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Seasonal snow is a main element of the global water cycle and climate system. Due to its strong influence on the radiation and energy balance, changes in snow extent tend to amplify climate fluctuations. Terrestrial snow covers up to 50 million km2 of the Northern Hemisphere in winter and is characterised by high spatial and temporal variability. Therefore satellite observations provide the only means for timely and complete observations of the global snow cover.

The IPCC Working Group 1 report, published 2013, identifies a clear trend of decrease in seasonal snow extent during recent decades. The importance of accurate data on the global snow cover has been addressed in the WCRP-CliC Workshop and "WCRP Grand Challenges and the Cryosphere in a Changing Climate", held in Tromsö, 16-18 October 2013. In order to improve the knowledge of the temporal dynamics and physical properties of snow as a component of the coupled climate system, the need to "produce better global-scale datasets of snow cover, SWE, and snow thermal properties by drawing together local and remote sensing observations" has been identified as an important goal". Also in the WMO Global Cryosphere Watch Workshop in January 2013 the need for evaluating and consolidating snow products based on different satellite sensors and retrieval methods was identified.

The Quality Control framework for Earth Observation (QA4EO), which consists of a set of seven guidelines, is endorsed by the Committee on Earth Observation Satellites, and has been developed by the satellite calibration and validation (Cal/Val) communities to meet the needs of the Earth Observation communities. These QA4EO guidelines have been written with the aid of national metrology institutes of the United States and Europe and, where appropriate, are based on best practices of the wider EO and non-EO communities. Within this context, the SPPA team manages a series of projects, including Satellite Snow Product Intercomparison and Evaluation Exercise (SnowPEx), addressing sensor calibration and traceability, as well as end-to end product traceability and uncertainty estimations. QA4EO-SnowPEx is an inter-comparison and validation exercise.


Access SnowPEx

Visit the SnowPEx website and access data


Contact Information

If you have any questions about this project, contact:

Dr. Thomas Nagler
Address: ENVEO IT GmbH, Technikerstrasse 21a, 6020 Innsbruck, Austria
Organisation: ENVEO IT GmbH

Dr. Philippe Goryl
Address: ESA-ESRIN, Via Galileo Galilei Frascati (RM), 00044 Italy
Organisation: ESA

Activity Consortium

ENVEO IT GmbH logo
ENVEO IT GmbH, Innsbruck Austria (PI) 
Environment Canada logo
Environment Canada, Toronto, Canada 


Finnish Environment Institute logo
Finnish Environment Institute, Helsinki, Finland 
Natural Resources Canada logo
Natural Resources Canada, Ottawa, Canada