Co-polarization channel imbalance determination by the use of bare soil |
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| Institution: | 1. The State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, PR China;2. The School of Resource and Environmental Science, Wuhan University, PR China;1. Museum für Naturkunde, Leibniz Institute of Evolution and Biodiversity Research at the Humboldt University, Invalidenstr. 43, D – 10115 Berlin, Germany;2. University of Koeln, Institute of Biology, Gronewaldstr. 2, D 50931 Koeln, Germany;3. Friedhofstraße 9 D 66894 Käshofen, Germany;4. Department of Natural Sciences, National Museum of Scotland, Edinburgh, EH1 1JF, UK;1. State Key Lab of Precision Measuring Technology and Instruments, Tianjin University, 92 Weijin Road, Nankai District, Tianjin, China;2. Systems Engineering Research Institute, China State Shipbuilding Corporation (CSSC), 5 Yuetanbei Street, Xicheng District, Beijing, China |
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| Abstract: | This paper describes a novel technique which determines the co-polarization channel imbalance by the use of natural bare soil, instead of a trihedral corner reflector (CR). In polarimetric synthetic aperture radar (PolSAR) remote sensing, the polarimetric calibration (PolCAL) is the key technique in quantitative earth parameter measurement. In general, the current PolCAL process can be separated into two parts. The first part tries to estimate the crosstalk and the cross-polarization (x-pol) channel imbalance components by the reflection symmetry and the reciprocity properties, without a CR. Then, at least one trihedral CR is required to determine the co-polarization (co-pol) channel imbalance; however, it is not always possible to deploy a CR in difficult terrain such as desert. In this paper, we utilize bare soil as a stable reference target, and four common natural constraints of bare soil are evaluated to determine the co-pol channel imbalance, without the use of a CR. It should be mentioned that we do not propose to replace the CR by a natural target, but we utilize the natural target to enhance the PolCAL accuracy when a CR is missing. The four constraints are: (1) the consistency of the polarimetric orientation angle (CPOA) between the PolSAR POA and the digital elevation model (DEM) derived POA; (2) the unitary zero POA (UZPOA) of a flat ground surface; (3) the zero helix (ZHEX) component of the ground surface; and (4) the unitary version of the previous zero helix (UZHEX). In the theoretical part of this paper, we demonstrate that the forth constraint is the most suitable in different scenes. We then propose a multi-scale algorithm to further improve the robustness of the co-pol channel imbalance determination. In the experimental part, we apply our new methods to simulated airborne SAR (AIRSAR) and real uninhabited aerial vehicle SAR (UAVSAR) data. Without the use of any CR, the recovered results show that the estimated amplitude and phase error of the co-pol channel imbalance are less than 0.5 dB and 5°, respectively. |
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| Keywords: | Polarimetric SAR Calibration Bare soil Channel imbalance Polarimetric orientation angle Helix |
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