Polarimetric calibration of synthetic aperture radar onboard the ALOS satellite

ALOS卫星上合成孔径雷达的偏振校准

基本信息

批准号：
14550366
负责人：
FUJITA Masaharu
金额：
$ 2.18万
依托单位：
Tokyo Metropolitan Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14550366/
关键词：
polarization preserving reflector polarization rotating reflector radar polarimetry Van Atta array polarization grid Faraday rotation ALOS PALSAR 合成開口レーダポーラリメトリック較正 ALOS レトロディレクティブ特性

项目摘要

Polarimetric radar usually has polarimetric transfer errors in its antennas. It is therefore necessary to remove its influence for correct application of the system. The procedure is called polarimetric calibration. There are several approaches for polarimetric calibration; however, they have disadvantages as well as advantages. We investigated a new approach to use two reference targets, i.e. polarization preserving and polarization selective reflectors. Validation of the approach was made by using the data taken with Spaceborne Imaging Radar C (SIR-C) and showed the its good and performance for spaceborne synthetic aperture radar (SAR) calibration. SAR to be onboard the ALOS (advanced land observing satellite) uses the L-band radar wave and it may suffer from the influence of Faraday rotation within the ionosphere. The amount of Faraday rotation may vary with several parameters, so we have to estimate it and compensate its influence. The countermeasure was also investigated by using … More polarization rotating reflector and the new approach has been propposed.We need to use the reflectors as described above. We developed new polarization rotating reflector by using the concept of Van Atta array. It has a capability of source tracking, so it does not need precise pointing of the reflector. Polarization rotating function was introduced by using dual-polarization antenna elements. When the reflector is of active design, the influence of direct scattering can be neglected; however, there are serious problems of direct scattering when it is of passive design. We proposed the quarter-wavelength displacement technique to suppress the direct scattering components. The technique was very simple, but effective to suppress the scattered field from the reflectors. We also had to develop polarization selective reflectors having high cross polarization discrimination ratio. When we use polarization grid, it is enough to use thin grid structure. However, it is not so easy to construct a large reflector with very thin grid. We applied the quarter-wavelength displacement technique to the polarization selective reflector using grid, and the result was satisfactory.Unfortunately, launch of the ALOS satellite is delayed, so we could not conduct the experiment on the PALSAR (Phased array L-band synthetic aperture radar). However, we had an opportunity to test the above algorithm and reflectors in the airborne synthetic aperture radar experiment conducted by JAXA and NICT. We regarded it as a preliminary test of the satellite experiment. We obtained the satisfactory results that the channel imbalance was within 1 dB, channel phase difference was within 6.2 degrees, and cross-polarization noise was less than -25 dB. This proved the validity of our approach and showed the promising role in the ALOS experiment. Less

极化雷达通常在其天线中具有极化转移误差。因此，有必要消除其影响到正确应用系统的影响。该过程称为极化校准。有多种偏振校准的方法。但是，它们具有缺点和优势。我们研究了一种使用两个参考目标的新方法，即保存和极化选择性反射器。通过使用使用Spaceborne Imaging Radar C（SIR-C）获取的数据进行验证，并显示其对SpaceBorne合成孔径雷达（SAR）校准的良好和性能。 SAR将在ALOS上进行ALO（高级土地观察卫星）使用L波段雷达波，并且可能会遭受Faraday旋转在电离层内的影响。法拉第旋转的量可能会随几个参数而变化，因此我们必须估算并弥补其影响。还通过使用……更多的极化旋转反射器和新方法研究了对策。我们需要使用如上所述的反射器。我们使用Van Atta阵列的概念开发了新的极化旋转反射器。它具有源跟踪的功能，因此它不需要精确指向反射器。通过使用双抛光天线元件引入极化旋转功能。当反射器具有主动设计时，可以忽略直接散射的影响；但是，当直接散射是被动设计时，存在严重的问题。我们提出了四分之一波长的位移技术来抑制直接散射组件。该技术非常简单，但有效地抑制了反射器的散射场。我们还必须开发具有高跨极化歧视比的极化选择性反射镜。当我们使用极化网格时，就足以使用薄网格结构。但是，用非常薄的网格构造大型反射器并不容易。我们使用网格将四分之一波长位移技术应用于极化选择性反射器，结果是令人满意的。但是，我们有机会测试上述算法和Jaxa和NICT进行的空中合成孔径雷达实验中的反射器。我们认为它是卫星实验的初步测试。我们获得了满意工厂的结果，即通道不平衡在1 dB之内，通道相位差在6.2度以内，交叉极化噪声小于-25 dB。这证明了我们方法的有效性，并在ALOS实验中表现出了承诺的作用。较少的