|Title:||Temporarily coherent point SAR interferometry|
Synthetic aperture radar.
Artificial satellites in earth sciences.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Land Surveying and Geo-Informatics|
|Pages:||xvii, 107 leaves : ill. (chiefly col.) ; 30 cm.|
|Abstract:||Spaceborne Interferometric Synthetic Aperture Radar (InSAR) has been proven very useful in assessing remotely ground displacements. InSAR measurements have contributed to better understanding of the processes and mechanisms of geohazards such as earthquakes, volcanoes and landslides. There are two major error sources in InSAR measurements, i.e., decorrelation due to temporal and geometric effects and phase errors introduced by spatial and temporal variations of the atmosphere. The error sources can in extreme cases render the InSAR technology useless. To reduce the errors in InSAR measurements, a relatively new technique, multi-temporal (MT) SAR interferometry, was proposed in the late 1990s. The technique has since then evolved into three categories. The first is commonly referred to as Persistent Scatterers InSAR (PSInSAR or PSI) and it deals with a time series of interferograms generated based on a single-master image. The second makes use of multi-master interferograms including the stacking analysis method and the Small BAseline Subset (SBAS) approach. The last category is an integration of the single- and multi-master interferogram analysis methods. Over the past ten years multi-temporal InSAR has been widely applied for monitoring ground deformation in urban and rural areas and for monitoring infrastructures such as dams, buildings, motorways, and pipelines. However one important limitation in current MT-InSAR methods is the difficulty in estimating correctly the phase ambiguities. Besides, the lack of methods to evaluate the accuracy of MTInSAR results when external data (e.g., levelling and GPS observations) are unavailable is also an issue of concern.|
A novel InSAR data analysis method termed Temporarily Coherent Point InSAR (TCPInSAR) is proposed in the thesis. The method can estimate deformation parameters reliably by avoiding the process of phase ambiguity estimation. The method arises from the fact that for a set of multi-master interferograms with short baselines, there are usually a sufficient number of arcs on which the double-difference phase components due to topographic errors and atmospheric artifacts are very small and the relative deformation rates between pairs of connected points are low. Therefore, the double-difference phase components of many such arcs are free from phase ambiguities. If only these arcs are taken as observations in estimating DEM errors and deformation rates, the complexity of parameter estimation can be reduced significantly. Included in the method are a series of innovations. To improve the density of TCPs, especially in areas with a small set of SAR images, we have developed a new TCP identification method based on offset statistics in range and azimuth directions. To make sure the selected TCPs can be connected extensively with relatively short arcs we have proposed an efficient point connection strategy that performs Delaunay triangulation locally. To retrieve the deformation rates reliably we have designed a least squares estimator with an outlier detector that can remove the arcs with phase ambiguities efficiently. To better consider the quality of individual interferograms we have improved the method of variance covariance estimation under the framework of least squares. After validating TCPInSAR technique using simulated datasets, we have applied the TCPInSAR method to the Los Angeles basin in southern California where structurally active faults such as Newport-Inglewood fault are believed capable of generating damaging earthquakes. Both the estimated long-term average subsidence and seasonal deformation in the basin are in good agreement with GPS observations from the Southern California Integrated GPS Network (SCIGN), indicating that the TCPInSAR method is effective for the retrieval of ground motions especially in areas where abundant multi-temporal SAR data are available and dense coherent points can be isolated. To demonstrate the performance of TCPInSAR method on changing landscapes where both the persistently and partially coherent points are available, we also applied the method to the southern part of Macau which is undergoing fast redevelopment.
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