A Research On Transmission Model Of Crossing Multimedia Underwater Target Optical Imaging

With the advantages such as quick,efficient and imageable,optical detection plays a more and more important role in marine detection.Using crafts like seaplane or remote sensing satellites becomes a more and more popular way to detect sea with the improving of detecting techniques.Comparing with traditional ways which using underwater detectors,detecting from air has to pass through air and sea-surface which brings more perturbances in detecting results because of multiple-medium environment.In order to make clear the influences that every factor caused,air,water-air interface and water body are separately analyzed.Then multiple-medium model of underwater optical imaging is formed by synthesize those analyses.In the part of air,sea fog is mainly discussed for the influence of air is small.Bulk density of granularity of particles in sea fog are discussed via droplet spectrum.Relationship between extinction coefficient and radius of particle that under the laser of 532 nm wavelength is calculated by using Mie scattering theory.Moreover,decline of light energy which transmitting in fog is also calculated,obtaining exponential decaying and some decay coefficients at specific visibility.In the water surface part,simulated water surface has to be established to get the parameters of every point at the surface so as to calculate the normal vector,which can help calculate complexed refractions caused by fluctuation of water surface that can change the direction and amplitude of rays.Simulated sea surface is built based on the statistical wave model.Magnitude and distribution of incidence angles and refraction angles are analyzed and counted,finding most of them are small that cannot cause palpable perturbance in detection.Sea water can absorb and scatter light,the former weakens amplitude which resulting a limited range of detection.The later not only weakens amplitude but also brings noises by back-scattered light which being received together with detecting light.Influences of every part of water body are being discussed,then Monte Carlo simulation is utilized to research the transmission of photons in water to find how light energy decaying and diffusing.Depolarization is also being researched by simulation using Stokes vector and Mueller matrix.Results shows the diffusing of light has a closing relationship with the distribution of particles which causing scattering,the outstanding anti-jam ability of polarization detection is also shown.At last simulation of imaging in crossing multiple-medium is done via combination of researches above.The influences of refraction are researched and the resulted images are evaluated by the method of SSIM(Structure Similarity).The comparation of detection using natural light and polarized light is shown.The results show that the scattering caused by water body has a significant impact on imaging and detection using polarized light has a better effect over using natural light under the same light intensity.