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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 1,081 records · Page 60
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NASA NTRS1991

Simulation of the spectral content of the 7.8-micron emission from Jupiter at high resolution

The present simulation of 1100-1400/cm region emissions ascribable to (C-12)H4, (C-13)H4, and CH3D, as seen by earth observers from a 4-km altitude, conclusively show that the polar hot-spots and other midlatitude features of broadband observations are stratospheric effects. Although signal enhancement in the broadband observations is obtained at increased Doppler shifts and zenith angles approaching zero, the magnitude in the former case is a function of stratospheric temperature.

Halthore, Rangasayi↗
NASA NTRS1992

ACTS T1-VSAT - The intelligent earth station

The functional design of the software for NASA's Advanced Communication Technology Satellite (ACTS) T1-VSAT (Very Small Aperture Terminal) is described. The design provides a flexible interface to allow customized control of a satellite network and to provide external processes with access to network capabilities without requiring modification to the network hardware or software. Some of the envisioned features are: automatic number location; dynamic reconfiguration of the number plan tables; security features of call priority, call preemption, and remote verification; automatic reconfiguration of least cost routing tables; circuit availability verification prior to call setup; audio and video conferencing; on demand broadband dial-up service; on demand dial-up broadband broadcast service; and ISDN. A brief review is also given of the ACTS satellite and network, the network management, and the ACTS T1-VSAT earth station.

Manning, John R.↗
NASA NTRS1992

Decimetric solar type U bursts - VLA and Phoenix observations

Observations of type U bursts, simultaneously detected by the VLA at 1.446 GHz and by the broadband spectrometer Phoenix in the 1.1-1.7 GHz frequency band on August 13, 1989 are reported. Extrapolations of the coronal magnetic field, assuming a potential configuration, indicate that the VLA 20 cm source demarcates an isodensity level. The source covers a wide angle of diverging magnetic field lines whose footpoints originate close to a magnetic intrusion of negative polarity into the main sunspot group of the active region with dominant positive polarity. The centroid of the 20-cm U-burst emission, which corresponds to the turnover frequency of the type U bursts and remains stationary during all U bursts, coincides with the apex of extrapolated potential field lines at a height of about 130,000 km. It is demonstrated that the combination of radio imaging and broadband dynamic spectra, combined with the magnetic field reconstruction from magnetograms, can constrain all physical parameters of a magnetic loop system.

Aschwanden, Markus J.↗
NASA NTRS1992

Radiation budget studies using collocated observations from advanced Very High Resolution Radiometer, High-Resolution Infrared Sounder/2, and Earth Radiation Budget Experiment instruments

Collocated observations from the Advanced Very High Resolution Radiometer (AVHRR), High-Resolution Infrared Sounder/2 (HIRS/2), and Earth Radiation Budget Experiment (ERBE) instruments onboard the NOAA 9 satellite are combined to describe the broadband and spectral radiative properties of the earth-atmosphere system. Broadband radiative properties are determined from the ERBE observations, while spectral properties are determined from the HIRS/2 and AVHRR observations. The presence of clouds, their areal coverage, and cloud top pressure are determined from a combination of the HIRS/2 and the AVHRR observations. The CO2 slicing method is applied to the HIRS/2 to determine the presence of upper level clouds and their effective emissivity. The AVHRR data collocated within the HIRS/2 field of view are utilized to determine the uniformity of the scene and retrieve sea surface temperature. Changes in the top of the atmosphere longwave and shortwave radiative energy budgets, and the spectral distribution of longwave radiation are presented as a function of cloud amount and cloud top pressure. The radiative characteristics of clear sky conditions over oceans are presented as a function of sea surface temperature and atmospheric water vapor structure.

Ackerman, Steven A.↗
NASA NTRS1992

Deep imaging of high redshift QSO fields below the Lyman limit. I - The field of Q0000-263 and galaxies at Z = 3.4

Results are presented for the first field completed in a new survey involving very deep imaging of the fields of high redshift QSOs which exhibit thick Lyman limit absorption systems that completely remove the QSO from the observed broadband UV bandpass. The broadband colors of galaxies near the QSO sightline are examined with knowledge of the redshifts of heavy element absorption systems already discovered in the QSO spectrum. It is suggested that the colors and magnitudes are more consistent with a moderately underluminous galaxy at z = 0.438. A galaxy is identified which is 2.3 mag fainter and is only 2.8 arcsec from the QSO sightline, which is undetected in the present UV bandpass, and could plausibly be associated with the object responsible for the 3.390-z damped Ly-alpha absorption system in the spectrum of Q0000-263.

Steidel, Charles C.↗
NASA NTRS1992

Tilt rotor hover aeroacoustics

The methodology, results, and conclusions of a study of tilt rotor hover aeroacoustics and aerodynamics are presented. Flow visualization and hot wire velocity measurement were performed on a 1/12-scale model of the XV-15 Tilt Rotor Aircraft in hover. The wing and fuselage below the rotor cause a complex recirculating flow. Results indicate the physical dimensions and details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Discrete frequency harmonic thickness and the loading noise mechanism were predicted using WOPWOP for the standard metal blades and the Advanced Technology Blades. The recirculating flow created by the wing below the rotor is a primary sound mechanism for a hovering tilt rotor. The effects of dynamic blade response should be included for fountain flow conditions which produce impulsive blade loading. Broadband noise mechanisms were studied using Amiet's method with azimuthally varying turbulence characteristics derived from the measurements. The recirculating fountain flow with high turbulence levels in the recirculating zone is the dominant source of broadband noise for a hovering rotor. It is shown that tilt rotor hover aeroacoustic noise mechanisms are now understood. Noise predictions can be made based on reasonably accurate aerodynamic models developed here.

Coffen, Charles David↗
NASA NTRS1993

Some effects of dust on photometry of high-z galaxies: Confounding the effects of evolution

Photometric observations of very distant galaxies--e.g., color vs. z or magnitude vs. z, have been used over the past decade or so in investigations into the evolution of the stellar component. Numerous studies have predicted significant color variations as a result of evolution, in addition to the shifting of different rest wavelengths into the band of observation. Although there is significant scatter, the data can be fit with relatively straightforward, plausible models for galaxian evolution. In very few cases are the effects of dust extinction included in the models. This is due in a large part to the uncertainty about the distribution and optical properties of the grains, and even whether or not they are present in significant numbers in some types of galaxies such as ellipticals. It is likely that the effects of dust on broadband observations are the greatest uncertainty in studies of very distant galaxies. We use a detailed Monte Carlo radiative transfer model within a spherical geometry for different star/dust distributions to examine the effects of dust on the broadband colors of galaxies as a function of redshift. The model fully accounts for absorption and angular redistribution in scattering. In this summary, we consider only the effects on color vs. redshift for three simple geometries each with the same total dust optical depth. Elsewhere at this conference, Capuano, Thronson, & Witt consider other effects of altering the relative dust/star distribution.

Thronson, H. A., Jr.↗
NASA NTRS1993

Imaging Spectrometers Using Concave Holographic Gratings

Imaging spectroscopy combines the spatial attributes of imaging with the compositionally diagnostic attributes of spectroscopy. For spacebased remote sensing applications, mass, size, power, data rate, and application constrain the scanning approach. For the first three approaches, substantial savings in mass and size of the spectrometer can be achieved in some cases with a concave holographic grating and careful placement of an order-sorting filter. A hologram etched on the single concave surface contains the equivalent of the collimating, dispersing, and camera optics of a conventional grating spectrometer and provides substantial wavelength dependent corrections for spherical aberrations and a flat focal field. These gratings can be blazed to improve efficiency when used over a small wavelength range or left unblazed for broadband uniform efficiency when used over a wavelength range of up to 2 orders. More than 1 order can be imaged along the dispersion axis by placing an appropriately designed step order-sorting filter in front of the one- or two-dimensional detector. This filter can be shaped for additional aberration corrections. The VIRIS imaging spectrometer based on the broadband design provides simultaneous imaging of the entrance slit from lambda = 0.9 to 2.6 microns (1.5 orders) onto a 128 x 128 HgCdTe detector (at 77 K). The VIRIS spectrometer was used for lunar mapping with the UH 24.in telescope at Mauna Kea Observatory. The design is adaptable for small, low mass, space based imaging spectrometers.

Gradie, J.↗
NASA NTRS1993

De-Dopplerization of aircraft acoustic signals

A de-Dopplerization scheme is devised and applied to both a tonal noise source, a XV-15 aircraft, and a broadband noise source, a F-18 aircraft. The procedure is developed from the conservation equations of fluid mechanics and is described in the paper. The corrected time history is constructed by using linear interpolation in the measured time history. This was made possible by knowing the position history of the aircraft provided by radar and/or laser tracking. The XV-15 data established that the scheme can accurately account for Doppler frequency shifts. The F-18 data confirms what has been noted in prediction models and static tests pertaining to broadband shock associated noise. That is, the peak frequency increases and the peaks broaden toward the jet axis. Another issue addressed in the study is the influence of correcting for spherical spreading and Doppler amplitude on the spectral shape and overall sound pressure levels of the source. Results from this investigation confirm that the dominant noise source in high-speed jets is due to turbulent mixing.

Kelly, Jeffrey J.↗
NASA NTRS1992

Far ultraviolet filters for the ISTP UV imager

The far ultraviolet (FUV) imager for the International Solar-Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: O I lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm-160 nm (LBH long) and 160 nm-180 nm (LBH long). We report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 22.3 and 29.6 percent at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance greater than 40 percent for LBH short and close to 60 percent for LBH long. Blocking of out-of-band wavelengths for all filters is better than 0.001 percent with the transmittance at 121.6 nm of less than 10 exp -6 percent.

Zukic, Muamer↗
NASA NTRS1993

High-resolution study of luminous infrared galaxies. I - The composite nature of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860)

The physical conditions in the ionized gas, the stellar population, and the kinematics of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860) are studied by high spatial resolution optical imaging and optical and near-IR spectroscopy of this luminous IR source. The broadband images show a compact nucleus, two weak spiral arms, a bar, a bulge, an inner ring, and a possible outer ring. The I-alpha image reveals bright emission-line regions associated with the Seyfert nucleus and an inner ring of intense star formation. The forbidden O III 5007-A image shows that the high-excitation gas is elongated perpendicularly to the direction of the bar, and reveals a bright compact object at about 40 arcsec NE of the nucleus which is undetectable in the broadband images. This object is interpreted as a dwarf young H II galaxy. The optical, near-IR, and FIR results show clear evidence that the nuclear and circumnuclear regions have composite and complex structure: a variable Seyfert 1 nucleus embedded in an intense and dusty star formation. environment.

Lipari, Sebastian↗
NASA NTRS1993

Quasi-random narrow-band model fits to near-infrared low-temperature laboratory methane spectra and derived exponential-sum absorption coefficients

Near-infrared 10/cm resolution spectra of methane obtained at various temperatures, pressures, and abundances are fit to a quasi-random narrow-band model. Exponential-sum absorption coefficients for three temperatures (112, 188, and 295 K), and 20 pressures from 0.0001 to 5.6 bars, applicable to the cold environments of the major planets, are then derived from the band model for the 230 wavelengths measured from 1.6 to 2.5 microns. RMS deviations between the laboratory and the exponential-sum synthetic transmissions are reported for the best fitting 50 wavelengths. Deviations relevant to broadband, 1-percent spectral resolution observations are also presented. The validity of exponential-sum coefficients derived from broadband (10/cm) transmission data is demonstrated via direct comparison with line-by-line calculations. The complete atlas of coefficients is available from the Planetary Data System-Planetary Atmospheres Discipline Node.

Baines, Kevin H.↗
NASA NTRS1993

Observations of aerosol by the HALOE experiment onboard UARS - A preliminary validation

The HALOE experiment measures vertical profiles of aerosol extinction at five infrared wavelengths. Four of these observations are obtained using a combination of gas filter and broadband radiometer measurements in bands of HF, HCl, CH4, and NO centered at wavelengths of 2.45, 3.40, 3.45, and 5.26 microns, respectively. The fifth is obtained using broadband radiometer measurements of CO2 transmission at 2.79 microns. Error analysis shows that the random extinction uncertainties are generally less than 10 percent in the aerosol layer, increasing to over 20 percent at the profile tops. HALOE spectral extinction measurements are shown to be consistent with predicted spectral extinction for stratospheric sulfate aerosol. Profile comparisons between HALOE and independent sources result in generally good agreement in the shape and magnitude of peak extinction and the altitude where the peak extinction occurs. In addition, global aerosol distributions obtained from the data are consistent with expected aerosol morphology. Although the validation is preliminary, the HALOE aerosol data appear to be of excellent quality and to accurately represent optical characteristics and distribution of the aerosols.

Hervig, Mark E.↗
NASA NTRS1993

A new near-infrared imaging study of AFGL 2688

The object AFGL 2688 is a bipolar nebula surrounding a post-asymptotic giant branch star and is in transition toward becoming a planetary nebula. We present new NIR images in the I, J, H, and K bandpasses. These images reveal a wealth of structure in the nebula not previously seen. We find that the northern lobe is not smooth, but clumpy. There is evidence in the I-band image for periodic variations in mass-loss rate. In addition, we present narrowband images centered on the V = 1 - 0 S(1) line of molecular hydrogen and nearby continuum. The narrowband images reveal that broadband flux found in the equatorial region is dominated by line emission from vibrationally excited molecular hydrogen. H2 emission is also present in the lobes. Our K-band images show the equatorial emission to be in the form of a ring or torus extending around the object at a distance R about 7 x 10 exp 16 (D/1 kpc) cm. Mechanisms for exciting the equatorial H2 emission are discussed; we conclude that shocks are the only plausible source. We have analyzed the broadband images using models which assume single scattering of photons from the central star. We find that the bipolar axis is inclined to the plane of the sky by i about 5 deg. The images are best reproduced by models in which the density of scattering dust decreases fairly rapidly with increasing stellar latitude, with little or no dust near the poles. Furthermore, the optical depth is found to have very little wavelength dependence, which implies that the dust in AFGL 2688 is different from that in the interstellar medium.

Latter, William B.↗
NASA NTRS1993

Potential markets for advanced satellite communications

This report identifies trends in the volume and type of traffic offered to the U.S. domestic communications infrastructure and extrapolates these trends through the year 2011. To describe how telecommunications service providers are adapting to the identified trends, this report assesses the status, plans, and capacity of the domestic communications infrastructure. Cable, satellite, and radio components of the infrastructure are examined separately. The report also assesses the following major applications making use of the infrastructure: (1) Broadband services, including Broadband Integrated Services Digital Network (BISDN), Switched Multimegabit Data Service (SMDS), and frame relay; (2) mobile services, including voice, location, and paging; (3) Very Small Aperture Terminals (VSAT), including mesh VSAT; and (4) Direct Broadcast Satellite (DBS) for audio and video. The report associates satellite implementation of specific applications with market segments appropriate to their features and capabilities. The volume and dollar value of these market segments are estimated. For the satellite applications able to address the needs of significant market segments, the report also examines the potential of each satellite-based application to capture business from alternative technologies.

Adamson, Steven↗
NASA NTRS1993

Filters for the International Solar Terrestrial Physics (ISTP) mission far ultraviolet imager

The far ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: O I lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm - 160 nm (LBH long) and 160 nm - 180 nm (LBH long). In this paper we report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 percent and 38.3 percent at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60 percent. Blocking of out-of-band wavelengths for all filters is better than 5x10(exp -3) percent with the transmittance at 121.6 nm of less than 10(exp -6) percent.

Zukic, Muamer↗
NASA NTRS1993

VUV thin films, chapter 7

The application of thin film technology to the vacuum ultraviolet (VUV) wavelength region from 120 nm to 230 nm has not been fully exploited in the past because of absorption effects which complicate the accurate determination of the optical functions of dielectric materials. The problem therefore reduces to that of determining the real and imaginary parts of a complex optical function, namely the frequency dependent refractive index n and extinction coefficient k. We discuss techniques for the inverse retrieval of n and k for dielectric materials at VUV wavelengths from measurements of their reflectance and transmittance. Suitable substrate and film materials are identified for application in the VUV. Such applications include coatings for the fabrication of narrow and broadband filters and beamsplitters. The availability of such devices open the VUV regime to high resolution photometry, interferometry and polarimetry both for space based and laboratory applications. This chapter deals with the optics of absorbing multilayers, the determination of the optical functions for several useful materials, and the design of VUV multilayer stacks as applied to the design of narrow and broadband reflection and transmission filters and beamsplitters. Experimental techniques are discussed briefly, and several examples of the optical functions derived for selected materials are presented.

Zukic, Muamer↗
NASA NTRS1993

Video transmission on ATM networks

The broadband integrated services digital network (B-ISDN) is expected to provide high-speed and flexible multimedia applications. Multimedia includes data, graphics, image, voice, and video. Asynchronous transfer mode (ATM) is the adopted transport techniques for B-ISDN and has the potential for providing a more efficient and integrated environment for multimedia. It is believed that most broadband applications will make heavy use of visual information. The prospect of wide spread use of image and video communication has led to interest in coding algorithms for reducing bandwidth requirements and improving image quality. The major results of a study on the bridging of network transmission performance and video coding are: Using two representative video sequences, several video source models are developed. The fitness of these models are validated through the use of statistical tests and network queuing performance. A dual leaky bucket algorithm is proposed as an effective network policing function. The concept of the dual leaky bucket algorithm can be applied to a prioritized coding approach to achieve transmission efficiency. A mapping of the performance/control parameters at the network level into equivalent parameters at the video coding level is developed. Based on that, a complete set of principles for the design of video codecs for network transmission is proposed.

Chen, Yun-Chung↗