Sample Extraction Bsaed on Helix Scattering for Polarimetric Sar Calibratio

Abstract

ABSTRACT:Polarimetric calibration (PolCAL) of Synthetic Aperture Radar (SAR) images is a significant preprocessing for further applications. Since the reflection symmetry property of distributed objects can provide stable constraints for PolCAL. It is reasonable to extract these reference samples before calibration. The helix scattering generally appears in complex urban area and disappears for a natural scatterer, making it a good measure to extract distributed objects. In this paper, a novel technique that extracts reflecting symmetry samples is proposed by using helix scattering. The helix scattering information is calculated by Yamaguchi four-component decomposition algorithm. An adaptive threshold selection algorithm based on generalized Gaussian distribution is also utilized to scale the helix scattering components automatically, getting rid of the problem of various numerical range. The extracting results will be taken as PolCAL reference samples and the Quegan method are utilized to calibrate these PolSAR images. A C-band airborne PolSAR data was taken as examples to evaluate its ability in improving calibration precision. Traditional method i.e. extracting samples with span power was also evaluated as contrast experiment. The results showed that the samples extracting method based on helix scattering can improve the Polcal precision preferably.

Polarimetric Calibration and Quality Assessment of the GF-3 Satellite Images

“…There are some studies that focus on PolCAL samples extraction, and here we extract these samples by using helix scattering. The pixels with low helix scattering component will be extracted as PolCAL samples [ 10 , 26 ]. From the PolSAR distortion model in Equation (1), we obtain the vector form, and then gain the average covariance matrix [ 27 ]: where matrix P is the crosstalk distortion matrix, and matrix F is the cross-imba matrix.…”

“…In this experiment, the size of the strips was 100*Ncol pixels, where the term ‘Ncol’ means the size of the image in the azimuth direction. Secondly, we utilized an automatic extracting method to extract proper reference samples for PolCAL [ 10 ], and we then computed the average covariance matrices. After the PolCAL, we carried out the accuracy analysis on both the calibrated and uncalibrated images.…”

“…The other is to convert uncalibrated PolSAR data to calibrated data using these PDMs [ 9 ]. A lot of research has been done on PolCAL since the first PolSAR system, i.e., Airborne Synthetic Aperture Radar (AIRSAR), was developed [ 10 ]. The early PolCAL methods were designed using different kinds of corner reflectors (CRs) or polarimetric active radar calibrators (PARCs) [ 11 ].…”