# Remote Sensing of Environmental Changes in Cold Regions: Methods, Achievements and Challenges
## 2 Principles and Methods
### Remote Sensing of Frozen Soil
#### 2.3.2 Surface Deformation  
In cold regions, climate change could significantly affect surface morphology (e.g., permafrost melting due to global warming), which may pose a threat to 70% of current infrastructure in Arctic permafrost regions by 2050 (Figure 3) [26]. Remote sensing technologies could offer a useful platform to better understand these geometric changes, especially those that guarantee high-resolution topography analysis [168]. [PERSON] et al. [169] used spaceborne InSAR data to map surface subsidence trends at a thermokarst landform located near Deadhorse on the North Slope of Alaska. The motivation of this study was the fact that the intrinsic dynamic thermokarst process of surface subsidence remains a challenge to quantify and is seldom examined using remote sensing methods. Subsequent InSAR analysis using  
Figure 3: Projected infrastructure hazard areas from degrading permafrost over the Northern Hemisphere by year 2050 [26]. The figure was reproduced with permission from [26], which is licensed under a Creative Commons Attribution 4.0 International License. Figure 2: Estimated annual non-frozen season in 2017 derived from three operational satellite FT data products, including: (**a**) SSM/I (37 GHz; 25-km), (**b**) AMSR2 (36.5 GHz; 6-km), and (**c**) SMAP (1.4 GHz; 9-km). Areas outside of the FT global domain for each product are shown in grey and white. Phased Array type L-band SAR (PALSAR) images revealed localized thermokarst subsidence of a few cm yr\({}^{-1}\) between 2006 and 2010. [PERSON] et al. (2010) used terrestrial laser scanning for quantifying surface deformation pertaining to underlying hydrological-thermal processes affecting active layer FT conditions in the Tibetan Autonomous Region (China). The Terrestrial Laser Scanner and six Trimble 5700 GNSS systems were deployed in the region between May 2014 and October 2015, where the site was monitored four times. The results indicated that as air temperature and precipitation increase with climate warming the active layer will become more unstable, exacerbating slope instability as phase changes (thawing and freezing) occur. [PERSON] and [PERSON] (2010) summarized recent developments (2010-2015) in remote sensing applications to detect and monitor landscape changes in permafrost regions, analyzing surface temperatures, snow cover, topography, surface water, vegetation cover, and disturbances from fire and human activities. According to this review, repeated light detection and ranging (LIDAR), InSAR, and airborne geophysics will be key tools for monitoring permafrost changes (topographic and subsurface) in Arctic and boreal regions. [PERSON] et al. (2012) stressed the fact that in situ monitoring of periglacial dynamics is essential for the study of periglacial morphology and the design of mitigation and adaptation measures for infrastructure in permafrost zones. The application of structure-from-motion photogrammetric techniques is relatively low-cost and easy to use (e.g., see (2013) for details), and provide capabilities for multi-temporal surveys of surface deformation. [PERSON] et al. (2014) used X-band SAR Interferometry for the detection of surface deformation in the Sichuan-Tibet Grid Connection Project Area (China). In this area, landslides, and debris flows triggered by climate change are becoming a major threat. Surface deformation time series observations were obtained through sequential TerraSAR X-band images. The analysis suggested that the deformation rate tends to increase dramatically during the late spring and late autumn, but with reduced deformation during colder winter months. [PERSON] et al. (2015) discussed the capability of high spatiotemporal resolution X-band microwave satellite data (obtained from the TerraSAR-X satellite) to quantify cliff-top erosion of an ice-rich permafrost riverbank in the central Lena Delta. The results indicated continuous erosion from June to September in 2014 and 2015 with no significant seasonality across the thawing season.