Spectral dependence of the diffuse attenuation coefficient of light in ocean waters: a reexamination using new data

A model devised earlier1,2 relating the spectral dependence of K(.), the attenuation coefficient for natural diffuse light in the ocean, to the value of K()) at a reference wavelength, is re-examined using recently acquired data. The original model was based on data obtained from 1 967 to 1 979 by various investigators using a variety of scanning submersible spectroradiometers in tropical to mid-latitude waters. New data were obtained by the Visibility Laboratory in a series of cruises from 1985 to 1987 covering ocean latitudes from 24.4° to 77.4°. These data are believed to be of uniformly high quality and have the advantage over the previous data in that they permit the determination of K()) profiles to 200 meters from data obtained simultaneously at all 12 wavelengths and over a time span of approximately 6 minutes, vice data recorded serially at each wavelength and at discrete depths over a time span of as much as one to two hours with the spectroradiometers. An examination of the variation in the spectral K(A)'s with latitude was prompted by a concern that the phytoplankton species distribution at high latitudes might differ sufficiently from that at tropical to mid-latitudes to require a change in the spectral K(.\) model. A comparison was also performed between 83 sets of spectral K(A)'s derived from the new data and K(X)'s predicted by the model using measured K(490) as an input index. Small systematic differences were found which are not believed to be significant for most applications, hence, no change in the model is recommended on the basis of these findings