5:15 PM - 7:15 PM
[STT40-P02] A Preliminary Investigation into Quantitative Evaluation of Slope-Related Phase Difference on Mountainous Region in L-Band SAR Interferograms
In L-band interferometric SAR (InSAR) analyses focused on mountainous areas, characteristic phase differences sometimes appear between the far and near sides of slopes, even though these differences are considered not to be caused by crustal deformation. Fujiwara (2023) suggests that these phase differences may be related to changes in soil moisture, but that study is mostly qualitative, and a thorough quantitative evaluation has not yet been conducted. Understanding the detailed causes of these phase differences is important for identifying and correcting noise factors in interferometric images, which will improve the accuracy of crustal deformation monitoring in mountainous regions.
In this study, we carried out SAR interferometric analyses of the Hidaka Mountains in Hokkaido, Japan, using multiple ALOS-2 datasets (SM1 mode: ascending path 122, U2-7, and descending path 17, U2-8). After applying atmospheric and ionospheric corrections, we generated interferograms by using a spatial filter that extracts only short-wavelength components, thereby removing long-wavelength phase variations. We then calculated the slope direction and angle for each pixel based on digital elevation data and examined how they relate to phase differences and coherence in the interferograms. In addition, we used rainfall data from the Automated Meteorological Data Acquisition System (AMeDAS) and soil moisture data from the Global Land Data Assimilation System (GLDAS) to explore possible connections between these environmental factors and the observed phase differences.
Our analysis shows that, in many cases, the far side of slopes has lower coherence and more varied phase values, while the near side often has higher coherence. Over half of the interferogram pairs displayed phase differences that follow the slope. These differences did not strongly depend on the time interval between observation dates or on the perpendicular baseline length, but they appeared more clearly in interferograms that included particular observation dates. Although multi-looking and Goldstein filtering reduced the phase differences between the far and near sides to some extent, a residual difference remained in some cases. We did not identify a clear correlation between the slope-related phase differences and changes in rainfall or soil moisture; however, during periods of prolonged rainfall, some pairs showed larger phase differences, indicating a need for more detailed analyses.
Because the relationship between these phase differences in mountainous areas and factors such as soil moisture is complex, more comprehensive analyses that account for surface scattering properties and vegetation cover are required. Although this presentation focuses on preliminary findings, a quantitative understanding of the causes behind mountain-specific phase differences can contribute to more precise crustal deformation monitoring, improved disaster risk assessment, and further advancements in remote sensing technology.
Acknowledgments: ALOS-2 data were provided based on the joint research agreement with Japan Aerospace Exploration Agency (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 from JMA based on the agreement.
In this study, we carried out SAR interferometric analyses of the Hidaka Mountains in Hokkaido, Japan, using multiple ALOS-2 datasets (SM1 mode: ascending path 122, U2-7, and descending path 17, U2-8). After applying atmospheric and ionospheric corrections, we generated interferograms by using a spatial filter that extracts only short-wavelength components, thereby removing long-wavelength phase variations. We then calculated the slope direction and angle for each pixel based on digital elevation data and examined how they relate to phase differences and coherence in the interferograms. In addition, we used rainfall data from the Automated Meteorological Data Acquisition System (AMeDAS) and soil moisture data from the Global Land Data Assimilation System (GLDAS) to explore possible connections between these environmental factors and the observed phase differences.
Our analysis shows that, in many cases, the far side of slopes has lower coherence and more varied phase values, while the near side often has higher coherence. Over half of the interferogram pairs displayed phase differences that follow the slope. These differences did not strongly depend on the time interval between observation dates or on the perpendicular baseline length, but they appeared more clearly in interferograms that included particular observation dates. Although multi-looking and Goldstein filtering reduced the phase differences between the far and near sides to some extent, a residual difference remained in some cases. We did not identify a clear correlation between the slope-related phase differences and changes in rainfall or soil moisture; however, during periods of prolonged rainfall, some pairs showed larger phase differences, indicating a need for more detailed analyses.
Because the relationship between these phase differences in mountainous areas and factors such as soil moisture is complex, more comprehensive analyses that account for surface scattering properties and vegetation cover are required. Although this presentation focuses on preliminary findings, a quantitative understanding of the causes behind mountain-specific phase differences can contribute to more precise crustal deformation monitoring, improved disaster risk assessment, and further advancements in remote sensing technology.
Acknowledgments: ALOS-2 data were provided based on the joint research agreement with Japan Aerospace Exploration Agency (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 from JMA based on the agreement.