The Accuracy of Faraday Rotation Estimation in Satellite Synthetic Aperture Radar Images
The Accuracy of Faraday Rotation Estimation in Satellite Synthetic Aperture Radar Images
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DOI：
10.1109/tgrs.2013.2284635
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发表时间：
2014-08-01
影响因子：
8.2
通讯作者：
Quegan, Shaun
中科院分区：
文献类型：
--
作者：
Rogers, Neil C.;Quegan, Shaun
星载线性极化合成孔径雷达（SAR）通过测量使用正交极化无线电波形成的图像之间的协方差，提供有关表面特性和散射体类型的信息。然而，电离层法拉第旋转（FR）和系统校准误差改变极化通道中的平衡，并使协方差矩阵失真。由于FR角度较大，在较低的无线电频率，本文重点介绍的生物量卫星，这是欧洲航天局的第7地球探测器使命，并将携带P波段（435 MHz）极化合成孔径雷达。其主要目标是通过将来自极化协方差矩阵的估计值与基于使用极化干涉测量法测量森林高度并利用高度-生物量异速生长关系的估计值相结合来测量森林生物量密度。四种方法估计FR从极化SAR的准确性评估使用模拟图像的森林生物量密度和系统误差（H/V通道不平衡，天线串扰和噪声）的范围内，并在一个大的传播FR角。所有方法都有偏置，这取决于FR、串扰分量的相对相位和通道不平衡相位。性能最好的方法估计FR优于5。在最坏情况下，所有FR角度的系统误差，因此生物量密度估计的准确性不应受到显著影响。然而，预计串扰相位在生物质天线波束上变化很大，这可能会导致FR偏置在整个条带上变化几度。这些影响可能会发生，即使在L波段数据的FR满足小的值。
Spaceborne linearly polarimetric synthetic aperture radar (SAR) provides information about surface properties and scatterer types by measuring the covariances between images formed using orthogonally polarized radio waves. However, ionospheric Faraday rotation (FR) and system calibration errors alter the balance in the polarimetric channels and distort the covariance matrix. Since FR angles are greater at lower radio frequencies, this paper focuses on the Biomass satellite, which is the European Space Agency's 7th Earth Explorer mission and will carry a P-band (435 MHz) polarimetric SAR. Its primary objective is to measure forest biomass density by combining estimates derived from the polarimetric covariance matrix with estimates based on measuring forest height with polarimetric interferometry and exploiting height-biomass allometric relations. The accuracy of four methods for estimating FR from polarimetric SAR is assessed using simulated images of forest with a range of biomass densities and system errors (H/V channel imbalances, antenna crosstalk, and noise) and over a large spread of FR angles. All methods have biases dependent on the FR, the relative phases of the crosstalk components, and the channel imbalance phase. The best performing method estimates FR to better than 5. under worst case system errors at all FR angles, so the accuracy of biomass density estimates should not be significantly affected. However, crosstalk phases are predicted to vary greatly across the Biomass antenna beam, and this could potentially cause the FR bias to vary by several degrees across the swath. These effects may occur even for the small values of FR met in L-band data.