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Topic: Emissivity

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	Emissivity
		Emissivity is the ratio of radiation emitted by a flbody or a surface and the theoretical radiation predicted by Planck’s law.
		Effective emissivity is affected by several variables, the most important of which are the geometric shape of the flbody, the uniformity of the flbody temperature, the surface emissivity and wavelength dependence.
		The effective emissivity of a sphere is dependant on the temperature uniformity, the interior surface emissivity and the ratio of the viewing port size to the sphere size.
	www.electro-optical.com /bb_rad/emissivity/emisivty.htm (773 words)

	The Emissivity Trail
		Emissivity is the hands-down favorite whipping boy for failure to obtain good results or explain ones that seem impossible.
		There's a paper on the website under steel applications which shows the theory and how the decision on emissivity settings can be made steel mills and by extension in many other applications of IR non-contact temperature sensors.
		Take them at the risk of losing your emissivity excuse and show them to the salesman who told you the subject was really simple (it is, of course, if you don't understand it; understanding takes some time and effort.
	www.temperatures.com /eindex.html (1008 words)

	FAR Associates: Emissivity
		Emissivity — A property of a material, measured as the emittance of a specimen of the material that is thick enough to be completely opaque and has an optically smooth surface.
		The widespread use of the term emissivity instead may be a wistful usage, implying the hope that the emittance of one sample defines that of another of the same material. Unfortunately, the probabilities are against this.
		As we have said, emissivity is the term in popular usage, and is understood to mean the value the operator needs to enter into the pyrometer.
	www.pyrometry.com /emissivity.php (813 words)

	Emissivity
		Emissivity is the ratio of radiation emitted by a flbody or a surface and the theoretical radiation predicted by the Planck's law.
		Effective emissivity is affected by several variables, the most important of which are the geometric shape of the flbody, the surface emissivity and wavelength dependence.
		Thus, for temperature-determination errors of less than 1 K and scene-object emissivities near 0.9, the emissivity of the object in both spatial bands must be the same to within 0.02.
	www.geocities.com /coalfire_homepage/Emissivity.html (401 words)

	Emissivity Adaptation
		The spatial variation of emissivity for this particular process, plasma arc welding, is mainly due to microstructural transformations taking place in the material during and after the welding process, and as a result, the appearance of all the samples is similar.
		Thus, the low temperature measurements were focused on identifying the influence of surface color on the emissive capability of the steel.
		These values are the mean emissivity values measured at various temperatures at a ‘clean’ unaffected by process transformations point, therefore, they include the combined effect of temperature as well as the effect of changes of color/surface condition during the experiments, such as carbonization during heating.
	www.tufts.edu /as/tampl/summer2000/projects/welding/high_temp.htm (3343 words)

	\|\| Spectrodyne, Inc. \|\| Optical Pyrometry and Emissivity
		Emissivity is still an issue at short wavelengths like 0.65 microns, but much less so than at longer wavelengths like 1.0 microns.
		A major issue with adjustable emissivity is that few people can agree on what the correct emissivity of a material is. In fact, the emissivity of a material is different at different temperatures, wavelengths and surface conditions.
		If an emissivity of 1.00 is chosen to calculate the temperature of a target from the filament current, then the temperature displayed is the brightness temperature.
	www.spectrodyne.com /Emissivity (624 words)

	Met Office: OBR - Surface reflectance and emissivity (Site not responding. Last check: 2007-10-29)
		The problem is that the emissivity of the land surface is not well characterised for snow, ice and desert surfaces.
		The objective of the microwave emissivity studies is to promote the characterisation of land-surface emissivity in order to allow the use of microwave data over land for purposes of estimating atmospheric humidity and temperature.
		Central to the study of emissivity is the measurement of microwave radiances under well measured atmospheric and surface conditions.
	www.metoffice.gov.uk /research/obr/radtran/surface.html (455 words)

	ETI Ltd - Emissivity Table
		Emissivity is a measure of the efficiency in which a surface emits thermal energy.
		It is defined as the fraction of energy being emitted relative to that emitted by a thermally fl surface (a fl body).
		The accuracy of the following figures is almost impossible to guarantee as the emissivity of a surface will not only alter with regard to texture and colour but also with its actual temperature at the time of measurement.
	www.etiltd.co.uk /downloads_emissivity_table.html (253 words)

	NPL: Thermal Metrology: Introductory Guides
		Spectral emissivity is a dimensionless number lying between 0 and 1, and is defined as the ratio of the energy radiated from a surface to that from a flbody at the same temperature, the same wavelength and under the same viewing conditions.
		Emissivity is not easy to measure accurately because it depends significantly on many physical and chemical properties, such as temperature, wavelength, angle, oxidation, roughness, heat treatment and so on.
		Often, the only way of being sure of the emissivity of a surface is to measure it, and there are two main ways to do this: calorimetric or radiometric.
	www.npl.co.uk /thermal/stuff/guide4.html (905 words)

	5.4 The emissivity profile and adiabatic models
		We have already argued that much of the emission in the inner region may come from a surface layer (Section 5.1) and the assumption that the radiating material expands with constant opening angle may be invalid.
		17, where we have normalized the adiabatic models to the observed emissivities at the beginnings of the flaring and outer regions.
		The adiabatic models predict emissivities which fall far more rapidly than is observed in the flaring region: the deceleration is too little and too late to compensate for the expansion.
	www.cv.nrao.edu /~abridle/3c31free/l2h/5_4_emissivity_profile_adia.html (618 words)

	ZyTemp -- Infrared Emissivity
		Understanding an object's emissivity, or its characteristic "radiance" is a critical component in the proper handling of infrared measurements.
		Concisely, emissivity is the ratio of radiation emitted by a surface or flbody and its theoretical radiation predicted from Planck's law.
		There are many variables that affect a specific object's emissivity, such as the wavelength of interest, field of view, the geometric shape of the flbody, and temperature.
	www.zytemp.com /tutorial/emissivity.asp (126 words)

	Emissivity (Site not responding. Last check: 2007-10-29)
		The emissivity is a property of a given surface necessary to quantify its heat exchanges with the environment by radiation.
		The emissivity of coated glass surfaces is determined according to procedures described in EN 673, EN 12898 and ISO 10292.
		The normal emissivity is then corrected with the help of a multiplicative correction factor to yield the corrected emissivity, i.e.
	www.brookes.ac.uk /thermes/emittance.htm! (284 words)

	Validation of High Temperature Emissivity Results
		The purpose of this experiment is to validate a model for the emissivity of stainless steel type 304 which we proposed in previous work.
		Such a model would be useful in modeling the temperature profile of a metal during the welding process, which has important consequences for the strength of a weld, and of the regions surrounding a weld.
		Also included are two graphs of the measured emissivities plotted next to the predicted values, one of the best matching data, and one of the worst.
	www.tufts.edu /as/tampl/summer2000/projects/welding/validation.htm (908 words)

	Tim Thompson on Emissivity (Site not responding. Last check: 2007-10-29)
		Emissivity is the ratio of thermal energy emission of the target object, over the thermal energy emission of a true flbody at the same temperature.
		In the case of real world stuff, what it is made out of does make a difference, and nature expresses that difference by a sort of efficiency; some things will emit more thermal radiation, even though they are at the same temperature as something else.
		Emissivity is always expressed as a number between zero and one.
	www.tim-thompson.com /emissivity.html (295 words)

	ARS \| Publication request: Estimation of Land Surface Window (8-12 Micrometer) Emissivity from Multi-Spectral Thermal ...
		However, wide spatial variations of emissivity can be observed in rocks and soils, which are recognized as one only surface type such as barren or bare soil in the classification map.
		This study focuses on estimating the window emissivity from the emissivities of the five channels on the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER).
		We compared the estimated window emissivities derived from the regression with the ones expected from the classification map and found significant difference ranging from -0.08 to +0.05.
	www.ars.usda.gov /research/publications/publications.htm?seq_no_115=139263 (418 words)

	EMISSIVITY
		As I mentioned, RTs are calibrated against a flbody having an emissivity of 1.0, but are used to measure the temperatures of surfaces having an emissivity of less than 1.0.
		Ratio units, which divide a short wavelength signal by a long wavelength signal, achieve a similar result as the two emissivities (short wavelength emissivity/long wavelength emissivity) divide out to 1.0 if and only if the two are the same, which happens for materials called “greybodies.
		Often, even very thin coatings on the surface can affect the emissivity value of the surface and (depending on the coating thickness) the correct emissivity value may be that of the coating, not the main substrate.
	www.temperatureconsultant.com /EMISSIVITY.htm (1091 words)

	Simultaneous determination of continental surface emissivity and temperature from NOAA 10/HIRS observations: Analysis ...
		Emissivity values as low as 0.7 may be observed around 8–10 μm or, at shorter wavelengths, around 4 μm, particularly over desert regions.
		An accurate and coherent, i.e., simultaneous, determination of surface temperature and emissivity is essential to greatly improve the estimation of the longwave surface energy budget and, consequently, to improve the performance of surface-atmosphere interaction models.
		Emissivity maps at a resolution of 1° × 1° and 1 month reveal strong signatures of sand at 8.3 and 4.0 μm and of carbonates at 11.1 μm.
	www.agu.org /pubs/crossref/2004.../2004JD004886.shtml (376 words)

	Pyrofiber emissivity measuring infrared thermometer fiber optic sensor
		The spectral emissivity (El) of most materials is not constant; it changes with the method of shaping or forming, the temperature, the atmosphere and the length of time in that atmosphere.
		Emissivity does not always increase with temperature and time and there is no visual means to intuitively estimate emissivity (snow is a good example).
		Emissivity measurements of the steel near the bath are not reproducible due to the specular surface; as the steel rises the surface becomes more diffuse and the emissivity increase.
	www.pyrometer.com /paper0993.htm (2230 words)

	ASTER Surface Emissivity Product Version 2
		In converting image Data Numbers (DN) to Emissivity there are no offsets, and the scaled values are obtained by multiplying the image DN by the appropriate scaling factor (value=DN*scaling factor).
		This is because the emissivities are affected to a greater extent by the downwelling irradiance if the have low vales, whereas temperatures are calculated from the least-affected, highest of the five emissivities.
		Furthermore, in the immediate vicinity of clouds, temperatures and emissivities may be increased because of radiative exchange between land and cloud.
	asterweb.jpl.nasa.gov /content/03_data/01_Data_Products/release_surface_emissivity_product.htm (1137 words)

	Infrared Imaging & Thermography engineering - high emissivity fibers and coatings (Site not responding. Last check: 2007-10-29)
		Emissivity is affected by the molecular make-up of the target, this is true.
		The emissivity of a material is a property of its molecular structure, transmissivty and absorbtion, all of which contribute to the targets "ability" to radiate energy.
		In the case used for crystal paints, yes they may change the E value of the material they are applied to, but not because of it's color, because of the differing crystals in the paints used to make up that color.
	www.eng-tips.com /viewthread.cfm?qid=74860&page=5 (702 words)

	INSC: MatProp: UO2: Emissivity
		found that the normal spectral emissivity at a wavelength of 10600 nm falls from 0.85 at 3120 K to 0.64 at 3670 K and to 0.4 at 4000 K. Further emissivity measurements of liquid UO are needed in the infrared and far infrared region to confirm these results.
		Total emissivities calculated with Eq.(6) increase from 0.79 at 300 K to 0.80 at 1000 K and 0.83 at 3120 K. These emissivities are consistently lower than the value given by Gentry.
		=10600 nm the normal spectral emissivity of liquid UO falls from 0.85 at 3120 K to 0.64 at 3670 K and to 0.4 at 4000 K. Further data are required at wavelengths in the infrared region to confirm these results and determine total emissivities for the liquid.
	www.insc.anl.gov /matprop/uo2/emis/wemis.php (1878 words)

	Emissivity: An Introduction
		For example, if at a given temperature and frequency a surface were to emit half the radiation of a flbody it's emissivity would be 0.5.
		Emissivity also varies with frequency, sometimes surfaces emit a lot of energy at one frequency and very little at another.
		If the emissivity is very low, some polished surfaces have an emissivity of 0.2 or less, then an accurate reading is unlikely to be possible.
	www.openxtra.co.uk /articles/emissivity_intro.php (1106 words)

	ASTER On-Demand L2 Surface Emissivity
		Emissivity is estimated using the Normalized Emissivity Method (NEM), and is iteratively compensated for reflected sunlight.
		The emissivity spectrum is normalized using the average emissivity of each pixel.
		These estimates are used to scale the normalized emissivity and compensate for reflected skylight with the derived refinement of emissivity.
	edcdaac.usgs.gov /aster/ast_05.html (294 words)

	Emissivity enhanced x-ray target
		The apparent emissivity as a function of the V-groove angle A was calculated for different base emissivities ranging from 0.2 to 0.9 for an included 180.degree.
		The calculations indicate increasing emissivity as the included angle A decreases, with the greatest increase in emissivity occurring for the initially low base emissivity, and less increase occurring for the highest base emissivity.
		This unexpected result indicates that the V-grooves are effective for increasing emissivity, without a significant decrease in emissivity upon application of the PCI coating which typically occurs on smooth graphite.
	www.devileye.net /catalog/laminated_glass_product/emissivity_enhanced_x-ray_target.html (3778 words)

	Mikron Emissivity Values Booklet Request Form
		Emissivity is a modifying factor used in single color thermometry to achieve a correct temperature reading.
		Emissivity, or radiating efficiency, of most materials is a function of surface condition, temperature and wavelength of measurement.
		In this booklet, values for the total emissivity of various surfaces, as well as spectral emissivity at a given temperature have been tabulated.
	www.mikroninfrared.com /news/emissbooklet.htm (116 words)

	Determination of effective emissivity and temperature over inhomogeneous land surfaces – Results from field ...
		However, the problem encountered in estimating emissivity is the heterogeneity of the land surface at a pixel resolution which makes it impossible to estimate the emissivity of a pixel from individual point measurements.
		For the determination of accurate surface temperature, estimation of emissivity at the sensor’s thermal channel is important.
		The emissivity of pure vegetation and soil pixels of the area are calculated based on the emissivity of pure vegetation and soil pixels of the area, since they are constant over the area.
	www.ias.ac.in /currsci/nov25/articles25.htm (1685 words)

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