| Bubbles in the upper ocean are ubiquitous and are formed primarily as a result of breaking waves, and secondarily as a result of biological activity. This thesis is concerned with the influence of these bubble populations on the optical properties of the upper ocean, primarily scattering, and on the subsequent influence on the radiative transfer of solar energy in the sea.; I have examined the optical properties of oceanic bubble populations from a theoretical, laboratory, and field perspective. Bubbles have a backscattering efficiency at least five times higher than phytoplankton, the most optically important component in the upper ocean. Theoretical predictions and laboratory observations confirm that organic film coatings will further enhance the scattering over the backward direction by a factor up to four. The critical angle scattering by bubbles resulting from the total reflectance at the local water-bubble surface (at angles of 60--80 degrees) is one order of magnitude higher than the scattering by any other particle of similar size. The effects of smaller bubbles (radius < 10 mum) on the derived phase function are modeled by assuming that the number of bubbles increases with decreasing size following the Junge distribution. The extension of the bubble size distribution to smaller sizes than are currently measured by a variety of techniques will alter the backscattering ratio of thus derived phase function by less than 20%, as long as the absolute value of the Junge exponent for submicron bubbles is <3; the most pronounced variations are restricted to angles less than 10°.; Based on historical in situ data on natural bubble populations, a model was developed to link the vertical distribution of the bubble layer in the upper ocean with wind speeds. Based on this model, I estimate that in the visible domain, the increased reflectance in the ocean as a result of strong winds, which produce bubbles and whitecaps simultaneously, is primarily attributable to underwater bubbles. This is in contrast to the common belief that high reflectance of whitecaps should dominate, even though this is true in the infrared wavelengths as our model suggested. As well, the color of the ocean will be shifted towards green. The presence of bubbles will cause an overestimate of chlorophyll concentration from remotely observed spectral reflectance; the situation will be more serious in clear water, where both atmospheric and bio-optical algorithms for ocean color remote sensing are assumed to be largely well constrained. The critical angle scattering of bubbles however, which mostly contributes to light coming out of the ocean at angles greater than 70°, has a limited influence on the remote sensing signals.; Field experiments were conducted to measure the variation of remote sensing reflectance and size distribution of bubbles within the ship wake zone in two different water regimes, namely, clear Equatorial Pacific Ocean and turbid coastal waters of New Jersey. While the color of ship wakes appear greener in clear waters, a shift of reflectance spectra towards blue, albeit slightly, was observed in turbid coastal waters. Colorless themselves, bubbles change the color of the ocean in a way that depends on the spectral backscattering of the background waters. A new method is also proposed to indirectly derive the spectral backscattering, which is difficult to measure correctly, from measurements of remote sensing reflectance, which are easily obtained. |
