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At least 1,189 records · Page 66
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NASA NTRS1992

Development of a tool-set for simultaneous, multi-site observations of astronomical objects

A network of ground and space based telescopes can provide continuous observation of astronomical objects. In a 'Target of Opportunity' scenario triggered by the system, any telescope on the network may request supporting observations. We propose to develop a set of data collection and display tools to support these observations. We plan to demonstrate the usefulness of this tool set for simultaneous multi-site observations of astronomical targets. Possible candidates for the proposed demonstration include the Extreme Ultraviolet Explorer, International Ultraviolet Explorer, ALEXIS, and sounding rocket experiments. Ground based observations operated by the University of California, Berkeley; the Jet Propulsion Laboratory; and Fairborn Observatory, Mesa, Arizona will be used to demonstrate the proposed concept. Although the demonstration will involve astronomical investigations, these tools will be applicable to a large number of scientific disciplines. The software tools and systems developed as a result of our work will be made available to the scientific community.

Chakrabarti, Supriya↗
NASA NTRS1993

Far infrared supplement. Third edition: Catalog of infrared observations (lambda greater than or equal to 4.6 micrometers)

The Far Infrared Supplement contains a subset of the data in the full Catalog of Infrared Observations (all observations at wavelengths greater than 4.6 microns). The Catalog of Infrared Observations (CIO), NASA RP-1294, is a compilation of infrared astronomical observational data obtained from an extensive literature search of scientific journals and major astronomical catalogs and surveys. The literature search is complete for years 1965 through 1990 in this third edition. The catalog contains about 210,000 observations of roughly 20,000 individual sources, and supporting appendices. The expanded third edition contains coded IRAS 4-band data for all CIO sources detected by IRAS. The appendices include an atlas of infrared source positions (also included in this volume), two bibliographies of catalog listings, and an atlas of infrared spectral ranges. The complete CIO database is available to qualified users in printed, microfiche, and magnetic tape formats.

Gezari, Daniel Y.↗
NASA NTRS1992

VLA and Trieste observations of type I storms, type IV and pulsations

A prime objective of this experiment was to determine whether type I or IV sources at 333 MHz contain features of small (arcsec) scale. With the VLA, our resolution was better than 4 arcsec. However, we never observed any structure of size smaller than about 30 arcsec, with the typical source sizes being between about 40 arcsec and 90 arcsec. Many observations were simultaneous with the Trieste Astronomical Observatory records at 327 MHz. The observations were made on two days in November 1988. On November 8 the observations were of a type I storm about two hours after a major flare. On November 14 they were mostly of the main phase of a type IV event, including pulsations of a kind rarely seen, strongly circularly polarized, and having a well-defined period of about 12 s. The size of the pulsating source was about 40 arcsec by 60 arcsec, and the brightness temperature was about 10 exp 9 K. We compare these pulsations with those observed earlier.

Zlobec, P.↗
NASA NTRS1992

Far-ultraviolet observations of the Crab Nebula using the Hopkins Ultraviolet Telescope

Observations of the FUV spectrum of the central portion of the Crab Nebula SNR using the Hopkins Ultraviolet Telescope (HUT) aboard the Astro-1 space shuttle mission in December 1990 are reported. The C IV 1549-A emission line shows two resolved components representing the front and back sides of the shell expanding at roughly +/- 1100 km/s. The He II 1640-A emission line shows only a blueshifted component corresponding to the near side of the shell. The HUT observation is compared to optical emission-line imagery and to archival IUE observations. This comparison indicates that a distribution emission component, consisting of either a number of individually faint filaments or a diffuse component, produces the bulk of the emission seen by HUT. A grid of photoionization models for the Crab Nebula filaments is calculated to infer the range of limits. The differing UV line ratios observed for these components indicates that varying carbon and/or He abundances are present in the observed material.

Blair, William P.↗
NASA NTRS1992

Coronal Magnetic Structures Observing Campaign. II - Magnetic and plasma properties of a solar active region

Simultaneous soft X-ray, microwave, and photospheric magnetic field observations were taken during the Coronal Magnetic Structures Observing Campaign. The plasma electron temperatures and emission measures determined from the X-ray data are used to predict the intensity and structure of the thermal bremsstrahlung emission at 20 and 6 cm. Comparing these predictions with the microwave observations, it is found that the 20 cm structure is very similar to that expected from the X-rays, but a substantial amount of the 6 cm emission was resolved out. The predicted 20 cm brightness temperatures are higher than the observed, requiring cool absorbing material (not greater than 500,000 K) between the hot X-ray plasma and the observer. The absorption mechanism in the cool plasma at 20 cm is most likely thermal bremsstrahlung, requiring coronal magnetic fields as high as 150 G. 'Coronal Magnetograms', made by extrapolating the photospheric longitudinal field using the Sakurai code, show that appropriate values of the total field are reached at heights of 6000-10,000 km above the photosphere (at many but not all locations).

Schmelz, J. T.↗
NASA NTRS1993

Pickup protons and water ions at Comet Halley - Comparisons with Giotto observations

The cometary ion pickup process along the sun-comet line at Comet Halley is investigated using a quasi-linear diffusion model including both pitch angle and energy diffusion, adiabatic compression, and convective motion with the solar wind flow. The model results are compared with energetic ion distributions observed by instruments on board the Giotto spacecraft. The observed power spectrum index of magnetic turbulence (gamma) is 2-2.5. The present simulation shows that when gamma was 2, the calculated proton distributions were much more isotropic than the observed ones. The numerical solutions of the quasi-linear diffusion equations show that the isotropization of the pickup ion distribution, particularly at the pickup velocity, is not complete even close to the bow shock. Given the observed turbulence level, quasi-linear theory yields pickup ion energy distributions that agree with the observed ones quite well and easily produces energetic ions with energies up to hundreds of keV.

Ye, G.↗
NASA NTRS1992

Coordination of multiwavelength groundbased and satellite observations of novae in outburst

Observational data on novae in outburst are reviewed, focusing on the information gained from ultraviolet spectroscopy. Topics discussed include a brief taxonomy of novae, the theoretical framework, observational diagnostics of the outburst, IUE satellite observations, and future trends in novae observations at many wavelengths using space-based observatories to augment the work of ground-based observers.

Shore, Steven N.↗
NASA NTRS1993

OSSE observations of NGC 4151

Observations of the Seyfert galaxy NGC 4151 with the Oriented Scintillation Spectrometer Experiment instrument on the Compton Gamma Ray Observatory are presented. A continuum spectrum is observed, which steepens exponentially with an e-folding energy of 39 +/- 2 keV over the 65-300 keV range. Source intensity variability of approximately 25 percent was seen during the observations, and no significant change in the spectral shape was detected. Simple pair models cannot explain the observed spectrum of NGC 4151, and repeated observations are required to determine whether this spectral shape is common or is even the dominant spectral state in this class of active galactic nuclei.

Maisack, M.↗
NASA NTRS1993

Satellite observation and mapping of wintertime ozone variability in the lower stratosphere

Comparison is made between 30 mbar ozone fields that are generated by a transport chemistry model utilizing the winds from the Goddard Space Flight Center stratospheric data assimilation system (STRATAN), observations from the LIMS instrument on Nimbus-7, and the ozone fields that result from 'flying' a mathematical simulation of LIMS observations through the transport chemistry model ozone fields. The modeled ozone fields were found to resemble the LIMS observations, but the model fields show much more temporal and spatial structure than do the LIMS observations. The 'satellite mapped' model results resemble the LIMS observations much more closely. These results are very consistent with the earlier discussions of satellite space-time sampling by Salby.

Geller, M. A.↗
NASA NTRS1992

Control design based on a linear state function observer

An approach to the design of low-order controllers for large scale systems is proposed. The method is derived from the theory of linear state function observers. First, the realization of a state feedback control law is interpreted as the observation of a linear function of the state vector. The linear state function to be reconstructed is the given control law. Then, based on the derivation for linear state function observers, the observer design is formulated as a parameter optimization problem. The optimization objective is to generate a matrix that is close to the given feedback gain matrix. Based on that matrix, the form of the observer and a new control law can be determined. A four-disk system and a lightly damped beam are presented as examples to demonstrate the applicability and efficacy of the proposed method.

Su, Tzu-Jeng↗
NASA NTRS1993

Remote sensing cloud properties from high spectral resolution infrared observations

A technique for estimating cloud radiative properties (spectral emissivity and reflectivity) in the IR is developed based on observations at a spectral resolution of approximately 0.5/cm. The algorithm uses spectral radiance observations and theoretical calculations of the IR spectra for clear and cloudy conditions along with lidar-determined cloud-base and cloud-top pressure. An advantage of the high spectral resolution observations is that the absorption effects of atmospheric gases are minimized by analyzing between gaseous absorption lines. The technique is applicable to both ground-based and aircraft-based platforms and derives the effective particle size and associated cloud water content required to satisfy, theoretically, the observed cloud IR spectra. The algorithm is tested using theoretical simulations and applied to observations made with the University of Wisconsin's ground-based and NASA ER-2 aircraft High-Resolution Infrared Spectrometer instruments.

Smith, William L.↗
NASA NTRS1992

A comparison of airborne and ground-based radar observations with rain gages during the CaPE experiment

The vicinity of KSC, where the primary ground truth site of the Tropical Rainfall Measuring Mission (TRMM) program is located, was the focal point of the Convection and Precipitation/Electrification (CaPE) experiment in July and Aug. 1991. In addition to several specialized radars, local coverage was provided by the C-band (5 cm) radar at Patrick AFB. Point measurements of rain rate were provided by tipping bucket rain gage networks. Besides these ground-based activities, airborne radar measurements with X- and Ka-band nadir-looking radars on board an aircraft were also recorded. A unique combination data set of airborne radar observations with ground-based observations was obtained in the summer convective rain regime of central Florida. We present a comparison of these data intending a preliminary validation. A convective rain event was observed simultaneously by all three instrument types on the evening of 27 July 1991. The high resolution aircraft radar was flown over convective cells with tops exceeding 10 km and observed reflectivities of 40 to 50 dBZ at 4 to 5 km altitude, while the low resolution surface radar observed 35 to 55 dBZ echoes and a rain gage indicated maximum surface rain rates exceeding 100 mm/hr. The height profile of reflectivity measured with the airborne radar show an attenuation of 6.5 dB/km (two way) for X-band, corresponding to a rainfall rate of 95 mm/hr.

Satake, Makoto↗
NASA NTRS1993

Well-resolved observations by ISEE 2 of ion dispersion in the magnetospheric cusp

During a prolonged period of southward IMF on October 30, 1978, the ISEE 2 spacecraft observed an unusually prolonged and distinct region of ion energy-time dispersion in the dayside dawn magnetosphere. Observed plasma features included the (1) presence of magnetosheath electrons and initial absence of magnetosheath ions and (2) subsequent arrival and energy-time dispersion of magnetosheath ions as the spacecraft transited outbound from 6.03 to 7.66 Earth radii. We use ISEE 2 ion measurements to illustrate these dispersive time-of-flight effects and to support our interpretation of a location in the north magnetospheric cusp. Ion energy dispersion persists for about 35 min and includes well-resolved sequences of magnetosheath and magnetospheric ion distributions. We focus primarily on observations and time-of-flight analysis of ions from the magnetosheath, which are observed simultaneously entering and exiting the cusp at different energies. We discuss the observational support and shortcomings of various ion injection locations and durations and conclude that quasi-steady merging at the dayside magnetopause, with ion dispersion caused by spacecraft motion away from the last closed field line, is the most likely scenario.

Phillips, J. L.↗
NASA NTRS1993

Mars Operational Environmental Satellite (MOES): A post-Mars Observer discovery mission

Mars Operational Environmental Satellite (MOES) is a Discovery concept mission that is designed to observe the global short-term weather phenomena on Mars in a systematic fashion. Even after the Mariner, Viking, and, soon, Mars Observer missions, crucial aspects of the martian atmosphere will remain unobserved systematically. Achieving a better understanding of the cycles of dust, water vapor, and ices on Mars requires detailed information about atmospheric transports of those quantities associated with the weather systems, particularly those arising in mid latitudes during fall and winter. It also requires a quantitive understanding of the processes responsible for the onset and evolution of dust storms on all scales. Whereas on Earth the system of geosynchronous and polar orbiting satellites provides continuous coverage of the weather systems, on Mars the time history of important events such as regional and global dust storms remains unobserved. To understand the transport of tracers in the martian atmosphere and particularly to identify their sources and sinks, it is necessary to have systematic global, synoptic observations that have yet to be attained. Clearly these requirements are not easy to achieve from a single spacecraft in orbit, but if we focus on specific regions of the planet, e.g., polar vs. low and mid latitudes, then it is possible to attain a nearly ideal coverage at a reasonable spatial and temporal resolution with a system of just two satellites. Mars Observer is about to yield good coverage of the polar latitudes, so we focus initially on the region not covered well in terms of diurnal coverage, and in terms of desired observations will provide the initial data for the numerical models of the martian weather and climate that can be verified only with better temporal and spatial data.

Limaye, Sanjay S.↗
NASA NTRS1993

Catalog of Infrared Observations, Third Edition

The Far Infrared Supplement contains a subset of the data in the full Catalog of Infrared Observations (all observations at wavelengths greater than 4.6 microns). The Catalog of Infrared Observations (CIO), NASA RP-1294, is a compilation of infrared astronomical observational data obtained from an extensive literature search of scientific journals and major astronomical catalogs and surveys. The literature search is complete for years 1965 through 1990 in this Third Edition. The Catalog contains about 210,000 observations of roughly 20,000 individual sources and supporting appendices. The expanded Third Edition contains coded IRAS 4-band data for all CIO sources detected by IRAS. The appendices include an atlas of infrared source positions (also included in this volume), two bibliographies of Catalog listings, and an atlas of infrared spectral ranges. The complete CIO database is available to qualified users in printed, microfiche, and magnetic-tape formats.

Gezari, Daniel Y.↗
NASA NTRS1994

Ultraviolet observations of astronomical sources

The final report on 'Ultraviolet Observations of Astronomical Sources,' which ran for a total of three years, roughly between 1 July 1988 and 14 Feb. 1993 is presented. During the first year, I worked at Indiana University; since October, 1989, I have been at Tennessee State University. This grant has supported my studies of archival International Ultraviolet Explorer (IUE) observations of zeta Aur binaries, cool stars that are paired with hot stars in binary systems. Such systems are important as a source of detailed knowledge about the structures of chromospheres and winds in cool giant and supergiant stars, since the hot star serves as a probe of many lines of sight through the cool supergiant star's outer atmosphere. By determining the physical conditions along many such lines of sight, a detailed two-dimensional map of the chromosphere and wind may be constructed. The grant grew out of my analysis of archival IUE observations of 31 Cyg in which I analyzed five epochs of an atmospheric eclipse that occurred in 1982. I fit the attenuation spectra of atmospheric eclipse throughout the ultraviolet (lambda(lambda)1175-1950 and lambda(lambda)2500-3100) with theoretically calculated spectra, thereby determining the physical properties of gas (mass column density of absorbers, temperature, and velocity spread) along each observed line of sight. A similar analysis for other such zeta Aur binaries was accomplished and theoretical models for the chromospheres of these stars based on my observations were constructed.

Eaton, Joel A.↗
NASA NTRS1994

Sulfur dioxide in the atmosphere of Venus 1 sounding rocket observations

In this paper we present ultraviolet reflectance spectra obtained during two sounding rocket observations of Venus made during September 1988 and March 1991. We describe the sensitivity of the derived reflectance to instrument calibration and show that significant artifacts can appear in that spectrum as a result of using separate instruments to observe both the planetary radiance and the solar irradiance. We show that sulfur dioxide is the primary spectral absorber in the 190 - 230 nm region and that the range of altitudes probed by these wavelengths is very sensitive to incidence and emission angles. In a following paper Na et. al. (1994) show that sulfur monoxide features are also present in these data. Accurate identification and measurement of additional species require observations in which both the planetary radiance and the solar irradiance are measured with the same instrument. The instrument used for these observations is uniquely suited for obtaining large phase angle coverage and for studying transient atmospheric events on Venus because it can observe targets within 18 deg of the sun while earth orbiting instruments are restricted to solar elongation angles greater than or equal to 45 deg.

Mcclintock, William E.↗
NASA NTRS1994

IRAS observations show that the Earth is embedded in a solar ring of asteroidal dust particles in resonant lock with the planet

We have analyzed all the infrared observations of the zodiacal cloud obtained in 1983 by the Infrared Astronomical Satellite (IRAS) and shown that when viewed at a constant elongation angle of 90 degrees, the elliptic brightness of the cloud is systematically greater by approx. 3 percent in the trailing direction than in the leading direction. This asymmetry is observed at all times of the year and in all three of the IRAS wavebands in which the zodiacal cloud is clearly observed. The orbits of cometary particles are highly eccentric and these particles are unlikely to be trapped in corotational resonances. Thus, the IRAS observations are evidence that the Earth is embedded in a ring of asteroidal particles. Similar rings are expected to be associated with Mars and Venus. The existence of asteroidal families and their associated dust bands (also discovered by IRAS) are evidence that the asteroid belt is a significant and maybe the dominant source of dust in the zodiacal cloud. These new observations give quantitative information both on the rate of transport of asteroidal dust to the Earth and on the rate of grinding down of the asteroid belt. Without resonant trapping most dust particles spiral past the Earth without striking the planet. However, most particles trapped in resonances are released from these resonances due to close encounter with the Earth. Thus, the ring may act as a funnel through which asteroidal particles are deposited in the Earth's atmosphere. This could have implications for the efficiency of the transport of carbonaceous material from the asteroid belt to the Earth and for the origin of life on the planet.

Dermott, Stanley F.↗