A COMPARATIVE STUDY OF IRRADIANCE, BEAM TRANSMITTANCE AND SCATTERING IN THE SEA NEAR BERMUDA1

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Abstract
Comparative measurements of a number of optical properties of the sea were made at 6 stations and at depths down to 245 m near Bermuda. In situ determinations included attenuation of natural radiant energy and reflectance between 375 and 651 mµ, beam transmittance and scattering, as well as polarization 90° to the beam. In the laboratory, scattering and degree of polarization were determined at 90° from water samples, while scattering was also measured at 45° to the beam. Both photovoltaic cells and photomultipliers were used as required.The irradiance and beam transmittance data indicate that the wide differences in attenuation at different stations are primarily due to variations in the amount of suspended matter both offshore and inshore provided that the coastal or partly enclosed water is in open communication with the sea. However, in Harrington Sound, which has only restricted communication with open water, the optical properties differ in indicating greater concentrations of yellow substance than at any other station. Scattering coefficients measured at 45° and 90° in the laboratory show an approximately linear correlation for Castle Harbour and North Shore stations. In general the scattering coefficients at 90° are systematically correlated with the degree of polarization so that plotting p‐log β yields a linear function whose slope depends on the nature of the particles suspended in the different water masses.In situ measurements of scattering and polarization usually were different from those in the laboratory. In clear Sargasso Sea water, for instance, in situ polarization was greater (75–80%) than it was in the laboratory (60%) although the scattering coefficients in the sea were definitely smaller. Further work is required to account for such discrepancies. Comparisons of in situ polarization of natural radiant energy with polarization from a light beam show that natural polarization decreases more rapidly than that from an artificial light beam as the amount of scattering increases. This effect results from the dependence of submarine polarization not only on scattering but also on directionality of the underwater radiant energy which diminishes for daylight with the amount of suspended matter.