Abstract

Sky reflectance $R_{\text{sky}}(\lambda )$ is used to correct in situ reflectance measurements in the remote detection of water color. We analyzed the directional and spectral variability in $R_{\text{sky}}(\lambda )$ due to adjacency effects against an atmospheric radiance model. The analysis is based on one year of semi-continuous $R_{\text{sky}}(\lambda )$ observations that were recorded in two azimuth directions. Adjacency effects contributed to $R_{\text{sky}}(\lambda )$ dependence on season and viewing angle and predominantly in the near-infrared (NIR). For our test area, adjacency effects spectrally resembled a generic vegetation spectrum. The adjacency effect was weakly dependent on the magnitude of Rayleigh- and aerosol-scattered radiance. The reflectance differed between viewing directions $5.4\pm 6.3\%$ for adjacency effects and $21.0\pm 19.8\%$ for Rayleigh- and aerosol-scattered $R_{\text{sky}}(\lambda )$ in the NIR. Under which conditions in situ water reflectance observations require dedicated correction for adjacency effects is discussed. We provide an open source implementation of our method to aid identification of such conditions.

© 2017 Optical Society of America

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