关键词: Fourier变换, 分数阶Fourier变换, 合成孔径雷达, 距离多普勒算法, 峰值旁瓣比, 积分旁瓣比, 脉冲压缩

Abstract:

The Traditional Range Doppler (RD) algorithm has become the most classic method in Synthetic Aperture Radar (SAR) image processing because of its advantages of easy implementation and high efficiency. However, its low imaging quality is unable to meet the needs of practical applications nowadays. To resolve this problem, we propose a high-performance imaging procesing algorithm (FrFT-RD) in this paper. The expression of optimal order of SAR range signals using fractional Fourier transform is deduced, and the corresponding formula of the azimuth direction is also given. The theoretical analysis shows that the optimal orders of the range and azimuth direction both depend on the SAR imaging parameters and are unique. Thus, the engineering practicability of FrFT-RD algorithm are large without iteration approaches. The construction of the FrFT-RD algorithm includes: Firstly, the FrFT-RD algorithm based on the traditional range Doppler algorithm is established in the fractional Fourier transform domain using the calculated optimal orders of the range and azimuth direction; Secondly, the fractional Fourier transform of corresponding order is used to process the range signals and the reference function of the range direction to complete the range pulse compression and the range cell migration correction (RCMC). The range signals are reconstructed by the inverse fractional Fourier transform (IFrFT) with the order of 1; Thirdly, the fractional Fourier transform of the corresponding order is used to process the azimuth signals and the reference function of the azimuth direction to complete the azimuth pulse compression. The azimuth signals are finally reconstructed by the inverse fractional Fourier transform (IFrFT) with the order of 1. By comparing results of airborne SAR simulation with spaceborne SAR measurement data, we find that the FrFT-RD algorithm significantly improves the imaging performance on resolution, and peak side lobe ratio (PSLR) compared to traditional RD algorithm. The resolutions of the range and azimuth directions are increased by 45.92% and 48.06%, respectively, and the PSLR and ISLR of the range and direction are decreased by 1.45 dB and 2.59 dB, respectively. While the Frft-RD algorithm almost has the same imaging performance as the traditional RD algorithm in PSLR and ISLR on the azimuth direction.

Key words: Fourier transform, fractional Fourier transform, Synthetic Aperture Radar, range doppler algorithm, peak side lobe ratio, integrated side lobe ratio, pulse compression