Remote sensing of snow resources in the Pyrenees

Snow in the PyreneesRemote sensing uses measurements of the electromagnetic spectrum to characterize the landscape, or infer properties of it, and in some cases, actually measure hydrologic state variables. Most of the remote sensing developments and applications are centered around satellite systems. One of the advantages of remote sensing is that the data can be acquired in remote areas, as mountain ranges, where information can be obtained about the natural and water resources, for example the snow cover extent.

In Catalonia (Spain), snow cover and the equivalent amount of water volume stored supplies an important part of the water that is used for irrigation and drinking water, especially for the city of Barcelona. Since several years, satellite imagery is used to obtain snow cover data in the Pyrenees. This information is used to respond to the high variation of runoff depth that can vary greatly from year to year because of the differences in the precipitation regime and the resulting seasonal snow cover.

Snow cover can be identified and observed with a range of remote sensing devices. Most of the applications are using the visible and near infrared region of the electromagnetic spectrum. Especially the red band of the Thematic Mapper on the Landsat satellite is used for snow cover mapping because of its strong contrast with snow-free areas.

An advantage of using visible satellite data for the detection of snow cover extent is the easiness of interpreting the data and to distinguish snow from snow-free areas. Besides, the visible satellite data is available in a range of spatial resolutions which allow the applications in small basins as are present in the Pyrenees.

A disadvantage of using the visible part of the electromagnetic spectrum is that nothing can be inferred from the measurements about the snow water equivalent. Estimation of snow resources will always have to be coupled with ground measurements of snow density and height. This is done using a number of ground stations installed in the Catalan Pyrenees. In addition, clouds can be a significant problem in restricting observations, especially when the used satellite system has a low observations frequency.

A considerable amount of data has been gathered during the years that monitoring of snow cover extent by satellite imagery is operational in Catalonia . The analysis of these data supports the prediction of water resources during the snow season and gives policymakers the tools to make decisions during the drought periods occuring in this region.

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