Allan J. Steed

Mesospheric minor species determinations from rocket and ground-based i.r. measurements

Abstract As part of the MAP/WINE campaign the infrared hydroxyl airglow layer was investigated at Kiruna, Sweden, by simultaneous measurements with rocket probes of OH≠ and O2(a1Δg) infrared emissions and concentrations of odd oxygen species (O and O3). Coordinated measurements of OH≠ and O2(a1Δg) zenith radiance and emission spectra and their time histories were made from the ground. The rocket-borne Λ = 1.55 μm radiometer ( ΔΛ ≊ 0.23 μm ) provided volume emission rates for OH for both rocket ascent and descent, showing a peak near 87 km with a maximum of nearly 106 photons sec−1 cm−3. The atomic oxygen distribution showed a concentration of about 1011 cm−3 between 88 and 100 km, dropping off sharply below 85 km. The ground-based radiometer at Λ = 1.56 μm, which had a similar filter bandpass to the rocket-borne instrument, yielded an equivalent of 130 kR for the total OH Δv = 2 sequence, which is consistent with the zenith-corrected rocket-based sequence radiance value of ≌ 110 kR. The rotational temperature of the OH night airglow obtained from the rotational structure of the OH M (3,1) band observed by the ground-based interferometer was about 195K at the time of the rocket measurement. Atomic oxygen concentrations were calculated from the OH profile and show agreement with the directly measured values. Atomic hydrogen concentrations of a few times 107 cm−3 near 85 km were inferred from the data set.

Cryogenic infrared radiance instrumentation for shuttle (CIRRIS 1A) instrumentation and flight performance

The Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) instrument, launched on the Shuttle Discovery (STS-39) on 28 April 1991, was developed to characterize the phenomenology and dynamics of ionospheric processes. The primary objective of the CIRRIS 1A mission was to obtain spectral and spatial measurements of infrared atmospheric emissions in the spectral region between 2.5 and 25 microns over altitudes ranging from the Earths surface to 260 km. The primary sensors are a Michelson interferometer/spectrometer and a multi-spectral radiometer, which share a common high off-axis rejection telescope. The sensor/telescope complex is enclosed in a cyogenic dewar. Excellent data were obtained from this mission, and preliminary analysis shows that all sensors performed well. This paper describes the experiment hardware, summarizes instrument performance during flight, and presents examples of significant results.

Infrared spectral measurements (450-2500 cm-1) of shuttle-induced optical contamination

The first shuttle-based infrared spectral measurements in the region beyond 800 nm were made during the STS-39 mission. A cryogenic Michelson interferometer in the CIRRIS-1A payload yielded high quality atmospheric IR spectra in the earthlimb observing mode. In addition, observations in the very high earthlimb and in the bay-to-space mode provided important opportunities to assess optical contamination. These observations have revealed spectrally-extended H2O and NO emissions as dominant in the region 450–2500 cm−1 under quiescent conditions. The viewing conditions, spectral and “spatial” (limb scan) distributions, and temporal behavior of the H2O emissions have resulted in their classification as shuttle-induced “cloud glow” optical contamination.

Extended-Field Large-Aperture Interferometer–Spectrometer for Airglow Surveys

The design of a field-of-view-widened interferometer for airglow survey work is discussed, and some preliminary airglow results are presented. The 4.5-cm aperture optics of the interferometer give a very large throughput gain compared with a conventional slit spectrometer. In addition, by using optical wedge compensators, the field of view is widened to over 5 degrees full angle, resulting in a field-widened throughput gain of approximately 100 compared with a standard Michelson interferometer of the same aperture size. Digital recording is used to achieve sufficient dynamic range and to aid in computation of the fast fourier transforms. A series of airglow spectra of the midlatitude sky in the spectral region from 0.6 micro to 0.9 micro down to a resolution of about 2 A are given for a sunset transition and also at night. Bright features are the vibration-rotation hydroxyl emission bands and the oxygen red lines. Particularly interesting are enhancement of these emissions during twilight and the observation of what may be vibrationally excited O(2) in the lower atmosphere.

Night sky spectral emission measurements (λ0.9–2.3 μm) using a field-widened interferometer–spectrometer

Measurements of atmospheric near-IR emissions using a field-of-view compensated interferometer are summarized, and an airglow atlas covering the lambda0.9-2.3-microm spectral range is given.

Electronic Scanning Spectrometer for Measurements of Rapidly Changing Spectra

This spectrometer has a resolution of 15 A over the spectral region 0.6-1 micro, and can obtain electronically read out spectra at selectable scanning rates of up to 10,000 scans/sec. The technique of using an image dissector as the detector holds promise of even faster scan rates. The NEI of 4.6 x 10(-5) W/cm(2) at 0.8 micro is comparable with that of ir streak films. The instrument is ruggedized for field and airborne use.

Cryogenically Cooled Fourier Transform Spectrometers

Very sensitive Fourier transform spectrometers (FTSs) have been developed for infrared measurements utilizing advanced technology to achieve stable operation at very low temperatures. All of the structural, optical, and detector components used to construct these spectrometers are cryogenically cooled to improve the sensitivity of their detectors and to eliminate unwanted background emission signals from the components. Various designs of cooled FTS systems which have been successfully used and tested by USU and AFGL are presented in the paper. The performance specifications, the advantages, and the limitations of each technique are discussed. Also, general evaluations of the advantages and the limitations of cooling an FTS are given.

Portable Compact Multifunction IR Calibrator

New infrared calibration test facilities are required to provide for the calibration of sensors that exhibit resolution in the microradian range and that utilize a large number of detectors in linear and area arrays. Simple collimators with low divergent beams are typically physically large, costly to cool, and provide only a partial calibration. Other capabilities such as multiple point sources, bar patterns and an extended-area source are needed. A compact portable multifunction calibrator is designed for future sensor systems that enables a linearity calibration for all detectors simultaneously using a near small area source ( Jones source), a high resolution mapping of the focal plane with 10 prad setability and with a blur of less than 100 prad, system spectral response calibration (radiometer) using a Michelson interferometer source, relative spectral response (spectrometer) using high-temperature external commercial blackbody simulators, and an absolute calibration using an internal low-temperature extended-area source. In addition, a scatter plate is available to provide a diffuse full-field and full-aperture but attenuated high-temperature radiation source, bar pattern reticles to provide direct evaluation of modulation transfer function and and bandpass filters to provide system parameter evaluation at selected wavelengths. The portable system is made compact through the use of a folded Gregorian collimator design and includes an extended-area source, scatter plate, and Jones source which are stowed in the system and can be switched into the beam.

Recent Auroral Measurements Using A Field-Widened Interferometer Spectrometer

Utah State University and Air Force Geophysics Laboratory have been developing field-widened interferometer systems since the late 1960s. These instruments have been developed primarily to remotely sense spectral emissions from the night sky in the near infrared. However, the systems also have application for making measurements of any dim extended source.

Calibration of a helium-cooled infrared spatial radiometer and grating spectrometer

Methods used by the Space Dynamics Laboratory of Utah State University (SDL/USU) to calibrate infrared sensors are described, using the Infrared Background Signature Survey (IBSS) spatial radiometer and grating spectrometer as examples. A calibration equation and a radiometric model are given for each sensor to describe their responsivity in terms of individual radiometric parameters. The calibration equation terms include dark offset, linearity, absolute responsivity, and measurement uncertainty, and the radiometric model domains include spatial, spectral, and temporal domains. A portable calibration facility, designed and fabricated by SDL/USU, provided collimated, extended, diffuse scatter, and Jones sources in a single cryogenic dewar. This multi-function calibrator allowed calibration personnel to complete a full calibration of the IBSS infrared radiometer and spectrometer in two 15-day periods. A calibration data system was developed to control and monitor the calibration facility, and to record and analyze sensor data.