See current research project 'Differential InSAR'

The Combination of GPS and InSAR to Address Ground Deformation Monitoring Applications

Elevations can be determined from Synthetic Aperture Radar (SAR) images by interferometric methods. This involves the use of two antennas, displaced either vertically or horizontally, installed on the same satellite or aircraft platform. One of the antennas transmits the signal, but both receive it, resulting in two images being created. The most accurate form of interferometric measurement is differential interferometry (InSAR), which involves the determination of elevation differences between two epochs of terrain measurement. In this case, the variations in the radar signal phases are determined between the two epochs, which reveal terrain surface deformations that may have occurred between the two occasions when the images were recorded. It is claimed that height differences as small as one centimetre can be detected by this method. Such a technique therefore has the potential of being a cost effective, near-continuous, remote method of measuring terrain subsidence due to mining, and ground movement due to land subsidence, earthquake or volcanic activity, etc.

There are significant challenges still to be overcome before reliable deformation measurements can be made on a routine basis using InSAR. One of the most promising approaches is to use ground GPS surveys in combination with InSAR in such a way that the techniques complement each other and the GPS can "calibrate" out the errors of InSAR.

A new research initiative is to use InSAR and GPS together to map the land subsidence of an area in which underground coal mining is taking place in the Appin/Picton area just south of Sydney. First experiments were undertaken starting February 2001. An ARC research grant has supported this research in 2002-2004. Download a PDF file giving further information on this project