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Sample records for matera cgs vlbi

  1. Matera CGS VLBI Analysis Center

    NASA Technical Reports Server (NTRS)

    Lanotte, Roberto

    2013-01-01

    This paper reports the VLBI data analysis activities at the Space Geodesy Center (CGS), Matera, from January 2012 through December 2012, and the contributions that the CGS intends to provide for the future as an IVS Analysis Center.

  2. The role of CGS/ASI in the Mediterranean area

    NASA Astrophysics Data System (ADS)

    Bianco, Giuseppe; Luceri, Vincenza; Pacione, Rosa

    2017-04-01

    The Centro di Geodesia Spaziale "G. Colombo" (CGS), of the Italian Space Agency (ASI), plays an important role in the geodetic research and products devoted to the Terrestrial Reference Frame realization. Global and regional geodetic products, based on the three space geodesy techniques hosted by CGS (SLR, VLBI, GNSS) are regularly submitted to the geodetic international organizations (IERS, ILRS, IVS, IGS). Moreover, the CGS hosts and operates an absolute gravimeter. Several space geodetic solutions are produced on a regular basis at the CGS geodetic data analysis center, such as daily GPS solutions of the station coordinates in the European area submitted to EUREF as well as daily and weekly estimates of the worldwide SLR network coordinates. In addition, the CGS produces multi-year VLBI and SLR solutions used as reference frame in the combination of multi-technique geodetic solutions. ASI/CGS manages the Italian GNSS fiducial network and delivers GNSS data to the users through the EUREF local data center GeoDAF. The permanent Italian geodetic network is still increasing in size and in the near future it will provide a challenging insight of the kinematics of the central Mediterranean area.

  3. JPSS CGS Evolution

    NASA Astrophysics Data System (ADS)

    Miller, S. W.; Grant, K. D.; Jamilkowski, M. L.

    2012-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). JPSS will contribute the afternoon orbit component and ground processing system. As such, the Joint Polar Satellite System replaces the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. It also replaces the ground processing component of both Polar-orbiting Operational Environmental Satellites, as well as components of the Defense Meteorological Satellite Program (DMSP) replacement, previously known as the Defense Weather Satellite System (DWSS), managed by the Department of Defense (DoD). The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and solar-geophysical observations of the earth, atmosphere and space. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS), which consists of a Command, Control and Communications Segment (C3S) and an Interface Data Processing Segment (IDPS). Both segments are developed by Raytheon Intelligence and Information Systems (IIS). The C3S is currently flying the Suomi National Polar Partnership (Suomi NPP) satellite and transfers mission data from Suomi NPP and between the ground facilities. The IDPS processes Suomi NPP satellite data to provide Environmental Data Records (EDRs) to NOAA and DoD processing centers operated by the United States government. When the JPSS-1 satellite is launched in early 2017, the responsibilities of the C3S and the IDPS will be expanded to support both Suomi NPP and JPSS-1. The CGS also employs its ground stations at Svalbard, Norway and McMurdo Station, Antarctica, along with a global fiber communications network, to provide data acquisition and routing for multiple additional missions. These include POES, DMSP, NASA

  4. International VLBI Service for Geodesy and Astrometry 2004 Annual Report

    NASA Technical Reports Server (NTRS)

    Behrend, Dirk (Editor); Baver, Karen D. (Editor)

    2005-01-01

    Contents include the following: Combination Studies using the Cont02 Campaign. Coordinating Center report. Analysis coordinator report. Network coordinator report. IVS Technology coordinator report. Algonquin Radio observatory. Fortaleza Station report for 2004. Gilmore Creek Geophysical Observatory. Goddard Geophysical and Astronomical observatory. Hartebeesthoek Radio Astronomy Observatory (HartRAO). Hbart, Mt Pleasant, station report for 2004. Kashima 34m Radio Telescope. Kashima and Koganei 11-m VLBI Stations. Kokee Park Geophysical Observatory. Matera GGS VLBI Station. The Medicina Station status report. Report of the Mizusawa 10m Telescope. Noto Station Activity. NYAL Ny-Alesund 20 metre Antenna. German Antarctic receiving Station (GARS) O'higgins. The IVS network station Onsala space Observatory. Sheshan VLBI Station report for 2004. 10 Years of Geodetic Experiments at the Simeiz VLBI Station. Svetloe RAdio Astronomical Observatory. JARE Syowa Station 11-m Antenna, Antarctica. Geodetic Observatory TIGO in Concepcion. Tsukuba 32-m VLBI Station. Nanshan VLBI Station Report. Westford Antenna. Fundamental-station Wettzell 20m Radiotelescope. Observatorio Astroonomico Nacional Yebes. Yellowknife Observatory. The Bonn Geodetic VLBI Operation Center. CORE Operation Center Report. U.S. Naval Observatory Operation Center. The Bonn Astro/Geo Mark IV Correlator.

  5. Matera Laser Ranging Observatory (MLRO): An overview

    NASA Technical Reports Server (NTRS)

    Varghese, Thomas K.; Decker, Winfield M.; Crooks, Henry A.; Bianco, Giuseppe

    1993-01-01

    The Agenzia Spaziale Italiana (ASI) is currently under negotiation with the Bendix Field Engineering Corporation (BFEC) of the Allied Signal Aerospace Company (ASAC) to build a state-of-the-art laser ranging observatory for the Centro di Geodesia Spaziale, in Matera, Italy. The contract calls for the delivery of a system based on a 1.5 meter afocal Cassegrain astronomical quality telescope with multiple ports to support a variety of experiments for the future, with primary emphasis on laser ranging. Three focal planes, viz. Cassegrain, Coude, and Nasmyth will be available for these experiments. The open telescope system will be protected from dust and turbulence using a specialized dome which will be part of the building facilities to be provided by ASI. The fixed observatory facility will be partitioned into four areas for locating the following: laser, transmit/receive optics, telescope/dome enclosure, and the operations console. The optical tables and mount rest on a common concrete pad for added mechanical stability. Provisions will be in place for minimizing the effects of EMI, for obtaining maximum cleanliness for high power laser and transmit optics, and for providing an ergonomic environment fitting to a state-of-the-art multipurpose laboratory. The system is currently designed to be highly modular and adaptable for scaling or changes in technology. It is conceived to be a highly automated system with superior performance specifications to any currently operational system. Provisions are also made to adapt and accommodate changes that are of significance during the course of design and integration.

  6. Matera Laser Ranging Observatory (MLRO): An overview

    NASA Astrophysics Data System (ADS)

    Varghese, Thomas K.; Decker, Winfield M.; Crooks, Henry A.; Bianco, Giuseppe

    1993-06-01

    The Agenzia Spaziale Italiana (ASI) is currently under negotiation with the Bendix Field Engineering Corporation (BFEC) of the Allied Signal Aerospace Company (ASAC) to build a state-of-the-art laser ranging observatory for the Centro di Geodesia Spaziale, in Matera, Italy. The contract calls for the delivery of a system based on a 1.5 meter afocal Cassegrain astronomical quality telescope with multiple ports to support a variety of experiments for the future, with primary emphasis on laser ranging. Three focal planes, viz. Cassegrain, Coude, and Nasmyth will be available for these experiments. The open telescope system will be protected from dust and turbulence using a specialized dome which will be part of the building facilities to be provided by ASI. The fixed observatory facility will be partitioned into four areas for locating the following: laser, transmit/receive optics, telescope/dome enclosure, and the operations console. The optical tables and mount rest on a common concrete pad for added mechanical stability. Provisions will be in place for minimizing the effects of EMI, for obtaining maximum cleanliness for high power laser and transmit optics, and for providing an ergonomic environment fitting to a state-of-the-art multipurpose laboratory. The system is currently designed to be highly modular and adaptable for scaling or changes in technology. It is conceived to be a highly automated system with superior performance specifications to any currently operational system. Provisions are also made to adapt and accommodate changes that are of significance during the course of design and integration.

  7. Supernova VLBI

    NASA Astrophysics Data System (ADS)

    Bartel, N.

    2009-08-01

    We review VLBI observations of supernovae over the last quarter century and discuss the prospect of imaging future supernovae with space VLBI in the context of VSOP-2. From thousands of discovered supernovae, most of them at cosmological distances, ˜50 have been detected at radio wavelengths, most of them in relatively nearby galaxies. All of the radio supernovae are Type II or Ib/c, which originate from the explosion of massive progenitor stars. Of these, 12 were observed with VLBI and four of them, SN 1979C, SN 1986J, SN 1993J, and SN 1987A, could be imaged in detail, the former three with VLBI. In addition, supernovae or young supernova remnants were discovered at radio wavelengths in highly dust-obscured galaxies, such as M82, Arp 299, and Arp 220, and some of them could also be imaged in detail. Four of the supernovae so far observed were sufficiently bright to be detectable with VSOP-2. With VSOP-2 the expansion of supernovae can be monitored and investigated with unsurpassed angular resolution, starting as early as the time of the supernova's transition from its opaque to transparent stage. Such studies can reveal, in a movie, the aftermath of a supernova explosion shortly after shock break out.

  8. The Italian VLBI Network: First Results and Future Perspectives

    NASA Astrophysics Data System (ADS)

    Stagni, Matteo; Negusini, Monia; Bianco, Giuseppe; Sarti, Pierguido

    2016-12-01

    A first 24-hour Italian VLBI geodetic experiment, involving the Medicina, Noto, and Matera antennas, shaped as an IVS standard EUROPE, was successfully performed. In 2014, starting from the correlator output, a geodetic database was created and a typical solution of a small network was achieved, here presented. From this promising result we have planned new observations in 2016, involving the three Italian geodetic antennas. This could be the beginning of a possible routine activity, creating a data set that can be combined with GNSS observations to contribute to the National Geodetic Reference Datum. Particular care should be taken in the scheduling of the new experiments in order to optimize the number of usable observations. These observations can be used to study and plan future experiments in which the time and frequency standards can be given by an optical fiber link, thus having a common clock at different VLBI stations.

  9. Tsukuba VLBI Correlator

    NASA Technical Reports Server (NTRS)

    Kurihara, Shinobu; Nozawa, Kentaro

    2013-01-01

    The K5/VSSP software correlator (Figure 1), located in Tsukuba, Japan, is operated by the Geospatial Information Authority of Japan (GSI). It is fully dedicated to processing the geodetic VLBI sessions of the International VLBI Service for Geodesy and Astrometry. All of the weekend IVS Intensives (INT2) and the Japanese domestic VLBI observations organized by GSI were processed at the Tsukuba VLBI Correlator.

  10. GSFC VLBI Analysis Center

    NASA Technical Reports Server (NTRS)

    Gordon, David; Ma, Chopo; MacMillan, Dan; Gipson, John; Bolotin, Sergei; Le Bail, Karine; Baver, Karen

    2013-01-01

    This report presents the activities of the GSFC VLBI Analysis Center during 2012. The GSFC VLBI Analysis Center analyzes all IVS sessions, makes regular IVS submissions of data and analysis products, and performs research and software development aimed at improving the VLBI technique.

  11. JPSS CGS Tools For Rapid Algorithm Updates

    NASA Astrophysics Data System (ADS)

    Smith, D. C.; Grant, K. D.

    2011-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). JPSS will contribute the afternoon orbit component and ground processing system of the restructured National Polar-orbiting Operational Environmental Satellite System (NPOESS). As such, JPSS replaces the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA and the ground processing component of both POES and the Defense Meteorological Satellite Program (DMSP) replacement known as the Defense Weather Satellite System (DWSS), managed by the Department of Defense (DoD). The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS), and consists of a Command, Control, and Communications Segment (C3S) and the Interface Data Processing Segment (IDPS). Both are developed by Raytheon Intelligence and Information Systems (IIS). The Interface Data Processing Segment will process NPOESS Preparatory Project, Joint Polar Satellite System and Defense Weather Satellite System satellite data to provide environmental data products to NOAA and DoD processing centers operated by the United States government. Under NPOESS, Northrop Grumman Aerospace Systems Algorithms and Data Products (A&DP) organization was responsible for the algorithms that produce the EDRs, including their quality aspects. For JPSS, that responsibility has transferred to NOAA's Center for Satellite Applications & Research (STAR). As the Calibration and Validation (Cal/Val) activities move forward following both the NPP launch and subsequent JPSS and DWSS launches, rapid algorithm updates may be required. Raytheon and

  12. VLBI Observing System for VSOP

    NASA Technical Reports Server (NTRS)

    Ulvestad, J. S.; Murphy, D. W.

    1996-01-01

    The very long baseline interferometry (VLBI) Space Observatory Program (VSOP) satellite is scheduled for launch in September 1996. This paper describes the VLBI observing system for VSOP and its differences from ground radio telescope VLBI systems.

  13. Deformations in VLBI antennas

    NASA Technical Reports Server (NTRS)

    Clark, T. A.; Thomsen, P.

    1988-01-01

    A study is presented of deformations in antennas with the emphasis on their influence on VLBI measurements. The GIFTS structural analysis program has been used to model the VLBI antenna in Fairbanks (Alaska). The report identifies key deformations and studies the effect of gravity, wind, and temperature. Estimates of expected deformations are given.

  14. GSFC VLBI Analysis center

    NASA Technical Reports Server (NTRS)

    Gordon, David; Ma, Chopo; MacMillan, Dan; Petrov, Leonid; Baver, Karen

    2005-01-01

    This report presents the activities of the GSFC VLBI Analysis Center during 2004. The GSFC Analysis Center analyzes all IVS sessions, makes regular IVS submissions of data and analysis products, and performs research and software development activities aimed at improving the VLBI technique.

  15. Haystack Observatory VLBI Correlator

    NASA Technical Reports Server (NTRS)

    Titus, Mike; Cappallo, Roger; Corey, Brian; Dudevoir, Kevin; Niell, Arthur; Whitney, Alan

    2013-01-01

    This report summarizes the activities of the Haystack Correlator during 2012. Highlights include finding a solution to the DiFX InfiniBand timeout problem and other DiFX software development, conducting a DBE comparison test following the First International VLBI Technology Workshop, conducting a Mark IV and DiFX correlator comparison, more broadband delay experiments, more u- VLBI Galactic Center observations, and conversion of RDV session processing to the Mark IV/HOPS path. Non-real-time e-VLBI transfers and engineering support of other correlators continued.

  16. Korean Geodetic VLBI Project

    NASA Astrophysics Data System (ADS)

    Kondo, T.; Kim, T.; Han, S.; Kwak, Y.; Oh, H.; Yi, S.; Bae, M.; Kim, K.; Moon, J.; Park, J.

    2009-04-01

    A permanent geodetic VLBI station with a 22-m diameter antenna will be newly constructed in Korea by the National Geographic Information Institute, Korea (NGII) for the project named Korea VLBI system for Geodesy (KVG) that aims at maintaining the Korean geodetic datum accurately. The KVG has started officially since October, 2008. The construction of all system will be completed by the end of 2011. In Korea, the Korea Astronomy and Space Science Institute (KASI) has already promoted Korean VLBI Network (KVN) project dedicated to radio astronomy since 2001, and three 21-m diameter antennas have been constructed at Seoul, Ulsan, and Jeju Island. Although their receivers have not yet been fully installed, the antenna is designed to be able to receive 22, 43, 86, and 129 GHz bands simultaneously. In parallel with the KVN project, the National Geographic Information Institute, Korea (NGII) has been planning to construct their own VLBI antenna dedicated to geodetic measurements since 2001 to maintain the Korean Geodetic Datum accurately on the International Terrestrial Reference Frame (ITRF). It also aims at a fundamental station in East Asia and will contribute to the better determination of the ITRF there. A grand design for KVG project realizing NGII's plan has been proposed by the Ajou University under the collaborations with the National Institute of Information and Communications Technology, Japan (NICT), National Astronomical Observatory, Japan (NAO), and the Geographical Survey Institute, Japan (GSI). The design of KVG antenna follows the VLBI2010 except for receiving frequencies and the diameter; VLBI2010 is the guideline for next generation's geodetic VLBI system compiled by the International VLBI Service for Geodesy and Astrometry (IVS). The antenna is designed to be able to receive 2, 8, 22, and 43 GHz bands simultaneously in order to carry out geodetic VLBI observations not only with current geodetic VLBI stations equipped with 2/8 GHz receivers but also

  17. VLBI2010: An Overview

    NASA Technical Reports Server (NTRS)

    Petrachenko, Bill

    2010-01-01

    The first concrete actions toward a next generation system for geodetic VLBI began in 2003 when the IVS initiated Working Group 3 to investigate requirements for a new system. The working group set out ambitious performance goals and sketched out initial recommendations for the system. Starting in 2006, developments continued under the leadership of the VLBI2010 Committee (V2C) in two main areas: Monte Carlo simulators were developed to evaluate proposed system changes according to their impact on IVS final products, and a proof-of-concept effort sponsored by NASA was initiated to develop next generation systems and verify the concepts behind VLBI2010. In 2009, the V2C produced a progress report that summarized the conclusions of the Monte Carlo work and outlined recommendations for the next generation system in terms of systems, analysis, operations, and network configuration. At the time of writing: two complete VLBI2010 signal paths have been completed and data is being produced; a number of VLBI2010 antenna projects are under way; and a VLBI2010 Project Executive Group (V2PEG) has been initiated to provide strategic leadership.

  18. Comparison of atmospheric parameters derived from GPS, VLBI and a ground-based microwave radiometer in Italy

    NASA Astrophysics Data System (ADS)

    Pacione, R.; Fionda, E.; Ferrara, R.; Lanotte, R.; Sciarretta, C.; Vespe, F.

    Integrated Precipitable Water Vapor (IPWV) derived from GPS, water vapor radiometer WVR-1100 and RAdiosonde OBservation (RAOB) have been compared for the Cagliari site (Italy) on a seasonal and annual bases. The comparison analysis on estimating IPWV among the three independent techniques (GPS, WVR-110 and RAOB) has shown high accuracy equal to 0.136 cm with a bias of -0.049 cm throughout 1999. Furthermore, a comparison has been made between the estimated atmospheric parameters, equivalent zenith tropospheric delay (ZTD) and horizontal gradient, as resulting from independent analyses of GPS and VLBI data for the three Italian collocated stations: Matera, Medicina and Noto. We have realized that VLBI ZTD estimates are lower than that obtained by GPS of about 1.0-1.5 cm, while the standard deviations range from 0.5 to 2.0 cm.

  19. VLBI Technology Development at SHAO

    NASA Technical Reports Server (NTRS)

    Zhang, Xiuzhong; Shu, Fengchun; Xiang, Ying; Zhu, Renjie; Xu, Zhijun; Chen, Zhong; Zheng, Weimin; Luo, Jintao; Wu, Yajun

    2010-01-01

    VLBI technology development made significant progress at SHAO in the last few years. The development status of the Chinese DBBC, the software and FPGA-based correlators, and the new VLBI antenna, as well as VLBI applications are summarized in this paper.

  20. Supernova research with VLBI

    NASA Astrophysics Data System (ADS)

    Bartel, Norbert; Bietenholz, Michael F.

    2016-06-01

    Core-collapse supernovae have been monitored with VLBI from shortly after the explosion to many years thereafter. Radio emission is produced as the ejecta hit the stellar wind left over from the dyingstar. Images show the details of the interaction as the shock front expands into the circumstellar medium. Measurements of the velocity and deceleration of the expansion provide information on both the ejecta and the circumstellar medium. VLBI observations can also search for the stellar remnant of the explosion, a neutron star or a black hole. Combining the transverse expansion rate with the radial expansion rate from optical spectra allows a geometric determination of the distance to the host galaxy. We will present results from recent VLBI observations, focus on their interpretations, and show updated movies of supernovae from soon after their explosion to the present.

  1. VLBI Correlators in Kashima

    NASA Technical Reports Server (NTRS)

    Sekido, Mamoru; Takefuji, Kazuhiro

    2013-01-01

    Kashima Space Technology Center (KSTC) is making use of two kinds of software correlators, the multi-channel K5/VSSP software correlator and the fast wide-band correlator 'GICO3,' for geodetic and R&D VLBI experiments. Overview of the activity and future plans are described in this paper.

  2. The European VLBI network

    NASA Technical Reports Server (NTRS)

    Schilizzi, R. T.

    1980-01-01

    The capabilities of the European very long baseline interferometry (VLBI) network are summarized. The range of baseline parameters, sensitivities, and recording and other equipment available are included. Plans for upgrading the recording facilities and the use of geostationary satellites for signal transfer and clock synchronization are discussed.

  3. VLBI2010 Feed Comparison

    NASA Technical Reports Server (NTRS)

    Petrachenko, Bill

    2013-01-01

    VLBI2010 requires a feed that simultaneously has high efficiency over the full 2.2-14 GHz frequency range. The simultaneity requirement implies that the feed must operate at high efficiency over the full frequency range without the need to adjust its focal position to account for frequency dependent phase centre variations. Two feeds meet this specification: The Eleven Feed developed at Chalmers University. (For more information, contact Miroslav Pantaleev, miroslav.pantaleev@chalmers.se. The Eleven Feed, integrated with LNA's in a cryogenic receiver, is available as a product from Omnisys Instruments, info@omnisys.se). The Quadruple Ridged Flared Horn (QRFH) developed at the California Institute of Technology. (For more information please contact Ahmed Akgiray, aakgiray@ieee.org or Sander Weinreb, sweinreb@caltech.edu) Although not VLBI2010 compliant, two triband S/X/Ka feeds are also being developed for the commissioning of VLBI2010 antennas, for S/X observations during the VLBI2010 transition period, and to support X/Ka CRF observations. The two feeds are: The Twin Telescopes Wettzell (TTW) triband feed developed by Mirad Microwave. (For more information please contact Gerhard Kronschnabl, Gerhard.Kronschnabl@bkg.bund.de) The RAEGE (Spain) triband feed developed at Yebes Observatory. (For more information please contact Jose Antonio Lopez Perez, ja.lopezperez@oan.es)

  4. CGS 8216: receptor binding characteristics of a potent benzodiazepine antagonist.

    PubMed

    Czernik, A J; Petrack, B; Kalinsky, H J; Psychoyos, S; Cash, W D; Tsai, C; Rinehart, R K; Granat, F R; Lovell, R A; Brundish, D E; Wade, R

    1982-01-25

    CGS 8216 is a novel nonbenzodiazepine that inhibited 3H-flunitrazepam (3H-FLU) binding to rat synaptosomal membranes in vitro at subnanomolar concentrations. It prevented the in vivo labeling of brain benzodiazepine receptors by 3H-FLU with the same potency as diazepam when given orally to mice. Pharmacologic tests showed that it was devoid of benzodiazepine-like activity but it antagonized the actions of diazepam in these tests. It did not interact with alpha- or beta- adrenergic, H1-histaminergic or GABA receptors but it inhibited adenosine-activation of cyclic AMP formation. Studies with 3H-CGS 8216 demonstrated that it bound specifically and with high affinity to rat forebrain membranes and was displaced by drugs with an order of potencies similar to that observed when 3H-diazepam and 3H-FLU were used as radioligands. The regional distribution of 3H-CGS 8216 binding sites in the brain was also similar to that of 3H-FLU. Dissociation of 3H-CGS 8216 binding was slow at 0 degrees C but increased with temperature and was almost complete within 1 min at 37 degrees C. Scatchard analyses were linear, yielding KD values of 0.044, 0.11 and 0.18 nM at 0, 25 and 37 degrees C, respectively; the Bmax value did not change appreciably with temperature and was approximately 1000 fmoles/mg protein. Using 3H-FLU, the value for Bmax as well as for the KD increased with temperature. The total number of binding sites determined for 3H-FLU was greater than that for 3H-CGS 8216 at each temperature. CGS 8216 exhibited mixed-type inhibition of 3H-FLU binding. GABA did not stimulate 3H-CGS 8216 binding whereas it enhanced 3H-FLU binding. CGS 8216 may be a useful ligand for probing the antagonist properties of the benzodiazepine receptor and is likely to exhibit interesting therapeutic effects.

  5. Tracking of Mars Express and Venus Express spacecraft with VLBI radio telescopes

    NASA Astrophysics Data System (ADS)

    Molera Calvés, G.; Pogrebenko, S. V.; Wagner, J.; Cimò, G.; Gurvits, L.; Duev, D.

    2010-12-01

    The ESA Mars Express and Venus Express spacecraft (S/C) have been observed for the last two years with the European VLBI radio telescopes of Metsähovi (FI), Wettzell (GE), Yebes (SP), Medicina, Matera, Noto (IT), Puschino (RU) and Onsala (SW). The campaign is in the framework of the assessment study and preparation of the European VLBI Network to the upcoming ESA and other deep space missions. It also offers new opportunities for applications of radio astronomy techniques to planetary science, geophysics and geodesy. Observations are carried out either in single- or multi-dish modes when S/C is locked to the ESA’s ESTRACK ground stations (Cebreros or New Nortia) observing the two way link. Data are recorded locally at the stations using standard VLBI equipment and transferred to the Metsähovi for processing. Further on, the data are transferred from Metsähovi to Joint Institute for VLBI in Europe for further post-analysis. High dynamic range of the S/C signal detections allowed us to determine the apparent topocentric frequency of the S/C carrier line and accompanying ranging tones down to milli-Hz spectral accuracy and to extract the phase of the S/C signal carrier line. With multi-station observations, the respective phases can be calibrated on the per-baseline basis using VLBI phase referencing technique and observations of background quasars close to S/C in their celestial position using far-field VLBI delay model for quasars and near-field model for S/C. The post-analysis of the S/C tracking data enables us to study several parameters of the S/C signals. Of these, the phase fluctuations of the signal can be used for characterization of the interplanetary plasma density fluctuations along the signal propagation line at different spatial and temporal scales and different solar elongations. These fluctuations are well represented by a near-Kolmogorov spectrum. Multi-station observations can distinguish the contributions of propagation effects in the plasma

  6. Analysis of Regional Deformations In Asia and North America Using Vlbi

    NASA Astrophysics Data System (ADS)

    Yang, Z.; Ma, C.; Luk, P. H.; Shum, C. K.

    Based on the NASA VLBI global solutions glb1123 (Ma, 1999) and glb2001(Ma, 2001), the vertical deformation rates (VDR) of the Kashima and Kashima34 VLBI stations in Japan were re-analysed using the rates of baseline length change from Kashima to 27 global VLBI stations, and from Kashima34 to 12 stations. The velocity vectors of the global VLBI stations were referenced to different ITRFs, i.e., ITRF96, ITRF97 and ITRF2000 for solution sensitivity studies. Using the Eulerian vectors (Sil- laed et al., 1998, Zhang et al., 1999) and based on NNR-NUVEL-1A, the correspond- ing horizontal deformation rates (HDR) of these two stations were also computed and analyzed. The VDR of Kashima34 relative to Kashima is estimated to be -4.2 +/- 0.7 mm/year, and the corresponding HDR of these two stations is 0.9 +/- 0.7 mm/year with AZ at 351.9 +/- 34.2 degrees. To validate the estimated relative deformation rates obtained above, baseline rates of the Kashima and Kashima34 stations relative to 9 common global VLBI stations, and baseline rates relative to 10 stations (9 stations plus Mojave12) have been determined to show that the similar conclusions have been reached. The 9 stations are DSS45 (Tidbinbilla, Australia), Hobert26 (Tasmania, Aus- tralia), Fairbanks (Gilmore Creek, Alaska, USA), Westford (USA), Hartebeesthoek (South Africa), Kauai (Hawaii, USA), Matera (Italy), Seshan25 (Shanghai, China), and Wettzell (Germany); and the additional station used is Mojave12 (USA). We have obtained the averaged relative VDR and HDR between the two stations separated by 300 m as -3.8 +/- 0.8 mm/year, 1.4 +/- 0.8 mm/year with AZ at 336.2 +/- 28.6 de- grees. In addition, the deformation rate of Shanghai, San Francisco, Yuma, Mojave12 and SC-VLBA station regional baselines are analyzed using a similar method and re- sults discussed. In conclusion, the rates of VLBI baseline lengths can be used to accu- rately determine the regional to fine-scale baseline deformations using existing VLBI

  7. Tsukuba 32-m VLBI Station

    NASA Technical Reports Server (NTRS)

    Kawabata, Ryoji; Kurihara, Shinobu; Fukuzaki, Yoshihiro; Kuroda, Jiro; Tanabe, Tadashi; Mukai, Yasuko; Nishikawa, Takashi

    2013-01-01

    The Tsukuba 32-m VLBI station is operated by the Geospatial Information Authority of Japan. This report summarizes activities of the Tsukuba 32-m VLBI station in 2012. More than 200 sessions were observed with the Tsukuba 32-m and other GSI antennas in accordance with the IVS Master Schedule of 2012. We have started installing the observing facilities that will be fully compliant with VLBI2010 for the first time in Japan.

  8. VLBI Data Longevity

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    2003-01-01

    The current cache of S/X-band geodetic/astrometric VLBI data accumulated since 1979 is approx.4.2 million observations and is increasing by approx.300,000 observations per year. The long time interval and access to all such VLBI data for re-analysis have contributed to their usefulness for the terrestrial and celestial reference frames, Earth orientation parameters, tidal and nontidal loading, and troposphere. While data access and integrity have been maintained through the Mark III data base system as storage devices and media have evolved, past transitions have been major projects. A new format and retention concept to ensure eternal archiving and access should make use of self-documentation, generalized media, network connectivity and multiple redundancy. Similarly permanent organizations or sequences of organizations are also necessary.

  9. Simulations of space VLBI

    NASA Technical Reports Server (NTRS)

    Murphy, D. W.; Wilkinson, P. N.

    1991-01-01

    The paper concentrates on the results from space VLBI simulations undertaken during the past four years, beginning with a study of the imaging potential of the proposed medium-term mission QUASAT, and continuing with the Japanese VSOP and Soviet Radioastron missions. The purpose of the study is to determine what quality of images can be expected from space VLBI, given realistic data errors and spacecraft orbits yielding incomplete UV coverage. Much of the paper is devoted to the problem of spurious symmetrization, and a method of overcoming this problem by using a set of UV-constraints is presented. Constraints limiting the imaging ability of the VSOP and Radioastron projects are discussed, and it is concluded that the application of constraints in either sky- or UV-plane will make it possible to overcome spurious symmetrization.

  10. The Southern Hemisphere VLBI experiment

    SciTech Connect

    Preston, R.A.; Meier, D.L.; Louie, A.P.; Morabito, D.D.; Skjerve, L.; Slade, M.A.; Niell, A.E.; Wehrle, A.E.; Jauncey, D.L.; Tzioumis, A.K.; Haystack Observatory, Westford, MA; California Univ., Los Angeles; CSIRO, Div. of Radiophysics, Epping; Sydney Univ.; Manchester Victoria Univ., Jodrell Bank )

    1989-07-01

    Six radio telescopes were operated as the first Southern Hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 GHz. This array provided VLBI modeling and hybrid imaging of celestial radio sources in the Southern Hemisphere, high-accuracy VLBI geodesy between Southern Hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination -45 deg. The goals and implementation of the array are discussed, the methods of modeling and hybrid image production are explained, and the VLBI structure of the sources that were observed is summarized. 36 refs.

  11. VLBI in ASIAA Contribution to Sub-Millimeter VLBI Network

    NASA Astrophysics Data System (ADS)

    Inoue, M.; Asada, K.; Chen, M. T.; Huang, Y. D.; Chen, C. P.; Matsushita, S.; Ho, P.

    2011-05-01

    A new effort has been launched to perform frontier VLBI studies in Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) with the addition of new staff members. The main targets of the new VLBI group are sub-mm and space VLBI to open new physics on super massive black holes (SMBHs) and related issues. Recent observations shows an exciting possibility to see event horizon of SMBH. To get high quality images of it, additional VLBI stations are essential, and site survey has been planned for a new sub-mm VLBI station somewhere in the world. Collaboration has been also discussed to increase the observing efficiency by providing a tracking station for the VSOP-2 project. To pursue these exciting projects, the group is planning to promote a larger science group in ASIAA.

  12. eVLBI at Wettzell

    NASA Astrophysics Data System (ADS)

    Dassing, Reiner; Kronschnabl, Gerhard

    Wettzell's radiotelescope is connected to 34 Mbps INTERNET connection. Since April, 2005, Wettzell is performing eVLBI observations for INT2 on a regular basis. The data is transfered to Tsukuba, and one day after the observations, the results of the correlation is produced. A gain of about 7 days is possible due to eVLBI.

  13. VLBI Data Interchange Format (VDIF)

    NASA Technical Reports Server (NTRS)

    Whitney, Alan; Kettenis, Mark; Phillips, Chris; Sekido, Mamoru

    2010-01-01

    One important outcome of the 7th International e-VLBI Workshop in Shanghai in June 2008 was the creation of a task force to study and recommend a universal VLBI data format that is suitable for both on-the-wire e-VLBI data transfer, as well as direct disk storage. This task force, called the VLBI Data Interchange Format (VDIF) Task Force, is the first part of a two-part effort, the second of which will address standardization of e-VLBI data-transmission-protocols. The formation of the VDIF Task Force was prompted particularly by increased e-VLBI activity and the difficulties encountered when data arrive at a correlator in different formats from various instruments in various parts of the world. The task force created a streaming packetized data format that may be used for real-time and non-realtime e-VLBI, as well as direct disk storage. The data may contain multiple channels of time-sampled data with an arbitrary number of channels, arbitrary #bits/sample up to 32, and real or complex data; data rates in excess of 100 Gbps are supported. Each data packet is completely self-identifying via a short header, and data may be decoded without reference to any external information. The VDIF task force has completed its work, and the VDIF standard was ratified at the 2009 e-VLBI workshop in Madrid.

  14. Methods and Tools for Product Quality Maintenance in JPSS CGS

    NASA Astrophysics Data System (ADS)

    Cochran, S.; Smit, P.; Grant, K. D.; Jamilkowski, M. L.

    2015-12-01

    NOAA's next-generation environmental satellite, the Joint Polar Satellite System (JPSS) replaces the current Polar-orbiting Operational Environmental Satellites (POES). JPSS satellites carry sensors which collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The first JPSS satellite was launched in 2011 and is currently NOAA's primary operational polar satellite. The JPSS ground system is the Common Ground System (CGS), and provides command, control, and communications (C3) and data processing (DP). A multi-mission system, CGS provides combinations of C3/DP for numerous NASA, NOAA, DoD, and international missions. In preparation for the next JPSS satellite, CGS improved its multi-mission capabilities to enhance mission operations for larger constellations of earth observing satellites with the added benefit of streamlining mission operations for other NOAA missions. This paper will discuss both the theoretical basis and the actual practices used to date to identify, test and incorporate algorithm updates into the CGS processing baseline. To provide a basis for this support, Raytheon developed a theoretical analysis framework, and the application of derived engineering processes, for the maintenance of consistency and integrity of remote sensing operational algorithm outputs. The framework is an abstraction of the operationalization of the science-grade algorithm (Sci2Ops) process used throughout the JPSS program. By combining software and systems engineering controls, manufacturing disciplines to detect and reduce defects, and a standard process to control analysis, an environment to maintain operational algorithm maturity is achieved. Results of the use of this approach to implement algorithm changes into operations will also be detailed.

  15. Incorporation of quality updates for JPSS CGS Products

    NASA Astrophysics Data System (ADS)

    Cochran, S.; Grant, K. D.; Ibrahim, W.; Brueske, K. F.; Smit, P.

    2016-12-01

    NOAA's next-generation environmental satellite, the Joint Polar Satellite System (JPSS) replaces the current Polar-orbiting Operational Environmental Satellites (POES). JPSS satellites carry sensors which collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The first JPSS satellite was launched in 2011 and is currently NOAA's primary operational polar satellite. The JPSS ground system is the Common Ground System (CGS), and provides command, control, and communications (C3) and data processing (DP). A multi-mission system, CGS provides combinations of C3/DP for numerous NASA, NOAA, DoD, and international missions. In preparation for the next JPSS satellite, CGS improved its multi-mission capabilities to enhance mission operations for larger constellations of earth observing satellites with the added benefit of streamlining mission operations for other NOAA missions. This paper will discuss both the theoretical basis and the actual practices used to date to identify, test and incorporate algorithm updates into the CGS processing baseline. To provide a basis for this support, Raytheon developed a theoretical analysis framework, and the application of derived engineering processes, for the maintenance of consistency and integrity of remote sensing operational algorithm outputs. The framework is an abstraction of the operationalization of the science-grade algorithm (Sci2Ops) process used throughout the JPSS program. By combining software and systems engineering controls, manufacturing disciplines to detect and reduce defects, and a standard process to control analysis, an environment to maintain operational algorithm maturity is achieved. Results of the use of this approach to implement algorithm changes into operations will also be detailed.

  16. Astrometry VLBI in Space (AVS)

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Reyes, George

    1995-01-01

    This paper describes a proposal for a new space radio astronomy mission for astrometry using Very Long Baseline Interferometry (VLBI) called Astrometry VLBI in Space (AVS). The ultimate goals of AVS are improving the accuracy of radio astrometry measurements to the microarcsecond level in one epoch of measurements and improving the accuracy of the transformation between the inertial radio and optical coordinate reference frames. This study will also assess the impact of this mission on astrophysics astrometry and geophysics.

  17. The AUSTRAL VLBI observing program

    NASA Astrophysics Data System (ADS)

    Plank, L.; Lovell, J. E. J.; McCallum, J. N.; Mayer, D.; Reynolds, C.; Quick, J.; Weston, S.; Titov, O.; Shabala, S. S.; Böhm, J.; Natusch, T.; Nickola, M.; Gulyaev, S.

    2017-07-01

    The AUSTRAL observing program was started in 2011, performing geodetic and astrometric very long baseline interferometry (VLBI) sessions using the new Australian AuScope VLBI antennas at Hobart, Katherine, and Yarragadee, with contribution from the Warkworth (New Zealand) 12 m and Hartebeesthoek (South Africa) 15 m antennas to make a southern hemisphere array of telescopes with similar design and capability. Designed in the style of the next-generation VLBI system, these small and fast antennas allow for a new way of observing, comprising higher data rates and more observations than the standard observing sessions coordinated by the International VLBI Service for Geodesy and Astrometry (IVS). In this contribution, the continuous development of the AUSTRAL sessions is described, leading to an improvement of the results in terms of baseline length repeatabilities by a factor of two since the start of this program. The focus is on the scheduling strategy and increased number of observations, aspects of automated operation, and data logistics, as well as results of the 151 AUSTRAL sessions performed so far. The high number of the AUSTRAL sessions makes them an important contributor to VLBI end-products, such as the terrestrial and celestial reference frames and Earth orientation parameters. We compare AUSTRAL results with other IVS sessions and discuss their suitability for the determination of baselines, station coordinates, source coordinates, and Earth orientation parameters.

  18. IVS Working Group 4: VLBI Data Structures

    NASA Technical Reports Server (NTRS)

    Gipson, John

    2010-01-01

    In 2007 the IVS Directing Board established IVS Working Group 4 on VLBI Data Structures. This note discusses the current VLBI data format, goals for a new format, the history and formation of the Working Group, and a timeline for the development of a new VLBI data format.

  19. Orbit determination of geosynchronous satellites by VLBI and differential VLBI

    NASA Technical Reports Server (NTRS)

    Yunck, T. P.; Wu, S. C.

    1982-01-01

    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.

  20. Radar and ground measurements on wheat fields over the Matera site: an experimental study

    NASA Astrophysics Data System (ADS)

    Mattia, Francesco; Gatti, Anna Maria; Posa, Franco; D'Alessio, Angelo; Notarnicola, Claudia; Sabatelli, Enzo; Rinaldi, Michele; Satalino, Giuseppe; Pasquariello, Guido; Le Toan, Thuy; Picard, Ghislain; Davidson, Malcolm

    2002-01-01

    This paper describes ground and radar measurements collected on wheat fields over the Matera site in Italy during the 2001 growing season. The objective of the paper is twofold. Firstly to investigate the relationship between the C-band backscatter with wheat biomass and with the underlying soil moisture content. Secondly to provide well documented data in order to validate electromagnetic scattering models for cereal crops. From March to June 2001 six ERS-2 overpasses of the site have been acquired. In addition, eight C-band ground-based scatterometer acquisitions, at HH and VV polarisation, with incidence angles ranging between 23° and 60° have been achieved. Coinciding with ERS-2 and scatterometer acquisitions ground data in terms of soil moisture, wheat biomass and canopy structure have been collected. This paper describes the experiments and presents the first data analysis.

  1. Upgrading and performance of the SAO laser ranging system in Matera

    NASA Technical Reports Server (NTRS)

    Maddox, J.; Pearlman, M.; Throp, J.; Wohn, J.

    1983-01-01

    The performance of the SAO lasers was improved considerably in terms of accuracy, range noise, data yield, and reliability. With the narrower laser pulse (2.5-3.0 nsec) and a new analog pulse processing system, the systematic range errors were reduced to 3-5 cm and range noise has been reduced to 5-15 cm on low satellites and 10-18 cm on Lageos. Pulse repetition rate was increased to 30 ppm and considerable improvement has been made in signal-to-noise ratio by using a 3 Angstrom interference filter and by reducing the range gate window down to 200-400 nsec. The first upgraded system was installed in Arequipa, Peru in the spring of 1982. The second upgraded system is now in operation in Matera, Italy. The third system is expected to be installed in Israel during 1984.

  2. Korea Geodetic VLBI Station, Sejong

    NASA Technical Reports Server (NTRS)

    Donghyun, Baek; Sangoh, Yi; Hongjong, Oh; Sangchul, Han

    2013-01-01

    The Sejong VLBI station officially joined the IVS as a new Network Station in 2012. This report summarizes the activities of the Sejong station during 2012. The following are the activities at the station: 1) VLBI test observations were carried out with the Tsukuba 34-m antenna of the GSI in Japan. As a result, the Sejong antenna needs to improve its efficiency, which is currently in progress, 2) A survey to connect the VLBI reference point to GNSS and ground marks was conducted, and 3) To see the indirect effects of RFI (Radio Frequency Interference) at this place, we checked the omni-direction (AZ 0? to 360?, EL fixed at 7?) for RFI influence.

  3. Algorithm Integration in the JPSS CGS in the JPSS-1 Era

    NASA Astrophysics Data System (ADS)

    Grant, K. D.; Ibrahim, W.

    2016-12-01

    NOAA and NASA are jointly acquiring the next-generation civilian weather satellite system: the Joint Polar Satellite System (JPSS). JPSS replaced the afternoon orbit component and ground processing of NOAA's old POES system. JPSS satellites carry sensors that collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The JPSS ground system is the Common Ground System (CGS), and provides command, control, communications (C3), data processing and product delivery. CGS provides combinations of these functions for numerous U.S. and international missions. CGS processes JPSS data to provide environmental data products (Sensor Data Records (SDRs) and Environmental Data Records (EDRs)) to NOAA and DoD centers. The first satellite, S-NPP, was launched 28 Oct 2011. JPSS-1 is scheduled to launch in January 2017. Currently CGS processes and delivers SDRs and EDRs for S-NPP and will continue for all JPSS missions. As the science improves, supplements, or replaces existing algorithms, changes require implementation into CGS. To shorten the time required, Raytheon developed methods enabling rapid integration into CGS. These include the Algorithm Development Library (ADL), the Algorithm Integration Framework (AIF) and the Accelerated Release Cycle (ARC). ADL enables scientist to develop algorithms and provide them in a form that are rapidly integrated into the baseline. Algorithms are not restricted to JPSS missions; it provides an environment that scientist use to create algorithms that plug into a CGS instantiation. The AIF allows direct integration of binary algorithms into CGS, without modification of the source. Finally, ARC provides a stable, rapid release cycle into CGS providing for shorter cycle times between updates and operations. This paper describes the tools and processes CGS implemented to speed the science to operations process, with an emphasis on support to the upcoming JPSS-1 Cal/Val.

  4. VLBI2010 PROOF-OF-CONCEPT GEODETIC VLBI SYSTEM

    NASA Astrophysics Data System (ADS)

    Beaudoin, C.; Niell, A. E.

    2009-12-01

    Geodetic Very Long Baseline Interferometry (VLBI) plays an important role in establishing the Terrestrial Reference Frame, measuring the Earth-orientation parameters (EOP), and understanding the properties of the Inner Core, among other geophysical phenomena. To enhance the science obtained from geodetic VLBI, NASA is funding the development of a new broadband geodetic VLBI microwave (2-12 GHz) system by the MIT Haystack Observatory, in cooperation with personnel from HTSI, NVI, and GSFC. This broadband system is intended to replace the operational S/X-band system currently deployed in the global geodetic VLBI network. The broadband capability of the new feed and receiver and the sustained data recording rate (up to 4 Gbps per band) supported by the digital back-end and Mark5C recorder will a) allow the use of relatively small (~12m) but fast slewing antennas to reduce the error due to atmosphere delay fluctuations and b) provide flexibility in frequency coverage to reduce sensitivity to external radio frequency interference, an increasing problem. A demonstration system has been implemented by installing the proof-of-concept feed, receiver, and data acquisition system on the single baseline composed of the 18m antenna in Westford MA and the 5m MV3 antenna at the Goddard Space Flight Center in Greenbelt MD. In our contribution we will describe the new geodetic VLBI system and discuss recent results. Future challenges and advances that will be needed in both hardware and software to achieve the required precision of the geodetic observables will also be presented.

  5. VLBI data, acquisition, environmental effects

    NASA Technical Reports Server (NTRS)

    Herring, Thomas A.

    1995-01-01

    During this quadrennium, very long baseline interferometry (VLBI) data acquisition and system development has focused on improving the accuracy of the system sufficiently to allow the determination of reliable estimates of height variations. Associated with this aim has been improvements in the determinations of horizontal velocity fields, monitoring water vapor delay using interferometric methods, and improvements to Earth rotation measurements. The primary aims of the improvements to height measurement accuracy have been to directly measure the contemporary magnitudes of post glacial rebound, and to determine a height reference system for measuring global sea level rise. High frequency Earth rotation studies have been carried out to better define the transformation parameters from an inertial coordinate system to an Earth fixed one, and to better understand the coupling between the components of the atmosphere-ocean-solid Earth system. Two major VLBI campaigns were carried out in support of these studies: (1) Epoch-92 in July 1992 and (2) Cont-94 in January 1994. Each of these campaigns lasted approximately two weeks and involved multiple VLBI networks operating simultaneously in addition to other space geodetic systems operating during these periods. Two major compilations of the VLBI results (and results from other space geodetic systems) have been published during this quadrennium.

  6. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Use of Space Link Extension (SLE) Protocol

    NASA Astrophysics Data System (ADS)

    Jamilkowski, M. L.; Cordier, G. R.; Johnson, L. M.; Tillery, C. J.

    2014-12-01

    NOAA & NASA are acquiring the next-generation civilian operational weather satellite -- Joint Polar Satellite System (JPSS). Contributing the afternoon orbit & ground system (GS) to replace current NOAA POES Satellites, its sensors will collect meteorological, oceanographic, climatological & solar-geophysical data. The JPSS Common Ground System (CGS), consisting of Command, Control & Communications (C3) and Interface Data Processing (IDP) segments, is developed by Raytheon. CGS now flies the Suomi National Polar-orbiting Partnership (S-NPP) satellite, transferring data between ground facilities, processing them into Environmental Data Records for NOAA & DoD weather centers, and expanding to support JPSS-1 in 2017. CGS Block 2.0 (B2.0) is the recent CDR-approved design to support both the current S-NPP and upcoming JPSS-1 missions. In B2.0, many important improvements were made to evolve CGS C3. One of those improvements is the addition of SLE services. The CCSDS SLE Protocol standard facilitates and significantly improves GS-to-Data Center communications. The CGS SLE architecture provides data reliability and resource scheduling and is scalable to support added missions. The JPSS CGS is a mature, tested solution for supporting operational weather forecasting for civil, military, and international partners as well as climate research. It features a flexible design that handles order-of-magnitude increases in data over legacy satellite ground systems and meets demanding science accuracy needs. The JPSS CGS is expandable to support additional ground station service providers with or without the deployment of additional JPSS ground hardware by using standard SLE Transfer Service protocol and offers opportunities to reduce costs and improve information Integration across missions. The Raytheon-built JPSS CGS provides the full common ground capability, from design and development through operations & sustainment. These features lay the foundation for the CGS future

  7. Managed and Supported Missions in the Joint Polar Satellite System (JPSS) Common Ground System (CGS)

    NASA Astrophysics Data System (ADS)

    Jamilkowski, M. L.; Grant, K. D.; Miller, S. W.; Cochran, S.

    2015-12-01

    NOAA & NASA are acquiring the next-generation civilian operational weather satellite: Joint Polar Satellite System (JPSS). Replacing the p.m. orbit & ground system (GS) of POES satellites, JPSS sensors will collect weather, ocean & climate data. JPSS's Common Ground System (CGS), made up of C3 & IDP parts and developed by Raytheon, now flies the Suomi National Polar-orbiting Partnership (S-NPP) satellite, transfers data between ground facilities, processes them into Environmental Data Records for NOAA's weather centers and evolves to support JPSS-1 in 2017. CGS processed S-NPP data creates many TBs/day across >2 dozen environmental data products (EDPs), doubling after JPSS launch. But CGS goes beyond this by providing data routing to other missions: GCOM-W1, Coriolis/Windsat, EOS, NSF's McMurdo Station, Defense Meteorological Satellite Program, and POES & MetOp satellites. Each system orbits 14 times/day, downlinking data 1-2 times/orbit at up to 100s of MBs/sec, to support the creation of 10s of TBs of data/day across 100s of EDPs. CGS's flexible, multimission capabilities offer major chances for cost reduction & improved information integration across the missions. CGS gives a vital flexible-expandable-virtualized modern GS architecture. Using 5 global ground stations to receive S-NPP & JPSS-1 data, CGS links with high-bandwidth commercial fiber to rapidly move data to the IDP for EDP creation & delivery and leverages these networks to provide added support to more missions. CGS data latency will be < 80 minutes. JPSS CGS is a mature, tested solution for support to operational weather forecasting for civil, military and international partners and climate research. It features a flexible design handling order-of-magnitude increases in data over legacy systems and meets tough science accuracy needs. The Raytheon-built CGS gives the full GS capability, from design & development through operations & sustainment, facilitating future evolution to support more missions.

  8. Accurate Spacecraft Positioning by VLBI Imaging

    NASA Astrophysics Data System (ADS)

    Zheng, Weimin; Tong, Fengxian; Shu, Fengchun

    2016-12-01

    VLBI is a radio astronomy technique with very high space angle resolution, and the Chinese VLBI Network has played an important role in the Chang'E series lunar mission. In the upcoming Chinese lunar and deep space missions, the ability to achieve higher resolution angular positions will be necessary. For these reasons, we have carried out research into accurate spacecraft positioning and have conducted several space vehicle phase-referencing positioning experiments using the Chinese VLBI Network and other VLBI antennas. This paper shows the VLBI spacecraft imaging position experiment results for the Chang'E lunar probes, the Mars Express probe, and the Rosetta probe. The results have validated phase reference VLBI with the milli-arcsecond level position resolution for deep space probes.

  9. GSFC VLBI Analysis Center Annual Report

    NASA Technical Reports Server (NTRS)

    Gordon, David; Ma, Chopo; MacMillan, Dan

    1999-01-01

    The GSFC VLBI group, located at NASA's Goddard Space Flight Center in Greenbelt, MD, is a part of the NASA Space Geodesy Program. Since its inception in the mid 1970's, this group has been involved with and been a leader in most aspects of geodetic and astrometric VLBI. Current major activities include coordination of the international geodetic observing program; coordination and analysis of the CORE program; VLBI technique development; and all types of data processing, analysis, and research activities.

  10. The future of VLBI observatories in space

    NASA Technical Reports Server (NTRS)

    Preston, R. A.; Jordan, J. F.; Burke, B. F.; Doxsey, R.; Morgan, S. H.; Roberts, D. H.; Shapiro, I. I.

    1983-01-01

    The angular resolution of radio maps made by earth-based VLBI observations can be exceeded by placing at least one element of a VLBI array into earth orbit. A VLBI observatory in space can offer the additional advantages of increased sky coverage, higher density sampling of Fourier components, and rapid mapping of objects whose structure changes in less than a day. This paper explores the future of this technique.

  11. Mark-III VLBI astrometry of pulsars

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.; Dewey, Rachel J.; Gwinn, Carl R.; Davis, Michael M.

    1991-01-01

    Differential 18-cm VLBI measurements of the position of PSR 1937 + 214 with respect to the quasar 1923 + 210 are reported. The preliminary results for VLBI minus timing position are +21 +/- 2 milliarcsec in right ascension and +14 +/- 9 milliarcsec in declination. The results show the value of combining the large collecting area of the Arecibo telescope with the Mk-III VLBI recording system.

  12. The celestial reference frame defined by VLBI

    NASA Technical Reports Server (NTRS)

    Ma, C.; Shaffer, D. B.

    1988-01-01

    VLBI currently produces the most accurate positions of celestial objects. From 1979 to 1987, 114 extragalactic radio sources have been observed with dual-frequency Mark III VLBI as part of the NASA Crustal Dynamics Project and the NGS POLARIS/IRIS program. The formal statistical errors of conventional celestial coordinates are as small as 0.3 milliarcseconds. The fundamental quantity measured by VLBI is the arc length between radio sources. Thus, it is suggested that VLBI be used to establish a coordinate reference frame based solely on radio positions, and that this system not necessarily be coupled to right ascension and declination.

  13. JPL VLBI Analysis Center Report for 2012

    NASA Technical Reports Server (NTRS)

    Jacobs, Chris

    2013-01-01

    This report describes the activities of the JPL VLBI Analysis Center for the year 2012. The highlight of the year was the successful MSL rover Mars landing, which was supported by VLBI-based navigation using our combined spacecraft, celestial reference frame, terrestrial reference frame, earth orientation, and planetary ephemeris VLBI systems. We also supported several other missions with VLBI navigation measurements. A combined NASA-ESA network was demonstrated with first Ka-band fringes to ESA's Malargue, Argentina 35 m. We achieved first fringes with our new digital back end and Mark 5C recorders.

  14. The Mark III VLBI System

    NASA Technical Reports Server (NTRS)

    Rogers, A. E. E.; Whitney, A. R.; Levine, J. I.; Nesman, E. F.; Webber, J. C.; Hinteregger, H. F.

    1988-01-01

    Geodetic measurements have errors in centimeter range. Collection of three reports describes both equipment and results of some measurements taken with Mark III very-long-baseline interferometry (VLBI) system. Has demonstrated high accuracy over short baselines, where phase-delay measurements used. Advanced hardware, called Mark III A, developed to improve system performance and efficiency. Original Mark III hardware and III A subsystem upgrades developed as part of NASA Crustal Dynamics Project at Haystack Observatory.

  15. Orbit determination of highly elliptical Earth orbiters using VLBI and delta VLBI measurements

    NASA Technical Reports Server (NTRS)

    Frauenholz, R. B.; Ellis, J.

    1983-01-01

    The feasibility of using very long baseline interferometric (VLBI) data acquired by the deep space network to navigate highly elliptical Earth orbiting satellites was shown. The navigation accuracy improvements achievable with VLBI and delta VLBI data types are determined for comparison with the Doppler capability. The sensitivity of the VLBI navigation accuracy to the baseline orientation relative to the orbit plane and the effects of major error sources such as gravitational harmonics and atmospheric are examined. It is found that VLBI measurements perform as well as strategies using conventional Doppler, while substantially reducing the required antenna support.

  16. The African VLBI network project

    NASA Astrophysics Data System (ADS)

    Loots, Anita

    2015-01-01

    The AVN is one of the most significant vehicles through which capacity development in Africa for SKA participation will be realized. It is a forerunner to the long baseline Phase 2 component of the mid-frequency SKA. Besides the 26m HartRAO telescope in South Africa, Ghana is expected to be the first to establish a VLBI-capable telescope through conversion of a redundant 32m telecommunications system near Accra. The most widely used receivers in the EVN are L-band and C-band (5 GHz). L-band is divided into a low band around the hydrogen (HI) line frequency of 1420 MHz, and a high band covering the hydroxyl line frequencies of 1612-1720 MHz. The high band is much more commonly used for VLBI as it provides more bandwidth. For the AVN, the methanol maser line at 6668 MHz is a key target for the initial receiver and the related 12178MHz methanol maser line also seen in star-forming regions a potential future Ku-band receiver. In the potential future band around 22GHz(K-band), water masers in star-forming regions and meg-maser galaxies at 22.235 GHz are targets, as are other radio continuum sources such as AGNs. The AVN system will include 5GHz and 6.668GHz receiver systems with recommendation to partner countries that the first upgrade should be L-band receivers. The original satellite telecommunications feed horns cover 3.8 - 6.4 GHz and should work at 5 GHz and operation at 6.668 GHz for the methanol maser is yet to be verified. The first light science will be conducted in the 6.7 GHz methanol maser band. Telescopes developed for the AVN will initially join other global networks for VLBI. When at least four VLBI-capable telescopes are operational on the continent, it will be possible to initiate stand-alone AVN VLBI. Each country where an AVN telescope becomes operational will have its own single-dish observing program. Capacity building to run an observatory includes the establishment of competent core essential observatory staff in partner countries who can train

  17. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Multimission Support

    NASA Astrophysics Data System (ADS)

    Jamilkowski, M. L.; Miller, S. W.; Grant, K. D.

    2014-12-01

    NOAA & NASA are acquiring the next-generation civilian operational weather satellite: Joint Polar Satellite System (JPSS). Contributing the afternoon orbit & ground system (GS) to replace current NOAA POES Satellites, its sensors will collect meteorological, oceanographic, climatological & solar-geophysical data. The JPSS Common Ground System (CGS), consisting of C3 and IDP segments, is developed by Raytheon. It now flies the Suomi National Polar-orbiting Partnership (S-NPP) satellite, transferring data between ground facilities, processing them into Environmental Data Records for NOAA & DoD weather centers, and expanding to support JPSS-1 in 2017.CGS now does data processing (DP) for S-NPP, creating many TBs/day across >2 dozen environmental data products (EDPs). This doubles after JPSS-1 launch. But CGS goes well beyond this by providing data routing support to other global missions.Those other missions are: GCOM-W1, Coriolis/Windsat, EOS, NSF's McMurdo Station, Defense Meteorological Satellite Program (DMSP), and POES & MetOp satellites. Each system orbits 14 times/day, downlinking data 1-2 times/orbit at up to 100s of MBs/sec, to support the creation of 10s of TBs of data/day across 100s of EDPs.CGS's flexible, multimission capabilities offer major chances for cost reduction & improved information integration across the missions. Raytheon has a unique ability to provide complex, highly-secure, multi-mission GSs. A flexible, expandable and virtualized modern GS architecture is vital -- CGS offers the solution.CGS supports 5 global ground stations receiving S-NPP & JPSS-1 mission data. These, linked with high-bandwidth commercial fiber, quickly transport data to the IDP for EDP creation & delivery. CGS data latency will be < 80 minutes. CGS leverages the fiber network to provide added support to many other missions.The JPSS CGS is a mature, tested solution for support to operational weather forecasting for civil, military and international partners and climate

  18. SAI VLBI Analysis Center Report 2012

    NASA Technical Reports Server (NTRS)

    Zharov, Vladimir

    2013-01-01

    This report presents an overview of the SAI VLBI Analysis Center activities during 2012 and the plans for 2013. The SAI AC analyzes all IVS sessions for computations of the Earth orientation parameters (EOP) and time series of the ICRF source positions and performs research and software development aimed at improving the VLBI technique.

  19. VLBI clock synchronization. [for atomic clock rate

    NASA Technical Reports Server (NTRS)

    Counselman, C. C., III; Shapiro, I. I.; Rogers, A. E. E.; Hinteregger, H. F.; Knight, C. A.; Whitney, A. R.; Clark, T. A.

    1977-01-01

    The potential accuracy of VLBI (very long baseline interferometry) for clock epoch and rate comparisons was demonstrated by results from long- and short-baseline experiments. It was found that atomic clocks at widely separated sites (several thousand kilometers apart) can be synchronized to within several nanoseconds from a few minutes of VLBI observations and to within one nanosecond from several hours of observations.

  20. Space VLBI and the Radio Reference Frame

    NASA Astrophysics Data System (ADS)

    Charlot, P.

    2009-08-01

    The current radio reference frame is defined by the VLBI positions of several hundreds of extragalactic sources measured with sub-milliarcsecond accuracy. We discuss whether space VLBI can be used to improve the accuracy of the frame, either directly by conducting absolute astrometric observations using space VLBI baselines, or in an indirect way by making available VLBI images of the reference frame sources with increased angular resolution. The VSOP-2 project, in its present state, is found to have the necessary capabilities for accurate absolute astrometry although there may be limitations due to scheduling constraints. Space VLBI images are essential for pinpointing accurately a stable reference feature within the extended structure of each source. In this respect, the VSOP-2 project may have a significant impact on the definition of the radio reference frame if targeting such reference frame sources on a regular basis.

  1. VLBI2010 Imaging and Structure Corrections

    NASA Technical Reports Server (NTRS)

    Collioud, Arnaud; Charlot, Patrick

    2010-01-01

    Simulations show that the next generation VLBI system is generally well suited for imaging extragalactic radio sources. In addition to revealing the morphology of the sources, simulated VLBI2010 images may also be used to generate structure correction maps, which characterize the impact of source structure on the VLBI measurements. By comparing structure corrections for a set of simulated images based on Monte-Carlo generated visibilities with theoretical structure corrections derived from the model, we assess the accuracy of VLBI2010 structure corrections. In the most favorable case (32-station network, source at declination +40 deg.), statistics demonstrate that the structure corrections obtained from simulated images are statistically close to the theoretical model ones, which seems very promising for the VLBI2010 system.

  2. Use of the VLBI delay observable for orbit determination of Earth-orbiting VLBI satellites

    NASA Technical Reports Server (NTRS)

    Ulvestad, J. S.

    1992-01-01

    Very long-baseline interferometry (VLBI) observations using a radio telescope in Earth orbit were performed first in the 1980s. Two spacecraft dedicated to VLBI are scheduled for launch in 1995; the primary scientific goals of these missions will be astrophysical in nature. This article addresses the use of space VLBI delay data for the additional purpose of improving the orbit determination of the Earth-orbiting spacecraft. In an idealized case of quasi-simultaneous observations of three radio sources in orthogonal directions, analytical expressions are found for the instantaneous spacecraft position and its error. The typical position error is at least as large as the distance corresponding to the delay measurement accuracy but can be much greater for some geometries. A number of practical considerations, such as system noise and imperfect calibrations, set bounds on the orbit-determination accuracy realistically achievable using space VLBI delay data. These effects limit the spacecraft position accuracy to at least 35 cm (and probably 3 m or more) for the first generation of dedicated space VLBI experiments. Even a 35-cm orbital accuracy would fail to provide global VLBI astrometry as accurate as ground-only VLBI. Recommended charges in future space VLBI missions are unlikely to make space VLBI competitive with ground-only VLBI in global astrometric measurements.

  3. The adenosine receptor antagonist CGS15943 reinstates cocaine-seeking behavior and maintains self-administration in baboons.

    PubMed

    Weerts, Elise M; Griffiths, Roland R

    2003-07-01

    Caffeine and the adenosine A(1) and A(2A) receptor antagonist CGS15943 produce many behavioral effects that are similar to those produced by classic stimulant drugs (e.g. cocaine and amphetamines). The current study evaluated whether CGS15943 would maintain self-administration and reinstate extinguished lever responding previously maintained by cocaine (i.e. cocaine-seeking) or by food (i.e. food-seeking). Reinstatement with CGS15943 was compared to cocaine, caffeine, and alprazolam. Up to 30 injections of 0.032 mg/kg cocaine or 30 deliveries of 1-g food pellets were available under a fixed ratio (FR10) schedule of reinforcement during daily 2-h sessions. For reinstatement tests, lever responses were extinguished by substituting saline for cocaine or by removing pellets from the mechanical feeder. After extinction of lever responding, acute "priming" doses (mg/kg, IV) of cocaine (0.1-3.2), the adenosine receptor antagonists caffeine (0.1-1.8) and CGS15943 (0.032-0.32) or the benzodiazepine receptor agonist alprazolam (0.1-1.8 mg/kg) were administered. The intravenous reinforcing effects of CGS15943 were also evaluated; each dose of CGS15943 (0.001-0.032 mg/kg) was substituted for cocaine for at least 10 days and until self-injection was relatively stable. Cocaine, caffeine and CGS15943, dose-dependently increased cocaine-seeking, where as alprazolam did not. Cocaine, caffeine and CGS15943 did not increase food-seeking. CGS15943 reinstated cocaine-seeking at rates that were comparable to those produced by cocaine. Pretreatment with the adenosine A(2) agonist CGS21680 decreased CGS15943-induced reinstatement of cocaine-seeking. In self-injection testing, CGS15943 was self-administered at levels greater than vehicle. An inverted U-shaped dose-effect function was obtained with peak mean rates maintained by 0.01 mg/kg CGS15943. The adenosine antagonist CGS15943 reinstated cocaine-seeking and functioned as an intravenous reinforcer. The finding that CGS21680 produced a

  4. The "Quasar" Network Observations in e-VLBI Mode Within the Russian Domestic VLBI Programs

    NASA Technical Reports Server (NTRS)

    Finkelstein, Andrey; Ipatov, Alexander; Kaidanovsky, Michael; Bezrukov, Ilia; Mikhailov, Andrey; Salnikov, Alexander; Surkis, Igor; Skurikhina, Elena

    2010-01-01

    The purpose of the Russian VLBI "Quasar" Network is to carry out astrometrical and geodynamical investigations. Since 2006 purely domestic observational programs with data processing at the IAA correlator have been carried out. To maintain these geodynamical programs e-VLBI technology is being developed and tested. This paper describes the IAA activity of developing a real-time VLBI system using high-speed digital communication links.

  5. VLBI2010 in NASA's Space Geodesy Project

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    2012-01-01

    In the summer of 20 11 NASA approved the proposal for the Space Geodesy Project (SGP). A major element is developing at the Goddard Geophysical and Astronomical Observatory a prototype of the next generation of integrated stations with co-located VLBI, SLR, GNSS and DORIS instruments as well as a system for monitoring the vector ties. VLBI2010 is a key component of the integrated station. The objectives ofSGP, the role of VLBI20 lOin the context of SGP, near term plans and possible future scenarios will be discussed.

  6. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Current Technical Performance Measures

    NASA Astrophysics Data System (ADS)

    Cochran, S.; Panas, M.; Jamilkowski, M. L.; Miller, S. W.

    2015-12-01

    ABSTRACT The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). The Joint Polar Satellite System will replace the afternoon orbit component and ground processing system of the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and geophysical observations of the Earth. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence, Information and Services (IIS), the CGS is a multi-mission enterprise system serving NOAA, NASA and their national and international partners. The CGS has demonstrated its scalability and flexibility to incorporate multiple missions efficiently and with minimal cost, schedule and risk, while strengthening global partnerships in weather and environmental monitoring. The CGS architecture is being upgraded to Block 2.0 in 2015 to "operationalize" S-NPP, leverage lessons learned to date in multi-mission support, take advantage of more reliable and efficient technologies, and satisfy new requirements and constraints in the continually evolving budgetary environment. To ensure the CGS meets these needs, we have developed 49 Technical Performance Measures (TPMs) across 10 categories, such as data latency, operational availability and scalability. This paper will provide an overview of the CGS Block 2.0 architecture, with particular focus on the 10 TPM categories listed above. We will provide updates on how we ensure the deployed architecture meets these TPMs to satisfy our multi-mission objectives with the deployment of Block 2.0.

  7. Kashima and Koganei 11-m VLBI Stations

    NASA Technical Reports Server (NTRS)

    Sekido, Mamoru; Ichikawa, Ryuichi

    2013-01-01

    Two 11-m VLBI antennas at Kashima and Koganei are continuously operated and maintained by the National Institute of Information and Communications Technology (NICT). This report summarizes the status of these antennas, the staff, and the activities in 2012.

  8. Earth Rotation Parameters from DSN VLBI: 1994

    NASA Technical Reports Server (NTRS)

    Steppe, J. A.; Oliveau, S. H.; Sovers, O. J.

    1994-01-01

    In this report, Earth Rotation Parameter (ERP) estimates ahve been obtained from an analysis of Deep Space Network (DSN) VLBI data that directly aligns its celestial and terrestrial reference frames with those of the International Earth Rotation Service (IERS).

  9. Earth Rotation Parameters from DSN VLBI: 1994

    NASA Technical Reports Server (NTRS)

    Steppe, J. A.; Oliveau, S. H.; Sovers, O. J.

    1994-01-01

    In this report, Earth Rotation Parameter (ERP) estimates ahve been obtained from an analysis of Deep Space Network (DSN) VLBI data that directly aligns its celestial and terrestrial reference frames with those of the International Earth Rotation Service (IERS).

  10. Updated Deep Space Communications Complex VLBI Processor

    NASA Astrophysics Data System (ADS)

    Navarro, R.; Rogstad, S.; Goodhart, C. E.; Sigman, E.; Soriano, M.; Wang, D.; White, Leslie A.; Jacobs, Christopher S.

    JPL VLBI Data Acquisition Modernization Program has two Current Purposes with two different recording systems. One for Radio Reference Frame and Time & Earth Motion Observations - Uses MarkIV formatters and Mark5A recorders. One for Double Differential One Way Ranging for spacecraft tracking - Uses Wideband VLBI Science Receiver. We are currently working on a new modernized system to merge functions into one new hardware platform. It will replace the current MarkIV, PCFS and Mark5-A equipment. The new system will be called the JPL Deep Space Communications Complex VLBI Processor (DVP) It is based on hardware development at JPL, NRAO and Haystack. It uses a JPL designed digitizer and the CASPER ROACH board to perform digital backend processing: sampling, channelization, formatting. It uses Mark5C disk units to record data. It aims for compatibility with other VLBI centers recording equipment while conforming to JPL DSN system interface requirements.

  11. Modernizing the JPL VLBI Correlator

    NASA Astrophysics Data System (ADS)

    Rogstad, S.; Goodhart, C. E.; Clark, J. E.; Finley, S.; Lanyi, G. E.; White, L. A.; Jacobs, Christopher S.>

    This poster will present the current capabilities of the JPL VLBI Correlator (JVC) and the general architecture of the equipment. In addition, the scientific and navigation uses of the JVC will be enumerated for background purposes. The JVC is a software correlator based on a Beowulf cluster of computers. It replaces a thirty year old correlator based on custom designed digital hardware. General comparisons between the old and new equipment will be made. The JVC makes use of a separate program, SoftC, to do the actual correlations. The JVC manages the sending of data to multiple machines in a Beowulf cluster each running SoftC in parallel on small chunks of the data. The basic architecture of SoftC will also be described.

  12. The RAEGE VLBI2010 radiotelescopes

    NASA Astrophysics Data System (ADS)

    Sust, Eberhard; López Fernández, José Antonio

    2012-09-01

    The goal of the RAEGE (Red Atlantica Estaciones Geodinamicas Espaciales) project is the establishment of a Spanish-Portuguese network of geodynamical and spatial geodesy stations by the installation and operation of four fundamental geodetic / astronomical stations provided with radio telescopes located at - Yebes, close to Madrid / Spain - Tenerife, Canary Islands / Spain - Santa Maria, Azores Islands / Portugal. VLBI 2010 radiotelescopes are belonging to a new generation of radiotelescopes suitable for high precision geodetical earth observation and measurements, that shall allow to built up a high precision global reference system. The design of the radiotelescopes has been finished by MT Mechatronics in summer 2011 and currently three radiotelescopes are being manufactured. The first one is scheduled for installation in summer 2012 at Yebes Observatory close to Madrid.

  13. VLBI survey at 2. 29 GHz

    SciTech Connect

    Preston, R.A.; Morabito, D.D.; Williams, J.G.; Faulkner, J.; Jauncey, D.L.

    1985-09-01

    VLBI observations at 2.29 GHz with fringe spacings of about 3 milliarcsec have been performed on 1398 radio sources spread over the entire sky. 917 sources were detected, including 93 percent of the identified BL Lacertae objects, 86 percent of the quasars, and 36 percent of the galaxies. The resulting catalog of compact radio sources is useful for various astrophysical studies and in the formation of VLBI celestial reference frames. 252 references.

  14. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Block 3.0 Communications Strategies

    NASA Astrophysics Data System (ADS)

    Miller, S. W.; Grant, K. D.; Ottinger, K.

    2015-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). The JPSS program is the follow-on for both space and ground systems to the Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and geophysical observations of the Earth. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence, Information and Services (IIS), the CGS is a globally distributed, multi-mission system serving NOAA, NASA and their national and international partners. The CGS has demonstrated its scalability and flexibility to incorporate multiple missions efficiently and with minimal cost, schedule and risk, while strengthening global partnerships in weather and environmental monitoring. In a highly successful international partnership between NOAA and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), the CGS currently provides data routing from McMurdo Station in Antarctica to the EUMETSAT processing center in Darmstadt, Germany. Continuing and building upon that partnership, NOAA and EUMETSAT are collaborating on the development of a new path forward for the 2020's. One approach being explored is a concept of operations where each organization shares satellite downlink resources with the other. This paper will describe that approach, as well as modeling results that demonstrate its feasibility and expected performance.

  15. VizieR Online Data Catalog: The Carnegie-Irvine Galaxy Survey (CGS). I. (Ho+, 2011)

    NASA Astrophysics Data System (ADS)

    Ho, L. C.; Li, Z.-Y.; Barth, A. J.; Seigar, M. S.; Peng, C. Y.

    2012-01-01

    All the images for CGS were taken with the du Pont 2.5m telescope, during the period 2003 February to 2006 June, spread over 69 nights and nine observing runs. Table 2 gives a log of the observations. Each galaxy was imaged in the Johnson B and V and Kron-Cousins R and I filters. (7 data files).

  16. Thermographic mapping of a complex vernacular settlement: the case study of Casalnuovo District within the Sassi of Matera (Italy)

    NASA Astrophysics Data System (ADS)

    Cardinale, Tiziana; Balestra, Alessandro; Cardinale, Nicola

    2015-04-01

    Never as in the Sassi of Matera (Italy), the parties have a volumetric material identity and a special construction condition for which, first of all, you need to know the whole to which they give life, and then the individual components and their connections. The distribution of these building artifacts in symbiotic connection with the connective calcareous texture that hosts them, resulted in a spontaneously harmonious figurative balance that characterizes the constructive expedients employed and the distributive and morphological solutions. This is the reason why the Sassi, and the overlooking Park of Rupestrian Churches of Matera Murgia have been entered in 1993 in the UNESCO World Heritage List. Our research focuses on a largely abandoned area within the Casalnuovo District, situated in the extreme south of the city, probably the place of the future Demoethnoanthropological Museum. It is known today that the particular shape of the area is made up of settlements mainly in cave; during the time architectures above ground, in a very limited number, filled almost completely the limited building space. Here there are the most archaic types and forms of building and wine cellars within the Sassi, essentially derive from the natural cave only slightly structured by man. The exterior construction complete the elementary cave and it is called lamione. The complexity of a built space like this one determines the need for a non-traditional approach, so you have to combine last generation tools and canonical ones for survey and energy diagnosis within a dialectic between memory, tradition and innovation, in order to identify solutions for an environment friendly recover of a cultural heritage such this one. Since the evaluation of the historical buildings conservation state using destructive techniques should be avoided to prevent the integrity of the cultural heritage, the development of non-destructive and non-contact techniques is very important. For this reason, an

  17. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Architecture Overview and Technical Performance Measures

    NASA Astrophysics Data System (ADS)

    Grant, K. D.; Johnson, B. R.; Miller, S. W.; Jamilkowski, M. L.

    2014-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). The Joint Polar Satellite System will replace the afternoon orbit component and ground processing system of the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and geophysical observations of the Earth. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence, Information and Services (IIS), the CGS is a multi-mission enterprise system serving NOAA, NASA and their national and international partners. The CGS provides a wide range of support to a number of missions. Originally designed to support S-NPP and JPSS, the CGS has demonstrated its scalability and flexibility to incorporate all of these other important missions efficiently and with minimal cost, schedule and risk, while strengthening global partnerships in weather and environmental monitoring. The CGS architecture will be upgraded to Block 2.0 in 2015 to satisfy several key objectives, including: "operationalizing" S-NPP, which had originally been intended as a risk reduction mission; leveraging lessons learned to date in multi-mission support; taking advantage of newer, more reliable and efficient technologies; and satisfying new requirements and constraints due to the continually evolving budgetary environment. To ensure the CGS meets these needs, we have developed 48 Technical Performance Measures (TPMs) across 9 categories: Data Availability, Data Latency, Operational Availability, Margin, Scalability, Situational Awareness, Transition (between environments and sites), WAN Efficiency, and Data Recovery Processing. This

  18. Advanced relativistic VLBI model for geodesy

    NASA Astrophysics Data System (ADS)

    Soffel, Michael; Kopeikin, Sergei; Han, Wen-Biao

    2017-07-01

    Our present relativistic part of the geodetic VLBI model for Earthbound antennas is a consensus model which is considered as a standard for processing high-precision VLBI observations. It was created as a compromise between a variety of relativistic VLBI models proposed by different authors as documented in the IERS Conventions 2010. The accuracy of the consensus model is in the picosecond range for the group delay but this is not sufficient for current geodetic purposes. This paper provides a fully documented derivation of a new relativistic model having an accuracy substantially higher than one picosecond and based upon a well accepted formalism of relativistic celestial mechanics, astrometry and geodesy. Our new model fully confirms the consensus model at the picosecond level and in several respects goes to a great extent beyond it. More specifically, terms related to the acceleration of the geocenter are considered and kept in the model, the gravitational time-delay due to a massive body (planet, Sun, etc.) with arbitrary mass and spin-multipole moments is derived taking into account the motion of the body, and a new formalism for the time-delay problem of radio sources located at finite distance from VLBI stations is presented. Thus, the paper presents a substantially elaborated theoretical justification of the consensus model and its significant extension that allows researchers to make concrete estimates of the magnitude of residual terms of this model for any conceivable configuration of the source of light, massive bodies, and VLBI stations. The largest terms in the relativistic time delay which can affect the current VLBI observations are from the quadrupole and the angular momentum of the gravitating bodies that are known from the literature. These terms should be included in the new geodetic VLBI model for improving its consistency.

  19. Advanced relativistic VLBI model for geodesy

    NASA Astrophysics Data System (ADS)

    Soffel, Michael; Kopeikin, Sergei; Han, Wen-Biao

    2016-10-01

    Our present relativistic part of the geodetic VLBI model for Earthbound antennas is a consensus model which is considered as a standard for processing high-precision VLBI observations. It was created as a compromise between a variety of relativistic VLBI models proposed by different authors as documented in the IERS Conventions 2010. The accuracy of the consensus model is in the picosecond range for the group delay but this is not sufficient for current geodetic purposes. This paper provides a fully documented derivation of a new relativistic model having an accuracy substantially higher than one picosecond and based upon a well accepted formalism of relativistic celestial mechanics, astrometry and geodesy. Our new model fully confirms the consensus model at the picosecond level and in several respects goes to a great extent beyond it. More specifically, terms related to the acceleration of the geocenter are considered and kept in the model, the gravitational time-delay due to a massive body (planet, Sun, etc.) with arbitrary mass and spin-multipole moments is derived taking into account the motion of the body, and a new formalism for the time-delay problem of radio sources located at finite distance from VLBI stations is presented. Thus, the paper presents a substantially elaborated theoretical justification of the consensus model and its significant extension that allows researchers to make concrete estimates of the magnitude of residual terms of this model for any conceivable configuration of the source of light, massive bodies, and VLBI stations. The largest terms in the relativistic time delay which can affect the current VLBI observations are from the quadrupole and the angular momentum of the gravitating bodies that are known from the literature. These terms should be included in the new geodetic VLBI model for improving its consistency.

  20. The Integrated Survey for Excavated Architectures: the Complex of Casalnuovo District Within the World Heritage Site "sassi" (matera, Italy)

    NASA Astrophysics Data System (ADS)

    Cardinale, T.; Valva, R.; Lucarelli, M.

    2015-02-01

    Never as within the complex of Sassi (Matera, South of Italy), the parties have a volumetric material identity and a special construction condition for which, first of all, you need to know the whole to which they give life, and then the individual components and their connections. In the course of time, in the Lucan city, there were stable and favorable conditions that allowed the development of an architectural language, of juxtaposition of the materials, interpenetration of space and conformation of the volumes, which generated an exceptional urban phenomenon. The distribution of these building artifacts in symbiotic connection with the connective calcareous texture that hosts them , resulted in a spontaneously harmonious figurative balance that characterizes the constructive expedients employed and the distributive and morphological solutions. This is the reason why the Sassi, and the overlooking Park of Rupestrian Churches of Matera Murgia, have been entered in 1993 in the UNESCO World Heritage List. The complexity of a built space, such as this one, determines the need for a non-traditional approach, so you have to combine last generation tools and canonical ones for survey, drawing and representation, within a dialectic between memory and design, tradition and innovation. For this reason, an appropriate cognitive apparatus has been set up for the entire technical process, making use of different non-destructive and non-contact techniques: digital photogrammetry, total station, laser scanner and thermography, in order to obtain a three-dimensional computer model, useful for the diagnosis and the preservation of the integrity of cultural heritage.

  1. Shuttle VLBI experiment. Technical working group summary report

    NASA Technical Reports Server (NTRS)

    Morgan, S. H. (Editor); Roberts, D. H. (Editor)

    1982-01-01

    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.

  2. DSN Network e-VLBI Calibration of Earth Orientation

    NASA Technical Reports Server (NTRS)

    Zhang, Liwei Dennis; Steppe, A.; Lanyi, G.; Jacobs, C.

    2006-01-01

    This viewgraph presentation reviews the calibration of the Earth's orientation by using the Deep Space Network (DSN) e Very Large Base Integration (VLBI). The topics include: 1) Background: TEMPO; 2) Background: UT1 Knowledge Error; 3) e-VLBI: WVSR TEMPO Overview; 4) e-VLBI: WVSR TEMPO Turnaround; 5) e-VLBI: WVSR TEMPO R&D Tests; and 6) WVSR TEMPO Test Conclusion.

  3. International VLBI Service for Geodesy and Astrometry 2014 Annual Report

    NASA Technical Reports Server (NTRS)

    Baver, Karen D. (Editor); Behrend, Dirk (Editor); Armstrong, Kyla L. (Editor)

    2015-01-01

    IVS is an international collaboration of organizations which operate or support Very Long Baseline Interferometry (VLBI) components. The goals are: 1. To provide a service to support geodetic, geophysical and astrometric research and operational activities. 2. To promote research and development activities in all aspects of the geodetic and astrometric VLBI technique. 3. To interact with the community of users of VLBI products and to integrate VLBI into a global Earth observing system.

  4. US Space VLBI Proposed Outreach Web Site

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The study of how VLBI might be pursued in space began in the late 1970's, when it was realized that the size of the earth was a serious limitation to the study of compact radio sources. By going to space, achieving angular resolution at radio wavelengths that could not be obtained with VLBI systems that were limited by the size of the earth, important tests could not be made of quasar models. The technology appeared to be within reach, and an early space VLBI concept, QUASAT, emerged as a joint project, involving both US and European scientists. In 1984, a workshop was held in Gross Enzerdorf, Austria, under joint sponsorship of NASA and the European Space Agency (ESA). The principal conclusion of the workshop was that a VLBI station in space, telemetering its data to ground data stations, working in connection with ground-based radio telescopes, would give the opportunity to achieve angular resolution of a few tens of micro-arc-seconds, and could develop high-quality radio maps of many classes of radio sources. The ground telemetry stations would also function as the source of a stable local oscillator for the spacecraft, which needs a highly stable frequency reference. The Deep Space Network of NASA could play a vital role in both the frequency-locking system and data acquisition. One outcome of the Gross Enzerdorf workshop was the convening, by COSPAR, of an ad hoc Committee on Space VLBI, to review and recommend procedures by which international collaboration on VLBI in space might be coordinated and promoted. In October 1985, the committee met in Budapest and recommended that the Inter-Agency Consultative Group (IACG) would be an appropriate body to coordinate VLBI activities in space. At the same time ESA convened a committee to explore the technical aspects of coordinating ground and space VLBI activities. At this stage both NASA and ESA were supporting preliminary studies of the QUASAT mission, with effective coordination between the two groups. The Soviet

  5. Refinement of Models for VLBI Analysis

    NASA Technical Reports Server (NTRS)

    Ma, C.

    1999-01-01

    Continual refinement of models and estimation methods is an integral part of improving VLBI measurements of Earth orientation and position along with advances in instrumentation and observing strategy. The modeling of the troposphere continues to be challenging with recent improvements in treating the mean gradient and gradient variations affecting the terrestrial reference frame scale and celestial declinations near the current limits of accuracy. Revised models of nutation and solid Earth tides are implemented in CALC 9.0 to conform to the latest IERS Conventions along with other changes to facilitate use by VLBI correlators. Using data since 1995 the celestial reference frame has been extended and improved consistent with the definition and 0.25 mas accuracy limit of the ICRF. The current definition of the VLBI terrestrial reference frame places a floor on the accuracy of station velocities at the 0.4 mm/yr level. The establishment of the IVS (International VLBI Service for Geodesy and Astrometry) in the past year will provide a forum for further improvements of VLBI data analysis.

  6. The Role of VLBI in the TRF

    NASA Astrophysics Data System (ADS)

    Ma, C.; MacMillan, D. S.

    2005-12-01

    The international VLBI network is a major contributor to the TRF by virtue of its 25-year data set and unique access to the celestial reference frame in which Earth orientation is defined. The TRF and EOP results are suboptimal, however, because of non-ideal station spatial distribution (arising from the vagaries of national interests and capabilities over the years), irregular temporal resolution (related to operational funding and other station activities), and heterogeneous equipment. Better modeling related to thermal, structural and tilt effects of the large VLBI antennas is needed to eliminate non-geodetic signatures and systematic biases. Modeling of the troposphere must always be improved and unified with other microwave techniques. The VLBI community is beginning the design of a new geodetic VLBI station to be deployed in an uniform, optimized global network including such features as small antenna size, much faster slewing, wide RF bandwidth, higher recording rates and data transmission via high-speed fiber along with automated correlation and analysis. Simulations of this enhanced VLBI capability for the TRF will be presented.

  7. Design of VLBI Array in South America

    NASA Astrophysics Data System (ADS)

    Carrara, E. A.; Abraham, Z.

    1990-11-01

    RESUMEN. Estudiamos la localizaci6n 6ptima de estaciones de \\ ras' en territorlo brasileno. Con una red VLBI de estaciones reales y ficti- cias simulamos observaciones. Se usan los datos generados de estps ex- perimentos para obtener Ia distribuci6n de brillo de radiofuentes fic- ticias por medlo de tecaicas de mapeo bIbrido. Se concluye que l mejor localizaci6n de estacionee'VLBI futuras, tomando en cuenta las estacio- nes de EUA y de Europa, se encuentra en el Norte-Noreste de razll. El analisis de los datos se hizo con los programas de CALTECH, los cuales estan instalados en una computadora VAX del Departamento de Astronomla del Instituto Astron6mico y Geoflsico de la Universidad de Sa"'o Paulo. ABSTRACT: In this work we study the optimum localization for future VLBI stations in the Brazilian territory. With a VLBI network of real and fictitious stations we make simulations of observations. The data generated in these experiments are used to obtain brightness distribution of a fictitious radio source by the hybrid mapping techniques. We conclude that the best localization of a future VLBI station taking into account the addition of US and European Stations, is roughly in North-Northeast sites in Brazil. The analysis of the data is made with the software of CALTECH, which is installed in the VAX computer of the Astronomy Department of Instituto e Geofisico - USP. Key `{` : INSTRUMENTS - INTERFEROMETRY

  8. Molecular Determinants of CGS21680 Binding to the Human Adenosine A2A Receptor.

    PubMed

    Lebon, Guillaume; Edwards, Patricia C; Leslie, Andrew G W; Tate, Christopher G

    2015-06-01

    The adenosine A2A receptor (A(2A)R) plays a key role in transmembrane signaling mediated by the endogenous agonist adenosine. Here, we describe the crystal structure of human A2AR thermostabilized in an active-like conformation bound to the selective agonist 2-[p-(2-carboxyethyl)phenylethyl-amino]-5'-N-ethylcarboxamido adenosine (CGS21680) at a resolution of 2.6 Å. Comparison of A(2A)R structures bound to either CGS21680, 5'-N-ethylcarboxamido adenosine (NECA), UK432097 [6-(2,2-diphenylethylamino)-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-tetrahydrofuran-2-yl]-N-[2-[[1-(2-pyridyl)-4-piperidyl]carbamoylamino]ethyl]purine-2-carboxamide], or adenosine shows that the adenosine moiety of the ligands binds to the receptor in an identical fashion. However, an extension in CGS21680 compared with adenosine, the (2-carboxyethyl)phenylethylamino group, binds in an extended vestibule formed from transmembrane regions 2 and 7 (TM2 and TM7) and extracellular loops 2 and 3 (EL2 and EL3). The (2-carboxyethyl)phenylethylamino group makes van der Waals contacts with side chains of amino acid residues Glu169(EL2), His264(EL3), Leu267(7.32), and Ile274(7.39), and the amine group forms a hydrogen bond with the side chain of Ser67(2.65). Of these residues, only Ile274(7.39) is absolutely conserved across the human adenosine receptor subfamily. The major difference between the structures of A(2A)R bound to either adenosine or CGS21680 is that the binding pocket narrows at the extracellular surface when CGS21680 is bound, due to an inward tilt of TM2 in that region. This conformation is stabilized by hydrogen bonds formed by the side chain of Ser67(2.65) to CGS21680, either directly or via an ordered water molecule. Mutation of amino acid residues Ser67(2.65), Glu169(EL2), and His264(EL3), and analysis of receptor activation either in the presence or absence of ligands implicates this region in modulating the level of basal activity of A(2A)R.

  9. Radio source stability and geodetic VLBI

    NASA Astrophysics Data System (ADS)

    Gattano, César; Lambert, Sébastien

    2016-04-01

    The observation of the Earth's rotation by VLBI is conditioned by the celestial reference frame that should be as stable as possible. The selection of the most stable sources therefore constitutes a major step in the construction of a celestial reference frame since their stability prevents time deformation of the axes with time. The assessment of astrometric stability, i.e., the time stability the radiocenter location as detected by the VLBI, is one of the methods that were used in previous ICRF realizations (works of M. Feissel-Vernier and ICRF2). We think the same method should be addressed for the construction of the ICRF3. We analyzed the radio source time series obtained from the analysis of the data from the permanent geodetic VLBI monitoring program of the IVS. We used several utils based on basic statistics and more advanced methods (Allan variance) in order to provide a preliminary classification of sources.

  10. Global and regional kinematics with VLBI

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    1994-01-01

    Since a VLBI station cannot operate in isolation and since simultaneous operation of the entire VLBI network is impractical, it is necessary to design observing programs with periodic observing sessions using networks of 3-7 stations that, when treated together, will have the necessary interstation data and network overlaps to determine the desired rates of change. Thus, there has been a mix of global, intercontinental, transcontinental, and regional networks to make measurements ranging from plate motions to deformation over a few hundred km. Over time, even networks focusing on regional deformation using mobile VLBI included large stations removed by several thousand km to increase sensitivity, determine EOP more accurately, and provide better ties to the terrestrial reference frame (TRF). Analysis products have also evolved, beginning with baseline components, and then to full three-dimensional site velocities in a global TRF.

  11. VLBI observations of 416 extragalactic radio sources

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Niell, A. E.; Preston, R. A.; Linfield, R. P.; Wehrle, A. E.; Faulkner, J.

    1986-01-01

    The Deep Space Network is establishing a high-accuracy Very Long Base Interferometry (VLBI) celestial reference frame. Presented are the VLBI results of observations of 416 radio sources with declination north of -45 degrees which were conducted at frequencies of 2.3 GHz and 8.4 GHz. At 2.3 GHz 323 of 391 radio sources observed were detected with a fringe spacing of 3 milliarcsec and a detection limit of approximately 0.1 Jy. At 8.4 GHz, 278 of 416 radio sources were detected with a fringe spacing of 1 milliarcsec and a detection limit of approximately 0.1 Jy. This survey was conducted primarily to determine the strength of compact components at 8.4 GHz for radio sources previously detected with VLBI at 2.3 GHz. Compact extragalactic radio sources with strong correlated flux densities at both frequencies are used to form a high-accuracy reference frame.

  12. Computational Imaging for VLBI Image Reconstruction

    NASA Astrophysics Data System (ADS)

    Bouman, Katherine L.; Johnson, Michael D.; Zoran, Daniel; Fish, Vincent L.; Doeleman, Sheperd S.; Freeman, William T.

    2016-03-01

    Very long baseline interferometry (VLBI) is a technique for imaging celestial radio emissions by simultaneously observing a source from telescopes distributed across Earth. The challenges in reconstructing images from fine angular resolution VLBI data are immense. The data is extremely sparse and noisy, thus requiring statistical image models such as those designed in the computer vision community. In this paper we present a novel Bayesian approach for VLBI image reconstruction. While other methods often require careful tuning and parameter selection for different types of data, our method (CHIRP) produces good results under different settings such as low SNR or extended emission. The success of our method is demonstrated on realistic synthetic experiments as well as publicly available real data. We present this problem in a way that is accessible to members of the community, and provide a dataset website (vlbiimaging.csail.mit.edu) that facilitates controlled comparisons! across algorithms.

  13. Lack of protective effect of thromboxane synthetase inhibitor (CGS-13080) on single dose radiated canine intestine.

    PubMed

    Barter, J F; Marlow, D; Kamath, R K; Harbert, J; Torrisi, J R; Barnes, W A; Potkul, R K; Newsome, J T; Delgado, G

    1991-03-01

    The effect of a thromboxane A2 synthetase inhibitor (CGS-13080) on canine intestine was studied using a single dose of radiation, and radioactive microspheres were used to determine resultant blood flow. Thromboxane A2 causes vasospasm and platelet aggregation and may play a dominant role in radiation injury. However, there was no effect on the intestinal blood flow diminution occurring after radiation in this laboratory model using this thromboxane A2 synthetase inhibitor.

  14. Lack of protective effect of thromboxane synthetase inhibitor (CGS-13080) on single dose radiated canine intestine

    SciTech Connect

    Barter, J.F.; Marlow, D.; Kamath, R.K.; Harbert, J.; Torrisi, J.R.; Barnes, W.A.; Potkul, R.K.; Newsome, J.T.; Delgado, G. )

    1991-03-01

    The effect of a thromboxane A2 synthetase inhibitor (CGS-13080) on canine intestine was studied using a single dose of radiation, and radioactive microspheres were used to determine resultant blood flow. Thromboxane A2 causes vasospasm and platelet aggregation and may play a dominant role in radiation injury. However, there was no effect on the intestinal blood flow diminution occurring after radiation in this laboratory model using this thromboxane A2 synthetase inhibitor.

  15. VizieR Online Data Catalog: The CGS. IV. Elliptical galaxies colors (Huang+, 2016)

    NASA Astrophysics Data System (ADS)

    Huang, S.; Ho, L. C.; Peng, C. Y.; Li, Z.-Y.; Barth, A. J.

    2016-07-01

    This work uses the multi-band optical images of nearby ellipticals from the Carnegie-Irvine Galaxy Survey (CGS; Ho et al. 2011, J/ApJS/197/21, Paper I). The observations were made using the 100 inch du Pont telescope at Las Campanas Observatory to provide high-quality Johnson/Kron-Cousins BVRI images during the period 2003 February to 2006 June. (1 data file).

  16. The recent progress of Chinese VLBI Network

    NASA Astrophysics Data System (ADS)

    Zheng, Weimin

    2015-08-01

    At present, Chinese VLBI Network (CVN) consists of 5 antennas (Seshan 25m, Urumqi 25m, Kunming 30m, Miyun 50m and Tianma 65m) and one data processing center in Shanghai Observatory, Chinese academy of sciences. It is a synthetic aperture radio telescope with the equivalent diameter up to 3000 Km. Through e-VLBI (electronic VLBI) technology, CVN is connected by the commuication network. It is a multi-purpose scientific research platform radio for geodesy, astronomy, as well as deep space exploration. In Geodesy, CVN is the component of the Crustal Movement Observation Network of China. Since the year of 2006, more than 20 geodetic domestic observations have been carried out. A set of phase-referencing observations of pulsars with CVN has carried out and got preliminary results. CVN also joined the Chinese lunar exploration Project from 2007 and supported 4 Chang’E series lunar probe missions. In Chang’E-3 mission, using the in-beam VLBI observations, the relative position accuracy of Rover and Lander is up to 1 meter.In recent years, we have updated the facilities of CVN from antenna, receivers, VLBI terminals to correlator. Participation of Tianma 65m antennas increases its performance. In 2012, Shanghai correlator was accepted as the IVS correlator. After upgrade, Shanghai correlator will try to provide the data process service for IVS community from 2015. To drive the construction of the planned VGOS (VLBI2010 Global Observing System) station, at least two VOGS 13m antenna will join CVN in the near future. Construction of the first VOGS antenna in Shanghai hopes to begin this year.The new VLBI correlator and digital terminal are under development. From participation in VGOS, we plan to study the earth rotation especially of high frequency and corresponding geophysical signals, to link China’s regional reference frame to ITRF, and etc. CVN is willing to join the research corporation with IVS, EVN, VLBA and AOV (Asia- Oceania VLBI Group for Geodesy and

  17. International VLBI Service for Geodesy and Astrometry

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

    2001-01-01

    This volume of reports is the 2000 Annual Report of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2000 Annual Report documents the work of these IVS components over the period March 1, 1999, through December 31, 2000. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2000.

  18. International VLBI Service for Geodesy and Astronomy

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

    2004-01-01

    This volume of reports is the 2003 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2003 Annual Report documents the work of the IVS components for the calendar year 2003, our fifih year of existence. The reports describe changes, activities, and progress of the IVS. Many thanks to all IVS components who contributed to this Annual Report. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2OO3

  19. Studies of Error Sources in Geodetic VLBI

    NASA Technical Reports Server (NTRS)

    Rogers, A. E. E.; Niell, A. E.; Corey, B. E.

    1996-01-01

    Achieving the goal of millimeter uncertainty in three dimensional geodetic positioning on a global scale requires significant improvement in the precision and accuracy of both random and systematic error sources. For this investigation we proposed to study errors due to instrumentation in Very Long Base Interferometry (VLBI) and due to the atmosphere. After the inception of this work we expanded the scope to include assessment of error sources in GPS measurements, especially as they affect the vertical component of site position and the measurement of water vapor in the atmosphere. The atmosphere correction 'improvements described below are of benefit to both GPS and VLBI.

  20. An evaluation of Comparative Genome Sequencing (CGS) by comparing two previously-sequenced bacterial genomes

    PubMed Central

    Herring, Christopher D; Palsson, Bernhard Ø

    2007-01-01

    Background With the development of new technology, it has recently become practical to resequence the genome of a bacterium after experimental manipulation. It is critical though to know the accuracy of the technique used, and to establish confidence that all of the mutations were detected. Results In order to evaluate the accuracy of genome resequencing using the microarray-based Comparative Genome Sequencing service provided by Nimblegen Systems Inc., we resequenced the E. coli strain W3110 Kohara using MG1655 as a reference, both of which have been completely sequenced using traditional sequencing methods. CGS detected 7 of 8 small sequence differences, one large deletion, and 9 of 12 IS element insertions present in W3110, but did not detect a large chromosomal inversion. In addition, we confirmed that CGS also detected 2 SNPs, one deletion and 7 IS element insertions that are not present in the genome sequence, which we attribute to changes that occurred after the creation of the W3110 lambda clone library. The false positive rate for SNPs was one per 244 Kb of genome sequence. Conclusion CGS is an effective way to detect multiple mutations present in one bacterium relative to another, and while highly cost-effective, is prone to certain errors. Mutations occurring in repeated sequences or in sequences with a high degree of secondary structure may go undetected. It is also critical to follow up on regions of interest in which SNPs were not called because they often indicate deletions or IS element insertions. PMID:17697331

  1. Space VLBI telecommunication characteristics, protection criteria, and frequency sharing

    NASA Technical Reports Server (NTRS)

    Gutierrez-Luaces, B. O.; Bishop, D. F.

    1994-01-01

    A brief description of the technical characteristics of space VLBI is made, emphasizing the VLBI cross-correlation process. The signal-to-noise ratio of the cross-correlation process should be maintained as large as possible for the duration of the observation. Protection of this process from unwanted interference is a primary objective. The telecommunication radio links required in a space VLBI system are identified and characterized. Maximum bandwidths are suggested, as well as the minimum carrier frequencies required for the telemetering and the phase-transfer radio links. Planned space VLBI system models-Radioastron (Russia), VLBI Space Observatory Project (VSOP) (Japan), and the DSN orbiting VLBI subnet. (United States)--are taken as a baseline to determine the interference criteria. It is concluded that existing interference criteria for near-Earth research satellites are suitable for the protection of the space VLBI systems planned.

  2. Adding a Mission to the Joint Polar Satellite System (JPSS) Common Ground System (CGS)

    NASA Astrophysics Data System (ADS)

    Miller, S. W.; Grant, K. D.; Jamilkowski, M. L.

    2014-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). The Joint Polar Satellite System will replace the afternoon orbit component and ground processing system of the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and geophysical observations of the Earth. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence, Information and Services (IIS), the CGS is a multi-mission enterprise system serving NOAA, NASA and their national and international partners. The CGS provides a wide range of support to a number of missions: 1) Command and control and mission management for the Suomi National Polar-orbiting Partnership (S-NPP) mission today, expanding this support to the JPSS-1 satellite and the Polar Free Flyer mission in 2017 2) Data acquisition via a Polar Receptor Network (PRN) for S-NPP, the Japan Aerospace Exploration Agency's (JAXA) Global Change Observation Mission - Water (GCOM-W1), POES, and the Defense Meteorological Satellite Program (DMSP) and Coriolis/WindSat for the Department of Defense (DoD) 3) Data routing over a global fiber Wide Area Network (WAN) for S-NPP, JPSS-1, Polar Free Flyer, GCOM-W1, POES, DMSP, Coriolis/WindSat, the NASA Space Communications and Navigation (SCaN, which includes several Earth Observing System [EOS] missions), MetOp for the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), and the National Science Foundation (NSF) 4) Environmental data processing and distribution for S-NPP, GCOM-W1 and JPSS-1 With this established infrastructure and existing suite of missions, the CGS

  3. Orbit determination of Tance-1 satellite using VLBI data

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Hu, X. G.; Huang, C.; Jiang, D. R.

    2006-01-01

    On 30 December, 2003, China successfully launched the first satellite Tance-1 of Chinese Geospace Double Star Exploration Program, i.e. "Double Star Program (DSP)", on an improved Long March 2C launch vehicle. The Tance-1 satellite is operating at an orbit around the earth with a 550km perigee, 78000km apogee and 28.5 degree inclination.VLBI technique can track Tance-1 satellite or even far satellites such as lunar vehicles. To validate the VLBI technique in the on-going Chinese lunar exploration mission, Shanghai Astronomical Observatory (SHAO) organized to track the Tance-1 satellite with Chinese three VLBI stations: Shanghai, Kunming and Urumchi Orbit Determination (OD) of the Tance-1 satellite with about two days VLBI dada, and the capability of OD with VLBI data are studied. The results show that the VLBI-based orbit solutions improve the fit level over the initial orbit. The VLBI-delay-based orbit solution shows that the RMS of residuals of VLBI delay data is about 5.5m, and about 2.0cm/s for the withheld VLBI delay rate data. The VLBI-delay-rate-based orbit solution shows that the RMS of residuals of VLBI delay rate data is about 1.3cm/s, and about 29m for the withheld VLBI delay data. In the situation of orbit determination with VLBI delay and delay rate data with data sigma 5.5m and 1.3cm/s respectively, the RMS of residuals are 5.5,m and 2.0cm/s respectively. The simulation data assess the performance of the solutions. Considering the dynamic model errors of the Tance-1 satellite, the accuracy of the position is about km magnitude, and the accuracy of the velocity is about cm/s magnitude. The simulation work also show the dramatic accuracy improvement of OD with VLBI and USB combined.

  4. Italian guidelines for energy performance of cultural heritage and historical buildings: the case study of the Sassi of Matera.

    NASA Astrophysics Data System (ADS)

    Negro, Elisabetta; Cardinale, Tiziana; Cardinale, Nicola

    2016-04-01

    The Sassi of Matera are a unique example in the world of rock settlement, developed from natural caves carved into the rock and then molded into increasingly complex structures inside two large natural amphitheatres: the Sasso Caveoso and the Sasso Barisano. Thanks also to this aspects Matera is an UNESCO world heritage site and was elected European Capital of Culture in 2019. Our research focuses on the compatibility of the energy efficiency measures applied in of Sassi buildings with the recent MiBACT (Italian Ministry of Cultural Heritage) guidelines on "Energy efficiency improvements in the cultural heritage" and AiCARR (Italian Association of Air Conditioning) guidelines on "Energy efficiency of historical building". One of the essential measures highlighted by Mibact guidelines is ensure the Indoor Environmental Quality improvement of the historical architecture in order to preserve their identity and cultural heritage. These paper aims to analyze energy and environmental performance of different buildings typology and monuments present in the Sassi site. The energy performance and microclimate measures conducted on different type of building by non-destructive measurements and laboratory tests in situ are useful to verify and quantify the thermal characteristics of the envelopes of the Mediterranean tradition and also to demonstrate their capacity to ensure internal comfort conditions. The calcarenite walls of vernacular building of Sassi show the excellent energy behavior of these constructions. But these material often present high moisture content which negatively influence the room microclimate in particular in presence of mural frescos and rocky churches. However these structures, once restored and in a condition of normal use, give indoor comfort within the limits of thermo-hygrometrics standards established by indices as the predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD). Another interesting consideration stated from our

  5. Earth Rotation Parameters from DSN VLBI: 1996

    NASA Technical Reports Server (NTRS)

    Steppe, J. A.; Oliveau, S. H.; Sovers, O. J.

    1996-01-01

    A despcription of the DSN VLBI data set and of most aspects of the data analysis can be found in the IERS Technical Note 17, pp. R-19 to R-32 (see also IERS Technical Note 19, pp. R-21 to R-27). The main changes in this year's analysis form last year's are simply due to including another year's data.

  6. The Mark 5C VLBI Data System

    NASA Technical Reports Server (NTRS)

    Whitney, Alan; Ruszczyk, Chester; Romney, Jon; Owens, Ken

    2010-01-01

    The Mark 5C disk-based VLBI data system is being developed as the third-generation Mark 5 disk-based system, increasing the sustained data-recording rate capability to 4 Gbps. It is built on the same basic platform as the Mark 5A, Mark 5B and Mark 5B+ systems and will use the same 8-disk modules as earlier Mark 5 systems, although two 8-disk modules will be necessary to support the 4 Gbps rate. Unlike its earlier brethren, which use proprietary data interfaces, the Mark 5C will accept data from a standard 10 Gigabit Ethernet connection and be compatible with the emerging VLBI Data Interchange Format (VDIF) standard. Data sources for the Mark 5C system will be based on new digital backends now being developed, specifically the RDBE in the U.S. and the dBBC in Europe, as well as others. The Mark 5C system is being planned for use with the VLBI2010 system and will also be used by NRAO as part of the VLBA sensitivity upgrade program; it will also be available to the global VLBI community from Conduant. Mark 5C system specification and development is supported by Haystack Observatory, NRAO, and Conduant Corporation. Prototype Mark 5C systems are expected in early 2010.

  7. VLBI Surveys of Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Kovalev, Y. Y.

    2009-08-01

    A review is given on the current status and selected results from large VLBI surveys of compact extragalactic radio sources made between 13 cm and 3 mm wavelengths and covering the entire sky. More than 4200 objects are observed and imaged with dynamic ranges from a hundred to several thousand at (sub)parsec scales. Implications to the VSOP-2 project are discussed.

  8. VLBI2010: The Astro-Geo Connection

    NASA Technical Reports Server (NTRS)

    Porcas, Richard

    2010-01-01

    VLBI2010 holds out promise for greatly increased precision in measuring geodetic and Earth rotation parameters. As a by-product there will be a wealth of interesting new astronomical data. At the same time, astronomical knowledge may be needed to disentangle the astronomical and geodetic contributions to the measured delays and phases. This presentation explores this astro-geo link.

  9. The BKG/IGGB VLBI Analysis Center

    NASA Technical Reports Server (NTRS)

    Thorandt, Volkmar; Nothnagel, Axel; Engelhardt, Gerald; Ullrich, Dieter; Artz, Thomas; Leek, Judith

    2013-01-01

    In 2012, the activities of the BKG/IGGB VLBI Analysis Center, as in previous years, consisted of routine computations of Earth orientation parameter (EOP) time series and of a number of research topics in geodetic VLBI. The VLBI group at BKG continued its regular submissions of time series of tropospheric parameters and the generation of daily SINEX (Solution INdependent EXchange format) files. Quarterly updated solutions have been computed to produce terrestrial reference frame (TRF) and celestial reference frame (CRF) realizations. Routine computations of the UT1-UTC Intensive observations include all sessions of the Kokee-Wettzell and Tsukuba-Wettzell baselines and the networks Kokee-Svetloe-Wettzell and Ny-degAlesund-Tsukuba-Wettzell. The VLBI group at BKG developed a procedure to get the most probable station positions of Tsukuba after the earthquake on March 11, 2011 for the epochs of the Intensive sessions. The analysis of the Intensive sessions with station Tsukuba could be resumed in February 2012. At IGGB, the emphasis has been placed on individual research topics.

  10. Earth Rotation Parameters from DSN VLBI: 1996

    NASA Technical Reports Server (NTRS)

    Steppe, J. A.; Oliveau, S. H.; Sovers, O. J.

    1996-01-01

    A despcription of the DSN VLBI data set and of most aspects of the data analysis can be found in the IERS Technical Note 17, pp. R-19 to R-32 (see also IERS Technical Note 19, pp. R-21 to R-27). The main changes in this year's analysis form last year's are simply due to including another year's data.

  11. The New Generation Russian VLBI Network

    NASA Technical Reports Server (NTRS)

    Finkelstein, Andrey; Ipatov, Alexander; Smolentsev, Sergey; Mardyshkin, Vyacheslav; Fedotov, Leonid; Surkis, Igor; Ivanov, Dmitrij; Gayazov, Iskander

    2010-01-01

    This paper deals with a new project of the Russian VLBI Network dedicated for Universal Time determinations in quasi on-line mode. The basic principles of the network design and location of antennas are explained. Variants of constructing receiving devices, digital data acquisition system, and phase calibration system are specially considered. The frequency ranges and expected values of noise temperature are given.

  12. Sheshan VLBI Station Report for 2012

    NASA Technical Reports Server (NTRS)

    Xia, Bo; Shen, Zhiqiang; Hong, Xiaoyu; Fan, Qingyuan

    2013-01-01

    This report summarizes the observing activities at the Sheshan station (SESHAN25) in 2012. It includes international VLBI observations for astrometry, geodesy, and astrophysics and domestic observations for satellite tracking. We also report on updates and on development of the facilities at the station.

  13. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Overview and Architectural Tenets

    NASA Astrophysics Data System (ADS)

    Miller, S. W.; Grant, K. D.; Jamilkowski, M. L.

    2013-12-01

    The National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) are jointly acquiring the next-generation civilian weather and environmental satellite system: the Joint Polar Satellite System (JPSS). The Joint Polar Satellite System will replace the afternoon orbit component and ground processing system of the current Polar-orbiting Operational Environmental Satellites (POES) managed by NOAA. The JPSS satellites will carry a suite of sensors designed to collect meteorological, oceanographic, climatological and geophysical observations of the Earth. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence and Information Systems (IIS), the CGS is a multi-mission enterprise system serving NOAA, NASA and their national and international partners. The CGS provides a wide range of support to a number of missions: 1) Command and control and mission management for the Suomi National Polar Partnership (S-NPP) mission today, expanding this support to the JPSS-1 satellite and the Polar Free Flyer mission in 2017 2) Data acquisition via a Polar Receptor Network (PRN) for S-NPP, the Japan Aerospace Exploration Agency's (JAXA) Global Change Observation Mission - Water (GCOM-W1), POES, and the Defense Meteorological Satellite Program (DMSP) and Coriolis/WindSat for the Department of Defense (DoD) 3) Data routing over a global fiber Wide Area Network (WAN) for S-NPP, JPSS-1, Polar Free Flyer, GCOM-W1, POES, DMSP, Coriolis/WindSat, the NASA Space Communications and Navigation (SCaN, which includes several Earth Observing System [EOS] missions), MetOp for the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), and the National Science Foundation (NSF) 4) Environmental data processing and distribution for S-NPP, GCOM-W1 and JPSS-1 The CGS architecture will receive a technology refresh in 2015 to satisfy several key

  14. The calmodulin inhibitor CGS 9343B inhibits voltage-dependent K{sup +} channels in rabbit coronary arterial smooth muscle cells

    SciTech Connect

    Li, Hongliang; Hong, Da Hye; Kim, Han Sol; Kim, Hye Won; Jung, Won-Kyo; Na, Sung Hun; Jung, In Duk; Park, Yeong-Min; Choi, Il-Whan; Park, Won Sun

    2015-06-15

    We investigated the effects of the calmodulin inhibitor CGS 9343B on voltage-dependent K{sup +} (Kv) channels using whole-cell patch clamp technique in freshly isolated rabbit coronary arterial smooth muscle cells. CGS 9343B inhibited Kv currents in a concentration-dependent manner, with a half-maximal inhibitory concentration (IC{sub 50}) value of 0.81 μM. The decay rate of Kv channel inactivation was accelerated by CGS 9343B. The rate constants of association and dissociation for CGS 9343B were 2.77 ± 0.04 μM{sup −1} s{sup −1} and 2.55 ± 1.50 s{sup −1}, respectively. CGS 9343B did not affect the steady-state activation curve, but shifted the inactivation curve toward to a more negative potential. Train pulses (1 or 2 Hz) application progressively increased the CGS 9343B-induced Kv channel inhibition. In addition, the inactivation recovery time constant was increased in the presence of CGS 9343B, suggesting that CGS 9343B-induced inhibition of Kv channel was use-dependent. Another calmodulin inhibitor, W-13, did not affect Kv currents, and did not change the inhibitory effect of CGS 9343B on Kv current. Our results demonstrated that CGS 9343B inhibited Kv currents in a state-, time-, and use-dependent manner, independent of calmodulin inhibition. - Highlights: • We investigated the effects of CGS 9394B on Kv channels. • CGS 9394B inhibited Kv current in a state-, time-, and use-dependent manner. • Caution is required when using CGS 9394B in vascular function studies.

  15. Multiwavelength VLBI observations of Sagittarius A*

    NASA Astrophysics Data System (ADS)

    Lu, R.-S.; Krichbaum, T. P.; Eckart, A.; König, S.; Kunneriath, D.; Witzel, G.; Witzel, A.; Zensus, J. A.

    2011-01-01

    Context. The compact radio, NIR, and X-ray source Sagittarius A* (Sgr A*), associated with the super massive black hole at the center of the Galaxy, has been studied with Very Long Baseline Interferometry (VLBI) observations performed on 10 consecutive days and at mm-wavelength. Aims: Sgr A* varies in the radio through X-ray bands and occasionally shows rapid flux density outbursts. We monitor Sgr A* with VLBI, aiming at the detection of related structural variations on the submilliarcsecond scale and variations of the flux density occurring after NIR-flares. Methods: We observed Sgr A* with the Very Long Baseline Array (VLBA) at 3 frequencies (22, 43, 86 GHz) on 10 consecutive days in May 2007 during a global multiwaveband campaign. From this we obtained accurate flux densities and sizes of the VLBI structure, which is partially resolved at mm-wavelength. Results: The total VLBI flux density of Sgr A* varies from day to day. The variability is correlated at the 3 observing frequencies with higher variability amplitudes appearing at the higher frequencies. For the modulation indices, we find 8.4% at 22 GHz, 9.3% at 43 GHz, and 15.5% at 86 GHz. The radio spectrum is inverted between 22 and 86 GHz, suggesting inhomogeneous synchrotron self-absorption with a turnover frequency at or above 86 GHz. The radio spectral index correlates with the flux density, which is harder (more inverted spectrum) when the source is brighter. The average source size (FWHM) does not appear to be variable over the 10-day observing interval. However, we see a tendency for the sizes of the minor axis to increase with increasing total flux, whereas the major axis remains constant. Towards higher frequencies, the position angle of the elliptical Gaussian increases, indicative of intrinsic structure, which begins to dominate the scatter broadening. At cm-wavelength, the source size varies with wavelength as λ2.12±0.12, which is interpreted as the result of interstellar scatter broadening

  16. VLBI height corrections due to gravitational deformation of antenna structures

    NASA Astrophysics Data System (ADS)

    Sarti, P.; Negusini, M.; Abbondanza, C.; Petrov, L.

    2009-12-01

    From an analysis of regional European VLBI data we evaluate the impact of a VLBI signal path correction model developed to account for gravitational deformations of the antenna structures. The model was derived from a combination of terrestrial surveying methods applied to telescopes at Medicina and Noto in Italy. We find that the model corrections shift the derived height components of these VLBI telescopes' reference points downward by 14.5 and 12.2 mm, respectively. No other parameter estimates nor other station positions are affected. Such systematic height errors are much larger than the formal VLBI random errors and imply the possibility of significant VLBI frame scale distortions, of major concern for the International Terrestrial Reference Frame (ITRF) and its applications. This demonstrates the urgent need to investigate gravitational deformations in other VLBI telescopes and eventually correct them in routine data analysis.

  17. Design Aspects of the VLBI2010 System - Progress Report of the IVS VLBI2010 Committee

    NASA Technical Reports Server (NTRS)

    Petrachenko, Bill; Niell, Arthur; Behrend, Dirk; Corey, Brian; Boehm, Johannes; Chralot, Patrick; Collioud, Arnaud; Gipson, John; Haas, Ruediger; Hobiger, Thomas; Koyama, Yasuhiro; MacMillan, Dan; Malkin, Zinvoy; Nilsson, Tobias; Pany, Andrea; Tuccari, Gino; Whitney, Alan; Wresnik, Joerg

    2009-01-01

    This report summarizes the progress made in developing the next generation VLBI system, dubbed the VLBI2010 system. The VLBI2010 Committee of the International VLBI Service for Geodesy and Astrometry (IVS) worked on the design aspects of the new system. The report covers Monte Carlo simulations showing the impact of the new operating modes on the final products. A section on system considerations describes the implications for the VLBI2010 system parameters by considering the new modes and system-related issues such as sensitivity, antenna slew rate, delay measurement error. RF1, frequency requirements, antenna deformation, and source structure corrections_ This is followed by a description of all major subsystems and recommendations for the network, station. and antenna. Then aspects of the feed, polarization processing. calibration, digital back end, and correlator subsystems are covered. A section is dedicated to the NASA. proof-of-concept demonstration. Finally, sections tm operational considerations, on risks and fallback options, and on the next steps complete the report.

  18. New VLBI Infrastructure for Earth Rotation Monitoring at Wettzell

    NASA Astrophysics Data System (ADS)

    Schüler, Torben; Nothnagel, Axel; Neidhardt, Alexander; Kronschnabl, Gerhard; Hugentobler, Urs; Kutterer, Hansjörg; Ihde, Johannes

    2014-05-01

    Very Long Baseline Interferometry (VLBI) is a key technology for precise monitoring of Earth's rotation. VLBI is the only space geodetic technique that allows for the determination of the absolute orientation of the Earth's rotation axis in space (nutation) and the absolute rotation angle of the Earth's body (UT1). VLBI is used to realize the International Celestial Reference Frame (ICRF) and contributes to the realization of the International Terrestrial Reference Frame (ITRF). In order to further improve accuracy, latency and availability of VLBI observations the International VLBI Service for Geodesy and Astrometry (IVS) developed the VLBI2010 concept aiming at more observations, larger bandwidth, and near-real time correlation. The implementation of the concept would allow for an uninterrupted high-accuracy monitoring of Earth's rotation. The Geodetic Observatory Wettzell is operated by the German Federal Agency for Cartography and Geodesy (BKG) together with Technische Universität Müchen (TUM) in the context of the Research Group Satellite Geodesy (FGS), a consortium of BKG, TUM, German Geodetic Research Institute (DFGI) and University of Bonn, Germany. The Wettzell observatory is on its way to operate a radio telescope triple: The 20 m radio telescope has been involved into geodetic VLBI observations since 1983. Recently two new 13.2 m VLBI telescopes were installed - the TWIN telescope - which adhere to the VLBI2010 concept and which will be part of VGOS, the newly developed VLBI Global Observing System of the International VLBI Service for Geodesy and Astrometry (IVS). Currently the high-frequency electronics, broadband receivers and feed horns, are being integrated and first operation is expected this year. The two telescopes allow for novel observation strategies, also in conjunction with the existing 20 m telescope. The upcoming new VLBI infrastructure will lead to more accurate, continuous and short-latency monitoring of the rotation of the Earth in

  19. Spacecraft Doppler tracking with a VLBI antenna

    NASA Astrophysics Data System (ADS)

    Comoretto, G.; Iess, L.; Bertotti, B.; Brenkle, J. P.; Horton, T.

    1990-02-01

    Preliminary results are reported from Doppler-shift measurements to the Voyager-2 spacecraft at a distance of 26 AU, obtained using the 32-m VLBI antenna at Medicina (Italy) during July and August 1988. The apparatus comprises the el-az antenna, an S-X-band receiver, a hydrogen maser to generate the reference signal, a Mark III VLBI terminal, and a digital tone extractor capable of isolating a tone of known frequency from a noisy signal and giving its phase and amplitude. A signal transmitted in S-band from the NASA Deep Space Network (DSN) station in Australia and retransmitted coherently in X-band by Voyager, was received 7 h 6 min later at Medicina and at the DSN station in Madrid. Sample data are presented graphically and shown to be of generally high quality; further in-depth analysis is under way.

  20. Spacecraft Doppler tracking with a VLBI antenna

    NASA Technical Reports Server (NTRS)

    Comoretto, G.; Iess, L.; Bertotti, B.; Brenkle, J. P.; Horton, T.

    1990-01-01

    Preliminary results are reported from Doppler-shift measurements to the Voyager-2 spacecraft at a distance of 26 AU, obtained using the 32-m VLBI antenna at Medicina (Italy) during July and August 1988. The apparatus comprises the el-az antenna, an S-X-band receiver, a hydrogen maser to generate the reference signal, a Mark III VLBI terminal, and a digital tone extractor capable of isolating a tone of known frequency from a noisy signal and giving its phase and amplitude. A signal transmitted in S-band from the NASA Deep Space Network (DSN) station in Australia and retransmitted coherently in X-band by Voyager, was received 7 h 6 min later at Medicina and at the DSN station in Madrid. Sample data are presented graphically and shown to be of generally high quality; further in-depth analysis is under way.

  1. SAND: Automated VLBI imaging and analyzing pipeline

    NASA Astrophysics Data System (ADS)

    Zhang, Ming

    2016-05-01

    The Search And Non-Destroy (SAND) is a VLBI data reduction pipeline composed of a set of Python programs based on the AIPS interface provided by ObitTalk. It is designed for the massive data reduction of multi-epoch VLBI monitoring research. It can automatically investigate calibrated visibility data, search all the radio emissions above a given noise floor and do the model fitting either on the CLEANed image or directly on the uv data. It then digests the model-fitting results, intelligently identifies the multi-epoch jet component correspondence, and recognizes the linear or non-linear proper motion patterns. The outputs including CLEANed image catalogue with polarization maps, animation cube, proper motion fitting and core light curves. For uncalibrated data, a user can easily add inline modules to do the calibration and self-calibration in a batch for a specific array.

  2. The VSOP-2 Space VLBI Mission

    NASA Technical Reports Server (NTRS)

    Hirabayashi, Hisashi; Murata, Yasuhiro; Murphy, David W.

    2002-01-01

    Following the success of the VLBI Space Observatory Program (VSOP), a next generation space VLBI mission, VSOP-2, is currently being planned. Higher observing frequencies, cooled receivers, increased bandwidths and larger telescope diameters will result in gains in resolution and interferometer sensitivity by factors of 10 over the VSOP mission. The use of phase-referencing by fast switching between a calibrator source and the target source is now being studied as this technique allows sources 50-150 times weaker to be observed depending on the frequency band. Such a capability would greatly enhance the VSOP-2 mission. Several other enhancements to the VSOP-2 mission are also presently under investigation including the VSOP-2 spacecraft operating at the same time as a US spacecraft to form what has come to be known as the iARISE (international ARISE) mission.

  3. Studies of ultracompact jets with space VLBI

    NASA Astrophysics Data System (ADS)

    Lobanov, Andrei

    Imaging and polarimetry of radio emission on microarcsecond scales provided by VSOP-2 and RadioAstron will offer a range of possibilities for studying ultracompact regions of relativistic jets and extreme vicinity of the central supermassive bodies in AGN. Both missions will address a number of outstanding problems in AGN physics, including the site and the mechanism of jet formation, acceleration of relativistic flows, structure of magnetic field in the vicinity of the central engine of AGN, and the fundamental question of the physical nature of the central massive objects in galaxies. Combining space VLBI observations with variability studies made in the X-ray, and gamma-ray bands will enable locating accurately the sites of high-enenrgy continuum production in AGN. Prospects and potentials of these lines of study with space VLBI will be reviewed.

  4. VLBI observations of 416 extragalactic radio sources

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Niell, A. E.; Preston, R. A.; Linfield, R. P.; Wehrle, A. E.; Faulkner, J.

    1986-01-01

    Very long baseline interferometry (VLBI) observations of 416 radio sources with declinations north of -45 deg have been conducted at frequencies of 2.3 and 8.4 GHz. At 2.3 GHz, 323 of 391 radio sources observed were detected with a fringe spacing of 3 milliarcsec and a detection limit of about 0.1 Jy. At 8.4 GHz, 278 of 416 radio sources were detected with a fringe spacing of 1 milliarcsec and a detection limit of about 0.1 Jy. This survey was conducted primarily to determine the strength of compact components at 8.4 GHz for radio sources previously detected with VLBI at 2.3 GHz. Compact extragalactic radio sources with strong correlated flux densities at both frequencies are used to form a high-accuracy reference frame.

  5. Multi-frequency imaging in VLBI

    NASA Astrophysics Data System (ADS)

    Likhachev, S.

    The new technique, multi-frequency imaging ( MFI) is developed. In VLBI, Multi-Frequency Imaging (MFI) consists of multi-frequency synthesis (MFS) and multi-frequency analysis (MFA) of the VLBI data obtained from observations on various frequencies. A set of linear deconvolution MFI algorithms is described. The algorithms make it possible to obtain high quality images interpolated on any given frequency inside any given bandwidth, and to derive reliable estimates of spectral indexes for radio sources with continuum spectrum. Thus MFI approach makes it is possible not only to improve the quality and fidelity of the images and also essentially to derive the morphology of the observed radio sources. (astro-ph/0412470)

  6. Spacecraft Doppler tracking with a VLBI antenna

    NASA Technical Reports Server (NTRS)

    Comoretto, G.; Iess, L.; Bertotti, B.; Brenkle, J. P.; Horton, T.

    1990-01-01

    Preliminary results are reported from Doppler-shift measurements to the Voyager-2 spacecraft at a distance of 26 AU, obtained using the 32-m VLBI antenna at Medicina (Italy) during July and August 1988. The apparatus comprises the el-az antenna, an S-X-band receiver, a hydrogen maser to generate the reference signal, a Mark III VLBI terminal, and a digital tone extractor capable of isolating a tone of known frequency from a noisy signal and giving its phase and amplitude. A signal transmitted in S-band from the NASA Deep Space Network (DSN) station in Australia and retransmitted coherently in X-band by Voyager, was received 7 h 6 min later at Medicina and at the DSN station in Madrid. Sample data are presented graphically and shown to be of generally high quality; further in-depth analysis is under way.

  7. Current Status of the Shanghai VLBI Correlator

    NASA Astrophysics Data System (ADS)

    Jiang, Wu; Shen, Zhiqiang; Shu, Fengchun; Chen, Zhong; Jiang, Tianyu

    2016-12-01

    Shanghai Astronomical Observatory has upgraded its DiFX cluster to 420 CPU cores and a 432-TB storage system at the end of 2014. An international network connection for the raw data transfer has also been established. The routine operations for IVS sessions including CRF, AOV, and APSG series began in early 2015. In addition to the IVS observations, the correlator is dedicated to astrophysical and astrometric programs with the Chinese VLBI Network and international joint VLBI observations. It also worked with the new-built Tianma 65-m radio telescope and successfully found fringes as high as at X/Ka and Q bands in late 2015. A more powerful platform is planned for the high data rate and massive data correlation tasks in the future.

  8. Progress on the VLBI Ecliptic Plane Survey

    NASA Astrophysics Data System (ADS)

    Shu, Fengchun; Petrov, Leonid; Jiang, Wu; McCallum, Jamie; Yi, Sang-oh; Takefuji, Kazuhiro; Li, Jinling; Lovell, Jim

    2016-12-01

    We launched the VLBI Ecliptic Plane Survey program in 2015. The goal of this program is to find all compact sources within 7.5° of the ecliptic plane which are suitable as phase calibrators for anticipated phase referencing observations of spacecrafts. We planned to observe a complete sample of the sources brighter than 50 mJy at 5 GHz listed in the PMN and GB6 catalogs that have not yet been observed with VLBI. By April 2016, eight 24-hour sessions had been performed and processed. Among 2,227 observed sources, 435 sources were detected in three or more observations. We also ran three eight-hour segments with the VLBA for improving the positions of 71 ecliptic sources.

  9. Monitoring of Earth Rotation by VLBI

    NASA Technical Reports Server (NTRS)

    Ma., Chopo; Macmillan, D. S.

    2000-01-01

    Monitoring Earth rotation with Very Long Baseline Interferometry (VLBI) has unique potential because of direct access to the Celestial Reference System (CRF and Terrestrial Reference System (TRF) and the feasibility of re-analyzing the entire data set. While formal precision of better than 0.045 mas for pole and 0.002 ms for UT 1 has been seen in the best 24-hr data, the accuracy of the Earth Orientation Parameter (EOP) time series as a whole is subject to logistical, operational, analytical and conceptual constraints. The current issues related to the VLBI data set and the CORE program for greater time resolution such as analysis consistency, network jitter and reference frame stability will be discussed.

  10. Radio VLBI and the quantum interference paradox

    NASA Astrophysics Data System (ADS)

    Singal, Ashok K.

    2016-12-01

    We address here the question of interference of radio signals from astronomical sources like distant quasars, in a very long baseline interferometer (VLBI), where two (or more) distantly located radio telescopes (apertures), receive a simultaneous signal from the sky. In an equivalent optical two-slit experiment, it is generally argued that for the photons involved in the interference pattern on the screen, it is not possible, even in principle, to know which of the two slits a particular photon went through and that any procedure to ascertain this destroys the interference pattern. But in the case of the modern radio VLBI, it is a routine matter to record the phase and amplitude of the voltage outputs from the two radio antennas on a recording media separately and then do the correlation between the two recorded signals later in an off-line manner. Does this not violate the quantum interference principle? We provide a resolution of this problem here.

  11. ERP Estimation using a Kalman Filter in VLBI

    NASA Astrophysics Data System (ADS)

    Karbon, M.; Soja, B.; Nilsson, T.; Heinkelmann, R.; Liu, L.; Lu, C.; Mora-Diaz, J. A.; Raposo-Pulido, V.; Xu, M.; Schuh, H.

    2014-12-01

    Geodetic Very Long Baseline Interferometry (VLBI) is one of the primary space geodetic techniques, providing the full set of Earth Orientation Parameters (EOP), and it is unique for observing long term Universal Time (UT1). For applications such as satellite-based navigation and positioning, accurate and continuous ERP obtained in near real-time are essential. They also allow the precise tracking of interplanetary spacecraft. One of the goals of VGOS (VLBI Global Observing System) is to provide such near real-time ERP. With the launch of this next generation VLBI system, the International VLBI Service for Geodesy and Astrometry (IVS) increased its efforts not only to reach 1 mm accuracy on a global scale but also to reduce the time span between the collection of VLBI observations and the availability of the final results substantially. Project VLBI-ART contributes to these objectives by implementing an elaborate Kalman filter, which represents a perfect tool for analyzing VLBI data in quasi real-time. The goal is to implement it in the GFZ version of the Vienna VLBI Software (VieVS) as a completely automated tool, i.e., with no need for human interaction. Here we present the methodology and first results of Kalman filtered EOP from VLBI data.

  12. GPS and CSS Radio Sources and Space-VLBI

    NASA Astrophysics Data System (ADS)

    Snellen, I.

    2009-08-01

    A short overview is given of the status of research on young extragalactic radio sources. We concentrate on Very Long Baseline Interferometric (VLBI), and space-VLBI results obtained with the VLBI Space Observatory Programme (VSOP). In 2012, VSOP-2 will be launched, which will allow VLBI observations at an unprecedented angular resolution. One particular question VSOP-2 could answer is whether some of the High Frequency Peakers (HFP) are indeed the youngest objects in the family of GPS and CSS sources. VSOP-2 observations can reveal their angular morphology and determine whether any are Ultra-compact Symmetric Objects.

  13. Multiband VLBI Observations of CTA102

    NASA Technical Reports Server (NTRS)

    Rantakyro, F. T.; Baath, L. B.; Dallacasa, D.; Jones, D. L.; Wehrle, A. E.

    1995-01-01

    The source CTA102, known to exhibit low frequency variability, has been observed at six epochs (three at lambda 32 cm, two at lambda 18 cm, and one at lambda l.3 cm) with intercontinental VLBI arrays. On the basis of the changes observed in the structure, we believe that the flux density variations at these wavelengths are due to intrinsic processes and not due to interstellar scintillation. This source exhibits behaviour suggestive of being expanding with a very high apparent transverse velocity.

  14. Multiband VLBI Observations of CTA102

    NASA Technical Reports Server (NTRS)

    Rantakyro, F. T.; Baath, L. B.; Dallacasa, D.; Jones, D. L.; Wehrle, A. E.

    1995-01-01

    The source CTA102, known to exhibit low frequency variability, has been observed at six epochs (three at lambda 32 cm, two at lambda 18 cm, and one at lambda l.3 cm) with intercontinental VLBI arrays. On the basis of the changes observed in the structure, we believe that the flux density variations at these wavelengths are due to intrinsic processes and not due to interstellar scintillation. This source exhibits behaviour suggestive of being expanding with a very high apparent transverse velocity.

  15. US Coast Guard GPS Information Center (GPSIC) and its function within the Civil GPS Service (CGS)

    NASA Technical Reports Server (NTRS)

    1993-01-01

    In 1987, the U.S. Department of Defense (DOD) formally requested that the U.S. Department of Transportation (DOT) take responsibility for providing an office that would respond to nonmilitary user needs for GPS information, data, and assistance. DOT accepted this responsibility and in February 1989, named the Coast Guard as their lead agency for the project. Since that time, the U.S. Coast Guard has worked with the U.S. Space Command to develop requirements and implement a plan for providing the requested interface with the civil GPS community. The Civil GPS Service (CGS) consists of four main elements: GPS Information Center (GPSIC) - provides GPS status information to civilian users of the system: Civil GPS Service Interface Committee (CGSIC) - established to identify civil GPS user technical information needs in support of the CGS program; Differential GPS (DGPS) - Coast Guard Research and Development Project; and PPS Program Office (PPSPO) - (Under development) will administer the program allowing qualified civil users to have access to the PPS signal. Details about the services these organizations provide are described.

  16. Utilization of mobile VLBI for geodetic measurements

    NASA Technical Reports Server (NTRS)

    Davidson, J. M.; Trask, D. W.

    1985-01-01

    Three mobile very long base interferometry (VLBI) systems were fabricated for the NASA Crustal Dynamics Project. These systems include the 9-meter-diameter MV-3 telescope. Since 1980, mobile systems operated in conjunction with several fixed base stations in the western United States as part of a geodetic survey program to determine relative motions and regional strain fields near the tectonic plate boundaries in California and Alaska. A description is given of the three mobile systems and the environment in which they must function. The inherent accuracy of mobile VLBI measurements is assessed, based on a consideration of major sources of error. Some recent results are presented which serve to illustrate various aspects of the error model and are of geodetic interest as they span the broad region surrounding the surface trace of the San Andreas Fault. These results indicate that baseline measurements utilizing the current mobile VLBI systems attained an accuracy of 2 cm or better in the horizontal plane. It is likely that crustal motions will be detected within the next few years, provided they are presently occurring at the geological rates.

  17. Utilization of Mobile VLBI for Geodetic Measurements

    NASA Technical Reports Server (NTRS)

    Davidson, J. M.; Trask, D. W.

    1985-01-01

    Three mobile very long base interferometry (VLBI) systems were fabricated for the NASA Crustal Dynamics Project. These systems include the 9-meter-diameter MV-3 telescope. Since 1980, mobile systems operated in conjunction with several fixed base stations in the western United States as part of a geodetic survey program to determine relative motions and regional strain fields near the tectonic plate boundaries in California and Alaska. A description is given of the three mobile systems and the environment in which they must function. The inherent accuracy of mobile VLBI measurements is assessed, based on a consideration of major sources of error. Some recent results are presented which serve to illustrate various aspects of the error model and are of geodetic interest as they span the broad region surrounding the surface trace of the San Andreas Fault. These results indicate that baseline measurements utilizing the current mobile VLBI systems attained an accuracy of 2 cm or better in the horizontal plane. It is likely that crustal motions will be detected within the next few years, provided they are presently occurring at the geological rates.

  18. VLBI2020: From Reality to Vision

    NASA Technical Reports Server (NTRS)

    Titov, Oleg

    2010-01-01

    The individual apparent motions of distant radio sources are believed to be caused by the effect of intrinsic structure variations of the active galactic nuclei (AGN). However, some cosmological models of the expanded Universe predict that systematic astrometric proper motions of distant quasars do not vanish as the radial distance from the observer to the quasar grows. These systematic effects can even increase with the distance, making it possible to measure them with high-precision astrometric techniques like VLBI. The Galactocentric acceleration of the Solar System barycenter may cause a secular aberration drift with a magnitude of 4 uas/yr. The Solar System motion relative to the cosmic microwave background produces an additional dipole effect, proportional to red shift. We analyzed geodetic VLBI data spanning from 1979 until 2009 to estimate the vector spherical harmonics in the expansion of the vector field of the proper motion of 687 radio sources. The dipole and quadrupole vector spherical harmonics were estimated with an accuracy of 1-5 as/yr. We have shown that over the next decade the geodetic VLBI may approach the level of accuracy on which the cosmological models of the Universe could be tested. Hence, it is important to organize a dedicated observational program to increase the number of measured proper motions to 3000.

  19. VLBI Ecliptic Plane Survey: VEPS-1

    NASA Astrophysics Data System (ADS)

    Shu, Fengchun; Petrov, Leonid; Jiang, Wu; Xia, Bo; Jiang, Tianyu; Cui, Yuzhu; Takefuji, Kazuhiro; McCallum, Jamie; Lovell, Jim; Yi, Sang-oh; Hao, Longfei; Yang, Wenjun; Zhang, Hua; Chen, Zhong; Li, Jinling

    2017-06-01

    We present here the results of the first part of the VLBI Ecliptic Plane Survey (VEPS) program. The goal of the program is to find all compact sources within 7\\buildrel{\\circ}\\over{.} 5 of the ecliptic plane that are suitable as calibrators for anticipated phase referencing observations of spacecraft, and determine their positions with accuracy at the 1.5 nrad level. We run the program in two modes: search and refine. In the search mode, a complete sample of all sources brighter than 50 mJy at 5 GHz listed in the Parkes-MIT-NRAO and Green Bank 6 cm (GB6) catalogs, except those previously detected with VLBI, is observed. In the refining mode, the positions of all ecliptic plane sources, including those found in the search mode, are improved. By 2016 October, thirteen 24 hr sessions that targeted all sources brighter than 100 mJy have been observed and analyzed. Among 3320 observed target sources, 555 objects have been detected. We also conducted a number of follow-up VLBI experiments in the refining mode and improved the positions of 249 ecliptic plane sources.

  20. ATS C-2 satellite VLBI experiment

    NASA Technical Reports Server (NTRS)

    Ramasastry, J.; Rosenbaum, B. M.

    1972-01-01

    A proposal is presented to conduct a satellite VLBI experiment using the ATS C-2 spacecraft. The main objectives of the experiment are: (1) precision spacecraft position determination with the VLBI technique and comparison of the L-band interferometric technique with the L-band R and R technique from the viewpoint of operational simplicity and precision, (2) comparison of the single differential Doppler and the wideband VLBI technique for such uses as tracking, geodesy, etc., (3) derivation of real time ionospheric corrections and phase scintillation effects utilizing simultaneous two-frequency (L- and C-band) tracking of the spacecraft in both time delay and Doppler interferometry, (4) development of techniques for precise time dissemination, particularly to marine users, through wideband time-delay interferometry, (5) development of techniques to use synchronous satellites as stable platforms in space in the area of marine geodesy, (6) station location and calibration, and (7) aid to L-band navigation experiments which utilize precise spacecraft position and time in deriving the user's position.

  1. Axis Offset Estimation of VLBI Telescopes

    NASA Astrophysics Data System (ADS)

    Krásná, Hana; Nickola, Marisa; Böhm, Johannes

    2014-12-01

    Axis offset models have to be applied for VLBI telescopes with pointing axes which do not intersect. In this work, we estimated the axis offsets for VLBI antennas in a global adjustment of suitable IVS 24-hour sessions (1984.0-2014.0) with the Vienna VLBI Software (VieVS). In particular, we focused on the two radio telescopes of the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in South Africa. For the older 26-m telescope we compared the estimated axis offset values before (6699.2 ± 0.5 mm) and after (6707.3 ± 0.8 mm) the bearing repair in 2010. A comparison with axis offset estimates from other geodetic techniques, such as GNSS or conventional local survey, was made. The estimated axis offset for the newer 15-m telescope (1495.0 ± 3.4 mm) agrees with the estimated value from the GPS survey in 2007. Furthermore, we assessed the influence of differences in the axis offsets on the estimated geodetic parameters, such as station coordinates or Earth Orientation Parameters.

  2. The East-Asian VLBI Network

    NASA Astrophysics Data System (ADS)

    Wajima, K.; Hagiwara, Y.; An, T.; Baan, W. A.; Fujisawa, K.; Hao, L.; Jiang, W.; Jung, T.; Kawaguchi, N.; Kim, J.; Kobayashi, H.; Oh, S.-J.; Roh, D.-G.; Wang, M. Wu, Y.; Xia, B.; Zhang, M.

    2016-02-01

    The East-Asian VLBI Network (EAVN) is the international VLBI facility in East Asia and is conducted in collaboration with China, Japan, and Korea. The EAVN consists of VLBI arrays operated in each East Asian country, containing 21 radio telescopes and three correlators. The EAVN will be mainly operated at 6.7 (C-band), 8 (X-band), 22 (K-band), and 43 GHz (Q-band), although the EAVN has an ability to conduct observations at 1.6 - 129 GHz. We have conducted fringe test observations eight times to date at 8 and 22 GHz and fringes have been successfully detected at both frequencies. We have also conducted science commissioning observations of 6.7 GHz methanol masers in massive star-forming regions. The EAVN will be operational from the second half of 2017, providing complementary results with the FAST on AGNs, massive star-forming regions, and evolved stars with high angular resolution at cm- to mm-wavelengths.

  3. APOD Mission Status and Observations by VLBI

    NASA Astrophysics Data System (ADS)

    Tang, Geshi; Sun, Jing; Li, Xie; Liu, Shushi; Chen, Guangming; Ren, Tianpeng; Wang, Guangli

    2016-12-01

    On September 20, 2015, 20 satellites were successfully launched from the TaiYuan Satellite Launch Center by a Chinese CZ-6 test rocket and are, since then, operated in a circular, near-polar orbit at an altitude of 520 km. Among these satellites, a set of four CubSats, named APOD (Atmospheric density detection and Precise Orbit Determination), are intended for atmospheric density in-situ detection and derivation via precise orbit. The APOD satellites, manufactured by DFH Co., carry a number of instruments including a density detector, a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI S/X beacon. The APOD mission aims at detecting the atmospheric density below 520 km. The ground segment is controlled by BACC (Beijing Aerospace Control Center) including payload operation as well as science data receiving, processing, archiving, and distribution. Currently, the in-orbit test of the nano-satellites and their payloads are completed, and preliminary results show that the precision of the orbit determination is about 10 cm derived from both an overlap comparison and an SLR observation validation. The in-situ detected density calibrated by orbit-derived density demonstrates that the accuracy of atmospheric mass density is approximately 4.191×10^{-14} kgm^{-3}, about 5.5% of the measurement value. Since three space-geodetic techniques (i.e., GNSS, SLR, and VLBI) are co-located on the APOD nano-satellites, the observations can be used for combination and validation in order to detect systematic differences. Furthermore, the observations of the APOD satellites by VLBI radio telescopes can be used in an ideal fashion to link the dynamical reference frames of the satellite with the terrestrial and, most importantly, with the celestial reference frame as defined by the positions of quasars. The possibility of observing the APOD satellites by IVS VLBI radio telescopes will be analyzed, considering continental-size VLBI observing networks and the small

  4. On the space monitoring of the Sassi and Murgia Park (Matera UNESCO site) using LANDSAT time series

    NASA Astrophysics Data System (ADS)

    Lanorte, Antonio; Nole, Gabriele; Manzi, Teresa; Lasaponara, Rosa

    2015-04-01

    This paper is focused on the preliminary results obtained in the framework of the Great relevance project " Smart management of cultural heritage sites in Italy and Argentina: Earth Observation and pilot projects funded by the Ministero degli Affari Esteri e della Cooperazione Internazionale --MAE, 17/04/2014, Prot. nr. 0090692, 2014-2016. A temporal series (1999-2011) of the LANDSAT TM data was used to carried out investigation in the Murgia Park enclosed in the Matera UNESCO site . The PCA was adopted to enhance regions of localized change in multi-temporal data sets (Lasaponara 2006). Both naturally vegetated areas (forest, shrub-land, herbaceous cover) and agricultural lands have been investigated in order to extract the most prominent natural and/or man induced alterations affecting soil and vegetation cover. Results from PCA were compared with independent data sets and field survey to evaluate the reliability of the obtained maps of the ongoing land degradation phenomenon. Such analyses can provide valuable information for an operational monitoring of the status of vegetation which is an indicator of the degree of stress namely any disturbance that adversely influences plants in response to natural hazards and/or anthropogenic activities. Our findings suggest that the Landsat TM time series can provide valuable information for environmental management policies involving biodiversity preservation and rational exploitation of natural and agricultural resources. Acknowledgement This research was performed within the framework of the Great relevance project " Smart management of cultural heritage sites in Italy and Argentina: Earth Observation and pilot projects funded by the Ministero degli Affari Esteri e della Cooperazione Internazionale --MAE, 17/04/2014, Prot. nr. 0090692, 2014-2016

  5. Caffeine and the analog CGS 15943 inhibit cancer cell growth by targeting the phosphoinositide 3-kinase/Akt pathway

    PubMed Central

    Edling, Charlotte E; Selvaggi, Federico; Ghonaim, Ragheda; Maffucci, Tania; Falasca, Marco

    2014-01-01

    Caffeine is a naturally occurring methylxanthine that acts as a non-selective adenosine receptor antagonist. Epidemiological studies demonstrated habitual coffee drinking to be significantly associated with liver cancer survival. We aimed to investigate the effects of caffeine and its analog CGS 15943 on hepatocellular carcinoma (HCC) and pancreatic cancer adenocarcinoma (PDAC). We demonstrate that caffeine and CGS 15943 block proliferation in HCC and PDAC cell lines by inhibiting the PI3K/Akt pathway. Importantly a kinase profiling assay reveals that CGS 15943 targets specifically the catalytic subunit of the class IB PI3K isoform (p110γ). These data give mechanistic insight into the action of caffeine and its analogs and they identify these compounds as promising lead compounds to develop drugs that can specifically target this PI3K isoform whose key role in cancer progression is emerging. PMID:24521981

  6. A Feasibility Study of Space VLBI for Geodesy and Geodynamics

    NASA Astrophysics Data System (ADS)

    Kulkarni, Madhav Narayan

    1992-01-01

    Space Very Long Baseline Interferometry (VLBI) is an extension of the ground based VLBI to the space. With the launching of two or more Space VLBI satellites in the future, Space VLBI observations will be available for astrometric, geodetic and geodynamic applications. This new technique holds potential for various important applications including monitoring Earth rotation and interconnection of the reference frames used in geodesy and geodynamics. The aim of this feasibility study has been to investigate the possibility of precise estimation of geodetic parameters, with emphasis on the Earth rotation parameters (ERP's), from Space VLBI observations. A brief description of the Space VLBI technique, it's possible applications, and the Space VLBI missions being planned has been given. Estimability analysis to investigate the estimability of geodetic parameters from Space VLBI observations has been carried out and a simplified mathematical model is derived in terms of estimable parameters. Results of sensitivity analysis carried out to study the sensitivity of the Space VLBI observables to the geodetic parameters of interest, including the number of these parameters and random errors in their a priori values, have been presented. Some of the dominant systematic effects including atmospheric refraction, solar radiation pressure and relativistic effects have also been investigated. Simulation studies have been carried out to study the influence of these systematic effects and a priori information on the estimation of the Earth rotation parameters. The results from the simulation studies indicate that it may be possible to use the Space VLBI technique for monitoring Earth rotation and polar motion, only if the orbital systematic effects can be modeled to a high degree of accuracy (or the satellites can be tracked, with high accuracy, independently), and precise a priori information on station coordinates from other sources is used. A brief description of the Space VLBI

  7. Joint Polar Satellite System (JPSS) Common Ground System (CGS) Technical Performance Measures of the Block 2 Architecture

    NASA Astrophysics Data System (ADS)

    Grant, K. D.; Panas, M.

    2016-12-01

    NOAA and NASA are jointly acquiring the next-generation civilian weather satellite system: the Joint Polar Satellite System (JPSS). JPSS replaced the afternoon orbit component and ground processing of NOAA's old POES system. JPSS satellites carry sensors that collect meteorological, oceanographic, climatological, and solar-geophysical observations of the earth, atmosphere, and space. The ground processing system for JPSS is known as the JPSS Common Ground System (JPSS CGS). Developed and maintained by Raytheon Intelligence, Information and Services (IIS), the CGS is a globally distributed, multi-mission system serving NOAA, NASA and their national and international partners. The CGS has demonstrated its scalability and flexibility to incorporate multiple missions efficiently and with minimal cost, schedule and risk, while strengthening global partnerships in weather and environmental monitoring. The CGS architecture has been upgraded to Block 2.0 to satisfy several key objectives, including: "operationalizing" the first satellite, Suomi NPP, which originally was a risk reduction mission; leveraging lessons learned in multi-mission support, taking advantage of newer, more reliable and efficient technologies and satisfying constraints due of the continually evolving budgetary environment. To ensure the CGS meets these needs, we have developed 48 Technical Performance Measures (TPMs) across 9 categories: Data Availability, Data Latency, Operational Availability, Margin, Scalability, Situational Awareness, Transition (between environments and sites), WAN Efficiency, and Data Recovery Processing. This paper will provide an overview of the CGS Block 2.0 architecture, with particular focus on the 9 TPM categories listed above. We will describe how we ensure the deployed architecture meets these TPMs to satisfy our multi-mission objectives with the deployment of Block 2.0.

  8. Estimability of geodetic parameters from space VLBI observables

    NASA Technical Reports Server (NTRS)

    Adam, Jozsef

    1990-01-01

    The feasibility of space very long base interferometry (VLBI) observables for geodesy and geodynamics is investigated. A brief review of space VLBI systems from the point of view of potential geodetic application is given. A selected notational convention is used to jointly treat the VLBI observables of different types of baselines within a combined ground/space VLBI network. The basic equations of the space VLBI observables appropriate for convariance analysis are derived and included. The corresponding equations for the ground-to-ground baseline VLBI observables are also given for a comparison. The simplified expression of the mathematical models for both space VLBI observables (time delay and delay rate) include the ground station coordinates, the satellite orbital elements, the earth rotation parameters, the radio source coordinates, and clock parameters. The observation equations with these parameters were examined in order to determine which of them are separable or nonseparable. Singularity problems arising from coordinate system definition and critical configuration are studied. Linear dependencies between partials are analytically derived. The mathematical models for ground-space baseline VLBI observables were tested with simulation data in the frame of some numerical experiments. Singularity due to datum defect is confirmed.

  9. VLBI Observations of the Radio Jet in 3C273

    NASA Astrophysics Data System (ADS)

    Unwin, S. C.; Davis, R. J.

    The authors present a new high dynamic range map of the quasar 3C 273, made from observations with a VLBI network of 12 telescopes. This new map at 18 cm wavelength has one of the highest dynamic ranges yet achieved with VLBI, and it shows the 'jet' extending to at least 180 milliarcsec, or 330 pc from the nucleus of the quasar.

  10. Construction of a New Geodetic VLBI Station in Korea

    NASA Astrophysics Data System (ADS)

    Kondo, T.; Kim, T.; Sasao, T.; Kwak, Y.; Oh, H.; Yi, S.; Hyun, D.; Bae, M.

    2008-12-01

    In Korea, KVN (Korean VLBI Network) project dedicated to radio astronomy is being promoted by Korea Astronomy and Space Science Institute (KASI), and three 21-m diameter antennas equipped with 22/43/86/129 GHz receivers have been already constructed at Seoul, Ulsan, and Jeju. On the other hand NGII (National Geographic Information Institute, Korea) has planned to construct their own antenna dedicated to geodetic VLBI measurements to maintain the Korean Geodetic Datum accurately. It also aims at a fundamental station in East Asia and will contribute to the better definition of the ITRF there. Grand design named KVG (Korea VLBI project for Geodesy) realizing NGII's plan has been proposed by Ajou University with collaborations from NICT (National Institute of Information and Communications Technology, Japan) and GSI (Geographical Survey Institute, Japan). KVG project got a national budget for construction formally this year (2008), and it has entered the three-year term of construction and development phase since October, 2008. A VLBI antenna will be constructed in Sejong city (about 120km south-southeast from Seoul) and its construction will be completed in 2011. The antenna is designed based on the VLBI2010 except for receiving frequencies and the diameter where VLBI2010 is the guideline for next generation's geodetic VLBI system compiled by IVS (International VLBI Service for Geodesy and Astrometry). Newly constructed antenna can receive 2/8/22/43 GHz band simultaneously in order to carry out geodetic VLBI observations not only with current geodetic VLBI stations equipped with 2/8 GHz receivers but also with KVN stations equipped with 22/43 GHz receivers. The antenna is also designed to be able to introduce a broadband feed and receivers in the future according to VLBI2010's suggestion. The diameter of antenna is chosen to be 22-m, which is larger than the VLBI2010's recommendation (13-m), to make astronomical VLBI observations of weak radio sources with KVN

  11. JPSS CGS C3S McMurdo Multimission Communications System

    NASA Astrophysics Data System (ADS)

    Higgins, C.; Urbano, J.; Jamilkowski, M. L.

    2011-12-01

    NOAA's next-generation civilian environmental satellite system, the Joint Polar Satellite System (JPSS) developed by NASA, will supply the afternoon orbit & ground system of the restructured NPOESS program. JPSS will replace NOAA's current POES system and ground processing part of both POES & DoD's Defense Weather Satellite System (DWSS). JPSS sensors will collect meteorological, oceanographic, climatological & solar-geophysical data. The command & data distribution part of the JPSS Common Ground System (CGS) is the Command, Control & Communications Segment (C3S), developed by Raytheon Intelligence & Information Systems. C3S manages the overall JPSS & DWSS missions from control & status of the space & ground assets to ensuring timely delivery of high-quality data to the Interface Data Processing Segment (IDPS). Key to C3S' data delivery system are 15 globally-distributed ground receptors developed by Raytheon Company which will collect up to 5 times the environmental data about 4 times faster than current polar-orbiting weather satellites. Then these data will be rapidly forwarded to weather centrals via the global fiber optic network for processing/production of data records for use in environmental prediction models. McMurdo Station, Antarctica is a major receptor site due to its high latitude. With the NSF, C3S completed the upgrade & expansion of their existing off-continent satellite communications (SATCOM) link with 60 Mbps of bandwidth outbound and 20 Mbps inbound to missions using McMurdo. C3S completed the 1st big milestone in 2008 increasjng bandwidth of 3 Mbps to/from Antarctica to 10 Mbps both ways. Raytheon's C3S also upgraded network infrastructure at McMurdo Station & Belrose Earth Station, Australia SATCOM sites. This provides routing support for several missions, plus expansion capabilities to support future missions at McMurdo. The upgrade completed in Dec 2010 to prepare for use of McMurdo Station to support new downlink capabilities, called the

  12. Mark 6 16-Gbps Next-Generation VLBI Data System

    NASA Astrophysics Data System (ADS)

    Whitney, Alan R.; Cappallo, Roger J.; Ruszczyk, Chester A.; SooHoo, Jason; Crew, Geoffrey B.

    2014-12-01

    The Mark 6 VLBI data system has been developed as a next-generation disk-based VLBI data system capable of supporting the goals of VLBI2010 and other very-high-data-rate VLBI applications, with a maximum sustained recording rate of 16 Gbps. Based on COTS data hardware and open-source software, the Mark 6 is designed to transition easily from the widely used Mark 5 system. Its features include a `scatter/gather' gather algorithm to ensure that data recording is not slowed by one or more slow or bad disks. The first field demonstration of a 16 Gbps/station VLBI experiment using Mark 6 in 2012 is reported. Existing Mark 5 systems are upgradeable to Mark 6, and existing Mark 5 SATA modules are upgradeable for compatibility with Mark 6.

  13. Combining VLBI and ring laser observations at normal equation level

    NASA Astrophysics Data System (ADS)

    Schartner, Matthias; Böhm, Johannes; Böhm, Sigrid; Schreiber, Karl Ulrich; Gebauer, André

    2017-04-01

    Observations from ring laser gyroscopes can be used to continuously monitor earth rotation with high resolution and without an external reference frame, which makes them unique in contrast to other techniques like VLBI or GNSS. A combination, however, of ring laser and VLBI data could potentially result in an improved accuracy of estimated earth rotation parameters. In this study, we use observations from the ring laser "G" (Grossring) located at Wettzell (Germany) and combine them with VLBI observations at the normal equation level. The Vienna VLBI and Satellite Software (VieVS) is used to set up the normal equations for each VLBI session as SINEX files. We present combined estimates for polar motion and length of day and assess the impact by the ring laser observations.

  14. The First Experiment with VLBI-GPS Hybrid System

    NASA Technical Reports Server (NTRS)

    Kwak, Younghee; Kondo, Tetsuro; Gotoh, Tadahiro; Amagai, Jun; Takiguchi, Hiroshi; Sekido, Mamoru; Ichikawa, Ryuichi; Sasao, Tetsuo; Cho, Jungho; Kim, Tuhwan

    2010-01-01

    In this paper, we introduce our GPS-VLBI hybrid system and show the results of the first experiment which is now under way. In this hybrid system, GPS signals are captured by a normal GPS antenna, down-converted to IF signals, and then sampled by the VLBI sampler VSSP32 developed by NICT. The sampled GPS data are recorded and correlated in the same way as VLBI observation data. The correlator outputs are the group delay and the delay rate. Since the whole system uses the same frequency standard, many sources of systematic errors are common between the VLBI system and the GPS system. In this hybrid system, the GPS antenna can be regarded as an additional VLBI antenna having multiple beams towards GPS satellites. Therefore, we expect that this approach will provide enough data to improve zenith delay estimates and geodetic results.

  15. DSN Beowulf Cluster-Based VLBI Correlator

    NASA Technical Reports Server (NTRS)

    Rogstad, Stephen P.; Jongeling, Andre P.; Finley, Susan G.; White, Leslie A.; Lanyi, Gabor E.; Clark, John E.; Goodhart, Charles E.

    2009-01-01

    The NASA Deep Space Network (DSN) requires a broadband VLBI (very long baseline interferometry) correlator to process data routinely taken as part of the VLBI source Catalogue Maintenance and Enhancement task (CAT M&E) and the Time and Earth Motion Precision Observations task (TEMPO). The data provided by these measurements are a crucial ingredient in the formation of precision deep-space navigation models. In addition, a VLBI correlator is needed to provide support for other VLBI related activities for both internal and external customers. The JPL VLBI Correlator (JVC) was designed, developed, and delivered to the DSN as a successor to the legacy Block II Correlator. The JVC is a full-capability VLBI correlator that uses software processes running on multiple computers to cross-correlate two-antenna broadband noise data. Components of this new system (see Figure 1) consist of Linux PCs integrated into a Beowulf Cluster, an existing Mark5 data storage system, a RAID array, an existing software correlator package (SoftC) originally developed for Delta DOR Navigation processing, and various custom- developed software processes and scripts. Parallel processing on the JVC is achieved by assigning slave nodes of the Beowulf cluster to process separate scans in parallel until all scans have been processed. Due to the single stream sequential playback of the Mark5 data, some ramp-up time is required before all nodes can have access to required scan data. Core functions of each processing step are accomplished using optimized C programs. The coordination and execution of these programs across the cluster is accomplished using Pearl scripts, PostgreSQL commands, and a handful of miscellaneous system utilities. Mark5 data modules are loaded on Mark5 Data systems playback units, one per station. Data processing is started when the operator scans the Mark5 systems and runs a script that reads various configuration files and then creates an experiment-dependent status database

  16. VLBI TRF determination via Kalman filtering

    NASA Astrophysics Data System (ADS)

    Soja, Benedikt; Karbon, Maria; Nilsson, Tobias; Glaser, Susanne; Balidakis, Kyriakos; Heinkelmann, Robert; Schuh, Harald

    2015-04-01

    The determination of station positions is one of the primary tasks for space geodetic techniques. Station coordinate offsets are usually determined with respect to a linear coordinate model after removing elastic displacements caused by mass redistributions within the Earth's system. In operational VLBI analysis, the coordinate offsets are estimated in a least-squares adjustment as a constant over the duration of a 24-hour VLBI experiment. Terrestrial reference frames (TRF) are usually derived by adjusting the normal equations that contain the 24-hour constant offsets in order to estimate a linear model, possibly including breaks, for the station positions. We have created a VLBI TRF solution without the assumption of negligible subdaily motion and of linear behavior on longer time scales by applying a Kalman filter. As a preparation for the upcoming VLBI Global Observing System (VGOS), which aims for continuous observations that are available in real-time, a Kalman filter has been implemented into the VLBI software VieVS@GFZ. In addition to the real-time capability, the filter offers the possibility of stochastically modeling the parameters of interest. For station coordinates, changes in a subdaily time frame occur, for instance, from un- or mismodeled geophysical effects. The models for tidal and non-tidal ocean, atmosphere, and hydrology loading are known to have deficiencies and inconsistencies which propagate into the estimated station coordinates. The stochastic model of the Kalman filter can be adapted to take these subdaily effects into account. Comparing the resulting station coordinate time series with daily values from a least squares fit, we have investigated to what extent and in which regions the loading models currently have deficiencies. Due to the high correlation between station height and tropospheric delays, it is possible that errors in one group of parameters are partly absorbed by the other group. To detect problems with correlations and to

  17. VLBI measurement of the secular aberration drift

    NASA Astrophysics Data System (ADS)

    Titov, O.; Lambert, S. B.; Gontier, A.-M.

    2011-05-01

    Aims: While analyzing decades of very long baseline interferometry (VLBI) data, we detected the secular aberration drift of the extragalatic radio source proper motions caused by the rotation of the Solar System barycenter around the Galactic center. Our results agree with the predicted estimate to be 4-6 micro arcseconds per year (μas/yr) towards α = 266° and δ = -29°. In addition, we tried to detect the quadrupole systematics of the velocity field. Methods: The analysis method consisted of three steps. First, we analyzed geodetic and astrometric VLBI data to produce radio source coordinate time series. Second, we fitted proper motions of 555 sources with long observational histories over the period 1990-2010 to their respective coordinate time series. Finally, we fitted vector spherical harmonic components of degrees 1 and 2 to the proper motion field. Results: Within the error bars, the magnitude and the direction of the dipole component agree with predictions. The dipole vector has an amplitude of 6.4 ± 1.5 μas/yr and is directed towards equatorial coordinates α = 263° and δ = -20°. The quadrupole component has not been detected. The primordial gravitational wave density, integrated over a range of frequencies less than 10-9 Hz, has a limit of 0.0042h-2 where h is the normalized Hubble constant is H0/(100 km s-1). We dedicate this work to the memory of Anne-Marie Gontier, our colleague and personal friend, and a widely recognized specialist of VLBI. She passed away shortly after this paper was submitted.Proper motion data is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A91

  18. U. S. Naval Observatory VLBI Analysis Center

    DTIC Science & Technology

    2013-06-01

    daily 1-hour duration Intensive observations were initiated using the VLBA antennas at Pie Town, NM and Mauna Kea , HI. High-speed network connections to...using the VLBA antennas at Pie Town, Nlvl and Mauna Kea , HI. IVS 2012 Annual Report 319 Report Documentation Page Form ApprovedOMB No. 0704-0188 Public...Pie Town, NM and Mauna Kea , HI. High-speed network connections to these two antennas are now routinely used for electronic transfer of VLBI data over

  19. VLBI2010: Networks and Observing Strategies

    NASA Technical Reports Server (NTRS)

    Petrachenko, Bill; Corey, Brian; Himwich, Ed; Ma, Chopo; Malkin, Zinovy; Niell, Arthur; Shaffer, David; Vandenberg, Nancy

    2004-01-01

    The Observing Strategies Sub-group of IVS's Working Group 3 has been tasked with producing a vision for the following aspects of geodetic VLBI: antenna-network structure and observing strategies; source strength/structure/distribution; frequency bands, RFI; and field system and scheduling. These are high level considerations that have far reaching impact since they significantly influence performance potential and also constrain requirements for a number of other \\VG3 sub-groups. The paper will present the status of the sub-group's work on these topics.

  20. Precise time transfer using MKIII VLBI technology

    NASA Technical Reports Server (NTRS)

    Johnston, K. J.; Buisson, J. A.; Lister, M. J.; Oaks, O. J.; Spencer, J. H.; Waltman, W. B.; Elgered, G.; Lundqvist, G.; Rogers, A. E. E.; Clark, T. A.

    1984-01-01

    It is well known that Very Long Baseline Interferometry (VLBI) is capable of precise time synchronization at subnanosecond levels. This paper deals with a demonstration of clock synchronization using the MKIII VBLI system. The results are compared with clock synchronization by traveling cesium clocks and GPS. The comparison agrees within the errors of the portable clocks (+ 5 ns) and GPS(+ or - 30 ns) systems. The MKIII technology appears to be capable of clock synchronization at subnanosecond levels and appears to be very good benchmark system against which future time synchronization systems can be evaluated.

  1. Precise time transfer using MKIII VLBI technology

    NASA Technical Reports Server (NTRS)

    Johnston, K. J.; Buisson, J. A.; Lister, M. J.; Oaks, O. J.; Spencer, J. H.; Waltman, W. B.; Elgered, G.; Lundqvist, G.; Rogers, A. E. E.; Clark, T. A.

    1984-01-01

    It is well known that Very Long Baseline Interferometry (VLBI) is capable of precise time synchronization at subnanosecond levels. This paper deals with a demonstration of clock synchronization using the MKIII VBLI system. The results are compared with clock synchronization by traveling cesium clocks and GPS. The comparison agrees within the errors of the portable clocks (+ 5 ns) and GPS(+ or - 30 ns) systems. The MKIII technology appears to be capable of clock synchronization at subnanosecond levels and appears to be very good benchmark system against which future time synchronization systems can be evaluated.

  2. VLBI Digital-Backend Intercomparison Test Report

    NASA Technical Reports Server (NTRS)

    Whitney, Alan; Beaudoin, Christopher; Cappallo, Roger; Niell, Arthur; Petrachenko, Bill; Ruszczyk, Chester A.; Titus, Mike

    2013-01-01

    Issues related to digital-backend (DBE) systems can be difficult to evaluate in either local tests or actual VLBI experiments. The 2nd DBE intercomparison workshop at Haystack Observatory on 25-26 October 2012 provided a forum to explicitly address validation and interoperability issues among independent global developers of DBE equipment. This special report discusses the workshop. It identifies DBE systems that were tested at the workshop, describes the test objectives and procedures, and reports and discusses the results of the testing.

  3. Reinforced Concrete Condition Assessment in Architectural Heritage. The Lion Chambers (Glasgow, UK) and the Theatre E. Duni (Matera, Italy)

    NASA Astrophysics Data System (ADS)

    Guida, A.; Dimitrijevic, B.; Pagliuca, A.

    2012-04-01

    The research objective is to provide new qualitative information on the strength of reinforced concrete structures of two prominent examples of modern architecture by using innovative, non-invasive testing techniques. The first one is Lion Chambers in Glasgow (Scotland, United Kingdom) designed by the architects Salmon, Son and Gillespie and completed in 1907. It was the second example of the use of François Hennebique's reinforced concrete system in a building in Glasgow and one of the earliest in Britain. The second example is Duni Theatre in Matera (Southern Italy), designed by the architect Ettore Stella and completed in 1949. The tests on the internal reinforced concrete columns were undertaken by using "SonReb" (SONic + REBound) method that enables assessing the concrete resistance by combining the speed of ultrasound waves and the index of surface bounce through a scleorometric test. In fact, the sclerometer index only gives information regarding the surface layer of the building's structure. In fact, due to the effects of the natural ageing, catalysed by the presence of humidity, surface layers of concrete are affected over time by carbonatation, which increases surface rigidity, providing as a result a greatly "altered" rebound index (much greater than one would have under normal conditions). On the other hand, the ultrasound speed, on the contrary to resistance, is inversely proportional to the age of the concrete (this seems to be due to the cracks that occur and reduce the speed). The hardening process continues over time with a consequent increase in resistance, which diminishes with the passage of time. The paper provides the results of the tests run on the structure of the Lion Chambers and the Duni Theatre. The tests carried out are the basis of a diagnostic project that is possible to implement and monitor to guarantee a deeper knowledge, with the goal of attaining a level of thorough understanding aimed at the preservation of "Modern Architecture

  4. VLBI observations of galaxies at high redshift

    NASA Astrophysics Data System (ADS)

    Schilizzi, R. T.; Gurvits, L. I.; Miley, G. K.; Bremer, M. A. R.; Röttgering, H. J. A.; Nan, R.; Chambers, K. C.; van Breugel, W. J. M.

    Subsets of fifteen high redshift radio galaxies have been observed with VLBI arrays at 327 MHz, 1.66 GHz or 5 GHz. Here we present results of VLBI imaging of four high redshift radio galaxies, three at 327 MHz and one at 1.66 GHz. Results so far show that 1) compact 1 kpc hotspots dominate the VLA components, 2) the magnetic field strengths in the hotspots are an order of magnitude higher than in Cygnus A, 3) the estimated ages of the sources are considerably longer than the radiative lifetimes of electrons in the hotspots, implying energy resupply, and 4) the ratios of overall size to hotspot size are consistent with the correlations found by Hardcastle et al (1998) for FR II radio galaxies and Snellen et al (1998) for GPS and CSS radio galaxies. We also investigate the possibility that the misalignment of the components to the southwest in 4C41.17 may be caused by deflection of the jet by an interstellar cloud of mass ~ 108 solar masses, possibly a proto globular cluster.

  5. Solving the polarization problem in ALMA-VLBI observations

    NASA Astrophysics Data System (ADS)

    Marti-Vidal, I.; Conway, J.; Lindqvist, M.; Roy, A. L.; Alef, W.; Zensus, A. J.

    The Atacama Large mm-submm Array (ALMA) is, by far, the most sensitive mm/submm telescope in the World. The ALMA Phasing Project (APP) will allow us to phase-up all the ALMA antennas and use them as one single VLBI station. This will be a key component of the Event Horizon Telescope (EHT), a Global VLBI array at millimeter wavelengths. A problem in the APP is the calibration and conversion of the polarization channels. Most VLBI stations record their signals in a circular basis, but the ALMA receivers record in a linear basis. The strategy that will be followed in the phased-ALMA VLBI observations will be to correlate in a "mixed" basis (i.e., linear versus circular) and convert the visibilities to a pure circular basis after the correlation. We have developed an algorithm to perform such a polarization conversion of the VLBI visibilities. In these proceedings, we present the basics of this algorithm and discuss on the polarization conversion in the general case where single dishes (besides phased arrays) record with linear receivers in VLBI observations. We show some results of our algorithm applied to realistic simulations, as well as a test with real VLBI observations at 86 GHz between the Onsala radiotelescope (recording in linear basis) and the Effelsberg radiotelescope (recording in circular basis).

  6. 11th European VLBI Network Symposium & Users Meeting

    NASA Astrophysics Data System (ADS)

    The Laboratoire d'Astrophysique de Bordeaux (LAB) at the University of Bordeaux (France), on behalf of the European VLBI Consortium, hosted the 11th European VLBI Network (EVN) Symposium and EVN Users Meeting on October 9-12, 2012. The Symposium was held at the "Chambre de Commerce et d'Industrie de Bordeaux", located in the "Palais de la Bourse", in the center of Bordeaux. The conference highlighted the latest scientific results and technical developments from VLBI, space VLBI and e-VLBI. All fields of astrophysics were concerned - stellar, galactic and extragalactic - as well as astrometry and planetary science. Presentations addressing synergy between (e-)VLBI and other new or planned radio facilities (ALMA, LOFAR, e-MERLIN,...) or instruments at other wavelengths (Fermi, CTA, Gaia,...) were also an integral part of the program. The scientific program was organized in 11 sessions including 71 oral presentations, with an additional 43 posters available for viewing during the entire length of the conference. An EVN Users Meeting was also held during one of the evening to foster interaction between the EVN users and the EVN organization. The symposium was attended by a total of 122 delegates originating from 47 institutes world-wide, sharing new VLBI science and innovations while also building links with other communities. The research leading to these results has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no 283393 (RadioNet3).

  7. A VLBI survey at 2.29 GHz

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Preston, R. A.; Williams, J. G.; Faulkner, J.; Jauncey, D. L.; Nicolson, G. D.

    1985-01-01

    The Deep Space Network (DSN) is establishing a high-accuracy VLBI celestial reference frame. The results of a search for suitable radio sources to be used in constructing this frame are given. The VLBI observations using DSN baselines at 2.29 GHz with fringe spacings of about 3 milliarcseconds have been performed on 1398 radio sources spread over the entire sky. Of those, 917 sources were detected including 93% of the identifed BL Lacertae objects, 86% of Quasars and 36% of galaxies. The resulting catalog of compact radio sources is also useful for various astrophysical studies and in the formation of VLBI celestial reference frames.

  8. Vienna VLBI Software: Current Release and Plans for the Future

    NASA Astrophysics Data System (ADS)

    Böhm, Johannes; Krásná, Hana; Böhm, Sigrid; Choliy, Vasyl; Hellerschmied, Andreas; Hofmeister, Armin; Karbon, Maria; Mayer, David; McCallum, Jamie; Madzak, Matthias; Nilsson, Tobias; Plank, Lucia; Shabala, Stanislav; Soja, Benedikt; Sun, Jing; Teke, Kamil

    2014-12-01

    The Vienna VLBI Software (VieVS) is a geodetic VLBI data analysis software written in Matlab. It has been developed and maintained at the Department of Geodesy and Geoinformation of the Vienna University of Technology since 2008. Recent improvements and extensions include a source structure simulator, additional estimable parameters in the global solution such as harmonic station position variations, and tools to observe satellites with VLBI radio telescopes and to analyze these observations. A highlight each year is the VieVS User Workshop which is held in September at TU Vienna. The VieVS Web site can be accessed at http://vievs.geo.tuwien.ac.at/.

  9. Study of correlation between overlay and displacement measured by Coherent Gradient Sensing (CGS) interferometry

    NASA Astrophysics Data System (ADS)

    Mileham, Jeffrey; Tanaka, Yasushi; Anberg, Doug; Owen, David M.; Lee, Byoung-Ho; Bouche, Eric

    2016-03-01

    Within the semiconductor lithographic process, alignment control is one of the most critical considerations. In order to realize high device performance, semiconductor technology is approaching the 10 nm design rule, which requires progressively smaller overlay budgets. Simultaneously, structures are expanding in the 3rd dimension, thereby increasing the potential for inter-layer distortion. For these reasons, device patterning is becoming increasingly difficult as the portion of the overlay budget attributed to process-induced variation increases. After lithography, overlay gives valuable feedback to the lithography tool; however overlay measurements typically have limited density, especially at the wafer edge, due to throughput considerations. Moreover, since overlay is measured after lithography, it can only react to, but not predict the process-induced overlay. This study is a joint investigation in a high-volume manufacturing environment of the portion of overlay associated with displacement induced by a single process across many chambers. Displacement measurements are measured by Coherent Gradient Sensing (CGS) interferometry, which generates high-density displacement maps (>3 million points on a 300 mm wafer) such that the stresses induced die-by-die and process-by-process can be tracked in detail. The results indicate the relationship between displacement and overlay shows the ability to forecast overlay values before the lithographic process. Details of the correlation including overlay/displacement range, and lot-to-lot displacement variability are considered.

  10. The Wavefront Clock Technique Applied to Current VLBI Systems

    NASA Astrophysics Data System (ADS)

    Kiuchi, Hitoshi; Kondo, Tetsuro

    1996-02-01

    A prototype wavefront clock system has been developed for application to current VLBI systems. The reference clock for both the front-end and back-end of a VLBI system is controlled at the observing site according to a calculated a priori delay rate. By using this system, fringe stopping is simultaneously performed on all received frequencies and both the upper side band (USB) and the lower side band (LSB) of a frequency-converter signal. Also, it can be used to reduce the large fringe rate (Doppler frequency) inherent in space VLBI, especially when used with an FX-type correlation proces sor. This wavefront clock method will be beneficial to users of conventional VLBI systems and will not require any modification. The reference point for the Doppler compensation can be taken at an ideal point , like the center of the Earth. Moreover, it is possible to use it as a pseudo-fringe simulator for checking the correlation processor.

  11. The Earth's nutation: VLBI versus IAU 2000A

    NASA Astrophysics Data System (ADS)

    Lambert, S.; Rosat, S.; Capitaine, N.; Souchay, J.

    2014-12-01

    The nutation measured by VLBI is compared with the IAU 2000A model. The differences are modeled empirically by adjusting the free core nutation and a number of tidal terms. The signal remaining in the residuals is discussed.

  12. JPL VLBI Analysis Center IVS Annual Report for 2004

    NASA Technical Reports Server (NTRS)

    Jacobs, Chris

    2005-01-01

    This report describes the activities of the JPL VLBI analysis center for the year 2004. We continue to be celestial reference frame, terrestrial reference frame, earth orientation, and spacecraft navigation work using the VLBI technique. There are several areas of our work that are undergoing active development. In 2004 we demonstrated 1 mm level troposphere calibration on an intercontinental baseline. We detected our first X/Ka (8.4/32 GHz) VLBI fringes. We began to deploy Mark 5 recorders and to interface the Mark 5 units to our software correlator. We also have actively participated in the international VLBI community through our involvement in six papers at the February IVS meeting and by collaborating on a number of projects such as densifying the S/X celestial frame creating celestial frames at K (24 GHz) and Q-bands ($# GHz)>

  13. Navigation of space VLBI missions: Radioastron and VSOP

    NASA Technical Reports Server (NTRS)

    Ellis, Jordan

    1993-01-01

    In the mid-1990s, Russian and Japanese space agencies will each place into highly elliptic earth orbit a radio telescope consisting of a large antenna and radio astronomy receivers. Very long baseline interferometry (VLBI) techniques will be used to obtain high resolution images of radio sources observed by the space and ground based antennas. Stringent navigation accuracy requirements are imposed on the space VLBI missions by the need to transfer an ultra-stable ground reference frequency standard to the spacecraft and by the demands of the VLBI correlation process. Orbit determination for the mission will be the joint responsibility of navigation centers in the U.S., Russia, and Japan with orbit estimates based on combining tracking data from NASA, Russian, and Japanese sites. This paper describes the operational plans, the inter-agency coordination, and data exchange between the navigation centers required for space VLBI navigation.

  14. ostglacial rebound from VLBI Geodesy: On Establishing Vertical Reference

    NASA Technical Reports Server (NTRS)

    Argus, Donald .

    1996-01-01

    I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan, 1995] and predictions from postglacial rebound predictions [Peltier, 1995].

  15. ostglacial rebound from VLBI Geodesy: On Establishing Vertical Reference

    NASA Technical Reports Server (NTRS)

    Argus, Donald .

    1996-01-01

    I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan, 1995] and predictions from postglacial rebound predictions [Peltier, 1995].

  16. VLBI2010 Receiver Back End Comparison

    NASA Technical Reports Server (NTRS)

    Petrachenko, Bill

    2013-01-01

    VLBI2010 requires a receiver back-end to convert analog RF signals from the receiver front end into channelized digital data streams to be recorded or transmitted electronically. The back end functions are typically performed in two steps: conversion of analog RF inputs into IF bands (see Table 2), and conversion of IF bands into channelized digital data streams (see Tables 1a, 1b and 1c). The latter IF systems are now completely digital and generically referred to as digital back ends (DBEs). In Table 2 two RF conversion systems are compared, and in Tables 1a, 1b, and 1c nine DBE systems are compared. Since DBE designs are advancing rapidly, the data in these tables are only guaranteed to be current near the update date of this document.

  17. VLBI: A Fascinating Technique for Geodesy and Astrometry

    NASA Technical Reports Server (NTRS)

    Schuh, H.; Behrend, Dirk

    2012-01-01

    Since the 1970s Very Long Baseline Interferometry (VLBI) has proven to be a primary space-geodetic technique by determining precise coordinates on the Earth, by monitoring the variable Earth rotation and orientation with highest precision, and by deriving many other parameters of the Earth system. VLBI provides an important linkage to astronomy through, for instance, the determination of very precise coordinates of extragalactic radio sources. Additionally, it contributes to determining parameters of relativistic and cosmological models. After a short review of the history of geodetic VLBI and a summary of recent results, this paper describes future perspectives of this fascinating technique. The International VLBI Service for Geodesy and Astrometry (IVS), as a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU), is well on its way to fully defining a next generation VLBI system, called VLBI2010. The goals of the new system are to achieve on scales up to the size of the Earth an accuracy of 1 mm in position and of 0.1 mm/year in velocity. Continuous observations shall be carried out 24 h per day 7 days per week in the future with initial results to be delivered within 24 h after taking the data. Special sessions, e.g. for monitoring the Earth rotation parameters, will provide the results in near real-time. These goals require a completely new technical and conceptual design of VLBI measurements. Based on extensive simulation studies, strategies have been developed by the IVS to significantly improve its product accuracy through the use of a network of small (approx 12 m) fast-slewing antennas. A new method for generating high precision delay measurements as well as improved methods for handling biases related to radio source structure, system electronics, and deformations of the antenna structures has been developed. Furthermore, as of January 2012, the construction of ten new VLBI2010 sites has been funded, with

  18. Millimetron and Earth-Space VLBI

    NASA Astrophysics Data System (ADS)

    Likhachev, S.

    2014-01-01

    The main scientific goal of the Millimetron mission operating in Space VLBI (SVLBI) mode will be the exploration of compact radio sources with extremely high angular resolution (better than one microsecond of arc). The space-ground interferometer Millimetron has an orbit around L2 point of the Earth - Sun system and allows operating with baselines up to a hundred Earth diameters. SVLBI observations will be accomplished by space and ground-based radio telescopes simultaneously. At the space telescope the received baseband signal is digitized and then transferred to the onboard memory storage (up to 100TB). The scientific and service data transfer to the ground tracking station is performed by means of both synchronization and communication radio links (1 GBps). Then the array of the scientific data is processed at the correlation center. Due to the (u,v) - plane coverage requirements for SVLBI imaging, it is necessary to propose observations at two different frequencies and two circular polarizations simultaneously with frequency switching. The total recording bandwidth (2x2x4 GHz) defines of the on-board memory size. The ground based support of the Millimetron mission in the VLBI-mode could be Atacama Large Millimeter Array (ALMA), Pico Valletta (Spain), Plateau de Bure interferometer (France), SMT telescope in the US (Arizona), LMT antenna (Mexico), SMA array, (Mauna Kea, USA), as well as the Green Bank and Effelsberg 100 m telescopes (for 22 GHz observations). We will present simulation results for Millimetron-ALMA interferometer. The sensitivity estimate of the space-ground interferometer will be compared to the requirements of the scientific goals of the mission. The possibility of multi-frequency synthesis (MFS) to obtain high quality images will also be considered.

  19. Spectral analysis of the VLBI pole path

    NASA Astrophysics Data System (ADS)

    Zuberi, Midhat; Smylie, Doug E.

    2009-12-01

    Modern observations of polar motion, using techniques such as Very Long Baseline Interferometry (VLBI), have reduced error levels by as much as three orders of magnitude, compared to classical astronometric methods. Here we focus on VLBI observations which are characteristically unequally spaced. We develop a very effective method of spectral analysis for unequally spaced time sequences. First, the least squares fit to the representation of the sequence by the Discrete Fourier Transform (DFT) is calculated, weighting the observations by the inverse square of the accompanying standard error. The coefficient matrix of the normal equations of this fit is nearly singular. It is subjected to a Singular Value Decomposition (SVD). In the usual application of SVD singular values are eliminated in order to improve the stability of the numerical system but no criterion is given for how many singular values to eliminate. To overcome this shortcoming, we introduce the Parseval condition which relates the mean square in the time domain to that in the frequency domain. Singular values are eliminated until Parseval's theorem is satisfied. Typically, the mean square in the frequency domain is many orders of magnitude too large. As singular values are eliminated, starting with the smallest and working upward, the mean square in the frequency domain appears to decrease monotonically until the Parseval relation is satisfied. Once the DFTs are found, spectral analysis and the estimation of confidence intervals proceed in the standard way. We perform a spectral analysis of the polar motion on 24.5 years of observations by using a Welch Overlapping Segment Analysis (WOSA) with four record segments of 14-year length with 75% overlap. Parameters of the Chandler wobble resonance are found as well as a detailed spectrum.

  20. Determination of UT1 by VLBI

    NASA Astrophysics Data System (ADS)

    Schuh, Harald; Boehm, Johannes; Englich, Sigrid; Nothnagel, Axel

    2010-11-01

    Very Long Baseline Interferometry (VLBI) is the only space geodetic technique which is capable of estimating the Earth's phase of rotation, expressed as Universal Time UT1, over time scales of a few days or longer. Satellite-observing techniques like the Global Navigation Satellite Systems (GNSS) are suffering from the fact that Earth rotation is indistinguishable from a rotation of the satellite orbit nodes, which requires the imposition of special procedures to extract UT1 or length of day information. Whereas 24 hour VLBI network sessions are carried out at about three days per week, the hour-long one-baseline intensive sessions (‘Intensives’) are observed from Monday to Friday (INT1) on the baseline Wettzell (Germany) to Kokee Park (Hawaii, U.S.A.), and from Saturday to Sunday on the baseline Tsukuba (Japan) to Wettzell (INT2). Additionally, INT3 sessions are carried out on Mondays between Wettzell, Tsukuba, and Ny-Alesund (Norway), and ultra-rapid e-Intensives between E! urope and Japan also include the baseline Metsähovi (Finland) to Kashima (Japan). The Intensives have been set up to determine daily estimates of UT1 and to be used for UT1 predictions. Because of the short duration and the limited number of stations the observations can nowadays be e-transferred to the correlators, or to a node close to the correlator, and the estimates of UT1 are available shortly after the last observation thus allowing the results to be used for prediction purposes.

  1. A VLBI survey at 2.29 GHz

    NASA Technical Reports Server (NTRS)

    Preston, R. A.; Morabito, D. D.; Williams, J. G.; Faulkner, J.; Jauncey, D. L.

    1985-01-01

    VLBI observations at 2.29 GHz with fringe spacings of about 3 milliarcsec have been performed on 1398 radio sources spread over the entire sky. 917 sources were detected, including 93 percent of the identified BL Lacertae objects, 86 percent of the quasars, and 36 percent of the galaxies. The resulting catalog of compact radio sources is useful for various astrophysical studies and in the formation of VLBI celestial reference frames.

  2. Generalized Linear Multi-Frequency Imaging in VLBI

    NASA Astrophysics Data System (ADS)

    Likhachev, S.; Ladygin, V.; Guirin, I.

    2004-07-01

    In VLBI, generalized Linear Multi-Frequency Imaging (MFI) consists of multi-frequency synthesis (MFS) and multi-frequency analysis (MFA) of the VLBI data obtained from observations on various frequencies. A set of linear deconvolution MFI algorithms is described. The algorithms make it possible to obtain high quality images interpolated on any given frequency inside any given bandwidth, and to derive reliable estimates of spectral indexes for radio sources with continuum spectrum.

  3. 22 GHz VLBI Survey: Status Report and Preliminary Results

    NASA Technical Reports Server (NTRS)

    Moellenbrock, G.; Fujisawa, K.; Preston, R.; Gurvits, L.; Dewey, R.; Hirabayashi, H.; Inoue, M.; Jauncey, D.; Migenes, V.; Roberts, D.; hide

    1994-01-01

    A ground-based VLBI survey to measure the visibilities and correlated flux densities in continuum at 22 GHz of more than 140 extragalactic radio sources has been conducted with baselines up to approximately 11 000 km. The project has been designed to help in preparation of target lists for VSOP and Radioastron Space VLBI missions as well as providing observational data for statistical study of structural properties at 22 GHz on sub-milliarcsecond scales for this large sample of extragalactic sources.

  4. VLBI studies of the nutations of the earth

    NASA Technical Reports Server (NTRS)

    Herring, T. A.

    1988-01-01

    The analysis of six years of VLBI data has yielded corrections to the coefficients of the seven largest terms in the IAU 1980 nutation series with periods of one year or less, with accuracies approaching the truncation error of this nutation series (0.1 mas). This paper examines the methods used to extract the nutation information from the VLBI data, the calculation of the uncertanties of the resultant corrections to the nutation-series coefficients, and current research on the earth's nutations.

  5. e-VLBI detection of SN2007gr

    NASA Astrophysics Data System (ADS)

    Paragi, Z.; Kouveliotou, C.; Garrett, M. A.; Ramirez-Ruiz, E.; van Langevelde, H. J.; Szomoru, A.; Argo, M.

    2007-09-01

    We observed the Type Ibc SN2007gr on 6-7 September for 12 hours (21:00-09:00 UTC) at 4.97 GHz with the the European VLBI Network (EVN) using the e- VLBI technique. Participating telescopes were Darnhall, Jodrell Bank (MkII), Medicina, Onsala, Torun and Westerbork (phased array of 14 telescopes). The aggregate bitrate was 256 Mbps, except for Darnhall which contributed with an effective data rate of 128 Mbps due to analog bandwidth restrictions.

  6. Simulation of Local Tie Accuracy on VLBI Antennas

    NASA Technical Reports Server (NTRS)

    Kallio, Ulla; Poutanen, Markku

    2010-01-01

    We introduce a new mathematical model to compute the centering parameters of a VLBI antenna. These include the coordinates of the reference point, axis offset, orientation, and non-perpendicularity of the axes. Using the model we simulated how precisely parameters can be computed in different cases. Based on the simulation we can give some recommendations and practices to control the accuracy and reliability of the local ties at the VLBI sites.

  7. The influence of indoor microclimate on thermal comfort and conservation of artworks: the case study of the cathedral of Matera (South Italy)

    NASA Astrophysics Data System (ADS)

    Cardinale, Tiziana; Rospi, Gianluca; Cardinale, Nicola; Paterino, Lucia; Persia, Ivan

    2014-05-01

    The Matera Cathedral was built in Apulian-Romanesque style in the thirteenth century on the highest spur of the "Civita" that divides "Sassi" district in two parts. The constructive material is the calcareous stone of the Vaglia, extracted from quarries in the area of Matera. The interior is Baroque and presents several artworks, including: mortars covered with a golden patina, a wooden ceiling, painted canvas and painting frescoes, three minor altars and a major altar of precious white marble, a nativity scene made of local painted limestone. The research had to evaluate the indoor microclimate during and after the restoration works, that also concern the installation of floor heating system to heat the indoor environments. Specifically, we have analyzed the thermal comfort and the effect that the artwork and construction materials inside the Cathedral of Matera have undergone. This evaluation was carried out in two different phases: in the first one we have investigated the state of the art (history of the site, constructive typology and artworks); in the second one we have done a systematic diagnosis and an instrumental one. The analysis were carried out in a qualitative and quantitative way and have allowed us to test indoor microclimatic parameters (air temperature, relative humidity and indoor air velocity), surface temperatures of the envelope and also Fanger's comfort indices (PMV and PPD) according to the UNI EN ISO 7730. The thermal mapping of the wall surface and of the artworks, carried out through thermal imaging camera, and the instrumental measurement campaigns were made both before restoration and after installation of the heating system; in addition measurements were taken with system on and off. The analysis thus made possible to verify that the thermo-hygrometric parameters found, as a result of the recovery operations, meet the limits indicated by the regulations and international studies. In this way, we can affirm that the indoor environment

  8. An algorithm of wideband bandwidth synthesis for geodetic VLBI

    NASA Astrophysics Data System (ADS)

    Kondo, Tetsuro; Takefuji, Kazuhiro

    2016-10-01

    A practical algorithm for wideband bandwidth synthesis (WBWS) for geodetic VLBI (very long baseline interferometry) is presented in this paper. A conventional bandwidth synthesis technique was developed for geodetic VLBI in the 1970s in order to increase the resolution of the observed delay by synthesizing multiple receiving frequency windows. The synthesized bandwidth has been expanding over the years and is now about 1 GHz. Recently, a wideband VLBI system consisting of multiple wideband frequency windows with a width of 1 GHz each and a total bandwidth exceeding 10 GHz has been proposed by the International VLBI Service for Geodesy and Astrometry (IVS) in order to achieve millimeter precision of position measurements. WBWS is a technique used for data processing in a wideband VLBI system. In conventional bandwidth synthesis, phase calibration (PCAL) signals are artificially injected at a front end and used to synthesize the channels. However, an algorithm without the use of PCAL signals was developed for WBWS so that it can be applied to a system without PCAL equipment. The algorithm includes the estimation of the differential total electron content in the ionosphere working with data with signal-to-noise ratios as low as 10 per band. The algorithm was successfully applied to 24 h continuous wideband VLBI observations.

  9. Uses of the ICRF and implications for future VLBI

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    2006-01-01

    Since its inception on 1 Jan 1998, the fundamental ICRF has been set by the VLBI positions of 212 "defining" extragalactic radio sources. In all there are approx.3000 sources with usefully accurate (< few mas) positions consistent with the ICRF. The uses of the ICRF include fundamental astrometry, monitoring of Earth orientation, and spacecraft navigation. For fundamental astrometry, stability and accuracy are most important, and realizations at different frequencies must be in proper registration. However, there is no preferred frequency, and the GAIA mission has the potential for an optical ICRF with 500,000 objects at the 50 microarcsec level some time after the planned 2011 launch. The radio ICRF should be properly prepared for a transition to assure long term stability and consistency. Earth orientation monitoring requires objects attached to the solid Earth, and VLBI will continue to be the fundamental technique. For this purpose it is essential that the new VLBI stations contemplated in the VLBI20l0 report be capable of observing a sufficiently large and well-distributed set of stable sources, and identifying these sources is an on-going effort. Spacecraft navigation by differential VLBI is planned using the Ka-band telemetry signal, and work has begun towards an ICRF realization suitable for this purpose. The balancing of different needs related to the VLBI ICRF will be discussed.

  10. ivg::ASCOT: Development of a New VLBI Software Package

    NASA Astrophysics Data System (ADS)

    Artz, Thomas; Halsig, Sebastian; Iddink, Andreas; Nothnagel, Axel

    2016-12-01

    The VLBI group of the Institute of Geodesy and Geoinformation of the University of Bonn (IGG) has started implementing a new analysis toolbox for VLBI observations. The main reason is the need for a flexible environment which allows for straightforward implementations of new scientific and software-related ideas for VLBI data analysis. Furthermore, we want to accumulate the developments, which have been performed in Bonn in recent years, under a unified software package. The software is implemented in C++ and should finally be able to perform scheduling of VLBI sessions and simulation of VLBI observations, as well as geodetic data analysis and intra-technique combination. Thus, it is named: IGG VLBI Group, Analysis, Scheduling and Combination Toolbox (ivg::ASCOT). Currently, we are able to perform single-session data analysis, at the stage when the ambiguities have been resolved. Furthermore, global solutions to derive celestial and terrestrial reference frames can be performed on the normal equation level. Intra-technique combinations of several solutions complete the initial functionality of the software package.

  11. The effect of the dynamic wet troposphere on VLBI measurements

    NASA Technical Reports Server (NTRS)

    Treuhaft, R. N.; Lanyi, G. E.

    1986-01-01

    Calculations using a statistical model of water vapor fluctuations yield the effect of the dynamic wet troposphere on Very Long Baseline Interferometry (VLBI) measurements. The statistical model arises from two primary assumptions: (1) the spatial structure of refractivity fluctuations can be closely approximated by elementary (Kolmogorov) turbulence theory, and (2) temporal fluctuations are caused by spatial patterns which are moved over a site by the wind. The consequences of these assumptions are outlined for the VLBI delay and delay rate observables. For example, wet troposphere induced rms delays for Deep Space Network (DSN) VLBI at 20-deg elevation are about 3 cm of delay per observation, which is smaller, on the average, than other known error sources in the current DSN VLBI data set. At 20-deg elevation for 200-s time intervals, water vapor induces approximately 1.5 x 10 to the minus 13th power s/s in the Allan standard deviation of interferometric delay, which is a measure of the delay rate observable error. In contrast to the delay error, the delay rate measurement error is dominated by water vapor fluctuations. Water vapor induced VLBI parameter errors and correlations are calculated. For the DSN, baseline length parameter errors due to water vapor fluctuations are in the range of 3 to 5 cm. The above physical assumptions also lead to a method for including the water vapor fluctuations in the parameter estimation procedure, which is used to extract baseline and source information from the VLBI observables.

  12. The effects of putative anxiogenic compounds (FG 7142, CGS 8216 and Ro 15-1788) on the rat corticosterone response.

    PubMed

    Pellow, S; File, S E

    1985-10-01

    The effects of FG 7142, CGS 8216 and Ro 15-1788, three compounds that are believed to produce anxiety by an action at benzodiazepine receptors in the CNS, are investigated on the plasma corticosterone concentrations in the rat both in the home cage and after exposure to novelty stress. FG 7142 (5 mg/kg) and CGS 8216 (10 mg/kg), but not Ro 15-1788 (4 or 10 mg/kg) increased basal corticosterone levels in the home cage, and all three compounds potentiated the increase in corticosterone concentrations observed after exposure to a novel environment. The relationship between the effects of drugs on corticosterone concentrations and on anxiety is considered in the light of these results.

  13. Phase I study of the oral nonsteroidal aromatase inhibitor CGS 20267 in postmenopausal patients with advanced breast cancer.

    PubMed

    Iveson, T J; Smith, I E; Ahern, J; Smithers, D A; Trunet, P F; Dowsett, M

    1993-01-15

    A phase I study was performed of CGS 20267, an oral nonsteroidal, highly potent, and selective aromatase inhibitor, in 21 postmenopausal patients with advanced breast cancer. The patients were recruited in 3 successive groups of 7, receiving 0.1, 0.5, and 2.5 mg p.o./day, respectively. All patients had received at least one prior endocrine treatment (range, 1-4), and six patients had received prior chemotherapy. The treatment was very well tolerated, and no toxicity was seen at any of the three doses. There was a statistically significant suppression of estradiol (E2) and estrone (E1) levels by 74% and 79% from baseline levels, respectively (P < 0.0001). Suppression occurred in all three patient groups, with many patients having serum concentrations of estradiol and estrone, which were below the limit of detection of the assays (3 and 10 pM, respectively), which corresponds to a maximum measurable estrogen suppression of 86%. CGS 20267 had no significant effect on serum levels of follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, cortisol, 17 alpha-hydroxyprogesterone, androstenedione, and aldosterone. Seven (33%, 95% confidence interval, 15-57%) of the 21 patients have responded to treatment (one complete remission, 6 partial remissions according to criteria of the Union Internationale contre le Cancer), and 6 are still responding to CGS 20267 (duration of response; 4+, 6+, 6+, 9+, 9, 12+, and 12+ months). Five have had stable disease for more than 3 months, and 9 had progressive disease. These results suggest that CGS 20267 is a very potent and specific aromatase inhibitor, and phase II studies are now required to confirm its clinical efficacy.

  14. Global VLBI Observations of Weak Extragalactic Radio Sources: Imaging Candidates to Align the VLBI and Gaia Frames

    NASA Technical Reports Server (NTRS)

    Bourda, Geraldine; Collioud, Arnaud; Charlot, Patrick; Porcas, Richard; Garrington, Simon

    2010-01-01

    The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames (International Celestial Reference Frame) with the highest accuracy. In this respect, it is found that only 10% of the ICRF sources are suitable to establish this link (70 sources), either because most of the ICRF sources are not bright enough at optical wavelengths or because they show extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we initiated a multi-step VLBI observational project, dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 optically-bright radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating optical and radio catalogs. The initial observations, aimed at checking whether these sources are detectable with VLBI, and conducted with the European VLBI Network (EVN) in 2007, showed an excellent 90% detection rate. This paper reports on global VLBI observations carried out in March 2008 to image 105 from the 398 previously detected sources. All sources were successfully imaged, revealing compact VLBI structure for about half of them, which is very promising for the future.

  15. ASI/CGS products and services in support of GNSS-meteorology

    NASA Astrophysics Data System (ADS)

    Pacione, Rosa; Pace, Brigida; Bianco, Giuseppe

    2013-04-01

    For more than a decade, ASI/CGS has supported ground-based GNSS meteorology in Europe participating in various projects such as MAGIC, COST-716, TOUGH, E-GVAP (phase I and II) and providing Zenith Tropospheric path Delays (ZTD) derived from a European network of GNSS stations covering mainly the central Mediterranean area. Working in close cooperation with the meteorological community, GNSS data are analyzed in order to provide ZTD with different latencies ranging from post-processing, useful for climate studies, to near-real time, for hourly assimilation into Numerical Weather Prediction (NWP) model. However advancements in NWP models (such as the Met Office UKV 1.5km model) with rapid update cycles require observations with improved timeliness and with greater spatial and temporal resolution than is currently available. To fulfil this requirement a sub-hourly PPP processing has been set-up, and is under evaluation, thanks to the availability of the IGS RT orbit and clock corrections. Moreover ZTD estimates are the input data for developing new and enhanced products: ZTD residuals fields and Integrated Water Vapour (IWV) maps. The former will be helpful in augmenting empirical tropospheric models for positioning applications. The latter are useful for nowcasting and severe weather monitoring since they let to follow IWV time evolution. We present an overview of the developed products and services; the new directions in support of NWP applications and the nowcasting and forecasting of severe weather events that emerge within E-GVAP phase III and the EU COST Action "Advanced Global Navigation Satellite Systems tropospheric products for monitoring Severe Weather Events and Climate" (GNSS4SWEC). Acknowledgements. This work has been carried out under ASI contract I-014-10-0.

  16. ( sup 3 H)CGS 21680, a selective A2 adenosine receptor agonist directly labels A2 receptors in rat brain

    SciTech Connect

    Jarvis, M.F.; Schulz, R.; Hutchison, A.J.; Do, U.H.; Sills, M.A.; Williams, M. )

    1989-12-01

    In the present study, the binding of a highly A2-selective agonist radioligand, (3H)CGS 21680 (2-(p-(2-carboxyethyl)-phenethylamino)-5'-N-ethylcarboxamido adenosine) is described. (3H)CGS 21680 specific binding to rat striatal membranes was saturable, reversible and dependent upon protein concentration. Saturation studies revealed that (3H)CGS 21680 bound with high affinity (Kd = 15.5 nM) and limited capacity (apparent Bmax = 375 fmol/mg of protein) to a single class of recognition sites. Estimates of ligand affinity (16 nM) determined from association and dissociation kinetic experiments were in close agreement with the results from the saturation studies. (3H)CGS 21680 binding was greatest in striatal membranes with negligible specific binding obtained in rat cortical membranes. Adenosine agonists ligands competed for the binding of 5 nM (3H)CGS 21680 to striatal membranes with the following order of activity; CGS 21680 = 5'-N-ethylcarboxamidoadenosine greater than 2-phenylaminoadenosine (CV-1808) = 5'-N-methylcarboxamidoadenosine = 2-chloroadenosine greater than R-phenylisopropyladenosine greater than N6-cyclohexyladenosine greater than N6cyclopentyltheophylline greater than S-phenylisopropyladenosine. The nonxanthine adenosine antagonist, CGS 15943A, was the most active compound in inhibiting the binding of (3H)CGS 21680. Other adenosine antagonists inhibited binding in the following order; xanthine amine congener = 1,3-dipropyl-8-(2-amino-4-chloro)phenylxanthine greater than 1,3-dipropyl-8-cyclopentylxanthine greater than 1,3-diethyl-8-phenylxanthine greater than 8-phenyltheophylline greater than 8-cyclopentyltheophylline = xanthine carboxylic acid congener greater than 8-parasulfophenyltheophylline greater than theophylline greater than caffeine.

  17. Tropospheric delay determination by Kalman filtering VLBI data

    NASA Astrophysics Data System (ADS)

    Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Zus, Florian; Dick, Galina; Deng, Zhiguo; Wickert, Jens; Heinkelmann, Robert; Schuh, Harald

    2015-09-01

    The troposphere is one of the most important error sources for space geodetic techniques relying on radio signals. Since it is not possible to model the wet part of the tropospheric delay with sufficient accuracy, it needs to be estimated from the observational data. In the analysis of very long baseline interferometry (VLBI) data, the parameter estimation is routinely performed using a least squares adjustment. In this paper, we investigate the application of a Kalman filter for parameter estimation, specifically focusing on the tropospheric delays. The main advantages of a Kalman filter are its real-time capability and stochastic approach. We focused on the latter and derived stochastic models for VLBI zenith wet delays, taking into account temporal and location-based differences. Compared to a static noise model, the quality of station coordinates, also estimated in the Kalman filter, increased as a result. In terms of baseline length and station coordinate repeatabilities, this improvement amounted to 2.3 %. Additionally, we compared the Kalman filter and least squares results for VLBI with zenith wet delays derived from GPS (Global Positioning System), water vapor radiometers, and ray tracing in numerical weather models. The agreement of the Kalman filter VLBI solution with respect to water vapor radiometer data was larger than that of the least squares solution by 6-15 %. Our investigations are based on selected VLBI data (CONT campaigns) that are closest to how future VLBI infrastructure is designed to operate. With the aim for continuous and near real-time parameter estimation and the promising results which we have achieved in this study, we expect Kalman filtering to grow in importance in VLBI analysis.

  18. VLBI and GPS-based Time-Transfer Using CONT08 Data

    NASA Technical Reports Server (NTRS)

    Rieck, Carsten; Haas, Ruediger; Jaldehag, Kenneth; Jahansson, Jan

    2010-01-01

    One important prerequisite for geodetic Very Long Baseline Interferometry (VLBI) is the use of frequency standards with excellent short term stability. This makes VLBI stations, which are often co-located with Global Navigation Satellite System (GNSS) receiving stations, interesting for studies of time- and frequency-transfer techniques. We present an assessment of VLBI time-transfer based on the data of the two week long consecutive IVS CONT08 VLBI campaign by using GPS Carrier Phase (GPSCP). CONT08 was a 15 day long campaign in August 2008 that involved eleven VLBI stations on five continents. For CONT08 we estimated the worst case VLBI frequency link stability between the stations of Onsala and Wettzell to 1e-15 at one day. Comparisons with GPSCP confirm the VLBI results. We also identify time-transfer related challenges of the VLBI technique as used today.

  19. First Phase Development of Korea-Japan Joint VLBI Correlator and Its Current Progress

    NASA Technical Reports Server (NTRS)

    Oh, Se-Jin; Roh, Duk-Gyoo; Yeom, Jae-Hwan; Kobayashi, Hideyuki; Kawaguchi, Noriyuki

    2010-01-01

    The first phase of the Korea-Japan Joint VLBI Correlator (KJJVC) development has been completed and installed to correlate the observed data from KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry) in October 2009. KJJVC is able to process 16 stations, a maximum of 8 Gbps/station, and 8,192 output channels for VLBI data. The system configuration, the experimental results, and future plans are introduced in this paper.

  20. Polarimetric VLBI with the Event Horizon Telescope

    NASA Astrophysics Data System (ADS)

    Fish, Vincent L.; Doeleman, S.; Marrone, D. P.; Lu, R.; Wardle, J. F.; EHT Collaboration

    2013-01-01

    The Event Horizon Telescope is a collaboration to observe the innermost accretion and outflow regions around supermassive black holes with an array of millimeter-wavelength telescopes. EHT observations have detected emission on scales of tens of microarcseconds around the black holes in the center of the Milky Way and M87. Non-polarimetric measurements have successfully been used to identify and model the Schwarzschild-radius-scale emission around these sources as well as to identify previously unresolvable structures in more distant AGNs and blazars, but new polarimetric data can provide additional information on the magnetic field strength and geometry in the jet launch and collimation region. Recent full-polarization VLBI observations with the EHT have detected polarized 1.3 mm emission arising on extremely small angular scales in a variety of extragalactic sources. We report on the results of these detections and detail the prospects for precision polarimetry thanks to the substantial EHT sensitivity improvements that will be realized over the next few years.

  1. Geodetic measurements with a mobile VLBI system

    NASA Technical Reports Server (NTRS)

    Niell, A. E.; Claflin, E. S.; Lockhart, T. G.; Macdoran, P. F.; Morabito, D. D.; Ong, K. M.; Resch, G. M.

    1980-01-01

    The Project ARIES 9 meter transportable antenna was used as one element of very long baseline interferometer (VLBI) to begin monitoring locations of six sites in California relative to large diameter fixed antennas at the NASA Deep Space Network, Goldstone, California, and at the Caltech Owens Valley Radio Observatory, Big Pine, California. An accuracy of about 6 cm in the horizontal components was demonstrated by comparison with measurements of the National Geodetic Survey. The root of mean square scatter of the lengths of the baselines between any pair of antennas was about 3 cm except for the Goldstone-JPL (Pasadena) baseline. In the period August 1974 to August 1977 the length of this baseline increased by 15 + or - 5 cm as JPL moved westward relative to Goldstone at the rate of 6 + or - 2 cm/year. The baseline lengths were unaffected by the uncertainties of UT1, polar motion, and tropospheric water vapor, which are the limitations to present three dimensional vector accuracies.

  2. New Generation VLBI: Intraday UT1 Estimations

    NASA Astrophysics Data System (ADS)

    Ipatov, Alexander; Ivanov, Dmitriy; Ilin, Gennadiy; Smolentsev, Sergei; Gayazov, Iskander; Mardyshkin, Vyacheslav; Fedotov, Leonid; Stempkovski, Victor; Vytnov, Alexander; Salnikov, Alexander; Surkis, Igor; Mikhailov, Andrey; Marshalov, Dmitriy; Bezrukov, Ilya; Melnikov, Alexey; Ken, Voytsekh; Kurdubov, Sergei

    2016-12-01

    IAA finished work on the creation of the new generation radio interferometer with two VGOS antennas co-located at Badary and Zelenchukskaya. 48 single baseline one-hour VLBI sessions (up to four sessions per day) were performed from 04 Nov to 18 Nov 2015. Observations were carried out using wideband S/X receivers, three X-band and one S-band 512 MHz channels at one or two circular polarizations. Sessions consisted of about 60 scans with a 22-second minimum scan duration. The stations' broadband acquisition systems generated 1.5-3 TB data per session, which were transferred via Internet to the IAA FX correlator. The accuracy of the group delay in a single channel was 10-20 ps, which allows the use of every single channel's observations for geodetic analysis without synthesis. 156 single channel NGS-cards were obtained in total. The RMS of the differences between UT1-UTC estimates and IERS finals values is 19 μs.

  3. The AuScope geodetic VLBI array

    NASA Astrophysics Data System (ADS)

    Lovell, J. E. J.; McCallum, J. N.; Reid, P. B.; McCulloch, P. M.; Baynes, B. E.; Dickey, J. M.; Shabala, S. S.; Watson, C. S.; Titov, O.; Ruddick, R.; Twilley, R.; Reynolds, C.; Tingay, S. J.; Shield, P.; Adada, R.; Ellingsen, S. P.; Morgan, J. S.; Bignall, H. E.

    2013-06-01

    The AuScope geodetic Very Long Baseline Interferometry array consists of three new 12-m radio telescopes and a correlation facility in Australia. The telescopes at Hobart (Tasmania), Katherine (Northern Territory) and Yarragadee (Western Australia) are co-located with other space geodetic techniques including Global Navigation Satellite Systems (GNSS) and gravity infrastructure, and in the case of Yarragadee, satellite laser ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) facilities. The correlation facility is based in Perth (Western Australia). This new facility will make significant contributions to improving the densification of the International Celestial Reference Frame in the Southern Hemisphere, and subsequently enhance the International Terrestrial Reference Frame through the ability to detect and mitigate systematic error. This, combined with the simultaneous densification of the GNSS network across Australia, will enable the improved measurement of intraplate deformation across the Australian tectonic plate. In this paper, we present a description of this new infrastructure and present some initial results, including telescope performance measurements and positions of the telescopes in the International Terrestrial Reference Frame. We show that this array is already capable of achieving centimetre precision over typical long-baselines and that network and reference source systematic effects must be further improved to reach the ambitious goals of VLBI2010.

  4. Mark 6 Next-Generation VLBI Data System

    NASA Astrophysics Data System (ADS)

    Whitney, A.; Lapsley, D.

    2012-12-01

    The Mark 6 VLBI data system is being developed by MIT Haystack Observatory as a next-generation disk-based VLBI data system capable of supporting the goals of VLBI2010, with a maximum sustained recording rate of 16 Gbps writing to an array of 32 magnetic disks. The Mark 6 is based on COTS hardware and open-source code and is being designed to transition easily from the widely used Mark 5 system. A successful 16 Gbps per station VLBI demonstration experiment was conducted with Mark 6 in late 2011 as a proof-of-concept. Haystack Observatory is collaborating with the NASA/GSFC High-End Network Computing Group in the selection of high-performance COTS hardware platforms and with Conduant Corporation in the development of a high-performance disk module for Mark 6. Existing Mark 5 systems will be upgradable to Mark 6, and existing Mark 5 SATA modules will be upgradeable for compatibility with Mark 6. The Mark 6 system is projected to be available to the VLBI community in late 2012.

  5. Systematic Effects in Earth Orientation Parameters Determined by VLBI

    NASA Astrophysics Data System (ADS)

    Schuh, H.; Heinkelmann, R.

    2015-12-01

    Very Long Baseline Interferometry (VLBI) is the only technique that directly connects on the observation level the realizations of ITRS and ICRS in terms of their orientation. Many applications in spacecraft navigation, fundamental astronomy, astrometry and geosciences depend on the Earth Orientation Parameters (EOP) determined by VLBI. Currently, under the IAG/IAU Joint Working Group on the Theory of Earth Rotation, activities are supported to advance the theory of Earth rotation. Some components of Earth Rotation, such as the free modes like the Free Core Nutation (FCN) are not predictable but rely entirely on the observation through VLBI. In our presentation we investigate the EOP when alternating various VLBI analysis options such as correction models, a priori parameters, and other choices with the aim to detect and quantify possible systematic effects. Our approach is purely empirical: we alternate certain analysis options and assess the differences with respect to the reference solution that adheres to the IERS Conventions (2010) and applies the standard parameterization. For demonstration we analyze the regular International VLBI Service for Geodesy and Astrometry (IVS) sessions IVS-R1 and IVS-R4.The IAG flagship component GGOS (Global Geodetic Observing System) aims to provide the EOP with an accuracy of 1 mm on the Earth surface (about 30 microarcseconds). This accuracy target will be applied as a limit to interpret the significance of the differences obtained in our comparisons.

  6. Correlated flux densities from VLBI observations with the DSN

    NASA Technical Reports Server (NTRS)

    Coker, R. F.

    1992-01-01

    Correlated flux densities of extragalactic radio sources in the very long baseline interferometry (VLBI) astrometric catalog are required for the VLBI tracking of Galileo, Mars Observer, and future missions. A system to produce correlated and total flux density catalogs was developed to meet these requirements. A correlated flux density catalog of 274 sources, accurate to about 20 percent, was derived from more than 5000 DSN VLBI observations at 2.3 GHz (S-band) and 8.4 GHz (X-band) using 43 VLBI radio reference frame experiments during the period 1989-1992. Various consistency checks were carried out to ensure the accuracy of the correlated flux densities. All observations were made on the California-Spain and California-Australia DSN baselines using the Mark 3 wideband data acquisition system. A total flux density catalog, accurate to about 20 percent, with data on 150 sources, was also created. Together, these catalogs can be used to predict source strengths to assist in the scheduling of VLBI tracking passes. In addition, for those sources with sufficient observations, a rough estimate of source structure parameters can be made.

  7. Tidal atmospheric and ocean loading in VLBI analysis

    NASA Astrophysics Data System (ADS)

    Girdiuk, Anastasiia; Schindelegger, Michael; Böhm, Johannes

    2016-04-01

    In VLBI (Very Long Baseline Interferometry) analysis, reductions for tidal atmospheric and ocean loading are commonly used according to the IERS Conventions. In this presentation we examine such loading corrections from contemporary geophysical models within routine VLBI processing and discuss the internal consistency of the applied corrections for various effects. In detail, two gravitational ocean tide models, FES2004 and the recent FES2012 atlas with a much finer horizontal resolution and an improved description of hydrodynamic processes, are employed. Moreover, the contribution of atmospheric tidal loading is also re-considered based on data taken from two providers of station displacements, Goddard Space Flight Center and the TU Wien group. Those two models differ in terms of the underlying meteorological data, which can be a reason for inconsistency of VLBI reductions and may lead to systematics in the VLBI products at tidal frequencies. We validate this assumption in terms of Earth rotation parameters, by a tidal analysis of diurnal and semi-diurnal universal time and semi-diurnal polar motion variations as determined with the Vienna VLBI Software. Applying the loading models in a consistent way still leads to unexplained residuals at about 4-5 μas in the diurnal polar motion band, thus limiting the possibility of assessing geophysical models at this particular frequency.

  8. VLBI observations of spacecraft with EVN radio telescopes

    NASA Astrophysics Data System (ADS)

    Duev, Dmitry

    2011-07-01

    PRIDE, the Planetary Radio Interferometry and Doppler Experiment initiative, focuses at enhancing the scientific return of prospective planetary missions by involving in the Earth-based segment of the missions a network of radio telescopes. PRIDE provides a direct characterisation of the planetary orbiters and surface elements (landers) signals by means of their Doppler and VLBI tracking. Such the tracking enables estimates of the spacecraft (S/C) state vectors which can be used for a variety of scientific applications. The experiment is beneficial to literally any planetary mission since PRIDE's requirements to the onboard instrumentation are minimal and are met on most planetary mission S/C irrespective to PRIDE. In this work, we present some preliminary results of recent test VLBI observations of spacecraft carried out using the European VLBI Network (EVN) telescopes in the phase-referencing mode. Some peculiarities of such the observations are described, for a S/C being a near-field source when observing with an Earth-based VLBI array of telescopes. The results of a narrow-band signal processing of the S/C signal, as well as test broad-band processing using the new software correlator SFX at the Joint Institute for VLBI in Europe (JIVE) are also presented.

  9. VLBI Data Acquisition Terminal Modernization at the Deep Space Network

    NASA Astrophysics Data System (ADS)

    García-Miró, C.; Rogstad, S. P.; Navarro, R.; Clark, J. E.; Naudet, C. J.; Jacobs, C. S.; Goodhart, C. E.; White, L. A.; Trinh, J. T.; Soriano, M.; Wang, D.; Sigman, E. H.; Luvalle, J. V.; Martinez, G.; Sotuela, I.; Pope, P. A.; Horiuchi, S.; Lobo, J.; Alonso, R.; Snedeker, L. G.

    2012-12-01

    The Deep Space Network (DSN) is replacing the aging Mark IV Data Acquisition Terminal (DAT) with a digital backend, the DSN VLBI Processor (DVP). It is based on the Wideband VLBI Science Receiver (WVSR), a custom-made open-loop digital receiver developed at JPL that is successfully supporting differential-VLBI for spacecraft navigation (DDOR) and other radio astronomy applications, e.g. Earth orientation, astrometry, and spectroscopy observations. From the WVSR the new acquisition terminal has inherited the Intermediate Frequency (IF) digitizer module, the firmware architecture, and monitor and control software. Among the new features, the DVP improves considerably the recording rate providing at least 2 Gbps with the goal of achieving 4 Gbps; uses a CASPER ROACH board for real-time Digital Signal Processing and channelization and streams the data into a Mark 5C recorder. This paper describes in detail the DVP in the context of similar digital developments (e.g., RDBE, DBBC). As the new backend will not use the standard Field System environment to perform the VLBI observations, efforts are under way to make it compatible with non-JPL correlators, providing monitor and calibration data in the appropriate format. Lately an important effort has been made in the DSN towards automation of VLBI data acquisition using the Automation Language for Managing DSN Operations (ALMO). The automation process will be adapted for the new DAT.

  10. VLBI Data Acquisition Terminal Modernization at the Deep Space Network

    NASA Astrophysics Data System (ADS)

    García-Miró, C.; Rogstad, S. P.; Navarro, R.; Clark, J. E.; Naudet, C. J.; Jacobs, Christopher S.; Goodhart, C. E.; White, L. A.; Trinh, J. T.; Soriano, M.; Wang, D.; Sigman, E. H.; Martinez, G.; LuValle, J. V.; Sotuela, I.; Pope, P. A.; Horiuchi, S.; Lobo, J.; ALonso, R.; Snedeker, L. G.

    2012-03-01

    The Deep Space Network (DSN) is replacing the aging Mark IV Data Acquisition Terminal (DAT) with a digital backend, the DSN VLBI Processor (DVP). It is based on the Wideband VLBI Science Receiver (WVSR), a custom-made open-loop digital receiver developed at JPL that is successfully supporting differential-VLBI for spacecraft navigation (DDOR) and other radio astronomy applications, e.g. Earth orientation, astrometry, and spectroscopy observations. From the WVSR the new acquisition terminal has inherited the Intermediate Frequency (IF) digitizer module, the firmware architecture, and monitor and control software. Among the new features, the DVP improves considerably the recording rate providing at least 2 Gbps with the goal of achieving 4 Gbps; uses a CASPER ROACH board for real-time Digital Signal Processing and channelization and streams the data into a Mark 5C recorder. This paper describes in detail the DVP in the context of similar digital developments (e.g., RDBE, DBBC). As the new backend will not use the standard Field System environment to perform the VLBI observations, efforts are under way to make it compatible with non-JPL correlators, providing monitor and calibration data in the appropriate format. Lately an important effort has been made in the DSN towards automation of VLBI data acquisition using the Automation Language for Managing DSN Operations (ALMO). The automation process will be adapted for the new DAT.

  11. Parallel algorithm of VLBI software correlator under multiprocessor environment

    NASA Astrophysics Data System (ADS)

    Zheng, Weimin; Zhang, Dong

    2007-11-01

    The correlator is the key signal processing equipment of a Very Lone Baseline Interferometry (VLBI) synthetic aperture telescope. It receives the mass data collected by the VLBI observatories and produces the visibility function of the target, which can be used to spacecraft position, baseline length measurement, synthesis imaging, and other scientific applications. VLBI data correlation is a task of data intensive and computation intensive. This paper presents the algorithms of two parallel software correlators under multiprocessor environments. A near real-time correlator for spacecraft tracking adopts the pipelining and thread-parallel technology, and runs on the SMP (Symmetric Multiple Processor) servers. Another high speed prototype correlator using the mixed Pthreads and MPI (Massage Passing Interface) parallel algorithm is realized on a small Beowulf cluster platform. Both correlators have the characteristic of flexible structure, scalability, and with 10-station data correlating abilities.

  12. Sensitivity evaluation of two VLBI2010 candidate feeds

    NASA Astrophysics Data System (ADS)

    Beaudoin, C.; Whittier, B.

    2011-07-01

    The VLBI2010 effort will usher in a new generation of geodetic VLBI observing systems possessing far more bandwidth than their predecessors. As such, MIT Haystack Observatory has been actively involved in the evaluation of broadband microwave feeds for the new Patriot 12m antenna installed at the Goddard Geophysical Astronomical Observatory in Greenbelt MD, USA. In our contribution to the meeting, we will present sensitivity measurements of the Patriot 12m antenna as fed by the Chalmers University of Technology design (i.e. the Eleven antenna) as well as a new California Institute of Technology design (i.e. the quadridge feed horn - QRFH) both of which have been realized in hardware prototypes and are considered to be contending feeds for VLBI2010.

  13. Centimeter repeatability of the VLBI estimates of European baselines

    NASA Technical Reports Server (NTRS)

    Rius, Antonio; Zarraoa, Nestor; Sardon, Esther; Ma, Chopo

    1992-01-01

    In the last three years, the European Geodetic Very Long Baseline Interferometry (VLBI) Network has grown to a total of six fixed antennas placed in Germany, Italy, Spain and Sweden, all equipped with the standard geodetic VLBI instrumentation and data recording systems. During this period of time, several experiments have been carried out using this interferometer providing data of very high quality due to the excellent sensitivity and performance of the European stations. The purpose of this paper is to study the consistency of the VLBI geodetic results on the European baselines with respect to the different degrees of freedom in the analysis procedure. Used to complete this study were both real and simulated data sets, two different software packages (OCCAM 3.0 and CALC 7.4/SOLVE), and a variety of data analysis strategies.

  14. The Impact of Radio Frequency Interference (RFI) on VLBI2010

    NASA Technical Reports Server (NTRS)

    Petrachenko, William

    2010-01-01

    A significant motivation for the development of a next generation system for geodetic VLBI was to address growing problems related to RFI. In this regard, the broadband 2-14 GHz frequency range proposed for VLBI2010 has advantages and disadvantages. It has the advantage of flexible allocation of band frequencies and hence the ability to avoid areas of the spectrum where RFI is worst. However, the receiver is at the same time vulnerable to saturation from RFI anywhere in the full 2-14 GHz range. The impacts of RFI on the VLBI2010 analog signal path, the sampler, and the digital signal processing are discussed. In addition, a number of specific RFI examples in the 2-14 GHz range are presented.

  15. VLBI Radar of the 2012 DA14 Asteroid

    NASA Astrophysics Data System (ADS)

    Nechaeva, M. B.; Dugin, N. A.; Antipenko, A. A.; Bezrukov, D. A.; Bezrukov, V. V.; Voytyuk, V. V.; Dement'ev, A. F.; Jekabsons, N.; Klapers, M.; Konovalenko, A. A.; Kulishenko, V. F.; Nabatov, A. S.; Nesteruk, V. N.; Putillo, D.; Reznichenko, A. M.; Salerno, E.; Snegirev, S. D.; Tikhomirov, Yu. V.; Khutornoy, R. V.; Skirmante, K.; Shmeld, I.; Chagunin, A. K.

    2015-03-01

    An experiment on VLBI radar of the 2012 DA14 asteroid was carried out on February 15-16, 2011 at the time of its closest approach to the Earth. The research teams of Kharkov (Institute of Radio Astronomy of the National Academy of Sciences of Ukraine), Evpatoria (National Space Facilities Control and Test Center), Nizhny Novgorod (Radiophysical Research Institute), Bologna (Istituto di Radioastronomia (INAF)), and Ventspils (Ventspils International Radioastronomy Center) took part in the experiment. The asteroid was irradiated by the RT-70 planetary radar (Evpatoria) at a frequency of 5 GHz. The reflected signal was received using two 32-m radio telescopes in Medicina (Italy) and Irbene (Latvia) in radiointerferometric mode. The Doppler frequency shifts in bi-static radar mode and interference frequency in VLBI mode were measured. Accuracy of the VLBI radar method for determining the radial and angular velocities of the asteroid were estimated.

  16. Comparison Campaign of VLBI Data Analysis Software - First Results

    NASA Technical Reports Server (NTRS)

    Plank, Lucia; Bohm, Johannes; Schuh, Harald

    2010-01-01

    During the development of the Vienna VLBI Software VieVS at the Institute of Geodesy and Geophysics at Vienna University of Technology, a special comparison setup was developed with the goal of easily finding links between deviations of results achieved with different software packages and certain parameters of the observation. The object of comparison is the computed time delay, a value calculated for each observation including all relevant models and corrections that need to be applied in geodetic VLBI analysis. Besides investigating the effects of the various models on the total delay, results of comparisons between VieVS and Occam 6.1 are shown. Using the same methods, a Comparison Campaign of VLBI data analysis software called DeDeCC is about to be launched within the IVS soon.

  17. Observing atmospheric tides in Earth rotation parameters with VLBI

    NASA Astrophysics Data System (ADS)

    Girdiuk, Anastasiia; Böhm, Johannes; Schindelegger, Michael

    2015-04-01

    In this study, we assess the contribution of diurnal (S1) and semi-diurnal (S2) atmospheric tides to variations in Earth rotation by analyzing Very Long Baseline Interferometry (VLBI) observations. Particular emphasis is placed on the dependency of S1 and S2 estimates on varying settings in the a priori delay model. We use hourly Earth rotation parameters (ERP) of polar motion and UT1 as determined with the Vienna VLBI Software (VieVS) from 25 years of VLBI observations and we adjust diurnal and semi-diurnal amplitudes to the hourly ERP estimates after disregarding the effect of high-frequency ocean tides. Prograde and retrograde polar motion coefficients are obtained for several solutions differing in processing strategies (with/without thermal deformation, time span of observations, choice of a priori ERP model and celestial pole offsets) and we compare the corresponding harmonics with those derived from atmospheric and non-tidal oceanic angular momentum estimates.

  18. Kalman Filter Analysis of SEARCH'92 VLBI Data

    NASA Astrophysics Data System (ADS)

    Herring, T. A.

    1994-09-01

    An analysis of the very long baseline interferometer data collected during the Epoch 1992 campaign is presented. A Standard analysis is discussed in which tidally coherent, diurnal and semidiurnal polar motion and UT1-UTC variations are applied prior to Kaiman filtering the VLBI data for stochastic estimates of 3-hourly binned estimated of pole position and UT1-UTC. Variams of this analysis are discussed to show the sensitivity of the results choiee of process noise parameters and the apriori applkatkm of die tidally coherent modeis. Here the residuals between a smoothed VLBI polar motion and UT1 apriori series are shown. For pole position, this apriori series is very similar to IERS Bulletin B. For UT1, the use of the VLBI series reduces by half the size of the UT 1 residuals compared to IERS Bulletin B.

  19. Development of a New VLBI Data Analysis Software

    NASA Technical Reports Server (NTRS)

    Bolotin, Sergei; Gipson, John M.; MacMillan, Daniel S.

    2010-01-01

    We present an overview of a new VLBI analysis software under development at NASA GSFC. The new software will replace CALC/SOLVE and many related utility programs. It will have the capabilities of the current system as well as incorporate new models and data analysis techniques. In this paper we give a conceptual overview of the new software. We formulate the main goals of the software. The software should be flexible and modular to implement models and estimation techniques that currently exist or will appear in future. On the other hand it should be reliable and possess production quality for processing standard VLBI sessions. Also, it needs to be capable of processing observations from a fully deployed network of VLBI2010 stations in a reasonable time. We describe the software development process and outline the software architecture.

  20. Australian geodetic VLBI network (AuScope): present and future.

    NASA Astrophysics Data System (ADS)

    Titov, Oleg

    2015-04-01

    The Australian geodetic Very Long Baseline Interferometry (VLBI) array (AuScope) consisting of three new 12-meter radio telescopes in Australia (Hobart, Katherine and Yarragadee), and a correlation facility in Perth that started operations in 2011. The daily positions of the AuScope array are estimated with a precision of a few mm, whereas their daily estimates vary within a range of 20-30 mm on the annual scale. This VLBI network also provides a substantial contribution to the improvement of the Celestial Reference Frame in the southern hemisphere. The plans for extension of the network in collaboration with the New Zealand and South Africa VLBI stations during 2015-2020 are discussed in this presentation.

  1. Universal Time Derived from VLBI, SLR and GPS

    NASA Astrophysics Data System (ADS)

    Gambis, D.; Essaifi, N.; Eisop, E.; Feissel, M.

    1994-09-01

    Universal Time Solution combined by IERS from individual series is mainly based on VLBI inertial techniques. Although satellite methods like SLR or GPS have reached a remarkable precision, they do not give access to a highly accurate non-rotating reference frame, which restricts the possibility of determining directly UT1 from their data processing. This is mainly due to uncertainties in the even zonal harmonics of the gravity field and in various modeis (ocean tides). We show here that it is still possible to combine the high-frequency fluctuations contained in GPS NUT1M series with the long-term variations in the VLBI Solution to derive a mixed UT1 (VLBI+GPS) Solution of great interest for its accuracy, time resolution but also for its economic advantage.

  2. The Automatic Calibration of Korean VLBI Network Data

    NASA Astrophysics Data System (ADS)

    Hodgson, Jeffrey A.; Lee, Sang-Sung; Zhao, Guang-Yao; Algaba, Juan-Carlos; Yun, Youngjoo; Jung, Taehyun; Byun, Do-Young

    2016-08-01

    The calibration of Very Long Baseline Interferometry (VLBI) data has long been a time consuming process. The Korean VLBI Network (KVN) is a simple array consisting of three identical antennas. Because four frequencies are observed simultaneously, phase solutions can be transferred from lower frequencies to higher frequencies in order to improve phase coherence and hence sensitivity at higher frequencies. Due to the homogeneous nature of the array, the KVN is also well suited for automatic calibration. In this paper we describe the automatic calibration of single-polarisation KVN data using the KVN Pipeline and comparing the results against VLBI data that has been manually reduced. We find that the pipelined data using phase transfer produces better results than a manually reduced dataset not using the phase transfer. Additionally we compared the pipeline results with a manually reduced phase-transferred dataset and found the results to be identical.

  3. 12th European VLBI Network Symposium and Users Meeting

    NASA Astrophysics Data System (ADS)

    Tarchi, Andrea; Giroletti, Marcello; Feretti, Luigina

    The Istituto di Radioastronomia (IRA) di Bologna and the Osservatorio Astronomico di Cagliari (OAC), on behalf of the European VLBI Consortium, hosted the 12th European VLBI Network (EVN) Symposium and Users Meeting. The Conference was held from 7th to 10th of October at the Hotel Regina Margherita, in the center of Cagliari. The latest scientific results and technical developments from VLBI, and, in particular, e-VLBI and space-VLBI (RadioAstron) outcomes were reported. The timing of this meeting coincided with the first successful observational tests of the Sardinia Radio Telescopes within the EVN, and with a number of results from new and upgraded radio facilities around the globe, such as e-MERLIN, ALMA, and the SKA pathfinders. The symposium was attended by 133 participants from all over the world, with the Asian community represented by more than 20 colleagues. The program of the meeting consisted of 70 oral contributions (including 8 invited speakers) and 50 poster that covered a very wide range of VLBI topics both in galactic and extragalactic astrophysics (e.g., AGN, stellar evolution from birth to death, astrometry, and planetary science) as well as technological developments and future international collaborations. The scientific program also included a visit to the 64-m Sardinia Radio Telescope (SRT) and the EVN Users Meeting, where astronomers have provided useful feedback on various matters regarding EVN operations. The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement No 283393 (RadioNet3). EDITORIAL BOARD: Andrea Tarchi, Marcello Giroletti, Luigina Feretti

  4. Direct Comparison of GPS and VLBI Velocity Estimates

    NASA Technical Reports Server (NTRS)

    Heflin, Michael

    1995-01-01

    Considerable effort has been made to collocate permanent GPS and VLBI sites for comparison. The global GPS solution is derived from daily measurements spanning four years while the VLBI solution is based on monthly measurements spanning more than 10 years. Current WRMS agreement of velocities is 3-5 mm/yr for horizontal rates and 6-10 mm/yr for vertical rates. Comparison of velocities is limited by the time span of GPS data. Positions agree at the level of 1-2 cm and their comparison is limited by the quality of the site ties. Best and worst agreement will be discussed along with possible sources of systematic error.

  5. High Frequency VLBI Studies of Sagittarius A* and NRAO 530

    NASA Astrophysics Data System (ADS)

    Lu, Ru-Sen

    2010-10-01

    Compact radio sources (Kellermann & Pauliny-Toth 1981) are widely accepted to be associated with supermassive black holes at the centers of active galaxies. Very long baseline interferometry (VLBI) observations at short millimeter wavelengths offer the unique advantage to look "deeper" into the central core regions. In this thesis we study two com pact radio sources (Sagittarius A* and NRAO 530) with high frequency VLBI techniques. As a starting point, we give in Chapter 1 a general introduction to observational properties of Active galactic nuclei (AGNs) and a theoretical basis. In Chapter 2, the compact radio source at the center of the Milky Way, Sagittarius A*, is reviewed. In Chapter 3, the technical basis of VLBI is outlined and then the difficulties of VLBI (and therefore the ways to improve) at short millimeter wavelengths are discussed. Due to its proximity, Sagittarius A* has the largest apparent event horizon of any black hole candidate and therefore it provides a unique opportunity for testing the SMBH paradigm. However, direct imaging of the nucleus is only accessible at short millimeter wavelengths due to the scatter broadening. In Chapter 4, we present results of an inter-day VLBI monitoring of Sagittarius A* at wavelengths of 13, 7, and 3 mm during a global observing campaign in 2007. We measure the flux density and source structure and study their variability on daily time scales. In addition to the VLBI monitoring of the Galactic Center, we present in Chapter 5 results of multi-epoch multi-frequency VLBI observations of the blazar nrao 530. NRAO 530 is an optically violent variable (OVV) source and was observed as a VLBI calibrator in our observations of Sagittarius A*. We investigate the spectral properties of jet components, their frequency-dependent position shifts, and variability of flux density and structure on daily time scales. Analysis of archival data over the last ten years allows us to study the detailed jet kinematics. Finally, a

  6. International VLBI Service for Geodesy and Astrometry 2011 Annual Report

    NASA Technical Reports Server (NTRS)

    Baver, Karen D. (Editor); Behrend, Dirk

    2012-01-01

    This volume of reports is the 2011 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2011 Annual Report documents the work of these IVS components over the period January 1, 2011 through December 31, 2011. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2011.

  7. Progress report on the Block 1 VLBI correlator implementation

    NASA Technical Reports Server (NTRS)

    Peterson, J. C.; Dillon, J. W.; Rogstad, D. H.

    1980-01-01

    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.

  8. International VLBI Service for Geodesy and Astrometry 2008 Annual Report

    NASA Technical Reports Server (NTRS)

    Behrend, Dirk; Baver, Karen D.

    2009-01-01

    This volume of reports is the 2008 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2008 Annual Report documents the work of these IVS components over the period January 1, 2008 through December 31, 2008. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2008.

  9. International VLBI Service for Geodesy and Astrometry 2007 Annual Report

    NASA Technical Reports Server (NTRS)

    Behrend, D. (Editor); Baver, K. D. (Editor)

    2008-01-01

    This volume of reports is the 2007 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2007 Annual Report documents the work of these IVS components over the period January 1, 2007 through December 31, 2007. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2007.

  10. e-VLBI observations of Cyg X-3

    NASA Astrophysics Data System (ADS)

    Tudose, V.; Paragi, Z.; Fender, R.; Spencer, R.; Garrett, M.; Rushton, A.

    2008-04-01

    We observed the X-ray binary Cyg X-3 on April 9th, 2008 for 9.5 hours, between 03:30-13:00 UT, at 5 GHz with the European VLBI Network (EVN) in e-VLBI mode (the data from the radio telescopes are sent over optical fibers in real-time to the correlator for processing). The radio telescopes participating in the experiment were: Cambridge, Medicina, Jodrell Bank MkII, Onsala (25 m), Torun and Westerbork (phased array).

  11. e-VLBI observations of SS 433 in outburst

    NASA Astrophysics Data System (ADS)

    Tudose, V.; Paragi, Z.; Trushkin, S.; Soleri, P.; Fender, R.; Garrett, M.; Spencer, R.; Rushton, A.; Burgess, P.; Kunert-Bajraszewska, M.; Pazderski, E.; Borkowski, K.; Hammargren, R.; Lindqvist, M.; Maccaferri, G.

    2008-11-01

    We have observed the X-ray binary SS 433 on November 6, 2008 between 13:48-18:35 UT at 5 GHz with the European VLBI Network (EVN) using the e-VLBI technique. The radio telescopes participating in the experiment were: Medicina, Onsala 25m, Torun, Jodrell Bank MkII and Cambridge. The X-ray binary SS 433 is in outburst. Trushkin & Nizhelskij (ATel #1819) reported a major flare already active during the RATAN-600 observations in the 1-22 GHz band on 2008 October 28.

  12. Differences Between S/X and VLBI2010 Operation

    NASA Technical Reports Server (NTRS)

    Hase, Hayo; Himwich, Ed; Neidhardt, Alexander

    2010-01-01

    The intended VLBI2010 operation has some significant differences to the current S/X operation. The presentation focuses on the problem of extending the operation of a global VLBI network to continuous operation within the frame of the same given amount of human resources. Remote control operation is a suitable solution to minimize operational expenses. The implementation of remote control operation requires more site specific information. A concept of a distributed-centralized remote control of the operation and its implications is presented.

  13. JPL VLBI Analysis Center IVS Annual Report for 2003

    NASA Technical Reports Server (NTRS)

    Jacobs, Chris

    2004-01-01

    This report describes the activities of the JPL VLBI Analysis Center for the year 2003. We continue to do celestial reference frame, terrestrial reference frame, and spacecraft navigation work using the VLBI technique. Tracking the two Mars Exploration Rover spacecraft was the highlight for the year. We continued improvements in the first sub-milliarcsecond global celestial reference frames at K-band (24 GHz) and Q-band (43 GHz). The K-band catalog more than doubled in size from 108 to 230 sources.

  14. Influence of CGS 21680, a selective adenosine A(2A) receptor agonist, on NMDA receptor function and expression in the brain of Huntington's disease mice.

    PubMed

    Ferrante, Antonella; Martire, Alberto; Armida, Monica; Chiodi, Valentina; Pézzola, Antonella; Potenza, Rosa Luisa; Domenici, Maria Rosaria; Popoli, Patrizia

    2010-04-06

    The effect of chronic treatment with the selective adenosine A(2A) receptor agonist CGS 21680 on N-Methyl-d-Aspartate (NMDA) receptor function and expression has been studied in the striatum and cortex of R6/2 mice, a genetic mouse model of Huntington's disease (HD). Starting from 8weeks of age, R6/2 and wild type (WT) mice were treated daily with CGS 21680 (0.5mg/kg i.p.) for 3weeks and the expression levels of NMDA receptor subunits were then evaluated. In addition, to study CGS 21680-induced changes in NMDA receptor function, NMDA-induced toxicity in corticostriatal slices from both R6/2 and WT mice was investigated. We found that CGS 21680 increased NR2A subunit expression and the NR2A/NR2B ratio in the cortex of R6/2 mice, having no effect in WT mice. In the striatum, CGS 21680 reduced NR1 expression in both R6/2 and WT mice while the effect on NR2A and NR2/NR2B expression was genotype-dependent, reducing and increasing their expression in WT and R6/2 mice, respectively. On the contrary, NMDA-induced toxicity in corticostriatal slices was not modified by the treatment in WT or HD mice. These results demonstrate that in vivo activation of A(2A) receptors modulates the subunit composition of NMDA receptors in the brain of HD mice.

  15. The adenosine A2A receptor agonist CGS 21680 decreases ethanol self-administration in both non-dependent and dependent animals.

    PubMed

    Houchi, Hakim; Persyn, Wolfgang; Legastelois, Rémi; Naassila, Mickaël

    2013-09-01

    There is emerging evidence that the adenosinergic system might be involved in drug addiction and alcohol dependence. We have already demonstrated the involvement of A2A receptors (A2AR) in ethanol-related behaviours in mice. Here, we investigated whether the A2AR agonist CGS 21680 can reduce ethanol operant self-administration in both non-dependent and ethanol-dependent Wistar rats. To rule out a potential involvement of the A1R in the effects of CGS 21680, we also tested its effectiveness to reduce ethanol operant self-administration in both heterozygous and homozygous A1R knockout mice. Our results demonstrated that CGS 21680 (0.065, 0.095 and 0.125 mg/kg, i.p.) had a bimodal effect on 10% ethanol operant self-administration in non-dependent rats. The intermediate dose was also effective in reducing 2% sucrose self-administration. Interestingly, the intermediate dose reduced 10% ethanol self-administration in dependent animals more effectively (75% decrease) when compared with non-dependent animals (57% decrease). These results suggest that the A2AR are involved in CGS 21680 effects since the reduction of ethanol self-administration was not dependent upon the presence of A1R in mice. In conclusion, our findings demonstrated the effectiveness of the A2AR agonist CGS 21680 in a preclinical model of alcohol addiction and suggested that the adenosinergic pathway is a promising target to treat alcohol addiction.

  16. Mobile VLBI and GPS measurement of vertical crustal motion

    NASA Technical Reports Server (NTRS)

    Kroger, P. M.; Davidson, J. M.; Gardner, E. C.

    1985-01-01

    Mobile Very Long Base Interferometry (VLBI) and Global Positioning System (GPS) geodetic measurements have many error sources in common. Calibration of the effects of water vapor on signal transmission through the atmosphere, however, remains the primary limitation to the accuracy of vertical crustal motion measurements made by either technique. The two primary methods of water vapor calibration currently in use for mobile VLBI baseline measurements were evaluated: radiometric measurements of the sky brightness near the 22 GHz emission line of free water molecules and surface meteorological measurements used as input to an atmospheric model. Based upon a limited set of 9 baselines, it is shown that calibrating VLBI data with water vapor radiometer measurements provides a significantly better fit to the theoretical decay model than calibrating the same data with surface meteorological measurements. The effect of estimating a systematic error in the surface meteorological calibration is shown to improve the consistency of the vertical baseline components obtained by the two calibration methods. A detailed error model for the vertical baseline components obtained indicates current mobile VLBI technology should allow accuracies of order 3 cm with WVR calibration and 10 cm when surface meteorological calibration is used.

  17. The first geodetic VLBI experiment with the Bologna radio telescope

    NASA Astrophysics Data System (ADS)

    Tomasi, P.; Mantovani, F.; Ambrosini, R.; Bombonati, A.; Grueff, G.

    1988-04-01

    The use of the Medicina VLBI station for geodetic observations was demonstrated. The Medicina-Wettzel and the Medicina-HartRAO (Hartebeesthoek Radio Astrophysical Observatory) baselines were determined as well as the Medicina (Bologna) antenna position. It is concluded that longer experiments are needed with more baselines involved to get a better solution for the Medicina position.

  18. Warkworth 12-m VLBI Station: WARK12M

    NASA Technical Reports Server (NTRS)

    Weston, Stuart; Takiguchi, Hiroshi; Natusch, Tim; Woodburn, Lewis; Gulyaev, Sergei

    2013-01-01

    The Warkworth 12-m radio telescope is operated by the Institute for Radio Astronomy and Space Research (IRASR) at AUT University, Auckland, New Zealand. Here we review the characteristics of the 12-m VLBI station and report on a number of activities and technical developments in 2012.

  19. A new VLBI data acquisition and processing system, K-4

    SciTech Connect

    Kiuchi, H.; Hama, S.; Imae, M.

    1994-12-31

    We have been developed a new VLBI system applicable to VLBA and VSOP. This system has been achieved by using a high speed A/D, digital filter and 32 MHz IRM. An XF type correlation processor has been developed by making use of Field Programmable Gate Array.

  20. Pulse strobing in VLBI for observation of geostationary earth satellites.

    NASA Astrophysics Data System (ADS)

    Gorodetskij, V. M.

    The possibility of broadband synthesis by pulse strobing for observation of slow-moving objects using standard MARK-1 VLBI processing methods is discussed. The possibility of increasing the SNR by using a special type of pulse function is indicated. A specific scheme for application of the method in satellite radiointerferometry is examined.

  1. Atmospheric tides in variations of VLBI station positions

    NASA Astrophysics Data System (ADS)

    Girdiuk, Anastasiia; Böhm, Johannes; Schindelegger, Michael

    2017-04-01

    The deformation of the Earth surface caused by atmospheric tidal mass variations is small compared to loading associated with ocean tides or solid Earth tides. Yet, due to an ever-growing data base of Very Long Baseline Interferometry (VLBI) observations, atmosphere-induced effects in variations of station positions can be estimated. We determine daily and sub-daily harmonic signals in station time series of 20 years, from 1995 to 2015, and find reasonable amplitudes for a number of sites. Particular emphasis is given to station Katherine in Australia, where a strong atmospheric signal at the diurnal frequency band is detected. We compare the amplitudes against those from loading providers, including TU Wien, Goddard Space Flight Center (GSFC) and the Global Geophysical Fluid Center (GGFC) with focus on the radial component. In this study, the analysis of VLBI observations is performed with the Vienna VLBI Software (VieVS). The amplitudes are estimated as global parameters from 10 years of VLBI observations as well as from special session-wise solutions with hourly estimates of station coordinates. In the latter case we had to change the standard parameterisation for the tropospheric delays in order to avoid fictitious deformation signals due to correlation. Furthermore, special attention is paid to tidal oceanic effects because they cannot be fully de-coupled from the atmospheric counterparts.

  2. Investigations of atmospheric refraction parameters derived from local VLBI observations

    NASA Astrophysics Data System (ADS)

    Halsig, Sebastian; Nothnagel, Axel

    2017-04-01

    Space-geodetic techniques, such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI) play a steadily increasing role in the understanding of the Earth's atmosphere, because atmospheric refraction parameters can be linked to the water vapor content in the atmosphere. However, in the field of geodesy, changing atmospheric conditions are referred to as perturbation effects, since the signals of space-geodetic techniques are delayed and affected by bending and attenuation effects relative to a theoretical path in vacuum. Local refraction effects are normally investigated by small scale GNSS networks. With a pair of radio telescopes at the Geodetic Observatory Wettzell in Bavaria (Germany), we are now able to carry out similar investigations with geodetic VLBI observations, which are affected by the same refraction phenomena. In this study, we investigate differential zenith wet delay estimates derived from various local VLBI sessions. For this purpose, specially designed so-called WHISP (Wettzell HIgh SPeed) sessions have been observed consisting of only two VLBI radio telescopes separated by only about 120m. One main advantage of the WHISP sessions is the considerably increased number of observations compared to traditional 24h-sessions.

  3. 223 GHz VLBI observations of 3C 273

    NASA Astrophysics Data System (ADS)

    Padin, S.; Woody, D. P.; Hodges, M. W.; Rogers, A. E. E.; Emerson, D. T.; Jewell, P. R.; Lamb, J.; Perfetto, A.; Wright, M. C. H.

    1990-09-01

    In the first 1.4 mm wavelength VLBI test observations, fringes have been detected on the active nucleus of 3C 273 on a baseline from Owens Valley Radio Observatory to Kitt Peak. The observations are consistent with a source whose angular size is smaller than 0.5 mas.

  4. Differences Between VLBI2010 and S/X Hardware

    NASA Technical Reports Server (NTRS)

    Corey, Brian

    2010-01-01

    While the overall architecture is similar for the station hardware in current S/X systems and in the VLBI2010 systems under development, various functions are implemented differently. Some of these differences, and the reasons behind them, are described here.

  5. Comparison of AuScope VLBI and GPS geodetic data

    NASA Astrophysics Data System (ADS)

    Plank, Lucia; Santamaría-Gómez, Alvaro; Lovell, James

    2015-04-01

    The AuScope geodetic Very Long Baseline Interferometry (VLBI) array consists of three telescopes on Australian territory, each of them co-located with Global Navigation Satellite Systems (GNSS) tracking stations. The high cadence VLBI observing program gives baselines and station coordinates of good quality, with baseline length repeatabilities (WRMS) of a few millimetres for the Australian baselines. In this contribution we present the latest VLBI results of regional and global experiments and compare them to baselines and site coordinates derived from GNSS data. For a thorough comparison, we use similar models for both, the VLBI and the GNSS data processing. Investigations of common tropospheric parameters and clock terms, as well as validations against the local ties as determined in the 2014 local surveys will supplement this study. Additional insight into the topic of technique specific errors is expected from the analysis of dedicated experiments with the two co-located telescopes at Hobart, the 26m legacy antenna and the new 12m dish.

  6. About the Compatibility of DORIS and VLBI Observations

    NASA Technical Reports Server (NTRS)

    Il'in, Gennady; Smolentsev, Sergey; Sergeev, Roman

    2010-01-01

    We investigated the compatibility of the DORIS and VLBI observations at Badary Observatory. The DORIS beacon stands at 100-m distance from the main radio telescope dish and transmits signals on two frequencies: 2036.25 MHz and 401.25 MHz. The latter frequency is modulated to send messages containing an ID number, timing information, data from the meteorological sensors, and engineering data (e.g., power). Both frequencies affect the S/X band radio telescope receivers. The parameters of the DORIS signals were measured at the outputs of the S/X band intermediate frequency amplifier. It was found that: (1) The level of RFI, produced by the DORIS beacon, practically corresponds to the level of the system (antenna plus receiver) noise signal and does not overload the S/X band receivers. (2) The DORIS 401.25 MHz signal is out of the frequency bands recorded during standard VLBI sessions. As a result, RFI from DORIS does not affect VLBI observations. This conclusion was confirmed after data correlations of actual VLBI observations that were conducted with the DORIS beacon turned on/off.

  7. Mobile VLBI and GPS measurement of vertical crustal motion

    NASA Technical Reports Server (NTRS)

    Kroger, P. M.; Davidson, J. M.; Gardner, E. C.

    1985-01-01

    Mobile Very Long Base Interferometry (VLBI) and Global Positioning System (GPS) geodetic measurements have many error sources in common. Calibration of the effects of water vapor on signal transmission through the atmosphere, however, remains the primary limitation to the accuracy of vertical crustal motion measurements made by either technique. The two primary methods of water vapor calibration currently in use for mobile VLBI baseline measurements were evaluated: radiometric measurements of the sky brightness near the 22 GHz emission line of free water molecules and surface meteorological measurements used as input to an atmospheric model. Based upon a limited set of 9 baselines, it is shown that calibrating VLBI data with water vapor radiometer measurements provides a significantly better fit to the theoretical decay model than calibrating the same data with surface meteorological measurements. The effect of estimating a systematic error in the surface meteorological calibration is shown to improve the consistency of the vertical baseline components obtained by the two calibration methods. A detailed error model for the vertical baseline components obtained indicates current mobile VLBI technology should allow accuracies of order 3 cm with WVR calibration and 10 cm when surface meteorological calibration is used.

  8. U.S. Naval Observatory VLBI Analysis Center

    NASA Technical Reports Server (NTRS)

    Boboltz, David A.; Fey, Alan L.; Geiger, Nicole; Dieck, Chris; Hall, David M.

    2013-01-01

    This report summarizes the activities of the VLBI Analysis Center at the United States Naval Observatory for the 2012 calendar year. Over the course of the year, Analysis Center personnel continued analysis and timely submission of IVS-R4 databases for distribution to the IVS. During the 2012 calendar year, the USNO VLBI Analysis Center produced two VLBI global solutions designated as usn2012a and usn2012b. Earth orientation parameters (EOP) based on this solution and updated by the latest diurnal (IVS-R1 and IVS-R4) experiments were routinely submitted to the IVS. Sinex files based upon the bi-weekly 24-hour experiments were also submitted to the IVS. During the 2012 calendar year, Analysis Center personnel continued a program to use the Very Long Baseline Array (VLBA) operated by the NRAO for the purpose of measuring UT1-UTC. Routine daily 1-hour duration Intensive observations were initiated using the VLBA antennas at Pie Town, NM and Mauna Kea, HI. High-speed network connections to these two antennas are now routinely used for electronic transfer of VLBI data over the Internet to a USNO point of presence. A total of 270 VLBA Intensive experiments were observed and electronically transferred to and processed at USNO in 2012.

  9. VLBI Observations of the Free Core Nutations

    NASA Astrophysics Data System (ADS)

    Smylie, D. E.

    2012-12-01

    At core scale lengths with periods from a few hours to days, the Coriolis acceleration dominates the Lorentz force density and core modes can be considered as purely mechanical. One of the most interesting core modes is the spin-over mode, which reflects the ability of the outer core to rotate about an axis different from that of either the inner core or the shell. It has a nearly diurnal period. In the Earth frame of reference, this mode produces the nearly diurnal retrograde wobble. In the space frame of reference it is accompanied by the free core nutations. When the flattening of the boundaries of the fluid outer core and the figure-figure gravitational coupling are taken into account, as well as the deformability of the boundaries, both a retrograde free core nutation and a prograde free core nutation are found. The retrograde free core nutation was first predicted by Poincare (1910) for a completly fluid, incompressible core bounded by a rigid shell. In a variational calculation of wobble-nutation modes in realistic Earth models, Jiang (1993) found the classical retrograde free core nutation (RFCN) but discovered a prograde free core nutation (PFCN) as well. VLBI residuals in longitude and obliquity compared to the 1980 IAU nutation series, and their standard errors, were downloaded from the Goddard Space Flight Center website, for the period August 3, 1979 to March 6, 2003, giving 3343 points over a span of 8617 days. In an overlapping segment analysis, the discrete Fourier transform (DFT) for each segment was found for the corresponding series of unequally spaced nutation residuals by singular value decomposition (SVD), with the number of singular values eliminated determined by the satisfaction of Parseval's theorem. Both the RFCN and the PFCN resonances were found in the resulting power spectrum. The nutation resonances were found to be in free decay, the half-life of the PFCN at 2620 days and that of the RFCN at 2229 days, with Ekman boundary layer

  10. Applying Kalman filtering to investigate tropospheric effects in VLBI

    NASA Astrophysics Data System (ADS)

    Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Heinkelmann, Robert; Liu, Li; Lu, Cuixian; Andres Mora-Diaz, Julian; Raposo-Pulido, Virginia; Xu, Minghui; Schuh, Harald

    2014-05-01

    Very Long Baseline Interferometry (VLBI) currently provides results, e.g., estimates of the tropospheric delays, with a delay of more than two weeks. In the future, with the coming VLBI2010 Global Observing System (VGOS) and increased usage of electronic data transfer, it is planned that the time between observations and results is decreased. This may, for instance, allow the integration of VLBI-derived tropospheric delays into numerical weather prediction models. Therefore, future VLBI analysis software packages need to be able to process the observational data autonomously in near real-time. For this purpose, we have extended the Vienna VLBI Software (VieVS) by a Kalman filter module. This presentation describes the filter and discusses its application for tropospheric studies. Instead of estimating zenith wet delays as piece-wise linear functions in a least-squares adjustment, the Kalman filter allows for more sophisticated stochastic modeling. We start with a random walk process to model the time-dependent behavior of the zenith wet delays. Other possible approaches include the stochastic model described by turbulence theory, e.g. the model by Treuhaft and Lanyi (1987). Different variance-covariance matrices of the prediction error, depending on the time of the year and the geographic latitude, have been tested. In winter and closer to the poles, lower variances and covariances are appropriate. The horizontal variations in tropospheric delays have been investigated by comparing three different strategies: assumption of a horizontally stratified troposphere, using north and south gradients modeled, e.g., as Gauss-Markov processes, and applying a turbulence model assuming correlations between observations in different azimuths. By conducting Monte-Carlo simulations of current standard VLBI networks and of future VGOS networks, the different tropospheric modeling strategies are investigated. For this purpose, we use the simulator module of VieVS which takes into

  11. Effect of the aromatase inhibitor CGS-16949A on pregnancy and secretion of progesterone, estradiol-17beta, prostaglandins E and F2alpha (PGE; PGF2alpha) and pregnancy specific protein B (PSPB) in 90-day ovariectomized pregnant ewes.

    PubMed

    Weems, Y S; Bridges, P J; LeaMaster, B R; Sasser, R G; Ching, L; Weems, C W

    2001-09-01

    The aromatase inhibitor CGS-16949A was used to determine whether CGS-16949A altered secretion of progesterone, estradiol-17beta, PGE (PGE1 + PGE2), PGF2alpha and PSPB. Ninety day pregnant ewes were ovariectomized and received vehicle, PGF2alpha, CGS-16949A or PGF2alpha+CGS-16949A. None of the ewes treated with PGF2alpha, CGS-16949A or PGF2alpha+CGS-16949A aborted (P > or = 0.05) during the 108-h experimental period. Treatment with CGS-16949A lowered (P < or = 0.05) progesterone in jugular venous plasma but concentrations of progesterone were not affected (P > or = 0.05) by treatment with PGF2alpha. Concentrations of estradiol-17beta and PSPB in jugular venous plasma and PGE in inferior vena cava plasma were decreased (P < or = 0.05) by treatment with CGS-16949A. Concentrations of PGF2alpha in inferior vena cava plasma were not affected (P > or = 0.05) by treatment with CGS-16949A. Decreases in estradiol-17beta occurred before decreases in PSPB, which was then followed by decreases in PGE (P < or = 0.05). It is concluded that these data support the hypothesis that estradiol-17beta regulates placental secretion of PSPB; PSPB regulates placental secretion of PGE; and PGE regulates placental secretion of progesterone during mid-pregnancy in ewes.

  12. VLBI real-time analysis by Kalman Filtering

    NASA Astrophysics Data System (ADS)

    Karbon, Maria; Soja, Benedikt; Nilson, Tobias; Heinkelmann, Robert; Liu, Li; Lu, Ciuxian; Xu, Minghui; Raposo-Pulido, Virginia; Mora-Diaz, Julian; Schuh, Harald

    2014-05-01

    Geodetic Very Long Baseline Interferometry (VLBI) is one of the primary space geodetic techniques. It provides the full set of Earth Orientation Parameter (EOP) and is unique for observing long term Universal Time (UT1) and precession/nutation. Currently the VLBI products are delivered with a delay of about two weeks from the moment of the observation. However, the need for near-real time estimates of the parameters is increasing, e.g. for satellite based navigation and positioning or for enabling precise tracking of interplanetary spacecraft. The goal is thus to reduce the time span between observation and the final result to less than one day. This can be archived by replacing the classical least squares method with an adaptive Kalman filter. We have developed a Kalman filter for VLBI data analysis. This method has the advantage that it is simultaneously possible to estimate stationary parameters, e.g. station positions, and to model the highly variable stochastic behavior of non-stationary parameters like clocks or atmospheric parameters. The filter is able to perform without any human interaction, making it a completely autonomous tool. In this work we describe the filter and discuss its application for EOP determination and prediction. We discuss the implementation of the stochastic models to statistically account for unpredictable changes in EOP. Furthermore, additional data like results from other techniques can be included to improve the performance. For example, atmospheric angular momentum calculated from numerical weather models can be introduced to supplement the short-term prediction of UT1 and polar motion. This Kalman filter will be extended and embedded in the newly developed Vienna VLBI Software (VieVS) as a completely autonomous tool enabling the VLBI analysis in near real-time and providing all the parameters of interest with the highest possible accuracy.

  13. Tropospheric delays derived from Kalman-filtered VLBI observations

    NASA Astrophysics Data System (ADS)

    Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Balidakis, Kyriakos; Lu, Cuixian; Anderson, James; Glaser, Susanne; Liu, Li; Mora-Diaz, Julian A.; Raposo-Pulido, Virginia; Xu, Minghui; Heinkelmann, Robert; Schuh, Harald

    2015-04-01

    One of the most important error sources in the products of space geodetic techniques is the troposphere. Currently, it is not possible to model the rapid variations in the path delay caused by water vapor with sufficient accuracy, thus it is necessary to estimate these delays in the data analysis. Very long baseline interferometry (VLBI) is well suited to determine wet delays with high accuracy and precision. Compared to GNSS, the analysis does not need to deal with effects related to code biases, multipath, satellite orbit mismodeling, or antenna phase center variations that are inherent in GNSS processing. VLBI data are usually analyzed by estimating geodetic parameters in a least squares adjustment. However, once the VLBI Global Observing System (VGOS) will have become operational, algorithms providing real-time capability, for instance a Kalman filter, should be preferable for data analysis. Even today, certain advantages of such a filter, for example, allowing stochastic modeling of geodetic parameters, warrant its application. The estimation of tropospheric wet delays, in particular, greatly benefits from the stochastic approach of the filter. In this work we have investigated the benefits of applying a Kalman filter in the VLBI data analysis for the determination of tropospheric parameters. The VLBI datasets considered are the CONT campaigns, which demonstrate state-of-the-art capabilities of the VLBI system. They are unique in following a continuous observation schedule over 15 days and in having data recorded at higher bandwidth than usual. The large amount of observations leads to a very high quality of geodetic products. CONT campaigns are held every three years; we have analyzed all CONT campaigns between 2002 and 2014 for this study. In our implementation of a Kalman filter in the VLBI software VieVS@GFZ, the zenith wet delays (ZWD) are modeled as random walk processes. We have compared the resulting time series to corresponding ones obtained from

  14. Power Spectral Analysis of Simultaneous VLBI and GPS Tropospheric Estimates

    NASA Astrophysics Data System (ADS)

    Ray, J.; Boehm, J.

    2004-12-01

    Observations by space geodetic techniques experience refraction and signal delay due to passage through the Earth's atmosphere. For high-accuracy positioning results, data analysts must account for these effects. Since independent path delay values of sufficient accuracy are not usually available, nuisance parameters are commonly added in the geodetic analysis. The general validity of such zenith path delay (ZPD) estimates as true atmospheric measures has been confirmed by comparison of results from independent radiometric and other techniques over many years. Biases and standard deviations in the sub-cm range are normally found, which is expected to be adequate as inputs to improve the forecast performance of numerical weather models. To better understand the noise characteristics of ZPD estimates from VLBI and GPS, we have examined the power spectra of simultaneous observations during a 15-day period in October 2002. The official combined ZPD products from the technique services have been used primarily, but series from individual analysis centers have also been included. For the seven sites studied, the power-law spectral indices over sub-daily intervals are close to -8/3, consistent with fully developed Kolmogorov turbulence, and flatten over longer periods. The VLBI series, sampled hourly, show white noise at levels of 0.7 to 1.5 mm for frequencies above 5 cycles per day. The simultaneous GPS series, sampled every 2 hours, display no indication of white noise except for one receiver with poor data analysis. The spectra of VLBI-GPS differences are generally flat but show possible signs of excess noise in some spectral bands. Based on these results, estimating VLBI ZPD values more often than every few hours should be reconsidered, especially if changes would strengthen other parameters. On the other hand, GPS-based ZPD estimates should be determined more frequently, at least hourly. Considering the greater reliability of the VLBI scale and the corresponding

  15. Landslide susceptibility assessment by using a neuro-fuzzy model: a case study in the Rupestrian heritage rich area of Matera

    NASA Astrophysics Data System (ADS)

    Sdao, F.; Lioi, D. S.; Pascale, S.; Caniani, D.; Mancini, I. M.

    2013-02-01

    The complete assessment of landslide susceptibility needs uniformly distributed detailed information on the territory. This information, which is related to the temporal occurrence of landslide phenomena and their causes, is often fragmented and heterogeneous. The present study evaluates the landslide susceptibility map of the Natural Archaeological Park of Matera (Southern Italy) (Sassi and area Rupestrian Churches sites). The assessment of the degree of "spatial hazard" or "susceptibility" was carried out by the spatial prediction regardless of the return time of the events. The evaluation model for the susceptibility presented in this paper is very focused on the use of innovative techniques of artificial intelligence such as Neural Network, Fuzzy Logic and Neuro-fuzzy Network. The method described in this paper is a novel technique based on a neuro-fuzzy system. It is able to train data like neural network and it is able to shape and control uncertain and complex systems like a fuzzy system. This methodology allows us to derive susceptibility maps of the study area. These data are obtained from thematic maps representing the parameters responsible for the instability of the slopes. The parameters used in the analysis are: plan curvature, elevation (DEM), angle and aspect of the slope, lithology, fracture density, kinematic hazard index of planar and wedge sliding and toppling. Moreover, this method is characterized by the network training which uses a training matrix, consisting of input and output training data, which determine the landslide susceptibility. The neuro-fuzzy method was integrated to a sensitivity analysis in order to overcome the uncertainty linked to the used membership functions. The method was compared to the landslide inventory map and was validated by applying three methods: a ROC (Receiver Operating Characteristic) analysis, a confusion matrix and a SCAI method. The developed neuro-fuzzy method showed a good performance in the

  16. VLBI Software Correlator at the Interferometric Tracking Center of the China Deep Space Network

    NASA Astrophysics Data System (ADS)

    Han, Songtao; Tang, Geshi; Chen, Lue; Cao, Jianfeng; Ren, Tianpeng; Wang, Mei

    2014-12-01

    With the development of computer techniques, the VLBI software correlator is more and more popular. This article presents the development and performance of the software correlator used in the Interferometric Tracking Center. The software correlator has the ability of VLBI data processing both for spacecraft navigation and VLBI geodesy. Also, the data formats of VSR (VLBI Science Receiver) and VSI (VLBI Standard Interface) are accommodated. The correlator is written modularly in the C programming language and operated by shell script. The complex vector mathematics of the IPP (Intel Integrated Performance Primitive) library is induced because the efficiency of computing can be improved greatly. Parallel algorithm processing is adopted in the software. We present the results of the multi-agency VLBI experiment conducted with the ESA Spacecraft Venus Express in May 2013 and the Chinese Chang'e-3 lunar navigation in December 2013, which verifies the performance of the software correlator.

  17. Positioning Reduction of Deep Space Probes Based on VLBI Tracking

    NASA Astrophysics Data System (ADS)

    Qiao, S. B.

    2011-11-01

    In the background of the Chinese Lunar Exploration Project and the Yinghuo Project, through theoretical analysis, algorithm study, software development, data simulation, real data processing and so on, the positioning reductions of the European lunar satellite Smart-1 and Mars Express (MEX) satellite, as well as the Chinese Chang'e-1 (CE-1) and Chang'e-2 (CE-2) satellites are accomplished by using VLBI and USB tracking data in this dissertation. The progress is made in various aspects including the development of theoretical model, the construction of observation equation, the analysis of the condition of normal equation, the selection and determination of the constraint, the analysis of data simulation, the detection of outliers in observations, the maintenance of the stability of the solution of parameters, the development of the practical software system, the processing of the real tracking data and so on. The details of the research progress in this dissertation are written as follows: (1) The algorithm is analyzed concerning the positioning reduction of the deep spacecraft based on VLBI tracking data. Through data simulation, it is analyzed for the effects of the bias in predicted orbit, the white noises and systematic errors in VLBI delays, and USB ranges on the positioning reduction of spacecraft. Results show that it is preferable to suppress the dispersion of positioning data points by applying the constraint of geocentric distance of spacecraft when there are only VLBI tracking data. The positioning solution is a biased estimate via observations of three VLBI stations. For the case of four tracking stations, the uncertainty of the constraint should be in accordance with the bias in the predicted orbit. White noises in delays and ranges mainly result in dispersion of the sequence of positioning data points. If there is the systematic error of observations, the systematic offset of the positioning results is caused, and there are trend jumps in the shape of

  18. Very Long Baseline Interferometry (VLBI) earth physics. [application to radio astronomy and interferometric earth surveys

    NASA Technical Reports Server (NTRS)

    Macdoran, P. F.

    1972-01-01

    The characteristics of the Michelson/Pease stellar interferometer are discussed. An analog of the interferometer using radio waves is described. The use of a conventional hard-wired interferometer with very long base line interferometry (VLBI) is analyzed. Mathematical models are developed to analyze the VLBI techniques. A summary of VLBI geodetic experiments is tabulated. The concept and application of the astronomical radio interferometric earth surveys (ARIES) are reported. A schematic diagram of ARIES implementation is provided.

  19. Very Long Baseline Interferometry (VLBI) earth physics. [application to radio astronomy and interferometric earth surveys

    NASA Technical Reports Server (NTRS)

    Macdoran, P. F.

    1972-01-01

    The characteristics of the Michelson/Pease stellar interferometer are discussed. An analog of the interferometer using radio waves is described. The use of a conventional hard-wired interferometer with very long base line interferometry (VLBI) is analyzed. Mathematical models are developed to analyze the VLBI techniques. A summary of VLBI geodetic experiments is tabulated. The concept and application of the astronomical radio interferometric earth surveys (ARIES) are reported. A schematic diagram of ARIES implementation is provided.

  20. Development of a Wideband VLBI System (GALA-V)

    NASA Astrophysics Data System (ADS)

    Sekido, Mamoru; Takefuji, Kazuhiro; Ujihara, Hideki; Tsutsumi, Masanori; Miyauchi, Yuka; Hasegawa, Shingo; Hobiger, Thomas; Ichikawa, Ryuichi; Koyama, Yasuhiro

    2014-12-01

    The VLBI group of the National Institute of Information and Communications Technology (NICT) has been developing a wideband VLBI observation system, which is semi-compliant with the VGOS system. Two small-diameter, transportable antennas and a 34-m antenna are prepared for wideband observations at the 3-14 GHz frequency range. This project, named ``GALA-V'', is intended to be used for precise frequency comparisons between widely separated atomic frequency standards. Several new challenges are being addressed in this project: (1) development of a wideband feed with narrow beam width for a large-diameter Cassegrain antenna, (2) development of a direct RF sampling data acquisition system, which samples the RF analog signal at 16 GHz. A prototype of the new wideband feed has been installed on the 34-m antenna at the end of 2013. The current status of this GALA-V project development is described in this report.

  1. International VLBI Service for Geodesy and Astrometry 2013 Annual Report

    NASA Technical Reports Server (NTRS)

    Baver, Karen D.; Behrend, Dirk; Armstrong, Kyla L.

    2014-01-01

    This volume of reports is the 2013 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2013 Annual Report documents the work of the IVS components for the calendar year 2013, our fifteenth year of existence. The reports describe changes, activities, and progress of the IVS. Many thanks to all IVS components who contributed to this Annual Report. With the exception of the first section and the last section, the contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2013.

  2. International VLBI Service for Geodesy and Astrometry: 1999 Annual Report

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor)

    1999-01-01

    This volume of reports is the 1999 Annual Report of the International VLBI Service for Geodesy and Astrometry -IVS. The individual reports were contributed by VLBI groups in the international geodetic community who constitute the components of IVS. The 1999 Annual Report documents the work of the IVS components for the year ending March 1, 1999, the official inauguration date of IVS. As the newest of the space technique services, IVS decided to publish this Annual Report as a reference to our organization and its components. The entire contents of this Annual Report also appear on the IVS website at: http://ivscc.gsfc.nasa.gov/pub/arl999. The IVS 1999 Annual Report will be a valuable reference for information about IVS and its components. This Annual Report will serve as a baseline from which we can measure the anticipated progress of IVS in coming years.

  3. Earth orientation determinations by short duration VLBI observations

    NASA Astrophysics Data System (ADS)

    Nothnagel, Axel; Zhihan, Qian; Nicolson, George D.; Tomasi, Paolo

    1994-03-01

    In May 1989 and April 1990 the radio telescopes of the Wettzell Geodetic Fundamental Station in Germany and of the Shanghai Observatory near Seshan in China observed two series of daily VLBI experiments of short duration for precise determination of UT1. In 1990 a few experiments were complemented by the Hartebeesthoek Radio Astronomy Observatory in South Africa and the Medicina telescope of the Bologna Istituto di Radioastronomia in Italy. Employing the South African station together with the east-west baseline formed by the observatories of Seshan and Medicina permitted simultaneous determinations of UT1 and polar motion. Here we report on the results of these observations. Comparing the UT1 results with those of the IRIS Intensive series gives a clear indication of the absolute accuracy of such short duration VLBI measurements which is estimated to be of the order of ±60 µs.

  4. Implementation and Testing of VLBI Software Correlation at the USNO

    NASA Technical Reports Server (NTRS)

    Fey, Alan; Ojha, Roopesh; Boboltz, Dave; Geiger, Nicole; Kingham, Kerry; Hall, David; Gaume, Ralph; Johnston, Ken

    2010-01-01

    The Washington Correlator (WACO) at the U.S. Naval Observatory (USNO) is a dedicated VLBI processor based on dedicated hardware of ASIC design. The WACO is currently over 10 years old and is nearing the end of its expected lifetime. Plans for implementation and testing of software correlation at the USNO are currently being considered. The VLBI correlation process is, by its very nature, well suited to a parallelized computing environment. Commercial off-the-shelf computer hardware has advanced in processing power to the point where software correlation is now both economically and technologically feasible. The advantages of software correlation are manifold but include flexibility, scalability, and easy adaptability to changing environments and requirements. We discuss our experience with and plans for use of software correlation at USNO with emphasis on the use of the DiFX software correlator.

  5. International VLBI Service for Geodesy and Astrometry 2012 Annual Report

    NASA Technical Reports Server (NTRS)

    Baver, Karen D.; Behrend, Dirk; Armstrong, Kyla L.

    2013-01-01

    This volume of reports is the 2012 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2012 Annual Report documents the work of the IVS components for the calendar year 2012, our fourteenth year of existence. The reports describe changes, activities, and progress ofthe IVS. Many thanks to all IVS components who contributed to this Annual Report. With the exception of the first section and parts of the last section (described below), the contents of this Annual Report also appear on the IVS Web site athttp:ivscc.gsfc.nasa.gov/publications/ar2012

  6. Using GPS and VLBI technology to maintain 14 digit synchronization

    NASA Technical Reports Server (NTRS)

    Ward, S. C.

    1984-01-01

    To facilitate the navigation of spacecraft to the outer planets, Jupiter and beyond, the JPL-NASA Deep Space Network (DSN) has implemented three ensembles of atomic clocks at widely separated locations. These clocks must be maintained, synchronized, to with a few parts in 10 to the 13th power of each other and, the entire group must be maintained, to a lesser degree, in synchronism with Coordinated Universal Time (UTC)NBS/USNO. Over the last 1 1/2 years the DSN has been using Global Positioning Satellites (GPS) and Very Long Baseline Interferometry (VLBI) technology to perform these critical Frequency and Time (F&T) synchronization tasks. A year of F&T synchronization data collected from the intercomparison of 3 sets of cesium and hydrogen maser driven clock ensembles through the use of GPS and VLBI techniques are covered. Also covered, are some of the problems met and limitations of these two techniques at their present level of technology.

  7. A Southern Hemisphere VLBI Survey on a 275-km Baseline

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Preston, R. A.; Faulkner, J.; Wehrle, A. E.; Jauncey, D. L.; Batty, M. J.; Haynes, R. F.; Wright, A. E.

    1983-01-01

    A very long base interferometry (VLBI) survey at 2.29 GHz was conducted using a 275 km baseline consisting of the NASA Deep Space Network tracking site in Tidbinbilla, Australia, and the 64 m antenna located at Parkes, Australia. The purpose of the survey was to identify sources in the southern sky possessing strong compact cores ( 0.1 arcseconds). Such sources will be used to form a reference frame for conducting VLBI geodesy experiments in the Southern Hemisphere. The 70 candidate sources were chosen to be south of -39 degrees declination, and only four had been previously observed from the northern hemisphere. Of the observed sources, 49 were found to have compact structure. In addition to determining correlated flux densities, the delay and delay rate observables of several detected sources were used to determine an estimate of the three dimensional location of the Parkes antenna relative to the Tidbinbilla site with a 1-sigma accuracy of 10 meters.

  8. Wide-Bandwidth Digital Backend System for VLBI

    NASA Astrophysics Data System (ADS)

    Whitney, A. R.

    2007-07-01

    Modern digital electronics now allow the replacement of aging VLBI analog backend systems with fully digital systems to provide numerous benefits, including: 1) uniform, repeatable, predictable performance, 2) low cost, 3) increased flexibility, 4) easy expandability, 6) easy transportability, and 5) flexible and rapid implementation through use of modern FPGA devices. A first-generation Digital Backend (DBE) system, based on a polyphase-filter-bank approach that can process four 500 MHz-bandwidth IF signals, has been built (for <15K), tested, and exercised in real-world VLBI experiments at rates to 4 Gbps/station. Tests at 8 Gbps/station are planned. A second-generation DBE system to process four 1 GHz-bandwidth IFs is now in development in collaboration with UC Berkeley and National Radio Astronomy Observatory; the cost of this system is expected to <10K.

  9. Optimizing the African VLBI Network for Astronomy and Geodesy

    NASA Astrophysics Data System (ADS)

    de Witt, A.; Mayer, D.; MacLeod, G.; Combrinck, L.; Petrov, L.; Nickola, M.

    2016-12-01

    The African VLBI Network will be a pan-African network of radio telescopes comprised of converted redundant satellite Earth-station antennas and new purpose-built radio telescopes. The first of these antennas, in Ghana, is currently being converted to a radio telescope and current funding is estimated to permit the conversion of two more antennas in Africa. These antennas will initially be equipped with a 5-GHz and 6.7-GHz receiver and the next receiver likely to be fitted is a 1.4-1.7-GHz receiver. While it would be advantageous for the AVN antennas to be able to participate also in geodetic and astrometric VLBI observations, there is no funding currently for this. In this paper we re-visit the scientific justifications for the AVN in an attempt to optimize the AVN for each science case, both astronomical and geodetic.

  10. An analysis and intercomparison of VLBI nutation estimates

    NASA Astrophysics Data System (ADS)

    Eubanks, T. M.; Steppe, J. A.; Sovers, O. J.

    Nutation estimates from long duration VLBI experiments conducted by the Deep Space Network and reduced at JPL were compared with similar estimates from the IRIS/Polaris data reduced at Harvard. The two series were found to have an rms difference of 1.6 milliarcsec or less, and both exhibited the existence of seasonal errors in the IAU 1980 nutation theory. Most of the observed seasonal discrepancies could be removed by changing the period of the free core resonance to 431.5 solar days. The VLBI data constrain the resonance damping time to be at least one decade, and possibly much longer. Any free core nutation has an amplitude of less than 1 milliarcsec. Crude estimates of the atmospheric forcing of this resonance indicate that meteorological forcing could easily explain the observed free core nutation.

  11. Using geodetic VLBI to test Standard-Model Extension

    NASA Astrophysics Data System (ADS)

    Hees, Aurélien; Lambert, Sébastien; Le Poncin-Lafitte, Christophe

    2016-04-01

    The modeling of the relativistic delay in geodetic techniques is primordial to get accurate geodetic products. And geodetic techniques can also be used to measure the relativistic delay and get constraints on parameters describing the relativity theory. The effective field theory framework called the Standard-Model Extension (SME) has been developed in order to systematically parametrize hypothetical violations of Lorentz symmetry (in the Standard Model and in the gravitational sector). In terms of light deflexion by a massive body like the Sun, one can expect a dependence in the elongation angle different from GR. In this communication, we use geodetic VLBI observations of quasars made in the frame of the permanent geodetic VLBI monitoring program to constrain the first SME coefficient. Our results do not show any deviation from GR and they improve current constraints on both GR and SME parameters.

  12. Astrometry of millijansky sources using a phase reference VLBI technique

    NASA Technical Reports Server (NTRS)

    Lestrade, Jean-Francois; Rogers, Alan E. E.; Niell, Arthur E.; Preston, Robert A.

    1988-01-01

    A technique for the reliable VLBI detection of weak (mJy at cm wavelengths) celestial radio sources such as radio stars, fast pulsars, and faint extragalactic objects is described and demonstrated. The coherence time is increased by observing a strong phase-reference source alternately with the program source, thus providing an accurate astrometric position relative to the reference source. Typical results are presented in tables, graphs, and a contour map and briefly characterized.

  13. Phase Calibration for the Block 1 VLBI System

    NASA Technical Reports Server (NTRS)

    Roth, M. G.; Runge, T. F.

    1983-01-01

    Very Long Baseline Interferometry (VLBI) in the DSN provides support for spacecraft navigation, Earth orientation measurements, and synchronization of network time and frequency standards. An improved method for calibrating instrumental phase shifts has recently been implemented as a computer program in the Block 1 system. The new calibration program, called PRECAL, performs calibrations over intervals as small as 0.4 seconds and greatly reduces the amount of computer processing required to perform phase calibration.

  14. Stability of VLBI, SLR, DORIS, and GPS positioning

    NASA Astrophysics Data System (ADS)

    Feissel-Vernier, M.; de Viron, O.; Le Bail, K.

    2007-12-01

    The residual signal in VLBI, SLR, DORIS and GPS station motion, after a linear trend and seasonal components have been removed, is analysed to investigate site-specific and technique-specific error spectra. The study concentrates on 60 sites with dense observation history by two or more space geodetic techniques. The solutions analysed are single-analysis center solutions currently available. The GPS data are taken from the IGS files. Statistical methods include the Allan variance analysis and the three-cornered hat algorithm. The site-specific noise level is found to be in the range 0.5-3.5 mm in either horizontal direction and 1-4.5 mm in height for most sites. The distribution of site-specific noise type includes both white noise and flicker noise. White noise is predominant in the East direction. Both types of noise are found in the North direction, with no particular geographical clustering.Technique-specific noise characteristics are estimated in several ways, leading to a white noise diagnostic for VLBI and SLR in all three local directions. DORIS has also white noise in the horizontal directions, whereas GPS has a flicker noise spectrum. The vertical noise spectrum is indecisive for both DORIS and GPS. The three-dimensional noise levels for the one-year sampling time are 1.7 mm for VLBI, 2.5 mm for SLR, 5.2 mm for DORIS, and 4.1 mm for GPS. For GPS, the long-term analysis homogeneity has a strong influence. In the case of a test solution reanalysed in a fully consistent way, the noise level drops to the VLBI level in horizontal and to the SLR level in vertical. The three-dimensional noise level for a one-year sampling time decreases to 1.8 mm. In addition, the percentage of stations with flicker noise drops to only about 20% of the network.

  15. Creation of a global geodetic network using Mark III VLBI

    NASA Technical Reports Server (NTRS)

    Ma, Chopo; Clark, Thomas A.; Ryan, James W.

    1986-01-01

    The positions of 15 permanent VLBI stations have been determined using Mark III with one-sigma uncertainties of less than 5 cm except for three stations in the Pacific. 46070 delay/delay rate observations acquired by the Crustal Dynamics Project and Polaris/IRIS from 1980-84 were included in a least squares solution to estimate the station positions, 44 radio source positions, and earth orientation parameters.

  16. Radio-planetary from tie from Phobos-2 VLBI data

    NASA Technical Reports Server (NTRS)

    Hildebrand, C. E.; Iijima, B. A.; Kroger, P. M.; Folkner, W. M.; Edwards, C. D.

    1994-01-01

    In an ongoing effort to improve the knowledge of the relative orientation (the 'frame tie') of the planetary ephemeris reference frame used in deep navigation and a second reference frame that is defined by the coordinates of a set of extragalactic radio sources, VLBI observations of the Soviet Phobos-2 spacecraft and nearby (in angle) radio sources were obtained at two epochs in 1989, shortly after the spacecraft entered orbit about Mars. The frame tie is an important systematic error source affecting both interplanetary navigation and the process of improving the theory of the Earth's orientation. The data from a single Phobos-2 VLBI session measure one component of the direction vector from Earth to Mars in the frame of the extragalactic radio sources (the 'radio frame'). The radio frame has been shown to be stable and internally consistent with an accuracy of 5 nrad. The planetary ephemeris reference frame has an internal consistency of approximately 15 nrad. The planetary and radio source reference frames were aligned prior to 1989 and measurements of occulations of the radio source 3C273 by the Moon. The Phobos-2 VLBI measurements provide improvement in the accuracy of two of the three angles describing a general rotation between the planetary and radio reference frames. A complete set of measurements is not available because data acquisition was terminated prematurely by loss of spacecraft. The analysis of the two Phobos-2 VLBI data sets indicates that, in the directions of the two rotation components determined by these data, the JPL planetary ephemeris DE200 is aligned with the radio frame as adopted by the International Earth Rotation Service within an accuracy of 20-40 nrad, depending on direction. The limiting errors in the solutions for these offsets are spacecraft trajectory (20 nrad), instrumental biases (19 nrad), and dependence of quasar coordinates on observing frequency (24 nrad).

  17. Planning of an Experiment for VLBI Tracking of GNSS Satellites

    NASA Technical Reports Server (NTRS)

    Tornatore, Vincenza; Hass, Ruediger; Molera, Guifre; Pogrebenko, Sergei

    2010-01-01

    As a preparation for future possible orbit determination of global navigation satellite system (GNSS) satellites by VLBI observations an initial three-station experiment was planned and performed in January 2009. The goal was to get first experience and to verify the feasibility of using the method for accurate satellite tracking. GNSS orbits related to a satellite constellation can be expressed in the Terrestrial Reference Frame. A comparison with orbit results that might be obtained by VLBI can give valuable information on how the GNSS reference frame and the VLBI reference frame are linked. We present GNSS transmitter specifications and experimental results of the observations of some GLONASS satellites together with evaluations for the expected signal strengths at telescopes. The satellite flux densities detected on the Earth s surface are very high. The narrow bandwidth of the GNSS signal partly compensates for potential problems at the receiving stations, and signal attenuation is necessary. Attempts to correlate recorded data have been performed with different software.

  18. Reference frame-induced errors in VLBI Earth rotation determinations

    NASA Astrophysics Data System (ADS)

    Heinkelmann, Robert; Karbon, Maria; Liu, Li; Lu, Cuixian; Mora-Diaz, Julian A.; Nilsson, Tobias J.; Raposo-Pulido, Virginia; Soja, Benedikt; Xu, Minghui; Schuh, Harald

    2014-05-01

    Earth Rotation is defined as the transformation between the Geocentric Celestial Reference System (GCRS) and the International Terrestrial Reference System (ITRS). It is a three-dimensional rotation which is described by the precession/nutation Q, the Earth rotation R, and the polar motion W matrices (IERS Coventions 2010): xGCRS = QRWxITRS. The actual determination of Earth Rotation by Very Long Baseline Interferometry (VLBI) is based on the reference frames involved in the VLBI analysis. VLBI is the only space-geodetic technique used for the realization of the International Celestial Reference System (ICRS), which is the geocentric celestial reference system (GCRS) practically realized to evaluate the above equation. Since the Earth Orientation Parameters (EOP) are obtained as 'session-wise parameters', they can suffer from any inconsistencies between session-wise TRF and CRF realizations. In this paper we assess the session-wise TRF and CRF differences by determining the respective transformation parameters of the adjusted terrestrial and celestial positions on a session basis to the catalogue coordinates, given by the International Terrestrial Reference Frame 2008 (ITRF2008) and the Second International Celestial Reference Frame (ICRF2).

  19. Subdaily Earth Rotation Models Estimated From GPS and VLBI Data

    NASA Astrophysics Data System (ADS)

    Steigenberger, P.; Tesmer, V.; MacMillan, D.; Thaller, D.; Rothacher, M.; Fritsche, M.; Rülke, A.; Dietrich, R.

    2007-12-01

    Subdaily changes in Earth rotation at diurnal and semi-diurnal periods are mainly caused by ocean tides. Smaller effects are attributed to the interaction of the atmosphere with the solid Earth. As the tidal periods are well known, models for the ocean tidal contribution to high-frequency Earth rotation variations can be estimated from space- geodetic observations. The subdaily ERP model recommended by the latest IERS conventions was derived from an ocean tide model based on satellite altimetry. Another possibility is the determination of subdaily ERP models from GPS- and/or VLBI-derived Earth rotation parameter series with subdaily resolution. Homogeneously reprocessed long-time series of subdaily ERPs computed by GFZ/TU Dresden (12 years of GPS data), DGFI and GSFC (both with 24 years of VLBI data) provide the basis for the estimation of single-technique and combined subdaily ERP models. The impact of different processing options (e.g., weighting) and different temporal resolutions (1 hour vs. 2 hours) will be evaluated by comparisons of the different models amongst each other and with the IERS model. The analysis of the GPS and VLBI residual signals after subtracting the estimated ocean tidal contribution may help to answer the question whether the remaining signals are technique-specific artifacts and systematic errors or true geophysical signals detected by both techniques.

  20. Search for exoplanets and brown dwarfs with VLBI

    NASA Astrophysics Data System (ADS)

    Katarzyński, K.; Gawroński, M.; Goździewski, K.

    2016-09-01

    The main aim of this work is to estimate possible radio GHz emission of extrasolar planets and brown dwarfs and to check if such radiation can be detected by Very Large Baseline Interferometers (VLBI). In the estimation we assume that the emission may originate in processes similar to those observed in the Jupiter system. The frequency of the radio emission that is produced in this system depends mostly on the magnetic field strength. Jupiter's magnetic field (˜9 G on average) allows for radiation from kHz frequencies up to 40 MHz. This is well below the frequency range of VLBI. However, it was demonstrated that the magnetic field strength in massive and young object may be up to two orders of magnitude higher than for Jupiter, which is especially relevant for planets around short-lived A type stars. This should extend the range of the emission up to GHz frequencies. We calculated expected flux densities of radio emission for a variety of hypothetical young planetary systems. We analysed two different emission scenarios, and found that the radiation induced by moons (process similar to Jupiter-Io interactions) appears to be less efficient than the emission generated by a stellar wind on a planetary magnetosphere. We also estimated hypothetical emission of planets and brown dwarfs located around relatively young and massive main-sequence A-type stars. Our results show that the emission produced by stellar winds could be detected by currently operating VLBI networks.

  1. Review of Space VLBI RadioAstron studies of AGN

    NASA Astrophysics Data System (ADS)

    Gurvits, Leonid; Kovalev, Yuri

    2016-07-01

    Space VLBI offers an unrivalled resolution in studies of the AGN phenomena. Since 2011, the Russia-led SVLBI mission RadioAstron conducts observations at 92, 18, 6 and 1.3 cm with baselines an order of magnitude longer than the Earth diameter, therefore offering an order of magnitude "sharper" view at the brightest radio sources than achieved with Earth-based VLBI systems. In our presentation we will review the current status of the RadioAstron's scientific programme. Over the first 4.5 years of the in-orbit operations, the mission achieved successful VLBI detections of extragalactic continuum radio sources at all four observing bands. To date, detections on SVLBI baselines have been obtained for more than 150 AGN's at projected baselines up to 350 000 km (about 28 Earth diameters, ED). The highest resolution achieved is 14 microarcscends from 1.3 cm observations. RadioAstron is an international project; it conducts observations with up to 30 Earth-based radio telescopes located on different continents. We will review results of total intensity and polarisation imaging with extreme angular resolution of blazars and nearby active galaxies. We will also discuss typical and maximum brightness temperatures of blazar cores from the AGN Survey obtained with RadioAstron. Physical implications for the AGN jets formation, magnetic field and emission mechanism will be discussed on the basis of the results obtained to date.

  2. Expected Improvements in VLBI Measurements of the Earth's Orientation

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    2003-01-01

    Measurements of the Earth s orientation since the 1970s using space geodetic techniques have provided a continually expanding and improving data set for studies of the Earth s structure and the distribution of mass and angular momentum. The accuracy of current one-day measurements is better than 100 microarcsec for the motion of the pole with respect to the celestial and terrestrial reference frames and better than 3 microsec for the rotation around the pole. VLBI uniquely provides the three Earth orientation parameters (nutation and UTI) that relate the Earth to the extragalactic celestial reference frame. The accuracy and resolution of the VLBI Earth orientation time series can be expected to improve substantially in the near future because of refinements in the realization of the celestial reference frame, improved modeling of the troposphere and non-linear station motions, larger observing networks, optimized scheduling, deployment of disk-based Mark V recorders, full use of Mark IV capabilities, and e-VLBI. More radical future technical developments will be discussed.

  3. Expected Improvements in VLBI Measurements of the Earth's Orientation

    NASA Technical Reports Server (NTRS)

    Ma, Chopo

    2003-01-01

    Measurements of the Earth s orientation since the 1970s using space geodetic techniques have provided a continually expanding and improving data set for studies of the Earth s structure and the distribution of mass and angular momentum. The accuracy of current one-day measurements is better than 100 microarcsec for the motion of the pole with respect to the celestial and terrestrial reference frames and better than 3 microsec for the rotation around the pole. VLBI uniquely provides the three Earth orientation parameters (nutation and UTI) that relate the Earth to the extragalactic celestial reference frame. The accuracy and resolution of the VLBI Earth orientation time series can be expected to improve substantially in the near future because of refinements in the realization of the celestial reference frame, improved modeling of the troposphere and non-linear station motions, larger observing networks, optimized scheduling, deployment of disk-based Mark V recorders, full use of Mark IV capabilities, and e-VLBI. More radical future technical developments will be discussed.

  4. Postglacial Rebound from VLBI Geodesy: On Establishing Vertical Reference

    NASA Technical Reports Server (NTRS)

    Argus, Donald F.

    1996-01-01

    Difficulty in establishing a reference frame fixed to the earth's interior complicates the measurement of the vertical (radial) motions of the surface. I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan] and predictions from postglacial rebound predictions [Peltier]. The optimal translation of the geocenter is 1.7mm/year toward 36degN, 111degE when determined from the motions of 10 VLBI sites. This translation gives a better fit of observations to predictions than does the VLBI reference frame used by Ma and Ryan, but the improvement is statistically insignificant. The root mean square of differences decreases 20% to 0.73 mm/yr and the correlation coefficient increases from 0.76 to 0.87. Postglacial rebound is evident in the uplift of points in Sweden and Ontario that were beneath the ancient ice sheets of Fennoscandia and Canada, and in the subsidence of points in the northeastern U.S., Germany, and Alaska that were around the periphery of the ancient ice sheets.

  5. Navigation of the space VLBI mission-HALCA

    NASA Technical Reports Server (NTRS)

    You, Tung Han; Ellis, Jordan; Mottinger, Neil

    1998-01-01

    In February 1997, the Japanese Space Agency ISAS launched the first space VLBI satellite, HALCA, with an 8 meter diameter wire mesh antenna and radio astronomy receivers capable of observing at 1.6, 4.8, and 22 Ghz. In a 560 by 21000 km orbit with a 6 hour period and 31 degree inclination, it observes celestial radio sources in conjunction with a world wide network of ground radio telescopes as part of an international collaborative effort which includes facilities in Japan, the U.S., Canada, Australia, and Europe. JPL is providing tracking and navigation support using a dedicated subnet of 11 meter antennas as well as co-observations using the DSN 70 meter antennas. This paper describes the spacecraft dynamics model and orbit determination strategies developed to meet the stringent trajectory accuracy requirements for generating predictions for the transfer of a stable uplink frequency to the spacecraft and for determining reconstructed orbits for delivery to the NRAO VLBI correlator and the international VLBI science community.

  6. Measuring Crustal Deformation in Europe by High Precision Geodetic VLBI

    NASA Astrophysics Data System (ADS)

    Campbell, J.; Nothnagel, A.; Vennebusch, M.

    2002-06-01

    At the western tip of the Eurasian plate, the European continent is besieged by thrusting and receding neighbour plates causing deformations and ruptures of the Earth's crust evidenced by earthquakes and volcanic outbursts. Measuring the extent and progress of crustal deformation has become one of the primary tasks of geodesists and geophysicists. Realizing that Europe enjoys one of the densest networks of radio telescopes especially equipped for high precision, geodetic VLBI has provided the incentive to organise a campaign of regular geodetic VLBI observations in the European network of fixed radio telescopes. The measurements have been carried out since the late eighties at an average rate of six sessions per year. From these data, site coordinates, baseline length changes and station velocity vectors have been derived with steadily increasing accuracy. The overall picture of the observed present-day site motions emulates quite well the pattern of tectonic motions inferred from the geotectonic setting of central Europe and the western Mediterranean. Interesting details are emerging for horizontal motions of the three stations in Italy, which are strongly affected by the complex interactions between the different tectonic regimes in this area. The accuracy of the vertical components is also improving with increasing length of the observational record, allowing to detect significant trends among the relative vertical motions of the sites. The geodetic VLBI network operations have received supportive funding by the European Union under the 2nd and 4th Framework Programmes.

  7. Postglacial Rebound from VLBI Geodesy: On Establishing Vertical Reference

    NASA Technical Reports Server (NTRS)

    Argus, Donald F.

    1996-01-01

    Difficulty in establishing a reference frame fixed to the earth's interior complicates the measurement of the vertical (radial) motions of the surface. I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan] and predictions from postglacial rebound predictions [Peltier]. The optimal translation of the geocenter is 1.7mm/year toward 36degN, 111degE when determined from the motions of 10 VLBI sites. This translation gives a better fit of observations to predictions than does the VLBI reference frame used by Ma and Ryan, but the improvement is statistically insignificant. The root mean square of differences decreases 20% to 0.73 mm/yr and the correlation coefficient increases from 0.76 to 0.87. Postglacial rebound is evident in the uplift of points in Sweden and Ontario that were beneath the ancient ice sheets of Fennoscandia and Canada, and in the subsidence of points in the northeastern U.S., Germany, and Alaska that were around the periphery of the ancient ice sheets.

  8. Results of the Huygens VLBI experiment and outlook for VLBI support for future missions to outer planets

    NASA Astrophysics Data System (ADS)

    Gurvits, Leonid; Pogrebenko, S. V.; Avruch, I. M.; Huygens VLBI Team

    Very Long Baseline Interferomtery (VLBI), a radio astronomy technique that offers the highest angular resolution and sensitivity, has progressed rapidly over the last years. It offers now a sub-kilometre-scale accuracy of position determination for weak transmitters at the distance of up to ten AU with minimal requirements for the composition of on-board instrumentation. Being combined with other advanced tracking techniques (such as DeltaDOR and two-way Doppler measurements), it brings about a possibility to conduct a variety of planetary science experiments with unprecedented accuracy. The VLBI technique was demonstrated for the Huygens Probe during its descent in the atmosphere and on the surface of Titan. Results of this experiment - the Probe descent trajectory reconstruction and diagnostics of the parachute motion - will be presented. Similar experiments are being considered for a number of prospective planetary missions under the ESA Cosmic Vision 2015-2025 Programme. In this review presentation we will discuss the basic principles of VLBI tracking of planetary missions and major specifications for the on-board and Earth-based segments of VLBI tracking experiments. We will also describe several potential applications of this technique for various experiments in the interest of atmosphere physics, geodynamics and other planetary science disciplines. Another attractive potential of the technique links it with the general mission support as an efficient diagnostic and navigation tool. In addition, Earth-based radio astronomy arrays might be considered as a receiving element for Direct-to-Earth transmission of mission-critical information from low-power planetary mission transmitters.

  9. Towards an Accurate Alignment of the VLBI Frame and the Future Gaia Optical Frame: Global VLBI Imaging Observations of a Sample of Candidate Sources for this Alignment

    NASA Astrophysics Data System (ADS)

    Bourda, G.; Collioud, A.; Charlot, P.; Porcas, R.; Garrington, S.

    2012-12-01

    The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest accuracy. However, the number of quasars that are bright at optical wavelengths (for the best position accuracy with Gaia), that have a compact core (to be detectable on VLBI scales), and that do not exhibit complex structures (to ensure a good astrometric quality) was found to be limited. It was then realized that the densification of the list of such objects was necessary. Therefore, we initiated a multi-step VLBI observational project, dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of ~450 optically- bright weak extragalactic radio sources, which have been selected by cross-correlating optical and radio catalogs. The initial observations, aimed at checking whether these sources are detectable with VLBI, and conducted with the European VLBI Network (EVN) in 2007, showed an excellent ~90% detection rate. The second step, dedicated to identifying the most point-like sources of the sample, by imaging their VLBI structures, was initiated in 2008. Approximately 25% of the detected targets were observed with the Global VLBI array (EVN+VLBA; Very Long Baseline Array) during a pilot imaging experiment, revealing that approximately 50% of them are point-like sources on VLBI scales. The rest of the sources were observed during three additional imaging experiments in March 2010, November 2010, and March 2011. In this paper, we present the results of these imaging campaigns and report plans for the final stage of the project, which will be dedicated to accurately measuring the VLBI position of the most point-like sources.

  10. Investigation of scale effects in the TRF determined by VLBI

    NASA Astrophysics Data System (ADS)

    Wahl, Daniel; Heinkelmann, Robert; Schuh, Harald

    2017-04-01

    The improvement of the International Terrestrial Reference Frame (ITRF) is of great significance for Earth sciences and one of the major tasks in geodesy. The translation, rotation and the scale-factor, as well as their linear rates, are solved in a 14-parameter transformation between individual frames of each space geodetic technique and the combined frame. In ITRF2008, as well as in the current release ITRF2014, the scale-factor is provided by Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) in equal shares. Since VLBI measures extremely precise group delays that are transformed to baseline lengths by the velocity of light, a natural constant, VLBI is the most suitable method for providing the scale. The aim of the current work is to identify possible shortcomings in the VLBI scale contribution to ITRF2008. For developing recommendations for an enhanced estimation, scale effects in the Terrestrial Reference Frame (TRF) determined with VLBI are considered in detail and compared to ITRF2008. In contrast to station coordinates, where the scale is defined by a geocentric position vector, pointing from the origin of the reference frame to the station, baselines are not related to the origin. They are describing the absolute scale independently from the datum. The more accurate a baseline length, and consequently the scale, is estimated by VLBI, the better the scale contribution to the ITRF. Considering time series of baseline length between different stations, a non-linear periodic signal can clearly be recognized, caused by seasonal effects at observation sites. Modeling these seasonal effects and subtracting them from the original data enhances the repeatability of single baselines significantly. Other effects influencing the scale strongly, are jumps in the time series of baseline length, mainly evoked by major earthquakes. Co- and post-seismic effects can be identified in the data, having a non-linear character likewise. Modeling the non

  11. Application of some integrated non-invasive sensing techniqes for conservation and restoration of the Underground Church and frescoes of S. Maria della Palomba's Sanctuary, Matera (Italy)

    NASA Astrophysics Data System (ADS)

    Lembo, Filiberto; Marino, Francesco P.; Ambrosecchia, Nicola

    2010-05-01

    Santa Maria della Palomba's Sanctuary was built in XV century on a pre-existing medioeval crypt, in a splendid landscape situation, on the front looking south of the ravine on which stands Matera, integrating in a wonderful way underground and sub divo building; in fairly following time one important cycle of frescoes renewed decoration of underground church. In the long run, felt the building into decay, structures and frescoes were flooded and damaged; so that from 1980 were executed important restoration works, realizing ventilation canals under the floor of hypogeic church, in which were incorporated heating pipes, joined to solar thermic panels, wanting to determine the thermo-hygrometric optimum conditions for conservation. Almost thirty years after, willing restorate the frescoes, it was necessary to caracterize completely and objectively physical existing conditions. So was used an integrated mix of some non-invasive sensing techniques: - internal and external high resolution Sanctuary's measurement, using laser scanner 3D, in WebGIS ambient, so as to specify, in particular, whether dimensional data of non accessible parts (thickness of rock-bank, morphology and way of lying down of fracture lines), whether consistence state of frescoes; - thermo-hygrometrical sensing of surfaces, using infrared thermography, during a time of two weeks, in correspondence of many storm, so that to establish the relation between eventual atmospherical conditions variations and changes in conditions of surfaces; - continuous sensing of condition of surfaces, by means of thermo-hygrometrical and temperature sounds; - continuous sensing of operating temperature, by means of a globothermometer; all these tools were linked in a net with a data logger, and informations were transmitted using Web to computer in the office of the Society responsible for the procedure. Remote sensing integrated system proved high liability, allowing many important functions : - to georefer all data

  12. Effects of CGS-13080, a thromboxane inhibitor, on pulmonary vascular resistance in patients after mitral valve replacement surgery.

    PubMed

    Kim, Y D; Foegh, M L; Wallace, R B; Ng, L; Ahmed, S W; Katz, N M; Siegelman, R; Franco, K; Douglas, F; Ku, E

    1988-09-01

    Pulmonary hypertension with an elevated pulmonary vascular resistance was observed during the immediate recovery period in patients who underwent mitral valve surgery. In eight such patients, intravenous infusion of CGS-13080, imidazo(1,5-a)pyridine-5-hexanoic acid (a thromboxane synthetase inhibitor), at a dose range of 0.08-0.1 mg/kg/hr, effectively reduced pulmonary hypertension (from a mean pulmonary arterial pressure of 36 +/- 2 to 31 +/- 2 torr) and pulmonary vascular resistance (from 339 +/- 38 to 238 +/- 37 dynes.sec.cm-5) within 30 minutes and remained reduced for the entire infusion period (48 hours in five patients and 18 hours in three patients). Mean arterial pressure or systemic vascular resistance were not significantly affected by the drug infusion. Serum thromboxane B2 levels (a stable metabolic product of thromboxane A2) were significantly reduced after administration of the compound, with the maximum effect of greater than 90% reduction. All patients tolerated the drug infusion without significant side effects.

  13. Comparison of VLBI, TV and traveling clock techniques for time transfer

    NASA Technical Reports Server (NTRS)

    Spencer, J. H.; Waltman, E. B.; Johnston, K. J.; Santini, N. J.; Klepczynski, W. J.; Matsakis, D. N.; Angerhofer, P. E.; Kaplan, G. M.

    1982-01-01

    A three part experiment was conducted to develop and compare time transfer techniques. The experiment consisted of (1) a very long baseline interferometer (VLBI), (2) a high precision portable clock time transfer system between the two sites, and (3) a television time transfer. A comparison of the VLBI and traveling clock shows each technique can perform satisfactorily at the five nsec level. There was a systematic offset of 59 nsec between the two methods, which we attributed to a difference in epochs between VLBI formatter and station clock. The VLBI method had an internal random error of one nsec at the three sigma level for a two day period. Thus, the Mark II system performed well, and VLBI shows promise of being an accurate method of time transfer. The TV system, which had technical problems during the experiment, transferred time with a random error of about 50 nsec.

  14. Fibre-optic delivery of time and frequency to VLBI station

    NASA Astrophysics Data System (ADS)

    Krehlik, P.; Buczek, Ł.; Kołodziej, J.; Lipiński, M.; Śliwczyński, Ł.; Nawrocki, J.; Nogaś, P.; Marecki, A.; Pazderski, E.; Ablewski, P.; Bober, M.; Ciuryło, R.; Cygan, A.; Lisak, D.; Masłowski, P.; Morzyński, P.; Zawada, M.; Campbell, R. M.; Pieczerak, J.; Binczewski, A.; Turza, K.

    2017-07-01

    The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.

  15. The State and Development Direction of the Geodetic VLBI Station in Korea

    NASA Technical Reports Server (NTRS)

    Ju, Hyunhee; Kim, Myungho; Kim, Suchul; Park, Jinsik; Kondo, Tetsuro; Kim, Tuhwan; Oh, Hongjong; Yi, Sangoh

    2010-01-01

    A permanent geodetic VLBI station with a 22-m diameter antenna will be newly constructed in Korea by the National Geographic Information Institute (NGII) under the project Korea VLBI system for Geodesy (KVG) that aims at maintaining the Korean geodetic datum accurately on the International Terrestrial Reference Frame (ITRF). KVG can receive 2, 8, 22, and 43 GHz bands simultaneously in order to conduct geodetic and astronomical VLBI observations with Korea astronomical VLBI stations along with geodetic observations with IVS stations. This simultaneous four-band receiving capability is a unique feature of the KVG system. The KVG has started officially in October 2008. A new geodetic VLBI station will be constructed at Sejong city (about 120 km south of Seoul and about 20 km north-northwest of Daejeon) and construction of all systems will be completed in 2011.

  16. Status of IADA: an Intelligent Assistant for Data Analysis in VLBI

    NASA Astrophysics Data System (ADS)

    Schwegmann, Wolfgang; Schuh, Harald

    2000-05-01

    A faster and semiautomatic data analysis is important if the VLBI procedure shall be accelerated. Most of the tasks during the VLBI data analysis are very complex and require typical knowledgebased techniques. Thus, a Knowledge-Based System (KBS) called JADA (Intelligent Assistant for Data Analysis in VLBI) is being built which can be adapted to different geodetic VLBI software packages. The concept of JADA is described and it is shown how the knowledge about the VLBI data analysis process can be modeled and applied to the data analysis by the problem solving component of the KBS, to automate the data analysis. An interface has to be developed to transfer data and information between the existing software, e.g. the Mark III data analysis software package SOLVE, and JADA. The concept of the interface and the data flow between the KBS and SOLVE is described.

  17. High-precision VLBI astrometry of radio-emitting stars

    NASA Astrophysics Data System (ADS)

    Lestrade, J.-F.; Preston, R. A.; Jones, D. L.; Phillips, R. B.; Rogers, A. E. E.; Titus, M. A.; Rioja, M. J.; Gabuzda, D. C.

    1999-04-01

    Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted as part of an astrometric program to link the Hipparcos optical reference frame to the radio extragalactic reference frame. We present the VLBI positions, proper motions and trigonometric parallaxes from this program in the ICRF (International Celestial Reference Frame). These astrometric parameters are absolute because they are directly measured relative to the distant quasars used as VLBI phase reference calibrators. The mean astrometric precision achieved relative to the calibrators is 0.36 milliarcsecond and the highest precision is for the RS CVn close binary sigma (2) CrB with formal uncertainties of 0.12 milliarcsecond for its relative position, 0.05 milliarcsecond for its annual proper motion and 0.10 milliarcsecond for its trigonometric parallax. In addition to the Hipparcos link, these observations have provided several new results. The distance to the nearby Tau-Auriga star forming region is 148 +/- 5 pc, determined directly through the VLBI trigonometric parallax of the Pre-Main-Sequence star HD283447 of this region. The orthogonality of the 2 orbital planes in the ternary system Algol is supported by new astrometric evidences. The proper motions of HR5110, HR1099 and IM Peg, regarded as possible guide stars for the NASA Gravity Probe B space mission, have formal precisions of 0.16, 0.31 and 0.40 milliarcsecond per year, respectively, and the mission requirement is 0.15 milliarcsecond per year. The close binary UX Ari is the only star that exhibits an acceleration larger than 3sigma and the most plausible cause is the gravitational interaction of a third body. The distances of the stars HD199178, IM Peg and AR Lac were uncertain by as much as 50% before our observations and are now 116 +/- 4, 97 +/- 6, 41.7 +/- 0.6 pc, respectively. The two X-ray binaries in our program, LSI61303 and Cyg X1, exhibit larger than expected post-fit position residuals. The

  18. Geodetic VLBI Observations with the Hat Creek Telescope

    NASA Astrophysics Data System (ADS)

    Shaffer, D. B.; NASA/Gsfc Geodetic VLBI Group

    1993-05-01

    Geodetic VLBI observations made with the Hat Creek 85' antenna were important contributions to the NASA Crustal Dynamics Program (CDP). Among other things, the CDP studied motions of the Earth's crustal plates and deformation in the vicinity of the San Andreas Fault in California. The 85' antenna was one of the three fundamental anchor points in California east of the San Andreas fault that were used from 1983 to 1991 to determine the motions at various mobile VLBI sites along the San Andreas and to determine the Pacific plate motions at Vandenberg Air Force Base and Ft. Ord (California) and Kauai (Hawaii). The Hat Creek site itself was found to be moving 10.6 +/- 0.4 (one sigma ) mm/yr to the WNW (PA 305deg ) with respect to a ``stable" eastern North America. Hat Creek is located near the western edge of the Northern Basin and Range province. Its motion is thought to be a combination of WNW extension across the Basin and Range, and a small component of NW elastic deformation due to the interaction between the North American and Pacific plates. Geodetic VLBI measurements from Hat Creek to the nearby Quincy and the more distant Ely (Nevada) and Platteville (Colorado) mobile sites were the key measurements in defining the extension rate for the Northern Basin and Range as 8 +/- 2 mm/yr (PA ~ 300deg ). Hat Creek was also the anchor point for measuring a 5 cm northward seismic displacement at the Ft. Ord mobile site due to the Loma Prieta earthquake. We will show the motion of California and Pacific basin sites for which Hat Creek contributed important data.

  19. International VLBI Service for Geodesy and Astrometry 2000 Annual Report

    NASA Technical Reports Server (NTRS)

    Vandenberg, N. R. (Editor); Baver, K. D. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    This volume of reports is the 2000 Annual Report of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2000 Annual Report documents the work of the IVS components for the period March 1, 1999 (the official inauguration date of IVS) through December 31, 2000. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2000. This book and the web site are organized as follows: (1) The first section contains general information about IVS, a map showing the location of the components, information about the Directing Board members, and the report of the IVS Chair; (2) The second section of Special Reports contains a status report of the IVS Working Group on GPS phase center mapping, a reproduction of the resolution making IVS a Service of the International Astronomical Union (IAU), and a reprint of the VLBI Standard Interface (VSI); (3) The next seven sections hold the component reports from the Coordinators, Network Stations, Operation Centers, Correlators, Data Centers, Analysis Centers, and Technology Development Centers; and (4) The last section includes reference information about IVS: the Terms of Reference, the lists of Member and Affiliated organizations, the IVS Associate Member list, a complete list of IVS components, the list of institutions contributing to this report, and a list of acronyms. The 2000 Annual Report demonstrates the vitality of the IVS and the outstanding progress we have made during our first 22 months.

  20. MultiView High Precision VLBI Astrometry at Low Frequencies

    NASA Astrophysics Data System (ADS)

    Rioja, María J.; Dodson, Richard; Orosz, Gabor; Imai, Hiroshi; Frey, Sandor

    2017-03-01

    The arrival of the Square Kilometer Array (SKA) will revitalize all aspects of Very Long Baseline Interferometry (VLBI) astronomy at lower frequencies. In the last decade, there have been huge strides toward routinely achieving high precision VLBI astrometry at frequencies dominated by tropospheric contributions, most notably at 22 GHz, using advanced phase-referencing techniques. Nevertheless, to increase the capability for high precision astrometric measurements at low radio frequencies (<8 GHz), an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. Observations at low frequencies are dominated by distinct direction-dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase-referencing calibrator. The MultiView technique holds the key to compensating for atmospheric spatial-structure errors, by using observations of multiple calibrators and two-dimensional interpolation in the visibility domain. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ∼100 μas astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit. MultiView will achieve its full potential with the enhanced sensitivity and multibeam capabilities of SKA and the pathfinders, which will enable simultaneous observations of the target and calibrators. Our demonstration indicates that the 10 μas goal of astrometry at ∼1.6 GHz using VLBI with SKA is feasible using the MultiView technique.

  1. A Strategic Independent Geodetic VLBI Network for Europe

    NASA Astrophysics Data System (ADS)

    Dale, Denise; Combrinck, Ludwig; de Witt, Alet

    2014-12-01

    Irregularities of the rotation of the Earth in space are described by the Earth Orientation Parameters (EOPs). An independent EOP network, applying the Very Long Baseline Interferometry (VLBI) technique and using the Vienna VLBI Software (VieVS), are strategically essential for Europe to minimize its reliance on foreign global support in terms of required infrastructure for the realization of such a network. The generation of independent EOPs is already achievable by countries such as the USA, the People's Republic of China, and the Russian Federation due to their large extent of land mass that allows for long baselines in both the North-South and East-West directions and thus allows for accurate determination of all EOPs. These three countries need not rely on foreign partnerships to generate EOPs, as they all have independent geodetic VLBI networks capable of determining EOPs for precise positioning, navigation, and satellite launch/orbital purposes. They also have or are developing independent Global Navigation Satellite Systems (GNSS) constellations; so does the European Union (EU). Accurate EOPs are essential for long-term orbital maintenance of GNSS constellations, leaving the EU GALILEO GNSS vulnerable and reliant on the three superpowers. Generation of accurate EOPs by Europe is not possible due to its much smaller land mass and thus smaller achievable baselines. Even though there are many radio telescopes spread across Europe, these are separated by relatively short distances. The proposed stations that will be used to investigate this independent EOP network for Europe are the WETTZELL radio telescope in Germany, two German owned radio telescopes, TIGOCONC in Concepción, Chile, and OHIGGINS in Antarctica, as well as the HartRAO radio telescope in South Africa.

  2. A higher density VLBI catalog for navigating Magellan and Galileo

    NASA Technical Reports Server (NTRS)

    Ulvestad, J. S.; Sovers, O. J.; Jacobs, C. S.

    1990-01-01

    The density of radio sources near the ecliptic in the astrometric JPL Very Long Baseline Interferometry (VLBI) catalog has been increased by over 50 percent since 1985. This density increase has been driven by the need for more sources for the VLBI navigation of the Magellan and Galileo spacecraft, but the sources also will be usable for Mars Observer and other future missions. Since the last catalog, including observations made through 1985, was published in 1988, a total of 21 radio sources has been added that fulfill the following criteria: (1) they lie within 10 deg of the ecliptic plane; (2) their correlated flux densities are above 0.2 Jy on at least one of the Deep Space Network intercontinental baselines at both 2.3 and 8.4 GHz; and (3) the source positions are known to better than 5 milliarcseconds (25 nanoradians). The density of such sources in the catalog has been increased from 15.6 per steradian to 25.2 per steradian. Ten more sources have been added that fulfill the last two criteria given above and lie between 10 deg and 20 deg from the ecliptic plane. Analysis shows that there may be approx. 70 more sources with correlated flux densities above 0.2Jy that are within approx. 20 deg of the ecliptic. However, VLBI navigation observations of the new and prospective sources with the 250-kHz bandwidth of the current operational system will require the use of two 70-m antennas in most cases. Including both old and new sources, if two 34-m antennas are used, there will be usable navigation sources within 10 deg of a spacecraft in only 30 percent of the ecliptic, and sources within 20 deg of a spacecraft over 70 percent of the ecliptic.

  3. Doppler measurements of an interplanetary satellite with a VLBI antenna

    NASA Technical Reports Server (NTRS)

    Gomoretto, G.; Iess, L.; Bertotti, Bruno; Grueff, G.; Brenkle, I. B.; Horton, A.

    1989-01-01

    In preparation for the Ulysses Gravitational Wave Experiment a Doppler detector has been constructed for the Bologna VLBI antenna and tested in a differential mode with the spacecraft Voyager 2 at 25 AU. In this mode the signal was sent from the Deep Space Network station in Canberra and received at Madrid and Bologna. The correlation between the received signals allows a discrimination between local and common noise sources. The successful test was performed in August, 1988 showed that special communication procedure will have to be implemented to allow a smooth and reliable operation during the real experiment.

  4. Precise Doppler tracking from the Medicina VLBI station

    NASA Astrophysics Data System (ADS)

    Ambrosini, R.; Comoretto, G.; Iess, L.; Messeri, A.

    1992-06-01

    The first opposition test of Doppler tracking the Ulysses spacecraft from the Medicina VLBI (Very Long Base Interferometry) station (Italy) proved its capability to perform a systematic search for gravitational waves. In house and JPL (Jet Propulsion Laboratory) data analysis showed that the target Allan variance of 3 x 10(exp -14) at 1000 s, planned for the DSN antennas was also achieved from the station. The main observation campaign during the second opposition phase will last for thirty continuous nights--from mid Feb. to mid Mar. 1992. The main hardware and software features developed for this application, together with some results of the first opposition test, are described.

  5. AuScope VLBI Project and Hobart 26-m Antenna

    NASA Technical Reports Server (NTRS)

    Lovell, Jim; Dickey, John; Reid, Brett; McCallum, Jamie; Shabala, Stas; Watson, Christopher; Ellingsen, Simon; Memin, Anthony

    2013-01-01

    This is a report on the activities carried out at the three AuScope VLBI observatories and the Hobart 26-m antenna. In 2012 the three AuScope 12-m antennas at Hobart (Hb), Katherine (Ke), and Yarragadee (Yg) completed their first full year of operations as an array. The Hobart 26-m antenna (Ho) continued to make a contribution to IVS, providing overlap with the Hb time series. In total the AuScope antennas and the Hobart 26 m observed for 146 antenna days in 2012. In this report we also briefly highlight our research activities during 2012 and our plans for 2013.

  6. Future Evolution of NASA's SLR and VLBI Networks

    NASA Technical Reports Server (NTRS)

    Bosworth, John M.; Carter, D.; Wildes, W.; Smith, David E. (Technical Monitor)

    2001-01-01

    Over the first half of this decade the NASA Space Geodesy Program is planning a major transformation of its existing (Satellite Laser Ranging) SLR network of stations and also further evolutionary changes to its network of (Very Long Base Interferometry) VLBI stations. These network changes will be made to meet the ever more demanding requirements of the earth and space science programs that these networks support while seeking through automation and electronic data communications to increase efficiency and decrease cost of operations and maintenance. The major aspects of the NASA plan will be outlined and the benefits to the scientific community will be addressed.

  7. The First Caltech-Jodrell Bank VLBI Survey

    NASA Astrophysics Data System (ADS)

    Xu, Wenge

    This thesis presents the author's major contributions to the first Caltech-Jodrell Bank VLBI survey (CJ1). It demonstrates convincingly that the VLBI snapshot technique is a reliable and highly efficient method of making images of large samples of objects. The CJ1 sample consists of 135 objects with 1.3 Jy > S_{rm 5 GHz} >= 0.7 Jy, delta(1950) >= 35^circ and | b| > 10 ^circ. The combination of the CJ1 sample with the Pearson-Readhead sample provides a complete, flux density limited sample of 200 objects with S _{rm 5 GHz} >= 0.7 Jy, delta(1950) >= 35^circ and | b| > 10^circ for which all of the objects accessible to Mark II VLBI have been mapped at both 5 GHz and 1.6 GHz. In this thesis we present the 5 GHz VLBI observations from the CJ1 survey and follow-up observations of 8 compact symmetric objects (CSO) or CSO candidates at 8.4 GHz. In addition, we present 5 GHz MERLIN observations of 20 objects and 1.4 GHz VLA observations of 92 objects in the CJ1 + PR sample. The VLA maps, together with L band (1.3-1.7 GHz) maps available in the literature, provide a complete set of VLA maps for the CJ1 + PR sample. Furthermore, we present new redshifts, optical counterparts and optical polarimetry measurements of the objects in the CJ1 sample. Based on morphological attributes on scales < 5 kpc and >=5 kpc, we identify six physically distinct classes in the CJ1 + PR sample, one of which is the CSO class. Identification of CSO's may have a profound impact on our understanding of AGN. Detailed study of one archetypal CSO, 2352 + 495, has demonstrated that the CSO's are likely a class of short-lived powerful galaxies. We have confirmed the bimodal distribution of the misalignment angle and identified that the peak near 90^circ is contributed by a group of objects with high optical polarization, high fractional core flux, high radio variability and flat radio spectrum. All of these are symptoms of relativistic beaming. The mean angular sizes of the CJ1 + PR objects show only

  8. Stability of VLBI, SLR, DORIS, and GPS positioning

    NASA Astrophysics Data System (ADS)

    Feissel-Vernier, M.; de Viron, O.; Le Bail, K.

    2007-06-01

    The residual signal in VLBI, SLR, DORIS and GPS station motion, after a linear trend and seasonal components have been removed, is analysed to investigate site-specific and technique-specific error spectra. The study concentrates on 60 sites with dense observation history by two or more space geodetic techniques. Statistical methods include the Allan variance analysis and the three-cornered hat algorithm. The stability of time-series is defined by two parameters, namely the Allan deviation for a one-year sampling time (noise level) and the slope of the Allan variance graph with its spectral interpretation (noise type). The site-specific noise level is found to be in the range 0.5-3.5 mm in either horizontal direction and 1-4.5 mm in height for most sites. The distribution of site-specific noise type includes both white noise and flicker noise. White noise is predominant in the East direction. Both types of noise are found in the North direction, with no particular geographical clustering. In the Up direction, the Northern hemisphere sites seem to be split in two large geographical sectors characterised either by white noise or by flicker noise signatures. Technique-specific noise characteristics are estimated in several ways, leading to a white noise diagnostic for VLBI and SLR in all three local directions. DORIS has also white noise in the horizontal directions, whereas GPS has a flicker noise spectrum. The vertical noise spectrum is indecisive for both DORIS and GPS. The three-dimensional noise levels for the one-year sampling time are 1.7 mm for VLBI, 2.5 mm for SLR, 5.2 mm for DORIS, and 4.1 mm for GPS. For GPS, the long-term analysis homogeneity has a strong influence. In the case of a test solution reanalysed in a fully consistent way, the noise level drops to the VLBI level in horizontal and to the SLR level in vertical. The three-dimensional noise level for a one-year sampling time decreases to 1.8 mm. In addition, the percentage of stations with flicker

  9. Theory of post-block 2 VLBI observable extraction

    NASA Technical Reports Server (NTRS)

    Lowe, Stephen T.

    1992-01-01

    The algorithms used in the post-Block II fringe-fitting software called 'Fit' are described. The steps needed to derive the very long baseline interferometry (VLBI) charged-particle corrected group delay, phase delay rate, and phase delay (the latter without resolving cycle ambiguities) are presented beginning with the set of complex fringe phasors as a function of observation frequency and time. The set of complex phasors is obtained from the JPL/CIT Block II correlator. The output of Fit is the set of charged-particle corrected observables (along with ancillary information) in a form amenable to the software program 'Modest.'

  10. Intra-accumbens injections of the adenosine A2A agonist CGS 21680 affect effort-related choice behavior in rats.

    PubMed

    Font, Laura; Mingote, Susana; Farrar, Andrew M; Pereira, Mariana; Worden, Lila; Stopper, Colin; Port, Russell G; Salamone, John D

    2008-09-01

    Nucleus accumbens dopamine (DA) participates in the modulation of instrumental behavior, including aspects of behavioral activation and effort-related choice behavior. Rats with impaired accumbens DA transmission reallocate their behavior away from food-reinforced activities that have high response requirements and instead select less-effortful types of food-seeking behavior. Although accumbens DA is considered a critical component of the brain circuitry regulating effort-related processes, emerging evidence also implicates adenosine A(2A) receptors. The present work was undertaken to test the hypothesis that accumbens A(2A) receptor stimulation would produce effects similar to those produced by DA depletion or antagonism. Three experiments assessed the effects of the adenosine A(2A) agonist CGS 21680 on performance of a concurrent choice task (lever pressing for preferred food vs. intake of less preferred chow) that is known to be sensitive to DA antagonists and accumbens DA depletions. Systemic injections of CGS 21680 reduced lever pressing but did not increase feeding. In contrast, bilateral infusions of the adenosine A(2A) receptor agonist CGS 21680 (6.0-24.0 ng) into the nucleus accumbens decreased lever pressing for the preferred food but substantially increased consumption of the less preferred chow. Injections of CGS 21680 into a control site dorsal to the accumbens were ineffective. Taken together, these results are consistent with the hypothesis that local stimulation of adenosine A(2A) receptors in nucleus accumbens produces behavioral effects similar to those induced by accumbens DA depletions. Accumbens adenosine A(2A) receptors appear to be a component of the brain circuitry regulating effort-related choice behavior.

  11. Understanding and managing health and environmental risks of CIS, CGS, and CdTe photovoltaic module production and use: A workshop

    SciTech Connect

    Moskowitz, P.D.; Zweibel, K.; DePhillips, M.P.

    1994-04-28

    Environmental, health and safety (EH&S) risks presented by CIS, CGS and CdTe photovoltaic module production, use and decommissioning have been reviewed and discussed by several authors. Several EH&S concerns exit. The estimated EH&S risks are based on extrapolations of toxicity, environmental mobility, and bioavailability data for other related inorganic compounds. Sparse data, however, are available for CIS, CGS or CdTe. In response to the increased interest in these materials, Brookhaven National Laboratory (BNL) has been engaged in a cooperative research program with the National Renewable Energy Laboratory (NREL), the Fraunhofer Institute for Solid State Technology (IFT), the Institute of Ecotoxicity of the GSF Forschungszentrum fair Umwelt und Gesundheit, and the National Institute of Environmental Health Sciences (NIEHS) to develop fundamental toxicological and environmental data for these three compounds. This workshop report describes the results of these studies and describes their potential implications with respect to the EH&S risks presented by CIS, CGS, and CdTe module production, use and decommissioning.

  12. Structure Corrections in Modeling VLBI Delays for RDV Data

    NASA Technical Reports Server (NTRS)

    Sovers, Ojars J.; Charlot, Patrick; Fey, Alan L.; Gordon, David

    2002-01-01

    Since 1997, bimonthly S- and X-band observing sessions have been carried out employing the VLBA (Very Long Baseline Array) and as many as ten additional antennas. Maps of the extended structures have been generated for the 160 sources observed in ten of these experiments (approximately 200,000 observations) taking place during 1997 and 1998. This paper reports the results of the first massive application of such structure maps to correct the modeled VLBI (Very Long Baseline Interferometry) delay in astrometric data analysis. For high-accuracy celestial reference frame work, proper choice of a reference point within each extended source is crucial. Here the reference point is taken at the point of maximum emitted flux. Overall, the weighted delay residuals (approximately equal to 30 ps) are reduced by 8 ps in quadrature upon introducing source maps to model the structure delays of the sources. Residuals of some sources with extended or fast-varying structures improve by as much as 40 ps. Scatter of 'arc positions' about a time-linear model decreases substantially for most sources. Based on our results, it is also concluded that source structure is presently not the dominant error source in astrometric/geodetic VLBI.

  13. VLBI observations of GNSS-satellites: from scheduling to analysis

    NASA Astrophysics Data System (ADS)

    Plank, Lucia; Hellerschmied, Andreas; McCallum, Jamie; Böhm, Johannes; Lovell, Jim

    2017-01-01

    The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites.

  14. VLBI for Gravity Probe B: the guide star, IM Pegasi

    NASA Astrophysics Data System (ADS)

    Bartel, N.; Bietenholz, M. F.; Lebach, D. E.; Ransom, R. R.; Ratner, M. I.; Shapiro, I. I.

    2015-11-01

    We review the radio very long baseline interferometry (VLBI) observations of the guide star, IM Peg, and three compact extragalactic reference sources, made in support of the NASA/Stanford gyroscope relativity mission, Gravity Probe B (GP-B). The main goal of the observations was the determination of the proper motion of IM Peg relative to the distant Universe. VLBI observations made between 1997 and 2005 yield a proper motion of IM Peg of -20.83 ± 0.09 mas yr-1 in α and -27.27 ± 0.09 mas yr-1 in δ in a celestial reference frame of extragalactic radio galaxies and quasars virtually identical to the International Celestial Reference Frame 2 (ICRF2). They also yield a parallax for IM Peg of 10.37 ± 0.07 mas, corresponding to a distance of 96.4 ± 0.7 pc. The uncertainties are standard errors with statistical and estimated systematic contributions added in quadrature. These results met the pre-launch requirements of the GP-B mission to not discernibly degrade the estimates of the geodetic and frame-dragging effects.

  15. The VLBI time delay function for synchronous orbits

    NASA Technical Reports Server (NTRS)

    Rosenbaum, B.

    1972-01-01

    The VLBI is a satellite tracking technique that to date was applied largely to the tracking of synchronous orbits. These orbits are favorable for VLBI in that the remote satellite range allows continuous viewing from widely separated stations. The primary observable, geometric time delay is the time difference for signal propagation between satellite and baseline terminals. Extraordinary accuracy in angular position data on the satellite can be obtained by observation from baselines of continental dimensions. In satellite tracking though the common objective is to derive orbital elements. A question arises as to how the baseline vector bears on the accuracy of determining the elements. Our approach to this question is to derive an analytic expression for the time delay function in terms of Kepler elements and station coordinates. The analysis, which is for simplicity based on elliptic motion, shows that the resolution for the inclination of the orbital plane depends on the magnitude of the baseline polar component and the resolution for in-plane elements depends on the magnitude of a projected equatorial baseline component.

  16. Amplitude Correction Factors of Korean VLBI Network Observations

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Sung; Byun, Do-Young; Oh, Chung Sik; Kim, Hyo Ryoung; Kim, Jongsoo; Jung, Taehyun; Oh, Se-Jin; Roh, Duk-Gyoo; Jung, Dong-Kyu; Yeom, Jae-Hwan

    2015-10-01

    We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22~GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C~454.3, NRAO~512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510-089, which are almost unresolved for baselines in a range of 350-477~km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We find that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.

  17. Resonances in solid Earth tides from VLBI observations

    NASA Astrophysics Data System (ADS)

    Gubanov, V. S.; Kurdubov, S. L.

    2015-05-01

    This work pertains to the area of exploratory research aimed at finding very fine features of the Earth's tidal deformations at the limit of the capabilities of present-day astrogeodetic observations. Based on an analysis of almost all the available VLBI observations performed within the framework of IVS (International VLBI Service) geodetic programs in 1980-2014, we have obtained the corrections to the theoretical values of complex and frequency-dependent tidal parameters (Love/Shida numbers) for the first time. Their frequency dependence arises from the resonances attributable to the retrograde free core nutation (RFCN). Our results largely confirm a high accuracy of the theory of Earth tides presented in the modern International astrogeodetic standard, the IERS Conventions (2010). However, statistically significant corrections have been found for some harmonics of the lunisolar tide-generating potential. For example, the correction to the real part of the Love number h for the wave K 1 with a frequency of 1 cpsd has turned out to be Δ h R = -0.0142 ± 0.0006, which may be indicative of a deeper resonance than that predicted by the theory in the region of diurnal tides.

  18. Plate tectonics from VLBI and SLR global data

    NASA Technical Reports Server (NTRS)

    Harrison, Christopher G. A.; Robaudo, Stefano

    1992-01-01

    This study is based on data derived from fifteen years of observations of the SLR (side-looking radar) network and six years of the VLBI (very long baseline interferometry) network. In order to use all available information VLBI and SLR global data sets were combined in a least squares fashion to calculate station horizontal velocities. All significant data pertaining to a single site contribute to the station horizontal motion. The only constraint on the solution is that no vertical motion is allowed. This restriction does not greatly affect the precision of the overall solution given the fact that the expected vertical motion for most stations, even those experiencing post glacial uplift, is well under 1 cm/yr. Since the average baseline is under 4,000 km, only a small fraction of the station vertical velocity is translated into baseline rates so that the error introduced in the solution by restricting up-down station movement is minimal. As a reference, station velocities were then compared to the ones predicted by the NUVEL-1 geological model of DeMets et al. (1990). The focus of the study is on analyzing these discrepancies for global plate tectonics as well as regional tectonic settings. The method used also allows us not only to derive horizontal motion for individual stations but also to calculate Euler vectors for those plates that have enough stations located on the stable interior like North America, Pacific, Eurasia, and Australia.

  19. VLBI of supernovae and gamma-ray bursts

    NASA Astrophysics Data System (ADS)

    Bartel, N.; Karimi, B.; Bietenholz, M. F.

    2017-04-01

    Supernovae and gamma-ray bursts (GRBs) are among the brightest events in the universe. Excluding Type Ia supernovae and short GRBs, they are the result of the core collapse of a massive star with material being ejectedwith speeds of several 1000 km/s to nearly the speed of light, and with a neutron star or a black hole left over as the compact remnant of the explosion. Synchrotron radiation in the radio is generated in a shell when the ejecta interact with the surrounding medium and possibly also in the central region near the compact remnant itself. VLBI has allowed resolving some of these sources and monitoring their expansion in detail, thereby revealing characteristics of the dying star, the explosion, the expanding shock front, and the expected compact remnant. We report on updates of some of the most interesting results that have been obtained with VLBI so far. Movies of supernovae are available from our website. They show the evolution from shortly after the explosion to decades thereafter, in one case revealing an emerging compact central source, which may be associated with shock interaction near the explosion center or with the stellar corpse itself, a neutron star or a black hole.

  20. VLBI observations of GNSS-satellites: from scheduling to analysis.

    PubMed

    Plank, Lucia; Hellerschmied, Andreas; McCallum, Jamie; Böhm, Johannes; Lovell, Jim

    2017-01-01

    The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites.

  1. The Essential Contribution of VLBI to Fundamental Astronomy

    NASA Astrophysics Data System (ADS)

    Capitaine, Nicole

    2002-06-01

    The adoption of the International Celestial Reference System MRS based on VLBI observations of extragalactic radio sources, by the International Astronomical Union (IAU), since 1st January 1998, has open a new era for astronomy. The MRS and the corresponding frame ICRF replaced the FK5 based on positions and proper motions of bright stars. According to its definition, the MRS is such that the barycentric directions of distant extragalactic objects show no global rotation with respect to these objects. The old dream of astronomers of an absolute reference for measuring the angular motion of celestial bodies has thus become reality. This results in an historical abandonment of the link of the celestial reference system with the motion of the Earth. This has to be taken into account by revising the current concepts of fundamental astronomy; IAU 2000 Resolutions provided new definitions for the celestial pole, Universal Time and parameters to be used in the transformation between celestial and terrestrial frames, in consistency with the properties of the ICRS. VLBI observations of Earth orientation referred to the ICRS provide very accurate determination of the actual celestial position of the pole and of the Earth's angle of rotation. This has led to significant improvements in the models for variations of Earth's angular velocity as well as for precession and nutation. Such models are very useful for astrometry and provide a better knowledge of the dynamics of the Earth's interior.

  2. VLBI observations of single stars, spatial resolution and astrometry

    NASA Astrophysics Data System (ADS)

    Pestalozzi, M.; Benz, A. O.; Conway, J. E.; Gudel, M.; Smith, K.

    VLBI studies can both spatially resolve single dMe stars and measure their positions at submilliarcsecond accuracy. The spatial resolution gives the brightness temperature and allows us to draw co nclusions about the nature of the emitting processes. In particular it is possib le to distinguish between thermal or non-thermal emission. The position accuracy gives better knowledge about the astrometric properties (like proper motion and parallax) especially for nearby stars. In this contribution recent results of c ontinuum VLBI observations towards two dMe stars (YZ CMi and AD Leo) at 8.4 GHz are presented. For YZ CMi an estimate of the size of the coronal emission is giv en (0.98 mas in diameter or 0.7 ±0.3 Rstar above the photosphere where Rstar refers to the photospheric radius). For AD Leo an upper limit is gi ven, i.e. the emitting region is shown to be < 0.8 Rstar. The position o f YZ CMi is found to differ by 32 mas form the Hipparcos catalogue, a discrepanc y mostly due to large errors in the listed proper motion (Pestalozzi et al. 2000 ).

  3. VLBI observations of GNSS-satellites: from scheduling to analysis

    NASA Astrophysics Data System (ADS)

    Plank, Lucia; Hellerschmied, Andreas; McCallum, Jamie; Böhm, Johannes; Lovell, Jim

    2017-07-01

    The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites.

  4. VLBI observations of Infrared-Faint Radio Sources

    NASA Astrophysics Data System (ADS)

    Middelberg, Enno; Phillips, Chris; Norris, Ray; Tingay, Steven

    2006-10-01

    We propose to observe a small sample of radio sources from the ATLAS project (ATLAS = Australia Telescope Large Area Survey) with the LBA, to determine their compactness and map their structures. The sample consists of three radio sources with no counterpart in the co-located SWIRE survey (3.6 um to 160 um), carried out with the Spitzer Space Telescope. This rare class of sources, dubbed Infrared-Faint Radio Sources, or IFRS, is inconsistent with current galaxy evolution models. VLBI observations are an essential way to obtain further clues on what these objects are and why they are hidden from infrared observations: we will map their structure to test whether they resemble core-jet or double-lobed morphologies, and we will measure the flux densities on long baselines, to determine their compactness. Previous snapshot-style LBA observations of two other IFRS yielded no detections, hence we propose to use disk-based recording with 512 Mbps where possible, for highest sensitivity. With the observations proposed here, we will increase the number of VLBI-observed IFRS from two to five, soon allowing us to draw general conclusions about this intriguing new class of objects.

  5. Radio astronomy interferometer network testing for a Malaysia-China real-time e-VLBI

    NASA Astrophysics Data System (ADS)

    Abidin, Zamri Zainal; Hashim, Shaiful Jahari; Wei, Lim Yang; Zhong, Chen; Rosli, Zulfazli

    2017-07-01

    The uv-coverage of the current VLBI network between Australia northern Asia will be significantly enhanced with an existence of a middle baseline VLBI station located in Malaysia. This paper investigated the connecting route of the first half of the Asia-Oceania VLBI network i.e. from Malaysia to China. The investigation of transmission network characteristics between Malaysia and China was carried out in order to perform a real-time and reliable data transfer within the e-VLBI network for future eVLBI observations. MyREN (Malaysia) and CSTNET (China) high-speed research networks were utilized for this proposed e-VLBI connection. Preliminary network test was performed by ping, traceroute, and iperf prior to data transfer tests, which were evaluated with three types of protocols namely FTP, Tsunami-UDT and UDT. The results showed that, on average, there were eighteen hops between Malaysia and China networks with 98 ms round trip time (RTT) delay. Overall UDP protocol has a better throughput compared to TCP protocol. UDP can reach a maximum rate of 90 Mbps with 0% packet loss. In this feasibility test, the VLBI test data was successfully transferred between Malaysia and China by utilizing the three types of data transfer protocols.

  6. New VLBI2010 scheduling strategies and implications on the terrestrial reference frames.

    PubMed

    Sun, Jing; Böhm, Johannes; Nilsson, Tobias; Krásná, Hana; Böhm, Sigrid; Schuh, Harald

    In connection with the work for the next generation VLBI2010 Global Observing System (VGOS) of the International VLBI Service for Geodesy and Astrometry, a new scheduling package (Vie_Sched) has been developed at the Vienna University of Technology as a part of the Vienna VLBI Software. In addition to the classical station-based approach it is equipped with a new scheduling strategy based on the radio sources to be observed. We introduce different configurations of source-based scheduling options and investigate the implications on present and future VLBI2010 geodetic schedules. By comparison to existing VLBI schedules of the continuous campaign CONT11, we find that the source-based approach with two sources has a performance similar to the station-based approach in terms of number of observations, sky coverage, and geodetic parameters. For an artificial 16 station VLBI2010 network, the source-based approach with four sources provides an improved distribution of source observations on the celestial sphere. Monte Carlo simulations yield slightly better repeatabilities of station coordinates with the source-based approach with two sources or four sources than the classical strategy. The new VLBI scheduling software with its alternative scheduling strategy offers a promising option with respect to applications of the VGOS.

  7. Study of Ionosphere Total Electron Content for the Broadband Geodetic VLBI Fringe Model

    NASA Astrophysics Data System (ADS)

    Mulero Hernandez, C. A.; Beaudoin, C. J.; Coster, A. J.; Erickson, P. J.; Niell, A. E.

    2013-12-01

    The radio telescopes used for Geodetic Very Long Baseline Interferometry (VLBI) receive signals from distant astronomical objects to provide a measure of the Earth's shape and variable rotation. However, the propagation of these signals through the Earth's ionosphere and any other plasma between the radio source and the telescope introduces a systematic error in the geodetic observable. This dispersive delay has become more critical in light of the accuracy goals set forth in the VLBI2010 specifications for the VLBI Geodetic Observing System (VGOS) which are 1mm for position and 0.1 mm/yr for stability. In order to achieve such geodetic accuracy, this error must be accurately removed. In this work we present an investigation of the accuracy of the dispersive component of delay as determined by the broadband geodetic VLBI technique. We will describe the features and implementation of a frequency-dependent forward model of this dispersive delay for VLBI. The application of this model yields an estimate of the combined ionospheric and extraterrestrial differential total electron content (TEC) using a nonlinear parametric search. We assess the quality of this VLBI-based differential TEC estimate by comparing it with differential TEC values obtained using GPS receivers near VLBI antennas.

  8. Current Status of the Development of a Transportable and Compact VLBI System by NICT and GSI

    NASA Technical Reports Server (NTRS)

    Ishii, Atsutoshi; Ichikawa, Ryuichi; Takiguchi, Hiroshi; Takefuji, Kazuhiro; Ujihara, Hideki; Koyama, Yasuhiro; Kondo, Tetsuro; Kurihara, Shinobu; Miura, Yuji; Matsuzaka, Shigeru; Tanimoto, Daisuke

    2010-01-01

    MARBLE (Multiple Antenna Radio-interferometer for Baseline Length Evaluation) is under development by NICT and GSI. The main part of MARBLE is a transportable VLBI system with a compact antenna. The aim of this system is to provide precise baseline length over about 10 km for calibrating baselines. The calibration baselines are used to check and validate surveying instruments such as GPS receiver and EDM (Electro-optical Distance Meter). It is necessary to examine the calibration baselines regularly to keep the quality of the validation. The VLBI technique can examine and evaluate the calibration baselines. On the other hand, the following roles are expected of a compact VLBI antenna in the VLBI2010 project. In order to achieve the challenging measurement precision of VLBI2010, it is well known that it is necessary to deal with the problem of thermal and gravitational deformation of the antenna. One promising approach may be connected-element interferometry between a compact antenna and a VLBI2010 antenna. By measuring repeatedly the baseline between the small stable antenna and the VLBI2010 antenna, the deformation of the primary antenna can be measured and the thermal and gravitational models of the primary antenna will be able to be constructed. We made two prototypes of a transportable and compact VLBI system from 2007 to 2009. We performed VLBI experiments using theses prototypes and got a baseline length between the two prototypes. The formal error of the measured baseline length was 2.7 mm. We expect that the baseline length error will be reduced by using a high-speed A/D sampler.

  9. Characterization of the binding of a novel nonxanthine adenosine antagonist radioligand, ( sup 3 H)CGS 15943, to multiple affinity states of the adenosine A1 receptor in the rat cortex

    SciTech Connect

    Jarvis, M.F.; Williams, M.; Do, U.H.; Sills, M.A. )

    1991-01-01

    The triazoloquinazoline CGS 15943 is the first reported nonxanthine adenosine antagonist that has high affinity for brain adenosine receptors. In the present study, the binding of (3H) CGS 15943 to recognition sites in rat cortical membranes was characterized. Saturation experiments revealed that (3H)CGS 15943 labeled a single class of recognition sites with high affinity and limited capacity. Competition studies revealed that the binding of (3H)CGS 15943 was consistent with the labeling of brain adenosine A1 receptors. Adenosine agonists inhibited 1 nM (3H)CGS 15943 binding with the following order of activity N6-cyclopentyladenosine (IC50 = 15 nM) greater than 2-chloroadenosine greater than (R)-N6-phenylisopropyladenosine greater than 5'-N6-ethylcarboxamidoadenosine greater than (S)N6-phenylisopropyladenosine greater than CGS 21680 greater than CV 1808 (IC50 greater than 10,000 nM). The potency order for adenosine antagonists was CGS 15943 (IC50 = 5 nM) greater than 8-phenyltheophylline greater than 1,3-dipropyl-8-(4-amino-2-chloro)phenylxanthine greater than 1,3-diethyl-8-phenylxanthine greater than theophylline = caffeine (IC50 greater than 10,000 nM). Antagonist inhibition curves were steep and best described by a one-site binding model. In contrast, adenosine A1 agonist competition curves were shallow, as indicated by Hill coefficients less than unity. Computer analysis revealed that these inhibition curves were best described by a two-site binding model. Agonist competition curves generated in the presence of 1 mM GTP resulted in a rightward shift and steepening of the inhibition-concentration curves, whereas antagonist binding was not altered in the presence of GTP. The complex binding interactions found with adenosine agonists indicate that (3H)CGS 15943 labels both high and low affinity components of the adenosine A1 receptor in the rat cortex.

  10. Submicrosecond comparison of international clock synchronization by VLBI and the NTS satellite

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Wardrip, S. C.; Bussion, J.; Oaks, J.; Mccaskill, T.; Warren, H.; Whitworth, G.

    1979-01-01

    The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared using both methods to synchronize the Cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain and Goldstone, California. Verification of the accuracy of both systems was examined. The VLBI experiments used the Wideband VLBI Data Acquisition System developed at the NASA Jet Propulsion Laboratory. The NTS Satellites were designed and built by the Naval Research Laboratory used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level.

  11. International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

    2004-01-01

    This volume is the proceedings of the third General Meeting of the International VLBI Service for Geodesy and Astromctry IVS), held in Otlawa, Canada, February 9-11,2004. The keynote of the third GM was visions for the next decade following the main theme of "Today's Results and Tomorrow's Vision". with a recognition that the outstanding VLBI results available today are the foundation and motivation for the next generation VLBI system requirements. The goal of the meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts.

  12. International VLBI Service for Geodesy and Astrometry 2012 General Meeting Proceedings

    NASA Astrophysics Data System (ADS)

    Behrend, D.; Baver, K. D.

    2012-12-01

    This volume is the proceedings of the seventh General Meeting (GM2012) of the International VLBI Service for Geodesy and Astrometry (IVS), held in Madrid, Spain, March 4-9, 2012. The seventh General Meeting was held in Madrid, Spain at the Centro de Estudios de Tecnicas Aplicadas (CETA) of the Spanish Ministerio de Fomento and was hosted by the Royal Observatory of Madrid. The conference was sponsored by the National Geographical Institute of Spain (IGN) and the IVS. The keynote of the seventh General Meeting was the evolution of a new VLBI network based on VLBI2010 technology under the theme "Launching the Next-Generation IVS Network".

  13. Combining VLBI and Gamma-Ray Satellite Observations in Blazar Research

    NASA Astrophysics Data System (ADS)

    Wiik, K.; Savolainen, T.; Valtaoja, E.

    2004-10-01

    VLBI enables us to observe synchrotron radiation from relativistic electrons in the innermost regions of blazars. According to the leptonic models, the same electrons pro- duce also the high-energy radiation component through inverse Compton scattering of seed photons. One demon- stration of the connection between high- and low-energy emission is the correlation found between VLBI compo- nent ejections and gamma-ray flares. VLBI can probe the physical parameters of emitting re- gions, like Lorentz factors and magnetic field direction, and can improve SED modeling by providing the spectra of individual jet components.

  14. Comparison of atmospheric parameters estimated from VLBI, GPS and microwave radiometer data.

    NASA Astrophysics Data System (ADS)

    Gradinarsky, L. P.; Haas, R.; Johansson, J. M.; Elgered, G.

    1999-03-01

    Very Long Baseline Interferometry (VLBI) is colocated with a permanent Global Positioning System (GPS) receiver and a Water Vapour Radiometer (WVR) at the Onsala Space Observatory (OSO). Both VLBI and GPS data are affected by the propagation delay of radio waves in the atmosphere, while the WVR is sensitive to the atmospheric emission close to the center of the 22 GHz water vapour emission line and provides wet delay estimates. The authors present a comparison of estimated atmospheric parameters (equivalent zenith wetdelay and linear horizontal delay gradients) derived from an independent analysis of simultaneous VLBI, GPS and WVR observations. They study and compare the estimated parameters using different elevation cut off angles for the analysis of VLBI data with those obtained from the GPS and the WVR data analyses. The parameters are estimated for 90, 180 and 360 minutes long intervals, which allows to study the averaging effect on the integrated parameters of the turbulent atmosphere.

  15. Submicrosecond comparison of intercontinental clock synchronization by VLBI and the NTS satellite

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Wardrip, S. C.; Bussion, J.; Oaks, J.; Mccaskill, T.; Warren, H.; Whitworth, G.

    1979-01-01

    The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared in May 1978 by using both methods to synchronize the cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain, and Goldstone, California. The VLBI experiments used the Wideband VLBI Data Acquisition System. The Navigation Technology Satellites were used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level. The VLBI system also obtained long-term stability information on the HP5061A004 cesium standards by measuring delta T/T over four 3- to 4-day intervals, obtaining stability estimates of (1 + or - 1)x10 to the -13th power for the combined timing systems.

  16. Wide-Band Data Transmission System Expected in the Next Generation Space VLBI Mission: VSOP-2

    NASA Technical Reports Server (NTRS)

    Murata, Yasuhiro; Hirabayashi, Hisashi

    2002-01-01

    Following the success of the VLBI Space Observatory Program (VSOP), a next generation space VLBI mission (VSOP-2) is currently being planned. We expect the data rate of more than 1 Gbps to get more sensitivity. Here we will present: (1) How to sample the data (on board), including the radiation test results which show we can have the 10 Gbps sampler LSI which can use in space; (2) Possibility of the bit rate more than 1 Gbps to downlink the VLBI data. We studied the link budget for the wide band data transmission, and discussed the various ideas which can get more than 1 Gbps; and (3) What kind of VLBI tracking station and recording system will be expected for the VSOP-2 mission? We will present the idea of using normal radio telescopes as a tracking station, and also review the possibility of recording and processing at the tracking stations and correlators.

  17. Height biases and scale variations in VLBI networks due to antenna gravitational deformations

    NASA Astrophysics Data System (ADS)

    Abbondanza, Claudio; Sarti, Pierguido; Petrov, Leonid; Negusini, Monia

    2010-05-01

    The impact of signal path variations (SPVs) caused by antenna gravity deformations on geodetic VLBI results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying these models, estimates of the antenna reference point (ARP) positions are shifted upward by 8.9 mm and 6.7 mm, respectively. The impact on other parameters is negligible. To infer the impact of antenna gravity deformations on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for other antennas according to their size. The effects are changes in VLBI heights in the range [-3,73] mm and a significant net scale increase of 0.3 - 0.8 ppb. This demonstrates the need to include SPV models in routine VLBI data analysis.

  18. Pulsar VLBI to Measure Cosmological Rotation and Study Pulsar Emission Regions

    NASA Astrophysics Data System (ADS)

    Gwinn, C. R.

    2009-08-01

    Pulsars are useful for measuring the rotation of the universe. Also, their emission regions provide interesting laboratories for plasma physics. I describe here how VLBI of pulsars, and the VSOP-2 spacecraft, can contribute to such studies.

  19. Wide-Band Data Transmission System Expected in the Next Generation Space VLBI Mission: VSOP-2

    NASA Technical Reports Server (NTRS)

    Murata, Yasuhiro; Hirabayashi, Hisashi

    2002-01-01

    Following the success of the VLBI Space Observatory Program (VSOP), a next generation space VLBI mission (VSOP-2) is currently being planned. We expect the data rate of more than 1 Gbps to get more sensitivity. Here we will present: (1) How to sample the data (on board), including the radiation test results which show we can have the 10 Gbps sampler LSI which can use in space; (2) Possibility of the bit rate more than 1 Gbps to downlink the VLBI data. We studied the link budget for the wide band data transmission, and discussed the various ideas which can get more than 1 Gbps; and (3) What kind of VLBI tracking station and recording system will be expected for the VSOP-2 mission? We will present the idea of using normal radio telescopes as a tracking station, and also review the possibility of recording and processing at the tracking stations and correlators.

  20. Preliminary results from a 7 station VLBI survey of OH masers in the galactic plane

    SciTech Connect

    Diamond, P.J.; Martinson, A.; Dennison, B.; Booth, R.S.; Winnberg, A.

    1988-11-01

    An initial analysis of a large VLBI survey of OH masers in the Galactic Plane reveals a correlation of maser component angular size with source distance. This correlation is presumably due to the effect of an intervening scattering medium.

  1. Preliminary Space VLBI Requirements for Observing Time on Ground Radio Telescopes

    NASA Technical Reports Server (NTRS)

    Meier, David L.; Murphy, David W.; Preston, Robert A.

    1992-01-01

    An initial estimate has been made of the observing time required on ground radio telescopes by the space VLBI missions Radioastron and VSOP. Typical science programs have been adopted for both missions.

  2. Status and Plans for the Vienna VLBI and Satellite Software (VieVS 3.0)

    NASA Astrophysics Data System (ADS)

    Gruber, Jakob; Böhm, Johannes; Böhm, Sigrid; Girdiuk, Anastasiia; Hellerschmied, Andreas; Hofmeister, Armin; Krásná, Hana; Kwak, Younghee; Landskron, Daniel; Madzak, Matthias; Mayer, David; McCallum, Jamie; Plank, Lucia; Schartner, Matthias; Shabala, Stas; Teke, Kamil; Sun, Jing

    2017-04-01

    The Vienna VLBI and Satellite Software (VieVS) is a geodetic analysis software developed and maintained at Technische Universität Wien (TU Wien) with contributions from groups all over the world. It is used for both academic purposes in university courses as well as for providing Very Long Baseline Interferometry (VLBI) analysis results to the geodetic community. Written in a modular structure in Matlab, VieVS offers easy access to the source code and the possibility to adapt the programs for particular purposes. The new version 3.0, released in early 2017, includes several new features, e.g., improved scheduling capabilities for observing quasars and satellites. This poster gives an overview of all VLBI-related activities in Vienna and provides an outlook to future plans concerning the Vienna VLBI and Satellite Software (VieVS).

  3. The search for reference sources for delta VLBI navigation of the Galileo spacecraft

    NASA Technical Reports Server (NTRS)

    Ulvestad, J. S.; Linfield, R. P.

    1986-01-01

    A comprehensive search was made in order to identify celestial radio sources that can be used as references for navigation of the Galileo spacecraft by means of VLBI observations. The astronomical literature was seached for potential navigation sources, and several VLBI experiments were performed to determine the suitability of those sources for navigation. The results of such work performed since mid-1983 is reported. A summary is presented of the source properties required, the procedures used to identify candidate sources, and the results of the observations of these sources. The lists of souces presented are not meant to be taken directly and used for VLBI navigation, but they do provide a means of identifying the radio sources that could be used at various positions along the Galileo trajectory. Since the reference sources nearest the critical points of Jupiter encounter and probe release are rather weak, it would be extremely beneficial to use a pair of 70-m antennas for the VLBI measurements.

  4. GPU Based Software Correlators - Perspectives for VLBI2010

    NASA Technical Reports Server (NTRS)

    Hobiger, Thomas; Kimura, Moritaka; Takefuji, Kazuhiro; Oyama, Tomoaki; Koyama, Yasuhiro; Kondo, Tetsuro; Gotoh, Tadahiro; Amagai, Jun

    2010-01-01

    Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.

  5. Determination of intercontinental baselines and Earth orientation using VLBI

    NASA Technical Reports Server (NTRS)

    Sovers, O. J.; Fanselow, J. L.; Purcell, G. H., Jr.; Rogstad, D. H.; Thomas, J. B.

    1982-01-01

    A series of experiments was conducted during the last decade to explore the capability of very long baseline interferometry (VLBI) to measure the crustal and rotational motions of the Earth with accuracies at the centimeter level. The observing stations are those of NASA's Deep Space Network in California, Spain and Australia. A multiparameter fit to the observed values of delay and delay rate yields radio source positions, polar motion, universal time, the precession constant, baseline vectors, and solid Earth tides. Source positions are obtained with formal errors of the order of 0''.01. UT1-UTC and polar motion are determined at 49 epochs, with formal error estimates for the more recent data of 0.5 msec for UT1-UTC and 2 to 6 mas for polar motion. Intercontinental baseline lengths are determined with formal errors of 5 to 10 cm. The Love numbers and Earth tide phase lag agree with the commonly accepted values.

  6. VLBI multi-epoch water maser observations toward massive protostars

    NASA Astrophysics Data System (ADS)

    Torrelles, José M.; Gómez, José F.; Patel, Nimesh A.; Curiel, Salvador; Anglada, Guillem; Estalella, Robert

    2012-07-01

    VLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated ``short-lived'' pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simultaneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similar to what is observed in low-mass protostars). In addition, with these observations it has been possible to identify new, previously unseen centers of high-mass star formation through outflow activity.

  7. First Broadband Results with a VLBI2010 System

    NASA Astrophysics Data System (ADS)

    Niell, A.; Avelar, W.; Beaudoin, C.; Cappallo, R.; Clark, T.; Corey, B.; Diegel, I.; Evangelista, M.; Figueroa, R.; Gordon, S.; Himwich, E.; Kodak, C.; Ma, C.; McWhirter, R.; Pazamickas, K.; Poirier, M.; Redmond, J.; Rogers, A.; Ruszczyk, C.; Smythe, D.; Whittier, J. SooHoo, M. Titus, B.

    2012-12-01

    The next generation geodetic VLBI instrument is being developed with a goal of 1 mm position uncertainty in twenty- four hours. The broadband signal chain, which is essential for obtaining the required delay accuracy from a network of relatively small antennas, has been implemented on the 12-meter antenna at the Goddard Space Flight Center, Maryland, USA, and on the 18-meter Westford antenna at Haystack Observatory, Massachusetts, USA. Data have been obtained in four 512 MHz bands spanning the range 3.2 to 9.9 GHz using commercially available broadband feeds, LNAs, digital back ends, and recorders. The first geodetic-style observing session has been completed. While demonstrating that the broadband hardware functions as expected, the six-hour session has illuminated areas of the scheduling, correlation, and post-correlation process that require improve, p.

  8. E-VLBI-activities at the FS Wettzell

    NASA Astrophysics Data System (ADS)

    Kronschnabl, Gerhard; Dassing, Reiner

    The FS-Wettzell carries out the daily-INTENSIVE observations which were required for the rapid determination of DUT1. The data volume is roughly 40 GB. So fare the data were shipped via currier services to the correlator which requires 2-3 days transportation time. The INTENSIVE time series is a real candidate for E-VLBI. It will reduce the delay due to data transport strongly. Considering the remote location of Wettzell - apart from the fast INTERNET links, considering the current high cost for a fast connection, in the next future the installation of a 34 Gbps-internet connection will be realistic. It will strongly support the data transmission on start the delay time to only a few hours. This report give an overview about the activities on the realisation of such a fast link. First attempts are reported made from the next nodal point at the University Regensburg, making use of a 155Mbps connection.

  9. Global reference frame: Intercomparison of results (SLR, VLBI and GPS)

    NASA Technical Reports Server (NTRS)

    Ma, Chopo; Watkins, Michael M.; Heflin, M.

    1994-01-01

    The terrestrial reference frame (TRF) is realized by a set of positions and velocities derived from a combination of the three space geodetic techniques, SLR, VLBI and GPS. The standard International TRF is constructed by the International Earth Rotation Service in such a way that it is stable with time and the addition of new data. An adopted model for overall plate motion, NUVEL-1 NNR, defines the conceptual reference frame in which all the plates are moving. In addition to the measurements made between reference points within the space geodetic instruments, it is essential to have accurate, documented eccentricity measurements from the instrument reference points to ground monuments. Proper local surveys between the set of ground monuments at a site are also critical for the use of the space geodetic results. Eccentricities and local surveys are, in fact, the most common and vexing sources of error in the use of the TRF for such activities as collocation and intercomparison.

  10. A VLBI resolution of the Pleiades distance controversy.

    PubMed

    Melis, Carl; Reid, Mark J; Mioduszewski, Amy J; Stauffer, John R; Bower, Geoffrey C

    2014-08-29

    Because of its proximity and its youth, the Pleiades open cluster of stars has been extensively studied and serves as a cornerstone for our understanding of the physical properties of young stars. This role is called into question by the "Pleiades distance controversy," wherein the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by the optical space astrometry mission Hipparcos is significantly different from the distance of 133.5 ± 1.2 pc derived with other techniques. We present an absolute trigonometric parallax distance measurement to the Pleiades cluster that uses very long baseline radio interferometry (VLBI). This distance of 136.2 ± 1.2 pc is the most accurate and precise yet presented for the cluster and is incompatible with the Hipparcos distance determination. Our results cement existing astrophysical models for Pleiades-age stars. Copyright © 2014, American Association for the Advancement of Science.

  11. New vertical geodesy. [VLBI measurements for earthquake prediction

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. H.

    1976-01-01

    The paper contains a review of the theoretical difference between orthometric heights and heights labeled geometric which are determined through use of an extraterrestrial frame of reference. The theory is supplemented with examples which portray very long baseline interferometry as a measuring system that will provide estimates of vertical crustal motion which are radically improved in comparison with those obtained from analysis of repeated geodetic levelings. The example of the San Fernando earthquake of 1971 is used to show how much estimates of orthometric and geometric height change might differ. A comment by another author is appended which takes issue with some of the conclusions of this paper. In particular, an attempt is made in the comment to rebut the conclusion that geodetic leveling is less reliable than VLBI measurements for determining relative elevation change of points separated by more than 56 km.

  12. New vertical geodesy. [VLBI measurements for earthquake prediction

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. H.

    1976-01-01

    The paper contains a review of the theoretical difference between orthometric heights and heights labeled geometric which are determined through use of an extraterrestrial frame of reference. The theory is supplemented with examples which portray very long baseline interferometry as a measuring system that will provide estimates of vertical crustal motion which are radically improved in comparison with those obtained from analysis of repeated geodetic levelings. The example of the San Fernando earthquake of 1971 is used to show how much estimates of orthometric and geometric height change might differ. A comment by another author is appended which takes issue with some of the conclusions of this paper. In particular, an attempt is made in the comment to rebut the conclusion that geodetic leveling is less reliable than VLBI measurements for determining relative elevation change of points separated by more than 56 km.

  13. Improved atmospheric mapping functions for VLBI and GPS

    NASA Astrophysics Data System (ADS)

    Niell, A. E.

    2000-10-01

    New mapping functions based on in situ meteorological parameters have been developed for calculating the radio path length through the atmosphere at elevations down to 3°. The hydrostatic component of the mapping function is related to the geopotential height of the 200 mb isobaric pressure level above the site and provides a factor of two improvement in accuracy and precision over previous hydrostatic mapping functions at mid-latitudes. The wet component of the mapping function is calculated from the vertical profile of wet refractivity at the site but will provide an improvement of only about twenty-five percent. However, since the effect of known errors in the hydrostatic mapping function dominates that from the wet component, except near the equator, implementation of these mapping functions should reduce the contribution of the atmosphere to errors in estimates by VLBI and GPS of both the vertical component of site position and the radio propagation delay due to water vapor in the atmosphere.

  14. Constraints on interseismic deformation at Japan trench from VLBI data

    NASA Technical Reports Server (NTRS)

    Argus, Donald F.; Lyzenga, Gregory A.

    1993-01-01

    Space geodetic data from very long baseline interferometry (VLBI) was used to estimate velocity relative to the plate interiors of two sites on the deforming leading edge at the Japan trench. Elastic models of interseismic deformation and results obtained were used to put constraints on the slip rate along the main thrust of the Japan subduction zone. Observed velocities reflect the sum of permanent west-northwest shortening in Honshu, elastic deformation due to locking of the main thrust fault at the Japan trench, and deformation associated with the subducting Phillipine plate. These velocities limit the locked segment of the main thrust at the Japan trench to 27 km vertically and 100 km along the dip. This indicates that the main Pacific plate thrust fault is not strongly coupled and probably does not generate strong earthquakes.

  15. Remote Control and Monitoring of VLBI Experiments by Smartphones

    NASA Astrophysics Data System (ADS)

    Ruztort, C. H.; Hase, H.; Zapata, O.; Pedreros, F.

    2012-12-01

    For the remote control and monitoring of VLBI operations, we developed a software optimized for smartphones. This is a new tool based on a client-server architecture with a Web interface optimized for smartphone screens and cellphone networks. The server uses variables of the Field System and its station specific parameters stored in the shared memory. The client running on the smartphone by a Web interface analyzes and visualizes the current status of the radio telescope, receiver, schedule, and recorder. In addition, it allows commands to be sent remotely to the Field System computer and displays the log entries. The user has full access to the entire operation process, which is important in emergency cases. The software also integrates a webcam interface.

  16. The AuScope Project and Trans-Tasman VLBI

    NASA Technical Reports Server (NTRS)

    Lovell, Jim; Dickey, John; Gulyaev, Sergei; Natusch, Tim; Titov, Oleg; Tingay, Steven

    2010-01-01

    Three 12-meter radio telescopes are being built in Australia (the AuScope project) and one in New Zealand. These facilities will be fully-equipped for undertaking S and X-band geodetic VLBI observations and correlation will take place on a software correlator (part of the AuScope project). All sites are equipped with permanent GPS receivers to provide co-location of several space geodetic techniques. The following scientific tasks of geodesy and astrometry are considered. 1. Improvement and densification of the International Celestial Reference Frame in the southern hemisphere; 2. Improvement of the International Terrestrial Reference Frame in the region; 3. Measurement of intraplate deformation of the Australian tectonic plate.

  17. Mark 6: A Next-Generation VLBI Data System

    NASA Astrophysics Data System (ADS)

    Whitney, A. R.; Lapsley, D. E.; Taveniku, M.

    2011-07-01

    A new real-time high-data-rate disk-array system based on entirely commercial-off-the-shelf hardware components is being evaluated for possible use as a next-generation VLBI data system. The system, developed by XCube Communications of Nashua, NH, USA was originally developed for the automotive industry for testing/evaluation of autonomous driving systems that require continuous capture of an array of video cameras and automotive sensors at ~8Gbps from multiple 10GigE data links and other data sources. In order to sustain the required recording data rate, the system is designed to account for slow and/or failed disks by shifting the load to other disks as necessary in order to maintain the target data rate. The system is based on a Linux OS with some modifications to memory management and drivers in order to guarantee the timely movement of data, and the hardware/software combination is highly tuned to achieve the target data rate; data are stored in standard Linux files. A kit is also being designed that will allow existing Mark 5 disk modules to be modified to be used with the XCube system (though PATA disks will need to be replaced by SATA disks). Demonstrations of the system at Haystack Observatory and NRAO Socorro have proved very encouraging; some modest software upgrades/revisions are being made by XCube in order to meet VLBI-specific requirements. The system is easily expandable, with sustained 16 Gbps likely to be supported before end CY2011.

  18. SN 1986J VLBI. III. The Central Component Becomes Dominant

    NASA Astrophysics Data System (ADS)

    Bietenholz, Michael F.; Bartel, Norbert

    2017-04-01

    We present a new 5 GHz global very-long-baseline interferometry (VLBI) image of supernova 1986J, observed in 2014 at t = 31.6 yr after the explosion, and compare it to previous images to show the evolution of the supernova. Our new image has a dynamic range of ˜100 and a background rms noise level of 5.9 μJy beam-1. There is no significant linear polarization, with the image peak <3% polarized. The latest image is dominated by a compact central component, whose flux density is now comparable to that of the extended supernova shell. This central component is marginally resolved with an FWHM of {900}-500+100 μ {as}, corresponding to a radius of {r}{comp}={6.7}-3.7+0.7× {10}16 {cm} for a distance of 10 Mpc. Using VLBI observations between 2002 and 2014, we measured the proper motions of both the central component and a hot spot to the NE in the shell relative to the quasar 3C 66A. The central component is stationary to within the uncertainty of 12 μas yr-1, corresponding to 570 km s-1. Our observations argue that the central component is located near the physical center of SN 1986J. The shell hot spot had a mean velocity of 2810 ± 750 km s-1 to the NE, which is consistent with its taking part in the homologous expansion of the shell seen earlier. The shell emission is evolving in a non-self-similar fashion, with the brightest emission shifting inward within the structure and with only relatively faint emission seen near the outer edge and the presumed forward shock. An animation of the explosion is available.

  19. Effects of the 2011 Tohoku Earthquake on VLBI Geodetic Measurements

    NASA Astrophysics Data System (ADS)

    MacMillan, D. S.; Kurihara, S.; Behrend, D.

    2011-12-01

    The VLBI antenna TSUKUB32 at Tsukuba, Japan regularly observes in 24-hour observing sessions once per week with the R1 operational network and on additional days with other networks on a more irregular basis. Further, the antenna is an endpoint of the single-baseline, 1-hour Intensive sessions observed on the weekends for determination of UT1. TSUKUB32 returned to normal operational observing 25 days after the earthquake. The antenna is 160 km west and 240 km south of the epicenter (about the same distance west of the plate subduction boundary). We looked at the transient behavior of the TSUKUB32 position time series following the earthquake and found that significant deformation is continuing. The eastward rate as of July 2011, 4 months after the earthquake, is 20 cm/yr greater than the long-term rate prior to the earthquake. The VLBI series agrees with the corresponding JPL GPS series (M. B. Heflin, http://sideshow.jpl.nasa.gov/mbh/series.html, 2011) measured by the co-located GPS antenna TSUK. The coseismic UEN displacement at Tsukuba was approximately (-90 mm, 550 mm, 50 mm). We examined the effect of the variation of TSUKUB32 position on EOP estimates and specifically how best to correct its position for estimation of UT1 in the Intensive experiments. For this purpose and to provide operational UT1, the IVS scheduled a series of weekend Intensive sessions observing on the Kokee-Wettzell baseline immediately before each of the two Tsukuba-Wettzell Intensive sessions. Comparisons between UT1 estimates from these pairs of sessions were used in validating a model for the post-seismic displacement of TSUKUB32.

  20. El Nino, La Nina and VLBI Measured LOD

    NASA Technical Reports Server (NTRS)

    Clark, Thomas A.; Gipson, J. M.; Ma, C.

    1998-01-01

    VLBI is one of the most important techniques for measuring Earth orientation parameters (EOP), and is unique in its ability to make high accuracy measurements of UT1, and its time derivative, which is related to changes in the length of day, conventionally called LOD. These measurements of EOP give constraints on geophysical models of the solid-Earth, atmosphere and oceans. Changes in EOP are due either to external torques from gravitational forces, or to the exchange of angular momentum between the Earth, atmosphere and oceans. The effect of the external torques is strictly harmonic and nature, and is therefore easy to remove. We analyze an LOD time series derived from VLBI measurements with the goal of comparing this to predictions from AAM, and various ENSO indices. Previous work by ourselves and other investigators demonstrated a high degree of coherence between atmospheric angular momentum (AAM) and EOP. We continue to see this. As the angular momentum of the atmosphere increases, the rate of rotation of the Earth decreases, and vice versa. The signature of the ENSO is particularly strong. At the peak of the 1982-83 El Nino increased LOD by almost 1 ms. This was subsequently followed by a reduction in LOD of 0.75 ms. At its peak, in February of 1998, the 1997-98 El Nino increased LOD by 0.8 msec. As predicted at the 1998 Spring AGU, this has been followed by an abrupt decrease in LOD which is currently -0.4 ms. At this time (August, 1998) the current ENSO continues to develop in new and unexpected ways. We plan to update our analysis with all data available prior to the Fall AGU.

  1. El Nino, La Nina and VLBI Measured LOD

    NASA Technical Reports Server (NTRS)

    Clark, Thomas A.; Gipson, J. M.; Ma, C.

    1998-01-01

    VLBI is one of the most important techniques for measuring Earth orientation parameters (EOP), and is unique in its ability to make high accuracy measurements of UT1, and its time derivative, which is related to changes in the length of day, conventionally called LOD. These measurements of EOP give constraints on geophysical models of the solid-Earth, atmosphere and oceans. Changes in EOP are due either to external torques from gravitational forces, or to the exchange of angular momentum between the Earth, atmosphere and oceans. The effect of the external torques is strictly harmonic and nature, and is therefore easy to remove. We analyze an LOD time series derived from VLBI measurements with the goal of comparing this to predictions from AAM, and various ENSO indices. Previous work by ourselves and other investigators demonstrated a high degree of coherence between atmospheric angular momentum (AAM) and EOP. We continue to see this. As the angular momentum of the atmosphere increases, the rate of rotation of the Earth decreases, and vice versa. The signature of the ENSO is particularly strong. At the peak of the 1982-83 El Nino increased LOD by almost 1 ms. This was subsequently followed by a reduction in LOD of 0.75 ms. At its peak, in February of 1998, the 1997-98 El Nino increased LOD by 0.8 msec. As predicted at the 1998 Spring AGU, this has been followed by an abrupt decrease in LOD which is currently -0.4 ms. At this time (August, 1998) the current ENSO continues to develop in new and unexpected ways. We plan to update our analysis with all data available prior to the Fall AGU.

  2. Mobile VLBI deployment plans of the Crustal Dynamics Project for the western United States and Alaska

    NASA Technical Reports Server (NTRS)

    Trask, D. W.; Vegos, C. J.

    1983-01-01

    Current plans for the Mobile VLBI program are addressed. Present mobile stations and their past activities are summarized, and past and future modes of obtaining data are compared, including the 'burst' and 'leap frog' modes. The observational campaign for Mobile VLBI is described, emphasizing the portions in Canada and Alaska. The extent to which the mobile stations are utilized and the ways in which the site visit yield may be increased are discussed.

  3. Space VLBI Polarimetry of IDV Sources: Lessons from VSOP and Prospects for VSOP-2

    NASA Astrophysics Data System (ADS)

    Bach, U.; Krichbaum, T. P.; Bernhart, S.; Impellizzeri, C. M. V.; Kraus, A.; Fuhrmann, L.; Witzel, A.; Zensus, J. A.

    2009-08-01

    To locate and image the compact emission regions in quasars, which are closely connected to the phenomenon of IntraDay Variability (IDV), space VLBI observations are of prime importance. Here we report on VSOP observations of a prominent IDV source, the BL Lac objects S5 0716+714. To monitor their short term variability, these sources were observed with VSOP at 5 GHz in several polarisation sensitive experiments, separated in time by one day to six days, in autumn 2000. Contemporaneous flux density measurements with the Effelsberg 100 m radio telescope were used to directly compare the single dish IDV with changes of the VLBI images. A clear IDV behaviour in total intensity and linear polarization was observed in 0716+714. Analysis of the VLBI data shows that the variations are located inside the VLBI core component of 0716+714. In good agreement with the single-dish measurements, the VLBI ground array images and the VSOP images, both show a decrease in the total flux density of ˜20 mJy and a drop of ˜5 mJy in the linear polarization of the VLBI core. No variability was found in the jet. These findings are supported by VLBA observations of five IDV sources, including 0716+714, in December 2000, that show a similar behaviour. From the variability timescales we estimate a source size of a few micro-arcseconds and brightness temperatures exceeding 1015 K. Independent of whether the interpretation of the IDV seen in the VLBI core is source intrinsic or extrinsic a lower limit of TB > 2×1012 K is obtained by model fitting of the VLBI-core. Our results show that future VSOP2 observations should be accompanied by a single dish monitoring not only to discriminate between source-extrinsic (interstellar scintillation) and source-intrinsic effects but to allow also a proper calibration and interpretation of ultra-high resolution VSOP2 images.

  4. Towards ICRF3:preparing the VLBI frame for future synergy with the Gaia frame

    NASA Astrophysics Data System (ADS)

    Charlot, Patrick; Bourda, Géraldine

    2012-08-01

    The European space astrometric mission Gaia to be launched in 2013 will produce a QSO - based celestial reference frame with unprecedented position accuracy and sky density. By the end of the decade, two highly - accurate reference frames will thus cohabit, the International Celestial Reference Frame (ICRF) derived from Very Long Baseline Interferometry (VLBI) data and the Gaia optical frame, both with individual source position accuracies below 100 microarcseconds. For consistency be tween optical and radio positions, it will be fundamental to align the two frames with the highest possible accuracy. This is important not only for continuity of celestial frames but also to exploit at best their synergies for astrophysics. The latter includes probing the Active Galactic Nuclei (AGN) jets properties and the physics of these objects by comparing the spatial location of the optical and radio emission re gions. The alignment between the VLBI and Gaia frames requires a large number of sources common to the two frames, i.e. radio - loud QSOs with position accurately known from both VLBI and Gaia. This implies that the sources must be brighter than magnitude 18 (so that their Gaia positions may be derived with the highest accuracy) and have compact VLBI structure on milliarcsecond scales (for highly - accurate VLBI positions). In this paper, we review the current source potential for this alignment based on the ICRF2 and an ongoing dedicated VLBI project aimed at finding additional weaker extragalactic radio sources for this purpose. We also stress that these sources must be monitored during the mission (especially their VLBI position stability and structure) in order to control their relevance for the alignment, and present the observations we envision to this end in the framework of the IVS and other VLBI networks.

  5. Mobile VLBI deployment plans of the Crustal Dynamics Project for the western United States and Alaska

    NASA Astrophysics Data System (ADS)

    Trask, D. W.; Vegos, C. J.

    Current plans for the Mobile VLBI program are addressed. Present mobile stations and their past activities are summarized, and past and future modes of obtaining data are compared, including the 'burst' and 'leap frog' modes. The observational campaign for Mobile VLBI is described, emphasizing the portions in Canada and Alaska. The extent to which the mobile stations are utilized and the ways in which the site visit yield may be increased are discussed.

  6. Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14

    NASA Astrophysics Data System (ADS)

    Haas, Rüdiger; Hobiger, Thomas; Kurihara, Shinobu; Hara, Tetsuya

    2016-04-01

    In 2007 the Geospatial Information Authority of Japan (GSI) and the Onsala Space Observatory (OSO) started a collaboration project aiming at determining the earth rotation angle, usually expressed as UT1-UTC, in near real-time. In the beginning of this project dedicated one hour long one-baseline experiments were observed periodically using the VLBI stations Onsala (Sweden) and Tsukuba (Japan). The strategy is that the observed VLBI data are sent in real-time via the international optical fibre backbone to the correlator at Tsukuba where the data are correlated with a software correlator and analyzed in near-real time with the c5++ VLBI data analysis software, thus producing UT1-UTC results with very low latency. The latency between the observation at the stations and the determination of UT1-UTC is on the order of a few minutes, thus we can talk about an ultra-rapid determination of UT1-UTC. An offline version of this strategy was adopted in 2009 for the regular VLBI intensive series INT-2, organized by the International VLBI Service for Geodesy and Astrometry (IVS), that involves Wettzell (Germany) and Tsukuba. Since March 2010 the INT-2 is using real-time e-transfer, too, and since June 2010 also automated analysis. Starting in 2009 the ultra-rapid approach was applied to regular 24 hour long IVS VLBI-sessions that involve Tsukuba and Onsala, so that ultra-rapid UT1-UTC results can be produced already during ongoing VLBI-sessions. This strategy was successfully operated during the 15 days long continuous VLBI campaigns CONT11 and CONT14. In this presentation we give an overview of the ultra-rapid concept, present the results derived during CONT11 and CONT14, and compare these ultra-rapid results to results derived from post-processing.

  7. Pharmacokinetic modelling of the haemodynamic effects of the A2a adenosine receptor agonist CGS 21680C in conscious normotensive rats.

    PubMed Central

    Mathôt, R A; Cleton, A; Soudijn, W; IJzerman, A P; Danhof, M

    1995-01-01

    1. The aim of the present investigation was to determine the relationship between the blood concentration and haemodynamic effects of the adenosine A2a receptor agonist, CGS 21680C (the sodium salt of 2-p-(2-carboxyethyl)phenylethylamino-5'-N-ethylcarboxamidoadeno sin e) in conscious normotensive rats. 2. Chronically cannulated rats were randomly assigned to three groups which received 300, 1000 or 3000 micrograms kg-1 (0.56, 1.9 or 5.6 mumol kg-1) of CGS 21680C intravenously over 15 min. The mean arterial blood pressure (MAP) and heart rate (HR) were monitored continuously during the experiment and serial arterial blood samples were taken for analysis of drug concentration. The ratio MAP/HR was also calculated, which may reflect changes in total peripheral resistance on the assumption that no changes in stroke volume occur. 3. For each individual rat the reduction in mean arterial pressure was related to the blood concentration according to the sigmoidal Emax model. The concentration-effect relationships were consistent for the different treatment groups. The potency based on free drug concentrations (EC50,u) was 5.8 ng ml-1 (11 nM) (mean +/- s.e.; n = 19) and correlated well with the reported adenosine A2a receptor affinity (Ki 19 nM). In comparison with the reduction in blood pressure, CGS 21680C exhibited a greater potency for the reduction of the ratio MAP/HR. 4. It is concluded that estimates can be obtained for the potency and intrinsic activity of adenosine A2a receptor agonists in vivo by pharmacokinetic-pharmacodynamic analysis of mean arterial pressure data in a rat model.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7773536

  8. Development of an e-VLBI Data Transport Software Suite with VDIF

    NASA Technical Reports Server (NTRS)

    Sekido, Mamoru; Takefuji, Kazuhiro; Kimura, Moritaka; Hobiger, Thomas; Kokado, Kensuke; Nozawa, Kentarou; Kurihara, Shinobu; Shinno, Takuya; Takahashi, Fujinobu

    2010-01-01

    We have developed a software library (KVTP-lib) for VLBI data transmission over the network with the VDIF (VLBI Data Interchange Format), which is the newly proposed standard VLBI data format designed for electronic data transfer over the network. The software package keeps the application layer (VDIF frame) and the transmission layer separate, so that each layer can be developed efficiently. The real-time VLBI data transmission tool sudp-send is an application tool based on the KVTP-lib library. sudp-send captures the VLBI data stream from the VSI-H interface with the K5/VSI PC-board and writes the data to file in standard Linux file format or transmits it to the network using the simple- UDP (SUDP) protocol. Another tool, sudp-recv , receives the data stream from the network and writes the data to file in a specific VLBI format (K5/VSSP, VDIF, or Mark 5B). This software system has been implemented on the Wettzell Tsukuba baseline; evaluation before operational employment is under way.

  9. Height bias and scale effect induced by antenna gravitational deformations in geodetic VLBI data analysis

    NASA Astrophysics Data System (ADS)

    Sarti, Pierguido; Abbondanza, Claudio; Petrov, Leonid; Negusini, Monia

    2011-01-01

    The impact of signal path variations (SPVs) caused by antenna gravitational deformations on geodetic very long baseline interferometry (VLBI) results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying these models in geodetic VLBI data analysis, estimates of the antenna reference point positions are shifted upward by 8.9 and 6.7 mm, respectively. The impact on other parameters is negligible. To simulate the impact of antenna gravitational deformations on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for other antennas according to their size. The effects of the simulations are changes in VLBI heights in the range [-3, 73] mm and a net scale increase of 0.3-0.8 ppb. The height bias is larger than random errors of VLBI position estimates, implying the possibility of significant scale distortions related to antenna gravitational deformations. This demonstrates the need to precisely measure gravitational deformations of other VLBI telescopes, to derive their precise SPV models and to apply them in routine geodetic data analysis.

  10. Relative deformation rates of collocated VLBI stations and comparisons with global solutions

    NASA Astrophysics Data System (ADS)

    Yang, Zhi-gen; Berube, M.; Searle, A.

    2005-07-01

    Based on the 3-dimensional velocity vectors of VLBI stations in the international terrestrial reference frame ITRF2000 and the earth's plate movement model NNR-NUVEL-1A and taking as constraints the observed rates of change of VLBI baseline lengths, we have estimated and discussed the local/regional crustal relative deformation between the stations in 6 collocated VLBI sites world-wide, and made comparisons with the VLBI global solution glb2003 and the result of VTRF2003. Our results indicate that between the collocated VLBI stations Kashima and Kashima34 of Japan and between the NRAO20 and NRAO85_3 stations of Unites States there probably exists a relative vertical deformation of ˜4mm/yr, that a ˜2 mm/yr difference between the vertical deformation rates of the Westford and Haystack stations is basically confirmed, and that there exists a relative vertical deformation rate of 1˜ mm/yr between the Kokee and Kauai stations. Our method seems to be effective for detecting local/regional crustal vertical deformation between collocated VLBI stations and for improving the ITRF solution.

  11. Development of Broadband VLBI System and its Application to T&F Transfer

    NASA Astrophysics Data System (ADS)

    Sekido, Mamoru; Takefuji, Kazuhiro; Ujihara, Hideki; Kondo, Tetsuro; Tsutsumi, Masanori; Miyauchi, Yuka; Kawai, Eiji; Takiguchi, Hiroshi; Hasegawa, Shingo; Ichikawa, Ryuichi; Hanado, Yuko; Koyama, Yasuhiro; Watabe, Ken-ichi; Suzuyama, Tomonari; Amemiya, Masaki; Fukuzaki, Yoshihiro; Komuro, Jun-ichi; Terada, Kenjiro; Namba, Kunitaka; Takahashi, Rumi; Okamoto, Yoshihiro; Ikeda, Takatoshi; Aoki, Tetsuo

    2015-08-01

    We are developing a new broadband VLBI system, named GALA-V, for frequency comparison. Atomic time standards connected to transportable small antennas are compared via broadband VLBI observation with large diameter antenna. Disadvantages of small antenna in sensitivity is compensated (1) by ten times wider frequency range of observation and (2) by joint observation with large diameter antenna. NICT has originally developed broadband feed system (6.5-15GHz) for Kashima 34m radio telescope. The system development and performance evaluation of the Gala-V system are being conducted at NICT (Koganei)- NMIJ (Tsukuba) baseline, where both NICT and NMIJ are institutes of maintaining their UTC.The broadband GALA-V system is designed to be compatible with the VGOS (VLBI2010 Global Observing System), which is the next generation geodetic VLBI system promoted by the IVS. We have successfully made the first VLBI observation between the new Ishioka 13m VGOS antenna of GSI and Kashima 34m antenna. Additionally super broadband VLBI observation over 8GHz bandwidth, and coherent signal synthesis for quite high delay resolution were achieved for the first time in the world. This paper will report recent progress of the broadband system development and results of frequency comparison experiments with the GALA-V system.

  12. VLBI-Gaia offsets favor parsec-scale jet direction in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Kovalev, Y. Y.; Petrov, L.; Plavin, A. V.

    2017-01-01

    Context. The data release 1 (DR1) of milliarcsecond-scale accurate optical positions of stars and galaxies was recently published by the space mission Gaia. Aims: We study the offsets of highly accurate absolute radio (very long baseline interferometry, VLBI) and optical positions of active galactic nuclei (AGN) to see whether or not a signature of wavelength-dependent parsec-scale structure can be seen. Methods: We analyzed VLBI and Gaia positions and determined the direction of jets in 2957 AGNs from their VLBI images. Results: We find that there is a statistically significant excess of sources with VLBI-to-Gaia position offset in directions along and opposite to the jet. Offsets along the jet vary from 0 to tens of mas. Offsets in the opposite direction do not exceed 3 mas. Conclusions: The presense of strong, extended parsec-scale optical jet structures in many AGNs is required to explain all observed VLBI-Gaia offsets along the jet direction. The offsets in the opposite direction shorter than 1 mas can be explained either by a non-point-like VLBI jet structure or a "core-shift" effect due to synchrotron opacity.

  13. On the potential of lunar observations in regular geodetic VLBI sessions

    NASA Astrophysics Data System (ADS)

    Klopotek, Grzegorz; Hobiger, Thomas; Haas, Rüdiger

    2017-04-01

    Artificial radio sources on the surface of the Moon enable us to observe lunar based transmitters with geodetic VLBI. Although during the last years a few dedicated VLBI experiments have already been carried out, the question still remains how and to what extend new information can be derived from observing such targets. Therefore, we perform Monte Carlo simulations using the c5++ software in order to evaluate how the inclusion of lunar observations into regular VLBI schedules would impact classical Earth-related target parameters of geodetic VLBI such as station coordinates and Earth Orientation Parameters, as well as how it would extend the possibilities to determine selenoidic parameters. Our study is based on modified IVS-R1 observing schedules, originally created by the International VLBI Service for Geodesy and Astrometry (IVS) to determine Earth Orientation Parameters, thus representing state-of-the-art VLBI observing programs. Based on our simulations, we demonstrate that an artificial radio source on the surface of the Moon can be located with both, accuracy and precision of better than 50 cm when observed along with quasars in the regular IVS-R1 session schedules. Moreover, we show that geodetic VLBI has the potential to improve our knowledge of lunar physical models and/or help to verify or update lunar ephemerides. We will discuss how the quality and quantity of lunar observations affect the uncertainty of the position of a non-moving artificial radio source located on the surface of the Moon and we highlight the factors limiting the determination of its position. Furthermore, we will reveal the impact of Moon VLBI observations on the determination of the Earth Orientation Parameters and VLBI station positions. We will also test the concept of VLBI lunar observations with simulations that reflect VGOS performance in terms of observation precision, number of scans and future network configurations. Thus, our simulations will provide valuable insights

  14. Detection of IR enhancement and evidence of disk formation around the Be star from SAX J2103.5+4545/ CGS 03588-00834

    NASA Astrophysics Data System (ADS)

    Camero-Arranz, A.; Nespoli, E.; Gutierrez-Soto, J.; Zurita, C.

    2012-06-01

    We report on recent IR observations of the Be/X-ray binary system SAX J2103.5+4545/ CGS 03588-00834, obtained with the 1.52 m Carlos Sánchez Telescope (Observatorio de Izaña, Tenerife, Spain), and on the evolution of the H-alpha equivalent width for this system measured with the spectrograph Albireo, at the 1.5 m telescope of the Observatorio de Sierra Nevada (Granada, Spain). Observations from 2011 December 26 up to 2012 June 10 showed and IR enhancement of the optical counterpart CGS 03588-00834, with the brightness varying from J = 11.90 +/- 0.05 mag, H = 11.51 +/- 0.06 mag and Ks = 11.33 +/- 0.08 mag (MJD 55921.0), to J = 11.02 +/- 0.06 mag, H = 10.61 +/- 0.03 mag and Ks = 10.3 +/- 0.1 mag (MJD 56088.0).

  15. VLBI observations of flared optical quasar CGRaBS J0809+5341

    NASA Astrophysics Data System (ADS)

    An, Tao; Cui, Yu-Zhu; Paragi, Zsolt; Frey, Sándor; Gurvits, Leonid I.; Gabányi, Krisztina É.

    2016-10-01

    A bright optical flare was detected in the high-redshift (z = 2.133) quasar CGRaBS J0809+5341 on 2014 April 13. The absolute magnitude of the object reached -30.0 during the flare, making it the brightest one (in flaring stage) among all known quasars so far. The 15-GHz flux density of CGRaBS J0809+5341 monitored in the period from 2008 to 2016 also reached its peak at the same time. To reveal any structural change possibly associated with the flare in the innermost radio structure of the quasar, we conducted a pilot very long baseline interferometry (VLBI) observation of CGRaBS J0809+5341 using the European VLBI Network (EVN) at 5 GHz on 2014 November 18, about seven months after the prominent optical flare. Three epochs of follow-up KaVA (Korean VLBI Network and VLBI Exploration of Radio Astrometry Array) observations were carried out at 22- and 43-GHz frequencies from 2015 February 25 to June 4, with the intention of exploring a possibly emerging new radio jet component associated with the optical flare. However, these high-resolution VLBI observations revealed only the milliarcsecond-scale compact "core" that was known in the quasar from earlier VLBI images, and showed no sign of any extended jet structure. Neither the size nor the flux density of the "core" changed considerably after the flare, according to our VLBI monitoring. The results suggest that any putative radio ejecta associated with the major optical and radio flare could not yet be separated from the "core" component, or the newly-born jet was short-lived.

  16. VLBI-derived troposphere parameters during CONT08

    NASA Astrophysics Data System (ADS)

    Heinkelmann, R.; Böhm, J.; Bolotin, S.; Engelhardt, G.; Haas, R.; Lanotte, R.; MacMillan, D. S.; Negusini, M.; Skurikhina, E.; Titov, O.; Schuh, H.

    2011-07-01

    Time-series of zenith wet and total troposphere delays as well as north and east gradients are compared, and zenith total delays ( ZTD) are combined on the level of parameter estimates. Input data sets are provided by ten Analysis Centers (ACs) of the International VLBI Service for Geodesy and Astrometry (IVS) for the CONT08 campaign (12-26 August 2008). The inconsistent usage of meteorological data and models, such as mapping functions, causes systematics among the ACs, and differing parameterizations and constraints add noise to the troposphere parameter estimates. The empirical standard deviation of ZTD among the ACs with regard to an unweighted mean is 4.6 mm. The ratio of the analysis noise to the observation noise assessed by the operator/software impact (OSI) model is about 2.5. These and other effects have to be accounted for to improve the intra-technique combination of VLBI-derived troposphere parameters. While the largest systematics caused by inconsistent usage of meteorological data can be avoided and the application of different mapping functions can be considered by applying empirical corrections, the noise has to be modeled in the stochastic model of intra-technique combination. The application of different stochastic models shows no significant effects on the combined parameters but results in different mean formal errors: the mean formal errors of the combined ZTD are 2.3 mm (unweighted), 4.4 mm (diagonal), 8.6 mm [variance component (VC) estimation], and 8.6 mm (operator/software impact, OSI). On the one hand, the OSI model, i.e. the inclusion of off-diagonal elements in the cofactor-matrix, considers the reapplication of observations yielding a factor of about two for mean formal errors as compared to the diagonal approach. On the other hand, the combination based on VC estimation shows large differences among the VCs and exhibits a comparable scaling of formal errors. Thus, for the combination of troposphere parameters a combination of the two

  17. Comparison of GNSS (EUREF) and VLBI (EVGA) tropospheric delays

    NASA Astrophysics Data System (ADS)

    Heinkelmann, Robert; Söhne, Wolfgang; Schuh, Harald

    2013-04-01

    The troposphere is the main contributor of noise and systematic errors in the analysis of space-geodetic techniques at radio frequencies, such as GNSS and VLBI. Nevertheless, if sufficiently understood, the troposphere may provide a common parameter space for the combined analysis and may thus play an important role for the International Association of Geodesy's (IAG) Global Geodetic Observing System (GGOS). With tropospheric parameters we denote the group of parameters associated with the modeling of the dry and wet constituents of the non-dispersive atmosphere, namely tropospheric delays and tropospheric gradients. Among those parameters, tropospheric delays have been used to measure and model atmospheric water vapor, a key parameter of the greenhouse effect and a driving factor for various climate feedback mechanisms, which is usually insufficiently observed by other meteorological techniques. Besides climate implications, the tropospheric delays provide a valuable basis for checking the consistency of individual contributions to a combined product (intra- as well as inter-technique-related). Various authors have determined and compared tropospheric delays among the space-geodetic techniques, but remaining discrepancies could not yet be completely assessed and explained. Our investigations are concerned with a closer look on the tropospheric delays obtained at European stations, which are associated with the European Reference Frame (EUREF) and the European part of the International Very Long Baseline Interferometry Service for Geodesy and Astrometry (IVS), called European VLBI Group for Geodesy and Astrometry (EVGA). Since 2012, time series of differences between the EUREF combined solution and the IVS combined solution are displayed on the EUREF Permanent Network's (EPN) webpage for nine stations at co-located sites (http://www.epncb.oma.be), covering the period from 1996 to present. Having in mind that interpolation due to different sampling rates is applied

  18. A Small-Radio-Telescope Network for VLBI

    NASA Astrophysics Data System (ADS)

    Shaffer, D. B.; Cobb, M. L.

    2004-12-01

    In the last several years, high schools, colleges, universities, and even some private amateur radio astronomers have put some 120 copies of the commercially-available Haystack Small Radio Telescope (SRT) into operation. Haystack Observatory is now working on a new version of the SRT, designed to be used in an interferometer (see paper by Vats and Rogers, this conference). We show how the new SRT, or other similar small radio telescopes, could be adapted for educational and scientific VLBI observations of continuum and OH line sources, with a relatively small additional investment. We propose that one or more large radio telescopes join a network of the small antennas, so that fringes would be readily detected between the large antenna(s) and the small antennas. An 85-foot antenna such as those at PARI or the 40-meter antenna of the Owens Valley Radio Observatory would serve nicely as a base station. Eventually, as data storage and transmission capacity continue to improve, the small antennas should be able to operate on their own. Our emphasis is on a simple, inexpensive VLBI system. The most critical item is good frequency standard. For observations at 21 or 18 cm, a rubidium standard is good enough. (Inexpensive Rb standards can be found on E-bay!) Local time at each station would come from GPS receivers which readily provide sub-microsecond timing accuracy. One-bit data sampling at rates on the order of 10 megasamples per second could be performed with a simple box interfaced to a PC via USB. Sampled data would first be recorded to the PC hard drive, and then sent on CD-ROM or DVD through the mail or by internet to a central correlation facility. Correlation and data analysis for the network would be performed on PCs as well. We suggest an observing scenario comprised of scans that are several minutes long and taken several times per hour during the apparition of a compact source. The total data for the 10-12 hours that a source is "up" for a USA network would

  19. Proceedings of the 6th European VLBI Network Symposium

    NASA Astrophysics Data System (ADS)

    Ros, Eduardo; Porcas, Richard W.; Lobanov, Andrei P.; Zensus, J. Anton

    This volume contains the papers presented at the 6th Symposium of the European VLBI Network, held in Bonn on 25-28 June 2002. The initial aim of these biennial gatherings of European VLBI practitioners was to review in a timely manner new results and technical developments related to Very Long Baseline Interferometry. Now, however, interest and participation in the EVN Symposia reaches far beyond Europe, reflecting the fact that scientific research and development programs are carried out to a high degree in international and often truly global collaborations. More than 120 scientists from around the world registered for participation in the Symposium. The Symposium was hosted by the Max-Planck-Institut für Radioastronomie and was held at the Gustav Stresemann Institut. In addition to the scientific sessions and poster presentations, the program included an EVN Users Meeting, an MPIfR versus Rest-of-the-World football match (highly appropriate given the competing World Cup event!), a visit to the MPIfR's 100m radio telescope in Effelsberg, and a Conference Dinner held in the nearby old walled town of Bad Müunstereifel. To maximize the usefulness of these proceedings (and possibly as a daring precedent) the Editors decided to demand the written versions of talks and posters and to complete the editorial work before the meeting, and to deliver the book to the participants at the beginning of the Symposium. We thank the authors for their cooperation in delivering publication-ready electronic manuscripts and for meeting the strict deadlines. It is highly gratifying that only a handful of the 100 presentations are not represented in this volume. The editors have made minor changes to some of the contributions in order to improve readability, and take responsibility for any errors arising from these changes. Besides the authors, many individuals have contributed to the preparation of the meeting and its proceedings. In addition to many members of the MPIfR staff, we

  20. Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters?

    NASA Astrophysics Data System (ADS)

    Ray, Jim; Kouba, Jan; Altamimi, Zuheir

    2005-12-01

    Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame, the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper on co-location ties (Ray and Altamimi in J Geod 79(4-5): 189-195, 2005), we have studied test combinations of very long baseline interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and

  1. Tidal Love and Shida numbers estimated by geodetic VLBI.

    PubMed

    Krásná, Hana; Böhm, Johannes; Schuh, Harald

    2013-10-01

    Frequency-dependent Love and Shida numbers, which characterize the Earth response to the tidal forces, were estimated in a global adjustment of all suitable geodetic Very Long Baseline Interferometry (VLBI) sessions from 1984.0 to 2011.0. Several solutions were carried out to determine the Love and Shida numbers for the tidal constituents at periods in the diurnal band and in the long-period band in addition to values of the Love and Shida numbers common for all tides of degree two. Adding up all twelve diurnal tidal waves that were estimated, the total differences in displacement with respect to the theoretical conventional values of the Love and Shida numbers calculated from an Earth model reach 1.73 ± 0.29 mm in radial direction and 1.15 ± 0.15 mm in the transverse plane. The difference in the radial deformation following from the estimates of the zonal Love numbers is largest for the semi-annual tide Ssa with 1.07 ± 0.19 mm.

  2. The Software Correlator of the Chinese VLBI Network

    NASA Technical Reports Server (NTRS)

    Zheng, Weimin; Quan, Ying; Shu, Fengchun; Chen, Zhong; Chen, Shanshan; Wang, Weihua; Wang, Guangli

    2010-01-01

    The software correlator of the Chinese VLBI Network (CVN) has played an irreplaceable role in the CVN routine data processing, e.g., in the Chinese lunar exploration project. This correlator will be upgraded to process geodetic and astronomical observation data. In the future, with several new stations joining the network, CVN will carry out crustal movement observations, quick UT1 measurements, astrophysical observations, and deep space exploration activities. For the geodetic or astronomical observations, we need a wide-band 10-station correlator. For spacecraft tracking, a realtime and highly reliable correlator is essential. To meet the scientific and navigation requirements of CVN, two parallel software correlators in the multiprocessor environments are under development. A high speed, 10-station prototype correlator using the mixed Pthreads and MPI (Massage Passing Interface) parallel algorithm on a computer cluster platform is being developed. Another real-time software correlator for spacecraft tracking adopts the thread-parallel technology, and it runs on the SMP (Symmetric Multiple Processor) servers. Both correlators have the characteristic of flexible structure and scalability.

  3. International VLBI Service for Geodesy and Astrometry: General Meeting Proceedings

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

    2002-01-01

    This volume contains the proceedings of the second General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), held in Tsukuba, Japan, February 4-7, 2002. The contents of this volume also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/gm2002. The key-note of the second GM was prospectives for the future, in keeping with the re-organization of the IAG around the motivation of geodesy as 'an old science with a dynamic future' and noting that providing reference frames for Earth system science that are consistent over decades on the highest accuracy level will provide a challenging role for IVS. The goal of the meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts. This volume contains 72 papers and five abstracts of papers presented at the GM. The volume also includes reports about three splinter meetings held in conjunction with the GM: a mini-TOW (Technical Operations Workshop), the third IVS Analysis Workshop and a meeting of the analysis working group on geophysical modeling.

  4. Digital Front End for Wide-Band VLBI Science Receiver

    NASA Technical Reports Server (NTRS)

    Jongeling, Andre; Sigman, Elliott; Navarro, Robert; Goodhart, Charles; Rogstad, Steve; Chandra, Kumar; Finley, Sue; Trinh, Joseph; Soriano, Melissa; White, Les; hide

    2006-01-01

    An upgrade to the very-long-baseline-interferometry (VLBI) science receiver (VSR) a radio receiver used in NASA's Deep Space Network (DSN) is currently being implemented. The current VSR samples standard DSN intermediate- frequency (IF) signals at 256 MHz and after digital down-conversion records data from up to four 16-MHz baseband channels. Currently, IF signals are limited to the 265-to-375-MHz range, and recording rates are limited to less than 80 Mbps. The new digital front end, denoted the Wideband VSR, provides improvements to enable the receiver to process wider bandwidth signals and accommodate more data channels for recording. The Wideband VSR utilizes state-of-the-art commercial analog-to-digital converter and field-programmable gate array (FPGA) integrated circuits, and fiber-optic connections in a custom architecture. It accepts IF signals from 100 to 600 MHz, sampling the signal at 1.28 GHz. The sample data are sent to a digital processing module, using a fiber-optic link for isolation. The digital processing module includes boards designed around an Advanced Telecom Computing Architecture (ATCA) industry-standard backplane. Digital signal processing implemented in FPGAs down-convert the data signals in up to 16 baseband channels with programmable bandwidths from 1 kHz to 16 MHz. Baseband samples are transmitted to a computer via multiple Ethernet connections allowing recording to disk at rates of up to 1 Gbps.

  5. Chandra HETGS and VLBI Observations of SS 433

    NASA Astrophysics Data System (ADS)

    Marshall, Herman L.; Roberts, David H.; Schulz, Norbert S.

    2017-01-01

    In a previous Chandra High Energy Transmission Grating Spectrometer (HETGS) observations of SS 433, we found a large Doppler shift change on a time scale of 20 ks, a time much shorter than the known dynamical times. The rapid change could be related to the formation and ejection of a jet knot, as observed in VLBI observations, perhaps as a leptonic jet impinges on a disk wind and shock heats it. New data were obtained to test this model in a long continuous HETGS observation. The VLBA and Chandra HETGS data were obtained but while no radio ejections were observed during the Chandra observation, there were interesting aspects to the observations. First, although the jet emission lines were expected to vary with the usual precession period (162 days) or with the period of the nodding motion (6.6 days), we did not detect the expected Doppler shifts in over 120 ks of exposure. Furthermore, there is new evidence for jet curvature that has not been previously reported.Support for this work was provided in part by the National Aeronautics and Space Administration (NASA) through the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 to MIT for support of the Chandra X-Ray Center (CXC), which is operated by SAO for and on behalf of NASA under contract NAS8-03060. Support was also provided by NASA under grant GO4-15040A to MIT.

  6. Prospects for UT1 Measurements from VLBI Intensive Sessions

    NASA Technical Reports Server (NTRS)

    Boehm, Johannes; Nilsson, Tobias; Schuh, Harald

    2010-01-01

    Very Long Baseline Interferometry (VLBI) Intensives are one-hour single baseline sessions to provide Universal Time (UT1) in near real-time up to a delay of three days if a site is not e-transferring the observational data. Due to the importance of UT1 estimates for the prediction of Earth orientation parameters, as well as any kind of navigation on Earth or in space, there is not only the need to improve the timeliness of the results but also their accuracy. We identify the asymmetry of the tropospheric delays as the major error source, and we provide two strategies to improve the results, in particular of those Intensives which include the station Tsukuba in Japan with its large tropospheric variation. We find an improvement when (1) using ray-traced delays from a numerical weather model, and (2) when estimating tropospheric gradients within the analysis of Intensive sessions. The improvement is shown in terms of reduction of rms of length-of-day estimates w.r.t. those derived from Global Positioning System observations

  7. A VLBI Resolution of the Pleiades Distance Controversy

    NASA Astrophysics Data System (ADS)

    Melis, Carl; Reid, Mark J.; Mioduszewski, Amy J.; Stauffer, John R.; Bower, Geoffrey C.

    2015-01-01

    The Pleiades is the best studied open cluster in the sky. It is one of the primary open clusters used to define the 'Zero Age Main Sequence' and hence it serves as a cornerstone for programs which use main-sequence fitting to derive distances to other clusters in the Milky Way Galaxy. This role is called into question by the 'Pleiades distance controversy' - the distance to the Pleiades from the Hipparcos space astrometry mission of about 120 pc is significantly different from the distance of 133 pc derived from other techniques. In order to resolve this issue, the Very Long Baseline Array combined with the Green Bank, Effelsberg, and Arecibo telescopes are being used to derive a new, independent trigonometric parallax distance to the Pleiades. From four Pleiades systems we find a distance of 136.2+/-1.2 pc, the most accurate and precise distance to the cluster yet measured. In this contribution we present preliminary parallaxes for the remaining four Pleiades systems not published in Melis et al. (2014, Science 345, 1029). Additionally, binary orbit model fits and preliminary stellar masses are presented for two multiple systems in our sample with significant orbital motion observed during our VLBI monitoring.Funding for this research came from the NSF through awards No. AST-1003318 and No. AST-1313428.

  8. Gamma-Ray Flares and VLBI Outbursts of Blazars

    NASA Astrophysics Data System (ADS)

    Romanova, M. M.; Lovelace, R. V. E.

    1997-01-01

    A model is developed for the time dependent electromagnetic--radio to gamma-ray--emission of active galactic nuclei, specifically, the blazars, based on the acceleration and creation of leptons at a propagating discontinuity or front of a self-collimated Poynting flux jet. The front corresponds to a discrete relativistic jet component as observed with very long baseline interferometry (VLBI). Equations are derived for the number, momentum, and energy of particles in the front taking into account synchrotron, synchrotron-self-Compton (SSC), and inverse-Compton processes as well as photon-photon pair production. The apparent synchrotron, SSC, and inverse Compton luminosities as functions of time are determined. Predictions of the model are compared with observations in the gamma, optical, and radio bands. The delay between the high-energy gamma-ray flare and the onset of the radio is explained by self-absorption and/or free-free absorption by external plasma. Two types of gamma-ray flares are predicted: Compton dominated or SSC dominated, depending on the initial parameters in the front. The theory is applied to the recently observed gamma-ray flare of the blazar PKS 1622-297 (Mattox et al. 1997). Approximate agreement of theoretical and observed light curves is obtained for a viewing angle θobs ~ 0.1 rad, a black hole mass M ~ 3 × 109 M⊙, and a magnetic field at the base of the jet B0 ~ 103 G.

  9. A Global Terrestrial Reference Frame from simulated VLBI and SLR data in view of GGOS

    NASA Astrophysics Data System (ADS)

    Glaser, Susanne; König, Rolf; Ampatzidis, Dimitrios; Nilsson, Tobias; Heinkelmann, Robert; Flechtner, Frank; Schuh, Harald

    2017-07-01

    In this study, we assess the impact of two combination strategies, namely local ties (LT) and global ties (GT), on the datum realization of Global Terrestrial Reference Frames in view of the Global Geodetic Observing System requiring 1 mm-accuracy. Simulated Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data over a 7 year time span was used. The LT results show that the geodetic datum can be best transferred if the precision of the LT is at least 1 mm. Investigating different numbers of LT, the lack of co-located sites on the southern hemisphere is evidenced by differences of 9 mm in translation and rotation compared to the solution using all available LT. For the GT, the combination applying all Earth rotation parameters (ERP), such as pole coordinates and UT1-UTC, indicates that the rotation around the Z axis cannot be adequately transferred from VLBI to SLR within the combination. Applying exclusively the pole coordinates as GT, we show that the datum can be transferred with mm-accuracy within the combination. Furthermore, adding artificial stations in Tahiti and Nigeria to the current VLBI network results in an improvement in station positions by 13 and 12%, respectively, and in ERP by 17 and 11%, respectively. Extending to every day VLBI observations leads to 65% better ERP estimates compared to usual twice-weekly VLBI observations.

  10. Analysis of Differences Between VLBI, GNSS and SLR Earth Orientation Series

    NASA Astrophysics Data System (ADS)

    MacMillan, D. S.; Pavlis, E. C.; Griffiths, J.

    2016-12-01

    We have compared polar motion series from VLBI, GNSS, and SLR where the reference frames were aligned to ITRF2008. Three objectives of the comparisons are 1) to determine biases between the techniques and 2) to determine the precisions of each technique via a 3-corner hat analysis after removing the relative biases, and 3) to evaluate the long-term stability of EOP series. Between VLBI and GPS or SLR, there are clear annual variations ranging from 25 to 100 µas in peak-to-peak amplitude. We investigate the possible causes of these variations. In addition, there are other apparent systematic bias and rate differences. From the point of view of VLBI, it is evident that there are VLBI network dependent effects, specifically between the operational R1 and R4 weekly 24-hour sessions. We investigate the origins of these differences including network station changes in these networks over the period from 2002-present. The EOP biases and precisions of the five IVS VLBI CONT campaigns (since 2002) are also analyzed since these sessions were each designed to provide the highest quality results that could be produced at the time. A possible source of biases between the geodetic techniques is the underlying reference frame used by each technique. We also consider the technique differences when ITRF2014 was applied instead of ITRF2008.

  11. Application of Geodetic VLBI Data to Obtaining Long-Term Light Curves for Astrophysics

    NASA Technical Reports Server (NTRS)

    Kijima, Masachika

    2010-01-01

    The long-term light curve is important to research on binary black holes and disk instability in AGNs. The light curves have been drawn mainly using single dish data provided by the University of Michigan Radio Observatory and the Metsahovi Radio Observatory. Hence, thus far, we have to research on limited sources. I attempt to draw light curves using VLBI data for those sources that have not been monitored by any observatories with single dish. I developed software, analyzed all geodetic VLBI data available at the IVS Data Centers, and drew the light curves at 8 GHz. In this report, I show the tentative results for two AGNs. I compared two light curves of 4C39.25, which were drawn based on single dish data and on VLBI data. I confirmed that the two light curves were consistent. Furthermore, I succeeded in drawing the light curve of 0454-234 with VLBI data, which has not been monitored by any observatory with single dish. In this report, I suggest that the geodetic VLBI archive data is useful to obtain the long-term light curves at radio bands for astrophysics.

  12. Status and plans for the future of the Vienna VLBI Software

    NASA Astrophysics Data System (ADS)

    Madzak, Matthias; Böhm, Johannes; Böhm, Sigrid; Girdiuk, Anastasiia; Hellerschmied, Andreas; Hofmeister, Armin; Krasna, Hana; Kwak, Younghee; Landskron, Daniel; Mayer, David; McCallum, Jamie; Plank, Lucia; Schönberger, Caroline; Shabala, Stanislav; Sun, Jing; Teke, Kamil

    2016-04-01

    The Vienna VLBI Software (VieVS) is a VLBI analysis software developed and maintained at Technische Universität Wien (TU Wien) since 2008 with contributions from groups all over the world. It is used for both academic purposes in university courses as well as for providing VLBI analysis results to the geodetic community. Written in a modular structure in Matlab, VieVS offers easy access to the source code and the possibility to adapt the programs for particular purposes. The new version 2.3, released in December 2015, includes several new parameters to be estimated in the global solution, such as tidal ERP variation coefficients. The graphical user interface was slightly modified for an improved user functionality and, e.g., the possibility of deriving baseline length repeatabilities. The scheduling of satellite observations was refined, the simulator newly includes the effect of source structure which can also be corrected for in the analysis. This poster gives an overview of all VLBI-related activities in Vienna and provides an outlook to future plans concerning the Vienna VLBI Software.

  13. Control System and Visualization of the VLBI Hardware Correlator at SHAO

    NASA Astrophysics Data System (ADS)

    Guo, Shaoguang; Xu, Zhijun; Gan, Jiangying; Zhang, Xiuzhong; Zhu, Renjie; Wu, Yajun; Xiang, Ying

    2014-12-01

    The VLBI system is comprised of VLBI stations, data preprocessing, correlator, post-correlator, SKD, orbit, location, and so on. The corrlator processor is the core equipment of the VLBI data preprocessing device; we can calculate important parameters such as the delay, delay rate, correlation amplitude, and interferometric phase from the correlator. Now our group has realized a complete software control system and an FPGA core for the hardware correlator on a CPCI board through the playback interface. We have also achieved the visualization of the processing data for convenience and the C/S architecture for controlling the PBI interface. In the future, our group will port the whole system to the Uniboard board--for speed improvement and supporting more modes. Recently, the real-time mode and post-correlation were tested during the CE-3 mission. The result was also checked to make sure our hardware correlator is fine. This paper describes the whole control system and its realization.

  14. General Relativistic Theory of the VLBI Time Delay in the Gravitational Field of Moving Bodies

    NASA Technical Reports Server (NTRS)

    Kopeikin, Sergei

    2003-01-01

    The general relativistic theory of the gravitational VLBI experiment conducted on September 8, 2002 by Fomalont and Kopeikin is explained. Equations of radio waves (light) propagating from the quasar to the observer are integrated in the time-dependent gravitational field of the solar system by making use of either retarded or advanced solutions of the Einstein field equations. This mathematical technique separates explicitly the effects associated with the propagation of gravity from those associated with light in the integral expression for the relativistic VLBI time delay of light. We prove that the relativistic correction to the Shapiro time delay, discovered by Kopeikin (ApJ, 556, L1, 2001), changes sign if one retains direction of the light propagation but replaces the retarded for the advanced solution of the Einstein equations. Hence, this correction is associated with the propagation of gravity. The VLBI observation measured its speed, and that the retarded solution is the correct one.

  15. Proceedings of the Sixth General Meeting of the International VLBI Service for Geodesy and Astrometry

    NASA Technical Reports Server (NTRS)

    Behrend, Dirk (Editor); Baver, Karen D. (Editor)

    2010-01-01

    This volume is the proceedings of the sixth General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), held in Hobart, Tasmania, Australia, February 7-13, 2010. The contents of this volume also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/gm2010. The keynote of the sixth GM was the new perspectives of the next generation VLBI system under the theme "VLBI2010: From Vision to Reality". The goal of the meeting was to provide an interesting and informative program for a wide cross-section of IVS members, including station operators, program managers, and analysts. This volume contains 88 papers. All papers were edited by the editors for usage of the English language, form, and minor content-related issues.

  16. Acceleration Term at ASL FRING as a Tool to Improve Space VLBI Sensitivity

    NASA Astrophysics Data System (ADS)

    Kogan, L.; Likhachev, S.; Girin, I.; Ladygin, V.

    2009-08-01

    Astro Space Locator (ASL) a new postcorrelation software has been created recently in Astro Space Center (ASC), Russia. This software is created specifically for space VLBI project such as Radioastron and VSOP. The delay for the ground based VLBI traditionally comprised of two terms: initial delay and its rate of change in time. For space VLBI, taking into account the third term (acceleration) can be required because the satellite orbit may not be known with such a high accuracy as rotation of the Earth. The ASL software solves for all three parameters: delay, fringe rate, and acceleration. In this paper we test this algorithm and demonstrate the advantage of taking into account the acceleration term.

  17. Complex demodulation in VLBI estimation of high frequency Earth rotation components

    NASA Astrophysics Data System (ADS)

    Böhm, S.; Brzeziński, A.; Schuh, H.

    2012-12-01

    The spectrum of high frequency Earth rotation variations contains strong harmonic signal components mainly excited by ocean tides along with much weaker non-harmonic fluctuations driven by irregular processes like the diurnal thermal tides in the atmosphere and oceans. In order to properly investigate non-harmonic phenomena a representation in time domain is inevitable. We present a method, operating in time domain, which is easily applicable within Earth rotation estimation from Very Long Baseline Interferometry (VLBI). It enables the determination of diurnal and subdiurnal variations, and is still effective with merely diurnal parameter sampling. The features of complex demodulation are used in an extended parameterization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS. The functionality of the approach was evaluated by comparing amplitudes and phases of harmonic variations at tidal periods (diurnal/semidiurnal), derived from demodulated Earth rotation parameters (ERP), estimated from hourly resolved VLBI ERP time series and taken from a recently published VLBI ERP model to the terms of the conventional model for ocean tidal effects in Earth rotation recommended by the International Earth Rotation and Reference System Service (IERS). The three sets of tidal terms derived from VLBI observations extensively agree among each other within the three-sigma level of the demodulation approach, which is below 6 μas for polar motion and universal time. They also coincide in terms of differences to the IERS model, where significant deviations primarily for several major tidal terms are apparent. An additional spectral analysis of the as well estimated demodulated ERP series of the ter- and quarterdiurnal frequency bands did not reveal any significant signal structure. The complex demodulation applied in VLBI parameter estimation could be demonstrated a suitable procedure for the reliable reproduction of

  18. Indirect approach to invariant point determination for SLR and VLBI systems: an assessment

    NASA Astrophysics Data System (ADS)

    Dawson, John; Sarti, Pierguido; Johnston, Gary M.; Vittuari, Luca

    2007-06-01

    We assess the accuracy of some indirect approaches to invariant point (IVP), or system reference point, determination of satellite laser ranging (SLR) and very long baseline interferometry (VLBI) systems using both observed and simulated survey data sets. Indirect IVP determination involves the observation of targets located on these systems during specific rotational sequences and by application of geometrical models that describe the target motion during these sequences. Of concern is that most SLR and VLBI systems have limited rotational freedom thereby placing constraint on the reliability of parameter estimation, including the IVP position. We assess two current approaches to IVP analysis using survey data observed at the Yarragadee (Australia) SLR and the Medicina (Italy) VLBI sites and also simulated data of a large rotationally constrained (azimuth-elevation) VLBI system. To improve reliability we introduce and assess some new geometric conditions, including inter-axis, inter-circle and inter-target conditions, to existing IVP analysis strategies. The error component of a local tie specifically associated with the indirect determination of SLR and VLBI IVP is less than 0.5 mm. For systems with significant rotational limits we find that the inter-axis and inter-circle conditions are critical to the computation of unbiased IVP coordinates at the sub-millimetre level. When the inter-axis and inter-circle geometric conditions are not imposed, we retrieve biased vertical coordinates of the IVP (in our simulated VLBI system) in the range of 1.2 3.4 mm. Using the new geometric conditions we also find that the axis-offset estimates can be recovered at the sub- millimetre accuracy (0.5 mm).

  19. EOP and scale from continuous VLBI observing: CONT campaigns to future VGOS networks

    NASA Astrophysics Data System (ADS)

    MacMillan, D. S.

    2017-07-01

    Continuous (CONT) VLBI campaigns have been carried out about every 3 years since 2002. The basic idea of these campaigns is to acquire state-of-the-art VLBI data over a continuous time period of about 2 weeks to demonstrate the highest accuracy of which the current VLBI system is capable. In addition, these campaigns support scientific studies such as investigations of high-resolution Earth rotation, reference frame stability, and daily to sub-daily site motions. The size of the CONT networks and the observing data rate have increased steadily since 1994. Performance of these networks based on reference frame scale precision and polar motion/LOD comparison with global navigation satellite system (GNSS) earth orientation parameters (EOP) has been substantially better than the weekly operational R1 and R4 series. The precisions of CONT EOP and scale have improved by more than a factor of two since 2002. Polar motion precision based on the WRMS difference between VLBI and GNSS for the most recent CONT campaigns is at the 30 μas level, which is comparable to that of GNSS. The CONT campaigns are a natural precursor to the planned future VLBI observing networks, which are expected to observe continuously. We compare the performance of the most recent CONT campaigns in 2011 and 2014 with the expected performance of the future VLBI global observing system network using simulations. These simulations indicate that the expected future precision of scale and EOP will be at least 3 times better than the current CONT precision.

  20. EOP and scale from continuous VLBI observing: CONT campaigns to future VGOS networks

    NASA Astrophysics Data System (ADS)

    MacMillan, D. S.

    2017-02-01

    Continuous (CONT) VLBI campaigns have been carried out about every 3 years since 2002. The basic idea of these campaigns is to acquire state-of-the-art VLBI data over a continuous time period of about 2 weeks to demonstrate the highest accuracy of which the current VLBI system is capable. In addition, these campaigns support scientific studies such as investigations of high-resolution Earth rotation, reference frame stability, and daily to sub-daily site motions. The size of the CONT networks and the observing data rate have increased steadily since 1994. Performance of these networks based on reference frame scale precision and polar motion/LOD comparison with global navigation satellite system (GNSS) earth orientation parameters (EOP) has been substantially better than the weekly operational R1 and R4 series. The precisions of CONT EOP and scale have improved by more than a factor of two since 2002. Polar motion precision based on the WRMS difference between VLBI and GNSS for the most recent CONT campaigns is at the 30 μ as level, which is comparable to that of GNSS. The CONT campaigns are a natural precursor to the planned future VLBI observing networks, which are expected to observe continuously. We compare the performance of the most recent CONT campaigns in 2011 and 2014 with the expected performance of the future VLBI global observing system network using simulations. These simulations indicate that the expected future precision of scale and EOP will be at least 3 times better than the current CONT precision.

  1. Opposite effects of the A2A receptor agonist CGS21680 in the striatum of Huntington's disease versus wild-type mice.

    PubMed

    Martire, Alberto; Calamandrei, Gemma; Felici, Fabio; Scattoni, Maria Luisa; Lastoria, Giusi; Domenici, Maria Rosaria; Tebano, Maria Teresa; Popoli, Patrizia

    2007-04-24

    Huntington's disease (HD) is an inherited neurodegenerative disorder. Adenosine A(2A) receptors (A(2A)Rs) are involved in excitotoxic/neurodegenerative processes, and A(2A)R ligands may be neuroprotective in models of HD. However, changes in the transcription, expression and function of A(2A)Rs have been reported to occur in HD models. The aim of the present work was to verify whether A(2A)R-mediated effects are altered in the striatum of transgenic HD (R6/2) versus wild-type (WT) mice. Extracellular field potentials (FPs) were recorded in corticostriatal slices from R6/2 mice in early (7-8 weeks) or frankly (12-13 weeks) symptomatic phases, and age-matched WT. In 12-13 weeks aged WT animals, the application of 75 microM NMDA induced a transient disappearance of the FP followed by an almost complete recovery at washout. In slices from HD mice, the mean FP recovery was significantly reduced (P<0.01 versus WT). A(2A)R activation oppositely modulated NMDA-induced toxicity in the striatum of HD versus WT mice. Indeed, the A(2A)R agonist CGS21680 reduced the FP recovery in slices from WT mice, while it significantly increased it in slices from R6/2 mice. In early symptomatic (7-8 weeks) mice, no differences were observed between WT and HD animals in terms of basal synaptic transmission and response to NMDA. At the same age, the behavioural effects elicited by CGS21680 were qualitatively identical in WT and HD mice. These findings may have very important implications for the neuroprotective potential of A(2A)R ligands in HD.

  2. A Kalman filter for combining high frequency Earth rotation parameters from VLBI and GNSS

    NASA Astrophysics Data System (ADS)

    Nilsson, T.; Karbon, M.; Schuh, H.

    2013-08-01

    We present a Kalman filter for combination of sub-diurnal Earth Rotation Parameters (ERP) estimated from different techniques. We test this filter by combining ERP estimated from VLBI and GPS for the CONT08 campaign. We find that the Kalman filter works and give reasonable results. The combined solution is dominated by the GPS data since the ERP from this technique have much lower formal errors. However VLBI is important for providing the absolute value of dUT1 since GPS is only sensitive to the time derivative of dUT1, i.e. the length of day.

  3. Crustal dynamics project data analysis, 1988: VLBI geodetic results, 1979 - 1987

    NASA Technical Reports Server (NTRS)

    Ma, C.; Ryan, J. W.; Caprette, D.

    1989-01-01

    The results obtained by the Goddard VLBI (very long base interferometry) Data Analysis Team from the analysis of 712 Mark 3 VLBI geodetic data sets acquired from fixed and mobile observing sites through the end of 1987 are reported. A large solution, GLB401, was used to obtain earth rotation parameters and site velocities. A second large solution, GLB405, was used to obtain baseline evolutions. Radio source positions were estimated globally while nutation offsets were estimated from each data set. Site positions are tabulated on a yearly basis from 1979 through 1988. The results include 55 sites and 270 baselines.

  4. EVN e-VLBI detections of MAXI J1659-152

    NASA Astrophysics Data System (ADS)

    Paragi, Z.; van der Horst, A. J.; Granot, J.; Taylor, G. B.; Kouveliotou, C.; Garrett, M. A.; Wijers, R. A. M. J.; Ramirez-Ruiz, E.; Kuulkers, E.; Gehrels, N.; Woods, P. M.

    2010-10-01

    We observed MAXI J1659-152 (Negoro et al. 2010, ATel #2873; Mangano et al. 2010, GCN #11296) following its sub-millimeter and centimeter radio detections (de Ugarte Postigo et al. 2010, GCN #11304; van der Horst et al. 2010, ATel #2874) with the European VLBI Network (EVN) in real-time e-VLBI mode on 30 September 2010, from 13:30 to 18:30 UT at 4.9 GHz. The participating telescopes were Cambridge, Effelsberg, Jodrell Bank (MkII), Hartebeesthoek, Medicina, Onsala, Torun and Westerbork sending data at a rate of ~1024 Mbps to the EVN Data Processor at JIVE.

  5. Postseismic Transient after the 2002 Denali Fault Earthquake from VLBI Measurements at Fairbanks

    NASA Technical Reports Server (NTRS)

    MacMillan, Daniel; Cohen, Steven

    2004-01-01

    The VLBI antenna (GILCREEK) at Fairbanks, Alaska observes in networks routinely twice a week with operational networks and on additional days with other networks on a more uneven basis. The Fairbanks antenna position is about 150 km north of the Denali fault and from the earthquake epicenter. We examine the transient behavior of the estimated VLBI position during the year following the earthquake to determine how the rate of change of postseismic deformation has changed. This is compared with what is seen in the GPS site position series.

  6. Arcsecond positions for milliarcsecond VLBI nuclei of extragalactic radio sources. III - 74 sources

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Preston, R. A.; Linfield, R. P.; Slade, M. A.; Wehrle, A. E.; Faulkner, J.; Jauncey, D. L.

    1985-01-01

    VLBI measurements at 2290 and 8420 MHz on baselines of 10,000 km have been used to determine the positions of the milliarcsecond nuclei in 74 extragalactic radio sources. Estimated accuracies range from 0.1 to 4.3 arcsec in both right ascension and declination with typical accuracies of about 0.3 arcsec. The observed sources are part of an all-sky VLBI catalog of milliarcsecond radio sources. Arcsecond positions have been determined for 819 sources. These positions are presently being used to identify optical counterparts in the southern hemisphere.

  7. Arcsecond Positions for Milliarcsecond VLBI Nuclei of Extragalactic Radio Sources. Part 3: 74 Sources

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Preston, R. A.; Linfield, R. P.; Slade, M. A.; Wehrle, A. E.; Faulkner, J.; Jauncey, D. L.

    1985-01-01

    VLBI measurements at 2290 MHz and 8420 MHz on baselines of 10,000 km between Deep Space Network stations have been used to determine the positions of the milliarcsecond nuclei in 74 extragalactic radio sources. Estimated accuracies range from 0.1 sec. to 4, 3 sec. in both right ascension and declination with typical accuracies of approx. 0.3 sec. The observed sources are part of an all-sky VLBI catalog of milliarcsecond radio sources. Arcsecond positions have now been determined for 819 sources. These positions are presently being used to identify optical counterparts in the Southern Hemisphere.

  8. Arcsecond positions for milliarcsecond VLBI nuclei of extragalactic radio sources. II - 207 sources

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.; Preston, R. A.; Slade, M. A.; Jauncey, D. L.; Nicolson, G. D.

    1983-01-01

    Time delay and fringe frequency measurements at 2.29 GHz have been obtained with VLBI on baselines of about 10,000 km, in order to determine the positions of milliarcsec nuclei in 207 extragalactic radio sources. Accuracy ranges are estimated to lie between 0.1 and 1.0 arcsec in both right ascension and declination, with all sources having uncertainties of less than 4 arcsec in both coordinates. These sources constitute part of an all-sky VLBI catalog of milliarcsec radio sources, for 752 of which arcsec positions have thus far been determined.

  9. Crustal dynamics project data analysis, 1987. Volume 1: Fixed station VLBI geodetic results, 1979-1986

    NASA Technical Reports Server (NTRS)

    Ryan, J. W.; Ma, C.

    1987-01-01

    The Goddard VLBI group reports the results of analyzing Mark III data sets from fixed observatories through the end of 1986 and available to the Crustal Dynamics Project. All full-day data from POLARIS/IRIS are included. The mobile VLBI sites at Platteville (Colorado), Penticton (British Columbia), and Yellowknife (Northwest Territories) are also included since these occupations bear on the study of plate stability. Two large solutions, GLB121 and GLB122, were used to obtain Earth rotation parameters and baseline evolutions, respectively. Radio source positions were estimated globally while nutation offsets were estimated from each data set. The results include 25 sites and 108 baselines.

  10. Crustal dynamics project data analysis, 1987. Volume 2: Mobile VLBI geodetic results, 1982-1986

    NASA Technical Reports Server (NTRS)

    Ma, C.; Ryan, J. W.

    1987-01-01

    The Goddard VLBI group reports the results of analyzing 101 Mark III data sets acquired from mobile observing sites through the end of 1986 and available to the Crustal Dynamics Project. The fixed VLBI observations at Hat Creek, Ft. Davis, Mojave, and OVRO are included as they participate heavily in the mobile schedules. One large solution GLB171 was used to obtain baseline length and transverse evolutions. Radio source positions were estimated globally, while nutation offsets were estimated from each data set. The results include 28 mobile sites.

  11. Recent Developments at the Joint Institute for VLBI in Europe (JIVE)

    NASA Astrophysics Data System (ADS)

    Mühle, S.; Campbell, R. M.; Szomoru, A.

    2011-07-01

    After an overview of the European VLBI Network (EVN) including new stations, upgrades and operational aspects, we will review the status and capabilites of the correlators at JIVE. The transition phase from the Mark IV hardware correlator to the SFXC software correlator has now reached the point where the first user experiments correlated on the SFXC correlator have been distributed. In addition, we will report on the expanded capabilities of real-time e-VLBI, which now comprises a significant fraction of EVN operations.

  12. A comparison of VLBI with the ICE-3G glacial rebound model

    NASA Technical Reports Server (NTRS)

    James, Thomas S.; Lambert, Anthony

    1993-01-01

    Crustal motion predicted by the ICE-3G glacial rebound model exhibits a pattern of tangential (horizontal) divergence away from the centers of uplift, which in North America and Europe are located around Hudson Bay and the Gulf of Bothnia. Tangential velocities reach peak magnitudes of 1-2 mm/yr, and must be included when predicting VLBI baseline length change rates due to postglacial rebound. Out of 18 observed VLBI baselines examined three are situated such that their predicted length rates are around their 2 sigma uncertainties or greater. It is encouraging that two of these baselines exhibit predicted length rates within 2 sigma of the observed rates.

  13. Preliminary design work on a DSN VLBI correlator. [Deep Space Network

    NASA Technical Reports Server (NTRS)

    Lushbaugh, W. A.; Layland, J. W.

    1978-01-01

    The Deep Space Network is in the process of fielding high-density digital instrumentation recorders for support of the Pioneer Venus 1978 entry experiment and other related tasks. It has long been obvious that these recorders would also serve well as the recording medium for very long base interferometry (VLBI) experiments with relatively weak radio sources, provided that a suitable correlation processor for these tape recordings could be established. The overall design and current status of a VLBI correlator designed to mate with these tape recorders are described.

  14. A comparison of VLBI with the ICE-3G glacial rebound model

    NASA Technical Reports Server (NTRS)

    James, Thomas S.; Lambert, Anthony

    1993-01-01

    Crustal motion predicted by the ICE-3G glacial rebound model exhibits a pattern of tangential (horizontal) divergence away from the centers of uplift, which in North America and Europe are located around Hudson Bay and the Gulf of Bothnia. Tangential velocities reach peak magnitudes of 1-2 mm/yr, and must be included when predicting VLBI baseline length change rates due to postglacial rebound. Out of 18 observed VLBI baselines examined three are situated such that their predicted length rates are around their 2 sigma uncertainties or greater. It is encouraging that two of these baselines exhibit predicted length rates within 2 sigma of the observed rates.

  15. Nutation determination by means of GNSS - Comparison with VLBI .

    NASA Astrophysics Data System (ADS)

    Capitaine, N.; Yao, K.

    2014-12-01

    Space geodetic techniques cannot be used for a direct determination of the nutation offsets due to deficiencies in the modeling of the satellite orbits. However, as shown first by Rothacher et al. 1999 and then Weber and Rothacher (2001), GPS can be used to estimate the time derivatives of nutation quantities, similarly to what is done on a regular basis for UT1-UTC rates (or LOD) estimation. We have revisited the potential of GNSS observations for nutation estimation with the high precision currently achieved by this technique. The computations have been carried out by means of a new software, which has been developed in Matlab in the framework of K. Yao's PhD (2013), based on the GPS observations analysis strategy of CNES-GRGS GINS software, but with a few specific characteristics. The reference system for orbit computations is different from that generally used in order to minimize the influence of the a priori values of precession-nutation and UT1-UTC. The method is based on the determination of the time derivatives of the GCRS CIP coordinates (X, Y) with high temporal resolution. The observations used are 3 years of GPS measurements from 1 January 2009, obtained from a dense and globally distributed reference station network. The Xdot and Ydot time series so obtained are then analyzed in order to determine the corrections to the amplitudes of the short periodic terms of the IAU 2000 nutation model. The methodology, time series and results of this analysis are compared with those obtained from Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources.

  16. VLBI Astrometry of the Millisecond Pulsar B1937+21

    NASA Astrophysics Data System (ADS)

    Dewey, Rachel J.; Ojeda, Maria Rose; Gwinn, Carl R.; Jones, Dayton L.; Davis, Michael M.

    1996-01-01

    We report the results of astrometric VLBI observations of PSR B1937+21. Observations of the pulsar and a nearby quasar were made at 1.67 GHz, using four antennas: Arecibo, the very large array, and the DSN 70 m antennas in California and Spain. We determine a position of α=19h39m38s.5611±0s.0003 and ρ=21°34'59".118±0.016 for the pulsar in the lERS extragalactic reference frame at epoch 1990.2. The accuracy of our result in right ascension is limited by systematic uncertainties in the ionospheric delay calibration, and larger-than-expected random scatter in the pulsar delays related to interstellar scintillation. The accuracy in declination is limited by the lack of a long north-south baseline in our experiment and the uncertainty of the location of the Arecibo antenna in the lERS celestial reference frame. When compared with the pulsar's timing position [Kaspi, et al., ApJ, 428, 713 (1994)] in the planetary ephemeris reference frame, our result yields a measurement of the offset of the lERS reference frame and the DE200 planetary ephemeris frame of Δα(IERS-DE200)=0.0008±0s0.0003 and Δρ(IERS-DE200)=-0.024±0.016, which is in reasonable agreement with the frame-tie rotation determined by Folkner et al. [ARA&A, 297, 279, (1994)].

  17. Ein eingebettetes Expertensystem zur Automatisierung der VLBI-Auswertung %t An embedded expert system for the automation of the VLBI data analysis

    NASA Astrophysics Data System (ADS)

    Schwegmann, Wolfgang

    2004-01-01

    Since its first application in the seventies geodetic Very Long Baseline Interferometry has become an important technique for geodesy, astronomy and geophysics. The goal of this thesis is the design and implementation of a system to automate the entire VLBI analysis procedure. On the one hand this allows to close the gap between the time of observation and the availability of results, on the other hand the few existing experts will be relieved from their routine burdens. To achieve this, knowledge-based methods from the field of research of artificial intelligence are used. An Intelligent Assistant for Data Analysis in VLBI (IADA) is developed as an embedded expert system. The term "embedded" is of particular interest, because embedding expert systems in the existing data processing environment is critical for the success of such a system. Embedding IADA in the existing analysis software by building a powerful interface guarantees the automation of the whole VLBI analysis procedure. The strong connection between the existing analysis software and the expert system developed here is an important contribution of the thesis, because generally expert systems suffer from the missing connections to the existing data processing environment.

  18. Combining GPS and VLBI earth-rotation data for improved universal time

    NASA Technical Reports Server (NTRS)

    Freedman, A. P.

    1991-01-01

    The Deep Space Network (DSN) routinely measures Earth orientation in support of spacecraft tracking and navigation using very long-baseline interferometry (VLBI) with the deep-space tracking antennas. The variability of the most unpredictable Earth-orientation component, Universal Time 1 (UT1), is a major factor in determining the frequency with which the DSN measurements must be made. The installation of advanced Global Positioning System (GPS) receivers at the DSN sites and elsewhere may soon permit routine measurements of UT1 variation with significantly less dependence on the deep-space tracking antennas than is currently required. GPS and VLBI data from the DSN may be combined to generate a precise UT1 series, while simultaneously reducing the time and effort the DSN must spend on platform-parameter calibrations. This combination is not straightforward, however, and a strategy for the optimal combination of these data is presented and evaluated. It appears that, with the aid of GPS, the frequency of required VLBI measurements of Earth orientation could drop from twice weekly to once per month. More stringent real-time Earth orientation requirements possible in the future would demand significant improvements in both VLBI and GPS capabilities, however.

  19. Crustal motion results derived from observations in the European geodetic VLBI network

    NASA Astrophysics Data System (ADS)

    Haas, Rüdiger; Gueguen, Erwan; Scherneck, Hans-Georg; Nothnagel, Axel; Campbell, James

    2000-10-01

    Geodetic VLBI observations have been performed with the European geodetic VLBI network since early 1990 on a regular basis. The purpose of these observations is to determine crustal motion in Europe and to establish a stable reference frame for other space geodetic techniques. Over the years the size of the network and the number of participating stations has steadily increased. Today, the network extends from the island of Sicily in the south to the island of Spitsbergen/Svalbard in the north and from the Iberian peninsula in the west to the Crimean peninsula in the east. The area covered by the network is affected by two main geodynamic processes which are post-glacial rebound effects in the northern part, and the evolution of the Alps-Apennines orogenic systems in the southern part. With nearly 10 years of VLBI observations the determination of crustal motion in Europe is carried out with high accuracy. Baseline measurements are achieved with an accuracy of a few parts per billion. We compare the evolution of baseline lengths and topocentric station displacements with geophysical models. Strain rates in Europe on a large scale are determined from the results of the VLBI analysis.

  20. A tutorial introduction to Very Long Base-line Interferometry (VLBI) using bandwidth synthesis

    NASA Technical Reports Server (NTRS)

    Molinder, J. I.

    1978-01-01

    The basic principles underlying very long baseline interferometry (VLBI) are described by using bandwidth synthesis. The basic signal processing approach is detailed. Summarized results show the tradeoff of measurement accuracy with spanned bandwidth, source strength, antenna size and efficiency, system noise temperature, and data volume. Minimization of required antenna time for a given baseline measurement accuracy is also discussed.

  1. Structure of Sagittarius A* at 86 GHz using VLBI Closure Quantities

    NASA Astrophysics Data System (ADS)

    Doeleman, S. S.; Shen, Z.-Q.; Rogers, A. E. E.; Bower, G. C.; Wright, M. C. H.; Zhao, J.-H.; Backer, D. C.; Crowley, J. W.; Freund, R. W.; Ho, P. T. P.; Lo, K. Y.; Woody, D. P.

    2000-12-01

    At radio wavelengths, VLBI images of the compact radio source Sagittarius A* (Sgr A*) in the Galactic Center are scatter broadened with a λ 2 dependence due to an intervening ionized medium. High frequency VLBI is the only technique available to see through this scattering and search for the intrinsic structure of Sgr A*. We present total intensity VLBI observations of Sgr A* at 86 GHz using a six station array including the VLBA antennas at Pie Town, Fort Davis and Los Alamos, the 12m antenna at Kitt Peak and the millimeter arrays at Hat Creek and Owens Valley. To avoid systematic errors due to imperfect antenna calibration, the data were modeled using interferometric closure information. The data are best modeled by a circular Gaussian brightness distribution of FWHM 0.18 +/- 0.02 mas (30Rsch for a 2.6*E6Msun Black Hole). The data are also shown to be consistent with an elliptical model corresponding to the scattering of a point source. The source structure in the N-S direction, which is less well determined than in the E-W direction due to the limited N-S (u,v) coverage of the array, is constrained to be less than 0.27 mas (45Rsch) by these measurements. These results are marginally consistent with reasonable extrapolations of intrinsic structure estimates obtained with VLBI at 7mm wavelength.

  2. Accuracy evaluation of the next-generation geodetic VLBI systems from first observations

    NASA Astrophysics Data System (ADS)

    Elosegui, P.; Ruszczyk, C. A.; Niell, A. E.; Rajagopalan, G.

    2016-12-01

    The rollout of the next-generation VLBI network has begun with the deployment in February 2016 of a new VLBI antenna at the Kokee Park Geophysical Observatory (KPGO), Hawaii, a joint effort of the NASA Goddard Space Flight Center, the United States Naval Observatory, and MIT Haystack Observatory. The new VLBI systems (a.k.a. the VLBI Global Observing System, or VGOS) are a key component for achieving the accuracy goals of the Global Geodetic Observing System (GGOS). Some salient observational features of VGOS, such as broadband (2-14 GHz) feeds, dual-polarization receivers, wideband digital backends, and fast-slewing small (12-13 m) antennas, address the need for improved geodetic accuracy by decreasing the observable noise while increasing sampling of the atmosphere. The VGOS system at KPGO joins the successful VGOS prototype systems at the Goddard Geophysical and Astronomical Observatory (GGAO), Maryland, and at Westford, Massachusetts, which have been making VGOS geodetic observations since December 2014. We will present preliminary geodetic results and an accuracy evaluation from these early VGOS observing sessions.

  3. Plans for an accurate alignment of the VLBI frame and the future Gaia frame

    NASA Astrophysics Data System (ADS)

    Bourda, G.; Charlot, P.

    2012-12-01

    The European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be fundamental to align the Gaia and VLBI frames with the highest accuracy. A proper alignment is also important in the framework of astrophysics, for example to probe properly the AGN jets properties and the physics of these objects. The VLBI-Gaia frame alignment requires quasars that are bright at optical wavelength, that have a compact radio core, and that do not exhibit complex structures. In this paper, we draw prospects for this alignment, based on the ICRF2 catalogue and an ongoing dedicated VLBI project designed to observe additional weaker extragalactic radio sources for this purpose. The list of suitable sources will have to be monitored to check the relevance of the sources for the alignment, especially in terms of position stability and structures. Accordingly, we present the observations we envision in the framework of the IVS and other VLBI networks, before and during the Gaia mission.

  4. Status and future plans for the Vienna VLBI Software VieVS

    NASA Astrophysics Data System (ADS)

    Nilsson, T.; Böhm, J.; Böhm, S.; Madzak, M.; Nafisi, V.; Plank, L.; Spicakova, H.; Sun, J.; Tierno Ros, C.; Schuh, H.

    2011-07-01

    The Vienna VLBI Software (VieVS) is a new VLBI analysis software which has been developed at the Institute of Geodesy and Geophysics of the Vienna University of Technology since 2008. In this software, which is written in Matlab, the most recent IERS Conventions and are implemented, and through a graphical user interface it is easy to use. Lately, two new modules have been added to the official version of VieVS. One is a simulation module (VIE_SIM) which allows to create simulated VLBI observations. The other is a global solution module (VIE_GLOB) which can be used for combining several sessions in a global solution in order to derive e.g. a terrestrial and/or a celestial reference frame. In this presentation an overview of VieVS and its current status will be given and its performance will be demonstrated by showing selected results. We also discuss the planned future developments of VieVS. These include the possibility to use external tropospheric delays obtained, e.g. by ray-tracing through numerical weather models, to use external ionospheric corrections from, e.g. GNSS TEC maps, and to implement a Kalman filter solution. We also plan to cover earlier steps in the VLBI data processing chain, like ambiguity resolution, which have not been considered so far in VieVS.

  5. Space VLBI observations of 3C 279 at 1.6 and 5 GHz

    NASA Technical Reports Server (NTRS)

    Piner, B. G.; Edwards, P. G.; Wehrle, A. E.; Hirabayashi, H.; Lovell, J. E.; Unwin, S. C.

    2000-01-01

    We present VLBI Space Observatory Programme (VSOP) observations of the gamma-ray blazar 3C 279 at 1.6 and 5 GHz made on 1998 January 9-10 with the HALCA satellite and ground arrays including the Very Long Baseline Array (VLBA).

  6. Improvement of supporting electronics system of H-clock at Sher Shan VLBI station.

    NASA Astrophysics Data System (ADS)

    Zhang, Weiqun

    1990-12-01

    The supporting electronics system is a very important part of the H-clock. The author improves the supporting electronics system of the two sets of H-clock at Sher Shan VLBI station. Some design ideas and results are described.

  7. THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

    SciTech Connect

    Dodson, R.; Rioja, M.; Imai, H.; Asaki, Y.; Hong, X.-Y.; Shen, Z.

    2013-06-15

    High-precision astrometric space very long baseline interferometry (S-VLBI) at the low end of the conventional frequency range, i.e., 20 cm, is a requirement for a number of high-priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in pulsar-black hole pairs and OH masers anywhere in the Milky Way and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8 m in size and with ionospheric atmospheres consistent with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high-quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.

  8. Aligning VLBI and Gaia Extragalactic Celestial Reference Frames: source selection scenario

    NASA Astrophysics Data System (ADS)

    Bourda, Geraldine; Charlot, Patrick; Collioud, Arnaud

    2015-08-01

    The European space astrometry mission Gaia will construct a dense optical celestial reference frame based on Quasi Stellar Objects. Accordingly, by 2020, two extragalactic celestial reference frames will coexist: the VLBI frame (Very Long Baseline Interferometry) in the radio domain, currently adopted by the IAU as the fundamental one, and the Gaia frame determined from direct optical observations of quasars by the satellite.For consistency between optical and radio positions of any celestial targets, it will be fundamental to align the Gaia and VLBI frames with the highest accuracy. This issue is also important in the framework of astrophysics, for example to probe properly the jets properties and the physics of the Active Galactic Nuclei.In this paper, based on the ICRF2 catalogue (International Celestial Reference Frame) and specific dedicated VLBI projects (e.g. designed to observe additional weaker extragalactic radio sources), we will discuss the selection of the VLBI-Gaia transfer sources, present our initiatives to reach this alignment, review the status of the various projects in question and draw plans for the future.

  9. ON THE CONNECTION OF THE APPARENT PROPER MOTION AND THE VLBI STRUCTURE OF COMPACT RADIO SOURCES

    SciTech Connect

    Moor, A.; Frey, S.; Lambert, S. B.; Bakos, J. E-mail: frey@sgo.fomi.hu E-mail: oleg.titov@ga.gov.au

    2011-06-15

    Many of the compact extragalactic radio sources that are used as fiducial points to define the celestial reference frame are known to have proper motions detectable with long-term geodetic/astrometric very long baseline interferometry (VLBI) measurements. These changes can be as high as several hundred microarcseconds per year for certain objects. When imaged with VLBI at milliarcsecond (mas) angular resolution, these sources (radio-loud active galactic nuclei) typically show structures dominated by a compact, often unresolved 'core' and a one-sided 'jet'. The positional instability of compact radio sources is believed to be connected with changes in their brightness distribution structure. For the first time, we test this assumption in a statistical sense on a large sample rather than on only individual objects. We investigate a sample of 62 radio sources for which reliable long-term time series of astrometric positions as well as detailed 8 GHz VLBI brightness distribution models are available. We compare the characteristic direction of their extended jet structure and the direction of their apparent proper motion. We present our data and analysis method, and conclude that there is indeed a correlation between the two characteristic directions. However, there are cases where the {approx}1-10 mas scale VLBI jet directions are significantly misaligned with respect to the apparent proper motion direction.

  10. Observations of the APOD satellite with the AuScope VLBI network

    NASA Astrophysics Data System (ADS)

    Hellerschmied, Andreas; Plank, Lucia; McCallum, Jamie; Sun, Jing; Lovell, Jim; Böhm, Johannes

    2017-04-01

    The Chinese APOD (Atmospheric density detection and Precise Orbit Determination) satellite, launched in September 2015, is the first LEO (Low Earth Orbit) satellite co-locating three space-geodetic techniques including VLBI. Being equipped with a dual-frequency GNSS receiver, an SLR retro-reflector and a VLBI beacon transmitting DOR tones in the S and X band it can be considered as a first prototype of a geodetic co-location satellite in space. Basically it is suitable to realize so-called space-ties, complementing the local-ties used nowadays to connect single-technique reference frame solutions in the ITRF combination. Due to the low orbit of about 470 km altitude and the accompanying high velocity of the satellite, VLBI observations become very challenging. In this contribution we discuss a series of VLBI observations of APOD which were carried out by the Australian AuScope network in late 2016. The applied satellite tracking and data acquisition schemes will be discussed along with first results of the geodetic data processing.

  11. VLBI Observations of GNSS Signals on the Baseline Hobart-Ceduna

    NASA Astrophysics Data System (ADS)

    Hellerschmied, Andreas; Böhm, Johannes; Kwak, Younghee; McCallum, Jamie; Plank, Lucia

    2016-12-01

    Observing GNSS satellites with geodetic VLBI opens a variety of new possibilities, which include promising applications in the field of inter-technique frame ties. Considering GNSS satellites as co-location platforms in space, such observations provide possibilities to directly connect the dynamic GNSS and the kinematic VLBI reference frames, which may result in improved future ITRF realizations. In our research we are trying to apply observation strategies that are commonly used in geodetic VLBI, i.e., the main observables are group delays derived from direct observations of GNSS satellite signals. However, clear strategies for the data acquisition and the geodetic analysis are still missing. To pave the way towards an operational application we established a workflow to plan, correlate, observe, and analyze VLBI observations to GNSS satellites. Based on these processes we carried out several successful experiments on the Australian baseline Hobart-Ceduna in 2015 in which we observed GLONASS and GPS satellites in the L1 and L2 bands. For the first time a connected processing chain from scheduling, to correlation, to data analysis has been realized. In this contribution we introduce our workflow and present first results.

  12. SWARM: A 32 GHz Correlator and VLBI Beamformer for the Submillimeter Array

    NASA Astrophysics Data System (ADS)

    Primiani, Rurik A.; Young, Kenneth H.; Young, André; Patel, Nimesh; Wilson, Robert W.; Vertatschitsch, Laura; Chitwood, Billie B.; Srinivasan, Ranjani; MacMahon, David; Weintroub, Jonathan

    A 32GHz bandwidth VLBI capable correlator and phased array has been designed and deployeda at the Smithsonian Astrophysical Observatory’s Submillimeter Array (SMA). The SMA Wideband Astronomical ROACH2 Machine (SWARM) integrates two instruments: a correlator with 140kHz spectral resolution across its full 32GHz band, used for connected interferometric observations, and a phased array summer used when the SMA participates as a station in the Event Horizon Telescope (EHT) very long baseline interferometry (VLBI) array. For each SWARM quadrant, Reconfigurable Open Architecture Computing Hardware (ROACH2) units shared under open-source from the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) are equipped with a pair of ultra-fast analog-to-digital converters (ADCs), a field programmable gate array (FPGA) processor, and eight 10 Gigabit Ethernet (GbE) ports. A VLBI data recorder interface designated the SWARM digital back end, or SDBE, is implemented with a ninth ROACH2 per quadrant, feeding four Mark6 VLBI recorders with an aggregate recording rate of 64 Gbps. This paper describes the design and implementation of SWARM, as well as its deployment at SMA with reference to verification and science data.

  13. A Model-free CAF Fringe Search Algorithm with Wavelet Boosting for VLBI Observation

    NASA Astrophysics Data System (ADS)

    Zhang, Tianyi; Meng, Qiao; Chen, Congyan; Zheng, Weimin; Liu, Wei; Yu, Quantao; Tong, Li

    2017-07-01

    Very-Long-Baseline interferometry (VLBI) is a powerful tool in radio astronomy, geodesy, and deep space exploration. Priori predicted delay models are needed to make interferometry fringes, but in some cases they would be difficult to get. This paper proposes an effective algorithm named CAF-W algorithm to search fringes from the raw data in a large search range without priori predicted delay models. The cross-ambiguity function (CAF) is used to make a time-frequency correlation in the delay-delay rate plane. The wavelet boosting algorithm is used to eliminate interference and enhance the CAF peak, whose position would give the delay and delay rate estimations. Incoherent averaging and sliding search window techniques are used to overcome the wide search range and the poor signal-to-noise ratio in VLBI observations. The CAF-W algorithm could be performed with fast algorithms so the computation burden is affordable. This algorithm has successfully achieved VLBI fringes from the raw data without priori predicted delay models in VLBI observations.

  14. Concepts for VLBI Station Control as Part of NEXPReS

    NASA Astrophysics Data System (ADS)

    Ettl, M.; Neidhardt, A.; Schönberger, M.; Alef, W.; Himwich, E.; Beaudoin, C.; Plötz, C.; Lovell, J.; Hase, H.

    2012-12-01

    In the Novel EXploration Pushing Robust e-VLBI Services-project (NEXPReS) the Technische Universität München (TUM) realizes concepts for continuous quality monitoring and station remote control in cooperation with the Max-Planck-Institute for Radio Astronomy, Bonn. NEXPReS is a three-year project, funded within the European Seventh Framework program. It is aimed to develop e-VLBI services for the European VLBI Network (EVN), which can also support the IVS observations (VLBI2010). Within this project, the TUM focuses on developments of an operational remote control system (e-RemoteCtrl) with authentication and authorization. It includes an appropriate role management with different remote access states for future observation strategies. To allow a flexible control of different systems in parallel, sophisticated graphical user interfaces are designed and realized. The software is currently under test in the new AuScope network, Australia/New Zealand. Additional system parameters and information are collected with a new system monitoring (SysMon) for a higher degree of automation, which is currently under preparation for standardization within the IVS Monitoring and Control Infrastructure (MCI) Collaboration Group. The whole system for monitoring and control is fully compatible with the NASA Field System and extends it.

  15. Homogenization of atmospheric pressure time series recorded at VLBI stations using a segmentation LASSO approach

    NASA Astrophysics Data System (ADS)

    Balidakis, Kyriakos; Heinkelmann, Robert; Lu, Cuixian; Soja, Benedikt; Karbon, Maria; Nilsson, Tobias; Glaser, Susanne; Andres Mora-Diaz, Julian; Anderson, James; Liu, Li; Raposo-Pulido, Virginia; Xu, Minghui; Schuh, Harald

    2015-04-01

    Time series of meteorological parameters recorded at VLBI (Very Long Baseline Interferometry) observatories allow us to realistically model and consequently to eliminate the atmosphere-induced effects in the VLBI products to a large extent. Nevertheless, this advantage of VLBI is not fully exploited since such information is contaminated with inconsistencies, such as uncertainties regarding the calibration and location of the meteorological sensors, outliers, missing data points, and breaks. It has been shown that such inconsistencies in meteorological data used for VLBI data analysis impose problems in the geodetic products (e.g vertical site position) and result in mistakes in geophysical interpretation. The aim of the procedure followed here is to optimally model the tropospheric delay and bending effects that are still the main sources of error in VLBI data analysis. In this study, the meteorological data recorded with sensors mounted in the vicinity of VLBI stations have been homogenized spanning the period from 1979 until today. In order to meet this objective, inhomogeneities were detected and adjusted using test results and metadata. Some of the approaches employed include Alexandersson's Standard Normal Homogeneity Test and an iterative procedure, of which the segmentation part is based on a dynamic programming algorithm and the functional part on a LASSO (Least Absolute Shrinkage and Selection Operator) estimator procedure. For the provision of reference time series that are necessary to apply the aforementioned methods, ECMWF's (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis surface data were employed. Special care was taken regarding the datum definition of this model. Due to the significant height difference between the VLBI antenna's reference point and the elevation included in geopotential fields of the specific numerical weather models, a hypsometric adjustment is applied using the absolute pressure level from the WMO

  16. Status and Prospects for Combined GPS LOD and VLBI UT1 Measurements

    NASA Astrophysics Data System (ADS)

    Senior, K.; Kouba, J.; Ray, J.

    2010-01-01

    A Kalman filter was developed to combine VLBI estimates of UT1-TAI with biased length of day (LOD) estimates from GPS. The VLBI results are the analyses of the NASA Goddard Space Flight Center group from 24-hr multi-station observing sessions several times per week and the nearly daily 1-hr single-baseline sessions. Daily GPS LOD estimates from the International GNSS Service (IGS) are combined with the VLBI UT1-TAI by modeling the natural excitation of LOD as the integral of a white noise process (i.e., as a random walk) and the UT1 variations as the integration of LOD, similar to the method described by Morabito et al. (1988). To account for GPS technique errors, which express themselves mostly as temporally correlated biases in the LOD measurements, a Gauss-Markov model has been added to assimilate the IGS data, together with a fortnightly sinusoidal term to capture errors in the IGS treatments of tidal effects. Evaluated against independent atmospheric and oceanic axial angular momentum (AAM + OAM) excitations and compared to other UT1/LOD combinations, ours performs best overall in terms of lowest RMS residual and highest correlation with (AAM + OAM) over sliding intervals down to 3 d. The IERS 05C04 and Bulletin A combinations show strong high-frequency smoothing and other problems. Until modified, the JPL SPACE series suffered in the high frequencies from not including any GPS-based LODs. We find, surprisingly, that further improvements are possible in the Kalman filter combination by selective rejection of some VLBI data. The best combined results are obtained by excluding all the 1-hr single-baseline UT1 data as well as those 24-hr UT1 measurements with formal errors greater than 5 μs (about 18% of the multi-baseline sessions). A rescaling of the VLBI formal errors, rather than rejection, was not an effective strategy. These results suggest that the UT1 errors of the 1-hr and weaker 24-hr VLBI sessions are non-Gaussian and more heterogeneous than expected

  17. An Improved Empirical Harmonic Model of the Celestial Intermediate Pole Offsets from a Global VLBI Solution

    NASA Astrophysics Data System (ADS)

    Belda, Santiago; Heinkelmann, Robert; Ferrándiz, José M.; Karbon, Maria; Nilsson, Tobias; Schuh, Harald

    2017-10-01

    Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable of measuring all the Earth orientation parameters (EOP) accurately and simultaneously. Modeling the Earth's rotational motion in space within the stringent consistency goals of the Global Geodetic Observing System (GGOS) makes VLBI observations essential for constraining the rotation theories. However, the inaccuracy of early VLBI data and the outdated products could cause non-compliance with these goals. In this paper, we perform a global VLBI analysis of sessions with different processing settings to determine a new set of empirical corrections to the precession offsets and rates, and to the amplitudes of a wide set of terms included in the IAU 2006/2000A precession-nutation theory. We discuss the results in terms of consistency, systematic errors, and physics of the Earth. We find that the largest improvements w.r.t. the values from IAU 2006/2000A precession-nutation theory are associated with the longest periods (e.g., 18.6-yr nutation). A statistical analysis of the residuals shows that the provided corrections attain an error reduction at the level of 15 μas. Additionally, including a Free Core Nutation (FCN) model into a priori Celestial Pole Offsets (CPOs) provides the lowest Weighted Root Mean Square (WRMS) of residuals. We show that the CPO estimates are quite insensitive to TRF choice, but slightly sensitive to the a priori EOP and the inclusion of different VLBI sessions. Finally, the remaining residuals reveal two apparent retrograde signals with periods of nearly 2069 and 1034 days.

  18. First 230 GHz VLBI fringes on 3C 279 using the APEX Telescope

    NASA Astrophysics Data System (ADS)

    Wagner, J.; Roy, A. L.; Krichbaum, T. P.; Alef, W.; Bansod, A.; Bertarini, A.; Güsten, R.; Graham, D.; Hodgson, J.; Märtens, R.; Menten, K.; Muders, D.; Rottmann, H.; Tuccari, G.; Weiss, A.; Wieching, G.; Wunderlich, M.; Zensus, J. A.; Araneda, J. P.; Arriagada, O.; Cantzler, M.; Duran, C.; Montenegro-Montes, F. M.; Olivares, R.; Caro, P.; Bergman, P.; Conway, J.; Haas, R.; Johansson, J.; Lindqvist, M.; Olofsson, H.; Pantaleev, M.; Buttaccio, S.; Cappallo, R.; Crew, G.; Doeleman, S.; Fish, V.; Lu, R.-S.; Ruszczyk, C.; SooHoo, J.; Titus, M.; Freund, R.; Marrone, D.; Strittmatter, P.; Ziurys, L.; Blundell, R.; Primiani, R.; Weintroub, J.; Young, K.; Bremer, M.; Sánchez, S.; Marscher, A. P.; Chilson, R.; Asada, K.; Inoue, M.

    2015-09-01

    Aims: We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods: We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5 h 230 GHz VLBI track with baseline lengths of 2800 Mλ to 7200 Mλ and a finest fringe spacing of 28.6 μas. Results: Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy beam-1, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region ≲ 38 μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ~ 38 μas. Conclusions: With APEX the angular resolution of 230 GHz VLBI improves to 28.6 μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.

  19. An updated set of nutations derived from the reanalysis of 3.5 decades VLBI observations

    NASA Astrophysics Data System (ADS)

    Zhu, Ping; Koot, Laurence; Rivoldini, Attilio; Dehant, Veronique

    2016-04-01

    The global VLBI observation started in the 1979. After that the qualities of the measurements are continuously improving by taking into account various instrumental and environmental effects. The MHB2000 models was introduced in 2002 (Mathews, et.al. 2002, [1]) and it has a good agreement (5 μas) on the short period nutation series (<400 days) with the values derived from 2 decades (1979-2000) VLBI data while a higher uncertainties up to 56 μas for those longer periods (>400 days) nutation series (Herring et.al. 2002). In MHB2000, the forcing frequencies of the nutation series are solved by least-squares fitting to the VLBI data in frequency domain. Koot et al. (2008), have processed another similar set of nutation series by inversing the time series of VLBI data (1984-2005) using a Bayesian approach. In the present work, we will repeat both approaches using the up-to-date 3.5 decades VLBI observations (1980-2014) meanwhile paying more attention on the results of longer period (>400 days). Finally some features of Earth's interior structure will be discussed based on the determined nutation series. [1] Mathews, P.M., Herring, T.A. & Buffett, B.A., 2002. Modeling of nutation and precession: new nutation series for nonrigid Earth and insights into the Earth's interior, J. Geophys. Res., 107, 2068, doi: 10.1029/2001JB000390. [2] Herring, T. A., P. M. Mathews, and B. A. Buffett, Modeling of nutation and precession: Very long baseline interferometry results, J. Geophys. Res., 107, B4, 2069, doi: 10.1029/2001JB000165, 2002 [3] Koot, L., Rivoldini, A., de Viron, O. & Dehant, V., 2008. Estimation of Earth interior parameters from a Bayesian inversion of very long baseline interferometry nutation time series, J. Geophys. Res., 113, 8414, doi: 10.1029/2007JB005409.

  20. VLBI observations of four radio quasars at z > 4: blazars or not?

    NASA Astrophysics Data System (ADS)

    Cao, H. M.; Frey, S.; Gabányi, K. É.; Paragi, Z.; Yang, J.; Cseh, D.; Hong, X.-Y.; An, T.

    2017-01-01

    Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift z > 4 with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134-0419 is firmly confirmed as a blazar with our VLBI observations, due to its relativistically beamed radio emission. Its radio jet extended to ˜10 milli-arcsec scale makes this source a promising target for follow-up VLBI observations to reveal any apparent proper motion. Another target, J0839+5112 shows a compact radio structure typical of quasars. There is evidence for flux density variability and its radio "core" has a flat spectrum. However, the EVN data suggest that its emission is not Doppler-boosted. The remaining two blazar candidates (J1420+1205 and J2220+0025) show radio properties totally unexpected from radio AGN with small-inclination jet. Their emission extends to arcsec scales and the Doppler factors of the central components are well below 1. Their structures resemble that of double-lobed radio AGN with large inclination to the line of sight. This is in contrast with the blazar-type modeling of their multi-band spectral energy distributions. Our work underlines the importance of high-resolution VLBI imaging in confirming the blazar nature of high-redshift radio sources.

  1. Parallax of a Mira variable R Ursae Majoris studied with astrometric VLBI

    NASA Astrophysics Data System (ADS)

    Nakagawa, Akiharu; Kurayama, Tomoharu; Matsui, Makoto; Omodaka, Toshihiro; Honma, Mareki; Shibata, Katsunori M.; Sato, Katsuhisa; Jike, Takaaki

    2016-10-01

    We have measured an annual parallax of the Mira variable R Ursae Majoris (R UMa) with the VLBI Exploration for Radio Astronomy (VERA). From the monitoring VLBI observations over a span of about two years, we detected H2O maser spots in the LSR velocity range from 37 to 42 km s-1. We derived an annual parallax of 1.97 ± 0.05 mas, and this gives a corresponding distance of 508 ± 13 pc. The VLBI maps revealed 72 maser spots distributed in an ˜110 au area around the expected stellar position. Circumstellar kinematics of the maser spots were also revealed by subtracting a systemic motion in the Hipparcos catalog from proper motions of each maser spot derived from our VLBI observations. Infrared photometry was also conducted to measure a K-band apparent magnitude, and we obtained a mean magnitude of mK = 1.19 ± 0.02 mag. Using the trigonometric distance, mK is converted to a K-band absolute magnitude of MK = -7.34 ± 0.06 mag. This result gives a much more accurate absolute magnitude for R UMa than previously provided. We solved a zero-point of the MK-log P relation for the Galactic Mira variables and obtained a relation of MK = -3.52 log P + (1.09 ± 0.14). Other long-period variables, including red supergiants, whose distances were determined with astrometric VLBI, were also compiled to explore the different sequences of the MK-log P relation.

  2. Combined Earth orientation parameters based on homogeneous and continuous VLBI and GPS data

    NASA Astrophysics Data System (ADS)

    Thaller, Daniela; Krügel, Manuela; Rothacher, Markus; Tesmer, Volker; Schmid, Ralf; Angermann, Detlef

    2007-06-01

    The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network. Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique- specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to get a deeper understanding of this singularity. With a rigorous combination of UT1 UTC and length of day (LOD) from VLBI and GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies

  3. EARLY SCIENCE WITH THE KOREAN VLBI NETWORK: THE QCAL-1 43 GHz CALIBRATOR SURVEY

    SciTech Connect

    Petrov, Leonid; Lee, Sang-Sung; Kim, Jongsoo; Jung, Taehyun; Oh, Junghwan; Sohn, Bong Won; Byun, Do-Young; Chung, Moon-Hee; Je, Do-Heung; Wi, Seog-Oh; Song, Min-Gyu; Kang, Jiman; Han, Seog-Tae; Lee, Jung-Won; Kim, Bong Gyu; Chung, Hyunsoo; Kim, Hyun-Goo

    2012-11-01

    This paper presents the catalog of correlated flux densities in three ranges of baseline projection lengths of 637 sources from a 43 GHz (Q band) survey observed with the Korean VLBI Network. Of them, 14 objects used as calibrators were previously observed, but 623 sources have not been observed before in the Q band with very long baseline interferometry (VLBI). The goal of this work in the early science phase of the new VLBI array is twofold: to evaluate the performance of the new instrument that operates in a frequency range of 22-129 GHz and to build a list of objects that can be used as targets and as calibrators. We have observed the list of 799 target sources with declinations down to -40 Degree-Sign . Among them, 724 were observed before with VLBI at 22 GHz and had correlated flux densities greater than 200 mJy. The overall detection rate is 78%. The detection limit, defined as the minimum flux density for a source to be detected with 90% probability in a single observation, was in the range of 115-180 mJy depending on declination. However, some sources as weak as 70 mJy have been detected. Of 623 detected sources, 33 objects are detected for the first time in VLBI mode. We determined their coordinates with a median formal uncertainty of 20 mas. The results of this work set the basis for future efforts to build the complete flux-limited sample of extragalactic sources at frequencies of 22 GHz and higher at 3/4 of the celestial sphere.

  4. VLBI observations of four radio quasars at z > 4: blazars or not?

    NASA Astrophysics Data System (ADS)

    Cao, H.-M.; Frey, S.; Gabányi, K. É.; Paragi, Z.; Yang, J.; Cseh, D.; Hong, X.-Y.; An, T.

    2017-05-01

    Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift z > 4 with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134-0419 is firmly confirmed as a blazar with our VLBI observations, due to its relativistically beamed radio emission. Its radio jet extended to ˜10 milliarcsec scale makes this source a promising target for follow-up VLBI observations to reveal any apparent proper motion. Another target, J0839+5112 shows a compact radio structure typical of quasars. There is evidence for flux density variability and its radio 'core' has a flat spectrum. However, the EVN data suggest that its emission is not Doppler-boosted. The remaining two blazar candidates (J1420+1205 and J2220+0025) show radio properties totally unexpected from radio AGN with small-inclination jet. Their emission extends to arcsec scales and the Doppler factors of the central components are well below 1. Their structures resemble that of double-lobed radio AGN with large inclination to the line of sight. This is in contrast with the blazar-type modelling of their multiband spectral energy distributions. Our work underlines the importance of high-resolution VLBI imaging in confirming the blazar nature of high-redshift radio sources.

  5. A GPS, VLBI and local tie inter-comparison: first results for the Australian AuScope Array

    NASA Astrophysics Data System (ADS)

    Johnston, G.; Titov, O.; Dawson, J. H.; Hu, G.

    2012-12-01

    AuScope is part of the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS) and has the objective of upgrading the accuracy of the terrestrial reference frame in Australia to 1 mm based on the development of new geodetic infrastructure which includes three new Very Long Baseline Interferometry (VLBI) observatories and 100 Global Navigation Satellite System (GNSS) stations. Each of the AuScope VLBI observatories, located at Hobart, Yarragadee and Katherine, are equipped with a 12.1 metre antenna designed and constructed by COBHAM Satcom, Patriot Products division. In a preliminary multi-technique inter-comparison, GPS data have been analysed in the Bernese software and VLBI and local tie data have been analysed in the in-house developed software OCCAM and Axis, respectively. Our experiences and techniques for undertaking local tie surveys of the Patriot antennas are overviewed, and results of the GPS, VLBI and local tie inter-comparison are presented.

  6. What is the impact of different VLBI analysis setups of the tropospheric delay on precipitable water vapor trends?

    NASA Astrophysics Data System (ADS)

    Balidakis, Kyriakos; Nilsson, Tobias; Heinkelmann, Robert; Glaser, Susanne; Zus, Florian; Deng, Zhiguo; Schuh, Harald

    2017-04-01

    The quality of the parameters estimated by global navigation satellite systems (GNSS) and very long baseline interferometry (VLBI) are distorted by erroneous meteorological observations applied to model the propagation delay in the electrically neutral atmosphere. For early VLBI sessions with poor geometry, unsuitable constraints imposed on the a priori tropospheric gradients is a source of additional hassle of VLBI analysis. Therefore, climate change indicators deduced from the geodetic analysis, such as the long-term precipitable water vapor (PWV) trends, are strongly affected. In this contribution we investigate the impact of different modeling and parameterization of the propagation delay in the troposphere on the estimates of long-term PWV trends from geodetic VLBI analysis results. We address the influence of the meteorological data source, and of the a priori non-hydrostatic delays and gradients employed in the VLBI processing, on the estimated PWV trends. In particular, we assess the effect of employing temperature and pressure from (i) homogenized in situ observations, (ii) the model levels of the ERA Interim reanalysis numerical weather model and (iii) our own blind model in the style of GPT2w with enhanced parameterization, calculated using the latter data set. Furthermore, we utilize non-hydrostatic delays and gradients estimated from (i) a GNSS reprocessing at GeoForschungsZentrum Potsdam, rigorously considering tropospheric ties, and (ii)) direct ray-tracing through ERA Interim, as additional observations. To evaluate the above, the least-squares module of the VieVS@GFZ VLBI software was appropriately modified. Additionally, we study the noise characteristics of the non-hydrostatic delays and gradients estimated from our VLBI and GNSS analyses as well as from ray-tracing. We have modified the Theil-Sen estimator appropriately to robustly deduce PWV trends from VLBI, GNSS, ray-tracing and direct numerical integration in ERA Interim. We disseminate all

  7. Atmospheric gradients from GNSS, VLBI, and DORIS analyses and from Numerical Weather Models during CONT14

    NASA Astrophysics Data System (ADS)

    Heinkelmann, Robert; Dick, Galina; Nilsson, Tobias; Soja, Benedikt; Wickert, Jens; Zus, Florian; Schuh, Harald

    2015-04-01

    Observations from space-geodetic techniques are nowadays increasingly used to derive atmospheric information for various commercial and scientific applications. A prominent example is the operational use of GNSS data to improve global and regional weather forecasts, which was started in 2006. Atmosphere gradients describe the azimuthal asymmetry of zenith delays. Estimates of geodetic and other parameters significantly improve when atmosphere gradients are determined in addition. Here we assess the capability of several space geodetic techniques (GNSS, VLBI, DORIS) to determine atmosphere gradients of refractivity. For this purpose we implement and compare various strategies for gradient estimation, such as different values for the temporal resolution and the corresponding parameter constraints. Applying least squares estimation the gradients are usually deterministically modelled as constants or piece-wise linear functions. In our study we compare this approach with a stochastic approach modelling atmosphere gradients as random walk processes and applying a Kalman Filter for parameter estimation. The gradients, derived from space geodetic techniques are verified by comparison with those derived from Numerical Weather Models (NWM). These model data were generated using raytracing calculations based on European Centre for Medium-Range Weather Forecast (ECMWF) and National Centers for Environmental Prediction (NCEP) analyses with different spatial resolutions. The investigation of the differences between the ECMWF and NCEP gradients hereby in addition allow for an empirical assessment of the quality of model gradients and how suitable the NWM data are for verification. CONT14 (2014-05-06 until 2014-05-20) is the youngest two week long continuous VLBI campaign carried out by IVS (International VLBI Service for Geodesy and Astrometry). It presents the state-of-the-art VLBI performance in terms of number of stations and number of observations and presents thus an

  8. VLBI observations of GNSS satellites on the baseline Hobart-Ceduna

    NASA Astrophysics Data System (ADS)

    Hellerschmied, Andreas; Böhm, Johannes; Kwak, Younghee; McCallum, Jamie; Plank, Lucia

    2016-04-01

    Observations of satellites of Global Navigation Satellite Systems (GNSS) with the geodetic Very Long Baseline Interferometry (VLBI) technique open a variety of new possibilities and promote the integration of these techniques within the framework of GGOS, the Global Geodetic Observing System of the IAG. Such observations provide possibilities to directly connect the dynamic GNSS and the kinematic VLBI reference frame, which may result in improved future ITRF realizations. In our research we are trying to apply observation strategies, which are commonly used in geodetic VLBI, i.e. the main observables are group delay values derived from direct observations and the subsequent correlations of GNSS satellite signals. However, data acquisition schemes for VLBI satellite observations are still at an experimental stage. Further research is required to establish an operational process chain, similar to that applied for natural radio sources, such as quasars, which are observed generally. In 2015 we successfully carried out several experiments on the Australian baseline Ceduna-Hobart. During these sessions, with a few hours duration each, GNSS satellites (GLONASS and GPS) were observed in the L1 and L2 band along with natural radio sources for calibrations. All experiments were based on schedule files created with the satellite scheduling module in the Vienna VLBI Software (VieVS). The recorded data were successfully correlated with the DiFX correlator software in combination with a suitable input model for near field targets. A preliminary analysis of the group delay measurements derived with the AIPS software suite was carried out with VieVS. Using this workflow we can achieve a measurement precision of the group delays down to a few picoseconds (5-30, depending on the satellite) over a 5 minutes track. Nevertheless, our results also show a residual signal of a few nanoseconds, which might be caused by the ionosphere or insufficient orbit modelling in the present state of

  9. Towards a four technique GGOS site: VLBI - DORIS compatibility tests at Wettzell

    NASA Astrophysics Data System (ADS)

    Klügel, Thomas; Didelot, Francois; Kodet, Jan; Kronschnabl, Gerhard; Mähler, Swetlana; Neidhardt, Alexander; Plötz, Christian; Saunier, Jérôme; Schüler, Torben; Walter, Jean-Marc

    2016-04-01

    Within the framework of a Global Geodetic Observing System (GGOS), co-location sites are of special importance for the evaluation and mutual control of the individual geodetic space techniques. At the Geodetic Observatory Wettzell a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) beacon could complete the geodetic instrumentation consisting of three Very Long Baseline Interferometry (VLBI) telescopes, two Laser Ranging (LR) systems and a number of multi- Global Navigation Satellite System (GNSS) stations. Integrating all fourth geodetic instrumentation into one site generates new problems with Electromagnetic Compatibility (EMC). While the VLBI system is designed to receive very weak signals from quasars, the DORIS beacon emits strong signals in the UHF frequency band at 401.25 MHz and in the S band at 2036.25 MHz. During the observation of quasars with VLBI there is a high risk of coupling DORIS S band signals into the VLBI receiving chain generating spurious signal and, in the worst case, overloading receiving chain electronics and risking its damage. Before a DORIS beacon is operated at the Geodetic Observatory Wettzell, it must be ensured that it can be operated alongside the VLBI system without any risk of damage or degradation of the measurement. Field tests under different setups were performed to assess the impact of the DORIS signal on the classical geodetic VLBI 20-m and the VGOS 13-m radio telescopes. Different locations on the observatory each at a distance of more than 100 m were occupied by the DORIS antenna. It has been shown that obstacles like buildings or earth mounds attenuate the signal up to 20 dB. However the power received at the input of the Low Noise Amplifiers (LNA) is still at a critical level when the radio telescope points towards the DORIS beacon. The quality of the correlated signals is not or barely affected at long baselines. At local baselines however, the DORIS emission as a common mode signal degrades

  10. Current results and developments in astrometric VLBI at the Jet Propulsion Laboratory

    NASA Technical Reports Server (NTRS)

    Purcell, G. H., Jr.; Cohen, E. J.; Fanselow, J. L.; Rogstad, D. H.; Skjerve, L. J.; Spitzmesser, D. J.; Thomas, J. B.

    1979-01-01

    The Jet Propulsion Laboratory's program of astrometric VLBI as one element of a navigation system for interplanetary spacecraft includes developing a radioastrometric source catalog, and a catalog of positions of compact extragalactic radio sources correct to about 0.01 arc sec. The three (64 m) antenna complexes of the Deep Space Network in Spain, Australia, and the U.S. are involved, each equipped to receive simultaneously at wavelengths of 13 and 3.6 cm with total system temperatures of about 20-25 K at both wavelengths. The program is to provide precise values of parameters used in navigational computations, including UT1 accurate to about 0.001s, and current values of polar motion to 30 cm. Bandwidth synthesis methods were applied to measure delays as well as rates regarding source positions derived from observations using the Mark II VLBI recording system which has a sampling rate of four million bits per second.

  11. Intercontinental clock synchronization with the block 1 VLBI system. [Deep Space Network

    NASA Technical Reports Server (NTRS)

    Roth, M. G.

    1982-01-01

    The Block 1 very long baseline interferometer (VLBI) operated by the Deep Space Network (DSN) to make weekly measurements of the relative epoch and rate offsets between the time standards in the global network of DSN stations is discussed. The precision of these measurements routinely achieves sub-microsecond levels for epoch offset and accuracies of better than one part in 10 to the 12th power for rate offset. The implementation of the phase calibrator system permits absolute measurement of epoch offset to better than 10 nanoseconds. With the near-real-time play-back and on-line storage of VLBI data, the Block 1 system typically produces clock parameters within 48 hours from the time of observation.

  12. A VLBI experiment using a remote atomic clock via a coherent fibre link

    PubMed Central

    Clivati, Cecilia; Ambrosini, Roberto; Artz, Thomas; Bertarini, Alessandra; Bortolotti, Claudio; Frittelli, Matteo; Levi, Filippo; Mura, Alberto; Maccaferri, Giuseppe; Nanni, Mauro; Negusini, Monia; Perini, Federico; Roma, Mauro; Stagni, Matteo; Zucco, Massimo; Calonico, Davide

    2017-01-01

    We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks. PMID:28145451

  13. A VLBI variance-covariance analysis interactive computer program. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Bock, Y.

    1980-01-01

    An interactive computer program (in FORTRAN) for the variance covariance analysis of VLBI experiments is presented for use in experiment planning, simulation studies and optimal design problems. The interactive mode is especially suited to these types of analyses providing ease of operation as well as savings in time and cost. The geodetic parameters include baseline vector parameters and variations in polar motion and Earth rotation. A discussion of the theroy on which the program is based provides an overview of the VLBI process emphasizing the areas of interest to geodesy. Special emphasis is placed on the problem of determining correlations between simultaneous observations from a network of stations. A model suitable for covariance analyses is presented. Suggestions towards developing optimal observation schedules are included.

  14. Radio Brightness Temperatures and Angular Dimensions of Recently Predicted Vl-Bi Small-Scale Structures

    NASA Astrophysics Data System (ADS)

    Opher, R.

    1990-11-01

    RESUMEN. Muestro que analisis recientes publicados de fuentes de radio galacticas y extragalacticas predicen estructuras en pequera escala en fuentes de radio extendidas, remanentes de supernova, vientos protoestelares, nubes moleculares, distorsiones del fondo de 3 K, enanas blancas magnetizadas, estrellas de tipo tardio y el Sol. Discuto las temperatu- ras de brillo de radio de estas estructuras y sus ditnensiones. Muestro que estas estructuras son detectables con las sensibilidades actuales de VLBI (o en el futuro cercano). ABSTRACT. I show that recently published analysis of galactic and extragalactic radio sources make predictions of small-scale structures in extended radio sources, supernovae remnants, protostellar winds, molecu- lar clouds, distortions of the 3 K background, magnetized white dwarf binaries, late-type stars and the sun. I discuss the radio brightness temperatures of these structures and their dimensions. I show that these structures are detectable with present (or near future) VLBI sensitivities. : RADIO SOURCES-EXTENDED

  15. A VLBI experiment using a remote atomic clock via a coherent fibre link

    NASA Astrophysics Data System (ADS)

    Clivati, Cecilia; Ambrosini, Roberto; Artz, Thomas; Bertarini, Alessandra; Bortolotti, Claudio; Frittelli, Matteo; Levi, Filippo; Mura, Alberto; Maccaferri, Giuseppe; Nanni, Mauro; Negusini, Monia; Perini, Federico; Roma, Mauro; Stagni, Matteo; Zucco, Massimo; Calonico, Davide

    2017-02-01

    We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks.

  16. From truck to optical fibre: the coming-of-age of eVLBI

    NASA Astrophysics Data System (ADS)

    Szomoru, A.; Biggs, A.; Garrett, M.; van Langevelde, H. J.; Olnon, F.; Paragi, Z.; Parsley, S.; Pogrebenko, S.; Reynolds, C.

    Spurred by the advent of disk-based recording systems and the nearly explosive increase of internet bandwidth, eVLBI (Parsley et al. te{parsley}) has undergone a remarkable development over the past two years. From ftp-based transfers of small amounts of astronomical data, through near real-time correlation (disk-buffered at the correlator), it has culminated this spring in the first three telescope real-time correlation at JIVE (Onsala, Westerbork and Jodrell Bank). In this paper we will give a review of this development and the current state of affairs. We will also address the current limitations and the way we may improve both bandwidth and reliability and finally we will discuss the opportunities a true high-bandwidth real-time VLBI correlator will provide. (astro-ph/0412686)

  17. Physical conditions near red giant and supergiant stars - An interpretation of SiO VLBI maps

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Ross, Randy R.

    1986-01-01

    Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.

  18. International VLBI Service for Geodesy and Astrometry: 2000 General Meeting Proceedings

    NASA Technical Reports Server (NTRS)

    Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

    2000-01-01

    This volume is the proceedings of the first General Meeting of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS), held in Koetzting, Germany, February 21-24, 2000. The content of this volume also appears on the IVS web site at: http://ivscc.gsfc.nasa.gov/publications/gm2000. The goal of the program committee for the General Meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts. The program included reports, tutorials, invited and contributed papers, and poster presentations. The tutorial papers should be particularly useful references because each one provides an overview and introduction to a topic relevant to VLBI.

  19. Observing ULXs with VLBI: the quest for intermediate-mass black holes

    NASA Astrophysics Data System (ADS)

    Paragi, Zsolt; Garrett, M. A.; Biggs, A. D.

    Some of the most extreme ultra-luminous X-ray sources (ULX) are good candidates for the long-sought missing link between stellar-mass and supermassive black holes. These hypothetic intermediate-mass black holes (IMBH) may be revealed by very high angular resolution very long baseline interferometry (VLBI) imaging. We show that these objects are naturally compact and bright enough to be detected with present-day technology. We estimate the minimum mass of black holes in nearby galaxies detectable by the European VLBI Network (EVN), and calculate the expected radio flux densities for various X-ray luminosities. Using recent EVN observations of M82 X-1, we derive an upper limit to the black hole mass of ˜500 M . We conclude that a relativistic jet cannot be responsible for beaming the X rays in this ULX.

  20. A VLBI experiment using a remote atomic clock via a coherent fibre link.

    PubMed

    Clivati, Cecilia; Ambrosini, Roberto; Artz, Thomas; Bertarini, Alessandra; Bortolotti, Claudio; Frittelli, Matteo; Levi, Filippo; Mura, Alberto; Maccaferri, Giuseppe; Nanni, Mauro; Negusini, Monia; Perini, Federico; Roma, Mauro; Stagni, Matteo; Zucco, Massimo; Calonico, Davide

    2017-02-01

    We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks.

  1. Compact Steep Spectrum 3CR radio sources - VLBI observations at 18 CM

    NASA Astrophysics Data System (ADS)

    Fanti, C.; Fanti, R.; Parma, P.; Schilizzi, R. T.; van Breugel, W. J. M.

    1985-02-01

    Results of a program to investigate the kiloparsec-sized radio structure of a representative sample of Compact Steep Spectrum (CSS) sources from the 3CR catalog (Jenkins et al., 1977) are presented. Ten objects (3C49,67, 119, 237, 241, 268.3, 287, 303.1, 343, 343.1) have been mapped at 18 cm with a resolution of about 30 marcsec using the European VLBI Network. In some cases the VLBI data have been supplemented by MERLIN observations at the same wavelength to enhance sensitivity to large-scale structure. The overall sizes of the CSS sources range from about 0.1 to 1 or 2 arcsec, corresponding to linear sizes of the order of 1 to 10 kpc. The morphological classification ranges from double to core-jet to complex; CSS quasars are generally core-jets or complex, while CSS radio galaxies are doubles, although not necessarily simple doubles.

  2. Physical conditions near red giant and supergiant stars - an interpretation of SiO VLBI maps

    NASA Astrophysics Data System (ADS)

    Alcock, Charles; Ross, Randy R.

    1986-11-01

    Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.

  3. Round-Trip System Available to Measure Path Length Variation in Korea VLBI System for Geodesy

    NASA Technical Reports Server (NTRS)

    Oh, Hongjong; Kondo, Tetsuro; Lee, Jinoo; Kim, Tuhwan; Kim, Myungho; Kim, Suchul; Park, Jinsik; Ju, Hyunhee

    2010-01-01

    The construction project of Korea Geodetic VLBI officially started in October 2008. The construction of all systems will be completed by the end of 2011. The project was named Korea VLBI system for Geodesy (KVG), and its main purpose is to maintain the Korea Geodetic Datum. In case of the KVG system, an observation room with an H-maser frequency standard is located in a building separated from the antenna by several tens of meters. Therefore KVG system will adopt a so-called round-trip system to transmit reference signals to the antenna with reduction of the effect of path length variations. KVG s round-trip system is designed not only to use either metal or optical fiber cables, but also to measure path length variations directly. We present this unique round trip system for KVG.

  4. Early science with the Korean VLBI network: evaluation of system performance

    SciTech Connect

    Lee, Sang-Sung; Byun, Do-Young; Kim, Jongsoo; Jung, Taehyun; Song, Min-Gyu; Oh, Chung Sik; Roh, Duk-Gyoo; Je, Do-Heung; Wi, Seog-Oh; Sohn, Bong Won; Oh, Se-Jin; Kim, Kee-Tae; Yeom, Jae-Hwan; Chung, Moon-Hee; Kang, Jiman; Han, Seog-Tae; Lee, Jung-Won; Kim, Bong Gyu; Chung, Hyunsoo; Petrov, Leonid; and others

    2014-04-01

    We report the very long baseline interferometry (VLBI) observing performance of the Korean VLBI Network (KVN). The KVN is the first millimeter-dedicated VLBI network in East Asia. The KVN consists of three 21 m radio telescopes with baseline lengths in a range of 305-476 km. The quasi-optical system equipped on the antennas allows simultaneous observations at 22, 43, 86, and 129 GHz. The first fringes of the KVN were obtained at 22 GHz on 2010 June 8. Test observations at 22 and 43 GHz on 2010 September 30 and 2011 April 4 confirmed that the full cycle of VLBI observations works according to specification: scheduling, antenna control system, data recording, correlation, post-correlation data processing, astrometry, geodesy, and imaging analysis. We found that decorrelation due to instability in the hardware at times up to 600 s is negligible. The atmosphere fluctuations at KVN baseline are partly coherent, which allows us to extend integration time under good winter weather conditions up to 600 s without significant loss of coherence. The post-fit residuals at KVN baselines do not exhibit systematic patterns, and the weighted rms of the residuals is 14.8 ps. The KVN is ready to image compact radio sources both in snapshot and full-track modes with residual noise in calibrated phases of less than 2 deg at 22 and 43 GHz and with dynamic ranges of ∼300 for snapshot mode and ∼1000 for full-track mode. With simultaneous multi-frequency observations, the KVN can be used to make parsec-scale spectral index maps of compact radio sources.

  5. Co-location of Space Geodetic Instruments at the "Quasar" VLBI Network Observatories

    NASA Astrophysics Data System (ADS)

    Finkelstein, A.; Ipatov, A.; Gayazov, I.; Shargorodsky, V.; Smolentsev, S.; Mitryaev, V.; Diyakov, A.; Olifirov, V.; Rahimov, I.

    2012-12-01

    This paper discusses the current status of creating the co-location stations at the observatories of the Russian VLBI network "Quasar". Satellite Laser Ranging systems "Sazhen-TM" manufactured by Research-and-Production Corporation "Precision Systems and Instruments" were installed at all observatories of the network in 2011. The main technical characteristics of the SLR system and the co-location of high-precision observational instruments at the observatories are presented in this paper.

  6. A New Try of Connecting Phase and Resolving Phase Delay in VLBI

    NASA Astrophysics Data System (ADS)

    He, Q. B.; Liu, Q. H.; Chang, S. Q.; Zheng, X.

    2016-11-01

    In the deep space exploration, the differential very long baseline interferometry (ΔVLBI) technique is often used. It can help to achieve better orbit and position determinations of spacecraft. But in the ΔVLBI observation, the correlation phases have gaps in time domain. Connecting the correlation phases without ambiguity 2π helps to resolve the phase delay and obtain spacecraft's orbit with a higher accuracy, and also can make contributions to the planetary science study. Meanwhile, the phase delay is a promising measurement in many fields because of its extremely high accuracy, but it's hard to be obtained. Thus we studied the correlation phase connection and phase delay resolution using the Chang'E-3 data. For the phase connection, we first implemented the idea that differential phase was changing in the same trend with a single spectral line's phase, and then we adjusted the phase ambiguities according to phase closure results. For the phase delay resolution, the method is using phases of two spectral lines which are spaced in a narrow band (1 MHz) to resolve the phase ambiguities. We calculated the phase delay of Chang'E-3 lander, and by only utilizing the VLBI phase delay results, we obtained the lander's location as 44.1239°N, 19.5106°W. The reference of the lander's location is 44.12189°N, 19.51129°W with an accuracy of 20 m. The difference between the two results is about one hundred meters, which proves that the VLBI phase delay can be used alone to determine the spacecraft's position.

  7. Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations

    NASA Astrophysics Data System (ADS)

    Artz, T.; Bernhard, L.; Nothnagel, A.; Steigenberger, P.; Tesmer, S.

    2012-03-01

    A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However, this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall, the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models below 4 μ as in PM and 0.25 μ s in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μ as for diurnal PM and 0.07 μ s for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy.

  8. The catalog of sources for geodetic VLBI from experiments which Kashima station participated in.

    NASA Astrophysics Data System (ADS)

    Takahashi, Y.

    Kashima station participated in many VLBI experiments such as CDP network experiments, JPL network experiments, Japan-Australia-Hawaii experiments and domestic experiments in Japan. Many sources have been observed in these experiments. The correlation amplitude both on a long (several thousand km) and short baseline (several 10 km), source positions and the resolution of the source structure have been obtained. The source positions define a celestial reference frame for the astrometry.

  9. Automated ambiguity estimation for VLBI Intensive sessions using L1-norm

    NASA Astrophysics Data System (ADS)

    Kareinen, Niko; Hobiger, Thomas; Haas, Rüdiger

    2016-12-01

    Very Long Baseline Interferometry (VLBI) is a space-geodetic technique that is uniquely capable of direct observation of the angle of the Earth's rotation about the Celestial Intermediate Pole (CIP) axis, namely UT1. The daily estimates of the difference between UT1 and Coordinated Universal Time (UTC) provided by the 1-h long VLBI Intensive sessions are essential in providing timely UT1 estimates for satellite navigation systems and orbit determination. In order to produce timely UT1 estimates, efforts have been made to completely automate the analysis of VLBI Intensive sessions. This involves the automatic processing of X- and S-band group delays. These data contain an unknown number of integer ambiguities in the observed group delays. They are introduced as a side-effect of the bandwidth synthesis technique, which is used to combine correlator results from the narrow channels that span the individual bands. In an automated analysis with the c5++ software the standard approach in resolving the ambiguities is to perform a simplified parameter estimation using a least-squares adjustment (L2-norm minimisation). We implement L1-norm as an alternative estimation method in c5++. The implemented method is used to automatically estimate the ambiguities in VLBI Intensive sessions on the Kokee-Wettzell baseline. The results are compared to an analysis set-up where the ambiguity estimation is computed using the L2-norm. For both methods three different weighting strategies for the ambiguity estimation are assessed. The results show that the L1-norm is better at automatically resolving the ambiguities than the L2-norm. The use of the L1-norm leads to a significantly higher number of good quality UT1-UTC estimates with each of the three weighting strategies. The increase in the number of sessions is approximately 5% for each weighting strategy. This is accompanied by smaller post-fit residuals in the final UT1-UTC estimation step.

  10. A new atmospheric ray-tracing algorithm and its use in VLBI analysis

    NASA Astrophysics Data System (ADS)

    Madzak, M.; Nafisi, V.; Böhm, J.; Schuh, H.

    2012-04-01

    Due to recent improvements of numerical weather models (NWM), ray-tracing has become an interesting and feasible method for different scientific purposes. One application in geosciences is the estimation of tropospheric delays for the correction of space geodetic techniques. Here, we present and discuss the recently developed ray-tracing algorithm from the Institute of Geodesy and Geophysics (IGG) at Vienna University of Technology. We use numerical weather model data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to estimate the tropospheric total delay by solving the Eikonal equation. In addition we discuss different methods and characteristics, such as interpolation methods, resolution of the data set and the use of different refractivity constants, and we present results and differences between a 2D- and 3D-ray-tracing algorithm. As quality validation we enter the derived tropospheric delays as a priori information in our VLBI analysis software package (Vienna VLBI Software). We analyze IVS Intensive sessions from July 2010 to October 2011 which are carried out for the estimation of UT1-UTC (DUT1). The measurement of this Earth rotation angle is needed in near real-time for the accurate prediction of Universal Time (UT1) as well as for navigation purposes. Due to the small number of observables per session most parameters, which are usually estimated in VLBI analyses, are fixed to their a priori values, which should be known as accurately as possible. As an external validation of our ray-traced delays we calculate Length-of-Day (LoD) from the VLBI-derived DUT1 values and compare these to LoD from GPS.

  11. The NASA VLBI2010 Proof-of-Concept Demonstration and Future Plans

    NASA Technical Reports Server (NTRS)

    Niell, Arthur

    2010-01-01

    The next generation geodetic VLBI instrument is being developed with a goal of 1 mm position uncertainty in twenty-four hours. We have implemented a proof-of-concept system for a possible VLBI2010 signal chain, from feed through recorder, on the Westford (Massachusetts, USA) 18-m and MV-3 (Maryland, USA) 5-m antennas. Data have been obtained in four 512 MHz bands spanning the range 3.5 to 11 GHz to investigate the sensitivity and phase delay capability of the system. Using a new phase cal design, the phases have been aligned across four bands spanning 2 GHz with an RMS deviation of approximately eight degrees. Several components of the system will be improved for the prototype version of VLBI2010, including the feed, digital backend, and recorder, and these will be installed on a 12-m antenna that has been purchased and is ready for installation at the Goddard Space Flight Center outside of Washington, D.C., USA, site of the MV-3 antenna.

  12. The Tropospheric Products of the International VLBI Service for Geodesy and Astrometry

    NASA Technical Reports Server (NTRS)

    Heinkelmann, Robert; Schwatke, Christian

    2010-01-01

    The IVS runs two tropospheric products: The IVS tropospheric parameter rapid combination monitors the zenith wet delay (ZWD) and zenith total delay (ZTD) of the rapid turnaround sessions R1 and R4. Goal of the combination is the identification and the exclusion of outliers by comparison and the assessment of the precision of current VLBI solutions in terms of tropospheric parameters. The rapid combination is done on a weekly basis four weeks after the observation files are released on IVS Data Centers. Since tropospheric and geodetic parameters, such as vertical station components, can significantly correlate, the consistency of the ZTD can be a measure of the consistency of the corresponding TRF as well. The ZWD mainly rely on accurate atmospheric pressure data. Thus, besides estimation techniques, modeling and analyst s noise, ZWD reflects differences in the atmospheric pressure data applied to the VLBI analysis. The second product, called tropospheric parameter long-term combination, aims for an accurate determination of climatological signals, such as trends of the atmospheric water vapor observed by VLBI. Therefore, the long-term homogeneity of atmospheric pressure data plays a crucial role for this product. The paper reviews the methods applied and results achieved so far and describes the new maintenance through DGFI.

  13. The Potential for a Ka-band (32 GHz) Worldwide VLBI Network

    NASA Technical Reports Server (NTRS)

    Jacobs, C. S.; Bach, U.; Colomer, F.; Garcia-Miro, C.; Gomez-Gonzalez, J.; Gulyaev, S.; Horiuchi, S.; Ichikawa, R.; Kraus, A.; Kronschnabl, G.; Lopez-Fernandez, J. A.; Lovell, J.; Majid, W.; Natusch, T.; Neidhardt, A.; Phillips, C.; Porcas, R.; Romero-Wolf, A.; Saldana, L.; Schreiber, U.; Sotuela, I.; Takeuchi, H.; Trinh, J.; Tzioumis, A.; deVincente, P.

    2012-01-01

    Ka-band (32 GHz, 9mm) Very Long Baseline Interferometric (VLBI) networking has now begun and has tremendous potential for expansion over the next few years. Ka-band VLBI astrometry from NASA's Deep Space Network has already developed a catalog of 470 observable sources with highly accurate positions. Now, several antennas worldwide are planning or are considering adding Ka-band VLBI capability. Thus, there is now an opportunity to create a worldwide Ka-band network with potential for high resolution imaging and astrometry. With baselines approaching a Giga-lambda, a Ka-band network would be able to probe source structure at the nano-radian (200 as) level ( 100X better than Hubble) and thus gain insight into the astrophysics of the most compact regions of emission in active galactic nuclei. We discuss the advantages of Ka-band, show the known sources and candidates, simulate projected baseline (uv) coverage, and discuss potential radio frequency feeds. The combination of these elements demonstrates the feasibility of a worldwide Ka network within the next few years!

  14. Determination of the Venus flyby orbits of the Soviet Vega probes using VLBI techniques

    NASA Technical Reports Server (NTRS)

    Ellis, J.; Mcelrath, Timothy P.

    1988-01-01

    In December 1984, the Soviet Union launched two identical Vega spacecraft with the dual objective of exploring Venus and continuing to rendezvous with the comet Halley. The two Vega spacecraft encountered Venus in mid-June 1985 and successfully deployed entry probes and wind-measuring balloons into the Venus atmosphere. An objective of the Venus Balloon experiment was to measure the Venus winds using differential VLBI from the balloon and the flyby bus. NASA's Deep Space 64 meter subnet was part of a world wide network organized to collect data from the Vega probes and balloons. A critical element of this experiment was an accurate determination of the Venus relative flyby orbits of the Vega spacecraft during the 46 hour balloon lifetime. Venus flyby solutions were independently determined by the Soviets using two-way range and Doppler from Soviet stations and by JPL using one-way Doppler and VLBI data collected from the DSN. The Vega flyby solutions determined by the Soviets using a sparse two-way tracking strategy with JPL solutions using the DSN VLBI data to complement the Soviet data and with solutions using only one-way data collected by the DSN were compared.

  15. THE IMPACT OF FREQUENCY STANDARDS ON COHERENCE IN VLBI AT THE HIGHEST FREQUENCIES

    SciTech Connect

    Rioja, M.; Dodson, R.; Asaki, Y.; Hartnett, J.; Tingay, S.

    2012-10-01

    We have carried out full imaging simulation studies to explore the impact of frequency standards in millimeter and submillimeter very long baseline interferometry (VLBI), focusing on the coherence time and sensitivity. In particular, we compare the performance of the H-maser, traditionally used in VLBI, to that of ultra-stable cryocooled sapphire oscillators over a range of observing frequencies, weather conditions, and analysis strategies. Our simulations show that at the highest frequencies, the losses induced by H-maser instabilities are comparable to those from high-quality tropospheric conditions. We find significant benefits in replacing H-masers with cryocooled sapphire oscillator based frequency references in VLBI observations at frequencies above 175 GHz in sites which have the best weather conditions; at 350 GHz we estimate a 20%-40% increase in sensitivity over that obtained when the sites have H-masers, for coherence losses of 20%-10%, respectively. Maximum benefits are to be expected by using co-located Water Vapor Radiometers for atmospheric correction. In this case, we estimate a 60%-120% increase in sensitivity over the H-maser at 350 GHz.

  16. Influence of ocean tides on the diurnal and semidiurnal earth rotation variations from VLBI observations

    NASA Astrophysics Data System (ADS)

    Gubanov, V. S.; Kurdubov, S. L.

    2015-05-01

    The International astrogeodetic standard IERS Conventions (2010) contains a model of the diurnal and semidiurnal variations in Earth rotation parameters (ERPs), the pole coordinates and the Universal Time, arising from lunisolar tides in the world ocean. This model was constructed in the mid-1990s through a global analysis of Topex/Poseidon altimetry. The goal of this study is to try to estimate the parameters of this model by processing all the available VLBI observations on a global network of stations over the last 35 years performed within the framework of IVS (International VLBI Service) geodetic programs. The complexity of the problemlies in the fact that the sought-for corrections to the parameters of this model lie within 1 mm and, thus, are at the limit of their detectability by all currently available methods of ground-based positional measurements. This requires applying universal software packages with a high accuracy of reduction calculations and a well-developed system of controlling the simultaneous adjustment of observational data to analyze long series of VLBI observations. This study has been performed with the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences. Although the results obtained, on the whole, confirm a high accuracy of the basic model in the IERS Conventions (2010), statistically significant corrections that allow this model to be refined have been detected for some harmonics of the ERP variations.

  17. Initial Results Obtained with the First TWIN VLBI Radio Telescope at the Geodetic Observatory Wettzell

    PubMed Central

    Schüler, Torben; Kronschnabl, Gerhard; Plötz, Christian; Neidhardt, Alexander; Bertarini, Alessandra; Bernhart, Simone; la Porta, Laura; Halsig, Sebastian; Nothnagel, Axel

    2015-01-01

    Geodetic Very Long Baseline Interferometry (VLBI) uses radio telescopes as sensor networks to determine Earth orientation parameters and baseline vectors between the telescopes. The TWIN Telescope Wettzell 1 (TTW1), the first of the new 13.2 m diameter telescope pair at the Geodetic Observatory Wettzell, Germany, is currently in its commissioning phase. The technology behind this radio telescope including the receiving system and the tri-band feed horn is depicted. Since VLBI telescopes must operate at least in pairs, the existing 20 m diameter Radio Telescope Wettzell (RTW) is used together with TTW1 for practical tests. In addition, selected long baseline setups are investigated. Correlation results portraying the data quality achieved during first initial experiments are discussed. Finally, the local 123 m baseline between the old RTW telescope and the new TTW1 is analyzed and compared with an existing high-precision local survey. Our initial results are very satisfactory for X-band group delays featuring a 3D distance agreement between VLBI data analysis and local ties of 1 to 2 mm in the majority of the experiments. However, S-band data, which suffer much from local radio interference due to WiFi and mobile communications, are about 10 times less precise than X-band data and require further analysis, but evidence is provided that S-band data are well-usable over long baselines where local radio interference patterns decorrelate. PMID:26263991

  18. The Potential for a Ka-band (32 GHz) Worldwide VLBI Network

    NASA Technical Reports Server (NTRS)

    Jacobs, C. S.; Bach, U.; Colomer, F.; Garcia-Miro, C.; Gomez-Gonzalez, J.; Gulyaev, S.; Horiuchi, S.; Ichikawa, R.; Kraus, A.; Kronschnabl, G.; hide

    2012-01-01

    Ka-band (32 GHz, 9mm) Very Long Baseline Interferometric (VLBI) networking has now begun and has tremendous potential for expansion over the next few years. Ka-band VLBI astrometry from NASA's Deep Space Network has already developed a catalog of 470 observable sources with highly accurate positions. Now, several antennas worldwide are planning or are considering adding Ka-band VLBI capability. Thus, there is now an opportunity to create a worldwide Ka-band network with potential for high resolution imaging and astrometry. With baselines approaching a Giga-lambda, a Ka-band network would be able to probe source structure at the nano-radian (200 as) level ( 100X better than Hubble) and thus gain insight into the astrophysics of the most compact regions of emission in active galactic nuclei. We discuss the advantages of Ka-band, show the known sources and candidates, simulate projected baseline (uv) coverage, and discuss potential radio frequency feeds. The combination of these elements demonstrates the feasibility of a worldwide Ka network within the next few years!

  19. Initial Results Obtained with the First TWIN VLBI Radio Telescope at the Geodetic Observatory Wettzell.

    PubMed

    Schüler, Torben; Kronschnabl, Gerhard; Plötz, Christian; Neidhardt, Alexander; Bertarini, Alessandra; Bernhart, Simone; la Porta, Laura; Halsig, Sebastian; Nothnagel, Axel

    2015-07-30

    Geodetic Very Long Baseline Interferometry (VLBI) uses radio telescopes as sensor networks to determine Earth orientation parameters and baseline vectors between the telescopes. The TWIN Telescope Wettzell 1 (TTW1), the first of the new 13.2 m diameter telescope pair at the Geodetic Observatory Wettzell, Germany, is currently in its commissioning phase. The technology behind this radio telescope including the receiving system and the tri-band feed horn is depicted. Since VLBI telescopes must operate at least in pairs, the existing 20 m diameter Radio Telescope Wettzell (RTW) is used together with TTW1 for practical tests. In addition, selected long baseline setups are investigated. Correlation results portraying the data quality achieved during first initial experiments are discussed. Finally, the local 123 m baseline between the old RTW telescope and the new TTW1 is analyzed and compared with an existing high-precision local survey. Our initial results are very satisfactory for X-band group delays featuring a 3D distance agreement between VLBI data analysis and local ties of 1 to 2 mm in the majority of the experiments. However, S-band data, which suffer much from local radio interference due to WiFi and mobile communications, are about 10 times less precise than X-band data and require further analysis, but evidence is provided that S-band data are well-usable over long baselines where local radio interference patterns decorrelate.

  20. Greenland Telescope (GLT) Project. "A Direct Confirmation of Black Hole with Submillimeter VLBI"

    NASA Astrophysics Data System (ADS)

    Nakamura, M.; Algaba, J. C.; Asada, K.; Chen, B.; Chen, M.-T.; Han, J.; Ho, P. H. P.; Hsieh, S.-N.; Huang, T.; Inoue, M.; Koch, P.; Kuo, C.-Y.; Martin-Cocher, P.; Matsushita, S.; Meyer-Zhao, Z.; Nishioka, H.; Nystrom, G.; Pradel, N.; Pu, H.-Y.; Raffin, P.; Shen, H.-Y.; Tseng, C.-Y.

    2013-12-01

    The GLT project is deploying a new submillimeter (submm) VLBI station in Greenland. Our primary scientific goal is to image a shadow of the supermassive black hole (SMBH) of six billion solar masses in M87 at the center of the Virgo cluster of galaxies. The expected SMBH shadow size of 40-50 μas requires superbly high angular resolution, suggesting that the submm VLBI would be the only way to obtain the shadow image. The Summit station in Greenland enables us to establish baselines longer than 9,000 km with ALMA in Chile and SMA in Hawaii as well as providing a unique u-v coverage for imaging M87. Our VLBI network will achieve a superior angular resolution of about 20 μas at 350 GHz, corresponding to ˜ 2.5 times of the Schwarzschild radius of the supermassive black hole in M87. We have been monitoring the atmospheric opacity at 230 GHz since August. 2011; we have confirmed the value on site during the winter season is comparable to the ALMA site thanks to high altitude of 3,200 m and low temperature of -50°C. We will report current status and future plan of the GLT project towards our expected first light on 2015-2016.

  1. Combining GPS and Terrestrial Methods In VLBI Antenna's Reference Point Determination

    NASA Astrophysics Data System (ADS)

    Sarti, P.; Vittuari, L.; Tomasi, P.

    Surveying the reference point of VLBI radiotelescopes within a local ground control network is, nowadays, a very important task. Reference point can be determined using a molteplicity of approaches. We have choosen and tested a purely theoretical ap- proach, writing two routines for best-fitting 3-D surfaces computation. Surveying the antenna structure as it moves in azimuth and elevation permits the determination of a set of points' positions that are used to determine best-fit spheres and planes whose intersections relates to VLBI antenna axes, i.e.: to the reference point. Our opera- tive dataset has been created during a 14 days campaign performed in June 2001 at Medicina (Bologna-Italy) observatory using both Kinematic GPS and two total sta- tions. GPS data have been analysed using both commercial (GeoGenius 2000 and Geotracer V2.29) and scientific software (GIPSY V.2.6.1). We will present the es- timated reference point's coordinates for the VLBI radiotelescope within ITRF2000 and a local reference frame obtained using KGPS and classical geodesy.

  2. Determination of the Venus flyby orbits of the Soviet Vega probes using VLBI techniques

    NASA Technical Reports Server (NTRS)

    Ellis, J.; Mcelrath, Timothy P.

    1988-01-01

    In December 1984, the Soviet Union launched two identical Vega spacecraft with the dual objective of exploring Venus and continuing to rendezvous with the comet Halley. The two Vega spacecraft encountered Venus in mid-June 1985 and successfully deployed entry probes and wind-measuring balloons into the Venus atmosphere. An objective of the Venus Balloon experiment was to measure the Venus winds using differential VLBI from the balloon and the flyby bus. NASA's Deep Space 64 meter subnet was part of a world wide network organized to collect data from the Vega probes and balloons. A critical element of this experiment was an accurate determination of the Venus relative flyby orbits of the Vega spacecraft during the 46 hour balloon lifetime. Venus flyby solutions were independently determined by the Soviets using two-way range and Doppler from Soviet stations and by JPL using one-way Doppler and VLBI data collected from the DSN. The Vega flyby solutions determined by the Soviets using a sparse two-way tracking strategy with JPL solutions using the DSN VLBI data to complement the Soviet data and with solutions using only one-way data collected by the DSN were compared.

  3. First geodetic VLBI sessions with the Chinese Deep Space Stations Jiamusi and Kashi

    NASA Astrophysics Data System (ADS)

    Xu, Dezhen; Dong, Guangliang; Wang, Guangli; Li, Haitao; Jiang, Wu

    2016-11-01

    The first three 24-h S/X dual-band geodetic VLBI sessions using two new Chinese Deep Space Stations (CDSSs), Jiamusi and Kashi, and four Chinese VLBI Stations (CVSs), Beijing, Kunming, Seshan, and Urumqi were conducted with the goal of improving the two CDSSs' positions, which were previously known to a few decimeters. Due to the limited frequency ranges of Jiamusi and Kashi, different but compatible frequencies for bandwidth synthesis were set at the CDSS and CVS stations. This paper presents the scheduling, correlation and fringe fit, and geodetic analysis of the observations. Final estimates of the station positions are obtained from the global solution using 5365 international VLBI sessions from August 3, 1979 through September 29, 2015. Position estimates for Jiamusi are accurate to 23, 35, and 41 mm in the X, Y, and Z directions, respectively, and for Kashi are accurate to 10, 20, and 16 mm. Precisions of the two CDSSs' positions are improved by a factor of 5-10 over previous values, which fully satisfies the requirements of the experiments and makes the first step towards the foundation and maintenance of the time-space reference frame based on the Chinese Deep Space Network (CDSN).

  4. On estimation of the free core nutation parameters from analysis of the VLBI celestial pole offsets

    NASA Astrophysics Data System (ADS)

    Brzezinski, A.

    2013-12-01

    The free core nutation (FCN) resonance influences Earth rotation in two different ways: 1) through resonant enhancement of the amplitudes of those forced nutation components which are close to the FCN frequency (indirect effect); 2) it gives rise to the free oscillation of the pole in response to the irregular nearly-diurnal geophysical forcing (direct effect). It is commonly believed that the best estimate of the FCN parameters, the space-referred period T and the quality factor Q, is that from the VLBI determination of the nutation amplitudes. The estimated values corresponding to the MHB2000 precession-nutatin model are T=-430 days and Q=20 000 with quite narrow uncertainty limits (429.93,430.48) and (18 870,21 280), respectively. Here we focus attention on determination of T and Q from analysis of the FCN signal observed by VLBI since 1984. The underlying stochastic model is similar to that applied since decades for analysis of the Chandler wobble, the so-called "pea-shooter" model proposed by Jeffreys (1940). We discuss here different ways of implementation of such model based on the methods of time series analysis. We also show and compare the FCN parameters derived from various available VLBI nutation data sets.

  5. Probing into the Shadow of Galactic Center Black Hole with Future Sub-millimeter VLBI

    NASA Astrophysics Data System (ADS)

    Shen, Z.-Q.

    2009-08-01

    Sgr A* is the closest massive black hole candidate with the largest angular size of its Schwarzschild radius (about 10 μas). Unfortunately, Sgr A* is not a suitable target for the next generation space-VLBI mission, VSOP-2, even at its highest frequency of 43 GHz. This is mainly because of its too big (scattering-broadened) apparent size compared to the angular resolution of VSOP-2, which makes space baselines unnecessary for the imaging study of Sgr A*. Rather, recent development of VLBI observations at shorter millimeter wavelengths has led to the firm detection of the intrinsic size of the emission region of Sgr A* (about 1 AU at 86 GHz). Future sub-millimeter VLBI observation is promising in resolving the shadow of Sgr A*, which could be a test of the general relativity in strong field regime. Our simulation demonstrates that visibility analysis can constrain the geometry of radio emitting region surrounding Sgr A*. We are on the verge of resolving the shadow of Sgr A*.

  6. Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14

    NASA Astrophysics Data System (ADS)

    Haas, Rüdiger; Hobiger, Thomas; Kurihara, Shinobu; Hara, Tetsuya

    2017-07-01

    We present earth rotation results from the ultra-rapid operations during the continuous VLBI campaigns CONT11 and CONT14. The baseline Onsala-Tsukuba, i.e., using two out of the 13 and 17 stations contributing to CONT11 and CONT14, respectively, was used to derive UT1-UTC in ultra-rapid mode during the ongoing campaigns. The latency between a new observation and a new UT1-UTC result was less than 10 min for more than 95% of the observations. The accuracy of the derived ultra-rapid UT1-UTC results is approximately a factor of three worse than results from optimized one-baseline sessions and/or complete analysis of large VLBI networks. This is, however, due to that the one-baseline picked from the CONT campaigns is not optimized for earth rotation determination. Our results prove that the 24/7 operation mode planned for VGOS, the next-generation VLBI system, is possible already today. However, further improvements in data connectivity of stations and correlators as well in the automated analysis are necessary to realize the ambitious VGOS plans.

  7. Direct estimation of tidally induced Earth rotation variations observed by VLBI

    NASA Astrophysics Data System (ADS)

    Englich, S.; Heinkelmann, R.; BOHM, J.; Schuh, H.

    2009-09-01

    The subject of our study is the investigation of periodical variations induced by solid Earth tides and ocean tides in Earth rotation parameters (ERP: polar motion, UT1)observed by VLBI. There are two strategies to determine the amplitudes and phases of Earth rotation variations from observations of space geodetic techniques. The common way is to derive time series of Earth rotation parameters first and to estimate amplitudes and phases in a second step. Results obtained by this means were shown in previous studies for zonal tidal variations (Englich et al.; 2008a) and variations caused by ocean tides (Englich et al.; 2008b). The alternative method is to estimate the tidal parameters directly within the VLBI data analysis procedure together with other parameters such as station coordinates, tropospheric delays, clocks etc. The purpose of this work was the application of this direct method to a combined VLBI data analysis using the software packages OCCAM (Version 6.1, Gauss-Markov-Model) and DOGSCS (Gerstl et al.; 2001). The theoretical basis and the preparatory steps for the implementation of this approach are presented here.

  8. Images of VLBI Calibrators from the BeSSeL Survey

    NASA Astrophysics Data System (ADS)

    Zhang, Bo

    2016-12-01

    The BeSSeL Survey is a VLBA Key Science project. The primary goal of the survey is to study the spiral structure and kinematics of the Milky Way, by measuring distances and proper motions to masers in regions of massive star formation across large portions of the Milky Way. To measure the distances of Masers via trigonometric parallaxes, the relative positions between the masers and extragalactic VLBI calibrators are determined with phase-referencing at different epochs spanning at least one year. The Masers usually serve as phase reference since they are much stronger than the calibrators, allowing integration times about one hour for the weak calibrators. In addition, the calibrators are often observed through the whole observing program, providing excellent uv-coverage for imaging. From the BeSSeL survey, there will be about 4,000 high-quality images of about 200 VLBI calibrators distributed near the Galactic plane. In this report, we present basic information of the VLBI calibrator images from the BeSSeL survey.

  9. Chang'E-3 spacecraft surface reflection causes turbulence on VLBI delay

    NASA Astrophysics Data System (ADS)

    He, Qingbao; Liu, Qinghui; Zheng, Xin

    2017-02-01

    The third Chinese lunar spacecraft Chang'E-3 (CE3) was launched in 2013, and very long baseline interferometry (VLBI) observations were performed to improve accuracy of its orbit determination. During all the observation time, VLBI group delay experienced very large turbulence, which was up to hundreds of picoseconds, and with variation period of a few tens of seconds. However, VLBI group delay of another lunar spacecraft Chang'E-5-T1 (CE5T1), which was launched in 2014, did not show such turbulence. Influences from the troposphere, ionosphere, ground instruments, and phase characteristics of the on board antennas were considered at first, but none of these were the main cause of this large turbulence. Further investigations were made on differential phase delay turbulence, signal-to-noise ratio, and layout of spacecraft. The investigation results indicated that the large turbulence on group delay was caused by an interference of reflected signals from the CE3 spacecraft surface. Simulations proved that the delay error caused by signal reflection varied with frequency and therefore caused large turbulence on group delay. To minimize the multipath effect caused by signal reflection, some possible solutions are presented.

  10. Observation model and parameter partials for the JPL VLBI parameter estimation software MODEST, 19 94

    NASA Technical Reports Server (NTRS)

    Sovers, O. J.; Jacobs, C. S.

    1994-01-01

    This report is a revision of the document Observation Model and Parameter Partials for the JPL VLBI Parameter Estimation Software 'MODEST'---1991, dated August 1, 1991. It supersedes that document and its four previous versions (1983, 1985, 1986, and 1987). A number of aspects of the very long baseline interferometry (VLBI) model were improved from 1991 to 1994. Treatment of tidal effects is extended to model the effects of ocean tides on universal time and polar motion (UTPM), including a default model for nearly diurnal and semidiurnal ocean tidal UTPM variations, and partial derivatives for all (solid and ocean) tidal UTPM amplitudes. The time-honored 'K(sub 1) correction' for solid earth tides has been extended to include analogous frequency-dependent response of five tidal components. Partials of ocean loading amplitudes are now supplied. The Zhu-Mathews-Oceans-Anisotropy (ZMOA) 1990-2 and Kinoshita-Souchay models of nutation are now two of the modeling choices to replace the increasingly inadequate 1980 International Astronomical Union (IAU) nutation series. A rudimentary model of antenna thermal expansion is provided. Two more troposphere mapping functions have been added to the repertoire. Finally, corrections among VLBI observations via the model of Treuhaft and lanyi improve modeling of the dynamic troposphere. A number of minor misprints in Rev. 4 have been corrected.

  11. Determination of nutation offsets by combining VLBI/GPS-produced normal equations

    NASA Astrophysics Data System (ADS)

    Kudryashova, Maria; Lambert, Sebastien; Dehant, Veronique; Bruyninx, Carine

    2010-05-01

    Longstanding routing operation of individual geodetic space- and ground-based techniques (like, for instance, VLBI, GNSS, LLR, etc.) revealed their strong and weak aspects. More effective use of these strengths as well as reduction of their weaknesses is possible by incorporating of the information collected by each individual technique into combined products. Such a consistent combination can be performed either by combination at the observational level or at the level of normal equations. We concentrate on the combination of normal equations gathered during VLBI/GPS-data processing. The main goal of this combination is to construct a time series of nutation offsets in the most consistent way. The objective of this presentation is to describe the developed strategy of combination and to present the current status of tits implementation. For the purpose of step-by-step validation of our procedure we use two-month-long time series of normal equations produced from VLBI and GPS observations by means of CALC/SOLVE and BERNESE v.5.0 software, respectively. Earth orientation parameter determination will, in our procedure, benefit from angle and rate observation for a unique estimation.

  12. The simulation of lunar gravity field recovery from D-VLBI of Chang’E-1 and SELENE lunar orbiters

    NASA Astrophysics Data System (ADS)

    Yan, Jianguo; Ping, Jingsong; Matsumoto, K.; Li, Fei

    2008-07-01

    The lunar gravity field is a foundation to study the lunar interior structure, and to recover the evolution history of the Moon. It is still an open and key topic for lunar science. For above mentioned reasons, it becomes one of the important scientific objectives of recent lunar missions, such as KAGUYA (SELENE) the Japanese lunar mission and Chang’E-1, the Chinese lunar mission. The Chang’E-1 and the SELENE were successfully launched in 2007. It is estimated that these two missions can fly around the Moon longer than 6 months simultaneously. In these two missions, the Chinese new VLBI (Very Long Baseline Interferometry) network will be applied for precise orbit determination (POD) by using a differential VLBI (D-VLBI) method during the mission period. The same-beam D-VLBI technique will contribute to recover the lunar gravity field together with other conventional observables, i.e. R&RR (Range and Range Rate) and multi-way Doppler. Taking VLBI tracking conditions into consideration and using the GEODYNII/SOVLE software of GSFC/NASA/USA [Rowlands, D.D., Marshall, J.A., Mccarthy, J., et al. GEODYN II System Description, vols. 1 5. Contractor Report, Hughes STX Corp. Greenbelt, MD, 1997; Ullman, R.E. SOLVE program: mathematical formulation and guide to user input, Hughes/STX Contractor Report, Contract NAS5-31760. NASA Goddard Space Flight Center, Greenbelt, Maryland, 1994], we simulated the lunar gravity field recovering ability with and without D-VLBI between the Chang’E-1 and SELENE main satellite. The cases of overlapped flying and tracking period of 30 days, 60 days and 90 days have been analyzed, respectively. The results show that D-VLBI tracking between two lunar satellites can improve the gravity field recovery remarkably. The results and methods introduced in this paper will benefit the actual missions.

  13. The Impact of the AuScope VLBI Observations and the Regional AUSTRAL Sessions on the TRF

    NASA Astrophysics Data System (ADS)

    Plank, L.; Lovell, J.; McCallum, J.; Boehm, J.; Shabala, S.; Mayer, D.; Sun, J.; Titov, O.; Weston, S.; Quick, J.; Rastorgueva-Foi, E.

    2014-12-01

    The AuScope VLBI array was built with the purpose to improve the terrestrial (TRF) and celestial reference frames in the southern hemisphere. Since 2010 the three 12-m antennas in Hobart (Tasmania), Katherine (Northern Territory) and Yarragadee (Western Australia) heavily contribute to the global VLBI observations coordinated by the International VLBI Service for Geodesy and Astrometry. In 2011, the AUSTRAL VLBI program was started, with more than 40 sessions being observed so far. In the AUSTRALs, the three AuScope antennas observe together with the new 15-m dish in Hartebeesthoek (South Africa) and the 12-m antenna in Warkworth (New Zealand). Recently, the planned observations have been expanded again, with 50 additional sessions scheduled until mid-2015, along with 3 continuous campaigns covering 15 days each. All AUSTRALs are recorded with an increased data rate of 1 Gbps, allowing to compensate for the reduced sensitivity of the generally smaller dish size. We evaluate the positive impact of the AuScope VLBI program on the global TRF. This is due to the increased number of observations and the improved homogeneity of the global VLBI network. All data collected within this intense observing program is analysed and geodetic results are presented. This includes time series of baseline lengths and station coordinates of the contributing stations. We compare the results obtained within the regional AUSTRAL sessions with the ones of the classical global VLBI networks and identify superiorities and shortcomings of both. The high number of sessions gives high accuracies and good repeatabilities of the determined parameters. Additionally, remaining variations of baseline lengths can be identified and are compared against by default un-modelled station motions due to hydrology and atmosphere loading. Finally, we give an outlook on future plans for the AuScope antennas and the AUSTRAL observing program: on future operations, expected improvements through hardware

  14. Application of ray-traced tropospheric slant delays to geodetic VLBI analysis

    NASA Astrophysics Data System (ADS)

    Hofmeister, Armin; Böhm, Johannes

    2017-02-01

    The correction of tropospheric influences via so-called path delays is critical for the analysis of observations from space geodetic techniques like the very long baseline interferometry (VLBI). In standard VLBI analysis, the a priori slant path delays are determined using the concept of zenith delays, mapping functions and gradients. The a priori use of ray-traced delays, i.e., tropospheric slant path delays determined with the technique of ray-tracing through the meteorological data of numerical weather models (NWM), serves as an alternative way of correcting the influences of the troposphere on the VLBI observations within the analysis. In the presented research, the application of ray-traced delays to the VLBI analysis of sessions in a time span of 16.5 years is investigated. Ray-traced delays have been determined with program RADIATE (see Hofmeister in Ph.D. thesis, Department of Geodesy and Geophysics, Faculty of Mathematics and Geoinformation, Technische Universität Wien. http://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-3444, 2016) utilizing meteorological data provided by NWM of the European Centre for Medium-Range Weather Forecasts (ECMWF). In comparison with a standard VLBI analysis, which includes the tropospheric gradient estimation, the application of the ray-traced delays to an analysis, which uses the same parameterization except for the a priori slant path delay handling and the used wet mapping factors for the zenith wet delay (ZWD) estimation, improves the baseline length repeatability (BLR) at 55.9% of the baselines at sub-mm level. If no tropospheric gradients are estimated within the compared analyses, 90.6% of all baselines benefit from the application of the ray-traced delays, which leads to an average improvement of the BLR of 1 mm. The effects of the ray-traced delays on the terrestrial reference frame are also investigated. A separate assessment of the RADIATE ray-traced delays is carried out by comparison to the ray-traced delays from the

  15. Application of ray-traced tropospheric slant delays to geodetic VLBI analysis

    NASA Astrophysics Data System (ADS)

    Hofmeister, Armin; Böhm, Johannes

    2017-08-01

    The correction of tropospheric influences via so-called path delays is critical for the analysis of observations from space geodetic techniques like the very long baseline interferometry (VLBI). In standard VLBI analysis, the a priori slant path delays are determined using the concept of zenith delays, mapping functions and gradients. The a priori use of ray-traced delays, i.e., tropospheric slant path delays determined with the technique of ray-tracing through the meteorological data of numerical weather models (NWM), serves as an alternative way of correcting the influences of the troposphere on the VLBI observations within the analysis. In the presented research, the application of ray-traced delays to the VLBI analysis of sessions in a time span of 16.5 years is investigated. Ray-traced delays have been determined with program RADIATE (see Hofmeister in Ph.D. thesis, Department of Geodesy and Geophysics, Faculty of Mathematics and Geoinformation, Technische Universität Wien. http://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-3444, 2016) utilizing meteorological data provided by NWM of the European Centre for Medium-Range Weather Forecasts (ECMWF). In comparison with a standard VLBI analysis, which includes the tropospheric gradient estimation, the application of the ray-traced delays to an analysis, which uses the same parameterization except for the a priori slant path delay handling and the used wet mapping factors for the zenith wet delay (ZWD) estimation, improves the baseline length repeatability (BLR) at 55.9% of the baselines at sub-mm level. If no tropospheric gradients are estimated within the compared analyses, 90.6% of all baselines benefit from the application of the ray-traced delays, which leads to an average improvement of the BLR of 1 mm. The effects of the ray-traced delays on the terrestrial reference frame are also investigated. A separate assessment of the RADIATE ray-traced delays is carried out by comparison to the ray-traced delays from the

  16. Identifying optimal tag-along station locations for improving VLBI Intensive sessions

    NASA Astrophysics Data System (ADS)

    Kareinen, Niko; Klopotek, Grzegorz; Hobiger, Thomas; Haas, Rüdiger

    2017-01-01

    Very Long Baseline Interferometry (VLBI) is a unique space-geodetic technique capable of direct observation of the Earth's phase of rotation, namely Universal Time (UT1). The International VLBI Service for Geodesy and Astrometry (IVS) conducts daily 1-h Intensive VLBI sessions to determine rapid variations in the difference between UT1 and Coordinated Universal Time (UTC). The main objective of the Intensive sessions is to provide timely UT1-UTC estimates. These estimates are especially crucial for Global Navigation Satellite Systems (GNSS). The monitoring of rapid variations in Earth rotation also provides insight into various geophysical phenomena. There is an ongoing effort to improve the quality of the UT1-UTC estimates from single-baseline Intensive sessions to realise the expected accuracy and to bring them to a better agreement with the 24-h VLBI sessions. In this paper, we investigate the possibility to improve the Intensives by including a third station in tag-along mode to these regularly observed sessions. The impact of the additional station is studied via extensive simulations using the c5++ analysis software. The location of the station is varied within a predetermined grid. Based on actual Intensive session schedules, a set of simulated observations are generated for the two original stations and each grid point. These simulated data are used to estimate UT1-UTC for every Intensive session scheduled during the year 2014 on the Kokee-Wettzell and Tsukuba-Wettzell baselines, with the addition of a third station. We find that in tag-along mode when a third station is added to the schedule we can identify areas where the UT1-UTC estimates are improved up to 67% w.r.t. the original single-baseline network. There are multiple operational VLBI stations in these areas, which could with little effort be included in a tag-along mode to the currently scheduled Intensive sessions, thus providing the possibility to improve the UT1-UTC estimates by extending the

  17. CGS-MSFSS Project report

    SciTech Connect

    Harvey-Collard, Patrick

    2015-10-27

    From January 2015 to July 2015, I was doing research at Sandia National Laboratories in Albuquerque, United States. My work there consisted of performing experimental measurements using Sandia’s unique silicon quantum computing platform. The project is about coupling donor spin quantum bits, or qubits, to quantum dots in a silicon nanostructure based on conventional microchip technology. During the project, I devised a new quantum state readout mechanism that allow better, longer lived measurement signals. The measurement (or readout) mechanism is key to any qubit architecture. Next, I was able to demonstrate a quantum manipulation of the two-electron spin states of the coupled donor and quantum dot system. This constitutes a breakthrough for donor spin qubits in silicon because it could enable larger systems consisting of many qubits. This project will lead to publications in scientific journals, presentations in international conferences, and generates exciting new opportunities for manipulating nature at the nanoscale.

  18. 1.3 mm WAVELENGTH VLBI OF SAGITTARIUS A*: DETECTION OF TIME-VARIABLE EMISSION ON EVENT HORIZON SCALES

    SciTech Connect

    Fish, Vincent L.; Doeleman, Sheperd S.; Beaudoin, Christopher; Bolin, David E.; Rogers, Alan E. E.; Blundell, Ray; Gurwell, Mark A.; Moran, James M.; Primiani, Rurik; Bower, Geoffrey C.; Plambeck, Richard; Chamberlin, Richard; Freund, Robert; Friberg, Per; Honma, Mareki; Oyama, Tomoaki; Inoue, Makoto; Krichbaum, Thomas P.; Lamb, James; Marrone, Daniel P.

    2011-02-01

    Sagittarius A*, the {approx}4 x 10{sup 6} M{sub sun} black hole candidate at the Galactic center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio Observatory's Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*.

  19. A experiment on radio location of objects in the near-Earth space with VLBI in 2012

    NASA Astrophysics Data System (ADS)

    Nechaeva, M.; Antipenko, A.; Bezrukovs, V.; Bezrukov, D.; Dementjev, A.; Dugin, N.; Konovalenko, A.; Kulishenko, V.; Liu, X.; Nabatov, A.; Nesteruk, V.; Pupillo, G.; Reznichenko, A.; Salerno, E.; Shmeld, I.; Shulga, O.; Sybiryakova, Y.; Tikhomirov, Yu.; Tkachenko, A.; Volvach, A.; Yang, W.-J.

    An experiment on radar location of space debris objects using of the method of VLBI was carried out in April, 2012. The radar VLBI experiment consisted in irradiation of some space debris objects (4 rocket stages and 5 inactive satellites) with a signal of the transmitter with RT-70 in Evpatoria, Ukraine. Reflected signals were received by a complex of radio telescopes in the VLBI mode. The following VLBI stations took part in the observations: Ventspils (RT-32), Urumqi (RT-25), Medicina (RT-32) and Simeiz (RT-22). The experiment included measurements of the Doppler frequency shift and the delay for orbit refining, and measurements of the rotation period and sizes of objects by the amplitudes of output interferometer signals. The cross-correlation of VLBI-data is performed at a correlator NIRFI-4 of Radiophysical Research Institute (Nizhny Novgorod). Preliminary data processing resulted in the series of Doppler frequency shifts, which comprised the information on radial velocities of the objects. Some results of the experiment are presented.

  20. Design and Development of a High-Speed Data-Acquisition System for the Korean VLBI Network

    NASA Astrophysics Data System (ADS)

    Oh, Se-Jin; Roh, Duk-Gyoo; Wajima, Kiyoaki; Kawaguchi, Noriyuki; Byun, Do-Young; Yeom, Jae-Hwan; Je, Do-Heung; Han, Seog-Tae; Iguchi, Satoru; Kawakami, Kazuyuki; Ozeki, Kensuke; Kobayashi, Hideyuki; Sasao, Tetsuo; Sohn, Bongwon; Kim, Jaeheon; Miyazaki, Atsushi; Oyama, Tomoaki; Kurayama, Tomoharu

    2011-12-01

    A new high-speed Data Acquisition System (DAS) has been developed for the millimeter-wave VLBI array newly constructed in Korea, the Korean VLBI Network (KVN). The KVN DAS is specially designed to support the most distinctive feature of the KVN, that is simultaneous reception of multiple frequency bands (22, 43, 86 and 129-GHz bands in the current KVN system) for realizing multi-frequency phase referencing, which is the key technology for successful millimeter-wave VLBI observations toward active galactic nuclei and astronomical maser sources. Although the basic functions of the KVN DAS succeed technological elements originally developed in the VERA (VLBI Exploration of Radio Astrometry) Project, essentially new designs have been introduced for the simultaneous processing of four data streams in the optical data-transmission system, the digital filter, and the digital spectrometer. The KVN DAS system consists of four Gigabit Samplers (GBS), Optical Transmission System (OTS), Digital Filter Bank (DFB), Digital Spectrometer (DSM), and the data recorder. The DFB realizes very flexible and phase-stable channelization of up to four data streams. The DSM facilitates quick look of power and cross-power spectra of observed data. The VLBI output data from the DFB are recorded to the Mark5B recorder with a maximum rate of 1-Gbps. We discuss in the present paper the primary specifications, designs, and experimental results of the KVN DAS system.