Speaker
Dr
Andreas Wiesmann
(GAMMA Remote Sensing)
Description
Remote sensing of snow with active and passive microwaves has a long tradition. Terrestrial instruments are used to investigate the interaction of snow with microwaves at selected locations, air- and space-borne sensors are used to image larger areas. While the terrestrial instruments are mobile and can be brought to selected test areas they are usually doing point measurements. Satellite based instruments on the other hand, have a given observation geometry and observation schedule. These constraints limit the potential to investigate dynamic processes in the snowpack spatially, especially of slopes. Terrestrial imaging radars such as the GPRI (GAMMA Portable Radar Interferometer), overcome some of these constraints due to their portability, operating range of several kilometers, image acquisition time of about 30 seconds and the possibility to do repeat acquisitions within minutes.
In our presentation we discuss results of campaigns conducted with a Ku-band imaging radar at selected locations in the Swiss Alps covering dry and wet snow conditions. The investigation covers the analysis of backscatter information spatially and in time as well as the interferometric analysis of the corresponding time series. The interferometric processing allows to gather interferometric phase and coherence information. The coherence computed from shorter and longer image pairs allows to investigate the temporal decorrelation within the snowpack. The phase changes are related to atmospheric effects, changes in the snowpack and motion.
The interferometric decorrelation is linked with changes in the snowpack structure. Consequently a drop in coherence is mainly an indicator for changes of the snowpack. They can be induced by short term effects like an avalanche release, or by slow restructuring such as snow metamorphism. If the correlation between two image acquisitions is high the interferometric phase can be interpreted. The phase reveals information about changes in the wave propagation to and from the target. Main contributions come from the displacement of the target area (e.g. speed and extent of creeping snow) along the line of sight, as well as changes in the atmospheric conditions.
The results provide new and valuable information and methods for the snow research community, in particular for the research in snow mechanics and avalanche dynamics. A validation campaign proved the accuracy of the displacement measurement. But the findings together with results form other recent SnowScat campaigns are also relevant for future research in the interaction of electromagnetic waves with snow and dedicated campaign and mission planning. In an outlook we will discuss this aspect and outline next steps.
Primary author
Dr
Andreas Wiesmann
(GAMMA Remote Sensing)
Co-authors
Dr
Christian Matzler
(GAMMA Remote Sensing)
Dr
Rafael Caduff
(GAMMA Remote Sensing)
