We propose to develop a low cost, easy to operate spectroradiometer system referred to as AquaFloat for measuring the near-surface underwater upwelling radiance at three to four adjustable depths within the top 1 - 1.5 m of the water column for accurate determination of water-leaving radiance and remote-sensing reflectance just above the surface. A sensor for measuring the downwelling irradiance above the sea surface will also be included. The sensors will provide data at high spectral resolution over a broad spectral range (300 - 950 nm) and will minimize the uncertainties of common approaches of free-falling profilers that generally do not provide good data close to the surface or buoy-based systems with multi-depth radiometers placed at depths of 1 m and deeper. These uncertainties are associated with extrapolation of subsurface measurements taken at depths of ~1 m or deeper to just below the surface and are particularly significant in the red and near-infrared parts of the spectrum due to effects of inelastic radiative processes even within the homogenous water column, as well as across the entire spectral range when the near-surface water column is optically heterogenous. By conducting simultaneous time series measurements at multiple near-surface depths, AquaFloat will also reduce errors due to variations in underwater light field associated with the effects of sea surface waves, intermittent bubble clouds, and changes in sky conditions, which can affect profiling measurements with a single radiance sensor. The low-cost design, ease and flexibility of use of AquaFloat will offer an improved tool for routine work aimed at the development and validation of in-water ocean color algorithms. In addition, by satisfying the appropriate radiometric accuracy requirements the AquaFloat can be useful in vicarious calibration activities of current and future satellite ocean color missions.
AquaFloat supports NASA ocean color-related calibration/validation activities for universities, NASA centers, and government labs. AquaFloat is easy to deploy in deep ocean, littoral regions, estuaries, and inland water bodies. Current and future missions (e.g., MODIS, VIIRS/JPSS, PACe, HyspIRI, GEO-CAPE, OLCI/Sentinel, SGLI/GCOM, GOCI) involving ocean color measurements will benefit from AquaFloat's near-sea surface radiometry. AquaFloat benefits NASA Ocean Biology and Biogeochemistry programs supporting satellite ocean color missions.
The AquaFloat sea surface radiometer will enhance the capabilities of existing marine radiometer sensors, improving applications of satellite and airborne ocean color remote sensing. This, in turn, will provide improvements in data for countries, states, municipalities, and research institutions to assess the conditions and trends within the aquatic environments and make informed decisions.