A high-accuracy multiwavelength radiometer for in situ measurements in thethermal infrared. Part I: Characterization of the instrument

The new infrared radiometer (conveyable low-noise infrared radiometer for m easurements of atmosphere and ground surface targets, or CLIMAT) is a highl y 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-mu m range. This instru ment is characterized by its portability (total mass less than 5 kg), its s elf-sufficiency, and its automated operation. It can be operated either man ually or automatically. The optical head of the instrument contains an obje ctive lens and a condenser mounted according to the Kohler design, providin g a uniform irradiation on the detector and a well-delimited field of view. The radiation is measured by a low-noise fast thermopile whose responsivit y is slightly temperature dependent. The radiometric noise expressed as an equivalent brightness temperature is on the order of 50 mK for a 1-mu m ban dwidth at room temperature. The application of a thermal shock reveals no n oticeable degradation of the measurements, even though the cavity of the th ermopile is not stabilized in temperature.