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At least 145 records · Page 8

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NASA NTRS1985

Mass loss from red giants - Infrared spectroscopy

A discussion is presented of IR spectroscopy, particularly high-resolution spectroscopy in the approximately 1-20 micron band, as it impacts the study of circumstellar envelopes. The molecular bands within this region contain an enormous amount of information, especially when observed with sufficient resolution to obtain kinematic information. In a single spectrum, it is possible to resolve lines from up to 50 different rotational/vibrational levels of a given molecule and to detect several different isotopic variants. When high resolution techniques are combined with mapping techniques and/or time sequence observations of variable stars, the resulting information can paint a very detailed picture of the mass-loss phenomenon. To date, near-IR observations have been made of 20 molecular species. CO is the most widely observed molecule and useful information has been gleaned from the observed rotational excitation, kinematics, time variability and spatial structure of its lines. Examples of different observing techniques are discussed in the following sections.

Wannier, P. G.↗

NASA NTRS1986

Planetary spectroscopy

Infrared spectroscopic studies of the solar system in support of spacecraft investigations were researched. The studies include the physical behavior of comets, the atmospheres of the gaseous planets, and the solid surfaces of satellites and asteroids. Studies of the gaseous and solid emanations of comets using the techniques of CCD spectroscopy and imaging were focused on. An intensive observational effort was mounted, to observe comet Halley with the recently developed state of the art CCD camera system. Comet P/Giacobini-Zinner was observed. The major emphasis was placed on spectroscopy and a synoptic spectrum at least once a month was obtained. A large number of images of Halley for particular emission species and continuum regions were also obtained. The species in vestigated were: C3 (4060 A), CO+ (4505), C2 (5139), NH2 (5980), H2O+ (6185), OI (6300) and CN (9180).

Fink, U.↗

NASA NTRS1986

Thermal imaging spectroscopy in the Kelso-Baker Region, California

The ability of the Thermal Infrared Multispectral Scanner (TIMS) data to identify rock composition using thermal-infrared spectroscopy was assessed. A region was selected with a wide range of rock and soil types in an arid environment, and the spectra acquired by TIMS was compared to laboratory spectra of collected samples. A TIMS image was acquired of the Kelso-Baker region in the Mojave desert of California at a surface resolution of approximately 7 m. This image was then used to map the areal extent of each geologic component. The TIMS data provided an excellent means for discriminating and mapping rocks of very similar mineralogy. These findings suggest that thermal-infrared spectroscopy can provide a powerful tool for identifying and mapping rock composition on the Earth and other terrestrial planets.

Christensen, Philip R.↗

NASA NTRS1986

Coherent Raman spectroscopy for supersonic flow measurments

In collaboration with NASA/Langley Research Center, a truly nonintrusive and nonseeding method for measuring supersonic molecular flow parameters was proposed and developed at Colorado State University. The feasibility of this Raman Doppler Velocimetry (RDV), currently operated in a scanning mode, was demonstrated not only in a laboratory environment at Colorado State University, but also in a major wind tunnel at NASA/Langley Research Center. The research progress of the RDV development is summarized. In addition, methods of coherent Rayleigh-Brillouin spectroscopy and single-pulse coherent Raman spectroscopy are investigated, respectively, for measurements of high-pressure and turbulent flows.

She, C. Y.↗

NASA NTRS1986

EUV astronomical spectroscopy with CCD detectors

The applicability of CCD detectors to astronomical extreme ultraviolet (EUV) spectroscopy (100-1250 A) is discussed. The advantages of CCDs in this spectral region include internal electron yield, the potential for very high quantum efficiency (about 50-90 percent), and broad wavelength response. Visible light suppression is achieved by a combination of low grating scattering, greater than unity electron yield in the EUV, and various filter techniques. For the current generation of CCDs, detection of only a few EUV photons will rapidly overwhelm the read noise; thus, for all practical S/N ratios used in astronomical spectroscopy, read noise will be negligible compared to the poisson statistics of the detected photons. A model based on experimental data for the quantum efficiency and electron yield of CCDs in the EUV is discussed.

Stern, R. A.↗

NASA NTRS1987

Energy-gap spectroscopy of superconductors using a tunneling microscope

A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High-resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 100-1000 greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy-gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory.

Le Duc, H. G.↗

NASA NTRS1988

High-speed assembly language (80386/80387) programming for laser spectra scan control and data acquisition providing improved resolution water vapor spectroscopy

An assembly language program using the Intel 80386 CPU and 80387 math co-processor chips was written to increase the speed of data gathering and processing, and provide control of a scanning CW ring dye laser system. This laser system is used in high resolution (better than 0.001 cm-1) water vapor spectroscopy experiments. Laser beam power is sensed at the input and output of white cells and the output of a Fabry-Perot. The assembly language subroutine is called from Basic, acquires the data and performs various calculations at rates greater than 150 faster than could be performed by the higher level language. The width of output control pulses generated in assembly language are 3 to 4 microsecs as compared to 2 to 3.7 millisecs for those generated in Basic (about 500 to 1000 times faster). Included are a block diagram and brief description of the spectroscopy experiment, a flow diagram of the Basic and assembly language programs, listing of the programs, scope photographs of the computer generated 5-volt pulses used for control and timing analysis, and representative water spectrum curves obtained using these programs.

Allen, Robert J.↗

NASA NTRS1987

Single-tone and two-tone AM-FM spectral calculations for tunable diode laser absorption spectroscopy

A generalized theory for optical heterodyne spectroscopy with phase modulated laser radiation is used which allows the calculation of signal line shapes for frequency modulation spectroscopy of Lorentzian gas absorption lines. In particular, synthetic spectral line shapes for both single-tone and two-tone modulation of lead-salt diode lasers are presented in which the contributions from both amplitude and frequency modulations are included.

Chou, Nee-Yin↗

NASA NTRS1988

Terrestrial imaging spectroscopy

Recent advances in imaging spectroscopy for remote sensing applications are discussed, reviewing the results of recent investigations. The advantages offered by the higher spectral resolution of imaging spectroscopy relative to scanners such as Landsat MSS and TM are explained; the design and performance of the Airborne Imaging Spectrometer (Vane et al., 1984) are described and illustrated with drawings, photographs, and sample images; data processing and analysis techniques are outlined; and applications to geological and botanical research are considered.

Vane, Gregg↗

NASA NTRS1988

Infrared spectroscopy of Jupiter and Saturn

High resolution infrared spectoscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn. The 5 micrometer spectral region, which is transparent to deep levels, is particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. These are tracers of convective and strongly non-equilibrium processes in the atmosphere. High resolution ground-based spectroscopy complements Voyager and Galileo measurements. Spectroscopy is sensitive to lower mixing levels for selected molecules, while the on-board mass spectrometers probe molecules that are spectroscopically inaccessible. Analysis and modeling of the 4.7 micrometer carbon monoxide in Jupiter was completed. CO is present at a mole fraction of 1.6 plus or minus 0.3 x 10 to the 9th power and concentrated in the troposphere. At this abundance, it must be convected upward from much deeper levels in Jupiter where the temperature is near 1100 K. Thus CO is a tracer of the deep atmosphere which is otherwise unobservable. The oxygen abundance in Jupiter (as measured by the CO abundance) is near solar. Chemical or physical process must deplete the major oxygen carrier, water. Germane, GeH4, was discovered on Saturn at amole fraction of 4 plus or minus 2 x 10 to the 10th power.

Knacke, Roger↗

NASA NTRS1988

Planetary Fabry-Perot spectroscopy

Application of high spectral resolution, Earth-based Fabry-Perot spectroscopy to the study of planetary atmospheres, for which current topics are outer planet HD and H2 spectra (atmospheric structure, D/H ratio), Mars CO2, CO, O2, and H2O spectra (atomspheric photochemistry), Venus H2O and HDO, associated laboratory spectroscopy (especially H2 overtone bands, HDO) was accomplished. Monochromatic charge coupled device (CCD) imaging photometry of the Jovian nebula, with images taken in rapid sequence among the diagnostic spectral lines of ionized sulfur species, provided self-supporting snapshots of the Jupiter/Io plasma conditions (spatially resolved electron and ion densities and temperatures), covering the post-Voyager period from 1981 and leading up to the Galileo tour in the early 1990s. High spectral resolution Fabry-Perot/charge coupled device (CCD) imaging of comets (OI, CI, and H2O(+) velocity maps and spatial distriubtions), and Io's charge exchanged neutral jet was studied.

Trauger, J. T.↗

NASA NTRS1988

The ATMOS (Atmospheric Trace Molecule Spectroscopy) experiment - An overview

The objective of the ATMOS experiment is to measure the concentrations and distributions of gases in the middle and upper atmosphere (10 to 120 km) by IR absorption spectroscopy. In 1985 high resolution (0.01/cm) IR occultation spectra of the atmosphere were recorded using a modified Michelson interferometer orbiting onboard the Space Shuttle. With the sun as the radiation source, a single spectrum was obtained every 2.2 seconds with S/N ratios of 100:1 or better. An overview of the data analysis techniques, implications for malecular spectroscopy, and results obtained from the mission is presented.

Brown, L. R.↗

NASA NTRS1990

Terrestrial-Imaging Spectroscopy

Report reviews history and state of art of terrestrial imaging spectroscopy. Discusses history, design, and performance of Airborne Imaging Spectrometer (AIS), which is pioneering sensor for terrestrial high-resolution remote sensing. Also discusses recent developments described in literature of imaging spectroscopy from three points of view: techniques for handling and analysis of spectral-image data, geological research, and botanical research. This field encompasses use of airborne and spaceborne imaging spectrometers to generate specialized maps for use in agriculture, geology, ecology, and related disciplines.

Vane, Gregg A.↗

NASA NTRS1990

Positron annihilation induced Auger electron spectroscopy

Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

Weiss, Alex↗

NASA NTRS1990

Monitoring of catalyst performance in CO2 lasers using frequency modulation spectroscopy with diode lasers

Closed-cycle CO2 laser operation with removal of O2 and regeneration of CO2 can be achieved by catalytic CO-O2 recombination. Both parametric studies of the optimum catalyst formulation and long-term performance tests require on line monitoring of CO, O2 and CO2 concentrations. There are several existing methods for molecular oxygen detection. These methods are either intrusive (such as electrochemical method or mass spectrometry) or very expensive (such as CARS, UV laser absorption). Researchers demonstrated a high-sensitivity spectroscopic measurement of O2 using the two-tone frequency modulation spectroscopy (FMS) technique with a near infrared GaAlAs diode laser. Besides its inexpensive cost, fast response time, nonintrusive measurements and high sensitivity, this technique may also be used to differentiate between isotopes due to its high spectroscopic resolution. This frequency modulation spectroscopy technique could also be applied for the on-line monitoring of CO and CO2 using InGaAsP diode lasers operation in the 1.55 microns region and H2O in the 1.3 microns region. The existence of single mode optical fibers at the near infrared region makes it possible to combine FMS with optical fiber technology. Optical fiber FMS is particularly suitable for making point-measurements at one or more locations in the CO2 laser/catalyst system.

Wang, Liang-Guo↗

NASA NTRS1989

Characterization of the surfaces of platinum/tin oxide based catalysts by Fourier transform spectroscopy (FTIR)

The Laser Atmospheric Wind Sounder (LAWS) Program has as one of its goals the development of a satellite based carbon dioxide laser for making wind velocity measurements. The specifications for this laser include the requirement that the laser operate at a repetition rate of 10 Hertz continuously for three years. Earth-based carbon dioxide lasers can operate for only a short time on a single charge of gas because the lasing action causes the CO2 to break down into CO and O2. Therefore, earth-based CO2 lasers are generally operated in a flow through mode in which the spent gas is continually exhausted and fresh gas is continually added. For a satellite based system, however, a recirculation system is desired because it is not practical to send up extra tanks of CO2. A catalyst which could enable a recirculating CO2 laser to function continuously for three years needs to be developed. In the development of a catalyst system there are many variables. Obviously, not all possible formulations can be tested for three years, therefore, an accurate model which is based on the reaction mechanism is needed. The construction of a multistep reaction mechanism is similar to the construction of a jigsaw puzzle. Different techniques each supply a piece of the puzzle and the researcher must put the pieces together. Transmission infrared spectroscopy was shown to be very useful in supplying some of the information needed to elucidate reaction mechanisms. The purpose was to see what kind of information might be obtained about the NASA catalyst using infrared absorption spectroscopy. Approximately 200 infrared spectra of the prototype Pt/tin oxide catalyst and its precursor components are observed under a variety of different conditions. The most significant observations are summarized.

Keiser, Joseph T.↗

NASA NTRS1990

High resolution spectroscopy in the microwave and far infrared

High resolution rotational spectroscopy has long been central to remote sensing techniques in atmospheric sciences and astronomy. As such, laboratory measurements must supply the required data to make direct interpretation of data for instruments which sense atmospheres using rotational spectra. Spectral measurements in the microwave and far infrared regions are also very powerful tools when combined with infrared measurements for characterizing the rotational structure of vibrational spectra. In the past decade new techniques were developed which have pushed high resolution spectroscopy into the wavelength region between 25 micrometers and 2 mm. Techniques to be described include: (1) harmonic generation of microwave sources, (2) infrared laser difference frequency generation, (3) laser sideband generation, and (4) ultrahigh resolution interferometers.

Pickett, Herbert M.↗

NASA NTRS1990

Electron-impact spectroscopy

The methods of electron impact spectroscopy and cross section measurements are discussed and compared to optical spectroscopy. A brief summary of the status of this field and the available data is given.

Trajmar, S.↗