干涉式被动微波成像仪二维频谱特征及误差分析

干涉式被动微波成像仪(干涉式综合孔径微波辐射计)利用不同距离的干涉天线对形成的基线对视场范围内亮温分布的空间频谱进行采样,进而反演得到亮温图像。首先介绍了干涉式被动微波成像仪的基本工作原理,在此基础上分析了空间图像的二维频谱特征,并能利用这些特征从采样频谱中初步分析出原始亮温中的某些特殊分布,证实了在反演亮温存在明显振荡的情况下,可以从振荡方向判断存在误差的基线的大致位置。还分析了成像仪的天线位置误差、信道的幅度和相位误差以及天线方向图误差对反演亮温的影响及特点。这些分析将为从反演图像判断干涉式被动微波成像仪误差类型和来源提供重要的判别依据,并为后续的反演图像增强算法的设计提供重要的参考。

2-D Frequency Spectrum Features and Error Analysis for Interferometric Passive Microwave Imager

The principle of Interferometric Passive Microwave Imager(Aperture Synthesis Interferometric Radiometers) is to sample the spatial frequency spectrum of the field of view(FOV) with different baselines,each of which is composed of a couple of interferometric antennas.The output is called visibility function or spatial sample spectrum.Then,the images of FOV can be reconstructed with different algorithms and methods,such as Fourier transformation,Clean algorithm,Maximum entropy method(MEM) and so on.This paper introduces the basic concept of Interferometric Passive Microwave Imager first,and presents several features of 2-D frequency spectrum,from which some special brightness distributions of the FOV can be concluded.On basis of those features,the directions and positions of baselines with errors can be identified approximately,when the oscillations in the reconstructed images are obvious.There are still residual system errors after calibration,which affect the spatial resolution,brightness resolution and accuracy.Therefore,four important errors(antenna position error,amplitude error and phase error in channels,and antenna pattern error),are analyzed in the paper,and baseline absence,which can be caused by antenna or correlator malfunctions,is also considered.And the effects caused by those errors in the reconstructed images,are presented. The analyses in the paper can provide the evidences to identify the error types and sources of Interferometric Passive Microwave Imager,and also can supply important references to design enhancement algorithm.