Development of the NPL wide-area MIR calibration source
A portable large area specular-diffuse secondary radiance transfer standard developed for the in-field calibration of remote sensing instrumentation for hot gas emission spectroscopy was designed, produced and characterised to a limited budget. The cavity has an aperture diameter of 102 mm was desig...
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University of Reading
2005
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| Online Access: | http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555860 |
| Summary: | A portable large area specular-diffuse secondary radiance transfer standard developed for the in-field calibration of remote sensing instrumentation for hot gas emission spectroscopy was designed, produced and characterised to a limited budget. The cavity has an aperture diameter of 102 mm was designed to have a known spectral radiance with a 1 % uncertainty in the 2.5 urn to 14 μm wavelength range. The prototype cavity is based around a grooved base that is electrically heated to temperatures up to 1000 K. The base has been applied with a high emittance coating, which was selected after extensive testing and does not deteriorate after repeated heating. Highly reflective walls surround the emitting base and are water-cooled. '. Coating selection was determined through reflectance measurements of both highly emitting and highly reflective coatings that were performed across the spectral range from 0.3 μm to 14 μm. The reflectance data was subsequently input into black body modelling software and Monte Carlo calculations were performed to optimise the design of the cavity. Problems regarding the heating elements within the emitting base lead to the development of a cost effective solution. Characterisation of the cavity was performed at a wavelength of 800 nm using filter radiometers. Large temperature discrepancies were observed across the cavity aperture and a correction factor was implemented to determine the temperature distribution across the cavity. The temperature distributions were input into black body modelling software and the cavity performance simulated. Radiance measurements of the cavity were performed using an FTIR spectrometer and the cavity emissivity determined to be 0.98 (±0.04) in the wavelength interval from 3.64 to 3.65 μm (the wavenumber interval from 2747 cm-I to 2740 cm"). |
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