Abstract
The Qinghai–Tibet Plateau (QTP) is heavily affected by climate change and has been undergoing serious permafrost degradation due to global warming. Synthetic aperture radar interferometry (InSAR) has been a significant tool for mapping surface features or measuring physical parameters, such as soil moisture, active layer thickness, that can be used for permafrost modelling. This study analyzed variations of coherence in the QTP area for the first time with high-resolution SAR images acquired from June 2014 to August 2016. The coherence variation of typical ground targets was obtained and analyzed. Because of the effects of active-layer (AL) freezing and thawing, coherence maps generated in the Beiluhe permafrost area exhibits seasonal variation. Furthermore, a temporal decorrelation model determined by a linear temporal-decorrelation component plus a seasonal periodic-decorrelation component and a constant component have been proposed. Most of the typical ground targets fit this temporal model. The results clearly indicate that railways and highways can hold high coherence properties over the long term in X-band images. By contrast, mountain slopes and barren areas cannot hold high coherence after one cycle of freezing and thawing. The possible factors (vegetation, soil moisture, soil freezing and thawing, and human activity) affecting InSAR coherence are discussed. This study shows that high-resolution time series of TerraSAR-X coherence can be useful for understanding QTP environments and for other applications.
Highlights
Permafrost is defined as soil or rock that remains at or below 0 ◦C for two or more consecutive years [1]
This study shows that high-resolution time series of TerraSAR-X coherence can be useful for understanding Qinghai–Tibet Plateau (QTP) environments and for other applications
The experimental results show that railway and highway hold high coherence during the whole observation, with the maximum coherence value greater than 0.8
Summary
Permafrost is defined as soil or rock that remains at or below 0 ◦C for two or more consecutive years [1]. The Qinghai–Tibet Plateau (QTP) is the region with greatest permafrost in the world, and it affects its surrounding environment and climate directly through atmospheric and hydrological processes [2,3]. The status of permafrost in Tibet is a sensitive indicator of global climate change. Long-term temperature measurements indicate that the lower altitudinal limit of permafrost has moved by 25 m in the north during the last 30 years [6,7]. The existence of the QTR has changed the thermal exchange between the ground surface and the atmosphere, and influenced the underlying permafrost environment, resulting in the increase of the ground temperature and acceleration of the process of permafrost degradation [8]
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