Conference Agenda

With advancements in radar remote sensing technology, observation platforms have evolved from satellites to unmanned aerial vehicles (UAVs) and ground-based systems. While satellite radar sensors provide high resolution and wide area coverage, their acquisition geometries and relatively long revisit cycles make it difficult to monitor steep terrain or rapidly changing surfaces. Ground-based radar systems offer a flexible alternative, allowing us to control when and how we observe these dynamic environments. In particular, when full-polarimetric data are acquired from ground-based radar systems, their very high temporal resolution enables daily or even hourly observations, providing significant advantages for monitoring dynamic environments such as diurnal changes in rice paddy canopy structure. However, the accuracy of polarimetric measurements might be degraded by systematic distortions such as channel imbalance and crosstalk. While these issues are well addressed in spaceborne systems, ground-based polarimetric radars require calibration because their antennas are independently deployed. In this study, we conducted polarimetric calibration of full-polarimetric interferometric data acquired by the Gamma Portable Radar Interferometer-II (GPRI-II), a ground-based Ku-band real-aperture radar. To ensure accurate calibration, three trihedral corner reflectors with 50 cm edge lengths were deployed at a distance of 200 meters from the radar. One reflector was used to derive the calibration parameters, while the remaining two were used to validate the results. The calibration process comprised azimuth beam squint correction, azimuth phase ramp removal, and polarimetric distortion calibration. Beam squint, caused by azimuth rotation-induced phase center shifts, was compensated by estimating squint angles from the GPRI-II equipment’s rotation speed and waveguide frequency. Azimuth-phase distortion, resulting from an offset between the mechanical rotation center and the antenna phase center, was modeled and removed using matched filtering. The calibration coefficients, including amplitude and phase imbalances, were derived from covariance matrices around the calibration reflector and applied to the full-polarimetric dataset. After calibration, co-polarized channels exhibited enhanced symmetry and phase consistency, while cross-polarized channels were effectively suppressed. The total phase offset between the co-polarized channels decreased from 27 ° to –1 °, indicating that their phase difference was almost completely corrected, which improved coherence and ensured more accurate polarimetric measurements. Cross-polarization isolation improved from approximately 33 dB to 34 dB, confirming minimal residual crosstalk. The calibration parameters also produced consistent improvements at the validation reflectors, while weaker responses observed at one site were attributed to clutter and minor misalignment. The results demonstrate that accurate polarimetric calibration of ground-based interferometric radar data can be effectively achieved using corner reflectors. The calibrated GPRI-II polarimetric data provide a reliable foundation for quantitative polarimetric analysis and can be further extended to studies on vegetation canopy structures and scattering properties.