How velocity extraction from Sentinel-2A/B affects the accuracy and availability of surface strain rate and stress: a case study of Helheim Glacier

Abstract Strain rate and stress are widely regarded as crucial indicators for quantifying glacier dynamics on sub-monthly scales. However, existing frameworks for quality assessment of both strain rate and stress in fast-moving glaciers remain insufficient, hindering the application of rheological analysis to complex dynamic natural processes. To address this gap, we first extract and evaluate the surface velocity fields and their gradients from Sentinel-2A/B imagery using the Normalised Cross-Correlation (NCC) approach for Helheim Glacier, eastern Greenland. The results indicate that the minimum time threshold significantly affecting velocity gradients is 10 days for the Sentinel-2A/B missions, and that the threshold varies with season. We further develop a method based on error theory to enhance the retrieval accuracy of strain rate and stress at sub-monthly baselines, thereby supporting high-resolution dynamic research on Helheim Glacier. Our evaluations demonstrate the applicability of the NCC method to sub-monthly time scales and rapidly changing regions, thereby contributing to the quantification of glacier changes in a warming world.