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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1975

Water vapor absorption spectra of the upper atmosphere /45-185 per cm/

The far IR nighttime absorption spectrum of the earth's atmosphere above 14 km is determined from observations of the bright moon. The spectra were obtained using a Michelson interferometer attached to a 30-cm telescope aboard a high-altitude jet aircraft. Comparison with a single-layer model atmosphere implies a vertical column of 3.4 plus or minus 0.4 microns of precipitable water on 30 August 1971 and 2.4 plus or minus 0.3 microns of precipitable water on 6 January 1972.-

Augason, G. C.↗
NASA NTRS1976

An investigation of the optimization of parameters affecting the implementation of fourier transform spectroscopy at 20-500 micron from the C-141 airborne infrared observatory

A program for 20-500 micron spectroscopy from the NASA flying C141 infrared observatory is being carried out with a Michelson interferometer. The parameters affecting the performance of the instrument are studied and an optimal configuration for high performance on the C-141 aircraft is recommended. As each parameter is discussed the relative merits of the two modes of mirror motion (rapid scan or step and integrate) are presented.

Thompson, R. I.↗
NASA NTRS1976

The measurement of carbon monoxide and methane in the National Capital Air Quality Control Region. I - Measurement systems

The Carbon Monoxide Pollution Experiment (COPE) and the National Capital Air Quality Control Region (NCAQCR) undertook a series of measurements of atmospheric CO and CH4 to determine the accuracy of the airborne COPE Correlation Interfer4meter. The device, a modified Michelson interferometer, measures the atmospheric column density of CO and CH4 at 2.3 microns with tropospheric measurement sensitivities of 70 and 10 PPB, respectively. Data for evaluating the remote measurements included atmospheric column density measurements at a ground truth site using a van-mounted infrared Fourier spectrometer; continuous ground level gas chromatographic measurements; and chromatographic data from atmospheric grab samples collected by aircraft and at ground locations. The instruments and sampling techniques used in the experiment are described in detail.

Lebel, P. J.↗
NASA NTRS1975

Line strengths of H2O and N2O in the 1900-kayser region

Laboratory measurements of the line strengths of H2O and N2O in the 1900-kayser spectral region are reported which were made with moderate resolution using a modification of a Michelson interferometer. The N2O analysis includes measurements of the line strengths of the P and R branches and the integrated strength of the Q branch of the nu-1 + nu-2(1) band as well as the integrated strengths of the Q branches of the nu-1 + nu-2(2) - nu-2 and nu-1 + nu-2(0) - nu-2(1) bands. The H2O data cover the region from 1830 to 1980 kaysers; they include line-strength measurements of 61 lines of the nu-2 band, 10 lines of the nu-2 band of H2(O-18), two lines of the nu-2 band of H2(O-17), and three lines of the 'hot' band transition 2 nu-2 - nu-2. The estimated uncertainties in the measured line strengths range from 7% to 20% for H2O, 10% to 25% for H2(O-18) and H2(O-17), and 4% to 8% for N2O.

Toth, R. A.↗
NASA NTRS1976

High spectral resolution ground-based observations of Venus in the 450-1250 cm sup-1 region

The thermal emission of Venus was recorded during the winter of 1970-1971, and in 1973 using the 2.7m telescope at McDonald Observatory. The double beam Michelson interferometer installed at the Coude focus was used. The spectrum was recorded between 400/cm and 1,400/cm. For the 1970 observations, the spectral resolution was 0.25/cm and the linear spatial resolution was 3/4 of the disk of Venus. In 1973 the spectral resolution was 0.20/cm with a spatial resolution 1/3 of the planetary disk. In addition to Venus, the moon, the sky adjacent to each object, and the zenith sky were recorded to help eliminate the absorption and emission effects of the earth's atmosphere.

Kunde, V. G.↗
NASA NTRS1976

Fourier and Hadamard transform spectrometers - A limited comparison

An encoding figure of merit is established for a detector-noise limited Fourier transform spectrometer (FTS) and compared to the comparable figure for a Hadamard transform spectrometer (HTS). The limitation of the Fourier system is partly that it does not truly Fourier analyze the radiation. Instead a cosine squared modulation is imposed on the different spectral frequencies. An additional difficulty is that neither the cosine nor the cosine squared functions form an orthonormal set. This makes the Fellgett's advantage (root-mean-squared figure of merit) for a single detector Michelson interferometer a factor of the square root of (N/8) greater than for a conventional grating instrument - rather than the square root of (N/2). The theoretical limit would be the square root of N.

Tai, M. H.↗
NASA NTRS1977

Spherical lamellar grating interferometer for airborne astronomical observations of far infrared objects

A lamellar-grating interferometer designed for airborne IR astronomy is described, and its response to a laboratory far-IR source and to Jupiter as viewed from NASA's Kuiper Airborne Observatory is discussed. The theory of lamellar-grating interferometers is reviewed, advantages over Michelson interferometers are noted, and the optical arrangement for the lamellar-grating instrument is indicated. The response of the instrument is illustrated using purged and unpurged spectra of a 1000-K blackbody source as well as a raw spectrum of Jupiter containing many absorption features (probably telluric) identified with rotation bands of H2O. It is noted that the interferometer's self-collimation allows for efficient operation with a minimum of auxiliary optics.

Pipher, J. L.↗
NASA NTRS1976

Laser heterodyne detection techniques

The principles of heterodyne radiometry are examined, taking into account thermal radiation, the Dicke microwave radiometer, photomixing in the infrared, and signal-to-noise considerations. The passive heterodyne radiometer is considered and a description is presented of heterodyne techniques in active monitoring systems. Attention is given to gas emissivities in the infrared, component requirements, experimental heterodyne detection of gases, a comparison of the passive heterodyne radiometer with the Michelson interferometer-spectrometer, airborne monitoring applications, turbulence effects on passive heterodyne radiometry, sensitivity improvements with heterodyning, atmosphere-induced degradation of bistatic system performance, pollutant detection experiments with a bistatic system, and the airborne laser absorption spectrometer. Future improvements in spectral flexibility are also discussed.

Menzies, R. T.↗
NASA NTRS1977

Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers

The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.

Erickson, E. F.↗
NASA NTRS1977

Spectrum and isotropy of the submillimeter background radiation

Infrared evidence referable to the spectrum and isotropy of the background radiation of the universe is considered, along with theoretical implications. Difficulties in the submillimeter region are indicated. Two types of anisotropy are treated: small-scale granularity (attributable to discrete sources such as galaxies or to condensation in the primordial plasma) and large-scale anisotropies; the anisotropies are discussed as possible indicators of the early history of the universe, and in relation to future possible generalized Michelson-Morley experiments (to detect effects on local physics of the existence of a universal rest frame). A complete blackbody spectrum is seen as the clear signature of the primordial fireball, and slight deviations from a perfect thermal spectrum (or perfect isotropy) are to be sought and scrutinized.

Muehlner, D.↗
NASA NTRS1977

The far-infrared spectrum of the core of Sagittarius B2

A Michelson interferometer aboard NASA's Kuiper Airborne Observatory has been used to measure the spectrum of Sgr B2 from 40 to 200 kaysers with 5-kayser resolution in a 1.4-arcmin beam. The measured spectrum is smooth and featureless with a broad maximum at about 85 kaysers. The data can be fitted analytically with a model corresponding to thermal emission by a uniform sla of dust filling the beam, with an average temperature of approximately 32 K, an optical depth at 100 microns of about 1.6, and a spectral index of the dust emissivity about 1.5. The absence of features implies either that the source is optically thick or that the emission spectrum of the individual grains is smooth in the passband. The possible physical significance of this model is discussed.

Erickson, E. F.↗
NASA NTRS1977

High spectral resolution ground-based observations of Venus in the 450- to 1250 kayser region

Ground-based observations of Venus were made with a 5-cm drive Michelson interferometer during December 1970 and December 1973. The thermal emission spectrum of the central portion of the apparent disk was recorded from 450-1250 kaysers with an apodized spectral resolution of 0.25 kaysers. All statistically significant sharp line-absorption features in the spectrum have been identified with gaseous CO2. Comparison between the observed spectrum and a synthetic spectrum computed from a model atmosphere, assuming gaseous CO2 and a sulfuric acid haze as opacity sources, indicates good agreement. A broad diffuse absorption feature associated with the sulfuric acid haze is evident in the 870- to 930 kayser region. With the exception of the rotational lines of the 927 kayser CO2 band, the above feature appears as a continuum down to 0.25 kayser resolution. In the 750- to 1250 kayser range, the spectrum exhibits moderate thermal contrast with maximum brightness temperatures of 234-238 K occurring near 825 kaysers. These temperatures are in general agreement with previous measurements.

Kunde, V. G.↗
NASA NTRS1977

The HF:HCl ratio in the 14-38 km region of the stratosphere

A balloon-borne high resolution Michelson interferometer recorded near infrared absorption spectra of the 1-0 fundamental vibration bands of HF and HCl in the stratosphere over Australia in March 1977. The ratio of the number density of HF to that of HCl as a function of stratospheric height was deduced from the measurements. Within estimated experimental error, the ratio is constant, its mean value being 0.1.

Farmer, C. B.↗
NASA NTRS1977

Fourier and Hadamard transform spectrometers - A limited comparison. II

A mathematical approach was used to compare interferometric spectrometers and Hadamard transform spectrometers. The principle results are reported, noting that the simple Hadamard spectrometer encodes more efficiently than a Michelson interferometer which, in turn, encodes less efficiently than is usually acknowledged. Hirschfeld's (1977) major objections to these findings are discussed, although it is noted that none of his objections is supported by evidence.

Harwit, M.↗
NASA NTRS1977

Infrared instrumentation on NASA airborne observatories

Two airborne observatories operated above much of the earth's atmosphere are providing effective platforms for infrared astronomical observations. A summary is given of the wide variety of instrumentation currently in use and continuing to be developed for these facilities. The classes of instruments include various far infrared photometers, filter wheel and grating spectrometers, Fourier transform spectrometers, Michelson and Fabry-Perot interferometers, a polarimeter, and a microwave line receiver.

Boggess, N. W.↗
NASA NTRS1978

Signal-to-noise ratios of multiplexing spectrometers in high backgrounds

Signal-to-noise ratios and the amount of multiplexing gain achieved with a Michelson spectrometer during detector and background noise are studied. Noise caused by the warm background is found in 10 and 20-micron atmospheric windows in high resolution Fourier spectroscopy. An equation is derived for the signal-to-noise ratio based on the number of channels, total time to obtain the complete spectrum, the signal power in one spectral element, and the detector noise equivalent power in the presence of negligible background. Similar expressions are derived for backgrounds yielding a noise equivalent power to a spectral element, and backgrounds having flat spectra in the frequency range under investigation.

Knacke, R. F.↗
NASA NTRS1978

A white-light amplitude interferometer with 180-degree rotational shear

The paper reports on the fabrication, alignment, and test techniques of an equal-path, wave-front, folding amplitude interferometer with 180-degree rotational shear. The device may be used for measuring atmospheric phase-perturbing properties and designing optical filters used in processing spatial information. The instrument has been used to photograph the Michelson Stellar interferometer fringes.

Breckinridge, J. B.↗
NASA NTRS1978

Germane in the atmosphere of Jupiter

Germane, GeH4, is a tetrahedral molecule like methane. The nu 3 fundamental mode of GeH4 falls in the middle of the 5-micrometer Jupiter window. Jupiter observations were made in December 1975 during three flights with the 0.9-m telescope of the Kuiper Airborne Observatory. The spectrometer is a rapid-scanning Michelson interferometer having InSb detectors at each of the two outputs. The germane identification procedure is based on a comparison of the obtained Jupiter spectrum with that of laboratory germane. It appears that the detection of GeH4 in Jupiter's atmosphere with a mixing ratio of 0.6 ppb is the smallest concentration of a trace constituent yet detected in a nonterrestrial planetary atmosphere. It is pointed out that a strict interpretation of thermochemical equilibrium predictions for the spectral line forming regions of Jupiter's atmosphere does not explain the observation of GeH4.

Fink, U.↗