Absorption coefficients of the ocean: Their measurement, and implications for remote sensing

The spectral energy distribution of the emergent radiant flux from the ocean is determined by the inherent optical properties of the water, especially the absorption coefficients. To interpret the remotely sensed spectral distribution in terms of ocean composition we need a data base relating seawater absorption spectra to composition, especially in terms of phytoplankton concentration and type, and soluble and detrital colour. Measurement of seawater absorption spectra is difficult because absorption is so low, and because of the confounding effects of scattering. The use of the integrating cavity absorption meter to overcome these problems is discussed, and an account is also given of the potential and limitations of seeking to estimate absorption coefficient values from in-water spectral irradiance data.