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20 December 1996 Airborne stratus measurement and comparison with NUALUM code
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Airborne measurement of stratus is being carried out by ONERA in order to validate NUALUM cloud simulation. The cloud top is measured by a circular variable filter cryogenic spectrometer SICAP. Two observation zenith angles are tested and the azimuth angle is variable. In situ liquid water content (LWC) measurement in performed by a Johnson Williams probe and compared with meteorological sounding. The liquid water content has been valuated inside a layer from 200m to 600m altitude. Mean LWC is equal to 0.3g/m3. Those values are typical of a stratus. The NUALUM cloud radiative transfer code has been developed at ONERA. The optical properties are computed by MIE theory. NUALUM includes the DISORT code to compute the multiple scattering in the cloud, by the mean of the discrete ordinates method. Spectral measurements show great variations of the radiation according to the azimuth angle when the wavelength is less than 4 micrometers . In this range of wavelength, radiation provides from solar reflection which is very sensitive to the scattering angle. Above 4 micrometers , thermal radiance increases. A good correlation is observed between the shape of the phase function of cloud particles and the radiance variation with scattering angle. NUALUM is in agreement with the stratus spectral measurements. During the experiment, sea spectral measurements have also been carried out. Solar reflection on the sea surface of the sea is specular and only occurs for low scattering angles.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Claire Malherbe, Pierre Simoneau, A. Boischot, Gerard Durand, and G. Gregoire "Airborne stratus measurement and comparison with NUALUM code", Proc. SPIE 2961, Satellite Remote Sensing and Modeling of Clouds and the Atmosphere, (20 December 1996);

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