Abstract
Abstract. A thermokarst lake is an important indicator of changes in climate, which cause considerable thermal distribution to the surrounding permafrost. The imaging radar has demonstrated the capability to determine when and which lakes freeze or do not freeze. In this paper, the temporal variability of C-band backscattering of thermokarst lakes at Beiluhe test area, is located on the central Qinghai- Tibet Plateau (QTP), were examined by 45 ENVISAT-ASAR imageries acquired in freeze up, ice duration and break-up stages. The SAR behaviour response for lake ice change are analysed with ASAR observation in experiments area. The results showed that the ice layer volume scattering and ice-water surface scattering were the two major scattering components in C-band VV polarization, which is also affected by the increase of bubble size, ice density and roughness of ice-water interface. According to this study, the timing of lake ice-on in fall and ice-off in spring for this geographic region can be identified in radar images by comparing radar backscatter from lake ice to its surrounding alpine meadow. When ice duration, the radar signature proved to be able to monitor the ice thickness over lake and deformation around the lake.
Highlights
Thermokarst lakes are widespread in tundra and boreal lowland region with thermal degradation of permafrost or melting of massive ground ice (Kokelj and Jorgenson 2013; Niu et al 2011)
Since SAR image data obtained by ENVISAT-ASAR are Level 1 Single Look Complex (SLC) in slant-range form, some preprocessing should be done at first, which includes: (1) Calibration: The digital number (DN) of the ASAR image could be converted to the backscattering coefficient σ0 at each image pixel; (2) Co-registration: This ensures that values of from different times and in different parts of the image are comparable
Strong northwest wind is prevailing in the Beiluhe Basin, the surface layer is disturbed and small ice crystals do not have enough time to congeal, frazil ice forms and progressively joins together to form a solid sheet that consists of tiny granular crystals in the surface
Summary
Thermokarst lakes are widespread in tundra and boreal lowland region with thermal degradation of permafrost or melting of massive ground ice (Kokelj and Jorgenson 2013; Niu et al 2011). The number of the thermokarst lakes and ponds has been increasing under the influence of recent climate warming in the continuous permafrost region along the Qing-Tibet railway and highway (Niu et al 2011). In comparison with high latitude lakes in other regions, relatively little study has been conducted on the QTP for the characteristics and impacts of thermokarst lakes (Ling et al 2012) due to the lack of continuous long-term ground obersvation, which calls for the use of remote sensing on the QTP (Song et al 2014)
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