3:30 PM - 5:00 PM
[SGD01-P14] Initiatives to utilize InSAR time series analysis for public survey
Keywords:InSAR Time Series Analysis, ALOS-2, public survey
Introduction
The Geospatial Information Authority of Japan (GSI) has been conducting Interferometric SAR (InSAR) analysis of Advanced Land Observing Satellite-2 (ALOS-2) images to monitor crustal deformation in Japan. Currently, the crustal deformation information from InSAR analysis is utilized to evaluate earthquake and volcanic activity.
One of GSI’s main missions is to maintain and manage "National coordinate", which is the reference of positions in various fields, such as public surveys, location-based services, and so on. However, InSAR analysis using 2 SAR observation data does not have sufficient precision due to various errors, such as tropospheric errors, and has not been utilized for maintaining “National coordinate”. On the other hand, in recent years the ALOS-2 observation data are accumulated since its launch in 2014, and we can measure crustal deformation precisely by InSAR time series analysis, which is a technique to greatly reduce errors and improve the accuracy of detecting anomalies by statistically processing a large number of interferograms.
Based on the above, we have been conducting InSAR time series analysis using ALOS-2 data for all of Japan and working on utilizing the results of the time series analysis to maintain and manage "National coordinate". In April 2022, we defined GSI's InSAR time series analysis as one of GSI’s basic surveys, which is a survey as the basis for all surveys in Japan, and the results of the analysis for Hokkaido and eastern Japan have been released by January 2023. Furthermore, we are considering how to measure vertical displacements with higher spatial resolution than before by InSAR time series analysis and leveling.
In this presentation, we will discuss the method of measuring vertical displacement with a high spatial resolution for public surveys.
Outline of InSAR time series analysis
We processed ALOS-2 data observed over 7 years from 2014 to 2021 for InSAR time series analysis using GSITSA (Kobayashi et al., 2018) which is the software developed by GSI. Interferograms used for InSAR time series analysis were applied tropospheric delay correction, ionospheric delay correction, and GNSS correction. In addition, in order to detect displacements that are not caused by plate motions and earthquakes, we estimated and removed tectonic wide-ranging and long-term deformation and co-seismic crustal deformation. The analysis results are not only displacement velocities in the satellite line-of-sight direction from descending and ascending orbits, but also quasi-vertical and quasi-east-west displacement velocities calculated by the 2.5D analysis (Fujiwara et al., 2000).
Method of measuring vertical displacement
The quasi-vertical displacement velocity of InSAR time series analysis is not completely consistent with the results of leveling surveys, because in the time series analysis, tectonic deformation estimated by GNSS was removed and some corrections were applied. Therefore, in order to obtain vertical displacement velocity with higher spatial resolution, it is necessary to consider a method by using both the results of the InSAR time series and leveling.
The method under consideration is as follows. First, a leveling is conducted in a part of the target area, and then calculate the difference between the leveling and the results of InSAR time series analysis at benchmarks. Finally, the results of the InSAR time series analysis are corrected by the difference between InSAR time series analysis and leveling, and we obtain vertical displacement in the target area. In this presentation, we will report on the details of the method under consideration.
Acknowledgments
ALOS-2 data were provided based on the joint research agreement with JAXA and under a cooperative research contract between GSI and JAXA. The ownership of ALOS-2 data belongs to JAXA.
The numerical weather model was provided by JMA based on an agreement.
Some of GNSS data were provided by JMA and NIED.
The Geospatial Information Authority of Japan (GSI) has been conducting Interferometric SAR (InSAR) analysis of Advanced Land Observing Satellite-2 (ALOS-2) images to monitor crustal deformation in Japan. Currently, the crustal deformation information from InSAR analysis is utilized to evaluate earthquake and volcanic activity.
One of GSI’s main missions is to maintain and manage "National coordinate", which is the reference of positions in various fields, such as public surveys, location-based services, and so on. However, InSAR analysis using 2 SAR observation data does not have sufficient precision due to various errors, such as tropospheric errors, and has not been utilized for maintaining “National coordinate”. On the other hand, in recent years the ALOS-2 observation data are accumulated since its launch in 2014, and we can measure crustal deformation precisely by InSAR time series analysis, which is a technique to greatly reduce errors and improve the accuracy of detecting anomalies by statistically processing a large number of interferograms.
Based on the above, we have been conducting InSAR time series analysis using ALOS-2 data for all of Japan and working on utilizing the results of the time series analysis to maintain and manage "National coordinate". In April 2022, we defined GSI's InSAR time series analysis as one of GSI’s basic surveys, which is a survey as the basis for all surveys in Japan, and the results of the analysis for Hokkaido and eastern Japan have been released by January 2023. Furthermore, we are considering how to measure vertical displacements with higher spatial resolution than before by InSAR time series analysis and leveling.
In this presentation, we will discuss the method of measuring vertical displacement with a high spatial resolution for public surveys.
Outline of InSAR time series analysis
We processed ALOS-2 data observed over 7 years from 2014 to 2021 for InSAR time series analysis using GSITSA (Kobayashi et al., 2018) which is the software developed by GSI. Interferograms used for InSAR time series analysis were applied tropospheric delay correction, ionospheric delay correction, and GNSS correction. In addition, in order to detect displacements that are not caused by plate motions and earthquakes, we estimated and removed tectonic wide-ranging and long-term deformation and co-seismic crustal deformation. The analysis results are not only displacement velocities in the satellite line-of-sight direction from descending and ascending orbits, but also quasi-vertical and quasi-east-west displacement velocities calculated by the 2.5D analysis (Fujiwara et al., 2000).
Method of measuring vertical displacement
The quasi-vertical displacement velocity of InSAR time series analysis is not completely consistent with the results of leveling surveys, because in the time series analysis, tectonic deformation estimated by GNSS was removed and some corrections were applied. Therefore, in order to obtain vertical displacement velocity with higher spatial resolution, it is necessary to consider a method by using both the results of the InSAR time series and leveling.
The method under consideration is as follows. First, a leveling is conducted in a part of the target area, and then calculate the difference between the leveling and the results of InSAR time series analysis at benchmarks. Finally, the results of the InSAR time series analysis are corrected by the difference between InSAR time series analysis and leveling, and we obtain vertical displacement in the target area. In this presentation, we will report on the details of the method under consideration.
Acknowledgments
ALOS-2 data were provided based on the joint research agreement with JAXA and under a cooperative research contract between GSI and JAXA. The ownership of ALOS-2 data belongs to JAXA.
The numerical weather model was provided by JMA based on an agreement.
Some of GNSS data were provided by JMA and NIED.