Study Of Target Detection And Estimation For Shipborne High Frequency Surface Wave Radar

High Frequency Surface Wave Radar (HFSWR), utilizing a vertical polarization electromagnetic wave that follows the curvature of the earth along the air-water interface with low propagation loss on highly conductive ocean surface, could detect and track targets beyond the horizon such as vessels on the sea and aircrafts at a low altitude. It provides a new technique for remote sensing of sea state and traffic control over the sea. Besides these characteristics, shipborne HFSWR also provide agility and maneuverability, which has attracted a number of countries' attention in decade's. Compared with the ashore HFSWR, the difficulty of signal processing in shipborne HFSWR is how to detect and estimate ships whose Doppler frequencies appeared in the spreading domain of the Bragg lines. The main purpose of this dissertation is to solve the problem both in theory and in practice.The dissertation firstly analyze the spreading mechanism of the Bragg line in shipborne HFSWR and present a mathematical spreading model, which are verified by experimental results from the shipborne HFSWR data collection experiment conducted in 1998. It is the vectorial summation of the platform motion with that of the clutter return from different directions within the radar range cell that results in spreading of the Bragg line. Therefore, the main interference for detection of targets in the spreading domain is the first order sea clutter returns from the direction different from targets' azimuth but with the same Doppler frequency with consideration of platform motion.By analogy with the ground clutter rejection in Airborne Early Warning (AEW) radar, Displaced Phase Center Antenna (DPCA) technique is extended for suppression of the first order sea clutter in shipborne HFSWR. Moreover, interpolation in spatial domain is proposed to retrieve signal for DPCA processing in consideration of the vibration of the platform motion. Simulation results show that the method can remarkably attenuate the first order sea clutter when the platform velocity slightly vibrates over the theoretical value. Furthermore DPCA processing with interpolation in temporal domain is given based on the space-time equivalence of signal, which dramatically ease the restriction on the platform velocity required by interpolation in spatial domain. Theoretical analysis shows that DPCA with interpolation in temporal domain can detect target if only the platform moves at constant velocity. It can be...