Conference Agenda

Radar interferometry is a technique capable of measuring precise surface displacement by analyzing the interferometric phase between two images acquired at different times. However, an interferogram generated from Synthetic Aperture Radar(SAR) data contains various phase components unrelated to displacement, including those from topography, orbital errors, earth curvature, atmosphere, and noise. Time-series interferometry techniques effectively remove these non-displacement phase signals. A prominent time-series method is Persistent Scatterer Interferometry (PSI), which monitors displacement using stable Persistent Scatterers(PS) identified over the acquisition period. While SAR-based PSI is widely applied to monitor phenomena such as ground subsidence, earthquakes, and volcanic activity, its long revisit period, typically several days, limits its ability to capture rapid, short-term displacements. Furthermore, SAR's side-looking imaging geometry can introduce geometric distortions such as layover, foreshortening, and shadow which may result in observational blind areas.

In contrast, ground-based radar(GBR) offers flexible control over acquisition time, location, and antenna geometry to specific monitoring objectives. GBR can acquire high-precision time-series data, making it highly effective for observing rapid and localized displacements. Consequently, it is extensively utilized in diverse applications, including the monitoring of slopes, landslides, glaciers, and subsidence. An advantage of GBR is that its fixed antenna position and comparatively smaller observation area inherently exclude topographic and earth’s curvature phases from the interferogram. However, GBR is highly susceptible to atmospheric phase delay caused by changing weather conditions. Temporal and spatial variations in temperature, humidity, and pressure alter the atmospheric refractivity. This fluctuation modifies the propagation path and velocity of the radar waves, inducing an atmospheric phase unrelated to actual surface displacement. This atmospheric phase significantly limits high-precision measurements, and its effect is particularly pronounced at higher frequencies.

This study aims to evaluate the atmospheric interferometric phase in the application of PSI to GBR, and to propose a correction method using meteorological data. The GPRI-II (Gamma Portable Radar Interferometer-II) system operates in the Ku-band, with a frequency range of 17.1-17.3 GHz. Data were acquired continuously for 33 hours(from 17:00, Sept 18, to 02:00, Sept 20, 2025) at an levee in South Korea, with a 5-minute interval. A total of 397 Single-Look Complex(SLC) images were collected. Synchronous temperature and humidity data were collected at the same interval from hygrometers co-located with corner reflectors(CR) on the levee. Barometric pressure data was obtained from a meteorological station 6 km away. The 33-hour dataset was divided into 11 distinct 3-hour sections. Using the first image of each section as the reference, we calculated the interferometric phase and the corresponding changes in meteorological conditions. A correlation analysis revealed the highest coefficient of determination (R² = 0.9) in the section 20:00 to 23:00. Subsequently, we calculated the atmospheric refractivity from the meteorological data to generate an atmospheric phase model. This model was then applied to correct the atmospheric phase in the SLC stack. Finally, PSI was performed using the first acquired image as the reference. The atmospheric correction was evaluated using the interferometric phase at two installed corner reflectors(CR1, CR2), under the assumption of zero actual displacement. Before correction, the standard deviations of the phase were 0.26 radians(CR1) and 0.36 radians(CR2). After correction, these values were significantly reduced to 0.12 radians and 0.14 radians, respectively. When converted to Line-of-Sight(LOS) displacement rate, the displacement rates decreased from 0.5 cm/hour(CR1) and 0.7 cm/hour(CR2) before correction, to 0.1 cm/hour and 0.0 cm/hour after correction. This study successfully demonstrates the generation of an effective atmospheric phase model from meteorological data and its utility in correcting atmospheric phases observed in permanent scatterers. We conclude that this methodology can be effectively utilized to enhance the precision of displacement monitoring in ground-based radar PSI applications.