Glacier mass changes in the Western Pamirs 2003-2024 from high-resolution stereo satellite images

The Pamir Mountains are an important target of current research: they constitute a crucial mountain water tower that is highly vulnerable to future climatic, environmental, and social change; and they contain glaciers experiencing limited early 21st-century mass loss despite climate warming. Due to geopolitical factors, the in-situ records in the region were interrupted during this period, and current assessments of glacier volume and mass change in this region are highly uncertain. A global assessment of geodetic mass balance from ASTER images has suggested a change in the mass balance regime in the region toward declining glacier health, but its uncertainties are very high. In this study, we leverage high-resolution (<5m) optical stereo images that compensate for the scarcity of in-situ snow and glacier observation to provide a mass balance estimate entirely independent of the ASTER dataset.

We analyze high-resolution SPOT5, SPOT6, and Pléiades stereo satellite images acquired since the 2000s over the Sangvor glacierized catchment in the Pamir mountains as a case study. We adopt a stereo image analysis workflow from the Ames Stereo Pipeline to process these data, including coregistration and bias correction, and to remove erroneous artifacts such as jitter-induced undulations. In addition to approximating and subtracting the undulation errors using Fourier transforms, for the results with insufficient correction, we adopt an empirical method that calculates the average value of the error in the cross-track direction of the image from the estimated satellite orbit and directly subtracts the averaged error in each along-track direction. We evaluate the elevation change uncertainty based on the patch approach and then quantify glacier mass balance spanning twenty years over our study domain. In order to empirically estimate the error in the spatially averaged elevation change in the study area, we sampled the area into a certain area, calculated the median of the elevation change in the stable terrain, and then calculated the mean of the absolute difference of these tiled median errors. Finally, we compare our results to those derived from ASTER DEMs for this period. Our results demonstrate the potential of very high-resolution satellite imagery for snow and glacier monitoring despite the challenge of short-interval observations and highlight the value of multiple independent, high-quality geodetic mass balance estimates to resolve changes over shorter periods.