InSAR Greece with Parallelized Persistent Scatterer Interferometry: A National Ground Motion Service for Big Copernicus Sentinel-1 Data

Ioannis Papoutsis,Stavroula Alatza,Constantinos Loupasakis,Alexis Apostolakis,Charalampos Kontoes

doi:10.3390/rs12193207

Abstract

Advances in synthetic aperture radar (SAR) interferometry have enabled the seamless monitoring of the Earth’s crust deformation. The dense archive of the Sentinel-1 Copernicus mission provides unprecedented spatial and temporal coverage; however, time-series analysis of such big data volumes requires high computational efficiency. We present a parallelized-PSI (P-PSI), a novel, parallelized, and end-to-end processing chain for the fully automated assessment of line-of-sight ground velocities through persistent scatterer interferometry (PSI), tailored to scale to the vast multitemporal archive of Sentinel-1 data. P-PSI is designed to transparently access different and complementary Sentinel-1 repositories, and download the appropriate datasets for PSI. To make it efficient for large-scale applications, we re-engineered and parallelized interferogram creation and multitemporal interferometric processing, and introduced distributed implementations to best use computing cores and provide resourceful storage management. We propose a new algorithm to further enhance the processing efficiency, which establishes a non-uniform patch grid considering land use, based on the expected number of persistent scatterers. P-PSI achieves an overall speed-up by a factor of five for a full Sentinel-1 frame for processing in a 20-core server. The processing chain is tested on a large-scale project to calculate and monitor deformation patterns over the entire extent of the Greek territory—our own Interferometric SAR (InSAR) Greece project. Time-series InSAR analysis was performed on volumes of about 12 TB input data corresponding to more than 760 Single Look Complex Sentinel-1A and B images mostly covering mainland Greece in the period of 2015–2019. InSAR Greece provides detailed ground motion information on more than 12 million distinct locations, providing completely new insights into the impact of geophysical and anthropogenic activities at this geographic scale. This new information is critical to enhancing our understanding of the underlying mechanisms, providing valuable input into risk assessment models. We showcase this through the identification of various characteristic geohazard locations in Greece and discuss their criticality. The selected geohazard locations, among a thousand, cover a wide range of catastrophic events including landslides, land subsidence, and structural failures of various scales, ranging from a few hundredths of square meters up to the basin scale. The study enriches the large catalog of geophysical related phenomena maintained by the GeObservatory portal of the Center of Earth Observation Research and Satellite Remote Sensing BEYOND of the National Observatory of Athens for the opening of new knowledge to the wider scientific community.

Highlights

Differential interferometric synthetic aperture radar (DInSAR) is a well-established technique used for measuring the Earth’s surface displacements, applicable in a variety of physical and anthropogenic and engineering processes, as well as for geologic and tectonic studies
The effectiveness of the P-persistent scatterers interferometry (PSI) chain was successfully tested on an unprecedented national-scale project that was built around the massive processing of more than 800 Sentinel-1 (A and B), interferometric wide-swath (IW) descending satellite pass single look complex (SLC) images, spanning from 2015 to 2019, covering the entire mainland of Greece
CoTnhcilsuswioonrkanpdroOvuidtleosokfour distinct contributions: First, we have delivered an open-source impleTmhiesntwatoirokn porfoavnidens df-otou-renddistpinecrstisctoentrisbcuatitoenresr: iFnitresrt,fewroemhetarvye pdipeelilvinereedbasaend oopnene-xsiosutirncge 722 implementation of an end-to-end persistent scatterer interferometry pipeline based on existing ISCE2 and stanford method for persistent scatterers (StaMPS) implementations, for which we parallelized the execution of several individual components

Summary

Introduction

Differential interferometric synthetic aperture radar (DInSAR) is a well-established technique used for measuring the Earth’s surface displacements, applicable in a variety of physical and anthropogenic and engineering processes, as well as for geologic and tectonic studies. Many techniques have been developed for multitemporal interferometry [10,11,12,13,14,15,16,17,18], with persistent scatterers interferometry (PSI) [10] and small baseline subset (SBAS) [11] being the most widely used methods for time-series analysis. PSI identifies persistent scatterers that are stable over the long time intervals of the SAR images [10,13], whereas SBAS focuses on the small baseline differential interferograms to minimize spatial decorrelation [11,15], which is an inherent noise source. A detailed and thorough review of PSI methods, including SBAS, can be found in Crosetto et al [19]

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