite-borne scatterometers using backscatter data from natural land targets helps to maintain scatterometer accuracy. Due to its temporal stability, the dry-snow zone of the Greenland ice sheet has been proposed in previous studies as a calibration target. Using QuikSCAT data, this letter examines the backscatter properties of the dry-snow zone that are relevant to Ku-band scatterometer calibration including temporal and spatial variabilities, and azimuth-angle and polarization and incidence-angle dependences. The backscatter is found to seasonally vary throughout the dry-snow zone by 0.4 dB on average. Small interannual variations (less than 1.5 dB over a nine year period) in the backscatter are also present in some regions. Azimuth modulation is generally less than 0.4 dB in magnitude and is not significant in some regions of the dry-snow zone. Melting and refreezing appear to cause the quasi-polarization ratio to temporarily decrease. Spatially consistent and relatively temporally stable regions that are well within the interior of the dry-snow zone are best suited as calibration sites.