Synthetic Aperture Microwave Radiometer Image Spectral Characteristics And Error Analysis

The principle of Synthetic Aperture Microwave Radiometer is to sample the spatial frequency spectrum of the field of view (FOV) with different baselines,each of which is composed of a pair of interferometric antennas. The outputs of the Synthetic Aperture Radiometer are called visibility function or spatial sample frequencies. And brightness temperature distribution 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 presents several features of 2-D frequency spectrum, from which some special brightness temperature 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 retrieved brightness temperature are obvious. The systematic errors have different effects on retrieved brightness temperature.Therefore, channel amplitude error and phase error, antenna position error, antenna pattern error and phase error and baseline absence, are analyzed in the paper. And the features of the effects caused by those errors in the retrieved images are presented. Furthermore, the paper gives the methods to identify the baselines with amplitude errors or (and) baseline absence, and to correct the retrieved brightness temperature. The simulation results prove that the correction method can signally improve the quality of the retrieved temperature and the retrieved images of the flight experiment.In the synthetic aperture antenna design, some actual restrictions will make the antenna work in the states of nonuniform frequency sample, which can result in the aliasing periodic extensions in space domain after reconstruction. The paper gives the condition of full alias-free FOV and the condition of existing alias-free FOV.The analyses in the paper can provide the methods to identify the error types and sources of Synthetic Aperture Microwave Radiometer, and also supply important references to the enhancement algorithm design and the Synthetic Aperture Antenna designs of nonuniform frequency samples.