Research On Guidance Information Processing Method For Strapdown Imaging Homing System

Strapdown imaging seeker has become one of development trends of missile guidance system for its many potential advantages, such as eliminating the tracking rate limits and structure limitations of gimbals while simultaneously reducing the mechanical complexity of implementation and calibration, improving the reliability and decreasing the weapon cost. However, the optical detector of strapdown imaging seeker is fixed rigidly to the missile body, and many traditional guidance information processing methods can not be applied directly, because of the change of detection reference and mode. So it is important both in theory and engineering to investigate the guidance information processing methods in the strapdown framework. This dissertation focuses on the guidance information processing of strapdown imaging homing system, and the main contributions are the following:1. The operation mechanism and characteristic of strapdown seeker system is deeply analyzed, and compared with the gimbal seeker system. For strapdown imaging homing system, the models of imaging motion and the background motion compensation arising from detector moving are constructed, which provide a base for deeper research on strapdown imaging homing system in dissertation.2. For moving target detection issue of strapdown imaging homing system, a novel moving target detection algorithm in 2D frequency domain is proposed based on extraction principle of motion energy of image sequences in 3D spatio-temporal frequency domain. The proposed algorithm is robust against pseudo-motion arising from background registration error, imaging noises, inherited from the motion detection algorithm in spatio-temporal frequency domain. Simultaneously, the algorithm can reduce the filter design complexity because of fewer processing dimensions. Thus it can be used as an effective method to the moving target detection problem of strapdown imaging homing system.3. The correlation tracking problem of strapdown imaging homing system is investigated. The target motion model in the field of view for strapdown imaging seeker is constructed firstly. Based on the proposed model, the image correlation tracker is designed to reduce search areas and improve tracking accuracy, where the theory of sigma-point Kalman filter (SPKF) is applied to treat the nonlinearity and the multiplicative noise deduced by missile attitude errors. SPKF is a new nonlinear filter, and has such advantages as high estimate precision, fast convergence and free of system form limitation. The proposed correlation tracking algorithm makes use of the SPKF predominance about dealing with nonlinearity and obtains satisfactory results about tracking gate setting and target position estimation.4. The template update problem is investigated to improve the target location accuracy with strapdown imaging seeker, and a novel improved variable-size template update strategy is given. Based on the optimal matching principle, two optimization processes are used by the proposed template update strategy, which in some degree overcomes the influences of target shape variety and template drifting problem. As a result, the tracking accuracy is improved effectively.5. The methods of line-of-sight (LOS) and LOS rate reconstruction in strapdown imaging system are investigated. Based on the analysis of decoupling missile attitude from the measurement of strapdown imaging seeker, a novel LOS reconstruction filter is proposed to obtain more precise inertial LOS information, where the adaptive SPKF (ASPKF) is applied. The key of inertial LOS reconstruction consists of missile attitude motion decoupled and noises filtering. So the joint estimation method consisting of missile attitude estimation and inertial LOS and LOS rate estimation is proposed, where the time-varying noise statistics estimator and SPKF are applied. Then a new path of getting more precise inertial LOS information is pioneered.6. The primary error sources and their propagation characteristics are analyzed in detail for strapdown imaging seeker information processing system. And the error propagation models of inertial LOS reconstruction are derived on the basis of the nonlinear mapping relation from body line-of-sight (LOS) angles and missile attitude angles to inertial LOS angles. The influence of missile attitude and relative position between missile and target on the inertial LOS reconstruction precision is discussed in accordance with the norm analysis of error transfer gains. In summary, this dissertation focuses on the guidance information processing in strapdown imaging seeker system. The corresponding motion detection, imaging tracking, as well as inertial LOS reconstruction are investigated profoundly, and computer simulations are conducted to verify the feasibility and effectivity of these proposed methods.