Deriving information on snow and vegetation from microwave remote sensing data
With a view to improving climate and weather forecasts as well as disaster prevention, the European Space Agency (ESA) determines the water content in upper soil layers worldwide. The surveys are conducted using satellite-mounted radiometers. A research project carried out in the Swiss Alps will now investigate how these satellites could be used to measure data about snow as well as frost in the soil.
Passive microwave remote sensing utilises objects' ability to emit electromagnetic radiation. The correlation between the emitted radiation and the material properties of the observed objects is used, for instance, to determine soil water content and the salt content of the uppermost layer of oceans worldwide. The impact of dry snow cover on low-frequency microwave emissions (L band, 1.4 GHz) has so far been overlooked. However, initial theoretical and experimental studies indicate that even dry snow influences L band microwave emissions, meaning that it may be possible to ascertain snow's properties based on the measured intensity of this microwave radiation. This is precisely the research objective of the SNSF's MicroVegSnow project, in which scientists experimentally and theoretically investigate the relationships between low-frequency microwave radiation and snow and soil properties.
The Swiss part of the MicroVegSnow project involves the Swiss Federal Institute for Forest, Snow and Landscape Research WSL conducting a three-year investigation of the influence of snow cover on radiation emitted by soil. To this end, during winter a radiometer measures the low-frequency microwave radiation of the snow-covered ground and the snow cover at the new Davos-Laret (Graubünden) test area. At the same time, snow temperature and density, air and soil temperature and soil water content will be calculated with a view to comparing radiation data with the physical properties of the snow and soil.
The Forschungszentrum Jülich (FZJ) research centre is conducting the same investigation in Germany on soil covered by vegetation.
2015 - 2018
The experiment on Weissenstein will determine how snow affects L band radiation emitted by the soil beneath it and what data about the snow itself can be derived from the radiation. Physical models of radiation emitted by snow-soil systems will be adapted and further developed on the basis of these findings. These models will be used to expand satellite remote sensing in the low-frequency microwave range on snow and vegetation-covered soil.
How does a radiometer work?
A radiometer picks up electromagnetic radiation in a particular frequency range and measures its intensity. It comprises an antenna, which is designed (shape and size) to receive the desired frequencies. The signal received is electronically processed and can then be assessed.