Abstract
Radar backscattering properties can be extremely sensitive to the freeze/thaw states of the ground surface. This study aims to evaluate the changes of L-band microwave scattering characteristics between thawed and frozen conditions by using polarimetric scattering mechanism indicators. ALOS PALSAR polarimetric mode data acquired in winter and spring seasons over Eastern Siberia are used in this study. Experimental results show that the actual scattering mechanisms and their seasonal variations over various forested and non-forested permafrost ecosystems can be successfully characterized by the polarimetric target decomposition parameters and the polarimetric coherences. In addition, fully polarimetric radar observations exhibit great potential for mapping land cover types and surficial features in the permafrost active layer. Particularly, the co-polarization coherences on the HV-polarization basis and circular-polarization basis were found to be very useful for discriminating different surficial geocryological characteristics in recently burnt forests and thermokarst regions.
Highlights
The active layer overlying permafrost generally undergoes drastic seasonal changes due to large temperature variations between the summer and winter seasons
Two Advanced Land Observing Satellite (ALOS) Phased Array L-band SAR (PALSAR) images acquired under frozen and thawed conditions were co-registered before analysis
Adaptive-Neighborhood (IDAN) filter was applied to multilook-processed PALSAR data to obtain quadrant would be a consequence of the differences in soil properties, e.g., density, moisture content and heat capacity, and active layer structures
Summary
The active layer overlying permafrost generally undergoes drastic seasonal changes due to large temperature variations between the summer and winter seasons. Seasonal freeze/thaw states can be spatially and temporally complex depending on landscape heterogeneity and local-scale variations in geocryological processes. Radar backscattering properties can be strongly sensitive to the freeze/thaw state of the land surface due to the large contrast in the dielectric constant of frozen and liquid water at microwave frequencies. Studies of seasonal variations of C-band radar signals with ERS and ENVISAT SAR data [1,2,3,4,5,6,7,8,9] showed a decrease in the backscattering coefficient of about 3 dB during the transition of trees from a thawed to a frozen state almost independently of tree species. A greater decrease in backscattering coefficients can be observed when tundra areas froze than when forested areas froze [1,3]
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