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

Abstract

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 −12dB 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.