Characterizing C-band backscattering from thermokarst lake ice on the Qinghai-Tibet Plateau

On the basis of weather observations and field measurements of lake ice, this study investigates multi-temporal C-band VV-polarized radar backscattering values from the thermokarst lakes and alpine meadow on the QTP during the period 2003-2010. In order to understand the scattering mechanism of lake ice, a scattering model is developed for lake ice that updates some assumptions adopted in previously developed models, including the roughness of the ice-water interface and the shape of vertically stacked centimeter-sized bubbles in the lake ice. We conclude the following: First, with a incidence angle range near 24°, the backscattering intensities of C-band VV-polarized ENVISAT-ASAR data exhibit a strong dependence on time, which is related to the processes of ice growth and decay on the QTP. Some unique backscattering characteristics of lake ice in this high-altitude region, as compared to those for high-latitude regions, are also discussed and documented in the paper. Secondly, the timing of lake ice-on in fall and ice-off in spring for this region can be identified in radar images by using a threshold of −12 dB for the backscatter intensity of the surrounding alpine meadow. Finally, the results of applying the scattering model indicate that surface scattering from the ice-water interface and volume scattering from gas bubbles embedded in the lake ice are the dominant scattering mechanisms for C-band VV polarized SAR and that the roughness of the ice-water interface and also bubble size are the most sensitive factors.