Abstract

Abstract. Persistent Scatterer Interferometry (PSI) is an advanced technique to map ground surface displacements of an area over a period. The technique can measure deformation with a millimeter-level accuracy. It overcomes the limitations of Differential Synthetic Aperture Radar Interferometry (DInSAR) such as geometric, temporal decorrelation and atmospheric variations between master and slave images. In our study, Sentinel-1A Interferometric Wide Swath (IW) mode descending pass images from May 2016 to December 2017 (23 images) are used to identify the stable targets called persistent scatterers (PS) over Bengaluru city. Twenty-two differential interferograms are generated after topographic phase removal using the SRTM 30 m DEM. The main objective of this study is to analyze urban subsidence in Bengaluru city in India using the multi-temporal interferometric technique such as PSI. The pixels with Amplitude Stability Index ≥ 0.8 are selected as initial PS candidates (PSC). Later, the PSCs having temporal coherence > 0.5 are selected for the time series analysis. The number of PSCs that are identified after final selection are reduced from 59590 to 54474 for VV polarization data and 15611 to 15596 for VH polarization data. It is interesting to note that a very less number of PSC are identified in cross-polarized images (VH). A high number of PSC have identified in co-polarized (VV) images as the vertically oriented urban targets produce a double bounce, which results in a strong return towards the sensor. The velocity maps obtained using VV and VH polarizations show displacement in the range of ± 20 mm year−1. The subsidence and the upliftment observed in the city shows a linear trend with time. It is observed that the eastern part of Bengaluru city shows more subsidence than the western part.

Highlights

  • Differential Interferometric Synthetic Aperture Radar (InSAR) is an efficient remote sensing tool for surface deformation mapping

  • These differential interferograms are Goldstein phase filtered before giving them as an input for time series analysis

  • It is interesting to note that a very less amount of PS candidates (PSC) are identified in crosspolarized images (VH)

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Summary

Introduction

Differential Interferometric Synthetic Aperture Radar (InSAR) is an efficient remote sensing tool for surface deformation mapping. Persistent Scatterer Interferometry (PSI) is an advanced DInSAR technique, which exploits multiple images of interferometric synthetic aperture radar (SAR) data to estimate deformation over an area. It overcomes the limitations of the DInSAR technique such as geometric, temporal decorrelation and atmospheric variations between images (Hanssen, 2001). The PSC are stable pixels that are present in all the selected images with the same scattering properties over time. It can be human-made objects like buildings, pipelines, electric poles or artificially installed corner reflectors. It is difficult to detect PSC in the rural areas due to the presence of agricultural fields or the vegetated areas that with time (Hooper et al, 2004)

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