SAR Imaging Of Targets Above The Ground Based On Electromagnetic Scattering

Synthetic aperture radar is not limited by external conditions such as light.It has the remarkable advantages of all-weather,all-time,long imaging distance and wide application range.It is one of the most widely used technologies in radar imaging technology.The unique advantages of SAR imaging are widely used in military and civil,such as remote sensing detection,resource exploration,prediction and reconnaissance.In general SAR imaging research,because the acquisition of measured data of complex targets above the ground is expensive,the theoretical simulation of SAR echo data has attracted extensive attention of scholars at home and abroad.In this paper,the PO-SBR-PTD hybrid method is used to establish the composite electromagnetic scattering model of complex targets above the ground.Based on the echo data obtained from the composite electromagnetic scattering model,combined with different SAR imaging algorithms,the SAR imaging of complex targets above the ground is studied,and the imaging results under different conditions are analyzed.The main work of this paper is as follows:1.Study on electromagnetic scattering of complex targets above the ground.Firstly,SBR-PTD method is used to calculate the scattering coefficients of simple targets such as Slicy model,T72 tank model and ZSU-23-4 self-propelled antiaircraft gun model.The single station RCS and bistatic RCS under different polarization modes,azimuth angles and incident angles are analyzed,and compared with the calculation results of MLFMM method in FEKO software.The two are in good agreement.Secondly,PO-SBR-PTD method is used to calculate the electromagnetic scattering of complex targets above the ground.The solution method is as follows: PO method is used to calculate the ground scattering field,SBR-PTD method is used to calculate the target scattering field,and ray tracing technology is used to solve the coupling field between the ground and the target.The electromagnetic scattering of flat plate,rough ground and T72 scale model is numerically simulated and compared with the results of mlfmm method to verify the effectiveness of the method.At the same time,the electromagnetic scattering characteristics of targets above single landform(soil)and two landforms(soil + asphalt pavement)are studied,and the differences among ground scattering field,target scattering field,coupling field and total scattering field are analyzed.2.Research on Stripmap SAR imaging of targets above the ground.Firstly,the imaging principle of striped SAR is introduced,and the RD algorithm flow and related formulas are deduced.Secondly,based on the SAR echo data obtained from the electromagnetic scattering model of complex targets above the ground,combined with RD algorithm,the strip SAR imaging simulation of complex targets above the ground is carried out.Finally,the SAR images of T72 tank and ZSU-23-4 self-propelled antiaircraft gun with different orientations above the ground are numerically simulated,and the similarity between the simulated image and the measured image in the U.S.MSTAR database is analyzed.The similarity between them can reach more than 70%.At the same time,the SAR images of the target above the ground under different incident angles are simulated.The results show that the shadow area of the target on the ground increases with the increase of the incident angle.The SAR images of T72 tank and ZSU-23-4 self-propelled anti-aircraft gun above two landforms(soil + asphalt pavement)and three landforms(soil + asphalt pavement +grass)are also simulated.3.Research on Spotlight SAR imaging of targets above the ground.Firstly,the principle of PFA algorithm is described in detail,the PFA algorithm flow is introduced,and the imaging formula is deduced.Secondly,the SAR echo data is obtained based on the composite electromagnetic scattering model,and the spotlight SAR imaging model of complex targets above the ground is established combined with PFA algorithm.Finally,the SAR images of T72 tank and ZSU-23-4 self-propelled antiaircraft gun in different directions are numerically simulated,and the similarity between them and the measured images in the U.S.MSTAR database is analyzed.The similarity between them is more than70%.The spotlight SAR images of complex targets above the ground at different incident angles are analyzed,and the SAR imaging simulation of multiple complex targets above the ground is carried out.At the same time,the spotlight SAR image containing complex targets above two landforms(soil + asphalt pavement)is simulated.4.Squint SAR imaging of targets above the ground.Firstly,this paper introduces the squint SAR imaging model,simulates the time-domain and frequency-domain SAR echo data of a single point target under different squint angles,and analyzes the characteristics of the echo data under squint.Secondly,the RD algorithm flow under squint is introduced in detail,and the imaging formula is deduced.Based on the echo data of composite scattering model and squint SAR imaging RD algorithm,the squint SAR images of T72 tank and ZSU-23-4 self-propelled antiaircraft gun with different downward directions above the ground are simulated.At the same time,the squint SAR imaging simulation of complex targets above the ground under different incident angles and different squint angles is carried out.It can be seen that the shadow of targets on the ground increases with the increase of incident angle.When the squint angle changes,The shadow of the target on the ground moves.Finally,squint SAR imaging of complex targets above two landforms(soil+ asphalt pavement).