Research On Degrading Mechnisam Of Echo Signal And Method Of Improving Imaging Quality In Laser Coherent Field Imaging

As a new kind of lensless high resolution imaging theory, laser coherent field imaging was developed in the last ten years. It was expected to solve the problem of the atmospheric turbulence and break through the diffraction limit. It shows outstanding advantage of high resolution in remote faint objects imaging. The theory has important scientific significance and application value in the field of national defense and remote sensing imaging. At present the research about the novel imaging technology at home and abroad focus on the principle demonstration and it has not been applied in engineering.When the most commonly equivalent spacing sampling imaging mode in laser coherent field imaging was applied in engineering practice, due to the influence of transmitting aperture array positioning error, atmosphere turbulence intensity scintillation and light intensity jitter error, system noise, it may unsatisify the basic imaging iterative condition of the equal aperture distance and equal light intensity with equal sampling frequency. So the above inevitable engineering error will affect the imaging quality. However the mechanism of degrading imaging is unclear till now. Therefore, in practical application, the imaging model need to be modified based on the existing coherent imaging theory. In order to improve the imaging quality of the coherent field imaging, the modifying imaging model should be established.From the perspective of laser aperture positioning error, multi beam intensity jitter and turbulence error, system noise, the paper revealed the degradation mechanism of the coherent field echo signal to imaging quality. Then based on the mechanism, it puts forward corresponding image enhancement methods, the details are as follows:Coherent field imaging is based on the condition of equal transmitting aperture spacing with the equal spectrum to reconstruct high-resolution image. Howerver,in the application inevitable aperture positioning error of laser transmitter aperture is a key factor to affect coherent field imaging quality.It proposes a novel method of improving imaging quality from the perspective of suppressing imaging quality influence of transmitting aperture spacing error. The theoretical equation of none-influencing frequency spectrum and imaging quality was proposed for the first time. To solve the above equation, an optimized method of linear programming was proposed and we got the optimized matrix of aperture spacing error. The correctness and validity of theoretical model has been verified in the simulation experiment. The results shows that the Strehl Ratio of imaging quality index can be improved about 1 times by the proposed method.The research can provide a theoretical basis of improving imaging quality and reasonably assigning transmitter aperture spacing accuracy of coherent field imaging telescope.Based on the theory of phase closure and spectrum reconstruction, the paper establishes the impacting theoretical model of laser echo signal coming from atmosphere turbulence intensity scintillation and multiple beam intensity jitter error. It reveals the degrading mechanism of laser echo spectrum signal and imaging quality inducing by light intensity jitter error. For the first time, it proposes a novel shaped laser array sampling model. The research shows that the novel method can eliminate the degradding influence of atmosphere turbulentce light scintillation efficient and laser intensity disturbance conveniently. It can improve the Strehl Ratio of imaging quality 30%. It provides a technical support to suppress the intensity scintillation.The purpose of this part is to settle the problem of quantitativly estimating ratio of detector noise and to analysize whether detecoror noise is the main noise or not in laser coherent field imaging system. The paper proposes a novel method of quantitative analysis detector noise ratio. Firstly, the SNR(signalt-to-noise) of the system was given by photoelectron statistics method. Secondly, estimating equation of SNR intermediate parameter was derived. A quantitative ratio model of detector noise to total noise was established by SNR equation and estimating equation of SNR intermediate parameter. Thirdly, the ratio model was tested and verified by theory analysis and experiment. The experiment result showed that in the specific experiment table, detector noise is about 52% of the total noise. Finally, the conclusion was acquired that the proposed metod can accurately and effectively estimate detector noise ratio to total noise. The novel method has the advantage of simplicity and effectiveness. It can be widely applied in quantitative analysing and measuring of detector noise in laser coherent imaging system.The paper researched the influencing echanism of laser echo signal caused by speckle noise, background light noise and detector noise. Based on the theory of homomorphic filtering and basis pursuit sparse denoising, it proposes a cascaded compound denoising method. The composite denoising method of speckle multiplicative noise and background additive noise can improve image contrast 0.21 and promote the Strehl Ratio of imaging quality 17% in coherent imaging system.The research reveals degrading mechanism of imaging quality induced by the laser aperture position error, the atmoshphere turbulence intensity scintillation effect and light intensity jitter error of multi-beam laser, system speckle noise factors. It provides effective theoretical guidance for imaging quality improvement in practical coherent field imaging system.This paper established error correction theoretical models of coherent field imaging. It enriched and developed the theory of laser coherent field imaging. The research provides effective theoretical foundation and technical support for further engineering application of coherent field imaging theory.