Underwater Turbulence Field Detection Based On Differential Image Motion

With the increase in human use of marine space, supervision of the underwater vehicle has become an important issue in the field of maritime safety. The area Underwater vehicle travels over will be disturbed by the drive unit, which forms a turbulence field with certain strength and certain spatial scale. Refractive index is related to seawater temperature and salinity. The destabilization of temperature and salinity in underwater turbulent field will result in inhomogeneous refractive index. So the undulation of refractive index can be measured as the indicator of turbulence intensity. To detect underwater turbulence field, we introduce the differential image motion(DIM) technology in to underwater detection, discuss about its basic theory, system implementation and measurement errors, and verify its availability by simulation and experiment.In this paper, the structure function of refractive index is derived based on the power spectral density with was given by Nikishov in 2000 year. A concise form of the structure function is obtained by numerical fitting. Next, we discuss about the optical statistical properties of the underwater turbulent flow field, calculate the Fried parameter of oceanic turbulence, get the Cross-correlation function and the autocorrelation function of the output optical field of oceanic turbulence. Then, the theoretical basis of underwater DIM is derived.Based on the theory and measurement principles of underwater DIM, the system structure and the optical system which used in underwater short-range detection are designed. To reduce the measurement error of underwater turbulence detection, we propose an adaptive deconvolution algorithm which increase the accuracy of image motion measurement. what’s more, we analyse the system errors of underwater DIM, derive the mathematical formula of series system errors, and propose the principle of parameter selection for low detection error.Finally, we assess the feasibility of underwater DIM by numerical method and experiment. It is proved that the underwater DIM is feasible for oceanic turbulence detection.