ISAR Imaging Of High Speed Moving Targets

Imaging radar is being more and more widely used in military and civil fields, which can work all-weather, day/night and long range and provide high resolution radar image. To image the high speed moving target such as missile, satellite, space debris with the image radar has important military and scientific research value.The main research in the paper is the inverse synthetic aperture radar (ISAR) imaging method for the high speed moving target. The compensation error and its effect caused by using the model of low speed moving target to compensate the high speed moving target echo is analyzed. The processing method of the linearly modulated stepped frequency (LMSF) signal has been further studied. The top areial detection and imaging method for the sea surface target are proposed as the application of imaging radar. The concrete contents are as follows:1. The three echo models often adopted in the radar signal processing are summarized, which are the precise echo model, the first order approximate model and 'stop-go' model. Based on the characteristic of the radar imaging, the application conditions of the linear frequency modulation (LFM) signal's first order approximate model and 'stop-go' model have been analyzed.2. A novel method for high speed moving targets ISAR imaging based on 'moving' reference dechirp signal is presented. The main steps are as follows. Firstly target translational track is estimated and based on which, the echo is compensated for the dechirping signal, accordingly, the internal-pulse compensation of the target echo and the coherent processing of the echo are accomplished. Then Keystone transform is applied to eliminate the scattering points migration through resolution cells (MTRC), and utilizing the phase focusing to banish effect of the high order motion parameter compensation error. Finally using the RD algorithm or instantaneous imaging algorithm to achieve the target ISAR image. The key point of the method is the target motion track fitting. Moreover the fitting precision is related with the number of the fitting pulses, so the relationship between the fitting precision and number of the fitting pulses is presented.3. The method of synthetic range profile for LMSF signal and the high speed moving target ISAR imaging algorithm based on the synthetic range profile are studied. To avoid spurious peaks, extracting loss and Doppler-coupling shift which exist in the traditional extracting algorithm in the method of the synthetic range profile, the paper describes a shift-extracting algorithm, which based on searching the maximum norm 1 of the range profile. Moreover the paper analyses the application condition of this searching algorithm, and gives the design method for system parameters. After that, the stepped compensation method of the LMSF radar ISAR imaging is presented. The application conditions of the first order approximate model and 'stop-go' model have been deduced in the process of imaging.4. The method of synthetic bandwidth (temporal synthetic bandwidth method and frequency synthetic bandwidth method) for LMSF signal and the high speed moving target ISAR imaging algorithm based on the synthetic bandwidth are studied. The motion compensation method for high speed moving target using the temporal synthetic bandwidth method and frequency synthetic bandwidth method are presented. The traditional frequency synthetic bandwidth is improved, and the application condition of the frequency synthetic bandwidth method is widened. The compensation error caused by the 'stop-go' model and the first order approximate model is analyzed. Focusing on the problem of precise estimation of the motion parameters, Doppler center estimation method in the SAR imaging motion compensation is introduced in the ISAR imaging. According to the characteristic of target echo in ISAR, the original method of Doppler center estimation is ameliorated, so that the precision level of the motion parameter estimation satisfies that of the synthetic bandwidth and ISAR imaging.5. The high speed moving target imaging method of phase coding signal is studied. The 'stop-go' model of the phase coding signal and the application conditions of the first approximate order model have been analyzed. The motion compensation method of the ISAR imaging of the phase coding signal is presented, which combining the wideband phase coding signal with the narrowband LSFM signal, and the narrowband signal is used to detect the target and measure the speed, the wideband signal to improve the precision measurement and the imaging.6. The top aerial detection and imaging method for the sea surface target have been further studied. The difficulty of the top aerial detection is analyzed, and the effective method that imaging the sea surface and target at one time, then eliminating the sea clutter from the image is presented. The monitor range of the imaging from the top air over the sea surface is given. The discussion is centred on the motion compensation method for top aerial imaging, correction method for range curvature and image division. Moreover, the methods and procedure of three-dimensional image is acquired by monopulse angle measurement approach.