Research Of The Airborne Synthetic Aperture Radar Imaging And The Auto-focus Algorithms

Airborne Synthetic Aperture Radar is a major vehicle for the working platform, whichworks in the microwave band. SAR has the whole weather and the whole day characteristicsthat observing two dimensions high resolution image of the object, now which has widelybeen applied in many field. In the system of the high resolution air-borne SAR, the phaseerror after the transmitter signal which influence the range compression and image qualitywill cause distortion of the radar echo signal. It is a key of SAR image quality to eliminate thephase error. This paper mainly investigated the Range-Doppler and the phase gradient autofocus algorithm of airborne SAR.High resolution borne Synthetic Aperture Radar (SAR) estimation methods of theRange-Doppler and the phase gradient auto focus algorithm are the main researched contentof this paper. The author mainly finished several following work. Firstly, SAR’s, basisprinciples are introduced in detail and some correlative ideas are analyzed and researchedsystematically. Secondly, image formation algorithms of classics, range-doppler (R-D)algorithm and Chirp Scaling algorithm from several sides, such as algorithms principles,realizing processes and applicable conditions，R-D algorithm’ characters are discussed indetail. Aimed at disadvantages of original of the R-D algorithm. This article is based on theoriginal range-doppler (RD) algorithm has certain second phase error and use the nearestdomain interpolation on range migration correction, and proposed an improved algorithm,improved algorithm increases the secondary range compression and uses the sincinterpolation for range migration correction. Based on real airborne SAR multiple sets of data,the universality, feasibility and validity of the algorithm are demonstrated and the originaldata using in the R-D algorithm can applicable to other imaging algorithms. Thirdly，thesummary of auto focus algorithm and the influence of phase errors to image quality isanalyzed detailedly. Improved phase gradient auto focus algorithm (PGA) which adapt themethod of the quadrature demodulation are proposed, the method is aimed to solve the sole ofstrong point of clutter interference in the complex scenes. Based on real airborne SARmultiple sets of data, the universality, feasibility and validity of the algorithm aredemonstrated in conclusion. We can find that improved algorithm shows the compensation results are obvious.