Towards a webcam-based snow cover monitoring network: methodology and evaluation

oleh: C. Portenier, F. Hüsler, S. Härer, S. Wunderle

Format: Article
Diterbitkan: Copernicus Publications 2020-04-01

Deskripsi

<p>Snow cover variability has a significant impact on climate and the environment and is of great socioeconomic importance for the European Alps. Terrestrial photography offers a high potential to monitor snow cover variability, but its application is often limited to small catchment scales. Here, we present a semiautomatic procedure to derive snow cover maps from publicly available webcam images in the Swiss Alps and propose a procedure for the georectification and snow classification of such images. In order to avoid the effort of manually setting ground control points (GCPs) for each webcam, we implement a novel registration approach that automatically resolves camera parameters (camera orientation; principal point; field of view, FOV) by using an estimate of the webcams' positions and a high-resolution digital elevation model (DEM). Furthermore, we propose an automatic image-to-image alignment to correct small changes in camera orientation and compare and analyze two recent snow classification methods. The resulting snow cover maps indicate whether a DEM grid is snow-covered, snow-free, or not visible from webcams' positions. GCPs are used to evaluate our novel automatic image registration approach. The evaluation reveals a root mean square error (RMSE) of 14.1&thinsp;m for standard lens webcams (<span class="inline-formula">FOV&lt;48</span><span class="inline-formula"><sup>∘</sup></span>) and a RMSE of 36.3&thinsp;m for wide-angle lens webcams (<span class="inline-formula">FOV≥48</span><span class="inline-formula"><sup>∘</sup></span>). In addition, we discuss projection uncertainties caused by the mapping of low-resolution webcam images onto the high-resolution DEM. Overall, our results highlight the potential of our method to build up a webcam-based snow cover monitoring network.</p>