Monitoring permafrost changes in central Yakutia using optical and polarimetric SAR data

The changes in the permafrost environment have been of interest as a sensitive indicator of changes in global climate conditions. Since changes in the soil and ecosystem of the permafrost active layer are spatially and temporally complex depending on many environmental factors, it is not easy to grasp climate-induced changes occurring in coupled atmospheric-ecological-geocryological systems. To understand the changes in the permafrost active layer, spatially detailed monitoring methods such as multi-spectral optical and Synthetic Aperture Radar (SAR) remote sensing technologies have been extensively applied to the permafrost observation. Optical and SAR systems observe different permafrost features due to significant differences in electromagnetic wave frequencies and imaging mechanisms. Therefore, most studies used optical and SAR data separately according to the purpose and characteristics of each study. The objective of this study is to explore the possibility of combined interpretation of optical and SAR data for identifying and understanding spatiotemporal details of the short- and long-term changes occurring in the permafrost active layer. Multi-spectral optical images acquired during the thawing period and L-band polarimetric SAR images acquired during the freezing period are used in this study in order to examine ecological characteristics and cryogenic processes, respectively. The result of analyzing the relationship between information obtained from optical and SAR sensors revealed that there was a significant correlation between winter changes in scattering properties observed in SAR data and summer land cover changes observed in optical data. The scattering characteristics of winter soil were found to be particularly related to the ecosystem changes in areas that can be explained by the thermokarst development process. Additional data from independent sources, such as elevation data, meteorological data, and long-term optical data, consistently supported the relationship between the winter SAR observations and the thermokarst-related ecosystem changes. The experimental results also elucidated that polarimetric scattering mechanism indicators representing the signal depolarization and surface roughness properties played an important role in deriving information related to the permafrost process from the winter SAR data.