Research On Clutter Suppression And Moving Target Detection Methods For Airborne/Space Based Radar

Airborne/space based radars,which equip the radar onto airplanes or satellites,can improve the detection range,area and the ability of anti-stealth and anti-damage effectively compared to conventional ground based radars.Therefore,the airborne/space based radar are favorable for moving targets detection and have valuable application prospects in battle reconnaissance,wide area surveillance and air/space early warning.When working at the mode of down-looking,the airborne/space based radar will face the influence of the strong ground clutter,which makes the moving target submerged under the clutter and hard to be detected.Then reliable clutter suppression methods will be quite important on moving targets detection for the airborne/space based radar.The reconnaissance mode and the early warning mode are two main modes of moving targets,which have been widely focused and deeply researched in recent years.The reconnaissance mode is mainly used for ground observation.The main observational targets of the reconnaissance mode are moving targets over the lands and seas.In the process of observation,this mode mainly focuses on the comprehensiveness and accuracy,which means getting the high-resolution image and detecting moving targets organically at the same time.To achieve this goal,estimating the radial velocity and relocating accurately for moving targets are also needed.The main observational targets of the early warning mode are moving targets in air,near space and space.Because the moving targets in air,near space and space moves much faster than the moving targets over the grounds and seas,the early warning mode pay more attention to the long-range detection and real time process.The space based radar which has the ability of global observation is better to meet the demand of long-range detection.However,long-range detection and earth rotation will cause the non-stationarity and ambiguity of clutter,thereby degrading the performance of clutter suppression and moving targets detection.Aiming at the problems mentioned above,the dissertation researches the methods of clutter suppression and moving targets for the airborne/space based radar.The main contents are listed as follow:1.The basic observation geometry model is built.The basic theories of clutter suppression and moving targets detection are researched.The space-time distribution of clutter is derived.The common indexes are introduced.2.Aiming to the detection,velocity estimation and relocation for moving targets simultaneously,a two-step method based on joint greatest of displaced phase center antenna(GO-DPCA)and local space time adaptive processing(STAP)in image domain.First,the imaging model of moving targets are derived.And the quantitative relationship between suppression gain and radial velocity of moving targets are analyzed.After that,moving targets are detected generally by GO-DPCA.Based on the results,false alarm targets are eliminated and the radial velocity of moving targets are estimated accurately by local STAP.Finally,the computational burden are analyzed while the simulated data and acquired data are processed.The experimental results indicate that the proposed method can have good performance of moving targets detection and radial velocity estimation while computational burdens can be decreased.3.Aiming to the trace detection of moving targets at the reconnaissance mode,a detection method based on multi-feature test statistic coherent change detection(MTFSCCD)is proposed.The statistical model for a SAR image pair is derived at first.Then the trace of moving targets is detected generally by CCD,whose detection result contains not only the trace but also the change of Natural scenes.After that,the characteristic of Radar cross section(RCS)and internal motion are analyzed for the Natural scenes like rivers and vegetations compared to the trace.Based on the analysis,multi-feature test statistics like the intensity and summation of the SAR image pair are proposed to eliminate the false alarm regions caused by the Natural scenes like rivers and vegetations.After elimination,the accurate detection result of the trace is gotten by the proposed method.Finally,a real dataset acquired by a millimeter wave airborne SAR system is processed.The experimental results indicate that the proposed method can decrease the probability of false alarm(PFA)effectively when detecting the trace of moving targets.4.Aiming to suppress the nonstationary clutter for space based early warning radar(SBEWR),two nonstationary clutter suppression methods based on elevation-azimuthDoppler three-dimensional(3D)processing are proposed.Based on the analysis of the elevation distribution for all range ambiguity components,an elevation adaptive filter(EAF)method based on oblique subspace projection is proposed.The method utilizes the oblique projection matrix to project the signal onto the subspace spanned by the near-range and farrange components along the subspace spanned by the mainlobe component.Then near-range nonstationary clutter component is suppressed by EAF.In addition,the characteristic of 3D distribution for nonstationary clutter is analyzed and the differences of nonstationary clutter between airborne early warning radar(AEWR)and SBEWR are researched.Then,a 3DSTAP method based on three improved dimension-reduced structures are proposed.The proposed structures use improved auxiliary beams to extract the training samples for clutter covariance estimation(CCM)so that notches are formed in the position of nonstationary clutter for removal.Finally,the simulated data is processed for validation.The simulation results indicate that both of the proposed two methods have better performance on nonstationary clutter suppression compared to conventional ones.Besides,the first proposed method is better at near-range nonstationary clutter suppression while the second proposed method can have narrower mainlobe width.5.Aiming to solve the problem of range and velocity ambiguity,a system design method based on multi-carry frequencies in intra-pulse and subarray dimensions is proposed.The signal is extended into carry frequency dimension by using stepped frequency signal in the intra-pulse dimension.Then,unambiguity clutter is extracted by beamforming in the carry frequency dimension for each unambiguous range wing.After that,the multiwavelength character corresponding to the multi-carry frequencies in the subarray dimension is used to suppress the velocity ambiguity.In addition,the method of constrain and design for system parameters is discussed based on the analysis of grating lobes in the carry frequency dimension,the position of range ambiguity,the duty factor of the system and the period of the velocity ambiguity.Finally,the simulation experiments are conducted.The experimental results indicate that the proposed method can suppress the range and velocity ambiguity effectively.And the area of range-velocity two dimensional blind zones for the proposed method is smaller than the area for the conventional phase array radar system.