Research On Radar Imaging Of The Complex Target At Sea

Inverse synthetic aperture radar system(ISAR)is a kind of high resolution imaging system,and the target at sea is an important target for researching ISAR imaging.Due to the ISAR image has an important role in the target identification,detection and tracking,and has a great application value in the military,civil and other fields.Therefore,the research has a very important significance in ISAR imaging of the target at sea.But the motion of the target is complex,make the ISAR imaging has certain difficulty.This thesis make the complex ship target as the research object,the main contents include the following two aspects:The thesis proposes a kind of ISAR imaging method based on the time-frequency distribution characteristics.The common time-frequency distribution when used for ISAR imaging of the ship target,multiple signal components will produce the cross terms because of these components interact,the cross terms will influence the ISAR image quality.So there is a method for suppress the cross terms,which used of RWT.If the target imaging is based on the traditional RWT,according to the instantaneous frequency will get the ISAR image.But the image effect is not very good because of the signal amplitude is change over time in the actual cases.To solve this problem,this thesis proposes a method based on RWT-Clean for the ship target ISAR imaging.The method of the thesis obtains the parameter values of every echo signal component by RWT combined with the clean,according to the instantaneous frequency and instantaneous amplitude improve the quality of ISAR imaging of the ship target.In the process of searching parameter that the chirp rate and frequency are obtained by RWT,if it make use of the traditional method,the computation is very big.So here will improve,there are a method which make use of change the search interval and search by two steps for obtaining the chirp rate and frequency parameter estimation of the signal.This method is not only get high resolution image but also reduce the computational complexity.Through the simulation experiment results show that the method is effective.The thesis proposes a kind of ISAR imaging method based on the time-chirp distribution(TCD)characteristics.Due to the complex motion of the ship target,make the azimuth of the echo signal have cubic phase and it can not be neglected.The ship target imaging quality will decline when based on the tradition method in this condition.To solve this problem of the ship target imaging,this thesis proposes a method based on TCD-Relax.The method make use of Relax and parameter estimation that there are the change of chirp rate and the chirp rate by combining the TCD distribution with Radon transform.The parameters will be used compensation the echo signal.According to the compensated echo signal obtain the center frequency,initial phase and magnitude.Finally,a ISAR image of the ship target is obtained.The simulation result shows that this method not only solved theproblem of imaging quality,but also improve the accuracy of parameter estimation.This thesis describes the background and imaging principle of ISAR images and then proposed two methods in time-frequency plane and time-chirp plane.Finally,the summary and outlook are made.