Developments in synthetic aperture radar interferometry for monitoring geohazards
Published:January 01, 2007
In 1993 synthetic aperture radar (SAR) interferometry (InSAR) was introduced to the wider remote sensing community with the publication of the interferogram depicting the ground deformation caused by the Landers earthquake. Although the power of interferometry was demonstrated, the conventional technique has not always been applicable in all operational scenarios. Over the last few years, however, a number of technical developments have emerged that provide a higher precision of motion rates, the extraction of specific motion histories, and precise targeting. This paper examines uses of differential SAR interferometry (DifSAR) for monitoring geohazards. Limitations of DifSAR will be discussed: lack of coherence, atmospheric refraction and targeting. It will be shown how some of these limitations can be overcome with persistent scatterer interferometry (PSI), which detects slow ground motion with annual rates of as little as a few millimetres, reconstructing a motion history based on the European Space Agency's SAR image archive. The technique permits the estimation and removal of the atmospheric phase, achieving higher accuracies than DifSAR. PSI relies on the availability of pre-existing ground features that strongly and persistently reflect back the signal from the satellite. However, in highly vegetated regions, PSI may not be applicable because of the lack of natural scatterers. To ensure motion measurement of the ground or structures at targeted locations, the NPA Group is developing InSAR using artificial radar reflectors, such as Corner Reflectors (CRs) or Compact Active Transponders (CATs). Both reflector types are still undergoing validation tests, but results show a high phase stability in both cases.
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Mapping Hazardous Terrain Using Remote Sensing
The dangers that we face from geohazards appear to be getting worse, especially with the impact of increasing population and global climate change. This collection of papers illustrates how remote sensing technologies - measuring, mapping and monitoring the Earth’s surface from aircraft or satellites - can help us to rapidly detect and better manage geohazards. The hazardous terrains examined include areas of landslides, flooding, erosion, contaminated land, shrink-swell clays, subsidence, seismic activity and volcanic landforms. Key aspects of remote sensing are introduced, making this a book that can easily be read by those who are unfamiliar with remote sensing. The featured remote sensing systems include aerial photography and photogrammetry, thermal scanning, hyperspectral sensors, airborne laser altimetry (LiDAR), radar interferometry and multispectral satellites (Landsat, ASTER). Related technologies and methodogies, such as the processing of Digital Elevation Models and data analysis using Geographical Information Systems, are also discussed.