2:15 PM - 2:30 PM
[STT39-09] Extraction of ground surface displacement in Saitama Prefecture using time-series InSAR analysis
Keywords:InSAR analysis, GNSS, ground surface displacement
In Japan, the land subsidence is on-going mainly in cities. In recent years, to observe ground movements, attention has been focused on a technology called InSAR analysis, which detects ground surface movements with high accuracy from satellites. However, the analysis includes noise due to differences in the electron density distribution in the ionosphere and water vapor distribution in the stratsphere, satellite orbit error, etc., and it is difficult to detect displacements in tremors. In addition, L-band SAR data is easily affected by the ionosphere and its variation, and low-frequency waves are often visible in an image, especially when targeting a wide area, making it even more difficult to observe ground movements. However, since the noise caused by these ionospheres and water vapor are independent, it has been confirmed that these noises can be statistically reduced by stacking all the data over multiple periods. In the InSAR analysis, it is important to solve the noise problems of the ionosphere, water vapor, and orbital error.
InSAR analysis is one of the important techniques for observing displacement because it has excellent features for wide-area observation regardless of the weather. In addition, the GNSS continuous observation point network established by the Geographical Survey Institute measures daily fluctuations at a certain point with high accuracy, and GNSS is also an important technology for observing displacements. It can be said that SAR, which excels in surface analysis, and GNSS, which excels in observing fluctuations at certain points, have a complementary relationship. By using this relationship, we tried to reduce noise and extract displacement over a wide area and with high accuracy by calibrating the InSAR data to match the actual displacements at the GNSS point.
In this study, ALOS-2 / PALSAR-2 is used for time-series analysis of interferometric SAR, and the phase difference images of each scene obtained continuously are calibrated using GNSS, which has a complementary relationship. By performing these phase addings, we propose a method for extracting the temporal and spatial displacements of the ground over a long period of time in more detail.
12 scenes of ALOS-2 / PALSAR-2 ascending orbit and 15 scenes of descending orbit were used for the analysis for about 5 years from 2015 to 2020 in eastern Saitama prefecture. Using a large number of GNSS data included in the scene, the displacement planes obtained from the InSAR analysis were first corrected by a least square method by approximating and interpolating the actual ground movements as linear model. In the analysis, sedimentation points with an average of 4 mm / year and a maximum of 12 mm / year were estimated and confirmed between 2015 and 2020 in a wide area around Satte City and Kuki City in Saitama Prefecture. It was also confirmed that there is a correlation between the sedimentation pattern and the leveling data. Harmonious calibration of SAR data using GNSS points leads to noise reduction and makes it possible to extract ground displacements over a wide area and with high accuracy.
InSAR analysis is one of the important techniques for observing displacement because it has excellent features for wide-area observation regardless of the weather. In addition, the GNSS continuous observation point network established by the Geographical Survey Institute measures daily fluctuations at a certain point with high accuracy, and GNSS is also an important technology for observing displacements. It can be said that SAR, which excels in surface analysis, and GNSS, which excels in observing fluctuations at certain points, have a complementary relationship. By using this relationship, we tried to reduce noise and extract displacement over a wide area and with high accuracy by calibrating the InSAR data to match the actual displacements at the GNSS point.
In this study, ALOS-2 / PALSAR-2 is used for time-series analysis of interferometric SAR, and the phase difference images of each scene obtained continuously are calibrated using GNSS, which has a complementary relationship. By performing these phase addings, we propose a method for extracting the temporal and spatial displacements of the ground over a long period of time in more detail.
12 scenes of ALOS-2 / PALSAR-2 ascending orbit and 15 scenes of descending orbit were used for the analysis for about 5 years from 2015 to 2020 in eastern Saitama prefecture. Using a large number of GNSS data included in the scene, the displacement planes obtained from the InSAR analysis were first corrected by a least square method by approximating and interpolating the actual ground movements as linear model. In the analysis, sedimentation points with an average of 4 mm / year and a maximum of 12 mm / year were estimated and confirmed between 2015 and 2020 in a wide area around Satte City and Kuki City in Saitama Prefecture. It was also confirmed that there is a correlation between the sedimentation pattern and the leveling data. Harmonious calibration of SAR data using GNSS points leads to noise reduction and makes it possible to extract ground displacements over a wide area and with high accuracy.