This effort was part of our work supporting the MODIS Ocean Color Algorithm. Karl Moore did much of this work as a Post-Doc, starting as the initial instrument work was completed. As part of this work we built a Whitecap Radiometer, which projected from the bow of the ship and provided the total radiance leaving the surface (including below the surface). The papers which resulted from this work were:

K. D. Moore, K. J. Voss, and H. G. Gordon, “Whitecaps: Spectral reflectance in the open ocean and their contribution to water leaving radiance” , Proc. Soc. Photo-Optical Instrumentation Engineers, 1997, 2963: 246-251.

K. D. Moore, K. J. Voss, and H. R. Gordon, “Spectral reflectance of Whitecaps: Instrumentation, calibration, and performance in coastal waters”, 1998, J. Atm. and Ocean. Techn., 15: 496-509.

Abstract: A measurement system for determining the spectral reflectance of whitecaps in the open ocean is described. The upwelling radiance is obtained from a ship by observing a small region of the water surface over time using a six-channel radiometer (410, 440, 510, 550, 670, and 860 nm) extended from the bow of the ship. Downwelling irradiance is simultaneously measured and used to provide surface reflectance. The system includes a TV camera mounted beside the radiometer that provides a visual reference of surface events. Air/water temperature and wind speed/direction are also measured along with global positioning system data. Calibration procedures and radiometric characterization of the system for operation under different sky conditions and solar zenith angles are emphasized so that full advantage is taken of ship time whenever whitecap events occur. The radiometer was operated at sea and examples of the spectral reflectance of different foam types (thick foam layers to thin residual patches) generated by the ship’s bow in coastal waters are presented and found to vary spectrally. The presence of submerged bubbles in the foam measurement results in a lower reflectance at the longer wavelengths. For wavebands in the visible region, the spectral reflectance values tend to equalize with higher reflecting foam from thicker foam layers.

K. D. Moore, K. J. Voss, and H. R. Gordon, “ Spectral reflectance of whitecaps: Their contribution to water leaving radiance”, 2000, J. Geophys. Res., 105: 6493 – 6499.

Abstract: A radiometric system, deployed from a ship, is used to measure directly the
influence of the presence of breaking waves (whitecaps) on the upwelling radiance above
the sea surface. Estimates of their remote sensing augmented spectral reflectance, i.e., the
temporally averaged or spatially averaged increase in the ocean’s reflectance over and
above the reflectance in the absence of breaking waves, are provided from measurements
in the tropical Pacific. The accuracy of these estimates is dependent on their ability to
determine radiometrically the background reflectance of the water. In the visible the
remote sensing augmented spectral reflectance of whitecaps measured in the open ocean
was found to be essentially independent of wavelength and in the range 0.001– 0.002 for
wind speeds of 9–12 m s21. This is in reasonably good agreement (within a factor of 2)
with earlier predictions based on the statistical relationship between fractional coverage
and wind speed and the estimated average reflectance of individual whitecaps. In the near
infrared (860 nm) the remote sensing augmented spectral reflectance falls to ;80% of its
value in the visible.