Detecting Surface Change and Avalanche Mapping
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Interferometric Synthetic Aperture Radar (also known as InSAR) uses remote sensing techniques to compare two or more synthetic aperture radar (SAR) images in order to detect changes in the earth’s surface over time as small as a few millimeters. The combined image analysis is represented by a color ramping indicating the differences in surface heights between the two original images and is called a SAR interferogram.
The European Space Agency presented findings on research using InSAR at its recent Fringe Workshop at ESRIN in Frascati, Italy. Due to the precise measurements take can be taking from InSAR, changes can be detected due to “Tectonic plates grinding past one another, the slow ‘breathing’ of active volcanoes, the slight sagging of a city street due to groundwater extraction, even the thermal expansion of a building on a sunny day.”
The technology has been used by scientists to detect that the historical town of Assisi, Italy has areas that are sinking by 7.5 mm per year. The German city of Bremerhaven was also discovered to have an annual subsidence of 7mm a year.
Interferometry has detected subsidence in Italy’s historic town of Assisi. Some areas are even sinking by 7.5 mm per year. Credits: L’Istituto per il Rilevamento Elettromagnetico dell’Ambiente (IREA).
Measurements by new software to process wide areas using differential interferometry show an average subsidence in Bremerhaven, Germany of 7 mm per year. Tracking surface changes is important for areas like this because it is home to an oil reservoir. Credits: Deutsche Zentrum für Luft und Raumfart (DLR).
ESA notes that the launch in 2013 of Sentinel-1 will provide additional SAR imagery to support InSAR analysis. Visit ESA’s site to download higher resolution images of these and other InSAR findings.
Innovators II–AvalRS is a pilot study that was initiated through the European Space Agency’s (ESA) Earth Observation Data User Element programme to monitor avalanche locations using satellite imagery. The program looked at known locations of avalanche falls and mapped them using high resolution satellite imagery and digital elevation model (DEM) data. By analyzing those locations, other avalanche locations could be identified using pattern recognition methods.
An article on the ESA site entitled “Satellites show potential for avalanche mapping“ describes the pilot project and notes:
The project tested two different approaches: one focusing on the texture of the avalanche deposits and the other focusing on topographic features of the avalanche such as aspect direction.
Both methods have yielded promising results. Avalanche deposits can easily be distinguished from undisturbed snow surfaces, rugged snow surfaces away from the avalanche and mixed textures such as sparse forest with snow
An avalanche at Dalsfjorden, Norway, detected and mapped using the ‘AvalRS’ algorithm. The red shows the extent of the avalanche, the blue shows smooth snow, the yellow shows forest and shadow and cyan shows rock. An earlier manually mapped outline is marked in blue. Credits: AvalRS Consortium
The study is still ongoing with work still to be done to distinguish between rocks and shadows and classifying areas within shadows. The results of the study will assist Norway’s Public Roads Administration in locating avalanche falls in order to close roads for safety reasons and to expedite the clearing of blocked roads, particularly in remote and isolated areas of the country.
In the United States, AvalancheMapping.org is focused on collecting and mapping avalanche and snowpit locations nationwide. The site also has a a software downloads page with links to software and database models for collecting avalanche and snowpit data.
Tags: avalanche mapping, esa, ESRIN, InSAR, Interferometric Synthetic Aperture Radar, remote sensing, surface change