Results from the ESA SnowPEx project concerning the evaluation of the Earth Observation-based snow products is presented, the focus being on the Northern Hemisphere (NH) Snow Extent (SE) daily products by different data providers. Comparison against daily at-ground observed Snow Depth is made, after first converting all the snow products and the in-situ observations to binary `snow/no-snow' information. We first introduce the datasets employed in the analyses, then describe the applied methodology and finally present the major findings obtained so far. The results presented here do not cover all the investigations carried out within SnowPEx and thus can be considered as an overview of preliminary results of the validation with in-situ data which will be complemented later when the comprehensive analysis of the results is completed.

The Sentinel satellite constellation series, developed and operated by the European Space Agency, represents the dedicated space component of the European Copernicus program, committed to long-term operational services in environment, climate and security. We developed, tested and evaluated an algorithm for generating maps of snowmelt area from C-band synthetic aperture radar (SAR) data of the Sentinel-1 mission. For snowmelt classification, a change detection method is applied, using multitemporal dual-polarized SAR data acquired in Interferometric Wide swath (IW) mode, the basic operation mode over land surfaces. Of particular benefit for wet snow retrievals are the high instrument stability, the high spatial resolution across the 250 km wide swath, and the short revisit time. In order to study the impact of polarization, we generated maps of melting snow using data of the VV-polarized channel, the VH-polarized channel and a combined VV- and VH-based channel using a weighting function that accounts for effects of the local incidence angle. Comparisons are performed with snow maps derived from Landsat images over study areas in the Alps and in Iceland. The pixel-by-pixel comparisons show good agreement between the snow products of the two sensors, with the best performance for retrievals based on the combined (VV and VH) channel and a minor decline for the VH-based product. The VV-based snowmelt extent product shows a drop-off in quality over areas with steep terrain because of the decreasing backscatter contrast of snow-covered versus snow-free surfaces on fore-slopes. The investigations demonstrate the excellent capability of the Sentinel-1 mission for operational monitoring of snowmelt areas.

CryoLand (2011–2015) is a project carried out within the 7th Framework of the European Commission aimed at developing downstream services for monitoring seasonal snow, glaciers and lake/river ice primarily based on satellite remote sensing. The services target private and public users from a wide variety of application areas, and aim to develop sustainable services after the project is completed. The project has performed a thorough user requirement survey in order to derive targeted requirements for the service and provide recommendations for the design and priorities of the service. In this paper we describe the methods used, the major findings in this user survey, and how we used the results to design and specify the CryoLand snow and land ice service. The user requirement analysis shows that a European operational snow and land ice service is required and that there exists developed cryosphere products that can meet the specific needs. The majority of the users were mainly interested not only in the snow services, but also the lake/river ice products and the glacier products were desired.

Information on avalanche activity or non-activity on local and regional scale is of great value for avalanche warning services, traffic authorities and experts responsible for safety in communities or ski resorts. In particular during bad weather condition, such information is available only very limited or not at all. The aim of the ESA IAP feasibility study "Improved Alpine Avalanche Forecast Service" was to investigate existing technology to overcome this gap. Of particular interest were radar-based techniques that have the potential to operate independently of daylight and weather conditions. For testing the observation of avalanche activity on a local scale, a terrestrial radar was installed at the WSL Institute for Snow and Avalanche Research SLF, illuminating the Dorfberg close to Davos, Switzerland during winter 2013/2014. On that slope, frequent natural as well as artificially triggered avalanches can be expected. The system acquired datasets at minute temporal resolution, which allows the production of coherence maps to detect avalanche events and also features such as snow creep and free-riders tracks. The spatial coverage of the terrestrial system was 6 km 2 for this experiment. On the regional scale, data from radar satellites with very high spatial resolution (< 3 m) were analyzed. A TerraSAR-X stripmap mode satellite frame, for example, covers 1500 km 2 and has a temporal resolution of 11 days. A combination of terrestrial and space-borne radar sensors could be a powerful tool to map avalanche activity for different scales during any weather condition. We present first results of terrestrial and space-borne avalanche activity mapping at Davos during the winter 2013/2014 and discuss capabilities and limitations for local and regional avalanche warning services.

Interferometric radar data (InSAR) offer the capability of measuring and monitoring the surface topography of glaciers and ice caps at high accuracy. Of particular interest are single-pass spaceborne InSAR systems such as X-SAR and the satellite formation TerraSAR-X (TSX)/TanDEM-X (TDX) because they are not affected by temporal decorrelation and changes in the atmospheric phase delay. The German-Italian dual antenna radar sensor X-SAR operated in February 2000 on the Shuttle Radar Topography Mission (SRTM), acquiring data over swath of 50 km width, mapping about 40 per cent of the land masses between 60°N and 56°S. SRTM/X-SAR delivered DEM data at slightly better relative vertical accuracy (6 m) and horizontal resolution (30 m) than the SIR-C sensor which also operated on SRTM but provided full area coverage. In June 2010 TDX was launched, flying in close formation with TSX, both forming a single-pass InSAR system with the objective of providing a global DEM with 12m × 12m horizontal sampling and <2m vertical relative accuracy. Digital elevation data acquired by InSAR at different epochs enable to map changes of glacier volume and to estimate the net mass balance over the time interval. We analyzed volume changes of glaciers in the Otztal Alps between February 2000 (SRTM/X-SAR) and February 2011 (TSX-TDX), showing significant down wasting of glaciers as known also from field campaigns and airborne studies. Because radar signals penetrate into snow and ice, the scattering phase centre of the radar signal and consequently the uncorrected topographic data are located up to a few metres below the actual snow and ice surface, the depth depending on the physical state of these targets. Because the topographic data in this study are derived from SAR systems operating at the same radar frequency (X-band), signal penetration is of minor concern for retrieving volume changes. The InSAR data show surface lowering up to 65 metres on the lower terminus of Hintereisferner. The total 2000 – 2011 volume change will be compared to in situ mass balance measurements for the glaciers Hintereisferner and Kesselwandferner.

To answer questions about linkages between changes in glaciers and climate change—e.g., How much of the current global sea-level rise can be attributed to melting glaciers?—more precise and quantitative studies of glaciers are required. This includes systematically extending the available in situ and remote sensing data, putting together a more-detailed world glacier inventory (WGI), continuing and strategically enlarging the global mass balance monitoring network, and conducting a rigorous uncertainty assessment of the available data series.