Study of space/time varying defocus characteristics of complex moving ship targets in SAR imaging
Synthetic aperture radar(SAR)can take images of ship targets at sea all-day and all-weather.However,the azimuth defocus of moving ships in high resolution SAR images has seriously affected the subsequent recognition for ship targets.Due to the non-cooperative nature of ship motion,the defocus characteristics of complex moving ship in SAR images have not been well understood.In this paper,based on the principle of SAR imaging,it has been theoretically deduced that the spatial-variability and time-variability of SAR echo signal phase errors caused by complex ship motion are the decisive factors that lead to the degradation of SAR image quality.On this basis,a SAR imaging simulator for complex moving ship targets is constructed.By simulating SAR imaging of ship point,line,and surface targets at different motion states and synthetic aperture times,the spatial/temporal defocus characteristics of SAR imaging for complex moving ship targets are revealed.Among them,spatial variability can cause non-uniform defocus of ships in SAR images.Time variability causes the ship to transform into an azimuthal energy band in SAR images.Finally,based on the spatial/temporal defocus characteristics,the development direction of future SAR motion ship refocusing technology is discussed.
synthetic aperture radar(SAR)defocus of shipsspace-varying phase errorDoppler time varyingrefocuse
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