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

A new UV submersible spectroradiometer has been employed to determine the diffuse attenuation coefficient for irradiance in the clearest natural waters [K(w)(lambda)] with emphasis on the spectral region from 300 to 400 nm. K(w)(lambda) can be related to the inherent optical properties of pure water, in particular the total absorption coefficient a(w)(lambda) and the molecular scattering coefficient b(m)(lambda), by means of equations derived from radiative transfer theory. We present an analysis showing that limiting values of K(w)(lambda) can be estimated from a(w)(lambda) and vice versa. Published a(w)(lambda) data, which show discrepancies much larger than their estimated accuracies, are briefly reviewed and then compared, via our analysis, with K(w)(lambda) 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.