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Spectral emissivity & brightness temperatures of platinum

Spectral emissivity and the relation of true temperatures and brightness temperatures of platinum
Robert E. Stephens
JOSA, Vol. 29, Issue 4, pp. 158-161 (1939)

Citation
R. E. Stephens, “Spectral emissivity and the relation of true temperatures and brightness temperatures of platinum,” J. Opt. Soc. Am. 29, 158-161 (1939)

ET10 Reflectometer Measures Emissivity

San Diego CA, USA –Surface Optics’ ET10 measures emissivity values in two most commonly used spectral regions, 3 to 5 and 8 to 12 microns.

Its main application is to produce emissivity values for the infrared cameras.

Advanced IR cameras require the input of an emissivity value for accurate temperature calculations. The emissivity values obtained from tables can be far from real leading to large temperature uncertainties.

The ET10 can be used in the lab or in the field and on small or large objects. With the ET10 one can measure emissivity of any surface in just a few seconds.

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Emissivity measurement and temperature correction accuracy considerations

Authors: Madding, Robert P.
Affiliation: AA(Inframetrics, Inc.)
Publication:
Proc. SPIE Vol. 3700, p. 393-401, Thermosense XXI, Dennis H. LeMieux; John R. Snell; Eds. (SPIE Homepage)
Publication Date:03/1999
Origin:SPIEAbstract Copyright:
(c) 1999 SPIE–The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Bibliographic Code: 1999SPIE.3700..393M
Abstract: Extraction of temperatures or temperature differences with thermography is not possible without knowledge of the target emissivity…

Emissivity Adaptation

A project under the Tufts University Research for Undergraduates 2000 Program described both theory and experiments related to welding of metals. Its report is online (CLICK HERE FOR FULL REPORT) and the Abstract is below.

Abstract

“The basic assumption behind the operating principle of modern thermal imaging thermometers is a “graybody approximation”. For a graybody, the emittance, reflectance and transmittance are constant for all wavelengths within the wavelengths within the waveband over which the instrument measures.

“In reality however, these factors change, and for applications that take place over a wide temperature range, the emissivity variation needs to be taken into account. This work suggests a method for an in-process emissivity identification and adaptation in order to dynamically calibrate infrared temperature measurement systems for applications like heat treatment, welding, cutting etc. A series of experiments has proven that once the spatial and temporal components of emissivity are decoupled, a model can be developed, which in conjunction with direct IR radiosity monitoring can provide information about the required emissivity compensation.”

Spectral Reflectivity of Epner Laser Gold

Courtesy of Epner Technology, Inc.

(CLICK ON GRAPH TO ENLARGE)
Almost everyone who attends the SPIE DSS Exposition and many other optical and optical engineering Conferences & Expos has received a gold-plated paper clip from Mr. David Epner, personally.

Well, the gold costing that Epner supplies to the optics industry has some interesting infrared reflectance (and emittance) properties.

Those properties, specifically the hemispherical spectral reflectance in the near, mid and far infrared is now available for all to view first hand on the Epner website.

A copy of the curve and the data related to it can be downloaded from the site, too.

Shown here, of course, is the Spectral Reflectance of “Laser Gold”, which as most know is the complement of Spectral Emittance at each and every wavelength from the formula: e(lambda) = 1 – r(lambda) – t(lambda),

where, respectively:

e is the emittance,
r is the reflectance,
t is the transmittance and
lambda is the wavelength (on this graph shown in units of micrometers). (Note: the usual expressions for these terms are in the Greek letters, epsilon, rho, tau and lambda and have been modified for use on this webpage)

The assumption most often made is that the transmittance of solid gold is zero, or so nearly so that it can be neglected.

That can be an false assumption in some cases according to the degree of precision required in a specific measurement situation. For instance, a very thin film of gold may be partially transparent especially in the long wavelength regions of the infrared and the optical properties on the material under the gold layer may come into play.Read More