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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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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

A geostationary imaging spectrometer TOMS instrument

One design for a geostationary Total Ozone Mapping Spectrometer (TOMS) with many desirable features is an imaging spectrometer. A preliminary study makes use of a 0.25 m Czerny-Turner spectrometer with which the Earth is imaged on a charge-coupled device (CCD) in dispersed light. The wavelength is determined by a movable grating which can be set arbitrarily by ground control. The signal integration time depends on wavelength but this system allows arbitrary timing by command. Special circumstances such as a requirement to track a low-lying sulfur dioxide cloud or a need to discriminate high level ozone from total ozone at midlatitudes could be obtained by adding a particular wavelength to the normally pre-programmed time sequence. The incident solar irradiance is measured by deploying a diffuser plate in the field of view. Individual detector elements correspond to scene elements in which the several wavelengths are serially sampled and the Earth radiance is compared to the incident sunlight. Thus the problem of uncorrelated drift of multiple detectors is removed.

Krueger, Arlin J.↗
NASA NTRS1988

Imaging spectrometer for high resolution measurements of stratospheric trace constituents in the ultraviolet

A high-resolution spectrometer has been developed for studies of minor constituents in the middle atmosphere at ultraviolet wavelengths. In particular, the instrument is intended for observations of upper stratospheric UV bands. The spectrometer has a slit width of 0.08 A obtained by means of an echelle grating and a cross-disperser grating. The image plane detector is an intensified CCD consisting of a high gain proximity focused image intensifier that is fiber optically coupled to a two-dimensional CCD array. An instantaneous bandwidth of 9.2 A is resolved across 488 pixels at 0.018 A/pixel, permitting simultaneous acquisition of multiple lines of selected OH bands and the neighboring background. The spectrometer and the approach have been successfully demonstrated as a technique for measuring the concentration of OH on two high-altitude balloon flights. This paper reports the instrument design and its achieved performance.

Torr, Marsha R.↗
NASA NTRS1987

The UCB/MPE Cassegrain Submillimeter Heterodyne Spectrometer

The UCB/MPE Submillimeter Heterodyne Spectrometer is a system for astronomical spectroscopy in the high-frequency atmospheric windows from 500 to 1000 GHz. It contains a molecular laser local oscillator, a cooled Schottky open structure mixer, a quasi-optical coupling system, and an acoustooptical spectrometer. The compact receiver mounts at the Cassegrain focus of large infrared astronomical telescopes. The receiver noise temperature on the telescope is approximately 3500 K (DSB) during observations of the CO J = 7-6 line at 806.652 GHz. The spectrometer's frequency resolution and instantaneous bandwidth (less than 2 MHz resolution across 1.1 GHz) are well suited for observations of molecular emission lines from a variety of astronomical sources.

Harris, A. I.↗
NASA NTRS1987

Imaging spectrometers for terrestrial and planetary remote sensing - A progress report

Attention is given to two major design approaches, the 'whiskbroom' and the 'pushbroom', in the present consideration of imaging spectroscopy for both planetary and terrestrial missions. A near-IR mapping spectrometer has been developed for the Galileo Jupiter Orbiter Mission; on the basis of this design, and incorporating focal plane array technology improvements, a family of imaging spectrometers exemplified by the Visual and IR Mapping Spectrometer is under development for other planetary missions.

Wellman, John B.↗
NASA NTRS1988

Preliminary analysis of Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) for mineralogic mapping at sites in Nevada and Colorado

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data for sites in Nevada and Colorado were evaluated to determine their utility for mineralogical mapping in support of geologic investigations. Equal energy normalization is commonly used with imaging spectrometer data to reduce albedo effects. Spectra, profiles, and stacked, color-coded spectra were extracted from the AVIRIS data using an interactive analysis program (QLook) and these derivative data were compared to Airborne Imaging Spectrometer (AIS) results, field and laboratory spectra, and geologic maps. A feature extraction algorithm was used to extract and characterize absorption features from AVIRIS and laboratory spectra, allowing direct comparison of the position and shape of absorption features. Both muscovite and carbonate spectra were identified in the Nevada AVIRIS data by comparison with laboratory and AIS spectra, and an image was made that showed the distribution of these minerals for the entire site. Additional, distinctive spectra were located for an unknown mineral. For the two Colorado sites, the signal-to-noise problem was significantly worse and attempts to extract meaningful spectra were unsuccessful. Problems with the Colorado AVIRIS data were accentuated by the IAR reflectance technique because of moderate vegetation cover. Improved signal-to-noise and alternative calibration procedures will be required to produce satisfactory reflectance spectra from these data. Although the AVIRIS data were useful for mapping strong mineral absorption features and producing mineral maps at the Nevada site, it is clear that significant improvements to the instrument performance are required before AVIRIS will be an operational instrument.

Kruse, Fred A.↗
NASA NTRS1988

Comparison of laboratory calibrations of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at the beginning and end of the first flight season

Spectral and radiometric calibrations of AVIRIS are described together with changes in instrument characteristics that occurred during the flight season. These changes include detachment of the optical fibers to two of the four AVIRIS spectrometers, degradation in the optical alignment of the spectrometers due to thermally induced and mechanical warpage, and breakage of a thermal blocking filter in one of the spectrometers. Means of improving the instrument are discussed.

Vane, Gregg↗
NASA NTRS1988

Comparison of hard X-ray spectra obtained by spectrometers on Hinotori and SMM and detection of 'superhot' component

Hard X-ray spectra in solar flares obtained by the broadband spectrometers aboard Hinotori and SMM are compared. Within the uncertainty brought about by assuming the typical energy of the background X-rays, spectra by the Hinotori spectrometer are usually consistent with those by the SMM spectrometer for flares in 1981. On the contrary, flares in 1982 persistently show 20-50-percent higher flux by Hinotori than by SMM. If this discrepancy is entirely attributable to errors in the calibration of energy ranges, the errors would be about 10 percent. Despite such a discrepancy in absolute flux, in the the decay phase of one flare, spectra revealed a hard X-ray component (probably a 'superhot' component) that could be explained neither by emission from a plasma at about 2 x 10 to the 7th K nor by a nonthermal power-law component. Imaging observations during this period show hard X-ray emission nearly cospatial with soft X-ray emission, in contrast with earlier times at which hard and soft X-rays come from different places.

Nitta, Nariaki↗
NASA NTRS1990

Integrated Grating Spectrometer

Proposed integrated grating spectrometer made in waveguide layer on silicon wafer. Occupies area of about 2 centimeters to 2nd power on wafer 0.4 mm thick. Operates in visible spectrum (wavelengths of 400 to 700 nm) and blazed to diffract in first order. Array of integrated grating spectrometers performs spectral analysis of picture elements along line. Optical fiber couples light from each picture element into separate integrated spectrometer. Technique enables continous independent variation, along grating, of pitch, curvature, and blaze angle. Grating designed to have large numerical aperture, zero aberration at two selected wavelengths, and very low aberration at intermediate wavelengths.

Lang, Robert J.↗
NASA NTRS1989

Scientific considerations in the design of the Mars Observer gamma-ray spectrometer

Cosmic-ray primary and secondary particles induce characteristic gamma-ray and neutron emissions from condensed bodies in our solar system. These characteristic emissions can be used to obtain qualitative and quantitative elemental analyses of planetary surfaces from orbital altitudes. Remote sensing gamma-ray spectroscopy has been successfully used to obtain elemental composition of the Moon and Mars during United States Apollo 15 and 16 missions and the Soviet Luna and Mars missions. A remote sensing gamma-ray and neutron spectrometer will be included aboard the United States Mars Observer Mission. If proper care is not taken in the design of the spectrometer and choice of materials in the construction of the detector system ahd spacecraft, the sensitivity of these remote sensing spectrometers can be greatly degraded. A discussion of these design and material selection problems is presented.

Arnold, J. R.↗
NASA NTRS1989

An EUV spectrometer for atmospheric remote sensing

This paper describes the Berkeley EUV Airglow Rocket Spectrometer (BEARS) experiment, designed to investigate the interactions between the solar ionizing radiation and the earth's upper atmosphere. The primary objective of this experiment is the verification the feasibility of using EUV observations as a quantitative diagnostic of the terrestrial atmosphere and its plasma environment. The expected information provided by spectroscopic measurements of EUV emission will include data on the excitation mechanisms, excitation rates, and branching ratios. The BEARS experimental package consists of a high-resolution EUV airglow spectrometer, a hydrogen Lyman-alpha photometer to measure both the solar radiations and the geocoronal emissions, and a moderate-resolution solar EUV spectrometer. In a test experiment, the instruments were carried aboard a four-stage sounding rocket to a peak altitude of about 960 km and obtained airglow spectra in the 980-1060 A range and in the 1300-1360 range.

Chakrabarti, S.↗
NASA NTRS1990

Development of mercuric iodide uncooled x ray detectors and spectrometers

The results obtained in the development of miniature, lowpower, light weight mercuric iodide, HgI2, x ray spectrometers for future space missions are summarized. It was demonstrated that HgI2 detectors can be employed in a high resolution x ray spectrometer, operating in a scanning electron microscope. Also, the development of HgI2 x ray detectors to augment alpha backscattering spectrometers is discussed. These combination instruments allow for the identification of all chemical elements, with the possible exception of hydrogen, and their respective concentrations. Additionally, further investigations of questions regarding radiation damage effects in the HgI2 x ray detectors are reported.

Iwanczyk, Jan S.↗
NASA NTRS1989

Column atmospheric water vapor retrievals from airborne imaging spectrometer data

High-spatial-resolution column atmospheric water vapor amounts were derived from spectral data collected by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). The quantitative derivation is made by curve fitting observed spectra with calculated spectra in the 1.14- and 0.94-micron water-vapor band absorption regions with a nonlinear least-squares technique. The precision of the retrieved column water vapor is approximately 5 percent. The derived column water vapor amounts are independent of the absolute surface reflectance. Curve fitting of spectra near 1 micron from areas covered with vegetation indicates that both the amount of atmospheric water vapor and the moisture content of vegetation can be retrieved simultaneously. It should be possible to measure column water vapor over land areas from satellite altitude with the proposed high-resolution imaging spectrometer or even the moderate-resolution imaging spectrometer.

Gao, Bo-Cai↗
NASA NTRS1990

Characterization and calibration of the EOIM-III flight mass spectrometer in a high velocity oxygen atom beam

Calibration and characterization of the quadrupole mass spectrometer component of the Evaluation of Oxygen Effects on Materials III (EOIM-III) space-flight experiment are reported in this paper. A high-velocity atom beam system was used to characterize the response of the flight mass spectrometer to high velocity oxygen atoms as well as the reaction/scattering products formed when the atom beam struck a surface. Carbon dioxide, carbon monoxide, and water were observed to form in the mass spectrometer whenever high velocity oxygen atoms were present. The major gaseous products formed from high-velocity atom-beam polymer reactions were easily detected and identified.

Koontz, S. L.↗
NASA NTRS1990

Infrared fiber coupled acousto-optic tunable filter spectrometer

A spectrometer design is introduced which combines an acoustooptic tunable filter (AOTF) and IR-transmitting flouride-glass fibers. The AOTF crystal is fabricated from TeO2 and permits random access to any wavelength in less than 50 microseconds, and the resulting spectrometer is tested for the remote analysis of gases and hydrocarbons. The AOTF spectrometer, when operated with a high-speed frequency synthesizer and optimized algorithms, permits accurate high-speed spectroscopy in the mid-IR spectral region.

Levin, K. H.↗
NASA NTRS1991

Acousto-optic tunable filter imaging spectrometers

A remote sensing multispectral imaging instrument is being developed that uses a high resolution, fast programmable acoustooptic tunable filter (AOTF) as the spectral bandpass filter. A compact and fully computer controllable AOTF-based imaging spectrometer that operates in the visible wavelength range (0.5-0.8 microns) has been built and tested with success. A second imaging spectrometer operating in the near-infrared wavelength range (1.2-2.4 microns) is also under experimental investigation. The design criteria meeting various system issues, such as imaging quality, spectral response, and field of view (FOV), are discussed. An experiment using this AOTF imaging spectrometer breadboard is described.

Chao, Tien-Hsin↗
NASA NTRS1992

Science applications of the Mars Observer gamma ray spectrometer

The Mars Observer gamma ray spectrometer will return data related to the elemental composition of Mars. The instrument has both a gamma ray spectrometer and several neutron detectors. The gamma ray spectrometer will return a spectrum nominally every 20 s from Mars permitting a map of the elemental abundances to be made. The gamma rays are emitted from nuclei involved in radioactive decay, from nuclei formed by capture of a thermal neutron, and from nuclei put in an excited state by a fast-neutron interaction. The gamma rays come from an average depth of the order of a few tens of centimeters. The spectrum will show sharp emission lines whose intensity determines the concentration of the element and whose energy identifies the element. The neutron detectors, using the fact that the orbital velocity of the Mars Observer spacecraft is similar to the velocity of thermal neutrons, determine both the thermal and epithermal neutron flux. By combining the results from both techniques it is possible to map the depth dependence of hydrogen in the upper meter as well. These data permit a variety of Martian geoscience problems to be addressed including the crust and mantle composition, weathering processes, volcanism, and the volatile reservoirs and processes.

Boynton, W. V.↗
NASA NTRS1992

Methane measurement by the Pioneer Venus large probe neutral mass spectrometer

The Pioneer Venus Large Probe Mass Spectrometer detected a large quantity of methane as it descended below 20 km in the atmosphere of Venus. Terrestrial methane and Xe-136, both originating in the same container and flowing through the same plumbing, were deliberately released inside the mass spectrometer for instrumental reasons. However, the Xe-136 did not exhibit behavior similar to methane during Venus entry, nor did CH4 in laboratory simulations. The CH4 was deuterium poor compared to Venus water and hydrogen. While the inlet to the mass spectrometer was clogged with sulfuric acid droplets, significant deuteration of CH4 and its H2 progeny was observed. Since the only source of deuterium identifiable was water from sulfuric acid, we have concluded that we should correct the HDO/H2O ratio in Venus water from 3.2 x 10(exp -2) to (5 plus or minus 0.7) x 10(exp -2). When the probe was in the lower atmosphere, transfer of deuterium from Venus HDO and HD to CH4 can account quantitatively for the deficiencies recorded in HDO and HD below 10 km, and consequently, the mysterious gradients in water vapor and hydrogen mixing ratios we have reported. The revision in the D/H ratio reduces the mixing ratio of water vapor (and H2) reported previously by a factor of 3.2/5. We are not yet able to say whether the methane detected was atmospheric or an instrumental artifact. If it was atmospheric, its release must have been episodic and highly localized. Otherwise, the large D/H ratio in Venus water and hydrogen could not be maintained.

Donahue, T. M.↗
NASA NTRS1993

Gamma Ray/neutron Spectrometers for Planetary Elemental Mapping

Los Alamos has designed gamma ray and neutron spectrometers for Lunar Scout, two robotic missions to map the Moon from 100 km polar orbits. Knowledge of the elemental composition is desirable in identifying resources and for geochemical studies and can be obtained using gamma ray and neutron spectrometers. Measurements with gamma ray and neutron spectrometers complement each other in determining elemental abundances in a planet's surface. Various aspects of the instruments are discussed.

Reedy, R. C.↗