What Sentinel-2 tells us about snow cover


THEIA has been generating and distributing a Snow product since end 2017 developed by Simon Gascoin from the CESBIO biosphere space research centre. Taking advantage of the European Sentinel-2 satellite’s revisit capability, this product detects snow cover with a resolution of 20 metres. The product is easy to use, well suited to the needs of local stakeholders and inspiring the wider European community.

Theia’s Snow product detects snow cover and thickness every five days with a resolution of 20 metres. It also enables snow persistence in areas of interest to be mapped over an entire hydrological year (from 1 August to 30 September).

Such information is of great value to scientists in hydrology and mountain ecology research laboratories, natural resource managers (water planning agencies, hydroelectricity generators and irrigation firms) and tourism stakeholders (ski resorts and tourists). Another unexpected development is that France’s national parks are even using the product to manage their flora and fauna.

Leveraging this experience, the team formed by Simon Gascoin at CESBIO and private firm Magellium responded to a request for proposals from the European Environment Agency (EEA) to supply a snow and ice cover product for 32 European nations.

Pan European High Resolution Snow and Ice Monitoring Product ordered by ESA https://www.eea.europa.eu/about-us/tenders/eea-dis-r0-18-014

A simple, closely tailored and inspiring product

The Snow product’s nomenclature—“snow”, “no snow” and “clouds”—is very easy to understand. Maps generated from Sentinel-2 data every five days are freely accessible from the Theia website at www.theia-land.fr/product/neige/.

Cyan = snow | Grey = no snow | White = cloud

This reliable product is available for all of France’s mountain ranges and the Atlas range in Morocco. In terms of development, the main area where the product could be improved is its ability to detect snow in dense forest.

The product is unmatched anywhere in the world. The US Geological Survey (USGS) offers temporary local maps showing fractional snow cover per pixel generated from Landsat data. The Theia product takes a different track, since it is automatic and determines whether there is snow cover or not. Feedback from users has nonetheless vindicated this choice since the product’s ease of use is much appreciated.

Multiple applications

Theia’s Snow product is already finding multiple real-world applications.

Gauging water resources


The product has fulfilled its initial intent of providing a clearer picture of a mountain range’s water resources. It enables comparison of snow cover from year to year at the same period, thus helping to predict flood risks and reservoir levels.

For tourism and biodiversity

The Snow product is also clearly a good way for ski resorts to keep regular track of snow cover. An online demonstrator is available with no need to download it.

Mountain range snow cover demonstrator:

In addition to the expected applications when work started on the product in 2015, new ones have emerged thanks to the data’s accessibility. Nature parks in particular appreciate being able to measure snow cover and thus anticipate movements of wildlife and plant growth.

Or for hiking in the mountains

We can of course imagine more personal uses for the product. Combined with hiking applications, it can for example help to locate paths covered in snow at a given date and better prepare trips to the mountains.