Persistent Scatterers Interferometry Synthetic Aperture Radar (PSInSAR)
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Abstract
Geophysical applications of radar interferometry (differential synthetic aperture radar interferometry, DInSAR) calculate the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (~100 pixels km-2), a competitive precision (~1 cm), and a useful observation cadence (1 pass month-1). They record movements in the crust, perturbations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar¡¦s trajectory or variations in its frequency standard.
While conventional InSAR has proven very effective in measuring deformation in regions of good coherence, it is clear from almost any volcano interferogram that there are large areas on most volcanoes where signals decorrelate and no measurement is possible. If the surface is vegetated, weathers appreciably or is prone to snow coverage, the scattering properties change with time and result in temporal decorrelation, i.e., the loss of interferogram coherence with time. There are also two other aspects of conventional InSAR that limit the number of scenes from which interferograms can be produced. The first is the distance between the spacecraft tracks at the two times scenes are acquired, known as the perpendicular baseline. A second limitation results from the changes in squint angle, the angle with which the spacecraft is looking forward or backward. A change in squint angle alters the SAR Doppler frequency and leads to additional decorrelation. These drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors (Persistent Scatterers, PS) and exploiting long temporal series of interferometric data.
We present here a new InSAR persistent scatterer (PSInSAR) method for analyzing episodic crustal deformation in non-urban environments, with application to volcanic settings. Our method for identifying PS pixels in a series of interferograms is based primarily on phase characteristics and finds low-amplitude pixels with phase stability that are not identified by the existing amplitude-based algorithm. Our method finds scatterers with stable phase characteristics independent of amplitudes associated with man-made objects, and is applicable to areas where conventional InSAR fails due to complete decorrelation of the majority of scatterers, yet a few stable scatterers are present.
Reference
Andrew Hooper, Howard Zebker, Paul Segall, and Bert Kampes, A new method for measuring deformation on volcanoes and other natural terrains using InSAR persistent scatterers, Geophys. Res. Lett., VOL. 31, L23611, 2004
Carlo Colesanti, Alessandro Ferretti, Claudio Prati, Fabio Rocca, Monitoring landslides and tectonic motions with the Permanent Scatterers Technique, Engineering Geology 68 (2003) 3 ¡V14
(Abstract) (Full text)
Didier Massonnet, Kurt L. Feigl, Radar Interferometry and Its Application to Changes in the Earth¡¦s Surface, Reviews of Geophysics, 36, 4 / November 1998 pages 441¡V500
(Abstract) (Full text)