A review of optical snow cover algorithms

The purpose of this report is to provide a review of optical snow cover algorithms to assist algorithm selection in the CryoRisk project. The first part of the report provides a brief review of the state of the art for snow cover retrieval algorithms developed internationally. The review covers classification algorithms (snow/non-snow algorithms), fractional snow cover algorithms (snow fraction per pixel) and multi-sensor algorithms. The report then goes into more details for algorithms developed and refined nationally by describing the algorithms, presenting results from algorithm evaluation and then discussing the evaluation results. The algorithms covered are the Norwegian-Linear-Reflectance-to-snow-cover (NLR) algorithm, NR’s cloud detection algorithm, NR’s new fractional snow cover algorithm and a multi-sensor time-series algorithm combining optical and synthetic aperture radar data. The algorithms and evaluations presented build on results from many projects carried out over a period of about ten years. The motivation for the national focus is that quite a lot of resources have been invested in research and development for snow cover retrieval algorithms in Norway, and it is then logical to build on this experience when developing an operational service. The last chapter provides recommendations for a process leading to operationalisation of algorithms in the CryoRisk project.