Analysis of Using the Parabolic Antenna as the Passive Calibrator for P-Band Spaceborne SAR Radiometric Calibration
Analysis of Using the Parabolic Antenna as the Passive Calibrator for P-Band Spaceborne SAR Radiometric Calibration
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抛物面天线作为P波段星载SAR辐射定标无源定标器的分析
DOI：
10.3390/rs13214300
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发表时间：
2021-10
期刊：
影响因子：
5
通讯作者：
Huang Jianjun
中科院分区：
文献类型：
--
作者：
Du Shaoyan;Hong Jun;Wang Yu;Qiu Tian;Xing Kaichu;Huang Jianjun
P波段星载合成孔径雷达系统面临着缺乏可用于辐射定标的参考目标的问题。传统的人工无源定标器（如三面角反射器）由于重量、尺寸、制造和安装成本等原因，很难应用于P波段SAR定标。抛物面天线由于其稳定的散射特性和大的RCS被认为是一种潜在的校准器。校准器的标准之一是方位向RCS方向图的波束宽度需要远大于SAR天线波束宽度，这便于对准和获得恒定的RCS值。通常认为，抛物面天线只有在与SAR传感器完全对准时才能使用。然而，P波段星载合成孔径雷达（SAR）系统由于波长较长，通常具有较宽的波束宽度。相比之下，抛物面天线的方位RCS方向图具有窄的波束宽度，这将导致校准器在合成孔径周期内的RCS不恒定，从而引入额外的校准误差。由于SAR天线波束宽度与RCS方向图波束宽度的不平衡性，抛物面天线作为定标器的准则可能需要进一步讨论。分析了抛物面天线RCS方向图对辐射定标的影响，建立了定量误差模型。在误差模型的基础上，对对准和失准两种情况进行了误差分析。理论分析表明，即使抛物面天线完全对准，如果不进行额外的误差补偿，校准精度也会下降。在未对准的情况下，即使引入较小的误差，抛物面天线也可以用于校准。为了验证这一结论，抛物面天线的RCS方向图被用于P波段成像仿真和校准仿真。结果表明，窄的RCS方向图将引入一个不可忽略的误差，在校准时完全对准。抛物面天线还可以在未对准的情况下帮助校准。此外，标定实验表明，经过误差模型补偿后，标定精度得到了有效提高。
The P-band spaceborne SAR system faces the problem of a lack of available reference targets for radiometric calibration. Traditional artificial passive calibrators such as trihedral corner reflectors may be hard to be adopted to P-band SAR calibration because of weight, size, manufacture, and installation cost. The parabolic antenna is considered as a potential calibrator due to its stable scattering characteristics and large RCS. One of the criteria of the calibrator is that the beamwidth of the azimuth RCS pattern needs to be much larger than the SAR antenna beamwidth, which is convenient for alignment and obtaining a constant RCS value. It is generally believed that the parabolic antenna can only be used when it is fully aligned to the SAR sensor. However, the P-band spaceborne SAR system usually has a wide beamwidth because of the long wavelength. In contrast, the azimuth RCS pattern of the parabolic antenna has a narrow beamwidth, which will cause inconstant RCS of the calibrator within the synthetic aperture period, thereby introducing an additional calibration error. Due to the imbalance between the SAR antenna beamwidth and the RCS pattern beamwidth, the criterion of using the parabolic antenna as a calibrator may need further discussion. This article analyzes the influence of the RCS pattern of the parabolic antenna on the radiometric calibration and establishes the quantitative error model. Based on the error model, the error analysis is carried out for the two cases of alignment and misalignment. The theoretical analysis shows that the calibration accuracy will decrease if without additional error compensation despite a fully aligned parabolic antenna. Under the case of misalignment, the parabolic antenna can also be used for calibration, even when introducing smaller errors. To verify this conclusion, the RCS pattern of a parabolic antenna is used for the P-band imaging simulation and calibration simulation. The results show that the narrow RCS pattern will introduce a non-negligible error in the calibration when fully aligned. The parabolic antenna can also assist in calibration in the case of misalignment. In addition, the calibration experiment shows that, after compensation with the error model, calibration accuracy has been effectively improved.
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