Developments in synthetic aperture radar interferometry for monitoring geohazards

Abstract

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.

Geological interpretation of current subsidence and uplift in the London area, UK, as shown by high precision satellite-based surveying

“…A example of such a time series graph from the present study is shown as Figure 6.1 by Bingley et al (2007), who note (p. 108) that 93% of these determinations of line-of-sight velocity have an uncertainty of ±0.25 mm a -1 or less. An example from other work is shown by Riedmann and Haynes (2007).…”

Applications of remote sensing for geohazard mapping in coastal and riverine environments

“…DifSAR mostly utilizes data from the European Space Agency's ERS series of satellites, as their orbits are more precisely determined than those of other radar satellites; furthermore, there is an extensive archive of ERS coverage, dating back to the early 1990s. A recent variant, persistent scatterer interferometry (PSI), uses at least 30 satellite radar images of a given area to reduce errors associated with the technique, resulting in millimetre-scale quantification of ground movement (for more details, see Riedmann & Haynes 2007).…”

Investigating radar cross sections of passive radar reflectors for C-band and X-band SAR satellite missions

“…Depending on the capacity of radar targets either to generate radar signals or just reflect ones generated by remote sources, radar reflectors can be either active or passive. Active radar reflectors are currently evolving, and the scientific literature of the last decade shows their potential [3][4][5][6][7][8][9] . Because of their low cost of construction and maintenance, passive artificial corners are even more diffused as radar reflectors in SAR applications.…”