GEO DATA

Data Articles

Data on Time-series Observation of Ground Subsidence in South Korea Using Sentinel-1 SAR Observations: Chanuk Lee, Jeongheon Ju, JangHun Kang, Seowon Kim, HeeJin An, Yuna Hong, Seokyeong Hwang, Sang-Hoon Hong; GEO DATA. 2024;6(4):495-504. Published online December 31, 2024; DOI: https://doi.org/10.22761/GD.2024.0048

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Abstract PDF: Ground subsidence is a phenomenon where surface materials sink due to a combination of natural and anthropogenic factors. South Korea has experienced human casualties and economic losses due to ground subsidence, such as sinkholes. Moreover, with the recent increase in earthquakes in the country, the importance of collecting and analyzing data for monitoring ground subsidence and surface displacement for disaster prevention is growing. This study monitored ground subsidence that occurred in South Korea from January 1, 2021 to December 31, 2022, while also observing other surface displacements. The study utilized synthetic aperture radar (SAR) satellite data, which, due to its high penetration capabilities of microwaves, is relatively unaffected by weather and day-night conditions, enabling wide-area observation with high spatial resolution, making it suitable for monitoring surface displacements. A total of 321 C-band Sentinel-1 SAR images, obtained between January 1, 2021 and December 31, 2022, were analyzed. Based on a perpendicular baseline distance of 200 meters and a time interval of 100 days, small baseline subset network were created. Time-series surface displacement data and velocity maps were produced to analyze the overall displacement patterns in the study areas.

Evaluation of Residual Phase from Orbit Accuracy Using TerraSAR-X/TanDEM-X SAR Observation: Yeojin Kim, Sang-Hoon Hong; GEO DATA. 2024;6(4):487-494. Published online December 31, 2024; DOI: https://doi.org/10.22761/GD.2024.0039

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Abstract PDF: Interferometric synthetic aperture radar (InSAR) is used to observe precise surface displacement and create digital elevation models by calculating the phase differences between two or more SAR images obtained over the same surface area. The phase of a repeat-pass interferogram can be expressed as the sum of contributions from topography, ground displacement, earth curvature, noise, and the satellite’s orbital phase component. For precise observations, removing unnecessary phase components is essential. Errors owing to the satellite’s orbit accuracy leave residual phases in the interferogram, which become a significant limitation for wide-area ground displacement monitoring using the InSAR technique. This study used four pairs of images acquired by TerraSAR-X in monostatic pursuit mode from October 2014 to February 2015 to analyze the residual phase caused by orbital errors. Since these images were acquired with a 10-second interval between the TerraSAR-X and TanDEM-X satellites, the phase coherence was maintained over time. The Tarim Basin in China was selected as the study area to minimize the impact of terrain distortion. By introducing a 0.5 m error into the x, y, and z components of the satellite position vectors and creating differential interferograms, it was found that the x component’s orbital error caused the largest residual phase, with linear residual phases observed in the north-south direction. Furthermore, various baselines ranging from -29.71 to 263.21 m were used to quantitatively compare the residual phases caused by orbital errors based on the perpendicular baseline. The residual phase was similar across the four differential interferograms, with approximately 3.49 π for the x component, 0.85 π for the y component, and 1.25 π for the z component. The residual phase resulting from simulated orbital errors was effectively mitigated using a 2D quadratic model.

Original Paper

Evaluation of Calibration Using Corner Reflector with Ground-Based Interferometric Radar: Je-Yun Lee, Jeong-Heon Ju, Sang-Hoon Hong; GEO DATA. 2024;6(1):32-42. Published online March 28, 2024; DOI: https://doi.org/10.22761/GD.2024.0002

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Abstract PDF: The accuracy of microwave remote sensing relies on the calibration of the radar measurement. It is important to estimate the radar cross-section (RCS) using a passive corner reflector (CR) or active transponder to evaluate the quality of imaging radar data. A strong and consistent RCS can be achieved by the acquisition of radar signals concentrated at specific angles during the CR calibration procedure. There are several types of CR depending on the shape and size such as triangular trihedrals, square trihedrals, dihedrals, spheres, or cylinders. In this study, we examine the RCSs using three types of CR with Ku-band ground-based real aperture radar equipment, the Gamma Portable Radar Interferometer-II. It can be easily deployed to acquire fully polarimetric radar observations. The initial experiment was conducted at Busan Sam-nak Auto Camping Site on November 1, 2023. The amplitude images show much higher backscattered radar signals at the CR location, whereas relatively lower power has been captured in the surrounding areas. The attenuation factors in the radar receivers could be useful to prevent saturation around the CR location at the line-of-sight direction. The experiment indicates that the different levels of the RCS measurements from three types of CRs could be utilized for calibration study with fully polarimetric radar observations.

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