Development of Automated Satellite Image Stacking Tool (ASIST) for ALOS-2 DInSAR and PSInSAR analysis

The ALOS-2 satellite, launched in May 2014, is equipped with Phased Array L-band Synthetic Aperture Radar-2 (PALSAR-2), which can acquire intensity and phase images of a wide area even at night without being affected by clouds. Therefore, differential interferometric SAR (DInSAR) analysis and time-series interferometric SAR (a typical method is Permanent Scatterers interferometric SAR, or PSInSAR) analysis have been utilized in such fields as ground subsidence monitoring. However, it is not easy to perform this analysis because it requires specialized data processing. In addition, although public domain software can analyze the intensity of SAR data, few programs can manipulate interferometry processing using the phase information of SAR data. Therefore, the author has developed a program (the Automated Image Stacking Tool, or ASIST) that can manipulate SAR processing, including digital elevation data download, interferometric pair data retrieval, image coregistration, satellite orbit estimation, topological and orbital fringe correction, and ortho-rectification without the skills in SAR data processing. The output is a GeoTIFF image of ortho-rectified intensity and phase (or differential phase) data, and it is also possible to generate arbitrary pairs of differential interferometric processing images. Using at least a dozen of these images enables time-series interferometric SAR analysis to be performed for more accurate long-term ground motion analysis. In addition to the above features, ASIST can automatically acquire and pre-process free data distributed by JAXA. Therefore, ASIST can improve the efficiency of analysis and processing time when combining SAR data with other physical quantities (precipitation, water vapor, altitude, etc.). ASIST has been available to the public since July 2021 for educational and research purposes [1] and allows DInSAR analysis to be performed. PSInSAR analysis is scheduled for implementation and release after FY2022. [1] JAXA's Automated Satellite Image Stacking Tool (ASIST) is now available for educational and research users (https://www.eorc.jaxa.jp/en/news/2021/nw210721.html)