Squint Sar Imaging Algorithm Research

Synthetic Aperture Radar (SAR) is the high science and technology radar that can take high resolution imaging for the ground target by using the synthetic aperture principle and pulse compression technique. Since the terrain, time and weather don't affect it, SAR has been widely applied in the areas of military and civil and it has brought great benefits in economics and society. Since the squint SAR has the security, the agility and the advantage in the application, it is a development aspect of the SAR imaging and it is necessary to be researched thoroughly. The dissertation thoroughly studies the squint SAR imaging; the main contents of it are as follows: 1. Based on the squint SAR working-mode, the dissertation carefully analyses the properties of the squint SAR system, including the Doppler characteristics of the target, azimuth resolution characteristic. Since the range migration in the squint SAR is bigger than range migration of the SAR imaging and destroys the imaging quality, the paper discusses in detail the effect of range migration on the phase precision, and indicates that the range equation should use high-order Taylor approximate in the squint SAR in order to achieve high precision imaging for the targets. The dissertation discusses the effect of range migration and the way of correct range migration in time domain and range-Doppler domain. 2. The range-Doppler (RD) algorithm is the conventional imaging algorithm for the side looking SAR. Due to greater range migration, the RD algorithm itself has deficiency for squint SAR, based on the conventional RD, the dissertation carefully discusses second range compression (SRC) algorithm, squint imaging mode (SIM) algorithm for squint SAR, and completes point target simulation using SRC and SIM. The dissertation compares the advantage and defect of these algorithms.3. Based on the squint SAR working-mode, the dissertation establishes the echo model of the radar signal using the squint range equation, and carefully analyses the instantaneous azimuth frequency and instantaneous Doppler frequency and the effect of range chirp on azimuth frequency by coupling between the range and azimuth signal, and brings the accurate expression to calculate the instantaneous Doppler frequency. Then combining the general CS algorithm, the paper proposes the nonlinear CS algorithm for forward-squint SAR imaging by inducing 3rd, 4th term and line frequency modulate rate approximation of the echo in 2D frequency domain, and accomplishes the point target imaging, gains high quality target images. 4. The step-transform algorithm stems from SPECAN algorithm, which is appropriate for side looking SAR; The Doppler frequency in the azimuth is a nonlinear FM and the Time Varying step-transform algorithm(TVST) can meet the need of nonlinear varying. The TVST algorithm need that parameters are matched regularly, which cannot be meted usually in fact. We alleviate the strict limit by making use of interpolation in frequency domain combined the inherent process.The study of the squint SAR imaging stands on the international foreland aspects, I am sure the study works will have definite reference and applications value for the study of SAR system design and imaging.