A High-Accuracy Multiwavelength Radiometer for In Situ Measurements in the Thermal Infrared. Part I: Characterization of the Instrument

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-?m 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-?m 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.