A Bragg-Like Point Extraction Method for Co-polarization Channel Imbalance Calibration

Abstract

Calibration by distributed targets is an important part of polarimetric calibration (PolCAL) without corner reflectors (CRs). Currently, both the correlation of HH and VV ($R_{\text{hhvv}}$) and the equivalent number of looks (ENL) constitute the common method for the extraction of Bragg-like points (BLPs) in order to calibrate the co-polarization channel imbalance $k$. However, strict assumptions about distributed targets and complex mathematical expressions regarding ENL limit the impact analysis of $k$ on $R_{\text{hhvv}}$ and ENL; thus, the fixed thresholds for $R_{\mathrm{hhvv}}$ and ENL can be obtained only by comparing the calibration errors with the CRs or simulated values in order to calibrate $k$ accurately. In some Earth observation and lunar exploration without CRs, the abovementioned conditions are not satisfied. In this article, a BLP extraction method is proposed for calibrating co-polarization channel imbalance $k$ in PolCAL. ${H}/{\bar{\alpha }}$ decomposition is utilized to deduce the specific scattering impacts of BLPs by different $k$ values first. Then, a dynamic selection method is proposed to reduce the influence of fixed thresholds and improve the extraction accuracy. Multiscene polarimetric synthetic aperture radar images from AIRSAR, ALOS, and GF-3 are utilized to verify the effectiveness of the proposed algorithm in the extraction of BLPs and the calibration results of $k$ obtained by applying the extracted BLPs.

Keywords

• Bragg -like points (BLPs)
• $k$ %22%2C%22default_operator%22%3A%22AND%22%7D%7D%7D"> co-polarization channel imbalance <named-content xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="LaTeX">$k$</tex-math> </inline-formula> </named-content>
• dynamic selection
• ${H}/{\bar{\alpha }}$ decomposition%22%2C%22default_operator%22%3A%22AND%22%7D%7D%7D"> <named-content xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="LaTeX">${H}/{\bar{\alpha }}$</tex-math> </inline-formula> </named-content> decomposition
• polarimetric synthetic aperture radar (PolSAR)