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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 523 records · Page 29
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NASA NTRS1992

The 8-13 micron spectrum of the young stellar object WL 16

Spectroscopy of WL 16 in the 8-13-micron region reveals a spectrum dominated by the hydrocarbon emission features at 7.7, 8.6, 11.25, and 12.7 microns. The emission plateau between the latter two features is detected, the first such detection in a young stellar object. The expected silicate feature is badly masked by the strong emission bands. Combining our spectra with the infrared spectral energy distribution indicates that silicate absorption is probably present.

Hanner, M. S.↗
NASA NTRS1992

Infrared (8-14 microns) remote sensing of soil particle size

Particle size of soils plays a significant role in erosion potential and other mechanical properties. Most soils are dominated by the residual mineral quartz, which displays prominent reststrahlen bands in the 8-14 microns atmospheric window. The Earth Observing System will likely provide world-wide multispectral imagery in the 8-14 microns region via the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument. The ratio of ASTER bands 10/14 can be used to estimate particle size in soils, if other ASTER bands are used to minimize the confusion factors provided by soil moisture, vegetation cover, soil organic content, and the presence of abundant minerals other than quartz. Use of band ratios minimizes the effects of poor surface temperature estimates, but maximizes the need for high signal-to-noise data.

Salisbury, John W.↗
NASA NTRS1993

Effect of micron-sized roughness on transition in swept-wing flows

Boundary-layer transition-to-turbulence studies are conducted in the Arizona State University Unsteady Wind Tunnel on a 45-degree swept airfoil. The pressure gradient is designed so that the initial stability characteristics are purely crossflow-dominated. Flow visualization and hot-wire measurements show that the development of the crossflow vortices is influenced by roughness near the attachment-line. Comparisons of transition location are made between a painted surface, a machine-polished surface, and a hand-polished surface. Then, isolated 6 micron roughness elements are placed near the attachment line on the airfoil surface under conditions of the final polish (0.25 micron rms). These elements amplify a centered stationary crossflow vortex and its neighbors, resulting in localized early transition. The diameter, height, and location of these roughness elements are varied in a systematic manner. Spanwise hot-wire measurements are taken behind the roughness element to document the enhanced vortices. These scans are made at several different chord locations to examine vortex growth.

Radeztsky, Ronald H., Jr.↗
NASA NTRS1991

Detection of metal stress in boreal forest species using the 0.67-micron chlorophyll absorption band

Several recent studies have shown that a shift of the red-edge inflection near 0.70 micron in vegetation reflectance spectra is an indicator of metal stress, partially attributable to changes in chlorophyll concentration. This 'red-edge shift', however, is difficult to detect and has been reported both toward longer (red) and shorter (blue) wavelengths. Our work demonstrates that direct measurement of the depth and width of the chlorophyll absorption band at 0.67 micron using digital feature extraction and absorption band characterization procedures developed for the analysis of mineral spectra is a more consistent indicator of metal stress. Additionally, the magnitude of these parameters is generally greater than that of the red edge shift and thus should be more amenable to detection and mapping using field and aircraft spectrometers.

Singhroy, Vernon H.↗
NASA NTRS1993

Blocked impurity band detectors applied to tunable diode laser spectroscopy in the 8- to 28-micron range

A novel tunable diode laser spectrometer operating at 8-28 microns is described. A blocked impurity band Si:As chip is employed as detector. This device operates in this wavelength range with high detectivity and adequate frequency response for the high-sensitivity techniques used. A combination of sweep averaging and second-harmonic detection at 22 kHz yielded signal-to-noise ratios of 1200 at wavelengths above 20 microns. The sensitivity and spectral resolution achieved are an order of magnitude better than those of Fourier instruments in this range, with an improvement in instrument time response of about 3000. Several molecular bands of CO2 and N2O are observed for what is, to our knowledge, the first time with this instrument. Examples of spectral line measurements are presented.

Sirota, J. M.↗
NASA NTRS1993

Solar magnetic field studies using the 12 micron emission lines. II - Stokes profiles and vector field samples in sunspots

Polarimetric observations at 12 microns of two sunpots are reported. The horizontal distribution of parameters such as magnetic field strength, inclination, azimuth, and magnetic field filling factors are presented along with information about the height dependence of the magnetic field strength. Comparisons with contemporary magnetostatic sunspot models are made. The magnetic data are used to estimate the height of 12 micron line formation. From the data, it is concluded that within a stable sunspot there are no regions that are magnetically filamentary, in the sense of containing both strong-field and field-free regions.

Hewagama, Tilak↗
NASA NTRS1993

Low threshold continuous operation of InGaAs/InGaAsP quantum well lasers at about 2.0 microns

The first low threshold continuous operation of InGaAs strained layer quantum well lasers at about 2.0 microns is reported. The threshold current density of 5-micron wide and 1.5 mm long ridge waveguide lasers was less than 380 A/sq cm. The external differential quantum efficiency of 1 mm long lasers was as high as 15 percent and laser operation was observed at temperatures as high as 50 C. The lasers are characterized by T(0) = 54 C which is the highest characteristic temperature ever achieved at this wavelength in any material system.

Forouhar, S.↗
NASA NTRS1993

Spectral imaging of the 3.3 and 11.3 micron emission bands in NGC 1333 - Discovery of spatially separate band emissions

Spectral images in the 3.3 and 11.3 micron IR emission band around the star SVS 3 in NGC 1333 indicate that the two bands have their origin in different locations, rendering them useless in estimates of the sizes of the molecules emitting the bands. This is in keeping with the emission bands' generation by a mixture of variously sized polycyclic aromatic hydrocarbons (PAHs) whose smallest species have been dehydrogenated in the vicinity of SVS 3. Hot bands and overtone/combination bands may account for the 3.4-micron band, rather than molecular side-groups of the PAHs.

Bregman, Jesse↗
NASA NTRS1993

Luminous infrared galaxies - Sizes at 10-32 microns

We have made estimates of the sizes of 19 infrared galaxies drawn from the highest luminosity galaxies detected by the IRAS survey. The techniques we used were to make multiaperture photometric measurements on the ground-based IR Telescope Facility and to compare these flux densities with the much broader beam measurements obtained by the IRAS survey. Our primary result is that most, but not all, of the galaxies in our sample are extended at 10-25 microns, with characteristic radii of a few hundred parsecs. This result directly supports the widely held assumption that the bulk of the infrared luminosity in these galaxies comes from a central starburst region rather than from the whole disk of the galaxy or from a compact nucleus. The compact nature of Arp 220 is confirmed by direct scans with a 2.9 arcsec aperture at 32 microns.

Wynn-Williams, C. G.↗
NASA NTRS1993

Characteristics of 0.8- and 0.2-microns gate length In(x)Ga(1-x) As/In(0.52)Al(0.48)As/InP (0.53 less than or equal to x less than or equal to 0.70) modulation-doped field-effect transistors at cryogenic temperatures

The performance characteristics of InP-based In(x)Ga(1-x)As/In(0.52)Al(0.48)As (0.53 is less than or equal to x is less than or equal to 0.70) pseudomorphic modulation-doped field-effect transistors (MODFET's) as a function of strain in the channel, gate, length, and temperature were investigated analytically and experimentally. The strain in the channel was varied by varying the In composition x. The temperature was varied in the range of 40-300 K and the devices have gate lengths L(sub g) of 0.8 and 0.2 microns. Analysis of the device was done using a one-dimensional self consistent solution of the Poisson and Schroedinger equations in the channel, a two-dimensional Poisson solver to obtain the channel electric field, and a Monte Carlo simulation to estimate the carrier transit times in the channel. An increase in the value of the cutoff frequency is predicted for an increase in In composition, a decrease in temperature, and a decrease in gate length. The improvements seen with decreasing temperature, decreasing gate length, and increased In composition were smaller than those predicted by analysis. The experimental results on pseudomorphic InGaAs/InAlAs MODFET's showed that there is a 15-30 percent improvement in cutoff frequency in both the 0.8- and 0.2-micron gate length devices when the temperature is lowered from 300 to 40 K.

Lai, Richard↗
NASA NTRS1993

3- to 13-micron spectra of Io

The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obtain 3- to 13-micron spectra of Io on June 14-16, 1991. The extinction correction and its error for each standard star (Alpha Boo, Alpha Lyr, and Mu UMa) were found individually by performing an unweighted linear fit of instrumental magnitude as a function of airmass. The model results indicate two significant trends: (1) modest differences between the two hemispheres at lower background temperatures and (2) a tendency to higher temperatures, smaller areas, and less power from the warm component at higher background temperatures with an increased contrast between the two hemispheres. The increased flux from 8 to 13 microns is due primarily to a greater area on the Loki (trailing) hemisphere for the warm component, although temperature also plays a role.

Noll, Keith S.↗
NASA NTRS1995

Two-micron Laser Atmospheric Wind Sounder (LAWS) pointing/tracking study

The objective of the study was to identify and model major sources of short-term pointing jitter for a free-flying, full performance 2 micron LAWS system and evaluate the impact of the short-term jitter on wind-measurement performance. A fast steering mirror controls system was designed for the short-term jitter compensation. The performance analysis showed that the short-term jitter performance of the controls system over the 5.2 msec round-trip time for a realistic spacecraft environment was = 0.3 micro rad, rms, within the specified value of less than 0.5 micro rad, rms, derived in a 2 micron LAWS System Study. Disturbance modes were defined for: (1) the Bearing and Power Transfer Assembly (BAPTA) scan bearing, (2) the spacecraft reaction wheel torques, and (3) the solar array drive torques. The scan bearing disturbance was found to be the greatest contributing noise source to the jitter performance. Disturbances from the fast steering mirror reaction torques and a boom-mounted cross-link antenna clocking were also considered but were judged to be small compared to the three principal disturbance sources above and were not included in the final controls analysis.

Manlief, Scott↗
NASA NTRS1995

Micron Accuracy Deployment Experiment (MADE), phase A. Volume 1

This report documents a Phase A In-STEP flight experiment development effort. The objective of the experiment is to deploy a portion of a segmented reflector on the Shuttle and study its micron-level mechanics. Ground test data are presented which projects that the on-orbit precision of the test article should be approximately 5 microns. Extensive hardware configuration development information is also provided.

Peterson, Lee D.↗
NASA NTRS1994

Is H2O present on Io? The detection of a new strong band near 3590/cm (2.79 microns)

A strong absorption band at 3590 +/- 20/cm (2.790 +/- 0.015 microns) has been discovered in the spectrum of Io using the Kuiper Airborne Observatory (KAO). The 2nu(sub 1) + nu(sub 3) combination mode of solid SO2 falls at this position. Since SO2 is abundant on Io it must contribute to the new band. However, a band due to H2O was predicted near this frequency in Io's spectrum based on laboratory experiments of H2O:SO2 mixed Io ice analogs which were used to assign the two weak, variable features at 3370 and 3170/cm (2.97 and 3.15 microns) to trace amounts of H2O frozen in solid SO2 on Io. The new band probably originates from both SO2 and H2O. Unfortunately, the spectral resolution of the data is insufficient to settle the issue of whether there are two resolvable components.

Salama, F.↗
NASA NTRS1994

On Io's 2.788-micron band: Origin by SO2 or H2O?

Laboratory reflectance spectra of SO2 frost and ice and thin H2O frost show that the recently reported band at 2.788 microns in Io's disk-integrated spectrum can be qualitatively explained by the presence of solid SO2 on Io's surface. However, the reported width of the Io band is too great to be explained by SO2 frost or ice alone. Lab spectra presented here, and other data cited here, show clearly that solid SO2 has a strong band at 2.789 microns, and that Io should have such a band. These results do not support the claim of Bregman et al. that H2O is the primary cause of the Io band.

Nash, Douglas B.↗
NASA NTRS1994

The Two Micron All Sky Survey

The Two Micron All Sky Survey (2MASS) will provide a uniform survey of the entire sky at three near-infrared wavebands: J(lambda(sub eff) = 1.25 micrometers), H(lambda(sub eff) = 1.65 micrometers), and K(sub s)(lambda(sub eff) = 2.16 micrometers). A major goal of the survey is to probe large scale structures in the Milky Way and in the Local Universe, exploiting the relatively high transparency of the interstellar medium in the near-infrared, and the high near-infrared luminosities of evolved low- and intermediate-mass stars. A sensitive overview of the near-infrared sky is also an essential next step to maximize the gains achievable with infrared array technology. Our assessment of the astrophysical questions that might be addressed with these new arrays is currently limited by the very bright flux limit of the only preceding large scale near-infrared sky survey, the Two Micron Sky Survey carried out at Caltech in the late 1960's. Near-infrared instruments based on the new array technology have already obtained spectra of objects 1 million times fainter than the limit of the TMSS! This paper summarizes the essential parameters of the 2MASS project and the rationale behind those choices, and gives an overview of results obtained with a prototype camera that has been in operation since May 1992. We conclude with a list of expected data products and a statement of the data release policy.

Kleinmann, S. G.↗
NASA NTRS1994

New composite reflectance spectra of Mars from 0.4 to 3.14 micron

To verify the quality and accuracy of Phobos-2 Imaging Spectrometer for Mars (ISM) spectra of Mars, we have performed comparisons with telescopic data obtained contemporaneously and which have spatial and spectral overlap with the ISM measurements. We find general agreement between the independently-calibrated data sets in terms of spectral shape and absorption band strength and position in the 0.77 to 0.93 micron overlap region. The telescopic data were scaled to the ISM reflectance values in this overlap region to yield new bright and dark region composite reflectance spectra from 0.40 to 3.14 microns. We ascribe the increase in band depth and overall spectral heterogeneity of the ISM data relative to previous telescopic observations to the more than order of magnitude increase in spatial resolution achieved by ISM from Martian orbit. Further increases in spatial resolution from future orbital imaging spectroscopic instruments can be expected to reveal even greater degrees of compositional and mineralogic diversity on Mars.

Mustard, John F.↗
NASA NTRS1994

Satellite remote sensing of H2SO4 aerosol using the 8- to 12-microns window region: Application to Mount Pinatubo

Monitoring stratospheric aerosols containing H2SO4 using the brightness temperature (BT) difference between 11 and 8.3 microns (BT(sub 8)-BT(sub 11)) spectral channels is demonstrated using theoretical calculations and satellite observations. Assuming an aqueous solution of 50% and 75% sulfuric acid, radiative transfer calculations indicate that over oceans an increase in the optical depth of the stratospheric aerosol results in an increase in BT(sub 8)-BT(sub 11). Theoretical simulations suggest that the technique is sensitive to visible optical depths greater than approximately 0.15. The simulations also demonstrate a lack of sensitivity to the particle size distribution. Changes in pre- and post-Pinatubo observations by the High-resolution Infrared Radiation Sounder 2 (HIRS2) on board the NOAA 10 are consistent with observed optical depth measurements and confirm the sensitivity of these channels to the presence of the aerosol. The technique is also applied to cold tropical convective clouds and desert regions where the signal, though evident, is less conclusive. Time series analysis is applied to the NOAA 10 and NOAA 12 combined BT(sub 8-BT(sub 11) observations to detect the periodicity of the spread of the volcanic aerosol. Over a region of the southern Pacific a 18- to 26-day period is present. Model simulations were conducted to demonstrate a trispectral with observations near 8, 11, and 12 microns. The trispectral approach has high potential in that the spectral signature of cirrus, water vapor, and H2SO4 aerosols are different. Observations from NOAA 10 and NOAA 11 are combined to demonstrate the capabilities of these infrared wavelengths of detecting the aerosol. The signal is clearly evident when a region of the South Atlantic is compared for pre- and post-Pinatubo conditions.

Ackerman, Steven A.↗