Study Of Sea Surface Targets Imaging Based On Hybrid SAR/ISAR Processing

Microwave imaging radar are able to resolve objects into their constituentparts and therefore provide more information of targets in the field of view,relying on sending large wide-bandwidth product linear FM signal and pulsecompression techniques to obtain high-resolution range, relying on radar’s ortargets’ movement formed the accumulated angle to obtain high resolution inazimuth. The Radar imaging techniques which are most commonly employed areSynthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR),SAR uses the motion of the radar to synthesise a large aperture, by coherentlyintegrating samples taken at different times, which correspond to differentpositions along the fling track. ISAR uses the rotational motion of the object toresolve points separated by a distance perpendicular to the radar line of sight.For most conditions of airborne surveillance of ships at sea both the aircraft andship target motions are present, thereby leading to corruption to eitherprocessing system, it is a typical hybrid SAR/ISAR case.The problem of imaging a moving ship at sea from a SAR radar requiresthe combination of the two techniques, which turn out not to be straightforward.Analysis the effects of either SAR motion on ISAR imaging, or of ISAR motionon SAR imaging, results in complicated sets of equations which provide littleinsight into the processing or image degradation. Thus it is not possible to“correct” for ship rotational motion in SAR imaging; a correctly focused imagewill be the projection defined by the composite rotation induced by both radarand target motions. The main contents are following:1. Introduce the basic principles of the airborne SAR, build the basicmodel of airborne SAR imaging of ships at sea, analysis the range migration ofSAR imaging.2. The motion compensation based on echo data is an effective way tocompensate the unwanted motion of radar. Several useful methods based onradar echo data are introduced to estimate radar parameters in this paper. Afterthe range walk correction and the phase correction, the radar platform isregarded as flying in the ideal flight.3. Moving target in a SAR image will cause blur and defocus, it is necessary to compensation phase error caused by the motion of target. Produce anew process of an SAR image involving moving targets from the motions ofboth the target and the observing platform.4. For ISAR imaging depends on the ship’s rotation relative to the radarline of sight, which mainly contains two parts: one originates from the relativemovement between the radar and ship, the other comes from the ship sway. TheTranslational motion is useless to ISAR imaging, it has to be compensated.