Research On Low-altitude Environment Perception Method For Helicopter-borne Rotating Synthetic Aperture Radar

With the explosive development of low-flying aircraft, such as helicopter-borne aircraft and so on, the flight safety and automomous flight of which arouses people’s wide concern. For the ability of a low altitude environment perception restricted platform load, the low echo signal-to-noise ratio, the traditional sampling of a large amount of data and other problems, we carry out the research that the stepped frequency radar low obstacles super resolution one dimensional imaging, stepped frequency waveform Rotor Synthetic Aperture Radar(ROSAR) imaging and a imaging method based on compressed sensing for Rotor Synthetic Aperture Radar.In order to avoid danger in a low altitude environment, perceive danger information in advance, improve the low obstacles’ imaging resolution, stepped frequency radar low-altitude obstacles super resolution one dimensional image is proposed. First, get the observation vector of the raw echo signal denoising, and construct a dictionary matrix; Then, obtain one dimensional super range image by the improved null space tuning algorithm. This method solves the conventional compressed sensing sentive to noise, the known number of scatter points and redundancy problems after the traditional method IFFT. It can be used stepped frequency radar low-altitude obstacle detection and location and is a prerequisite to achieve low-altitude aircraft self-hedging.Rotor Synthetic Aperture Radar makes use of helicopter rotor’s working characteristics to achieve 360°annular imaging. When compared to the flight real aperture, synthetic aperture increases due to the rotation. So ROSAR can detect the weaker target and get higher resolution. Directly transmiting large bandwidth linear frequency modulation signal ROSAR is difficult to meet the helicopter platform load size and weight requirements. ROSAR of transmiting center carrier freq Suency stepped instantaneous narrow-band waveform can reduce hardware complexity, but brings the efftctive accumulation problem during signal processing. To solve this problem, an imaging method based on Range Migration Correction(RMC) for stepped frequency ROSAR is proposed. First, the signal model of ROSAR using stepped-frequency waveform is derived; Second, the range migration correction in frequency domain is proposed; Third,the high-resolution images are achieved by using the Omega-K algorithm; Finally, the azimuth resolution performance is analyzed. Simulation results demonstrate the effectiveness and high resolution performance of the proposed method.For high-resolution, high repetition frequency Rotor Synthetic Aperture Radar Nyquist sampling of large amount of data and traditional algorithm complexity issues, ROSAR imaging method based on compressive sensing is presented. First, in the case of meeting the observed scene sparse characteristics, downsampling raw data is obtained by the sparse aperture method along the azimuth direction; Then, the traditional matched filtering method is used to realize pulse compression along the range direction; Finally, azimuth scatter coefficients can be reconstructed by solving the minimum 1l norm problems in the azimuth direction to complete the ROSAR images. Compared to the traditional Range-Doppler ROSAR imaging method, this method reduces the complexity of the algorithm, improves the azimuth resolution and lowers the azimuth sidelobe when reducing the required amount of raw data(compressed to 30%). Simulation results demonstrate the correctness of the analysis conclusion and effectiveness of the algorithm.