Accomplishments in optical measurement services

Nationwide Comparison of Infrared Reflectance Measurements

Set of NIST-calibrated infrared reflectance standards (51 mm diameter), as provided to the comparison participants

In partnership with the Department of Defense, the Division led a campaign to assess the accuracy and comparability of infrared reflectance measurements routinely performed by government and aerospace industry laboratories. The large number of participating laboratories, 21, reflected the great interest in infrared measurements. They are critical to the interpretation of infrared signatures of ground, air, and space vehicles; to the measurement of temperature using passive, non-contact infrared thermometry; and to the development of calibration targets for ground- and space-based environmental sensors, measuring sea-surface and atmospheric temperatures and cloud heights.

The campaign involved the exchange of sets of five infrared reflectance standards, three diffuse and two specular as shown at the right. Each of the participating organizations measured a set, with NIST measuring each of the sets both before and afterwards. Measurements covered the 2 μm to 14 μm wavelength range at a spectral resolution of 8 cm^-1 and with near-normal geometries.

The results demonstrated significant differences among the participants. Although a number of participants had results consistent with their calculated uncertainties, differences in reflectance units up to 0.1 (on a scale of 0 to 1) were not unusual, despite the participants’ uncertainty analysis suggesting that they should be much smaller. Participants failed to account for some significant uncertainty components present in the NIST uncertainty budget. A number of participants procured a set of the standards to keep for future calibration purposes. Future work will involve more complicated reflectance measurements, including varying the angle of illumination and characterizing the full bidirectional reflectance distribution function.

For more information, contact Leonard Hanssen.

A Best Selling Standard Reference Material

SRM 1921b is used throughout the world to calibrate infrared spectrometers. A portion of the transmittance spectrum is shown with arrows indicating the reference peaks of polystyrene.

Standard Reference Material (SRM) 1921 is a calibration standard for Fourier-transform (FT) infrared spectrometers. Since its release for public sale in 1994, it has sold more than 4000 units to both U.S. and international customers, including infrared instrument manufacturers, chemical companies, pharmaceutical companies, law enforcement and forensics agencies, research institutions, and government agencies.

SRM 1921 consists of a thin film of polystyrene whose infrared transmission spectrum has been well characterized in terms of the absolute positions of the spectral peaks and their uncertainties. Because this standard provides calibration of the wavelength scale that encompasses the fingerprint region of the infrared, it has made a significant impact in its users’ ability to accurately identify the chemical signatures of numerous compounds. Thus, it is frequently employed to satisfy the regulatory requirements of the pharmaceutical industry, as well as other standard practice methods. It is also used to validate peak measurement algorithms.

This SRM is the best selling SRM from Physics Laboratory, selling three times more than the next best seller. At the close of the 2009 fiscal year, SRM 1921b, the latest issue of SRM 1921, was the 7th best selling SRM at NIST.

For more information, contact Leonard Hanssen.

Missile-Defense Transfer Radiometer Ready for First Deployment

Timothy Jung works on the optical plate of the MDXR, which contains a cryogenic Fourier-transform spectrometer and other instrumentation necessary for absolute spectral calibrations.

In collaboration with the Missile Defense Agency (MDA), the Division has developed a new infrared transfer radiometer for the calibration of sensors and space chambers used in missile defense applications. The radiometer will help ensure that infrared sensors used to support missile defense programs, such as the Exo-atmospheric Kill Vehicle (EKV) and Standard Missile 3 (SM-3), can accurately discriminate the infrared signature of an incoming missile from that of decoys and the natural background of space.

The Missile Defense Transfer Radiometer (MDXR) had been in development for four years at the Division’s Low Background Infrared (LBIR) facility. It is an infrared radiometer with full spectral calibration capabilities, and replaces the filter-based transfer radiometer (BXR). The MDXR features numerous improvements, including a cryogenic Fourier-transform spectrometer (Cryo-FTS), an on-board absolute cryogenic radiometer (ACR), an internal blackbody reference, and an integrated collimator.

The Cryo-FTS can be used to measure high-resolution infrared spectra from 4 μm to 20 μm, using a calibrated blocked-impurity-band (BIB) detector. The on-board ACR can be used to calibrate the BIB detector and for absolute measurements of input signals. A set of filter wheels and a polarizer within the MDXR allow for filter-based and polarization-sensitive measurements. The optics of the MDXR enable measurements of both radiance and irradiance, and calibrations of both radiant and collimated sources.

The MDXR will be the NIST detector standard deployed to MDA facilities. Its broad functionality will allow a variety of measurements to be performed. First deployment will be at the Arnold Engineering and Development Center in late 2009.

For more information, contact Solomon Woods.

 

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