Ps-insar Measurement of Land Subsidence in Bangkok Metropolitan Area

It is well known that the metropolitan area of Bangkok, Thailand, has been subsiding during the past decades. This ground deformation has been monitored using leveling networks on annual basis since 1978. However, the employed technique is costly, time-consuming, and able to monitor only on a limited number of benchmarks. InSAR (Interferometric Synthetic Aperture Radar), which can provide sub-centimeter accuracy when time series analysis method such as PSI is employed, has the additional advantage of having a large number of observations. Therefore, it is an attractive alternative technique to such task. Permanent Scatterer InSAR (PSI) is employed in this study to determine land subsidence in Bangkok Metropolitan Area. We used 13 Radarsat-1 Single Look Complex images in Fine Beam Mode (F1N) acquired from October 2005 to February 2009. The interferograms generated by DORIS, and StaMPS were then used to perform PS analysis. Result from PSI reveals subsidence rates as large as 15 mm/year in eastern central Bangkok with respect to other areas detected as stable. Unwrapping errors may affect also our results due to the sub-optimal number of images in the time-series and also from orbital errors of Radarsat-1 which has no on-board GPS. Nevertheless, PSI successfully detects more than 300,000 pixels that can serve as monitoring points, a number that is two orders of magnitude greater than all benchmarks of the level network in Bangkok. As such the study clearly demonstrates the potential of PSI as operational tool for geodetic task like land subsidence monitoring.