Revised spectral optimization approach to remove surface-reflected radiance for the estimation of remote-sensing reflectance from the above-water method

Abstract

The effective sea-surface skylight reflectance ( ρ ) is an important parameter for removing the contribution of surface-reflected radiance when measuring water-leaving radiance ( L w ) using the above-water approach (AWA). Radiative simulations and field measurements show that ρ varies spectrally. To improve the determination of L w (and then remote sensing reflectance, R rs ) from the AWA, we further developed a wavelength-dependent model for ρ to remove surface-reflected radiance, which is applied with a spectral optimization approach for the determination of R rs . Excellent agreement was achieved between the AWA-derived and skylight-blocked approach (SBA)-obtained R rs (coefficient of determination > 0.92, mean absolute percentage deviation < ∼ 11% for R rs > 0.0005 sr -1 ), even during high wave conditions. We found that the optimization approach with the new ρ model worked very well for a wide range of water types and observation geometries. For developing remote sensing algorithms and evaluating satellite products, it would be beneficial to apply this approach to current and historical above-water in situ measurements of R rs to improve the quality of these data. In addition, this approach could also increase the number of useable spectra where previously rendered unusable when processed with a traditional scheme.