Research On Modeling And Experiment For Inverse Synthetic Aperture LADAR System

Inverse Synthetic Aperture LADAR(ISAL)is an active super-resolution imaging technology.The basic concept comes from Inverse Synthetic Aperture Radar(ISAR)in microwave imaging yield.In principle,imaging resolution of ISAL is independent of the optical aperture of system and target range,therefore,it can obtain high-resolution imaging of long-range target under limited equipment volume.Compared with ISAR,ISAL has higher imaging resolution,faster imaging speed and it’s image can reflect the optical reflection characteristics of the target,with the advantage of short optical wavelength.Therefore,it has significant advantages in long-range high-resolution imaging and target feature recognition.Aimed at long-range ISAL system,this paper researches it from two aspects: system modeling and experiment.The system modeling part includes the establishment of echo signal model,perception model and simulation model,the experiment part includes ISAL system design and optimization,as well as long-range outdoor imaging experiment.The specific research contents and results are as follows.1.Based on ISAL imaging principle,considering the spatial distribution of laser signal,a complete ISAL echo model is established under as few assumptions as possible,and obtain the perception model in vector form based on echo signal model.Besides,this paper state ISAL imaging principle from the perspective of optical holography.Compared with the traditional explanation from the perspective of electromagnetic field,the physical meaning of this method is more intuitive.In addition,based on ISAL echo generation process,considering each model in transmission link,ISAL system simulation model is established.Finally,the ISAL imaging simulation of three-dimensional target is completed.2.ISAL imaging is studied for Model Based Imaging Reconstruction(MBIR)algorithm.Compared with traditional ISAL imaging algorithm,MBIR has better speckle and noise suppression ability,the reconstructed result is more closed to optical image.Point at the problem that the model of the algorithm is complex and the low efficiency of gradient free line search,this paper presents an improved algorithm.From the perspective of optical imaging,the Markov relationship among complex reflection coefficient,reflectivity and measurement signal is established and the optimization model of the original MBIR algorithm is simplified.Furthermore,the substitution function with simple gradient form and relatively steep change is used to replace the original Q-GGMRF prior model to improve the solution efficiency.At last,the proposed algorithm’s effectiveness,robustness and computational efficiency is verified by simulation data and long-range outdoor experiment data.3.A ISAL experiment system for long-range target outdoor imaging verification experiment is designed and built,this system have been used in Hefei Science Island.Point at the problem that the inequality of IQ modulator’s photoelectric response introduce amplitude distortion of laser signal,detailed analysis is given.The self heterodyne detection method is proposed for the first time to measure and compensate the amplitude distortion of laser signal.This method can be realized just by data of reference channel in practical application,external equipment and optical measurement is not needed.Data in fiber and 1km outdoor experiment verified the effectiveness in improving echo signal’s power and imaging quality in range direction.Finally,7km expand target imaging experiment is carried out,the ISAL system is optimized by the field of telescope and local oscillator.7km expand target imaging is realized with only 2.56 m J emission laser power.