The Method Study And System Design On Muti-parameter Measurement And Three Dimensional Imaging In Underwater Environment

In recent years,with the deepening of China's understanding of the value of marine strategy and the increasingly fierce competition for marine rights and interests,building a powerful marine country has become an increasingly important development strategy.Among them,the construction of intelligent marine monitoring capacity,including the measurement of water inherent parameters and depth distribution,lays the necessary foundation for the comprehensive development of marine economy and the promotion of sustainable ocean activities.This thesis relies on the pre-research project “XX target detection based on XX technology” of the National Defense “Twelfth Five-Year Plan”general equipment department undertaken by the research group,developing a Marine environment systhesis sensing system capable of capturing information of p H value and the salinity,intergrated by 3D imaging function.The no-core optical fiber structure p H sensor,Abbe refraction architechture salinity sensor and 3D imaging based on range gated mechanism are adopted in the technology selection.The integrated scheme design of the whole prototype is completed,furthermore,the key technologies of p H sensor and 3D imaging involved are studied.The main research contents and innovation achievements are as follows:(1)When coating a no-core fiber with a p H sensitive gel,the change of the environmental p H value leads to the change of the refractive index of the coating,which produces a modulation relationship for the mode leakage of optical signal transmitted through the fiber.Based on this principle,a p H sensor with no core fiber structure is developed.The coating is made of TEOS gel,and coated by dipp-coating method with high reproducibility.When the gel was loaded with cresol red,chlorophenol red and bromophenol blue as the p H indicator,the measurement range reaches 1?13.The sensing linearity on a 2 cm size sensor reaches 99.7%.(2)The noise model of 3D range gated imaging system is systematically analyzed.Started from studying the range variance equation,the influence of system noise characteristics,environmental factors and module configuration parameters on the performance of 3D imaging system,including ranging accuracy,ranging range and spatial resolution,is deduced in analytical form.The following principles are revealed: intensity random noise and timing jitter of devices causes degradation of ranging accuracy.The medium absorption effect worsens the performance of the accuracy to the long-distance target,ultimately limiting the range of the distance measuring range.The medium scattering effect reduces the spatial resolution of the system,especially for the long-distance and low reflectivity targets.When the reflective signal from the target surface is submerged by the medium scattering noise,the 3D recovery results show occlusion effect and outlier noise.According to the analysis results,modules of 3D imaging system are selected,and the prototype construction and supporting software design are completed.(3)In order to optimize the configuration parameters of 3D imaging system to improve the signal-to-noise ratio,the intelligent parameter configuration method is studied.Based on the slice-scanning ranging principle,the traditional eye pattern model used to characterize the range gated resolution is improved,so that it can be used to characterize the ranging accuracy performance of 3D imaging system without demanding a cooperative target.An Gaussian process regression based method to optimize the eye pattern quality online is designed.All adjustable parameters of modules are globally optimized in the absence of knowing the specific characteristics of the device and the parameters of the imaging environment.For verifying the environmental adaptability of the optimization method,the imaging experiments under various water environment such as deep sea,coast and harbor are simulated in a tank.The result shows that after several iterations,the system configuration parameters including laser Q-switching delay,image intensifier gate width and gain reach convergence,and the ranging accuracy is improved accordingly.(4)In order to overcome the degradation of spatial resolution caused by underwater strong scattering environment,a multi-pulse discrimination denoising algorithm is developed based on the scattering imaging model.Under the Bayesian image estimation framework,PSF is introduced to describe the generation of blurred image sequence,and ICM optimization algorithm is designed to update the reflection and scattering image iteratively.The results of 3D reconstruction are much better than the traditional methods in the aspects of target contour reconstruction and ranging accuracy.Hence the external noise introduced by the environment is depressed.The underwater long-distance imaging experiment of the prototype system in the basin achieves a ranging accuracy of better than3% within 10 m detection distance.Also an experiment conducted in the water tank verifies its robustness to environment.The marine environment-aware photoelectric measurement system designed in this thesis has abundant measurement data and a wide range of applications.In addition,the developed measurement device has a relatively low cost and small size,which also ensures its flexible deployment method and can be installed in the future on various vessels and hydrologic stations to provide environmental awareness and support various mission requirements.At present,the prototype has achieved the project requirements in the sea trial,and successfully meeting the acceptance criteria.