EVALUATION ON THE POTENTIAL OF L-BAND ALOS PALSAR IMAGERIES FOR DEM GENERATION AND LAND SUBSIDENCE DETECTION USING INSAR/DINSAR TECHNIQUES

摘要

Multitemporal synthetic aperture radar (SAR) imageries have been utilized by interferometric SAR technique for DEM generation and by differential interferometric SAR (DInSAR) technique for sub-centimeter accuracy measurement of surface movements such as land subsidence and seismic-induced motions. However, due to decorrelation problem, the use of InSAR/DInSAR in tropical areas has always been problematic and their applications have been mostly limited to arid, non-vegetated or highly-urbanized areas where coherence between multitemporal imageries could be maintained. This research investigates the potential of L-Band ALOS PALSAR imageries for DEM generation and land subsidence in Thailand. A part of Chiangmai in the north of Thailand and Bangkok capital city were selected as two test sites. Chiangmai comprises an urban area surrounded by forest and rugged mountains, but Bangkok is extremely flat with elevation ranges from 0.5 to 1.5 meters above mean sea level (MSL). The PALSAR images for two areas were acquired on 11 June 2007 and 27 July 2007 for Chiangmai, and 25 November 2007 and 11 April 2008 for Bangkok in Fine Beam Dual Mode (FBD). It was found that, for DEM generation, an interferometry can be produced for the whole area even with 46-day interval between the image pair. A result from previous monostatic systems using shorter wavelength like C-band ERS1/2 could only achieve by special tandem mission. Further, a 2-pass DInSAR technique using 90-m resolution SRTM DEM to remove topographic phase has been applied on SAR image pair from Chiangmai and Bangkok. The final result for Chiangmai shows only small wobbles interpreted as phase differences occurred from different atmospheric conditions between the two SAR image acquisitions, and the time interval is too short to allow for the detection of any motion signal because of the low-subsidence area. In contrast, we found that the final result for Bangkok proved that DlnSAR can be an alternative means to obtain measurements of the surface displacement for less time consuming. Nevertheless, it is obvious that PALSAR L-Band images are much less prone to decorrelation problem and have great potential to advance geodetic applications of InSAR/DlnSAR in this tropical part of the world.