SpectralEmissivity & Emittance

| Useful Data | Practices Measuring or Avoiding | Background & Theory|


by Curt H. Liebert and Ralph D. Thomas, NASA Lewis Research Center (Downloadable PDF File), APRIL 1968.

“Measurements were made at temperatures of 300°, 882′, and 1074′ K of the normal was doped with a r s e n i c spectral emissivity of opaque, highly doped silicon. The silicon and boron to electron carrier concentrations of 2. 2X101′, 3. %lo1′, and 8 . 5 ~ 1 0 ~ ‘ electrons per cubic centimeter and hole carrier concentrationsof 6. 2X101′ and 1 . 4 ~ 1 0 holes per cubic centimeter. The 30 K emissivity data were obtained at wavelengths from 2.5 to 35 microns. The high temperature emissivities were measured from 3.5 to 1 4 . 8 microns. Carrier concentrations and direct-current resistivity of the silicon were also measured. The carrier concentrations were determined from Hall measurements made at 30 K. The direct-current resistivity was measured at temperatures from 30 to 1200’ K. These quantities (among others) were used in analytical calculations of the emissivities. Agreement of the Hagan-Rubens theory with experiment was found at wavelengths greater than 12 microns and at 30 K. Good agreement of the free carrier absorption theory with experiment w a s achieved at all wavelengths and temperatures investigated. The free carrier absorption theory predicts the emissivity in terms of the index of of these quantities are presented. A refraction and the absorption index. The values comparison of the values of the absorption index obtained herein with those obtained from the literature showed good qualitative agreement.”

Normal Spectral Emittance of Some Metals, Carbon and SiC

The “Emissivity” page on the FAR Associates website includes a discussion of their unique instrument along with graphs and some tables of spectral emissivity values are evidently all reproduced from the Thermophysical Properties of Matter, Vol. 7: Thermal Radiative Properties, Y.S. Touloukian and D.P. DeWitt, IFI/Plenum, New York, 1970.

These include curves for: Carbon (Graphite), Tungsten, Aluminum, Copper, Iridium, Iron, Molybdenum, Silicon Carbide, Stainless Steel and Titanium.

The ASTER Spectral Library

The ASTER spectral library, is a compilation of almost 2000 spectra of natural and man made materials that is searchable by material. The search returns a list of materials that match your search criteria, you can see a scaled plot of the spectrum and the ancillary information information for the spectrum, you can also download the spectral data.

Data and (No. of samples) are: Minerals (1348), Rocks (244), Soils (58), Vegetation (4), Water, Snow & Ice (9), Man made materials (56), Lunar (17) and Meteorites (60)

Surface Spectral Emissivity Derived from MODIS Data

A downloadable PDF Format copy of a technical paper by Yan Chen, Sunny Sun-Mack, SAIC, Hampton, VA USA and Patrick Minnis, David F. Young, William L. Smith, Jr., Atmospheric Sciences, NASA Langley Research Center, Hampton, VA USA. A paper that was presented at SPIE’s 3rd International Asia-Pacific Environmental Remote Sensing Symposium 2002: entitled Remote Sensing of the Atmosphere, Ocean, Environment, and Space, in Hangzhou, China, October 23-27, 2002.

ABSTRACT: “Surface emissivity is essential for many remote sensing applications including the retrieval of the surface skin temperature from satellite-based infrared measurements, determining thresholds for cloud detection and for estimating the emission of longwave radiation from the surface, an important component of the energy budget of the surface-atmosphere interface. In this paper, data from the Terra MODIS (MODerate-resolution Imaging Spectroradiometer) taken at 3.7, 8.5, 10.8, 12.0 ?m are used to simultaneously derive the skin temperature and the surface emissivities at the same wavelengths. The methodology uses separate measurements of the clear-sky temperatures that are determined by the CERES (Clouds and Earth’s Radiant Energy System) scene classification in each channel during  the daytime and at night. The relationships between the various channels at night are used during the day when solar reflectance affects the 3.7-?m data. A set of simultaneous equations is then solved to derive the emissivities. Global results are derived from MODIS. Numerical weather analyses are used to provide soundings for correcting the observed radiances for atmospheric absorption. These results are verified and will be available for remote sensing applications.”