Spectral Variability of Sky and Sun Glint in Hyperspectral Above-surface Reflectance Observations
In this study, we used 3C to process an extensive 5-year data set of continuous above-surface hyperspectral observations from the Long Island Sound Coastal Observatory (LISCO), recorded in a fixed direction and at wind speeds ranging up to 15 m/s. Measurements were conducted in burst mode and yield a representative sample of Lr variability for each measurement cycle. Implications of commonly used averaging schemes for such measurement series are discussed, corroborating to an automated quality-control scheme.
A spectrally resolved sky radiance distribution model was then used in combination with Cox-Munk wave-slope statistics to validate the observed spectral variability in Lr with regards to wind speed, aerosol concentration, illumination/viewing geometry, and sun glint contamination.
Both observed and simulated Lr independently indicate that spectral dependencies of the sky light distribution and the contribution of sun glint may not be neglected for observations recorded at wind speeds exceeding 5 m/s. This finding is specifically relevant for coastal and inland waters that feature low reflectance values in the blue and ultra-violet spectral regions where Rayleigh-scattered sky light is most intense and variable.