AquaFloat:A Near-Surface Hyperspectral Radiometer System for Improved Ocean Color Measurements within the UV-VIS-NIR Spectral Region

In P-I we demonstrated a low cost, easy to operate sea-surface-spectroradiometer system, AquaFloat, for measuring the underwater upwelling radiance at 3 adjustable depths close to the sea surface within the top 1 m for determination of water-leaving radiance amp; remote-sensing reflectance just above the surface. A sensor for measuring the downwelling irradiance above the sea surface is also included. The sensors provide data at high spectral resolution over the UV-VIS-NIR and minimize the uncertainties of common approaches, e.g., free falling profilers that generally do not provide good data close to the surface and buoy-based systems with a single-depth radiometer placed at near-surface depth or multi-depth radiometers placed at depths of 1 m and deeper. The uncertainties associated with extrapolation of subsurface measurements taken at a single depth or depths of ~1 m and deeper to just below the surface are particularly significant in the red and NIR spectrum even in optically uniform water column owing to effects of inelastic Raman scattering by water molecules. By conducting time series measurements, AquaFloat reduces errors due to variations in underwater light field associated with the effects of sea surface waves, vertical changes in water inherent optical properties including the effects of intermittent bubble clouds, and changes in sky conditions, which can affect profiling measurements. The low-cost design, ease, and flexibility of use of AquaFloat offers an improved tool for routine work aimed at the development and validation of in-water ocean color algorithms. These features of AquaFloat also facilitate the use of multiple systems in special experiments to map horizontal variability in remote-sensing reflectance; subpixel variability within the GSD of a satellite sensor or various events in optically complex coastal waters as red-tide blooms and river plumes. AquaFloat is useful in vicarious calibration of current amp; future satellite ocean color missions.