The Key Technologies For SAR Scene Matching Missile Guidance

The precision guided weapon, which makes use of synthetic aperture radar (SAR) technology, not only improves the all-weather and all-day capabilities, but also increases the capabilities of detecting concealed and camouflage targets. Focused on the exigent requirements of precision guidance technology, four subjects are researched in this dissertation: SAR raw signal simulation, SAR real-time image preprocessing, SAR reference image preparation and SAR scene matching.The main achievements and contributions of the dissertation are as follows:1. The technology of SAR raw signal simulation under conditions of flight trajectory deviation and complex terrain is studied. A method of backscatter modeling, which combines the digital elevation model (DEM) and orthography, is introduced since the traditional modeling methods have problems in simulating the difference in backscatter properties and terrain undulation simultaneously. The method models the three-dimensional scene with high fidelity. The influence of flight trajectory deviation on slant range and raw signal is analyzed, and the two-dimensional expression in frequency domain of raw signal with motio errors is derived. A fast raw signal simulation method which combines the time domain and the frequency domain is proposed based on the large flight trajectory diviation, and the validity of the method is also discussed.2. The preprocessing method for speckle noise suppression and geometric distortion correction in SAR real-time image is studied, which includes two main aspects: (1) In order to decrease the computation time of traditional methods for speckle noise suppression, a compromise method between suppression performance and calculation speed is introduced. (2) A novel geometric correction method, which corrects the geometric distortion in azimuth direction in the process of motion compensation, and then corrects the geometric distortion in range direction in succession, is proposed based on the fact that the Doppler center has no relationship with the terrain undulation for missile-borne SAR. The method decreases the computation complexity greatly. In order to refine the method, several improvements are made on it. Then, some experiments are accomplished based on the refined methods, and some rules of geometric correction method selection are acquired.3. The technology of SAR reference image preparation under complex terrain is studied, which includes: (1) In order to resolve the problems of SAR matching area selection, such as the constrain conditions are excessive, and the construction of feature criterions and predicting functions is difficult, a hierarchical way of selecting optimal scene matching area is presented. The method solves the difficulties in constructing predicting function by feature selecting hierarchically, and provides a reference for choosing better SAR matching areas. (2) Based on the fact that it is difficult to extract precise control points (CP) in SAR images under complex terrain, an automatic SAR reference image preparation method based on DEM and SAR layover is developed. The method improves the geometric accuracy by an improved CP detection method and a two-stage CP matching method. The influence of motion errors and DEM errors is also analyzed, which is important for application.4. The technology of SAR scene matching is studied. A coarse-to-fine image matching method, which combines the gray and scale invariant feature transform (SIFT) point feature, is proposed according to the characters of SAR scene matching, such as the sizes of real-time image and reference image are both large, the imaging angles and the imaging platforms of them are different. In order to decrease the computation time and the sensitivity to rotation and scaling change of the cross-correlation matching method, a matching method based on wavelet transform and multi-scale circular template fusion is introduced to satisfy the requirements of the real-time and robust. In order to overcome the problems when SIFT is used in SAR image, a preprocessing and an outlier filtering method is presented to improve the accuracy of SIFT features, based on which the sub-pixel matching accuracy is reveived.A large amount of experiments based on simulative and real datas are accomplished to show the significance of the study.