Thermal infrared transfer radiometer (TXR)

Thermal-infrared Transfer Radiometer (TXR) is used for verifying radiance scales in the thermal-infrared spectral region of near-room-temperature extended-area blackbody sources either in vacuum chambers or ambient condition laboratories. The TXR is a portable radiometer with two channels, one at 5 µm and the other at 10 µm. It uses a photovoltaic InSb detector for the 5-µm channel, and a photovoltaic mercury cadmium telluride (MCT) detector for the 10-µm channel. The detectors, filters, and reflective optics are built into a liquid-nitrogen cryostat, and the entire radiometer is vacuum/cryogenic compatible and designed to be deployed inside of the typical space-simulating vacuum chambers used for space-flight instrument calibrations. The TXR has a self-contained vacuum jacket and liquid-nitrogen reservoir, and so can be also used in a typical laboratory environment with the outer case of the cryostat at ambient pressure and room temperature. This allows it to be characterized and calibrated by a full array of infrared facilities in the Optical Technology Division at NIST, much of it in an ambient laboratory environment.

The uncertainty for radiance measurements using the TXR is of the order of 0.2 % or better. The total uncertainty depends not only on the transfer uncertainty but also the uncertainty of the primary radiance scale used to calibrate it at NIST. NIST is currently improving several methods for calibrating the TXR. The primary method uses either the ambient background water bath blackbody and/or the MBIR Large Area Blackbody for the absolute calibration. Another is a system-level approach using a laser-illuminated integrating sphere at the NIST SIRCUS facility. The TXR has been successfully deployed about six different times during the past several years to several different aerospace calibration facilites, where it performed in-situ measurements of various sources in a space-simulating chambers. These measurements were used to verify the infrared radiance scales in currently used by several NASA, NOAA, DOE, and DOD satellite programs. The TXR is maintained at NIST when it is not on a deployment.