10 December 2014 Transmittance of upwelling radiance at the sea surface measured in the field
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Abstract
The transmittance of upwelling radiance at the air-water interface is a critical quantity in ocean color remote sensing and is usually approximated as a constant (~0.54) for nadir-viewing geometries. Despite its important role, the radiance transmittance has never been measured and validated. In this paper, we present direct measurements of the spectral radiance transmittance in calm seas. The measurements were obtained by a customized instrument package equipped with two collocated radiometers. One radiometer measures the upwelling radiance just below the surface (Lu(0-)) while the other one directly records the water-leaving radiance (Lw) simultaneously. The ratio of measured Lw to Lu(0-) provides the transmittance. Our analyses suggest that the transmittance remains constant within ultraviolet and visible domain (350–700 nm) and is generally consistent with the theoretical approximations. In particular, the observed transmittance is within ±10% of the theoretical value for most portions of the spectral bands (350–600 nm). Within the red portion of the spectrum, the deviations are larger but are still less than 20%. The field observations suggest an optical closure is reached.
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Jianwei Wei, Jianwei Wei, Zhongping Lee, Zhongping Lee, Nima Pahlevan, Nima Pahlevan, Marlon Lewis, Marlon Lewis, } "Transmittance of upwelling radiance at the sea surface measured in the field", Proc. SPIE 9261, Ocean Remote Sensing and Monitoring from Space, 926105 (10 December 2014); doi: 10.1117/12.2073431; https://doi.org/10.1117/12.2073431
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