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  • Author or Editor: Gérard Brogniez x
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Gérard Brogniez, Christophe Pietras, Michel Legrand, Philippe Dubuisson, and Martial Haeffelin

Abstract

The performances of the new conveyable low-noise infrared radiometer for measurements of atmosphere and ground surface targets, or CLIMAT, are presented for in situ measurements. For this, quantitative analyses were carried out on measurements performed with a prototype during various field experiments. The accuracy of the radiometric measurements controlled by using a field blackbody is estimated for severe environmental conditions. Two modes of operation and two types of targets are described. Ground-based measurements of the sky radiance are compared to radiative transfer calculations that use atmospheric profiles from radiosoundings as input parameters. Sea surface temperatures estimated from airborne CLIMAT measurements are compared to satellite retrievals. These experiments constitute a first set of quantitative tests of the CLIMAT radiometer for ground-based and airborne remote sensing applications. They demonstrate that CLIMAT can be considered for future studies on clouds and aerosols, sea water, and surface such as ice, vegetation, bare soil, and rocks.

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Michel Legrand, Christophe Pietras, Gérard Brogniez, Martial Haeffelin, Nader Khalil Abuhassan, and Michaël Sicard

Abstract

The new infrared radiometer (conveyable low-noise infrared radiometer for measurements of atmosphere and ground surface targets, or CLIMAT) is a highly sensitive field instrument designed to measure brightness temperatures or radiances in the infrared, from the ground level, or from an aircraft. It can be equipped with up to six channels in the 8–14-μm range. This instrument is characterized by its portability (total mass less than 5 kg), its self-sufficiency, and its automated operation. It can be operated either manually or automatically. The optical head of the instrument contains an objective lens and a condenser mounted according to the Köhler design, providing a uniform irradiation on the detector and a well-delimited field of view. The radiation is measured by a low-noise fast thermopile whose responsivity is slightly temperature dependent. The radiometric noise expressed as an equivalent brightness temperature is on the order of 50 mK for a 1-μm bandwidth at room temperature. The application of a thermal shock reveals no noticeable degradation of the measurements, even though the cavity of the thermopile is not stabilized in temperature.

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Odran Sourdeval, Gérard Brogniez, Jacques Pelon, Laurent C.-Labonnote, Philippe Dubuisson, Frédéric Parol, Damien Josset, Anne Garnier, Michaël Faivre, and Andreas Minikin

Abstract

In the frame of validation of the spatial observations from the radiometer IIR on board CALIPSO, the two airborne campaigns Cirrus Cloud Experiment (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 Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) in space and time collocation. For this purpose, a Falcon-20 aircraft was equipped with the Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE)-New Generation (NG) and the thermal infrared radiometer Conveyable Low-Noise Infrared Radiometer for Measurements of Atmosphere and Ground Surface Targets (CLIMAT)-Airborne Version (AV), whose spectral characteristics are strongly similar to those of the infrared imaging radiometer (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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