Calibrations and Uncertainties of Low Background IR Test Chambers using the BXR: Adriaan Carter, Raju Datla – NIST; Timothy Jung – Jung Research and Development Corp.

ABSTRACT: The Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST) is responsible for the development and operation of infrared transfer radiometers that provide absolute irradiance calibrations to medium and low background IR test chambers that are used to calibrate remote sensors for the Missile Defense Agency (MDA). The BXR is a filter based radiometer that uses an As doped Si BIB detector and can calibrate IR test chambers to a total combined uncertainty of less than 3% (1 σ) and routinely achieves 2% Type A uncertainties (1 σ) at irradiances as low as to 10-13 W/cm2/µm. The BXR is calibrated using a 10 cm collimator (10CC) whose output is tied to one of several Absolute Cryogenic Radiometers (ACRs) maintained at the LBIR facility. Strengths and weaknesses in the calibration transfer from the ACR, through the 10CC and BXR, to the IR Test Chamber will be discussed. The ability to calibrate IR Test Chambers well depends on specific the specific design of each chamber. Design issues that are important for calibration accuracy will be discussed using specific examples encountered during BXR calibration activities.

Radiometers for Absolute Calibrations at 1 pW of Total Infrared Power: Adriaan Carter, Raju Datla – NIST; Solomon Woods, Stephen Carr, Timothy Jung – Jung Research and Development Corp.

ABSTRACT: The Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST) is developing two radiometers designed to provide infrared radiation calibrations at power levels down to 1 pW with accuracy on the order of 0.1%. Each instrument will have a noise floor of ~1 fW and they will be used together to disseminate new low power calibrations to the LBIR customer base. The first radiometer is an ACR (Absolute Cryogenic Radiometer) controlled using a SQUID-based (Superconducting Quantum Interference Device) high resolution thermometer, allowing ~1 fW sensitivity and better than 99.93% broadband visible and infrared absorption. The second radiometer is a trap detector made with two custom designed Si:As BIB(Blocked Impurity Band) devices mounted in a trapping configuration. The BIB trap will also have ~1 fW sensitivity and is designed to have a very flat spectral response in the wavelength range of 4 µm -28 µm with quantum efficiency > 99%. Design details and performance results and ranges of operation for the two radiometers will be discussed.

Progress in On–orbit SI–traceable Radiance Measurements for CLARREO: Jonathan Gero, John Dykema, James Anderson, Stephen Leroy – Harvard University

ABSTRACT: Satellite measurements pinned to international standards are needed to monitor the Earth's climate, quantify human influence thereon, and test forecasts of future climate change. The International System of Units (SI) provides ideal measurement standards for radiometry as they can be realized anywhere, at any time in the future. Achieving SI-traceable radiance measurements from space is a novel requirement, and requires specialized sensor design and a disciplined experimental methodology. We discuss an approach to confer on-orbit traceability in radiance for a calibration blackbody, through instrument design, pre-flight calibration and on-orbit diagnostics.

We present a method to characterize the emissivity of a spaceborne blackbody and the instrument line-shape (ILS) of a spectrometer using a Quantum Cascade Laser (QCL) based reflectometer. QCLs allow the realization of on-orbit reflectometry that directly observes blackbody surface properties. We present experimental data verifying that the QCL reflected radiance signal can be measured by an Earth-observing spectrometer with adequate signal-to-noise ratio. The QCL can also be used to realize a monochromatic, spatially uniform source of infrared radiation to directly measure the spectrometer's ILS. The quantifiable characteristics of the ILS, including width, symmetry, and shape, can be inverted to obtain diagnostic information about the optical alignment and integrity of the detector, as well as nonlinearities in the detector signal chain.

Results of a NIST–led Inter–laboratory Comparison of Infrared Reflectance: Leonard Hanssen, Boris Wilthan – NIST

ABSTRACT: The National Institute of Standards and Technology (NIST) has undertaken a comprehensive nationwide intercomparison of infrared spectral reflectance. The 25 participants represent government agencies, contractors, equipment manufacturers, measurement service laboratories, and standards laboratories. The transfer standard samples are of both specular and diffuse types, high and low reflectance, as well as with spectral structure, forming a set of 6. Near-normal spectral reflectance over the infrared spectral range of approximately 2.5 to 14 µm, is the measured quantity. NIST produce, measured and delivered a complete set of transfer standard samples to each participant. After measurements by the participants, the sets were returned to NIST for repeated measurement, as a check against any change due to contamination, shipping damage, etc. Results will be presented and discussed. They should provide a reasonable indication of the state-of-the-art of infrared spectral reflectance measurement across the nation. At the same time, the intercomparison provides traceability, for the participant, to a national scale, which should lead to improvement of the measurement accuracy and comparability of infrared optical property measurements.

Spectral Characterization of Infrared Radiometers and Imagers: Sergey Mekhontsev – NIST; Vladimir Khromchenko – USU/Space Dynamics Laboratory; Jinan Zeng, Leonard Hanssen, Joe O'Connell, Joe Rice – NIST

ABSTRACT: We are reporting a recent addition to the functionality of the NIST Advanced Infrared Radiometry and Imaging (AIRI) laboratory, which provides metrological support of thermal sources, radiometers and imagers operating at ambient background temperatures. The most recent development has been the addition of a capability to evaluate the relative spectral responsivity of IR radiation thermometers and imagers. Such information is vital for interpretation of the end user measurement results, especially in the case of spectrally selective targets. An optical setup of the IR Relative Responsivity (IR3) tool is built around a circular variable filter (CVF) similar to the one employed in the AIRI spectral radiance comparator. A blackbody source with a maximum temperature of 1100 °C is used as a radiation source. The spectral responsivity scale is based on a pyroelectric detector with a reflective dome. This paper includes data on optical power level and spectral resolution across the working spectral range, uncertainty evaluation data, including spatial and spectral stray light components, as well as actual results of characterization of two pyrometers, an imager and NIST TXR radiometer. We will also discuss and demonstrate a new technique for characterization of pyrometers and imagers having only temperature readout output. It is anticipated that spectral responsivity measurements will soon be offered as part of a comprehensive package for the characterization of IR radiometers and pyrometers.