PsInSAR Radar Interferometry
This dissertation demonstrates the applicability of the space-borne interferometric synthetic aperture radar (InSAR) technique for measuring the ground surface displacement at various temporal and spatial scales. The dissertation focuses on optimisation of the InSAR technique for ground deformation monitoring applications due to earthquakes, underground mining, and groundwater extraction activities.
There are four main factors which have limited the use of InSAR techniques for ground surface displacement monitoring, especially for co-seismic displacement mapping and mine subsidence monitoring applications. These four factors have been discussed and investigated in this dissertation, namely: (1) temporal and spatial decorrelation, (2) phase discontinuity due to rapid deformation, (3) atmospheric disturbances, and (4) retrieval of the 3-D deformation vector. The performance of different SAR satellites for land deformation monitoring was assessed based on the first two limitations. The results from both simulation and real data analysis have suggested that the C- and X-band satellites were not suitable for mapping the surface displacement over vegetated areas or rapidly deforming areas. SAR satellite missions with longer radar wavelength, higher incident angle and finer ground imaging resolution are preferred in order to minimise the impact of the first two limitations. An approach has been developed and implemented to address the third limitation using small-stack SAR differential interferograms. A solution to the fourth limitation has been suggested based on using multiple DInSAR deformation results, which are taken from different incidence angles, from both ascending and descending satellite orbits. Investigations have been carried out using InSAR pairs acquired from different viewing geometries to map the displacement due to underground mining in three dimensions.
Persistent Scatterer Interferometry (PSI) is a recently developed SAR analysis technique which overcomes the shortcomings of conventional InSAR techniques by utilising long time series of interferometric SAR image data. A modified PSI technique has been proposed in this dissertation to enhance the utility of the conventional PSI technique. The main features of the proposed technique are: (1) improvement in the estimation and removal of orbital error and atmospheric error components, (2) improvement in the precision of PS point identification as well as the displacement estimated from the less reliable PS candidates, and (3) maximisation of total PS point identified while preserving accuracy. The capability of the proposed technique for urban subsidence monitoring has been demonstrated using both ENVISAT ASAR data and ALOS PALSAR data over Beijing City, China. Cross-validation has been carried out between the results obtained from the ENVISAT and ALOS data. Good correlations have been observed from the new PSI results from the ENVISAT and ALOS data. The ENVISAT
ASAR results showed good agreement with the continuous GPS measurements. The line-of-sight displacement rates derived from the new PSI results generated by both datasets were used to derive the vertical and horizontal displacement rates.