High Squint Airborne SAR Imaging Algorithn

Synthetic aperture radar (SAR) is a high-resolution imaging system of ground targets withall-time and all-weather capability by means of synthetic aperture principle and pulse compressiontechnique. The accuracy of image is not affected by the influence of weather conditions(e.g. lightand clouds). SAR has been widely used in military and civil fields with the characteristic of remotetargets detection and location.SAR image formation is based on a coherent processing approach to build a long azimuthsynthetic aperture. Squint SAR imaging is more flexible compared to side-glance SAR. By meansof adjusting the beam pointing via antenna which can imaging the targets in front of the airborne orbehind the airborne and revisit the desired zones repeatedly. This dissertation studies the SARimaging in large squint model based on the SAR imaging principle. The main contents ofarrangements are as follows:(1) Summarizing the key techniques of SAR system, including range and azimuth resolution,stationary phase principle, focusing depth etc. This chapter analyses the properties of the squintSAR system, especially range cell migration. Since the range cell migration in squint model isgreater than in the side-glance model, which deteriorates the quality of image. The effect of rangcell migration on phase accuracy is discussed and the results indicate that high-order Taylorapproximation range equation should be used in order to improve the precision of image.(2) The Range-Doppler (RD) and Chirp Scaling (CS) algorithms are introduced to process SARdata. Both of the two algorithms have deficiencies when processing large squint SAR data soimproved RD and CS algorithms are proposed to process squint SAR data with simulations toverify the efficiency of improved algorithms.(3) Presenting a novel range scaling formulation for the processing of highly squint data. Thechirp scaling function introduces a range dependent shift in the range chirp signal which can assumevalues as high as several MHz then the range Impulse Response Function will deteriorate. In thischapter a new scaling factor with the subtraction of the offset (at the Doppler centroid frequency) isproposed which leads to an equalization of the rang migration. Several simulation resultsdemonstrate the validity of the proposed algorithms.