L. S. Dolin, I. M. Levin

The paper presents an overview of the underwater imaging problem. A history of this problem is given. A universal underwater imaging theory is intended for computing image parameters and the maximal visibility distance of an extended target with inhomogeneous reflectance for various, including laser, underwater imaging systems. We consider the main elements of this theory: image transfer equation, beam spread function and modulation transfer function, the algorithms for computing image parameters of a target of limited size and the maximal visibility distance in water. Parameters of underwater light field, which are necessary for these algorithms, are given as a result of solution of the radiative transfer equation in terms of the water inherent optical properties. We present also a universal model of water inherent optical properties for wavelength close to 550 nm which makes it possible to determine all IOPs required for the underwater imaging theory using only the water attenuation coefficient or even Secchi depth. An algorithm for calculating the signal/noise ratio and the maximal sighting range in water are presented and used for comparison of efficiency of the imaging systems of various types. The main directions of the current investigations on the underwater imaging problem are considered, in particular, imaging through wavy sea surface.

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