Radiance Distribution in the Upper Layers of the Sea

The angular distribution of underwater radiance for green light has been studied in the upper turbid layers of the Gullmar fjord by means of a radiance meter which is lowered in the sea along a guide wire with a fixed orientation. A theoretical discussion considers the different components entering into the light field, viz. direct sunlight, skylight, and scattered light. On the basis of available measurements of the volume scattering function the scattered light is evaluated by integrating light scattered from the predominant sun beam alone. The experimental angular distributions of radiance compare well with the theoretical distributions. In particular it is demonstrated that the radiance in the angle interval  ± 45° from the sun attains a maximum below the surface.