SpectralEmissivity & Emittance

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ET10 Reflectometer Measures Emissivity

San Diego CA, USA –Surface Optics’ ET10 measures emissivity values in two most commonly used spectral regions, 3 to 5 and 8 to 12 microns.

Its main application is to produce emissivity values for the infrared cameras.

Advanced IR cameras require the input of an emissivity value for accurate temperature calculations. The emissivity values obtained from tables can be far from real leading to large temperature uncertainties.

The ET10 can be used in the lab or in the field and on small or large objects. With the ET10 one can measure emissivity of any surface in just a few seconds.

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Systematic Errors in the Measurement of Emissivity Caused by Directional Effects

In the Optics InfoBase, by the American Institute of Physics’ Optical Society of America:
Authors: Abraham Kribus, Irna Vishnevetsky, Eyal Rotenberg, and Dan Yakir

Applied Optics, Vol. 42, Issue 10, pp. 1839-1846
Keywords (OCIS):
(120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors
(260.3060) Physical optics : Infrared
(300.2140) Spectroscopy : Emission
Accurate knowledge of surface emissivity is essential for applications in remote sensing (remote temperature measurement), radiative transport, and modeling of environmental energy balances…  » View Full Text: PDF


This web site gives the executive summary and table of contents for the Field Guide.

Here’s a summary of what the Field Guide is all about in the words of its authors:


“Because of the rapid advance of airborne and satellite sensor technology in providing higher spectral resolution over progressively broader wavelength regions, there is a need for more (and more accurate) field measurements to complement overhead data. The purpose of this field guide is to facilitate such ground-based measurements, first through a review of the environmental factors affecting such measurements, second through an evaluation of the instrumentation involved, and third through a suggested approach to the measurement process.

“In evaluating environmental factors affecting spectral measurements in the field, the sources of radiance from a target are discussed in both the reflectance and emittance regions of the spectrum, as well as how those sources are modified by atmospheric attenuation and scattering, and the presence of clouds and wind.

“Another factor affecting all spectral measurements in the field is the computer typically used for instrument control and data storage. Computers tend to be the universal weak link in field spectrometers, because of their typical low tolerance for bright sunlight, temperature extremes, windblown dust, and rain. Various solutions to the computer problem are discussed, including the acquisition of hardened computers.

“The most commonly used field spectrometers are described, with advice on how to get the most out of each instrument. Then the pros and cons of each instrument are discussed with regard to different applications.

“Finally, how to approach field measurements is described, beginning with a thorough testing of a field instrument (and the field instrument user) in the laboratory. Approaches to data collection, record keeping, data reduction, and data analysis are discussed. A major conclusion is that much greater support for data analysis is necessary to reach the full potential of spectroscopic remote sensing for target identification”.

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