Study Of Monopulse Radar Target Three Dimensional Imaging And Recognition

Radar imaging is widely applied in the fields of precision guidance, target recognition and air traffic control. But the range-Doppler image of Inverse Synthetic Aperture Radar (ISAR) cannot capture the true shape of maneuvering target. Monopulse three-dimensional imaging, reconstructed from three-dimensional spatial coordinates (range, pitch, azimuth) of scatter points of the target measured by monopulse radar, is consistent with the real size of target and less sensitive to maneuvering motion and very useful in improving the quality of recognition. However, problems such as three-dimensional motion compensation and angle glint still exist. This thesis addresses monopulse three-dimensional imaging technique and target recognition methods. The research highlights method of angle glint suppression in monopulse angular measurement, target three-dimensional imaging in the background of sea clutter and automatic target recognition based on radar three-dimensional imaging.A brief description of the thesis is given as follows:1 .In monopulse angular measurement of short-range targets, angle glint will be the primary error source. The magnitude of errors may exceed the size of the target. Therefore, effective methods of angle glint suppression must be developed to improve the precision of angular measurement. Pattern modulation of difference beam echoes due to the tangential motion of target is investigated firstly. Relations between the spectrum width of high-range-resolution profile of difference beam echoes and angle motion parameter of target are analyzed then. A novel method of angle motion parameters estimation is presented. It can suppress the angle glint effectively since the angle motion parameter of target is obtained through searching the global maximum entropy of the high-range-resolution profile. An extended method of angle motion estimation and compensation based on the ISAR imaging for difference beam echoes is presented subsequently.2.Clutter is a serious problem in target detection, imaging and recognition. As airborne radar observes targets on the sea surface at high grazing angle approaching 90°, scatter coefficientσ₀ becomes so great (around +10dB) that targets will be completely submerged by sea clutter in the range profiles of echoes. This paper reports an exploratory development on sea clutter suppression in such condition. Firstly, ISAR imaging is applied to get the image of target in the sea clutter background. Secondly, the sea clutter in ISAR image plane is suppressed by the proposed method based on Radon transform. Finally, the monopulse three-dimension imaging method is applied. In this way, the effects of sea clutter at high grazing angle are eliminated and the monopulse three-dimension image of target on the sea surface can be obtained.3.This thesis presents an exploratory development on the automatic radar target recognition method utilizing monopulse three-dimension imaging technique. Computer Aided Design (CAD) technique is used for constructing the template of target firstly. Templates are then modified depending on the target's attitude estimated from monopulse three-dimension image. Target recognition is accomplished by a maximal degree of fusion classifier with morphological filter. The process of three-dimension target recognition is simulated in the end.The dissertation is organized as follows:Chapter 1 provides the background, scientific significance of radar target imaging and recognition, a literature review of previous work and an overview of this research.Chapter 2 describes methods of high-range-resolution processing, ISAR technique and principle of ISAR based monopulse three-dimensional imaging.Chapter 3 in particular presents an effective method for angle glint suppression using monopulse angular measurement. It also provides a novel method of high-range-resolution profile based on maximum entropy, together with an extended method of angle motion estimation and compensation based on the ISAR imaging for difference beam echoes.Chapter 4 describes research methods about sea clutter suppression in target three-dimension imaging at high grazing angle. A novel method based on Radon transform to eliminate the effects of sea clutter is presented.Chapter 5 provides methods of three-dimensional imaging in wide-band phased array radar. Simulations of dechirping and DBF (digital beam forming) technique based monopulse three-dimensional imaging in two tracking modes ( step and continuous mode) in wide-band phased array radar are conducted.Chapter 6 describes research methods about target recognition utilizing monopulse three-dimension imaging technique. Methods of template modification, attitude estimation and target classification are detailed.Chapter 7 provides a summary of the dissertation, unsolved problem and development of monopulse target three-dimensional imaging and recognition for future research.