Optical properties of the clearest natural waters (200–800 nm)

Abstract

A new UV submersible spectroradiometer has been employed to determine the diffuse attenuation coefficient for irradiance in the clearest natural waters [K_w(λ)] with emphasis on the spectral region from 300 to 400 nm. K_w(λ) can be related to the inherent optical properties of pure water, in particular the total absorption coefficient a_w(λ) and the molecular scattering coefficient b_m(λ), by means of equations derived from radiative transfer theory. We present an analysis showing that limiting values of K_w(λ) can be estimated from a_w(λ) and vice versa. Published a_w(λ) data, which show discrepancies much larger than their estimated accuracies, are briefly reviewed and then compared, via our analysis, with K_w(λ) data (our own new and previously published data as well as relevant data of others). This comparative analysis and new data allow a consistent and accurate set of optical properties for the clearest natural waters and for pure fresh water and saltwater to be estimated from 300 to 800 nm.