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水下湍流中温度、盐度对光学系统成像质量影响分析
The Effect of Temperature and Salinity on Imaging Quality of Optical System in Underwater Turbulence

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孙枢为 1,2,3   王昊 2,3   汪伟 1,2 *   李鹏 1,2   康福增 2   谢小平 1,2  
文摘 针对湍流对水下成像系统的影响,基于Yao折射率起伏功率谱,推导了平面波的波结构函数,完善了水下光学成像模型,其优势在于将难以测量的微观参量如动能耗散率和温度耗散率,用平均温度和平均盐度等宏观参量代替。数值仿真了不同平均温度与平均盐度条件下水下湍流通过改变波前,进而对成像系统调制传递函数产生影响。仿真结果表明,平均温度与平均盐度升高,均会造成系统成像质量下降,进一步研究发现平均盐度增加,不同空间频率的调制传递函数值均线性下降,且下降幅度基本一致;随着平均温度升高,调制传递函数值线性下降,且高频成分的调制传递函数值下降得更快。为验证成像模型的正确性,设计搭建了3 m长的水下光学成像实验平台,利用相机记录分辨率板透过湍流的成像情况,得到不同平均温度与平均盐度条件下的调制传递函数曲线。对比实验与仿真结果发现,在平均温度10 ℃~30 ℃与平均盐度0 ppt~30 ppt范围内,对比度随平均温度与平均盐度变化趋势相同。该研究对水下光学成像系统的设计优化及水下图像处理具有一定的参考价值。
其他语种文摘 Underwater imaging technology is a critical means to explore the ocean. With the development of underwater imaging technology, it is found that underwater turbulence is an important factor that restricts the imaging quality of optical system. Turbulence is a phenomenon of small vortices occurring at the interface due to different flow rates of each part of the medium. This physical phenomenon can directly lead to changes in the refractive index of the medium. Thus, it can change the wavefront structure of the beam, affect the modulation transfer function, and ultimately cause the degradation of the image quality at the receiving end. Most of the studies about turbulence on beam is based on refractive index and power spectrum, and the researches on turbulence is based on Nikishov's power spectrum. In this power spectrum, eddy diffusion rate is constant, does not relate to the average water temperature and the average salinity which can influence on eddy diffusion rate. Thus, the turbulence caused by the refractive index models still needs further refinement. Later, some scholars improved the refractive index fluctuation power spectrum. In this model, the average temperature and average salinity are used to characterize the vortex diffusion rate, and the refractive index fluctuation power spectrum model based on temperature and salinity is established. Compared with Nikishov's power spectrum, the power spectrum model is more complete, but the temperature variance dissipation rate and kinetic energy dissipation rate used to characterize turbulence intensity cannot be measured in the experiment, resulting in a gap between the simulation model and practical applications. In order to study the effect of underwater turbulence on the imaging quality of optical systems, we deduced the wave structure function and established an underwater optical imaging model based on the refractive index fluctuation power spectrum contained with temperature and salinity. The effects of temperature and salinity on the modulation transfer function under turbulent conditions are simulated. For verifying the reliability of the turbulence imaging model, a 3-m long underwater optical imaging experiment platform is designed and built. A water pump and water tank are used to create a turbulence region with controllable turbulence intensity. A CCD camera also plays a part of the region to image the resolution plate, thus analyzing the imaging quality. By controlling the experimental conditions, the imaging results under different temperatures and different salinity conditions are obtained. On this basis, the modulation transfer function is analyzed after the ensemble average obtained by several experiments. The results show that the modulation transfer function of the image decreases with the increase of temperature and salinity. Further studies show that the contrast of different spatial frequencies decreases linearly with the increase of salinity, and the decrease amplitude is basically the same. With the increase of temperature, the MTF basically conforms to the linear decline law, and the MTF of high-frequency components decreases faster. The experimental results show that the imaging quality under turbulent conditions is affected more by temperature than salinity, and the experimental results are consistent with the simulation results. This research has certain reference value for the design optimization and development of underwater optical systems.
来源 光子学报 ,2022,51(12):1211004 【核心库】
DOI 10.3788/gzxb20225112.1211004
关键词 水下湍流 ; 折射率起伏功率谱 ; 波结构函数 ; 调制传递函数 ; 温度 ; 盐度
地址

1. 中国科学院西安光学精密机械研究所光子网络技术研究室, 西安, 710119  

2. 中国科学院西安光学精密机械研究所, 瞬态光学与光子技术国家重点实验室, 西安, 710119  

3. 中国科学院大学, 北京, 100049

语种 中文
文献类型 研究性论文
ISSN 1004-4213
学科 物理学
基金 国家重点研发计划 ;  中国科学院A类战略性先导科技专项 ;  中国科学院西部之光人才培养计划
文献收藏号 CSCD:7394993

参考文献 共 21 共2页

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引证文献 1 篇

1 贺锋涛 基于卷积神经网络的水下湍流探测技术 光子学报,2024,53(1):0111004
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