A 1-km 2 area located 2 km off the Florida Panhandle (30 22 6 N; 86 38 7 W) was selected as the site to conduct high-frequency acoustic seafloor penetration, sediment propagation, and bottom scattering experiments [1]. Side scan, multibeam, and normal incidence chirp acoustic surveys as well Manuscript
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 s -•. 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. IntroductionBecause of the relatively small radiance backscattered into the atmosphere from below the ocean surface (the water-
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.
The design, construction, and performance of a new high-resolution underwater bathymetric prototype system (L-Bath) with extended imaging capability is presented. The design offers simultaneous reflectance and depth information on a pixel-by-pixel basis so that high-resolution reflectance and bathymetric maps of underwater targets can be provided with exact registration. The design supports operation in shallow coastal waters under daylight conditions where high turbidity and the influence of ambient backscatter are particularly limiting for underwater imaging systems. Its configuration is similar to existing laser line scanning systems but uses a pulsed laser for the source and a fixed field-of-view high-resolution linear charge-coupled device (CCD) as receiver. The pulsed laser allows short camera integration times, thereby reducing the influence of the ambient daylight signal, and the fixed field of view of the detector provides a precision nonmoving multielement receiver with imaging capability. As the laser sweeps across the field of view of the CCD, the position and signal strength of each laser target spot is imaged, permitting a measure of bathymetry and reflectance. Using the CCD, a highresolution slice through the reflected target spot radiance distribution is imaged so that system resolution can exceed the target spot size. The image of the target spot radiance distribution, modified by in-water scattering and target reflectance, provides new opportunities for image manipulation compared to typical underwater laser line scanning based systems. The simultaneous acquisition of reflectance and bathymetric maps permits discrimination capability between real objects of relief from scene reflectance variations.
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