Development of a five-band multi-spectral infrared radiometer for low temperature measurements

Abstract

A five-band infrared radiometer has been developed for the measurement of spectral radiance and radiance temperature at low temperatures. The optical system of this radiometer consists of a scanning plane reflecting mirror, five narrow-band interference filters in the 6–12 μm band, a mirror-type rotating chopper, a cold source, a hot source, and a HgCdTe semiconductor detector. Measurement of radiance temperature and spectral radiance using this radiometer is carried out automatically using a personal computer. The calibration of the output signal for each spectral channel of the radiometer is carried out exactly using a blackbody source with an accurate temperature controller. The short-time stability of the radiometer is estimated to be within 0.2% mean deviation for the main spectral channel. The temperature detection sensitivity of a radiometer is evaluated as the noise equivalent temperature difference (NETD) for the optical and measuring system; the NETD for the main spectral channel is estimated to be about <0.2 °C. The minimum detectable radiance for the main spectral channel is also estimated to be about <0.002 mW/cm2 sr μm. For confirmation of the long-time stability of the radiometer, the measurement of the radiometer output ratio between the blackbody source at a temperature of 15 °C and the hot source at a constant temperature of 40 °C is carried out over 3 h; the long-time stability of measurement for the main spectral channel is estimated to be within ±0.3 °C mean deviation. The variation over time of the spectral radiance and the radiance temperature of the cloud in the sky was actually measured using the radiometer, and its usefulness was clarified.

Tunable filter comparator for spectral calibration of near-ambient temperature blackbodies

“…These results demonstrate a relative SSE of 4 10 3 − × within a 25 mm diameter source and indicate that SSE correction ≤ 3mK at 75º C. To test the measurement reproducibility, the same high quality waterbath BB was used twice: as a reference and as a unit under test with T = 50.073 C. The second high quality waterbath blackbody was used as another reference with a temperature 23.00º C [11]. The temperature of the first water bath BB was measured by the TFC and a platinum resistance thermometer (PRT).…”

“…Alternatively, there is another approach to the calibration of a near ambient BB based on relative measurements [2,3,4]. For calibration purposes, two blackbodies of known temperature and emissivity are used and the system response function is calculated.…”

Development of two-band infrared radiometer for irradiance calibration of target simulators

“…4, it is shown that the radiometer output voltage greatly depends on the set temperature of the blackbody source and the spectral channel, which can be explained by a few dominant factors including the wavelength dependence of the spectral transmittance of each optical filter, the numbers of neutral density filters, the spectral responsivity of the detector, and the spectral radiance of the blackbody source. 16 For example, the curves of SW seem like moving the curves of MW right by a distance, which means the trend of SW and MW is similar, but the voltage of MW is larger than the voltage of SW at the same temperature. This is mainly because the wavelength dependence of the spectral transmittance of each optical filter and the spectral responsivity of the detector.…”

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody

“…The radiometric characterization of the BB was performed using the tunable-filter comparator (TFC), which is based on relative radiance measurements [11][12][13]. Two reference blackbodies of known temperature and emissivity are used for calculation of the system response function.…”