Foam effect on the sea surface emissivity in the 8–14 μm region

[1] The effect of foam on the sea surface emission has been studied in the microwave region, but its effect on thermal infrared emissivity and temperature has not been sufficiently analyzed in the literature. This paper presents thermal infrared measurements of foam-covered seawaters carried out under controlled conditions using a multichannel radiometer working in the 8–14 μm region. The experimental data show a negligible foam effect at low observation angles but a significant increase of emissivity with foam at angles above 45°. Differences between foam and foam-free emissivities are about +0.04 for observation angles of 65°, depending slightly on the radiometric spectral band. The effect of foam is to reduce the angular variation of seawater emissivity. The foam and foam-free emissivity differences yield to differences up to 2.5 K in terms of sea surface temperature (SST), even larger than 1.2 K when the SST is retrieved from satellite using a split window technique. The correction of the foam effect on emissivity could be performed using an estimate of the fraction of sea covered by foam. This correction could improve the SST retrieval, mainly for measurements at large observation angles.

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