SpectralEmissivity & Emittance

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Measuring the spectral emissivity of rocks and the minerals that form them

Measuring the spectral emissivity of rocks and the minerals that form them, By Miroslav Danov, Dimitar Stoyanov, and Vitchko Tsanev.

It is an online paper at the SPIE news room website. The tagline for the paper reads:

“A new ground-based technique measures minerals in their natural conditions, a prerequisite for satellite data processing”.

The paper discusses a new measurement technique that uses both a scanning FTIR spectrometer and a gold-plated hemispherical mirror and provides data from tests using limestone as the test subject material.

Several references are cited, as follows:

Jingmin Dai, Xinbei Wang, Guibin Yuan, Fourier transform spectrometer for spectral emissivity measurement in the temperature range between 60 and 1500°C, J. Phy. 13, pp. 63-66, 2005.

S. Fonti, Spectral emissivity as a tool for the interpretation of Martian data: A laboratory approach, 32nd Annual Lunar and Planetary Science Conference, no. 1279, pp. 12-16, 2001.

A. M. Baldridge, P. R. Christensen, A laboratory technique for thermal infrared measurement of hydrated samples, 38th Lunar and Planetary Science Conference, pp. 2407, 2007. Lunar and Planetary Science XXXVIII, held March 12-16, 2007 in League City, Texas. LPI Contribution No. 1338

Z. Wan, D. Ng, J. Dozier, Spectral emissivity measurements of land-surface materials and related radiative transfer simulations, Adv. Space Reg. 14, no. 3, pp. 91-94, 1994.

T. W. Stuhlinger, E. L. Dereniak, F. O. Bartell, Bidirectional reflectance distribution function of gold-plated sandpaper, Appl. Optics 20, no. 15/1, 1981.

ASU Thermal Emission Spectra of Silicate, Carbonate, Sulfate, Phosphate, Halide, and Oxide Minerals

The spectral library is hosted by the Mars Space Flight Facility at Arizona State University (ASU) consists of thermal infrared emission spectra (typically 2000 – 220 cm-1) of a variety of geologic materials.

It is open and free, but one needs to register with a valid email address and take the time to learn how to access the data and obtain plots. It is not a trivial task.

Each spectrum comes with descriptive information, sample quality, and a comments field that describes any appropriate, related information.

To quote from the introduction to the library about the sources of data:

“Emission spectra were acquired using a Nicolet Nexus 670 interferometric spectrometer equipped with a CsI beamsplitter and an uncooled deuterated triglycine sulfate (DTGS) detector; the spectral range of the instrument is from 2000 — 220 cm-1 (5 — ~45 microns). Both the spectrometer and the sample chamber/glovebox were continuously purged with nitrogen gas during sample analysis to minimize atmospheric H2O and CO2 which also have absorption features in the 2000-220 cm-1 region of the spectrum. The particulate samples were heated in an oven to 80°C to improve the signal to noise ratio during spectral analysis (this temperature is maintained during analysis by placement of the sample cup on a heater element). The samples were raised into a water-cooled sample chamber that closely approximates a blackbody cavity [Ruff et al., 1997]. A total of 270 scans at 2-cm-1 sampling were taken over ~7 minutes and averaged together by the spectrometer. In the case of a hand sample, active heating during measurement is not possible. Hand samples were taken directly from the oven and placed into the sample chamber and 180 scans were taken over a period of ~5 minutes to minimize the effects of sample cooling. The spectral calibration method is a variation of method 1 of Christensen and Harrison [1993] as described in detail by Ruff et al., [1997].”

References cited above:

“Christensen, P.R., and S.T. Harrison, Thermal infrared emission spectroscopy of natural surfaces: Application to desert varnish coatings on rocks, J. Geophys. Res., 98 (B11), 19,819-19,834, 1993.“Christensen, P.R., J.L. Bandfield, V.E. Hamilton, D.A. Howard, M.D. Lane, J.L. Piatek, S.W. Ruff, and W.L. Stefanov, A thermal emission spectral library of rock-forming minerals, J. Geophys. Res., 105,9735-9739, 2000. {ED NOTE: PDF DOWNLOAD}

“Feely, K.C. and P.R. Christensen, Quantitative compositional analysis using thermal emission spectroscopy: Application to igneous and metamorphic rocks, J. Geophys. Res., 104, 24195-24210, 1999.

“Lane, M.D. and P.R. Christensen, Thermal infrared emission spectroscopy of salt minerals predicted for Mars, Icarus, 135, 528-536, 1998.””Lane, M.D., Midinfrared emission spectroscopy of sulfate and sulfate-bearing minerals, American Mineralogist, in press, 2006.

“Ruff, S.W., P.R. Christensen, P.W. Barbera, and D.L. Anderson, Quantitative thermal emission spectroscopy of minerals: A laboratory technique for measurement and calibration, J. Geophys. Res., 102, 14,899-14,913, 1997.”

Further reference publications related to the work at ASU may be viewed on the ASU website.

TES and Spectral Emissivity Curves: Quartz, Feldspar & Hornblende

This linked website discusses the background and flight of the instrument and also provides some interesting spectral emissivity curves for Quartz (SiO2), Feldspar* and Hornblende** and an equal mixture of the two,

The TES instrument first flew aboard the Mars Observer spacecraft that was lost. The TES instrument was rebuilt and launched along with instruments aboard the new Mars Global Surveyor spacecraft.

The purpose of the TES device is to measure the spectral distribution of thermal infrared radiation emitted from Martian surfaces. The TES technique, can tell us much about the geology and atmosphere of Mars.

One can learn much about this method and the device by visiting the Arizona State University website pages that provide much more detail and background and reading through the TES News Archives.

[NOTE: The above curves actually exist on the Arizona State University website on their webpage address: http://tes.asu.edu/MARS_SURVEYOR/MGSTES/mixed_spec.gif]

Quartz, Feldspar & Hornblende Spectral Emissivies

The Thermal Emission Spectrometer is a scientific instrument and also Thermal Emission Spectroscopy is a measurement technique.

* K-feldspar end member KAlSi3O8, Albite end member NaAlSi3O8 or Anorthite end member CaAl2Si2O according to the Wikipedia article on Feldspar.
** The general formula (for Hornblende) can be given as (Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 , according to the Wikipedia article on Hornblende..

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.”