Automated High-Resolution Satellite Image Registration Using Supraglacial Rivers on the Greenland Ice Sheet

Abstract

High-resolution satellite imagery raises new prospects for detailed study of the Greenland ice sheet (GrIS) surface processes and ice discharge. However, dramatic spatiotemporal variability of ice surface reflectance and features poses significant challenges for registration of satellite imagery. This study proposes a new feature-based registration method to register high-resolution panchromatic images of the ice sheet ablation zone. Its idea is to use relatively stable supraglacial rivers as tie points for automated image registration. A first demonstration is made using WorldView-1/2/3 panchromatic images (spatial resolution 0.5 m) as follows: first, supraglacial rivers are delineated using spectral analysis, nonlocal means denoising, Gabor filtering, and path opening. Next, buffer and overlay tools are combined to generate an area of interest and eliminate tie point outliers, yielding subset of high-confidence tie points for registration. Finally, a coherent point drift algorithm is applied to match these tie points and implement registration. Results show that the proposed method demonstrates good performance, despite a heterogeneous ice surface background that complicates river delineation. Accuracy of image registration negatively correlates with seasonal spatiotemporal variability of supraglacial river patterns, suggesting that for the best results, repeat images and time-adaptive techniques should be used. For time-stable meltwater channels, however, the method offers a novel, automated way to register high-resolution satellite imagery of the GrIS ablation zone. Well-registered ice surface high-resolution images reveal that short-term (1-2 week) variations in surface melting rate affect channel morphology (drainage densities and channel widths) significantly, whereas a signal from background advection by flowing ice is not apparent.