Reserch On SAR Imaging And Ground Moving Target Indication Approach For Heliborne Rotary Synthetic Aperture Radar

Radar imaging technology is a remote sensing detection technology that uses high resolution radar as the platform to transmit microwave electromagnetic signals in frequency band,and combines the signal processing method to obtain electromagnetic scattering characteristics of the observed target.Its detection range is longer,and it has the advantages of all-day and all-weather operation.Synthetic aperture radar(SAR),with the help of high-precision twodimensional resolution capability,can obtain the imaging results of observation scenes,the position and motion parameters of moving ground targets in the region and other information.It is widely used in the fields of people's livelihood and national defense,such as land and resources monitoring,urban planning,address surveying,disaster relief or battlefield situational awareness.Rotary-type synthetic aperture radar(Ro SAR)is a new system developed by combining the characteristics of helicopter platform.Through the curve track formed by the rotation of radar antenna,directional virtual synthetic aperture can be constructed.No matter the helicopter platform is in any maneuver mode such as hovering or forward,high-precision imaging results of surrounding airspace can be obtained.Antenna rotation can collect multi-angle electromagnetic scattering information of the target,but it also leads to more complex phase history of the target echo signal,which requires proper processing in the imaging process to obtain close to the real focusing imaging results.The traditional two-dimensional SAR image is the projection of real three-dimensional objects on the distance and azimuth,and there are usually problems such as inversion of top and bottom.How to restore the height information of the target in the observation scene with the combination of radar multi-channel antenna and super resolution technology has become a problem worth studying.On the other hand,the detection of moving targets in the scene is Ro SAR system is one of the important application direction,SAR and ground moving target detection(GMTI),can use for a long time coherent accumulation for moving target coarse focus on results,and then through the clutter suppression processing to further improve the dynamic target letter to noise ratio,thus improve the performance of GMTI.How to effectively realize clutter suppression and moving target parameter estimation by combining the different characteristics of single/multi-channel radar system is also of research significance and application value.Based on the national ”973” plan and national Natural Science Foundation of China,this paper studies the key technologies in Ro SAR imaging and ground moving target detection carried by helicopters.The main contents of this paper can be summarized as follows:1.Aiming at the image distortion caused by non-uniform sampling interval of azimuth time of rotary SAR under the condition of azimuth wide beam,a Ro SAR imaging algorithm based on azimuth Chirp Z Transform(CZT)is proposed to realize scene focusing under azimuth wide beam.Based on the detailed analysis of the azimuth resolution of the system,the 2-D spectral approximate expression of the echo signal was obtained by means of Taylor series expansion and series inversion.By using CZT method,the variable scale processing of output azimuth sampling interval is accomplished quickly,and uniform azimuth sampling interval is obtained,which eliminates image distortion in azimuth wide beam imaging results.2.In the forward Ro SAR imaging geometric model,there is not only the azimuth velocity of antenna scanning but also the forward velocity of the platform.Therefore,the variation of target slant distance process reflects more complex spatial variation characteristics in the spectrum of the echo signal.A modified imaging algorithm based on the Keystone transforms is proposed for the Heliborne forward Ro SAR system.With the forward-moving Ro SAR imaging configuration,the relationship between the platform forward movement and the space-variant characteristics of the spectrum is given to construct the corresponding phase compensation function.A modified second-order keystone transform is used to correct the space-variant range cell migration term,meanwhile,the range-variant distortion in azimuth is removed by using the Chirp Z transform.3.A moving target detection method based on Time-Doppler chirp varying(TDCV)is proposed for the single channel rotary synthetic aperture radar(SAR).First use the conventional Ro SAR-CZT algorithm to get a picture of a focused image as the original image,and then for the same set of radar echo data,using the proposed method in the process of imaging,respectively in the azimuth time domain and doppler domain corresponding matched filter structure,realizes the doppler rate change,and get a new image.By comparing the two images,it can be found that the position of the stationary clutter in the scene basically remains unchanged,but for the moving target,its radial velocity will cause the moving target to offset along the distance,and the radial velocity of the moving target determines the offset.The clutter energy in the image can be effectively eliminated and the detection performance of moving targets in the image domain can be improved.