Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Very long baseline interferometry”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Early results from a prototype VLBI clock monitoring system

Four sets of experiments were conducted to measure the relative epoch offsets between atomic clocks in California, Australia, and Spain by means of very long baseline interferometry (VLBI). The experiments were conducted using an incomplete R & D VLBI system with a number of inherent limitations. The results indicate that the measurement objective of epoch offset to 10 nanoseconds will be met. Tables show the measured offset, the residual to fit, and the square root Allan variance. Graphs show the rate change and the rate reset.

Yunck, T. P.↗
NASA NTRS1980

VLBI system for weekly measurement of UT1 and polar motion: Preliminary results

The DSN implementation of a system for measuring UT1 and polar motion using very long baseline interferometry (VLBI) is currently being tested. The VLBI experiments are being conducted on a weekly basis on each of two intercontinental baselines. During a 17 day period in September 1979, data were obtained for seven consecutive experiments using an early version of that system. Those experiments were used to refine the estimation procedure to be used in the operational system and to provide a preliminary assessment of the performance of the system.

Roth, M.↗
NASA NTRS1980

Progress report on the Block 1 VLBI correlator implementation

The Block 1 VLBI Processor Subsystem (VPS) of the Very Long Baseline Interferometry (VLBI) System for the determination of station clock-sync parameters, UT1 and polar motion, and station platform parameters and for use in spacecraft tracking is discussed. The Block 1 VPS performs three basic functions: it receives the 500 kbit/sec video data over the GCF wideband data lines from each of the three DSN 64 m antennas; it cross correlates data; and it performs several postcorrelation data reduction operations on the correlated data including calibration, editing, and parameter estimation.

Peterson, J. C.↗
NASA NTRS1980

DSN system performance test software

The software support group of the Deep Space Network support section is continuing the development of system performance test (SPT) software for the Deep Space Network. During the past two and one-half years, test software was developed for a new system, Radio Science, and many new features were added to existing software. Plans are underway for implementation of test software for the very long baseline interferometry system and the network data processing area. A description of the elements of the SPT software is provided.

Leppla, F. B.↗
NASA NTRS1980

Test and evaluation of water vapor radiometers

The accuracy of very long baseline interferometry in geodetic and astrometric applications is primarily limited by the propagation delays through the troposphere. The part of this delay that is most difficult to predict is due to atmospheric water vapor which can contribute up to about 40 cm of excess propagation path at microwave frequencies. The water vapor content in the atmosphere is variable and is not well correlated with surface meteorological variables. The brightness temperature measured near the transition of water vapor at 22.2 GHz and the propagation delay due to water vapor, or wet path length, are well correlated. This correlation is not perfect because the absorption coefficient and index of refraction do not have the same dependence on temperature and pressure.

Moran, J.↗
NASA NTRS1980

Crustal dynamics project observing plan for highly mobile systems 1981 - 1986

Measurement of crustal motion in the western United States and other tectonically active regions makes use of fixed, movable and highly mobile satellite laser ranging and very long baseline interferometry systems. Measurement of the rotational dynamics of the Earth as well as regional deformation and plate motion are discussed.

Frey, H.↗
NASA NTRS1981

Developing new architectures for the Block 2 VLBI correlator system

The overall LSI (large-scale integrated circuits) architecture design and current status of the VBLI (very long baseline interferometry) block 2 correlator is addressed. The VBLI correlator algorithms demand a computing system that provides a throughput of hundreds of millions of instructions per second to perform cross-correlation detection for six baselines. The LSI technology lights the way for the computation of complex parallel process and is raising the upper bound of computerization.

Peterson, J. C.↗
NASA NTRS1981

Transformation from proper time on earth to coordinate time in solar system barycentric space-time frame of reference. I. II

It is noted that in order to obtain accurate computed values of earth-based range and Doppler observables of a deep space probe, an expression is required for the difference between coordinate time (t) in the solar system barycentric space-time frame of reference and proper time (tau) recorded on a fixed atomic clock on earth. This is part 1 of a two-part article which obtains an expression for the coordinate time/proper time difference that can be used in deriving computed values of observations of a spacecraft or celestial body located anywhere in the solar system. The expression can also be used in computing Very Long Baseline Interferometry data types. In part 1, expression for the coordinate time/proper time difference is obtained that is a function of position and velocity vectors of the major celestial bodies of the solar system and the atomic clock on earth which reads proper time. This expression is transformed in part 2 to a function of time and the earth-fixed coordinates of the atomic clock.

Moyer, T. D.↗
NASA NTRS1981

Estimation of the propagation delay through the troposphere from microwave radiometer data

Microwave propagation delay through the troposphere is studied as a means of estimating the adverse effect of atmospheric water vapor on the accuracy of measurements made with very long baseline interferometry. Vertical profiles of temperature and water vapor density were obtained from a total of 240 radiosonde launches taken simultaneously at three New England locations in 1974; all studies were made at the 19 and 22.2 GHz frequency operating range of the radiometers. The wet path length in the zenith direction could be estimated from the surface water vapor density to an accuracy of 5 cm for the summer data and 2 cm for winter data, and with the brightness temperatures, it could be estimated to an accuracy of 0.3 cm. Two dual-frequency radiometers were also used to determine the accuracy of prediction of the path length from real radiometry data. The rms error for the estimation of wet path length from surface meteorological parameters was 3.2 cm, and for the radiometer brightness temperatures the rms error was 1.5 cm.

Moran, J. M.↗
NASA NTRS1981

VLBI observations of the nucleus of the radio galaxy Cygnus A

The central component of the radio galaxy Cygnus A has been observed in several (very long baseline interferometry) experiments between 1975 and 1979, and the results have been combined to derive a model for the brightness distribution. Some 65% of the nuclear emission appears to come from a compact core. The remaining flux density comes from a more extended region (or regions) up to 4 or 5 mas away lying along a position angle near 100 deg, which is close to that of the extended lobes. Evidence that compact central components reflect the collimation and transport of energy to the outer lobes of radio galaxies is discussed, and several interpretations of the observed asymmetries are considered.

Kellermann, K. I.↗
NASA NTRS1980

Methods of using closure phases in radio aperture synthesis

A simple iterative algorithm for reconstructing the images of compact radio sources from very-long-baseline interferometry (VLBI) measurements of visibility amplitudes and 'closure' phases is described. The method makes efficient use of redundant sampling of spatial frequencies by making a global solution of phase 'closure' equations for a complete set of observations.

Rogers, A. E. E.↗
NASA NTRS1981

A proposal to conduct a Caribbean plate project involving the application of space technology to the study of Caribbean geology

The Caribbean plate project is designed to improve current understanding of geological resources and geological hazards within the Caribbean region. Models of mineral occurrence and genesis (including energy resources) on a regional scale, which contribute to nonrenewable resource investigations. Models of lithospheric stress and strain on a regional scale, which contribute to forecasting geological hazards such as earthquakes and major volcanic eruptions are developed. Geological information is synthesize, and research tools provided by space technology the study of the Earth's crust are used. The project was organized in a thematic fashion, to focus on specific geological aspects of the Caribbean plate which are considered to be key factors in developing the types of models described. The project adopts a synoptic perspective in seeking to characterize the three dimensional structure, composition, state of stress, and evolution of the entire Caribbean plate. Geological information derived from analysis of space acquired data is combined with information provided by conventional methods to obtain insight into the structure, composition, and evolution of the Earth's crust. In addition, very long baseline interferometry and laser ranging techniques, which are also based upon the use of space technology, obtain information concerning crustal motion that, in turn, provides insight into the distribution and localization of crustal stress.

Wadge, G.↗
NASA NTRS1982

Shuttle VLBI experiment. Technical working group summary report

The gain in interferometric resolution of extragalactic sources at radio frequencies which can be achieved by placing a very long baseline interferometry (VLBI) antenna in space is quantitatively described and a VLBI demonstration experiment using a large deployable antenna, which if realized could be a very acceptable first venture for VLBI in space is discussed. A tutorial on VLBI, a summary of the technology available for the experiment, and a preliminary mission scenario are included.

Morgan, S. H.↗
NASA NTRS1980

Wideband Delta VLBI for deep space navigation

Developments in the area of deep space tracking and navigation during the last decade are briefly reviewed, and advantages offered by wideband differential Very Long Baseline Interferometry (Delta VLBI) are discussed. Delta VLBI data from a spacecraft and an angularly nearby extragalactic radio source promise to provide a factor of five improvement in deep space navigation accuracies as compared with those presently obtained by conventional radiometric tracking. Results of a restricted bandwidth demonstration of wideband Delta VLBI employing the Voyager spacecraft are analyzed.

Brown, D. S.↗
NASA NTRS1981

Establishment of terrestrial reference frames by new observational techniques

It is anticipated that terrestrial reference systems for geodynamics studies which include adopted plate motion models will be introduced for the analysis of both LAGEOS satellite and very long baseline interferometry ranging data. One of the possible approaches involves adjustment of ground station coordinates in conjunction with solutions for Universal Time 1 (UT1) and polar motions as functions of time. Another method uses principal value decomposition to reduce the number of degrees of freedom being solved for by three. In a third alternative, the values of UT1 and polar motion derived from the available data by means of the initial set of coordinates are kept fixed, and an appropriate block of data is reanalyzed using the previously determined values of UT1 and polar motion so that a new set of station coordinates can be derived.

Bender, P. L.↗
NASA NTRS1982

Orbit determination of geosynchronous satellites by VLBI and differential VLBI

Four approaches to radio interferometric tracking of geosynchronous satellites are analyzed and compared. Quasar-based differential very-long-baseline interferometry, which requires a very sensitive receiver, can achieve meter-level position accuracy with a two-baseline system. Satellite-based differential VLBI gives somewhat lower accuracy with a compact, inexpensive receiver. Nondifferential VLBI, using less precise media and clock calibrations obtained by observing the GPS satellites, still gives 5-10 m position accuracy with two baselines. For a sufficiently inclined orbit, all interferometric approaches can yield six-component satellite state from a single baseline.

Yunck, T. P.↗
NASA NTRS1982

Radio interferometric detection of a traveling ionospheric disturbance excited by the explosion of Mount St. Helens

A large-amplitude traveling ionospheric disturbance (TID) was detected over Owens Valley, California, on May 18, 1980, by a highly sensitive very long baseline interferometry (VLBI) radio astronomy experiment. This TID is interpreted as the response of the ionosphere to a gravity wave excited in the neutral atmosphere by the explosion of Mount St. Helens that took place at 1532 UT on that day. A model, invoking the point-excitation of internal gravity waves in an isothermal atmosphere, which fits observations of the TID at several other stations, leads to identification of the features observed in the VLBI data. Small-amplitude higher-frequency changes in the ionosphere were detected for several hours after the passage of the large-amplitude Mount St. Helens TID, but it is not clear whether these were excited by the passage of the gravity wave or were background fluctuations.

Roberts, D. H.↗