Exploring the limits for sky and sun glint correction of hyperspectral above-surface reflectance observations

Above-surface radiance observations of water need to be corrected for reflections on the surface to derive reflectance. The three-component glint model (3C) [ Opt. Express 25 , A742 ( 2017 ) OPEXFF 1094-4087 10.1364/OE.25.0000A1 ] was developed to spectrally resolve contributions of sky and sun glint to the surface-reflected radiance signal L r ( λ ) , and for observations recorded at high wind speed and with fixed-position measurement geometries that frequently lead to significant sun glint contributions. Performance and limitations of 3C are assessed for all relevant wind speeds, clear sky atmospheric conditions, illumination/viewing geometries, and sun glint contamination levels. For this purpose, a comprehensive set of L r ( λ ) spectra was simulated with a spectrally resolved sky radiance distribution model and Cox–Munk wave slope statistics. Reflectances were also derived from an extensive four-year data set of continuous above-surface hyperspectral observations from the Long Island Sound Coastal Observatory, allowing to corroborate 3C processing results from simulations and measurements with regard to sky and sun glint contributions. Simulation- and measurement-derived L r ( λ ) independently indicate that spectral dependencies of the sky light distribution and sun glint contributions may not be neglected for observations recorded at wind speeds exceeding 4 m / s , even for sun glint-minimizing measurement geometries (Sun-sensor azimuth angle Δ ϕ = 90 − 135 ° ). These findings are in accordance with current measurement protocols for satellite calibration/validation activities. In addition, it is demonstrated that 3C is able to reliably derive water reflectance for wind speeds up to 8 m/s and Δ ϕ > 20 ° .