ASTM E307-72(2002)

ASTM E307-72(2002):

Standard Test Method for Normal Spectral Emittance at Elevated Temperatures

Developed by Subcommittee: E21.04

Book of Standards Volume: 15.03
"1. Scope

"1.1 This test method describes a highly accurate technique for measuring the normal spectral emittance of electrically conducting materials or materials with electrically conducting substrates, in the temperature range from 600 to 1400 K, and at wavelengths from 1 to 35 ?m.

"1.2 The test method requires expensive equipment and rather elaborate precautions, but produces data that are accurate to within a few percent. It is suitable for research laboratories where the highest precision and accuracy are desired, but is not recommended for routine production or acceptance testing. However, because of its high accuracy this test method can be used as a referee method to be applied to production and acceptance testing in cases of dispute.

"1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.

"1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use."

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS. PART 5

Title: STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS. PART 5. NORMAL SPECTRAL EMITTANCE, 800-1400 K (ABSTRACT BELOW)
DOWNLOAD FULL REPORT IN PDF FORMAT


Corporate Author : NATIONAL BUREAU OF STANDARDS GAITHERSBURG MD

Personal Author(s) : Harrison, William N. ; Richmond, Joseph C. ; Shorten, Frederick J. ; Joseph, Horace M.

Handle / proxy Url : http://handle.dtic.mil/100.2/AD426846

Report Date : NOV 1963

Pagination or Media Count : 99

Abstract: Equipment and procedures were developed to measure normal spectral emittance of specimens that can be heated by passing a current through them, at temperatures in the range of 800 to 1400 K, and over the wavelength range of 1 to 15 microns. A data-processing attachment for the normal spectral emittance equipment was designed to (1) automatically correct the measured emittance for '100% line' and 'zero line' errors on the basis of previously-recorded calibration tests; (2) record the corrected spectral emittance values and wavelengths at preselected wavelength intervals on punched paper tape in form suitable for direct entry into an electronic digital computer; and (3) to compute during a spectral emittance test on a specimen the total normal emittance, or absorptance for radiant energy of any known spectral distribution of flux, of the specimen. Working standards of normal spectral emittance having low, intermediate and high emittance values, respectively, were prepared and calibrated for use in other laboratories to check the operation of equipment and procedures used for measuring normal spectral emittance.

Spectral Emittance...Ash-Like Deposits

Spectral Emittance of Particulate Ash-Like Deposits: Theoretical Predictions Compared to Experimental Measurement, Journal of Heat Transfer -- April 2004 -- Volume 126, Issue 2, pp. 286-289

S. P. Bhattacharya

Cooperative Research Centre for Clean Power from Lignite, 8/677 Springvale Road, Mulgrave, Victoria 3170, Australia
(Received September 11, 2002; revised July 1, 2003)

From  the Abstract: "This note presents results of a theoretical and experimental investigation on the emittance of particulate deposits."

Source Abstract

Cool Roofing Samples (Emittance)

The Heat Island Group at Lawrence Berkeley National Laboratory, Berkeley, CA have measured solar reflectance of roofing samples with an UV-VIS-NIR Spectrometer with an integrating sphere and they measured the spectral emittance of the samples with a FTIR Spectral Emissometer. The following writeup and graphs are from their webpageat eetd.lbl.gov/HeatIsland/CoolRoofs/Samples.html


"Below are examples of complete reflectance and emittance data for several metal roofing samples made of cool roofing materials. These measurements show examples of complete laboratory information needed to determine radiative heat exchange by a roof which, in turn, can be used to estimate peak roof temperatures.

"The spectral solar reflectance is the total reflectance (diffuse and specular) as a function of wavelength, across the solar spectrum (wavelengths of 0.3 to 2.5 µm). It is used to compute the overall solar reflectance, using a standard solar spectrum as a weighting function. It also contains the information in the visual range (0.4 to 0.7 µm) which is sufficient to compute the color coordinates for color matching with other materials.

"The spectral thermal emittance (the graphs on the right) contains the information for computing the overall thermal emittance, using a blackbody curve as the weighting function. The spectral range is about 5 to 40 µm. If the spectral thermal emittance is approximately a horizontal line (a "gray" body), then the overall emittance is adequate for computing longwave radiative radiative exchange between the roof and the atmosphere. If the spectral thermal emittance deviates markedly from a horizonal line, then the details of the spectral emittance and the atmospheric emittance are necessary for a complete computation.

Note that the hunter green sample (middle graph) looks green to the eye because of the reflectance "bump" at 0.5 µm. The average solar reflectance, at 0.086, is almost as low as black (zero).""The burgundy sample (bottom graph) looks red due to the increase in reflectance near 0.7 µm. The visible reflectance is only about 0.1, but the relatively high reflectance in the near infrared (0.7 to 2.5 µm) yields an overall solar reflectance of 0.226."The emittance for all these samples is roughly 0.9, with an abrupt fall-off near 6 µm. Link to: Roof Heat Transfer > Emittance"

"

Galvalume (top graph), due to the inclusion of aluminum metal in the zinc anti-corrosion coating, is more reflective to sunlight than traditional galvanized steel which has a solar reflectance around 0.5.A further coating, with a clean acrylic material (low graph), can be used to raise the infrared emittance without significantly changing the solar reflectance.

Emissivity Tips at IRINFO.ORG

For your reference, there are several that deal with emittance that may be of interest to you.

For your convenience, they are on the IRINFO.org web pages at the following links:

www.irinfo.org/tip_of_week_2004.html#t02092004

www.irinfo.org/tip_of_week_2004.html#t04052004

www.irinfo.org/tip_of_week_2003.html#t09292003

www.irinfo.org/tip_of_week_2004.html#t08022004

www.irinfo.org/tip_of_week_2005.html#t09122005

www.irinfo.org/tip_of_week_2005.html#t09192005

www.irinfo.org/tip_of_week_2005.html#t09262005

<a href="http://www.irinfo.org/tip_of_week_2007.html#t05282007" title="http://www.irinfo.org/tip_of_week_2007.html" target="_blank">www.irinfo.org/tip_of_week_2007.html#t05282007

Enjoy!

Emissivity and Optical Properties of UO(2)

Emissivity and Optical Properties of UO₂

• Discussion of Data Assessment/Analysis


• References

Tabulated Values:

• Table 1: Normal Spectral Emissivity of Premelted UO₂ at a Wavelength of 630 nm


• Table 2: Normal Spectral Emissivity of Liquid UO₂ at a Wavelength of 630 nm

Graphs:

• Fig. 1: UO₂ Emissivity


• Fig. 2: Average Refractive Index of UO₂


• Fig. 3: Average Refractive Index of UO₂ from Measurements of Bober et al.


• Fig. 4: Average UO₂ Absorption coefficient from Measurements of Bober et al.

NASA Tech Reports Emittance Abstracts

A Search on the NASA website results in the following abstracts






DETERMINATION OF THE EMISSIVITY OF MATERIALS

Author(s): Askwyth, W. H.
Abstract: Space power systems - emissivity of candidate materials for snap-8 powerplant
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2006-11-06
Accession Number: 63N11697; Document ID: 19630001823; Report Number: PWA-2088





Determination of emissivity of materials quarterly progress report, 1 jul. - 30 sep. 1962

Author(s): Askwyth, W. H.; Hayes, R. J.
Abstract: No Abstract Available
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2006-11-06
Accession Number: 67N83465; Document ID: 19670084086; Report Number: NASA-CR-83756, PWA-2128





EMITTANCE OF MATERIALS SUITABLE FOR USE AS SPACECRAFT RADIATOR COATINGS

Author(s): Askwyth, W. H.; Hayes, R. J.; Mikk, G.
Abstract: Emittance measurements of materials suitable for spacecraft radiator coatings
NASA Center: NASA (non Center Specific)
Publication Year: 1963
Added to NTRS: 2006-11-06
Accession Number: 63A24987; Document ID: 19630028928





Measurement of spectral normal emittance of materials under simulated spacecraft powerplant operating conditions

Author(s): Askwyth, W. H.; House, R. D.; Lyons, G. J.
Abstract: Spectral normal emittance of materials under simulated space environment
NASA Center: NASA (non Center Specific)
Publication Year: 1963
Added to NTRS: 2006-11-06
Accession Number: 64N10959; Document ID: 19640001050





THE EMITTANCE OF MATERIALS SUITABLE FOR USE AS SPACECRAFT RADIATOR COATINGS

Author(s): Askwyth, W. H.; Hayes, R. J.; Mikk, G.
Abstract: Emittance of materials suitable for use as spacecraft radiator coatings
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2006-11-06
Accession Number: 63N10264; Document ID: 19630000390; Report Number: ARS PAPER-2538-62





THE EMITTANCE OF MATERIALS SUITABLE FOR USE AS SPACECRAFT RADIATOR COATINGS

Author(s): Askwyth, W. H.; Hayes, R. J.; Mikk, G.
Abstract: Measurements of total hemispherical emittance for materials suitable for high-temperature spacecraft radiation coatings
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2006-11-06
Accession Number: 63A11692; Document ID: 19630015633; Report Number: ARS PAPER 62-2538





A SIMPLE TECHNIQUE FOR DETERMINING TOTAL HEMISPHERICAL EMITTANCE BY COMPARING TEMPERATURE DROPS ALONG COATED FINS

Author(s): Askwyth, W. H.; Curry, R.; Lundberg, W. R.
Abstract: Determination of total hemispherical emittance by comparing temperature drops along coated fins
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2006-11-06
Accession Number: 62N17085; Document ID: 19620007085





Measurement of total hemispherical emittance of structural materials and coatings under simulated spacecraft conditions

Author(s): Askwyth, W. H.; Mikk, G.
Abstract: Hemispherical emittance of structural materials and amp coatings under simulated spacecraft conditions over wide temperature range
NASA Center: NASA (non Center Specific)
Publication Year: 1963
Added to NTRS: 2006-11-06
Accession Number: 64N10962; Document ID: 19640001053





Determination of the emissivity of materials

Author(s): Askwyth, W. H.; Hayes, R. J.; House, R. D.; Mikk, G.
Abstract: No Abstract Available
NASA Center: NASA (non Center Specific)
Publication Year: 1962
Added to NTRS: 2004-11-03
Accession Number: 76N78693; Document ID: 19760073652; Report Number: NASA-CR-148751, PWA-2206(VOL.1)





Determination of the emissivity of materials

Author(s): Askwyth, W. H.
Abstract: No Abstract Available
NASA Center: NASA (non Center Specific)
Publication Year: 1961
Added to NTRS: 2004-11-03
Accession Number: 82N70372; Document ID: 19820065104; Report Number: NASA-CR-164941, PWA-2043

Measurement of spectral emissivity of samples, coatings and infrared sources

A reference laboratory for calibration of infrared instruments was established at Risø, Denmark in 1996.

The following services are offered for customers:

• calibration service of infrared thermometers and calibration sources;


• calibration of FTIR spectrometers and advanced infrared instrumentation;


• measurement of spectral emissivity of samples, coatings and infrared sources;


• consultative service and information.

An introduction to non-contact measurement of temperature is given in the report "Measurement of Temperature by Means of Infrared Instruments", Risø-R-862(DA).

The report (in Danish) is available on request.

Risø National Laboratory
Technical University of Denmark – DTU
Frederiksborgvej 399 · P.O. 49 · DK-4000 Roskilde ·
Tel: +45 4677 4677
Fax: +45 4677 5688
Email: risoe@risoe.dk
EAN: 5798000416611 · CVR: DK42154113

Optical Properties Measurements, Data and 3D Models

Surface Optics Corporation (SOC) operates a world-class measurement facility equipped for the most demanding spectral measurement tasks for spectral directional and bidirectional reflectance measurements for modeling, simulation, special effects and more.

Spectral measurements can be made in wavelength regions from the ultraviolet to long wave infrared and include one or all of the following types of reflectance measurements:

Directional or hemispheric reflectance: the fraction of the light incident on a sample at a given angle that is reflected back into the hemisphere.

Bidirectional Reflectance Distribution Function (BRDF): the distribution of light, described as a function of two angles, reflected back into the hemisphere from light incident at a given angle on a sample.

Monostatic Bidirectional Reflectance(enhanced backscatter measurement): a small portion of the BRDF measured at the direct backscattered angle using a laser interferometric reflectometer.

SOC also develops and expands on its off-the-shelf library of optical properties data for a variety of materials. This library can be purchased in whole or in part at considerable savings over the cost of individual measurements.

For more information on our database and its contents contact SOC.

You can also download the Optical Properties Database brochure.

A list of FAQs regarding the database, and information on using the databases in 3D sensor simulation.

1. Spectral Reflectance Data for (52) rocks, (29) soils, (28) vegetation types, (41) construction materials, (38) paints, and (12) fabrics from 0.3 to 25 microns.


2. Hemispherical, Directional, Diffuse and Specular


3. Surface temperatures versus time-of-day, climate and orientation


4. Complete solution for visual and infrared radiance simulation.

3D Models for Sensor Simulation

SOC is constantly developing computationally efficient polygonal models for accurate sensor simulation.

Unlike visual simulation models, sensor models require an intimate understanding of the physical nature and physics responsible for the signature of an object.

SOC's extensive background in both Infrared and Radar sensor simulation and analysis is incorporated into all of our 3D models.

Evaluating Emittance in the Lab or Field

NASA Portable Infrared Reflectometer Designed and Manufactured

The optical properties of materials play a key role in spacecraft thermal control. In space, radiant heat transfer is the only mode of heat transfer that can reject heat from a spacecraft.

One of the key properties for defining radiant heat transfer is emittance, a measure of how efficiently a surface can reject heat in comparison to a perfect black body emitter.

Heat rejection occurs in the infrared region of the spectrum, nominally in the range of 2 to 25 micrometer.

To calculate emittance, one obtains the reflectance over this spectral range, calculates spectral absorptance by difference, and then uses Kirchhoff’s Law and the Stefan-Boltzmann equation to calculate emittance.

Portable infrared reflectometer for evaluating emittance. Photo from NASA

A portable infrared reflectometer, the SOC–400t, was designed and manufactured to evaluate the emittance of surfaces and coatings in the laboratory or in the field.

It was developed by Surface Optics Corporation under a contract with the NASA Glenn Research Center at Lewis Field to replace the Center’s aging Gier-Dunkle DB–100 infrared reflectometer.

The specifications for the new instrument include a wavelength range of 2 to 25 micrometer; reflectance repeatability of ±1 percent; self-calibrating, near-normal spectral reflectance measurements; a full scan measurement time of 3.5 min, a sample size of 1.27 cm (0.5 in.); a spectral resolution selectable from 4, 8, 16, or 32 cm^–1; and optical property characterization utilizing an automatic integration to calculate total emittance in a selectable temperature range.

The computer specified to drive the software is a laptop with a menu-driven operating system for setup and operation, a full data base manager, and a full data analysis capability through MIDAC Grams/32 software (MIDAC Corporation, Irvine, California).

Spectral scanning is achieved through the use of a Fourier Transform Infrared (FTIR) Michelson interferometer. In addition, the reflectometer’s size and weight make it conducive to portable operation.

Although most of the planned uses for the instrument are expected to be in the laboratory, some field operations are anticipated. The only requirement for field operation is a source of power (115 V alternating current).

NASA Glenn took delivery of this world-unique, portable infrared reflectometer in January 1999. It is a resounding success, and an evaluation of thermal control materials for NASA and aerospace customers is currently underway.

Find out more about this research.

Glenn contact: Dr. Donald A. Jaworske, (216) 433–2312, Donald.A.Jaworske@grc.nasa.gov

Author: Dr. Donald A. Jaworske

Headquarters program office: OSS (ATMS)

Programs/Projects: Space Power, ISS, Aerospace Industry

Journal of the Atmospheric Sciences

Article: pp. 1459–1472 | Abstract | PDF (1.02M)

Infrared Emittance of Water Clouds

Petr Chýlek^a, Peter Damiano^a, and Eric P. Shettle^b

a. Atmospheric Science Program, Department of Physics and Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada
b. Optical Sciences Division, Naval Research Laboratory, Washington, D.C.

Chýlek, P., P. Damiano, and E.P. Shettle, 1992: Infrared Emittance of Water Clouds. J. Atmos. Sci., 49, 1459–1472.

ABSTRACT

A simple approximation has been developed for the infrared emittance of clouds composed of water spheres based on the absorption approximation for the emittance and on the polynomial approximation to the Mie absorption efficiency. The expression for the IR emittance is obtained in a simple analytical form as a function of the liquid water content and two size distribution parameters, namely, the effective radius and effective variance. The approximation is suitable for numerical weather prediction, climate modeling, and radiative transfer calculations. The accuracy, when compared to the exact Mie calculation and integration over the size distribution, is within a few percent, while the required computer time is reduced by several orders of magnitude. In the limit of small droplet sizes, the derived IR emittance reduces to a term proportional to the liquid water content.

18 Emissivity FAQs at evitherm

Emissivity & other infrared-optical properties FAQs at the evitherm website,
evitherm is the European Virtual Institute for Thermal Metrology

---

Click on the number below for an answer on the evitherm website...

C1. What is the emissivity of a surface?
C2. Why is emissivity important?
C3. How is emissivity used?
C4. Is it easy to measure emissivity?
C5. Is it possible to predict or calculate emissivity?
C6. What type of emissivity should I use for my application: total emissivity or spectral emissivity?
C7. What is the emissivity of painted metal surfaces and how does it depend on layer thickness?
C8. Which surfaces behave like a grey body?
C9. What is the emissivity of a layer of gas?
C10. Where can I find information on the emissivity of a given surface?
C11.How can I measure the emissivity of a surface using an IR-thermometer?
C12. What is the difference between emissivity and emittance?
C13. What is a radiant barrier?
C14. What is a low-e coating?
C15. What is low-e glass?
C16. What is a selective absorber?
C17. Is a knowledge of emissivity important for contactless temperature measurements?
C18. What is infrared thermography?

Furnace radiation modelling

Furnace radiation modeling

Location: Industrial Research Limited (IRL): Measurement Standards Laboratory of New Zealand
Their Client: New Zealand Refining Company
The Topic: Infrared radiation thermometry for furnace tube temperature measurement
Client benefit: High quality measurement leads to better plant control, reduced risk and increased profitability

Most of this article is from the writeup on the IRL website.

Industrial Research undertook furnace radiation modeling for the New Zealand Refining Company which operates several large furnaces in many stages of the production of gasoline (Also known around the world variously as "petrol" and "benzene").

Thermal infrared radiation thermometry, or IR Thermometry, is the only feasible method for obtaining temperature measurements of many furnaces and the process tubes within.

The technology is not new, it was known that the measurements suffer from errors stemming from several environmental factors such as reflection of background thermal radiation and absorption and emission of the emitted & reflected radiation (from the surfaces being measured, by furnace gases.

Variations in the spectral emissivity and reflectivity of the materials comprising the surfaces being measured also influence the resulting temperature measurements.

The New Zealand Refining Company used the knowledge and background offered by Industrial Research's Measurement Standards Laboratory in furnace radiation modelling to obtain more accurate measurements.

The service gave increased confidence that safe and efficient operating parameters were being maintained. As a result, the plant can operate more efficiently through the operators being able to better predict plant life and tube life.

Inconel, Inconel-X and Type 347 SS

Effects of Preoxidation Treatments on Spectral Normal and Total Normal Emittance of Inconel, Inconel-X and Type 347 Stainless Steel


Authors: Wayne S. Slemp; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER


Abstract:

The spectral/normal-emittance values of several oxidized surfaces prepared by varying the preoxidation treatments or oxidation time for inconel, Inconel-X, and type 347 stainless steel were determined at temperatures of 900, 1,200, l,500, and 1,800 F over a wavelength range of 1 to l5 microns. Polishing, grit blasting, etching, or combinations of these preparations were used as preoxidation treatments. These values were compared for 900 and 1,800 F to determine the effects of these treatments on the spectral-normal-emittance values. Significant effects of preoxidation treatments and oxidation times on the spectral normal emittances of oxidized inconel, Inconel-X, and type 3k7 stainless steel are presented. In general, if a grit-blasted surface is etched before being oxidized, the final oxidized surface will have a lower emittance but will be more adherent and uniform. Of the two types of grit used in this study, the coarser grit provided the higher emittance. Polishing provided the lowest emittance of all specimens tested. In the one set of tests in which oxidation time was varied (on the inconel specimens), increasing oxidation time increased the emittance; however, increasing the time beyond 2 hours produced no further effect.

NIST IR Spectral Emittance Lab

The Optical Properties measurements laboratory at The USA National Institute of Standards & Technology (NIST), a part of the Optical Technology Division of the PHYSICS Laboratory has been developing a full spectral emissivity (emittance) measurement capability.

This facility enables the measurement of spectral emittance using the direct method of radiance comparison of the sample with a blackbody reference source. Spectral emissivity is a key physical property in the determination of radiation transfer and balance.

Numerous industrial and scientific applications, such as remote sensing and single- and multi-band pyrometry, require its accurate determination.

_{Layout of the NIST Setup for Direct and Indirect Infrared Spectral Emittance Measurements}

The sample emittance is determined through a series of measurement steps. The first step is a measurement of the sample’s hemispherical-directional reflectance at the measurement temperature and at a single wavelength matched to the filter radiometer. A diode laser or broadband source input to the integrating sphere, is selected based on the temperature and rough emittance value of the sample. The reflectance is obtained via comparison to a calibrated standard.

The second step is a relative radiance measurement of the sample to a blackbody at the same wavelength. The integrating sphere is removed for the second step. The temperature is then calculated from the results of these two steps. This procedure has the benefit of obtaining the temperature of the sample from the region on the sample identical to that for which the infrared spectral emittance is measured. It also makes use of the steep short wavelength edge of the Planck function for sensitive (and higher accuracy) temperature measurement.

Finally, the Fourier transform infrared spectrometer is used to compare the sample spectral radiance to that of the reference blackbody source as a ratio, and the sample emittance is obtained from the ratio and Planck’s Law using the sample and blackbody temperatures.

Alternatively, spectral directional emittance can be determined indirectly from reflectance and transmittance measurements described in Infrared Spectrophotometry. These capabilities have limits of temperature, measurement geometry and sample type.
Specifications / Capabilities:

The facility consists of a set of reference blackbody sources mounted on a motorized stage for selection; interchangeable sample heater/mounts on motorized translation and rotation stages; a removable visible/near-infrared integrating sphere for measuring the sample temperature above 500 K; low scatter interface optics to image the 3 mm to 5 mm central region of the sample or blackbody source onto a water cooled field stop; the field stop is re-imaged onto either a Fourier transform spectrophotometer equipped with beamsplitters and detectors to cover a spectral range from the visible through the far infrared or a set of filter radiometers mounted on a motorized translation stage for temperature scale transfer between the blackbody sources and for sample temperature determination (together with the integrating sphere); a sectored purge enclosure for the entire beam path; electrical supply, signal, purge gas (Ar, or N2), and cooling water subsystems; control of system elements and data processing via several PC computers using LabView software programs.

Each blackbody contains calibrated platinum resistance thermometer (PRT) or thermocouple (TC) temperature sensors. These are used to control and monitor changes in the blackbody temperature. For absolute temperature determination, two fixed point BB furnaces with interchangeable crucibles (containing Ag, Al, Zn, Sn and In) are used.

Filter radiometers (with filters at 650 nm, 900 nm, 1550 nm, and 2400 nm) are used to transfer the scale from the fixed points to 4 variable temperature blackbody’s covering a temperature range of 250 K to 1400 K. The spectral emissivities of the blackbodies have been calculated using a Monte Carlo ray tracing algorithm with input of the measured spectral reflectance of the cavity wall materials or coatings.

Associated Programs/Projects:

Infrared optical properties of materials and components
Fourier transform infrared spectrometer (FTIS) facility

Selected Publications

Infrared Spectral Emissivity Characterization Facility at NIST, L.M. Hanssen, S.N. Mekhontsev, and V.B. Khromchenko,Proc. SPIE 5405, 112 (2004).

Temperature-Resolved Infrared Spectral Normal Emissivity of SiC and Pt-10Rh for Temperatures up to 900 C

Use of a High Temperature Integrating Sphere Reflectometer for Surface Temperature Measurements, L.M. Hanssen, M. Noorma, A.V. Prokhorov, S.N. Mekhontsev, and C.P. Cagran, Intl. J. Thermophysical Prop.

Beginner's Guide to (Spectral) Emissivity

Introductory Guide to Emissivity

This is an introductory page on the National Physical Laboratory (NPL) website in the UK.

It has several such sketches as on the left showing the concept of the "radiometric method" of emissivity measurement and discusses both the concepts and measurement methods used to quantify spectral and total emissivity values.

The page also features links to other resource materials on the subject and a list of reference books.

Red, White & Blue Blackbodies?

It is not an oxymoron, nor a quote from Yogi Berra.

Real Blackbodies do not exist, at least on Earth. Only approximations or simulations are real. We use them to calibrate IR Thermometers, Radiation Pyrometers and Thermal Imagers.

Technically they should have a spectral emissivity very close to 1.0. How close, you might ask? Read on.
Max Planck needed the concept of a perfect absorber of electromagnetic, thermal radiation to develop his theory of Thermal Emission of Radiation in 1899. Fortunately, Gustav Kirchhoff had already develped the foundation for them forty years earlier.

A perfect blackbody is perfectly absorbing to all the thermal radiation incident upon it. For that reason it had, necessarily, to be opaque and non-reflecting.

By logical reasoning, it was also clear that the same device had to be a perfect emitter of thermal radiation related to its absolute temperature, that is, temperature on the Absolute or Kelvin Temperature Scale.

There are several radiation equations or "Laws" that have been developed to describe the physics of thermal emission properties. They are well explained in a number of texts and shown in some detail in the online Hyper Physics website.

In an online Java applet, one can see visually also the three main radiation laws in graphic action; the temperature on the screen is shown on a column in a thermometer on the right side, and you can change it by clicking and/or dragging on it with your mouse.

If someone asks about the color of a blackbody, you can always refer them to this great set of webpages by Mitchell Charity at MIT.
They show both the temperature from 1000 K to 29,800 K (of course below about 700 K blackbodies actually look black to the human eye) . As can be seen on this page, red, white and blue blackbodies are possible!

There aren't many 29,800 K blackbodies on Earth, but astronomers & AstroPhysicists see them all the time. How do you think they measure the temperatures of stars?

So, now you know, there can be both Red and Blue Blackbodies!

The devices used by calibration laboratories to calibrate and check the calibration of IR Thermometers, Radiation Thermometers and Infrared Thermal Imagers are not perfect (and seldom Blue, but often appearing Black, Red, Orange, Yellow and even White), but they can be very close to perfect.

The closer to perfection, the higher the cost of them also.

A blackbody having a spectral emissivity of 0.99 would have, at best, an error of about ± 1% in emitted thermal radiation or radiance, at a stable operating temperature and could be used to calibrate Infrared Thermometers.

The thermometers would be limited in their calibration uncertainty, since the radiance they emit would be uncertain to at least ± 1%.

Depending upon the radiance to temperature relationship for the temperature in question, that could mean a bigger or smaller effective temperature calibration uncertainty that could be assigned to a thermometer being calibrated.

That's another issue for another time, but , if you can't wait, one of the best explanations (and a lot more) that we have seen on that subject is in a 547 KB, downloadable PDF file from Land Instruments.

Effects of atmosphere, temperature and emittance on reflected and emitted energy

A NASA report by R. Kumar, dated Sep 1, 1977, available online and downloadable as a PDF document.

ABSTRACT:

The effects of temperature and emittance on the relative magnitude of reflected energy and emitter energy from a target including atmospheric effects was studied. From the calculations of energy reflected and emitted from a target including atmospheric effects using LOWTRAN 3 programs for midlatitude summer model, the following conclusions were obtained (1) At 3.5 micrometers q is considerably less than 1 except at high temperatures and for high emittance (2) at 4 micrometers q is of the order of magnitude equal to 1 for most targets and (3) at 4.6 micrometers, q is considerably greater than 1 at high temperatures and high emittance. In addition, incident atmospheric emission reflected from the target was found to be negligible except for targets having low temperature and low emittance.

New System for Spectral Emissivity Measurements & Spectral Emissivity of Metals at the University of Duisburg

On the 13-15 June, 2001, in Budapest, Hungary, the 12th International Conference on Thermal Measurements and Thermogrammery (THERMO) was held.

Among the papers were two by Prof. Dr.-Ing. W. Bauer, Dipl.-Phys., A. Moldenhauer, Dipl.-Phys. & M. Rink of the Gerhard Mercator Universität Duisburg, Germany

The first presentation was entitled:

"New System for Spectral Emissivity Measurements at the University of Duisburg"

(Click on the link to access the Abstract in PDF Format)

The second was:

"Spectral emissivities of metals dependent on heat-treating processes".

(Click on the link to access the Abstract in PDF Format)

Other papers by the members of the Duisburg Universitat have their abstracts listed on this Conference information page, also.

Contacts for more information are:

Prof. Dr. Ing. W. Bauer, Gerhard-Mercator-Universität, Duisburg, Germany

Fachbereich 8, Fachgebiet Energieeinsatz(Germany)
47048 Duisburg
Tel.: +49 203/379-3629
Fax.: +49 203/379-3464

Prof. Dr. Ing. W. Bauer

Email: bauer [at] ihg.uni-duisburg.de

and

Thomas Funke Dipl.-Ing.


Email: Thomas.Funke [at] uni-duisburg.de

Homepage: www.ihg.uni-duisburg.de/energieeinsatz/

Spectral and Total Emissivity Measurement Services at Near Ambient Temperatures

The National Physical Laboratory in The UK offers a title="Emissivity Measurement Service -PDF Downloadable Brochure" target="_blank">spectral emissivity measurment service (downloadable brochure - PDF 284kb) through its Infrared Optical Spectroscopy group to measure the spectral emissivity as needed by customers.

They also offer related calibration measurement services on their webpage as stated below:

"Optical Properties of Materials Measurement Service offers calibrations in the areas of Spectrophotmetry (reflectance and transmittance measurements, colorimetry, measurement of appearance) and Infrared Spectrometric Measurements (reflectance and transmittance measurement)"

On another webpage they repeat much of what's in the downloadable document above and provide both equations and an informative sketch to illustrate the various measurement parameters involved.

Additionally, they provide a list of related reference documents that support the technologies involved in the services. These are quoted below:

"CLARKE, F.J.J. Measurement of the radiometric properties of materials for building and aerospace applications. Proc. Soc. Photo-Opt. Instrum. Eng., 1980, 234, 40-47.

CLARKE, F J J, and LARKIN, J A. Measurement of total reflectance, transmittance and emissivity over the thermal IR spectrum. Infrared Physics, 1985, 25, 359-367.

CLARKE, F J J, and LARKIN, J A. Emissivity determined from hemispherical reflectance and transmittance throughout the thermal infrared spectrum. High Temp. - High Press., 1985, 17, 89-96.

CLARKE, F J J and LARKIN, J A. Improved techniques for the NPL hemispherical reflectometer. Proc. Soc. Photo-Opt. Instrum. Eng., 1988, 917, 7-14."