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An advanced decoupled polarimetric calibration method for the LuTan-1 hybrid- and quadrature-polarimetric modes.

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Title: An advanced decoupled polarimetric calibration method for the LuTan-1 hybrid- and quadrature-polarimetric modes.
Authors: Liu, Lizhi (AUTHOR), Huang, Lijie (AUTHOR), Wang, Yiding (AUTHOR), Lu, Pingping1 (AUTHOR) lupp@aircas.ac.cn, Li, Bo (AUTHOR), Li, Liang (AUTHOR), Wang, Robert (AUTHOR), Wu, Yirong (AUTHOR)
Source: ISPRS Journal of Photogrammetry & Remote Sensing. Mar2026, Vol. 233, p310-327. 18p.
Subjects: Polarimetry, Faraday effect, Polarimetric remote sensing
Abstract: During solar maximum, low-frequency spaceborne Polarimetric Synthetic Aperture Radar (PolSAR) systems suffer ionosphere-induced distortions that couple with system-induced polarimetric distortions. High-precision decoupled polarimetric calibration is therefore essential for obtaining high-fidelity PolSAR data. Existing point-target calibration methods lack a general approach for unbiased estimation of polarimetric distortion across multiple polarimetric modes and calibrator combinations, particularly under spatiotemporally varying ionospheric conditions. To address this, we derive the necessary conditions for unbiased estimation and propose a General Polarimetric Calibration Method (GPCM) applicable to various configurations. In addition, Enhanced Multi-Look Autofocus (EMLA), a modified STEC inversion method, is introduced for precise inversion of Slant Total Electron Content (STEC), enabling estimation of the spatiotemporally varying Faraday rotation angle for system distortion decoupling and PolSAR data compensation. GPCM applied to LuTan-1 HP and QP data results in HH/VV amplitude and phase imbalances of 0.0433 dB (STD: 0.017) and − 0.60° (STD: 1.02°), respectively, measured on trihedral corner reflectors. Calibration results also indicate that QP mode isolation exceeds 39 dB, while estimated axial ratios for HP mode are lower than 0.115 dB. Under comparable conditions, the results of GPCM are consistent with the Freeman analytical method. Furthermore, EMLA outperforms existing STEC inversion methods (COA, MLA, and GIM-based mapping), achieving a mean absolute difference of 1.95 TECU compared with in-situ measurements while demonstrating applicability to general scenes. Overall, the effectiveness of GPCM and EMLA in the LuTan-1 calibration mission is confirmed, indicating their potential for future PolSAR calibration tasks. The primary calibrated experimental dataset is publicly available at https://radars.ac.cn/web/data/getData?dataType=HPSAREADEN&pageType=en. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:During solar maximum, low-frequency spaceborne Polarimetric Synthetic Aperture Radar (PolSAR) systems suffer ionosphere-induced distortions that couple with system-induced polarimetric distortions. High-precision decoupled polarimetric calibration is therefore essential for obtaining high-fidelity PolSAR data. Existing point-target calibration methods lack a general approach for unbiased estimation of polarimetric distortion across multiple polarimetric modes and calibrator combinations, particularly under spatiotemporally varying ionospheric conditions. To address this, we derive the necessary conditions for unbiased estimation and propose a General Polarimetric Calibration Method (GPCM) applicable to various configurations. In addition, Enhanced Multi-Look Autofocus (EMLA), a modified STEC inversion method, is introduced for precise inversion of Slant Total Electron Content (STEC), enabling estimation of the spatiotemporally varying Faraday rotation angle for system distortion decoupling and PolSAR data compensation. GPCM applied to LuTan-1 HP and QP data results in HH/VV amplitude and phase imbalances of 0.0433 dB (STD: 0.017) and − 0.60° (STD: 1.02°), respectively, measured on trihedral corner reflectors. Calibration results also indicate that QP mode isolation exceeds 39 dB, while estimated axial ratios for HP mode are lower than 0.115 dB. Under comparable conditions, the results of GPCM are consistent with the Freeman analytical method. Furthermore, EMLA outperforms existing STEC inversion methods (COA, MLA, and GIM-based mapping), achieving a mean absolute difference of 1.95 TECU compared with in-situ measurements while demonstrating applicability to general scenes. Overall, the effectiveness of GPCM and EMLA in the LuTan-1 calibration mission is confirmed, indicating their potential for future PolSAR calibration tasks. The primary calibrated experimental dataset is publicly available at https://radars.ac.cn/web/data/getData?dataType=HPSAREADEN&pageType=en. [ABSTRACT FROM AUTHOR]
ISSN:09242716
DOI:10.1016/j.isprsjprs.2026.01.035