High resolution processing of hybridstrip-map/spotlight mode SAR

Synthetic aperture radars have traditionally operated in either the spotlight mode, in which the coverage is limited, or in the strip-map mode, in which the resolution is limited. It is shown that, by steering the radar antenna about a point further away from the radar than the centre of the area being imaged, illumination times between that of strip-map and spotlight mode are achieved, thus resulting in different combinations of resolutions and spot sizes than is the case for traditional spotlight mode. The theory underlying this mode is derived from first principles, and it is shown that strip-map and spotlight modes are limiting cases. A wavenumber domain processing technique is presented that correctly compensates for range curvature and its equivalence to range Doppler processing described mathematically. This technique results in focused images and is applied to both simulated and real data. The advantages of this mode are a reduced data rate at high resolution, the use of a higher gain antenna, and achieving high resolution over an area larger than that possible in the spotlight mode. This technique may be applied to both space and airborne radar where a combination of high resolution and wide area coverage is important.