A QUANTITATIVE STUDY OF THE RADIANCE DISTRIBUTION AND ITS VARIATION IN OCEAN SURFACE WATERS

Abstract

The radiance distribution provides complete information regarding the geometrical structure of the ambient light field within the ocean. A quantitative study of the radiance field in the dynamic ocean water is presented in this thesis work. The study starts with the development of a novel radiance camera for the measurement of the full spherical radiance distribution at the ocean surface and depth. Nonlinear response functions are designed and advanced radiometric calibrations are developed. The resulting camera measures the radiance distribution in absolute units over an extremely high dynamic range at fast rates. With the newly obtained radiance data, I have examined the fine structure of both the downwelling and upwelling radiance distribution and its variation with depth in optically diverse water types. The fully specified radiance distribution data are used to derive all apparent optical properties and some inherent optical properties including the absorption coefficient. With the camera fixed at shallow depths, I have observed and determined the sea surface wave disturbance of the radiance distribution. It is found that the radiance fluctuates anisotropically with regard to its amplitude and periodicity. Typical spatial structures of the dynamic radiance field are identified and shown relevant to the surface waves and the solar zenith angles. The variability in the radiance field also propagates to the irradiance field; the variability is pronounced in measured irradiance depth profiles in the upper layers of the ocean. The statistics of the irradiance fluctuations along the water depth, including the dominant frequency and coefficient of variation, are derived using wavelet techniques and fitted to novel analytic models. The results from the irradiance depth-profile decomposition are in agreement with theoretical models and other independent measurements. This thesis work represents the first attempt to quantify the full light field and its variability in dynamic ocean waters and is of significant relevance to many other optics-related applications.