Abstract
Abstract. Persistent Scatterer Interferometry (PSI) is a satellite-based Synthetic Aperture Radar (SAR) remote sensing technique used to measure and monitor land deformation from a stack of interferometric SAR images. This work concerns X-band PSI and, in particular, PSI based on very high resolution (VHR) StripMap CosmoSkyMed and TerraSAR-X SAR imagery. In fact, it mainly focuses on the technical aspects of deformation measurement and monitoring over urban areas. A key technical aspect analysed in this paper is the thermal expansion component of PSI observations, which is a result of temperature differences in the imaged area between SAR acquisitions. This component of PSI observations is particularly important in the urban environment. This is an interesting feature of PSI, which can be surely used to illustrate the high sensitivity of X-band PSI to very subtle displacements. Thermal expansion can have a strong impact on the PSI products, especially on the deformation velocity maps and deformation time series, if not properly handled during the PSI data processing and analysis, and a comprehensive discussion of this aspect will be provided in this paper. The importance of thermal expansion is related to the fact that the PSI analyses are often performed using limited stacks of images, which may cover a limited time period, e.g. several months only. These two factors (limited number of images and short period) make the impact of a non-modelled thermal expansion particularly critical. This issue will be illustrated considering different case studies based on TerraSAR-X and CosmoSkyMed PSI data. Besides, an extended PSI model which alleviates this problem will be described and case studies from the Barcelona metropolitan area will demonstrate the effectiveness of the proposed strategy.
Highlights
The Persistent Scatterer Interferometry (PSI) technique (Ferreti et al, 2000, 2001), introduced in the late 1990s, has proven to be an effective tool to measure surface displacement from which numerous disciplines have benefited
The standard Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques exploit the information contained in the radar phase of at least two complex Synthetic Aperture Radar (SAR) images acquired at different times over the same area
The new model is more accurate than those used in the standard PSI techniques because it explains the behaviour of PSI observations using three components, and three unknown parameters, instead of two: (i) the linear deformation velocity, which is related to the temporal baselines of interferograms; (ii) the Residual Topographic Error (RTE), related to the perpendicular baselines of interferograms; and (iii) the thermal expansion parameter, which is related to the average temperature differences at the time of acquisition of the images
Summary
The Persistent Scatterer Interferometry (PSI) technique (Ferreti et al, 2000, 2001), introduced in the late 1990s, has proven to be an effective tool to measure surface displacement from which numerous disciplines have benefited. PSI offers wide area coverage associated to a relatively high spatial resolution, which allows monitoring an entire metropolitan area, obtaining a global outlook of the deformation phenomena, while keeping at the same time the capability to measure individual structures and buildings Another main advantage of PSI is its high sensitivity, of the order of 1 mm/year, to small deformations. This technique exploits periodic and relatively low-cost spaceborne data acquisitions and this remote capability allows obtaining a potential reduction in the amount of ground-based observations, achieving simplified logistics operations and reducing personnel time and costs. Several case studies illustrating parameter estimability and the consequences if the thermal component is not properly handled during the PSI processing and analysis are presented and discussed
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