Front squint SAR imaging method based on hypersonic aircraft at level flight section

Abstract

The invention discloses a front squint SAR imaging method based on a hypersonic aircraft at the level flight section. The front squint SAR imaging method mainly solves the problem that orientation pulses are compressed to distort on the condition of a small front squint angle of a high-speed platform. The front squint SAR imaging method includes the first step of obtaining radar echo signals, the second step of carrying out time domain calibration distance walking processing on the radar echo signals, the third step of carrying out distance linear frequency scaling processing after the time domain calibration distance walking processing, and obtaining two-dimensional frequency domain signals, the fourth step of carrying out range pulse compression and secondary pulse compression processing on the two-dimensional frequency domain signals, the fifth step of carrying out azimuth pulse compression and space-variant compensation processing on range processing results, and the sixth step of carrying out geometric distortion correction on azimuth processing results to obtain front squint SAR images. The front squint SAR imaging method reduces imaging complexity, and realizes high-precision front squint SAR imaging on the condition of the hypersonic platform; obtained geometric distortion correction images are favorable for follow-up SAR image processing and application and can be used for ground target recognition, scene matching and the like.

Description

technical field [0001] The invention belongs to the technical field of radar, and relates to a synthetic aperture radar (SAR) imaging method, which can be used for two-dimensional imaging of ground scenes by forward squint SAR in the level flight section of a hypersonic vehicle. Background technique [0002] Hypersonic vehicles have become a research hotspot in various countries in recent years. The United States, Russia, France, Germany, Japan, India and other countries are all conducting research in this area. Hypersonic aircraft can fly at Mach 5-10, and can achieve global strikes in two hours, which has extremely high application potential. The radar imaging of the hypersonic vehicle carrier has extremely high research value, and the forward-squinting SAR imaging is an important mode of hypersonic vehicle imaging. [0003] Due to the high flight speed and forward squint imaging of the hypersonic vehicle, the SAR echo signal will have a very large range migration, and th...

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Problems solved by technology

[0005] The first method, nonlinear frequency scaling algorithm, such as Guangcai Sun, Xiuwei Jiang, Mengdao Xing, Zhijun Qiao, Yirong Wu, Zheng Bao in the paper "Focus improvement of highly squinted data based on azimuth nonlinear scaling" (IEEE transaction on geoscience and remote sensing VOL49, O6, JUNE2011.) proposed an azimuth nonlinear frequency-variation standard ANCS algorithm. This algorithm considers the Doppler space-variation and range space-variation of the range modulation frequency, and can accurately detect large scenes with forward oblique angles of view. Imaging, but the algorithm is highly complex, the algorithm has a large amount of calculation, and it can only be used for non-real-time imaging. It is very unsuitable for hypersonic platforms with high real-time requirements

[0006] The second method is the decoupled EFSA algorithm, such as Liu Gaogao, Zhang Linrang, Liu Nan, Liu Xin, Zhang Bo, and Chen Guangfeng in the paper "Research on Imaging Algorithms for Hypersonic Vehicles" (Journal of Xidian University (Natural Science Edition) ) 2012, 39(5): 93-100) proposed a decoupled extended FM variable scale EFSA algorithm, which refers to the missile-borne FM continuous wave imaging model, and can be decoupled at a large forward oblique angle of view. Distortion and high-precision imaging. The simulation results in the literature show that good imaging processing can be performed when the front squint angle is above 50°, but the problem of space-adjustment frequency variability caused by further reduction of the front squint angle is not considered. When the front squint angle is smaller, The performance of the algorithm is severely degraded, and the imaging effect is degraded

[0007] The third method is a linear frequency-variable scaling algorithm based on time-domain corrected distance walking, such as Wu Yong, Song Hongjun, and Peng Jin in the paper "SAR High Squint CS Imaging Algorithm Based on Time-Domain De-Ambulation" (Journal of Electronics and Information Technology, 2010 , 32(3):593-598) proposed a time-domain de-ambulatory linear scaling CS algorithm, which can perform good imaging on large forward squint scenes, but this algorithm does not consider high speed and forward squint The spatial variability of the azimuth modulation frequency in the case of angle of view leads to azimuth focus distortion in the case of high-speed forward squint, the imaging effect of point targets becomes poor, and the imaging of surface targets is almost impossible

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