Study On Imaging Algorithms For Missile-borne SAR In Multiple Modes

As the precision guidance weapons are playing increasingly important role in modernwarfare, high-precision integrated guidance techniques have been the focus of defenseindustry development for all the countries. In masses of the integrated guidance techniques,the combination of Synthetic Aperture Radar (SAR) and Inertial Navigation System (INS) hasgained growing attention due to its multiple intrinsic advantages. Equipped with SAR&INS,the missile can exploit the high resolution images obtained by SAR for scene matching withthe reference images stored in the computer on missile, calculate the real time position ofitself to correct the INS errors, and finally get a high attacking probability. However, becauseof the great difference in motion characteristics between missile and conventional carrierssuch as airplane and satellite, it is difficult to directly use traditional SAR imaging algorithmsin missile-borne SAR. Meanwhile, to provide sufficient target feature information for scenematching, missile-borne SAR needs the capability of wide-swath imaging. In addition, missilerequires the identical direction for imaging and flight in attack paragraph, in which thepeculiar left/right ambiguity problem leads to great difficulty for imaging.Based on all above, this dissertation makes a study on missile-borne SAR imaging inmultiple operating modes. The main research results are as follows:1. The wide-swath imaging method for missile-borne ScanSAR is studied. Accordingto the traditional sub-aperture separation imaging method, the features of target echoedsignals are analyzed. Two problems i.e. the spatial variation of the linear range cell migrationand Doppler center are presented, as well as the rule of sub-aperture separation and amodified Range-Doppler algorithm. Further, for the practical demand, the geometriccorrection equation for sub-aperture images with the existence of side movement is deduced.The point target simulation validates the effectiveness of the method proposed in thisdissertation, which lays a foundation for scene matching.2. The research of wide-swath imaging algorithm based on the model of themissile-borne SAR in decline paragraph is conducted. Motivated by high resolution imagingof the full aperture, we firstly analyze the spatial variation properties of all the terms in theechoed signal2D spectrum of missile-borne SAR based on the series reversion method. Then,corresponding to the analysis results, with the combination of CZT (Chirp-Z Transform)algorithm, we design an imaging scheme. Additionally, the modified CZT algorithm isderived, and the imaging flow and computational load analysis is given. The simulationexperiments confirm the feasibility of this method. 3. With respect to the problem of multi-variables coupling in the wide-swath imagingof missile-borne SAR in decline paragraph, we investigate a parameterized de-couplingmethod. In the existing2D echoed signal spectrum of missile-borne SAR in the declineparagraph obtained by series reversion method, there are five coupled variables, only three ofwhich can be processed by conventional SAR imaging algorithms. By analyzing thecharacteristics of the signal in decline paragraph and the imaging model, we present a methodto parameterize the other two variables with the slant range variable, attributed to the specialform of the equation expressions and the geometric features of the imaging model. On thebasis of the new parameterized2D spectrum, CS (Chirp-Scaling) algorithm is deduced.Simulations verify that this parameterized de-coupling method can effectively improve theimaging accuracy in the range direction and it is promising to enhance the performance ofextended wide-swath imaging.4. Following the high resolution imaging of full aperture, an analysis method for2Dsignal spectrum of missile-borne in decline paragraph is presented. For the characteristics ofthe imaging model in this paragraph, by imitating the imaging method with curve trace inspace-borne, we make a reasonable approximation for the slant range expression. With thisequation, the2D Fourier transform of the signal is directly derived. Then the stationary phasepoint can be solved by using the classical Cardano’s formula. And thus the signal2Dspectrum can be obtained, based on which the corresponding imaging algorithm isdemonstrated. The effectiveness of the proposed method for imaging in decline paragraph isvalidated by the simulations.5. The problems in forward-looking missile-borne SAR are also studied. By makingcomparisons, we select the double-antenna system and analyze the slope range equation inthis system. The basic problem of the left/right ambiguity for forward-looking imaging isfigured out. With the analysis on the signal features in the double-antenna system, we putforward a scheme to solve the left/right ambiguity by using the beam-forming with rangedelay difference between different antennas. Then a range processing algorithm andde-ambiguity algorithm in azimuth direction is designed. The point target simulation testifiesthe validity of this method.