GRSG Conference 2022: Orbit to Outcrop

Poster Title: Monitoring land subsidence by using InSAR along a large-scale area: the Aswan dam case study, Egypt

Author: Amira Ahmed


The interferometric Synthetic Aperture Radar (InSAR) technique is one of the most effective techniques to monitor and measure the land surface deformation related to events such as earthquakes, volcanic eruptions, landslides and land subsidence, especially when related to groundwater exploitation. This technique can work day and night and in all-weather with wide spatial coverage and high spatial resolution.

By measuring the phase differences between two SAR images acquired in different epochs over the same area, InSAR can measure the ground movement during a defined time interval. In the last two decades several SAR satellites have been launched, for instance, ENVISAT ASAR, TerraSAR-X, Cosmos-skyMed, ALOS-2/PALSAR-2, and Sentinel-1. In particular, sentinel-1 provided an unprecedented characterization of global coverage and a short revisit time of 6 or 12 days, leading to a strong increase of the demand for monitoring land deformation not only at a local scale but also at a regional scale and over a long period of time.

In general, the sentinel-1 image with Interferometric Wide Swath (IW) acquisition mode consists of three sub-swaths, each swath consists of a series of complex bursts. Although the sentinel- 1 data are freely available, monitoring large-scale ground deformation is challenging because of the large computational burden and complexity of the image. Given the increasing availability of computational infrastructures, InSAR processing for complete scenes over large areas is becoming more and more feasible.

One way of processing an entire SAR scene is to process each swath individually and in parallel, which is regarded as the most effective way to reduce the time consumption and complexity of the processing steps for large number of scenes.

This study illustrates a possibly effective way to monitor land deformation over a large-scale study area using an open-source software package GMTSAR. GMTSAR can be used for the two most common InSAR approaches, Persistent Scatterer (PSI) and Small Baseline Subset (SBAS). The workflow presented in this research is separated into five parts; downloading sentinel-1 images with the orbit files, splitting the master and slaves images into three sub-swaths, co-registrating between separated swaths and interferogram generation, debrusting and merging between the separated interferogram to interpret the full InSAR image, and finally applying the targeted 3D image stacking technique, i.e. either PSI or SBAS.

The workflow was applied to the area around the Aswan dam in Egypt to assess subsidence and uplift from 2019 till 2020 and showed promising results and showing the potential of using  InSAR big data to monitor land deformation at large scale.