Study Of Aircraft Electromagnetic Scattering Echo Simulation And ISAR Imaging Method

Thanks to the capacity of all-day,all-time,far-range observation and imaging of noncooperative targets,inverse synthetic aperture radar(ISAR)imaging has been widely applied in air defense and early warning,situation perception,and sea surface monitor,etc.Nowadays,the researches on motion compensation and imaging methods for smoothly moving rigid targets have been relatively mature.However,in the actual ISAR imaging scene,the wings of an aircraft will be affected by the airflow and will vibrate.Hence,the aircraft is no longer an ideal rigid body.It is difficult to apply traditional ISAR imaging methods which are only suitable of rigid targets.Meanwhile,due to the importance and sensitivity of the ground-based ISAR system in the military field,the public real data of aircrafts of latest ground-based ISAR systems can be hardly found.Therefore,this thesis will study the electromagnetic scattering echo simulation and ISAR imaging methods of the aircraft.The vibrating characteristics of the wings will be analyzed and the high fidelity radar echoes can be obtained.By dealing with the inconsistent motions of the main body and wings of the aircraft,the focused images can be acquired.The main research contents of the thesis are presented as follows:1.The principle of ISAR imaging is discussed and the motion characteristics of the aircraft are analyzed.Firstly,the ISAR observation model is analyzed to establish the ISAR imaging echo signal model,and the basic scheme of range-Doppler(RD)imaging is given.Then,the basic principles of motion compensation are introduced.The flowcharts of the classical envelope alignment,auto-focusing and migration through range cells(MTRC)correction algorithms are discussed.After that,an aircraft motion model is established to lay the theoretical foundation for the later study of aircraft echo simulation and imaging algorithms.Finally,based on the rigid point target and aircraft point target models,the RD imaging algorithm is simulated and the defocusing phenomenon of the aircraft imaging result induced by vibrating wings is analyzed.2.Aiming at the problem that the echoes of the main body and the vibrating wings of an aircraft are difficult to accurate simulate,a high-fidelity electromagnetic scattering echoes simulation method is proposed.Firstly,through the analysis of the aircraft structure and motion characteristics,the aircraft model is segmented.The electromagnetic scattering characteristics of the main body and wings of the aircraft are calculated using the large facet physical optics method,respectively.Then,the instantaneous motion postures of different components are computed under the predetermined observation scene.The instantaneous radar line of sight is derived based on the coordinate system transformation of the given trajectory.After that,through the analysis of the occlusion relationship between the main body and the wings,the electromagnetic scattering echo simulation process is proposed.Finally,simulation experiments verify the effectiveness of the proposed algorithm.3.Aiming at the problems of the wing vibration parameter estimation and ISAR imaging of the aircraft,a particle swarm optimization-based vibration parameter estimation and focused ISAR imaging method is proposed.Firstly,this chapter analyzes the differences between the echo signal of the main body and the wings.A mathematical model for wing vibration echo signal parameter estimation is established.Then,a particle swarm optimization-based wing vibration parameter optimization method is proposed.The vibration parameter compensation phase is constructed to separate the echoes of the main body and the wings.Then,a entropy minimization-based auto-focusing algorithm is applied to the echoes of the main body and the wing to achieve focused imaging processing of the whole aircraft.Finally,the effectiveness of the proposed algorithm is verified using the high fidelity simulation echoes of the aircraft obtained in Chapter 3.