Andrew Shumway

SABER ground calibration

This paper describes ground calibration of a 10-channel infrared (1.27-17 µm wavelength) radiometer instrument known as sounding of the atmosphere using broadband emission radiometry (SABER). SABER is one of four experiments that will fly on the thermosphere, ionosphere, mesosphere, energetics and dynamics (TIMED) mission to be launched in 2001. SABER will be used to measure atmospheric infrared emissions from the earthlimb. Ground calibration testing was completed in September 1999. Subsequent data analyses and report generation was completed in June 2000. This paper provides an overview of the instrument design, calibration approach, calibration equation and radiometric model. It also describes the SABER ground calibration facility, survey of calibration results and calibration radiance uncertainty.

SOFIE instrument overview

Space Dynamics Laboratory (SDL) recently designed, built, and delivered the Solar Occultation for Ice Experiment (SOFIE) instrument as the primary sensor in the NASA Aeronomy of Ice in the Mesosphere (AIM) instrument suite. AIMs mission is to study polar mesospheric clouds (PMCs). SOFIE will make measurements in 16 separate spectral bands, arranged in eight pairs between 0.29 and 5.3 μm. Each band pair will provide differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun through the limb of the atmsophere during solar occulation as AIM orbits Earth. A pointing mirror and imaging sun sensor coaligned with the detectors are used to track the sun during occulation events and maintain stable alignment of the sun on the detectors. This paper outlines the mission requirements and goals, gives an overview of the instrument design, fabrication, testing and calibration results, and discusses lessons learned in the process.

SOFIE Instrument Model and Performance Comparison

Space Dynamics Laboratory (SDL), in partnership with GATS, Inc., designed, built, and calibrated an instrument to conduct the Solar Occultation for Ice Experiment (SOFIE). SOFIE is the primary infrared sensor in the NASA Aeronomy of Ice in the Mesosphere (AIM) instrument suite. AIMs mission is to study polar mesospheric clouds (PMCs). SOFIE will make measurements in 16 separate spectral bands, arranged in 8 pairs between 0.29 and 5.3 μm. Each band pair will provide differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun through the limb of the atmosphere during solar occultation as AIM orbits Earth. A fast steering mirror and imaging sun sensor coaligned with the detectors will track the sun during occultation events and maintain stable alignment of the Sun on the detectors. This paper outlines the instrument specifications and resulting design. The success of the design process followed at SDL is illustrated by comparison of instrument model calculations to calibration results, and lessons learned during the SOFIE program are discussed. Relative spectral response predictions based on component measurements are compared to end-to-end spectral response measurements. Field-of-view measurements are compared to design expectations, and radiometric predictions are compared to results from blackbody and solar measurements. Measurements of SOFIE detector response non-linearity are presented, and compared to expectations based on simple detector models.

Temperature effects on reflectance and emittance measurements of Martin Black and Enhanced Martin Black surfaces

Martin Black and enhanced Martin Black samples were heated above 620 K and also cooled to 77 K while the directional reflectance and emittance were measured in the spectral region of 1.35 to 26 micrometer. Little emittance variation was found for both surfaces below 300 K. From 77 K to 315 K Martin Black emittance was 98.5% or greater from 7.5 to 24 micrometer. Similarly, enhanced Martin Black emittance was 96% or greater. Furthermore, these conditions apply up to 620 K. Significant reflectance variations below 7.5 micrometer were observed at ambient temperature after baking samples at 620 K both in air and vacuum environments. Reflectance variations as a function of temperature from 300 to 620 K were measured. Humidity and vacuum exposure effects on the surface reflectance properties were also investigated. Post-backed sample reflectance near 5 micrometer was extremely sensitive to ambient air exposure.

Thermal Earth Resource Monitoring Instrument (THERMI) size, weight and power reduction

The Thermal Earth Resource Monitoring Instrument (THERMI) has been designed to meet stringent Landsat heritage requirements with reduced size, weight and power (SWaP). The instrument design provides Earth resource monitoring through the use of two long-wave infrared bands that measure the land surface temperatures. These bands are especially valuable for monitoring water resources and water use. Instrument subsystems, including electronics, cryocooler, thermal management, optical telescope assembly, focal plane module, in-flight calibrator, and scene select mirror were studied and conceptually designed to reduce overall THERMI SWaP. Reductions in SWaP make it possible for THERMI to fit on a small satellite bus with room available for an additional optical instrument. Since mission cost historically correlates well with mass and power on-orbit, it is expected that significant cost savings will result from the predicted SWaP reductions.

SOFIE instrument ground calibration update

Space Dynamics Laboratory (SDL), in partnership with GATS, Inc., designed and built an instrument to conduct the Solar Occultation for Ice Experiment (SOFIE). SOFIE is an infrared sensor in the NASA Aeronomy of Ice in the Mesosphere (AIM) instrument suite. AIMs mission is to study polar mesospheric clouds (PMCs). SOFIE will make measurements in 16 separate spectral bands, arranged in 8 pairs between 0.29 and 5.3 μm. Each band pair will provide differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun through the limb of the atmsophere during solar occulation as AIM orbits Earth. The AIM mission was launched in April, 2007. SOFIE originally completed calibration and was delivered in March 2006. The design originally included a steering mirror coaligned with the science detectors to track the sun during occultation events. During spacecraft integration, a test anomaly resulted in damage to the steering mirror mechanism, resulting in the removal of this hardware from the instrument. Subsequently, additional ground calibration experiments were performed to validate the sensor performance following the change. Measurements performed in this additional phase of calibration testing included SOFIE end-to-end relative spectral response, nonlinearity, and spatial characterization. SDLs multifunction infrared calibrator #1 (MIC1) was used to present sources to the instrument for calibration. Relative spectral response (RSR) measurements were performed using a step-scan Fourier transform spectrometer (FTS). Out-of-band RSR was measured to approximately 0.01% of in-band peak response using the cascaded filter Fourier transform spectrometer (CFFTS) method. Linearity calibration was performed using a calcium fluoride attenuator in combination with a 3000K blackbody. Spatial characterization was accomplished using a point source and the MIC1 pointing mirror. These techniques are described in detail, and resulting SOFIE performance parameters are presented and compared to original SOFIE calibration results.

Control of molecular contamination and outgassing of the SOFIE instrument

The Solar Occultation for Ice Experiment (SOFIE) instrument is one of three science instruments for the Aeronomy of Ice in the Mesosphere (AIM) mission. SOFIE is used to measure solar attenuation by mesospheric ice aerosols during each observatory sunrise and sunset using an 8-channel (16-detector) differential absorption radiometer. It directly views the sun and compares the near UV to the mid-IR spectral response during exo-atmospheric and endo-atmospheric measurements. Deposition of molecular films can degrade the reflectance and transmittance of SOFIEs optics. During on-orbit performance, it may be possible for the extended solar exposure to promote photochemical deposition and darkening effects in the UV. This paper will review the methods used to derive and verify contamination control budgets for particulate and molecular contamination during the fabrication and testing of the SOFIE instrument. Reported results include the molecular surface cleanliness throughout integration and test as well as outgassing measurements using internal and external quartz crystal microbalances. This information provides important baseline data for future correlation of instrument outgassing and potential photo-deposited contamination effects should they occur during on-orbit solar exposure

Cryogenic infrared radiometer for transferal of NIST radiometric standards

The Space Dynamics Laboratory at Utah State University designed and constructed two identical cryogenic mid- infrared radiometers that will be used as NIST-traceable radiometric calibration transfer standards. The radiometer design is similar to the NIST BXR radiometer and thus may be calibrated at NIST using the same sources and procedures used with the BXR. Important features of these radiometers include a single element, chopped indium antimonide detector cooled by a Stirling-cycle cryocooler, two 8-position filter wheels populated with spectral and neutral density filters, and an indium antimonide focal plane array (FPA) that can be temporarily positioned at the field stop for alignment and diagnostics. This paper presents the design and results of the as-built optical and thermal performance of these radiometers. It also presents the testing set up and calibration philosophy and approach.

Focus optimization of the SPIRIT III radiometer

The SPIRIT III (spatial infrared imaging telescope) radiometer is the primary instrument aboard the midcourse space experiment (MSX), which was launched on 24 April 1997. The Space Dynamics Laboratory at Utah State University (SDL/USU) developed and implemented a ground-based procedure to optimize the focus of the SPIRIT III radiometer. The procedure used point source data acquired during ground measurements. These measurements were obtained with a calibration source consisting of an illuminated pinhole near the focus of a cryogenically cooled collimator. Simulated point source measurements were obtained at multiple focus positions by translating the pinhole along the optical axis inside and outside the optimum focus of the collimator. The radiometer was found to be slightly out of focus, and the detector focal plane arrays were moved to positions indicated by the test results. This method employed a single cryogenic cycle to measure both the distance and direction needed to adjust each array for optimal focus. The results of the SPIRIT III on- orbit stellar point source observation demonstrate the success of the technique. This paper describes the method and hardware used to achieve focus optimization.