Satellite measurements show hidden water content of snow

As spring arrives, many people are generally interested in the snow vanishing. Others are more interested in the water that is stored in the snow layer. Satellite measurements can show the extent and water content of the snow coverage, and where it will melt.

Scientists from SMHI are part of a European research project aiming to develop new, simpler ways of using satellite data about snow and ice.

Data from optical satellites can show the spread of snow coverage on a detailed level. Changes in the spread show where the snow has melted. This is valuable information in situations with high flows in watercourses as the snow melts.

“Information about where the snow layer has disappeared can provide support in assessing where in the watercourses the water levels might be expected to rise further, or whether the peak has already been reached,” says David Gustafsson, a hydrology scientist at SMHI.

Karta med snötäckningsgrad 1 april 2013
Data from optical satellites can show the spread of snow coverage on a detailed level. On 1 April large parts of Sweden were covered by snow, and the only bare ground was in the south-west (green on the map). In dark purple areas the degree of snow coverage was over 91%. Grey areas were obscured by cloud and snow coverage data are therefore unavailable. Enlarge Image

Water content of snow important

To assess the amount of water formed as the snow layer melts, i.e. the water content of the snow, the microwave radiation that naturally emanates from the Earth’s surface is measured. This is largely affected by the amount of snow on the ground.

Combined with information about the structure of the snow, it is possible to calculate how much water the snow contains. This can give a forecast of how much water the thaw will contribute to the watercourses.

“It is difficult to calculate the water content of snow, but this is probably the most important criterion for, say, the hydro power industry, along with an assessment of water availability and the risk of drought in the summer to come.”

Dialogue with users part of the development

With information about the water content of snow, the power industry can better plan power production and how much water needs to be used from the water reserves.

“In dialogue with users, we have prioritised developing information about the degree of snow coverage and the amount of water the snow contains. We’ve also looked at how we can show where the snow is melting,” Gustafsson explains.

Wet snow indicates snow melt

The scientists can identify the areas where the snow is melting by having the satellites measure whether the snow layer has a dry or a wet surface. When snow melts, the amount of liquid water in the snow layer increases and the snow becomes wet. A wet surface on the snow layer indicates that the snow is melting.

During the winter of 2012/2013, a pilot service is available with daily updates of the degree of snow coverage and the snow/water ratio. The system should be fully up and running by next winter. The system is also being developed to process and provide data from the future European Sentinel satellites.

As part of the project, the scientists are also striving to make data available in a simpler, more cost-effective way. The services will allow users to describe the area they are interested in and only retrieve data for that area, thus reducing the volumes of data that need to be retrieved, stored and processed by users.

The Cryoland project is part of the EU’s Seventh Framework Programme (FP7) for research and development.