Research On Low Frequency UWB-SAR Calibration Technique

The calibration techniques are the premises of the quantitative analysis of synthetic aperture radar (SAR) data, and the quantitative relationship between the measurements and targets can be achieved by calibration. The developments and applications of the low frequency ultra wide band (UWB) SAR system are very important for military affairs. With the consideration of the characteristics of the low frequency UWB-SAR system, the radiometric calibration, polarimetric calibration and the motion status calibration are studied deeply in this thesis.The study background of the low frequency UWB-SAR is given in chapter 1. The SAR calibration hierarchy model is proposed, and the calibration concepts and strategies are discussed clearly. With the hierarchy model, the peculiarities and technical difficulties of the low frequency UWB-SAR are analyzed, and the approach of system calibration is determined.The fundamental problems of the low frequency UWB-SAR calibration are studied in chapter 2. Firstly, with the consideration of the frequency and aspect angle dependent parameters of the low frequency UWB-SAR, the radar equation for calibration is proposed. Secondly, the calibration model for the system is proposed, and the calibration errors can be analyzed based on this model. Finally, the information process model of the low frequency UWB-SAR is given, and antenna pattern and the impulse response function of the system are discussed.The radiometric calibration methods of low frequency UWB-SAR are studied in chapter 3. Firstly, based on the geometric relationship of SAR system, the low frequency, UWB and wide-angle electromagnetic scattering models of calibrators are achieved, using the moment method and the asymptotic waveform evaluation technique. Secondly, the effects of antenna pattern on system performance and extraction methods of antenna pattern are discussed. The correction methods of attenna pattern in time domain and frequency domain are proposed. Finally, the external and internal calibration methods and the processing of calibration data are studied.The polarimetric calibration methods for low frequency UWB-SAR are studied in chapter 4. Firstly, polarimetric electromagnetic scattering characteristics of the calibrators are studied. Secondly, based on the system characteristics and information process model, the polarimetric calibration model is proposed. Finally, the polarimetric calibration methods based on echo data and image data are proposed, and computer simulations validate the methods.The motion status calibration methods of the low frequency UWB-SAR are discussed in chapter 5. Firstly, the motion error model for the system is proposed, and accuracy of the model is satisfied under the condition of wide beamwidth. Secondly, the motion error extraction method is studied using reflectivity displacement method. Finally, the correction methods for the motion...