scholarly journals VLBI Measurements of Radio Source Positions at Three U.S. Stations

1981 ◽  
Vol 63 ◽  
pp. 329-336
Author(s):  
Shu-Hua Ye
Keyword(s):  
Radio Source ◽  
Radio Astronomy ◽  
Data Reduction ◽  
Geodetic Survey ◽  
Time Span ◽  
National Geodetic Survey ◽  
Owens Valley ◽  
Radio Observatory ◽  
The U.S

AbstractResults of VLBI measurement of 14 radio source positions at three U.S. stations during the MERIT short campaign is presented. Comparisons with other solutions are given, together with the comparisons between several radio source catalogues.During the MERIT short campaign, several observatories cooperated in VLBI measurements organized jointly by the U.S. National Geodetic Survey (NGS) and the National Aeronautics and Space Administration (NASA). There were two 7-day observations arranged from Sept. 26 to Oct. 2 and from Oct. 16 to Oct. 22, with time span nearly 23 hours per day. Details of the observation and data reduction have been published elsewhere (1). This paper deals with radio source positions determined by three U.S. stations, the Haystack Observatory, the Harvard Radio Astronomy Station (HRAS) and the Owens Valley Radio Observatory (OVRO).

scholarly journals Earth Rotation Information Derived from Merit and Polaris VLBI Observations

1981 ◽  
Vol 63 ◽  
pp. 97-122 ◽  
Author(s):  
D. S. Robertson ◽  
W. E. Carter
Keyword(s):  
Earth Rotation ◽  
The United States ◽  
Geodetic Survey ◽  
West Germany ◽  
National Geodetic Survey ◽  
Space Observatory ◽  
Paper Briefly ◽  
Owens Valley ◽  
Radio Observatory ◽  
Onsala Space Observatory

AbstractIn September and October 1980, the National Geodetic Survey, jointly with the National Aeronautics and Space Administration and several other agencies and institutions, conducted a series of astronomical radio interferometry (VLBI) observing sessions to support the IAU/IUGG MERIT short campaign. A total of 14 days of observations, organized into two 7-day sessions, was collected by three observatories in the United States (Harvard Radio Astronomy Station (HRAS), Haystack Observatory, and Owens Valley Radio Observatory) and the Onsala Space Observatory in Sweden. Chilbolton Observatory, England, and Effelsberg Observatory, West Germany, also participated on some days. Immediately following the MERIT campaign, NGS initiated a series of 24-hour observing sessions, spaced at approximately 2-week intervals, as a pilot program to project POLARIS. All of these sessions included two observatories, HRAS and Haystack, and Onsala participated in about half of the sessions. The MERIT and POLARIS observations were made with the third generation MARK III VLBI system using procedures and schedules designed to yield high quality geodetic information, including Earth rotation values. This paper briefly traces the planning, observing, and data processing activities, and presents the Earth rotation information thus far derived from the data.

A Method for the Evaluation of Vertical Crustal Movement from Scattered Geodetic Relevellings

1974 ◽  
Vol 11 (5) ◽  
pp. 605-610 ◽  
Author(s):  
P. Vaníček ◽  
D. Christodulidis
Keyword(s):  
Chesapeake Bay ◽  
Statistical Significance ◽  
Geodetic Survey ◽  
National Geodetic Survey ◽  
Specific Level ◽  
Vertical Crustal Movement ◽  
Crustal Movements ◽  
Velocity Surface ◽  
Vertical Crustal Movements ◽  
The U.S

The existing techniques for the quantitative evaluation of vertical crustal movements from geodetic spirit levelling have one common feature. They can deal only with a complete network of systematically relevelled connected lines. This paper presents a method, based on the least-squares fitting of a velocity surface, capable of using scattered as well as connected relevelled segments. A facility to choose a specific level of statistical significance of the results is built in. The performance of the method is tested on data for the vicinity of Chesapeake Bay. The results compare well with those of the U.S. National Geodetic Survey.

scholarly journals 40. Radio Astronomy (Radio Astronomie)

1991 ◽  
Vol 21 (1) ◽  
pp. 449-475
Keyword(s):  
Radio Source ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Aperture Synthesis ◽  
Considerable Progress ◽  
Radio Interferometry ◽  
Owens Valley ◽  
Digital Correlator ◽  
Under Construction

The following commission members have contributed to this report:W.J. Altenhoff, H. Andernach, J. Baars, R. Chini, R.J. Cohen, J.J. Condon, Y. Fukui, R. Güsten, J.M. van der Hulst, C. Henkel, W. Huchtmeier, M. Ishiguro, T. Krichbaum, M, Kundu, A. Lazenby, W. Reich, P. Roelfsema, S.E. Thorsett, R. Tuffs, CM. Walmsley, H. Wendker, R. Wielebinski, T.L. Wilson (organizer), A. WitzelAperture Synthesis Telescopes - Commissioning tests and observations have been made using three antennas in the Australia Telescope (AT), spaced up to 2km apart, and the first image of a radio source observed at 6cm was produced in 1989. The IRAM millimeter array in France comprizing three 15-m antennas has been commissioned at 3mm. A fourth antenna is planned as well as operation at 1mm. The three element Berkeley-Illinois-Maryland Array (BIMA) at Hat Creek is being expanded to six 6-m antennas and a new correlator with 1024 channel up to 830MHz bandwidth. Plans to expand to 9 antennas are final. The Owens Valley three-element millimeter array has been operated at 1mm, the shortest wavelength for the radio interferometry; a digital correlator with 500MHz bandwidth is under construction and the array will be extended to 6 antennas. In Japan at NRO the Nobeyama Millimeter Array equipped with SIS receivers and 320MHz bandwidth "FX" correlator is now operational at 3mm and 7mm wavelengths. New SIS receivers for 1mm and 2mm are under construction and a sixth 10-m antenna is planned. The Cambridge 5-km telescope, now the Ryle Telescope, has been substantially upgraded. The overall sensitivity of the instrument is being increased by a factor of ~20. The Giant Metrewave Radio Telescope, being built at Khodad near Pune in India, has made considerable progress and is expected to be operational by 1992-93.

scholarly journals The road to quasars

2014 ◽  
Vol 10 (S313) ◽  
pp. 190-195 ◽  
Author(s):  
K. I. Kellermann
Keyword(s):  
Radio Source ◽  
Optical Measurements ◽  
Radio Sources ◽  
Optical Counterpart ◽  
Owens Valley ◽  
True Nature ◽  
Radio Observatory ◽  
The Road ◽  
Lunar Occultation ◽  
Faint Galaxy

AbstractAlthough the extragalactic nature of 3C 48 and other quasi stellar radio sources was discussed as early as 1960 by John Bolton and others, it was rejected largely because of preconceived ideas about what appeared to be unrealistically high radio and optical luminosities. Not until the 1962 occultations of the strong radio source 3C 273 at Parkes, which led Maarten Schmidt to identify 3C 273 with an apparent stellar object at a redshift of 0.16, was the true nature understood. Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as the very luminous nuclei of galaxies.Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first cataloged in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions which were measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard. Although an accurate radio position had been obtained earlier with the OVRO interferometer, inexplicably 3C 273 was initially misidentified with a faint galaxy located about an arc minute away from the true quasar position.

Multi-GNSS Single-Difference Baseline Processing at NGS with newly developed M-PAGES software

2021 ◽  
Author(s):  
Bryan Stressler ◽  
Andria Bilich ◽  
Clement Ogaja ◽  
Jacob Heck
Keyword(s):  
Geodetic Survey ◽  
Integer Ambiguity ◽  
National Geodetic Survey ◽  
Processing Strategy ◽  
Dual Frequency ◽  
Software Suite ◽  
Legacy Software ◽  
Double Differences ◽  
Single Difference ◽  
Gps Observations

<p>The U.S. National Geodetic Survey (NGS) has historically processed dual-frequency GPS observations in a double-differenced mode using the legacy software called the Program for the Adjustment of GPS Ephemerides (PAGES). As part of NGS’ modernization efforts, a new software suite named M-PAGES (i.e., Multi-GNSS PAGES) is being developed to replace PAGES. M-PAGES consists of a suite of C++ and Python libraries, programs, and scripts built to process observations from all GNSS constellations. The M-PAGES team has developed a single-difference baseline processing strategy that is suitable for multi-GNSS. This approach avoids the difficulty of forming double-differences across systems or frequencies, which may inhibit integer ambiguity resolution. The M-PAGES suite is expected to deploy to NGS’ Online Positioning User Service (OPUS) later this year. Here, we present the processing strategy being implemented along with a performance evaluation from sample baseline solutions obtained from data collected within the NOAA CORS Network.</p>

Preliminary report on some aftershocks of the December 28, 1966 earthquake in Northern Chile

1968 ◽  
Vol 58 (3) ◽  
pp. 843-850 ◽  
Author(s):  
Andrew M. Pitt ◽  
James O. Ellis
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Preliminary Report ◽  
Main Shock ◽  
Geodetic Survey ◽  
Northern Chile ◽  
The U.S

abstract Epicenters of aftershocks of the December 28, 1966 earthquake in northern Chile lie in a 75-km north-trending zone 20 to 30 km off the coastline. The epicenter for the main shock, as determined by the U.S. Coast and Geodetic Survey, is about 10 km north of the southern end of the aftershock zone. The aftershocks are about 30 km deep in the model used for locations; this places them in the lower crust or upper mantle. The aftershocks have no apparent relation to any surface faults.

The experimental geoid 2020 – the first joint geoid model for the North American and Pacific Geopotential Datum 

2021 ◽  
Author(s):  
Yan Ming Wang ◽  
Xiaopeng Li ◽  
Kevin Ahlgren ◽  
Jordan Krcmaric ◽  
Ryan Hardy ◽  
...  
Keyword(s):  
North American ◽  
Gravity Data ◽  
The United States ◽  
Geodetic Survey ◽  
Airborne Gravity ◽  
Data Sets ◽  
National Geodetic Survey ◽  
Geoid Model ◽  
Satellite Gravity ◽  
The North

<p>For the upcoming North American-Pacific Geopotential Datum of 2022, the National Geodetic Survey (NGS), the Canadian Geodetic Survey (CGS) and the National Institute of Statistics and Geography of Mexico (INEGI) computed the first joint experimental gravimetric geoid model (xGEOID) on 1’x1’ grids that covers a region bordered by latitude 0 to 85 degree, longitude 180 to 350 degree east. xGEOID20 models are computed using terrestrial gravity data, the latest satellite gravity model GOCO06S, altimetric gravity data DTU15, and an additional nine airborne gravity blocks of the GRAV-D project, for a total of 63 blocks. In addition, a digital elevation model in a 3” grid was produced by combining MERIT, TanDEM-X, and USGS-NED and used for the topographic/gravimetric reductions. The geoid models computed from the height anomalies (NGS) and from the Helmert-Stokes scheme (CGS) were combined using two different weighting schemes, then evaluated against the independent GPS/leveling data sets. The models perform in a very similar way, and the geoid comparisons with the most accurate Geoid Slope Validation Surveys (GSVS) from 2011, 2014 and 2017 indicate that the relative geoid accuracy could be around 1-2 cm baseline lengths up to 300 km for these GSVS lines in the United States. The xGEOID20 A/B models were selected from the combined models based on the validation results. The geoid accuracies were also estimated using the forward modeling.</p>

scholarly journals The presence of interstellar scintillation in the 15 GHz interday variability of 1158 OVRO-monitored blazars

2019 ◽  
Vol 489 (4) ◽  
pp. 5365-5380 ◽  
Author(s):  
J Y Koay ◽  
D L Jauncey ◽  
T Hovatta ◽  
S Kiehlmann ◽  
H E Bignall ◽  
...  
Keyword(s):  
Flux Density ◽  
High Energy ◽  
Short Term ◽  
Owens Valley ◽  
Hot Stars ◽  
Radio Observatory ◽  
Interstellar Scintillation ◽  
The Galaxy ◽  
Rare Class

ABSTRACT We have conducted the first systematic search for interday variability in a large sample of extragalactic radio sources at 15 GHz. From the sample of 1158 radio-selected blazars monitored over an ∼10 yr span by the Owens Valley Radio Observatory 40-m telescope, we identified 20 sources exhibiting significant flux density variations on 4-d time-scales. The sky distribution of the variable sources is strongly dependent on the line-of-sight Galactic H α intensities from the Wisconsin H α Mapper Survey, demonstrating the contribution of interstellar scintillation (ISS) to their interday variability. 21 per cent of sources observed through sightlines with H α intensities larger than 10  rayleighs exhibit significant ISS persistent over the ∼10 yr period. The fraction of scintillators is potentially larger when considering less significant variables missed by our selection criteria, due to ISS intermittency. This study demonstrates that ISS is still important at 15 GHz, particularly through strongly scattered sightlines of the Galaxy. Of the 20 most significant variables, 11 are observed through the Orion–Eridanus superbubble, photoionized by hot stars of the Orion OB1 association. The high-energy neutrino source TXS 0506+056 is observed through this region, so ISS must be considered in any interpretation of its short-term radio variability. J0616−1041 appears to exhibit large ∼20 per cent interday flux density variations, comparable in magnitude to that of the very rare class of extreme, intrahour scintillators that includes PKS0405−385, J1819+3845, and PKS1257−326; this needs to be confirmed by higher cadence follow-up observations.

scholarly journals Some Considerations in the Use of Very-Long-Baseline-Interferometry to Establish Reference Coordinate Systems for Geodynamics

1980 ◽  
Vol 56 ◽  
pp. 205-216
Author(s):  
Douglas S. Robertson
Keyword(s):  
Reference Frames ◽  
Geodetic Survey ◽  
Limiting Factors ◽  
Radio Sources ◽  
National Geodetic Survey ◽  
Terrestrial Reference Frames ◽  
Long Baseline ◽  
Lithospheric Plates ◽  
Long Time ◽  
The Stability

AbstractPresent knowledge of the number, distribution, proper motion and structures of extragalactic radio sources indicates that there should be no problem in defining a celestial reference frame with stabilities of a few milliseconds of arc over time spans of the order of a decade. One of the limiting factors appears to be the structure of the sources. By measuring and monitoring these structures, the stability could probably be improved by as much as one or two orders of magnitude. Even without this improvement, a network of properly distributed fixed observatories making regular interferometric observations of these radio sources could be used to define a terrestrial coordinate system that could be maintained at the few centimeter level over indefinitely long time periods. Such a stable terrestrial reference system would be useful for a host of modern geodetic and geodynamic applications, including, in particular, studies of the time varying deformations and relative motions of lithospheric plates. The National Geodetic Survey has already begun work on a three station base network of permanent observatories under project POLARIS as a first step toward implementing the new celestial and terrestrial reference frames. It is hoped that others will join in the effort and make the new reference frames a reality by the middle of this decade.

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