Validation of IIR/CALIPSO Level 1 Measurements by Comparison with Collocated Airborne Observations during CIRCLE-2 and Biscay '08 Campaigns
Résumé
In the frame of validation of the spatial observations from the radiometer IIR onboard CALIPSO, the two airborne campaigns 'CIRCLE-2' and 'Biscay 08' took place in 2007 and 2008 in the western part of France, over the Atlantic Ocean. During these experiments, remote sensing measurements were made over cirrus clouds, right under the track of CALIPSO in space and time collocation. For this purpose, a Falcon-20 aircraft was equipped with the lidar LEANDRE-NG and the thermal infrared radiometer CLIMAT-AV, whose spectral characteristics are strongly similar to those of IIR. In situ measurements were also taken in cirrus clouds during 'CIRCLE-2'. After comparisons, consistent agreements are found between brightness temperatures measured by CLIMAT-AV and IIR. However, deviations in the brightness temperature measurements are still observed, mainly in the 8.6-μm channels. Simulations using a radiative transfer code are performed along a perfectly clear sky area to show that these dissimilarities are inherent in slight differences between the spectral channels of both radiometers, and in differences between their altitudes. Cloudy and imperfectly clear areas are found to be harder to interpret, but the measurements are still coherent by taking into account experimental uncertainties. In the end, IIR measurements can be validated unambiguously.
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