GPS Derived Tropospheric Delay Corrections to Radar Interferometry

Synthetic Aperture Radar Interferometry (InSAR) has been recognised as a well-suited tool for topographic mapping and ground deformation monitoring applications. However, the spatially and temporally variable tropospheric delay represents a major limitation to InSAR applications. On the other hand, it has become feasible to derive tropospheric corrections from continuous GPS for InSAR due to the rapid development of continuously operating reference stations (CORS). For example, the average spacing between GPS stations is 25 km for the GEONET of Japan and even less for the SCIGN of the US. A between-site and between-epoch double-differencing algorithm for the generation of tropospheric corrections to InSAR results based on GPS observations is proposed. CORS observations from the GEONET and SCIGN are selected to estimate the tropospheric conditions, double differenced, and interpolated to produce corrections to InSAR. It has been found that the inverse distance weighted and kriging interpolation methods are more suitable than the spline method, and differential corrections as much as several centimetres may have to be applied in order to ensure sub-centimetre accuracy for the InSAR result. The methodology is then used to analyse some differential ERS InSAR results in order to detect land subsidence in the Kanto Plains around Tokyo. A SPOT HRV image obtained 18 minutes after one of the SAR image takings reveals cloud distribution patterns that are similar to the fringe features in the interferograms, strongly suggesting that the InSAR results are contaminated by tropospheric delays. Therefore, continuous GPS data from the GEONET are processed using both the Bernese and GIPSY software to generate tropospheric corrections using the double difference algorithm. Although the cloud pattern cannot be identified with confidence from the GPS derived tropospheric delays, it is suggested that the interpolated image of between-site, single-differenced tropospheric delay can be provided by a CORS centre as a routine product to assist InSAR.