Discriminating surface deformation types and assessing LOS interpretation applicability using ascending and descending Sentinel-1 InSAR in the permafrost zone of the Qinghai-Tibet Engineering Corridor

Warming and wetting on the Qinghai-Tibet Plateau (QTP), together with increasing engineering disturbance, have accelerated permafrost degradation along the Qinghai-Tibet Engineering Corridor (QTEC), inducing surface deformation that threatens infrastructure stability and environmental safety. Interferometric synthetic aperture radar (InSAR) has become an effective tool for large-scale deformation monitoring; however, conventional single-orbit ascending or descending observations measure only one-dimensional line-of-sight (LOS) displacement. Because LOS deformation represents a projection of actual ground motion, it cannot always be directly interpreted as vertical uplift or subsidence, especially where horizontal displacement is significant. In this study, ascending and descending Sentinel-1 InSAR observations from 25 February 2017 to 31 March 2022 were integrated to decompose two-dimensional deformation components, namely east-west and vertical displacement, in the permafrost zone of the QTEC. Based on the decomposed results, surface-deformation types were discriminated, and the interpretation applicability of conventional single-orbit LOS observations was quantitatively evaluated using vertical deformation as a reference. The results show that single-orbit LOS deformation can reasonably represent vertical deformation in 52.84 % of the study area, whereas the remaining 47.16 % is dominated by horizontal displacement and is therefore unsuitable for direct interpretation as uplift or subsidence. These findings highlight the necessity of distinguishing deformation types before interpreting LOS deformation and provide practical guidance for improving the reliability of InSAR-based deformation monitoring and engineering-risk assessment in permafrost corridors.