Underwater Optics

Abstract Four major subjects of the underwater optics are especially important, both for fundamental study of interaction between light and water and for various technical applications. These are (1) inherent optical properties (IOP) of natural waters; (2) propagation of natural and artificial light in the water; (3) optical methods for investigation of natural waters, and (4) underwater imaging. These four items form the main content of the paper and determine the titles of its four main sections. Section 2 presents the definitions of IOP determining light absorption and scattering in water. Methods of measuring IOP are discussed, and data on spatial and spectral distributions of IOP in natural waters are given. Physical and empirical low‐parametric models considered in the section make it possible to determine the whole set of IOP distributions, based on few measurements. Section 3 deals with the underwater light fields. Methods for solving the radiative transfer equation are considered. The section presents data on the solar irradiance and angular radiance distributions near the sea surface and at the sea depth, as well as on the light field of artificial sources. Optical methods for investigation of natural waters are discussed in Sect. 4. This section is mainly concerned with the problem of remote sensing of phytoplankton, suspended and dissolved matters by measuring the ocean color, with the account of algorithms for atmospheric correction of satellite measurements. Finally, Sect. 5 is devoted to the problem of underwater imaging. The presented theory connects the image parameters, such as modulation transfer function, contrast, signal/noise ratio with the parameters of light sources, detectors, water, and target. Comparison of the sighting range and spatial resolution in water ensured by different underwater imaging systems is given.