The Imaging Technology Research Of The Ship Target Based On The Hybrid Of SAR And ISAR

The detection and imaging of ship plays an important role in many fields.In the military field,it can be used for reconnaissance and destruction of enemy ships and in the civil use,it can be used for fishing boats,cruise,tracking and navigation.The ship's radar imaging platform has many kinds,such as shore based radar,satellite borne radar,and airborne radar etc.The paper discuss the imaging of ship based on the working mode of airborne radar.The operation mode of the radar on the plane is the standard SAR model when the scaned target is stationary.When doing a simulation the of a stationary ship model,we can calculate the ship's RCS and calculate the ship model by SAR based on RCS.At the same time,when the ship is on the sea,the radar imaging of the ship will produce multipath reflection based on the sea surface,with the hull of the ship also having a cover phenomenon.But in practice,the motion of a ship is a multi-dimensional complex motion,which includes both the motion along a certain direction and the three-dimensional rotation caused by the factors such as sea wave and wind speed.The operating mode of the radar in a stationary position is the standard ISAR model when the moving target is imaged over a long distance.Therefore,the way of the airborne radar imaging ships with complex motion patterns in the ocean,includes not only the SAR imaging model,but also the ISAR imaging mode.So the signal processing needs to deal with the signal by mixing the SAR and ISAR algorithm at the same time which is also called the hybrid of SAR and ISAR ship imaging.When the ship moves,the motion of the ship will be very complicated,and the ship model can be represented by selecting some points of the ship.In this paper,the basic principles of SAR and ISAR are discussed respectively,and the dispersion model of ship is simulated based on RD algorithm.At the same time,the hybrid of SAR and ISAR imaging process and methods are discussed respectively,and the imaging simulation of the ship is carried out based on the theory of double RD.The ship multidimensional rotation caused by the waves,wind and other factors of will make doppler echo frequency change with time.And this paper use the method of time-frequency analysis and chirplet method to get the instantaneous imaging of ship,which greatly improves the resolution of the ship.The paper is arranged as follows.Firstly,the simulation theory of SAR and ISAR is introduced with the simulation of ship target being carried out.Because of the different working mechanisms between the SAR and ISAR model,there are also differences in the RD algorithms for signal processing.At the same time,the motion of radar and the translation of the ship will blur the image and reduce the resolution in the both of the imaging process of SAR and ISAR,so it is necessary to compensate the motion separately.This paper makes SAR imaging of ship's ships through the RCS of various parts of the ship.The RCS of different parts of the ship can be obtained by calculation or software simulation because of the different Angle of incident input and material.In addition,when radar waves are fired into the ship on the sea surface,the ship has a covering effect and a multi-diameter reflection of the sea surface.By calculating the scattered RCS,the SAR image of the ship model can be obtained.When the ship is in a state of movement,because of the relative complexity of the ship movement,some points can be picking up to represent ship model to be discussed.During the process of ship imaging by an airbone radar,the relative motion is complex containing ship's rotational motion,plane flight along a route and the ship moving which will seriously affect the imaging quality,so the hybrid of SAR and ISAR model of double RD algorithm has been proposed and applied.The hybrid of SAR and ISAR is proposed for the echo signal analysis and processing of SAR and ISAR.Besides,because of the time-varying signals caused by the ship rotation,the time-frequency analysis is applied to obtain a high resolution imaging of ship.Because of the influence of cross terms in the time-frequency analysis,the results of imaging is still fuzzy to a certain extent,the instantaneous image ships can be getted by adopting the method of Chirplet decomposition of signal.The Chirplet method can effectively reduce cross-term and maintain high time-frequency aggregationto result an imaging of the ship in higher resolution.