Brooks Range Perennial Snowfields: Extent Detection via Satellite and from the Field in Alaska

Perennial snowfields, such as those found in the Brooks Range in Alaska, are a critical component of the ecosystem. Snowfields influence downslope hydrology, vegetation, geology, permafrost, and serve as habitat for an array of wildlife species, including caribou, which are a crucial food and cultural resource for rural Native Alaskan subsistence hunters. In this study, perennial snowfield extents in the Brooks Range were derived from Synthetic Aperture Radar (SAR) and from multi-spectral satellite imagery via the Sentinel-1 (S1) and Sentinel-2 (S2) constellations. Snow covered area (SCA) extents were quantified for four melt seasons (2016 to 2019) using multi-spectral analysis in S2 and by creating a SAR backscatter change detection algorithm for S1. Results of the remote sensing were evaluated by comparison with field data acquired across multiple spatial resolutions and geographic domains, including helicopter points and on-the-ground, manually collected SCA. Additionally, pixel-wise melt onset and freeze-up dates were derived for a focused collection of perennial snowfields using an S1 SAR backscatter intensity differencing approach. Evaluations of the SAR change detection algorithm via comparison with results from the optical imagery analysis, and with field acquired data, indicate that the SAR algorithm performs best in small, focused geographic sub-domains, while the multi-spectral analysis performs well across multiple spatial scales. This may be the result of SAR algorithm dependency on dynamic backscatter thresholding and radiometric slope corrections for mountainous terrain.