Research On Error Analysis And External Calibration For Mirrored Aperture Synthesis

Aperture synthesis radiometer(ASR)form a large observation aperture by a thinned array of small-aperture antennas,which has the advantages of light weight and instantaneous imaging without mechanical scanning.However,with the development of synthetic aperture technology,some of its defects are gradually exposed.In order to satisfy the high spatial resolution,there are hundreds of antennas and thousands of correlators in the spaceborne ASR,which greatly increases the complexity of the system.In order to reduce the complexity of system structure and signal processing,Mirrored Aperture Synthesis(MAS)was proposed by Huazhong University of Science and Technology(HUST).Compared with aperture synthesis,MAS can achieve the same spatial resolution with fewer antennas.However,the good imaging performance of MAS is based on the ideal hardware conditions.There are various errors in the actual system,which lead to the degradation and even distortion of the reconstructed bright temperature image.Therefore,modeling and correcting the errors are the key to obtain a high-quality reconstructed bright temperature image for MAS.In this thesis,the errors in one-dimensional and two-dimensional aperture synthesis are analyzed firstly.The errors are classified into three types by the error source: reflector error,channel error and antenna error.Error modeling and simulation are carried out to analyze the influence of different errors on the reconstructed bright temperature image.The errors are classified into four types by the role in the correlation output: azimuth-independent multiplicative error,azimuth-related multiplicative error,fixed offset additive error and random offset additive error.Azimuth-independent multiplicative error and fixed offset additive error are the main errors in MAS.The calibration methods for the main errors are presented,which make use of external single noise source and external reference scene,respectively.The theoretical derivation and simulation analysis of the calibration methods are given,and experiments are carried out on the experiment system of MAS at the V band(MAS-V)developed by HUST.Simulation and experimental results show that the two calibration methods can effectively improve the quality of the reconstructed bright temperature image.