Spectral Emissivity & Emittance

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 affectsthe 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.”

The Raytek North America website includes a table for the emissivity of a large range of non-metallic materials that includes common building materials, ceramics, glasses and natural materials including ice & water in as many as four wavelength regions.

Wavebands covered include 1.0 micrometer (micron), 5.0 microns, 7.9 microns and the 8-14 micron band. No specific data and the limits of the various wavebands and there are many instances where the wavelength region is labelled as “nr” meaning “Not Recommended”.

Data available includes 24 sample of vegetation ranging from the Leaf of the Algerian Ivy (Hedera canariensis algerian ivy) to the Leaf of Sweet Gum tree (liquidamber styreciflua), one sample of bark of the Eucalyptus tree and three sample of dry grass.

Commentary of the site data reads:

“Vegetation Green vegetation typically has a very high emissivity because it is structured and contains water. Senescent (dry) vegetation has a more variable emissivity, especially in the 3 to 5 µm region, which depends on the type and structure of the cover type, the dryness, and so forth.”

Data is provided on: 9 samples of Nebraska Soil Lab, 14 samples of Oklahoma Soil, 10 samples of Death Valley, CA Soil, 10 samples of Railroad Valley, Nevada playa Soil, 2 samples of Railroad Valley, NV soil powder, 6 samples of Koehn, CA, 3 samples of Concord MA Soil, 9 samples of Page Arizona Sandy Soil, 2 samples of Goleta , CA Beach Sand, 3 samples of Soil - Prepared by ICESS, and more.

Commentary of the data reads:

“Soil and Sands exhibit stronger spectral features than many others. The “restralen” bands of quartz sand cause strong spectral features between 8 and 10 microns that depend on the grain size. The signature in the 3 to 5 µm region depends strongly on the water and organic content. The dryer, purer soils have lower emissivities in this region.”