COMPARISON OF HH AND VV POLARIZATIONS FOR DEFORMATION ESTIMATION USING PERSISTENT SCATTERER INTERFEROMETRY

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Research areas:
Year:
2017
Type of Publication:
Article
Keywords:
synthetic aperture radar, interferometry, persistent scatterers, deformation, polarization
Authors:
Divya Sekhar Vaka, Y.S.Rao Shweta Sharma
Abstract:
Persistent Scatterer Interferometry technique (PSI) exploits time series of interferometric data to estimate deformation over an area. The process involves analysing stable phase pixels from differential interferograms formed with respect to a single master. In this study, eight RADARSAT-2 C-band fine quad polarization images from 2014 to 2016 are used to identify Persistent Scatterer (PS) points and estimate deformation over Vijayawada city in India. With a full graph approach, 29 interferograms are produced. All the interferograms are unwrapped to aid stable deformation estimation. The prime objective of our research is to study the effect of HH and VV polarizations in PS point selection and deformation estimation. Initially, pixels with Amplitude Stability Index > 0.75 are selected as PS points. Later, PS pixels exhibiting temporal coherence > 0.75 are selected for deformation estimation. Before refinement, PS points for HH and VV polarization are identified as 49409 and 48395 respectively, whereas, after refinement, they are 30137 and 40678. Atmospheric Phase Screen (APS) is estimated and removed using inverted residuals approach. After APS removal, mean line of sight (LOS) displacement and velocity maps are generated. A linear model is used to invert displacements into velocities. Velocity obtained using HH polarized data ranges from +17 to-20 mm/year, and for VV it ranges from +15 to -15 mm/year. The spatial trend is linear throughout the observation period except in Oct. 2014. Deformation around this month shows up and down pattern. We attribute this to the devastating Hudhud cyclone thathit the state of Andhra Pradesh in Oct. 2014. Atmospheric variations due to the presence of strong troposphere component varied radar signal delay before and after the cyclone. Excluding this phenomenon, time series plots of selected points showed linear deformation pattern in both polarizations.
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