The Comparison of VLBI Data Analysis Using Software Globl and Globk

NASA Astrophysics Data System (ADS)

Guangli, W.; Xiaoya, W.; Jinling, L.; Wenyao, Z.

The comparison of different geodetic data analysis software is one of the quite of- ten mentioned topics. In this paper we try to find out the difference between software GLOBL and GLOBK when use them to process the same set of VLBI data. GLOBL is a software developed by VLBI team, geodesy branch, GSFC/NASA to process geode- tic VLBI data using algorithm of arc-parameter-elimination, while GLOBK using al- gorithm of kalman filtering is mainly used in GPS data analysis, and it is also used in VLBI data analysis. Our work focus on whether there are significant difference when use the two softwares to analyze the same VLBI data set and investigate the reasons caused the difference.

Tropospheric Delay Raytracing Applied in VLBI Analysis

NASA Astrophysics Data System (ADS)

MacMillan, D. S.; Eriksson, D.; Gipson, J. M.

2013-12-01

Tropospheric delay modeling error continues to be one of the largest sources of error in VLBI analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from ECMWF data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption does not reflect reality, we have determined the raytrace delay along the signal path through the troposphere for each VLBI quasar observation. We determined the troposphere refractivity fields from the pressure, temperature, specific humidity and geopotential height fields of the NASA GSFC GEOS-5 numerical weather model. We discuss results from analysis of the CONT11 R&D and the weekly operational R1+R4 experiment sessions. When applied in VLBI analysis, baseline length repeatabilities were better for 66-72% of baselines with raytraced delays than with VMF1 mapping functions. Vertical repeatabilities were better for 65% of sites.

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.

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)

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.

Troposphere Delay Raytracing Applied in VLBI Analysis

NASA Astrophysics Data System (ADS)

Eriksson, David; MacMillan, Daniel; Gipson, John

2014-12-01

Tropospheric delay modeling error is one of the largest sources of error in VLBI analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from European Centre for Medium Range Forecasting (ECMWF) data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption does not reflect reality, we have instead determined the raytrace delay along the signal path through the three-dimensional troposphere refractivity field for each VLBI quasar observation. We calculated the troposphere refractivity fields from the pressure, temperature, specific humidity, and geopotential height fields of the NASA GSFC GEOS-5 numerical weather model. We discuss results using raytrace delay in the analysis of the CONT11 R&D sessions. When applied in VLBI analysis, baseline length repeatabilities were better for 70% of baselines with raytraced delays than with VMF1 mapping functions. Vertical repeatabilities were better for 2/3 of all stations. The reference frame scale bias error was 0.02 ppb for raytracing versus 0.08 ppb and 0.06 ppb for VMF1 and NMF, respectively.

Goddard Geophysical and Astronomical Observatory

NASA Technical Reports Server (NTRS)

Redmond, Jay; Kodak, Charles

2001-01-01

This report summarizes the technical parameters and the technical staff of the Very Long Base Interferometry (VLBI) system at the fundamental station Goddard Geophysical and Astronomical Observatory (GGAO). It also gives an overview about the VLBI activities during the previous year. The outlook lists the outstanding tasks to improve the performance of GGAO.

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.

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.

First Space VLBI Observations and Images Using the VLBA and VSOP

NASA Astrophysics Data System (ADS)

Romney, J. D.; Benson, J. M.; Claussen, M. J.; Desai, K. M.; Flatters, C.; Mioduszewski, A. J.; Ulvestad, J. S.

1997-12-01

The National Radio Astronomy Observatory (NRAO) is a participant in the VSOP Space VLBI mission, an international collaboration led by Japan's Institute of Space and Astronautical Science. NRAO has committed up to 30% of scheduled observing time on the Very Long Baseline Array (VLBA), and corresponding correlation resources, to Space VLBI observations. The NRAO Space VLBI Project, funded by NASA, has been working for several years to complete the necessary enhancements to the VLBA correlator and the AIPS image processing system. These developments were completed by the time of the successful launch of the VSOP mission's Halca spacecraft on 1997 February 12. As part of the in-orbit checkout phase, the first Space VLBI fringes from a VLBA observation were detected on 1997 June 12, and the VSOP mission's first images, in both the 1.6- and 5-GHz bands, were obtained shortly thereafter. In-orbit test observations continued through early September, with the first General Observing Time (GOT) scientific observations beginning in July. Through mid-October, a total of 20 Space VLBI observations, comprising 190 hours, had been completed at the VLBA correlator. This paper reviews the unique features of correlation and imaging of Space VLBI observations. These include, for correlation, the ephemeris for an orbiting VLBI ``station'' which is not fixed on the surface of the earth, and the requirement to close the loop on the phase-transfer process from a frequency standard on the ground to the spacecraft. Images from a number of early tests and scientific observations are presented. NRAO's user-support program, providing expert assistance in data analysis to Space VLBI observers, is also described.

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)>

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.

The effect of meteorological data on atmospheric pressure loading corrections in VLBI data analysis

NASA Astrophysics Data System (ADS)

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

2015-04-01

Earth's crustal deformation is a manifestation of numerous geophysical processes, which entail the atmosphere and ocean general circulation and tidal attraction, climate change, and the hydrological circle. The present study deals with the elastic deformations induced by atmospheric pressure variations. At geodetic sites, APL (Atmospheric Pressure Loading) results in displacements covering a wide range of temporal scales which is undesirable when rigorous geodetic/geophysical analysis is intended. Hence, it is of paramount importance that the APL signal are removed at the observation level in the space geodetic data analysis. In this study, elastic non-tidal components of loading displacements were calculated in the local topocentric frame for all VLBI (Very Long Baseline Interferometry) stations with respect to the center-of-figure of the solid Earth surface and the center-of-mass of the total Earth system. The response of the Earth to the load variation at the surface was computed by convolving Farrell Green's function with the homogenized in situ surface pressure observations (in the time span 1979-2014) after the subtraction of the reference pressure and the S1, S2 and S3 thermal tidal signals. The reference pressure was calculated through a hypsometric adjustment of the absolute pressure level determined from World Meteorological Organization stations in the vicinity of each VLBI observatory. The tidal contribution was calculated following the 2010 International Earth Rotation and Reference Systems Service conventions. Afterwards, this approach was implemented into the VLBI software VieVS@GFZ and the entirety of available VLBI sessions was analyzed. We rationalize our new approach on the basis that the potential error budget is substantially reduced, since several common errors are not applicable in our approach, e.g. those due to the finite resolution of NWM (Numerical Weather Models), the accuracy of the orography model necessary for adjusting the former as

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

NASA Astrophysics Data System (ADS)

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

2015-08-01

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

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.

Troposphere gradients from the ECMWF in VLBI analysis

NASA Astrophysics Data System (ADS)

Boehm, Johannes; Schuh, Harald

2007-06-01

Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02 and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a priori gradients are used.

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

Comparison of Superconducting and Spring Gravimeters at the Mizusawa VLBI Observatory of the National Astronomical Observatory of Japan

NASA Astrophysics Data System (ADS)

Miura, Satoshi; Ikeda, Hiroshi; Kim, Tae-Hee; Tamura, Yoshiaki

2017-04-01

Continuous microgravity monitoring is utilized to gain new insights into changes in the subsurface distribution of magma and/or fluid that commonly occur beneath active volcanoes. Rather new superconducting and spring gravimeters, iGrav#003 and gPhone#136 are collocated with a superconducting gravimeter, TT#70 at the Mizusawa VLBI Observatory of the National Astronomical Observatory of Japan, since the end of September, 2016 in order to evaluate those performances before field deployment planned in 2017. Calibration of iGrav#003 was carried out by collocation with an absolute gravimeter FG5 of the Earthquake Research Institute, University of Tokyo (Okubo, 2016, personal comm.) at a Fundamental Gravity Station in Sendai in July, 2016. Based on the scale factors of iGrav#003 obtained by the calibration and of gPhone#136 provided by the manufacturer (Micro-g LaCoste, Inc.), tidal analyses are performed by means of BAYTAP-G (Tamura et al., 1991, GJI). Amplitudes and phases of each major tidal constituent mutually agree well within ±4 % and ±3 degrees, respectively. The instrumental drift rate of iGrav#003 is very low, about 5 micro-Gal/month, whereas that of gPhone#136 is very high, about 500 micro-Gal/month. The high drift rate of gPhone#136, however, is well approximated by a quadratic function at present and can be removed. The detrended time series of gPhone#136 shows good agreement with iGrav#003 time series in the overall feature: gravity fluctuations with amplitudes of about a few micro-Gal and with durations of a few days, which may be due to variations in the moisture content of the topmost unsaturated sedimentary layer and the water table height. It suggests that both instruments may capture volcanic signals associated with pressure changes in magma chambers, dike intrusion/withdrawing, and so on. iGrav#003 will be installed in the Zao volcanological observatory of Tohoku University located at about 3 km from the summit crater, and gPhone#136 will be

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.

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

Tropospheric delay ray tracing applied in VLBI analysis

NASA Astrophysics Data System (ADS)

Eriksson, David; MacMillan, D. S.; Gipson, John M.

2014-12-01

Tropospheric delay modeling error continues to be one of the largest sources of error in VLBI (very long baseline interferometry) analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from European Centre for Medium-Range Weather Forecasts data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption is not true, we have instead determined the ray trace delay along the signal path through the troposphere for each VLBI quasar observation. We determined the troposphere refractivity fields from the pressure, temperature, specific humidity, and geopotential height fields of the NASA Goddard Space Flight Center Goddard Earth Observing System version 5 numerical weather model. When applied in VLBI analysis, baseline length repeatabilities were improved compared with using the VMF1 mapping function model for 72% of the baselines and site vertical repeatabilities were better for 11 of 13 sites during the 2 week CONT11 observing period in September 2011. When applied to a larger data set (2011-2013), we see a similar improvement in baseline length and also in site position repeatabilities for about two thirds of the stations in each of the site topocentric components.

New VLBI Observing System 'OCTAVE-Family' to Support VDIF Specifications with 10 GigE for VERA, JVN, and Japanese e-VLBI (OCTAVE)

NASA Astrophysics Data System (ADS)

Oyama, T.; Kono, Y.; Suzuki, S.; Mizuno, S.; Bushimata, T.; Jike, T.; Kawaguchi, N.; Kobayashi, H.; Kimura, M.

2012-12-01

The new VLBI observing system (OCTAVE-Family) has been designed and developed based on the VSI-H and VDIF specifications at NAOJ (National Astronomical Observatory of Japan). It consists of 1) a high speed 8-Gsps 3-bit ADC (OCTAD) enabling us to acquire not only wide intermediate frequencies but also radio frequencies up to 50 GHz, 2) a converter (OCTAVIA) between one 10 GigE port and four 2 Gbps input and output ports conformable to VSI-H, 3) new recorders (OCTADISK and OCTADISK2) at rates of 4.5 Gbps and above 8 Gbps, and 4) a high speed software correlator system (OCTACOR) using GICO3 which was developed by NICT. These OCTAVE systems are connected via 10 GigE network with VDIF and VSI specifications. These components are used for VERA, JVN (Japanese VLBI network), and KJJVC (Korea-Japan Joint VLBI Correlator).

Goddard Geophysical and Astronomical Observatory

NASA Technical Reports Server (NTRS)

Figueroa, Ricardo

2013-01-01

This report summarizes the technical parameters and the technical staff of the VLBI system at the fundamental station GGAO. It also gives an overview about the VLBI activities during the report year. The Goddard Geophysical and Astronomical Observatory (GGAO) consists of a 5-meter radio telescope for VLBI, a new 12-meter radio telescope for VLBI2010 development, a 1-meter reference antenna for microwave holography development, an SLR site that includes MOBLAS-7, the NGSLR development system, and a 48" telescope for developmental two-color Satellite Laser Ranging, a GPS timing and development lab, a DORIS system, meteorological sensors, and a hydrogen maser. In addition, we are a fiducial IGS site with several IGS/IGSX receivers. GGAO is located on the east coast of the United States in Maryland. It is approximately 15 miles NNE of Washington, D.C. in Greenbelt, Maryland.

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.

Analysis of Polar Motion Series Differences Between VLBI, GNSS, and SLR

NASA Astrophysics Data System (ADS)

MacMillan, Daniel; Pavlis, Erricos

2017-04-01

We have compared polar motion series from VLBI, GNSS, and SLR generated with a reference frame aligned to ITRF2008. Three objectives of the comparisons are 1) to determine biases between the techniques, 2) to determine the precision of each technique via a 3-corner hat analysis after removing the relative biases, and 3) to evaluate the long-term stability of polar motion series. Between VLBI, GNSS,and SLR, there are clear variations ranging from 20 to 60 µas in peak-to-peak amplitude. We investigate the possible causes of these variations. In addition, there are other apparent systematic biases and rate differences. There are VLBI network dependent effects that appear in the VLBI-GNSS and VLBI-SLR differences, 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 polar motion biases and precisions of the five IVS VLBI continuous observing CONT campaigns (since 2002) are also analyzed since these 2-week campaigns were each designed to provide the highest quality results that could be produced at the time. A possible source of bias between the three techniques is the underlying chosen sub-network used by each technique to realize the adopted reference frame. We also consider the technique differences when ITRF2014 is used instead of ITRF2008

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.

Analysis of Vlbi, Slr and GPS Site Position Time Series

NASA Astrophysics Data System (ADS)

Angermann, D.; Krügel, M.; Meisel, B.; Müller, H.; Tesmer, V.

Conventionally the IERS terrestrial reference frame (ITRF) is realized by the adoption of a set of epoch coordinates and linear velocities for a set of global tracking stations. Due to the remarkable progress of the space geodetic observation techniques (e.g. VLBI, SLR, GPS) the accuracy and consistency of the ITRF increased continuously. The accuracy achieved today is mainly limited by technique-related systematic errors, which are often poorly characterized or quantified. Therefore it is essential to analyze the individual techniques' solutions with respect to systematic differences, models, parameters, datum definition, etc. Main subject of this presentation is the analysis of GPS, SLR and VLBI time series of site positions. The investigations are based on SLR and VLBI solutions computed at DGFI with the software systems DOGS (SLR) and OCCAM (VLBI). The GPS time series are based on weekly IGS station coordinates solutions. We analyze the time series with respect to the issues mentioned above. In particular we characterize the noise in the time series, identify periodic signals, and investigate non-linear effects that complicate the assignment of linear velocities for global tracking sites. One important aspect is the comparison of results obtained by different techniques at colocation sites.

Refined discrete and empirical horizontal gradients in VLBI analysis

NASA Astrophysics Data System (ADS)

Landskron, Daniel; Böhm, Johannes

2018-02-01

Missing or incorrect consideration of azimuthal asymmetry of troposphere delays is a considerable error source in space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). So-called horizontal troposphere gradients are generally utilized for modeling such azimuthal variations and are particularly required for observations at low elevation angles. Apart from estimating the gradients within the data analysis, which has become common practice in space geodetic techniques, there is also the possibility to determine the gradients beforehand from different data sources than the actual observations. Using ray-tracing through Numerical Weather Models (NWMs), we determined discrete gradient values referred to as GRAD for VLBI observations, based on the standard gradient model by Chen and Herring (J Geophys Res 102(B9):20489-20502, 1997. https://doi.org/10.1029/97JB01739) and also for new, higher-order gradient models. These gradients are produced on the same data basis as the Vienna Mapping Functions 3 (VMF3) (Landskron and Böhm in J Geod, 2017.https://doi.org/10.1007/s00190-017-1066-2), so they can also be regarded as the VMF3 gradients as they are fully consistent with each other. From VLBI analyses of the Vienna VLBI and Satellite Software (VieVS), it becomes evident that baseline length repeatabilities (BLRs) are improved on average by 5% when using a priori gradients GRAD instead of estimating the gradients. The reason for this improvement is that the gradient estimation yields poor results for VLBI sessions with a small number of observations, while the GRAD a priori gradients are unaffected from this. We also developed a new empirical gradient model applicable for any time and location on Earth, which is included in the Global Pressure and Temperature 3 (GPT3) model. Although being able to describe only the systematic component of azimuthal asymmetry and no short-term variations at all, even these

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.

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.

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.

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.

VLBI Observations of Geostationary Satellites

NASA Astrophysics Data System (ADS)

Artz, T.; Nothnagel, A.; La Porta, L.

2013-08-01

For a consistent realization of a Global Geodetic Observing System (GGOS), a proper tie between the individual global reference systems used in the analysis of space-geodetic observations is a prerequisite. For instance, the link between the terrestrial, the celestial and the dynamic reference system of artificial Earth orbiters may be realized by Very Long O Baseline Interferometry (VLBI) observations of one or several satellites. In the preparation phase for a dedicated satellite mission, one option to realize this is using a geostationary (GEO) satellite emitting a radio signal in X-Band and/or S-Band and, thus, imitating a quasar. In this way, the GEO satellite can be observed by VLBI together with nearby quasars and the GEO orbit can, thus, be determined in a celestial reference frame. If the GEO satellite is, e.g., also equipped with a GNSS-type transmitter, a further tie between GNSS and VLBI may be realized. In this paper, a concept for the generation of a radio signal is shown. Furthermore, simulation studies for estimating the GEO position are presented with a GEO satellite included in the VLBI schedule. VLBI group delay observations are then simulated for the quasars as well as for the GEO satellite. The analysis of the simulated observations shows that constant orbit changes are adequately absorbed by estimated orbit parameters. Furthermore, the post-fit residuals are comparable to those from real VLBI sessions.

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.

Italy INAF Analysis Center Report

NASA Technical Reports Server (NTRS)

Negusini, M.; Sarti, P.

2013-01-01

This report summarizes the activity of the Italian INAF VLBI Analysis Center. Our Analysis Center is located in Bologna, Italy and belongs to the Institute of Radioastronomy, which is part of the National Institute of Astrophysics. IRA runs the observatories of Medicina and Noto, where two 32-m VLBI AZ-EL telescopes are situated. This report contains the AC's VLBI data analysis activities and shortly outlines the investigations into the co-locations of space geodetic instruments.

Haystack Analysis Center

NASA Technical Reports Server (NTRS)

Niell, Arthur; Cappallo, Roger; Corey, Brian; Titus, Mike

2013-01-01

Analysis activities at Haystack Observatory are directed towards improving the accuracy of geodetic measurements, whether these are from VLBI, GNSS, SLR, or any other technique. Those analysis activities that are related to technology development are reported elsewhere in this volume. In this report, a preliminary analysis of the first geodetic sessions with the new broadband geodetic VLBI system is reported.

On the Impact of Inhomogeneities in Meteorological Data on VLBI Data Analysis

NASA Astrophysics Data System (ADS)

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

2016-12-01

In this study, we address the issue of the quality of meteorological data employed for VLBI data analysis. We use data from six numerical weather models (NWMs) to form references on which the homogenization process is based. We explore the impact of the choice of NWM as well as the way to extract data from it. Among our findings is that data from the surface fields of NWMs are not suitable for either geodetic analysis or homogenization efforts, whether they are in their original form or after they have been compensated for the height difference between the orography of the NWM and the actual elevation. The reason lies in the fact that for 77% of the VLBI stations a height bias larger than 2.5 mm appears, as well as an average bias in the zenith wet delay estimates of 12.2 mm. Should the proposed extraction approach be followed, the difference between operational and reanalysis NWMs is not significant for such an application. Our conclusions are based on the analysis of VLBI data over 13 years.

Current Limitations on VLBI Accuracy

NASA Technical Reports Server (NTRS)

Ma, Chopo; Gipson, John; MacMillan, Daniel

1998-01-01

The contribution of VLBI to geophysics and geodesy arises from its ability to measure distances between stations in a network and to determine the orientation of stations in the network as well as the orientation of the network with respect to the external reference frame of extragalactic radio objects. Integrating nearly two decades of observations provides useful information about station positions and velocities and the orientation of the Earth, but the complications of the real world and the limitations of observing, modeling and analysis prevent recovery of all effects. Of the factors that limit the accuracy of seemingly straightforward geodetic parameters, the neutral propagation medium has been subject to the greatest scrutiny, but the treatment of the mapping function, the wet component and spatial/temporal inhomogeneities is still improving. These affect both the terrestrial scale and consistency over time. The modeling of non-secular site motions (tides and loading) has increased in sophistication, but there are some differences between the models and the observations. VLBI antennas are massive objects, so their behavior is quite unlike GPS monuments, but antenna deformations add some (generally) unmodeled signal. Radio sources used in geodetic VLBI observations are selected for strength and (relative) absence of structure, but apparent changes in position can leak into geodetic parameters. A linear rate of change of baseline or site parameters is the simplest model and its error improves with time span. However, in most cases the VLBI data distribution is insufficient to look for real non-linear behavior that might affect the average rate. A few sites have multiple VLBI antennas, and some show small differences in rate. VLBI intrinsically measures relative positions and velocities, but individual site positions and velocities are generally more useful. The creation of the VLBI terrestrial reference frame, which transforms relative information into

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

The VLBI Data Analysis Software νSolve: Development Progress and Plans for the Future

NASA Astrophysics Data System (ADS)

Bolotin, S.; Baver, K.; Gipson, J.; Gordon, D.; MacMillan, D.

2014-12-01

The program νSolve is a part of the CALC/SOLVE VLBI data analysis system. It is a replacement for interactive SOLVE, the part of CALC/SOLVE that is used for preliminary data analysis of new VLBI sessions. νSolve is completely new software. It is written in C++ and has a modern graphical user interface. In this article we present the capabilities of the software, its current status, and our plans for future development.

VLBI2010 Demonstrator Project

NASA Astrophysics Data System (ADS)

Niell, A.

2008-12-01

The next generation geodetic VLBI instrument is being developed with a goal of 1 mm position uncertainty in twenty-four hours. Knowing that spatial and temporal fluctuations in the atmosphere delay are a major component of the error in position determination, the VLBI2010 committee has carried out a large number of simulations to arrive at design goals for the antenna system. These goals are fast slewing antennas and high delay precision per observation. With existing and anticipated data recording capabilities, these translate to an antenna diameter of 12 m or larger and a per-observation delay precision of approximately 4 psec. The major innovation for the VLBI2010 concept that allows the use of relatively small antennas to achieve these goals is the proposal to observe in four frequency bands, instead of the two currently used, in order to gain the higher precision of phase delays compared to the group delay. The other advance that enables the use of small antennas is the significant increase in data acquisition rates that has been made possible by the development of disk-based recorders and digital back ends. To evaluate this concept, a prototype of the feed-to-recorder system has been implemented by the Broadband Development Team* on two antennas, the 5 m MV-3 antenna at Goddard Space Flight Center near Washington, D.C., and the 18 m Westford antenna at Haystack Observatory near Boston. The system includes a broadband feed and low noise amplifiers covering the range approximately 2 GHz to 13 GHz, all cooled to 20K; a newly developed phase calibration generator; a flexible local oscillator (LO) that allows selection of any band in the range of the feed/LNAs; Digital Back End; and a disk-based recorder capable of a sustained rate of 2 gigabits per second (gbps). Four sets of the LO/DBE/recorder chain are used at each antenna to give a total record rate of 8 gbps. The systems have been successfully used in the band 8.5 to 9 GHz with one set of the recorder chain

Geodetic Observatory Wettzell - 20-m Radio Telescope and Twin Telescope

NASA Technical Reports Server (NTRS)

Neidhardt, Alexander; Kronschnabl, Gerhard; Schatz, Raimund

2013-01-01

In the year 2012, the 20-m radio telescope at the Geodetic Observatory Wettzell, Germany again contributed very successfully to the International VLBI Service for Geodesy and Astrometry observing program. Technical changes, developments, improvements, and upgrades were made to increase the reliability of the entire VLBI observing system. In parallel, the new Twin radio telescope Wettzell (TTW) got the first feedhorn, while the construction of the HF-receiving and the controlling system was continued.

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.

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.

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.

Impact of different NWM-derived mapping functions on VLBI and GPS analysis

NASA Astrophysics Data System (ADS)

Nikolaidou, Thalia; Balidakis, Kyriakos; Nievinski, Felipe; Santos, Marcelo; Schuh, Harald

2018-06-01

In recent years, numerical weather models have shown the potential to provide a good representation of the electrically neutral atmosphere. This fact has been exploited for the modeling of space geodetic observations. The Vienna Mapping Functions 1 (VMF1) are the NWM-based model recommended by the latest IERS Conventions. The VMF1 are being produced 6 hourly based on the European Centre for Medium-Range Weather Forecasts operational model. UNB-VMF1 provide meteorological parameters aiding neutral atmosphere modeling for VLBI and GNSS, based on the same concept but utilizing the Canadian Meteorological Centre model. This study presents comparisons between the VMF1 and the UNB-VMF1 in both delay and position domains, using global networks of VLBI and GPS stations. It is shown that the zenith delays agree better than 3.5 mm (hydrostatic) and 20 mm (wet) which implies an equivalent predicted height error of less than 2 mm. In the position domain and VLBI analysis, comparison of the weighted root-mean-square error (wrms) of the height component showed a maximum difference of 1.7 mm. For 48% of the stations, the use of VMF1 reduced the height wrms of the stations by 2.6% on average compared to a respective reduction of 1.7% for 41% of the stations employing the UNB-VMF1. For the subset of VLBI stations participating in a large number of sessions, neither mapping function outranked the other. GPS analysis using Precise Point Positioning had a sub-mm respective difference, while the wrms of the individual solutions had a maximum value of 12 mm for the 1-year-long analysis. A clear advantage of one NWM over the other was not shown, and the statistics proved that the two mapping functions yield equal results in geodetic analysis.

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

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.

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.

Tectonic motion site survey of the National Radio Astronomy Observatory, Green Bank, West Virginia

NASA Technical Reports Server (NTRS)

Webster, W. J., Jr.; Allenby, R. J.; Hutton, L. K.; Lowman, P. D., Jr.; Tiedemann, H. A.

1979-01-01

A geological and geophysical site survey was made of the area around the National Radio Astronomy Observatory (NRAO) to determine whether there are at present local tectonic movements that could introduce significant errors to Very Long Baseline Interferometry (VLBI) geodetic measurements. The site survey consisted of a literature search, photogeologic mapping with Landsat and Skylab photographs, a field reconnaissance, and installation of a seismometer at the NRAO. It is concluded that local tectonic movement will not contribute significantly to VLBI errors. It is recommended that similar site surveys be made of all locations used for VLBI or laser ranging.

Testing impact of the strategy of VLBI data analysis on the estimation of Earth Orientation Parameters and station coordinates

NASA Astrophysics Data System (ADS)

Wielgosz, Agata; Tercjak, Monika; Brzeziński, Aleksander

2016-06-01

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable to realise the Celestial Reference Frame and tie it with the Terrestrial Reference Frame. It is also the only technique, which measures all the Earth Orientation Parameters (EOP) on a regular basis, thus the role of VLBI in determination of the universal time, nutation and polar motion and station coordinates is invaluable. Although geodetic VLBI has been providing observations for more than 30 years, there are no clear guidelines how to deal with the stations or baselines having significantly bigger post-fit residuals than the other ones. In our work we compare the common weighting strategy, using squared formal errors, with strategies involving exclusion or down-weighting of stations or baselines. For that purpose we apply the Vienna VLBI Software VieVS with necessary additional procedures. In our analysis we focus on statistical indicators that might be the criterion of excluding or down-weighting the inferior stations or baselines, as well as on the influence of adopted strategy on the EOP and station coordinates estimation. Our analysis shows that in about 99% of 24-hour VLBI sessions there is no need to exclude any data as the down-weighting procedure is sufficiently efficient. Although results presented here do not clearly indicate the best algorithm, they show strengths and weaknesses of the applied methods and point some limitations of automatic analysis of VLBI data. Moreover, it is also shown that the influence of the adopted weighting strategy is not always clearly reflected in the results of analysis.

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.

Integration of Reference Frames Using VLBI

NASA Technical Reports Server (NTRS)

Ma, Chopo; Smith, David E. (Technical Monitor)

2001-01-01

Very Long Baseline Interferometry (VLBI) has the unique potential to integrate the terrestrial and celestial reference frames through simultaneous estimation of positions and velocities of approx. 40 active VLBI stations and a similar number of stations/sites with sufficient historical data, the position and position stability of approx. 150 well-observed extragalactic radio sources and another approx. 500 sources distributed fairly uniformly on the sky, and the time series of the five parameters that specify the relative orientation of the two frames. The full realization of this potential is limited by a number of factors including the temporal and spatial distribution of the stations, uneven distribution of observations over the sources and the sky, variations in source structure, modeling of the solid/fluid Earth and troposphere, logistical restrictions on the daily observing network size, and differing strategies for optimizing analysis for TRF, for CRF and for EOP. The current status of separately optimized and integrated VLBI analysis will be discussed.

VLBI-SLR Combination Solution Using GEODYN

NASA Technical Reports Server (NTRS)

MacMillan, Dan; Pavlis, Despina; Lemoine, Frank; Chinn, Douglas; Rowlands, David

2010-01-01

We would like to generate a multi-technique solution combining all of the geodetic techniques (VLBI, SLR, GPS, and DORIS) using the same software and using the same a priori models. Here we use GEODYN software and consider only the VLBI-SLR combination. Here we report initial results of our work on the combination. We first performed solutions with GEODYN using only VLBI data and found that VLBI EOP solution results produced with GEODYN agree with results using CALC/SOLVE at the 1-sigma level. We then combined the VLBI normal equations in GEODYN with weekly SLR normal equations for the period 2007-2008. Agreement of estimated Earth orientation parameters with IERS C04 were not significantly different for the VLBI-only, SLR-only, and VLBI+SLR solutions

Metsahovi Radio Observatory - IVS Network Station

NASA Technical Reports Server (NTRS)

Uunila, Minttu; Zubko, Nataliya; Poutanen, Markku; Kallunki, Juha; Kallio, Ulla

2013-01-01

In 2012, Metsahovi Radio Observatory together with Finnish Geodetic Institute officially became an IVS Network Station. Eight IVS sessions were observed during the year. Two spacecraft tracking and one EVN X-band experiment were also performed. In 2012, the Metsahovi VLBI equipment was upgraded with a Digital Base Band Converter, a Mark 5B+, a FILA10G, and a FlexBuff.

Observing APOD with the AuScope VLBI Array

PubMed Central

Sun, Jing; Cao, Jianfeng

2018-01-01

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype—suitable for practical observation tests—combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission. PMID:29772732

Observing APOD with the AuScope VLBI Array.

PubMed

Hellerschmied, Andreas; McCallum, Lucia; McCallum, Jamie; Sun, Jing; Böhm, Johannes; Cao, Jianfeng

2018-05-16

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype-suitable for practical observation tests-combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission.

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.

Receiving And Data Acquisition Systems Of Rt-32 For Vlbi Observations / Rt-32 Uztveršanas Un Datu Reģistrācijas Sistēmas Vlbi Novērojumiem

NASA Astrophysics Data System (ADS)

Bezrukovs, Vl.; Shmeld, I.; Nechaeva, M.; Trokss, J.; Bezrukovs, D.; Klapers, M.; Berzins, A.; Lesins, A.; Dugin, N.

2012-12-01

Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methanol maser single dish observations. The apparatus system of RT-32 is equipped with two independent VLBI data acquisition systems: TN-16, and DBBC in combination with MK5b. Both systems are employed in interferometric observations depending on the purpose of experiment and the enabled radiotelescopes. The current status of RT-32, the availability of its receiving and data acquisition units for VLBI observations and the previous VLBI sessions are discussed. Radioteleskops RT-32 ir Ventspils Starptautiskajam Radioastronomijas Centram (VSRC) piederoša pilnas piedziņas 32 m diametra paraboliskā antena. Pašreiz visaktuālākie VSRC veicamie darbi ir saistīti ar RT-32 uztverošās aparatūras un datu reģistrēšanas sistēmas labošanu un modernizāciju. Viens no radioastronomiskās observatorijas galvenajiem zinātniskajiem uzdevumiem ir sevišķi lielas bāzes interferometriskie (VLBI) novērojumi centimetru viļņu garumu diapazonā sadarbībā ar pasaules VLBI tīkla partneriem, t

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.

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.

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.

Monte Carlo Simulations for VLBI2010

NASA Astrophysics Data System (ADS)

Wresnik, J.; Böhm, J.; Schuh, H.

2007-07-01

Monte Carlo simulations are carried out at the Institute of Geodesy and Geophysics (IGG), Vienna, and at Goddard Space Flight Center (GSFC), Greenbelt (USA), with the goal to design a new geodetic Very Long Baseline Interferometry (VLBI) system. Influences of the schedule, the network geometry and the main stochastic processes on the geodetic results are investigated. Therefore schedules are prepared with the software package SKED (Vandenberg 1999), and different strategies are applied to produce temporally very dense schedules which are compared in terms of baseline length repeatabilities. For the simulation of VLBI observations a Monte Carlo Simulator was set up which creates artificial observations by randomly simulating wet zenith delay and clock values as well as additive white noise representing the antenna errors. For the simulation at IGG the VLBI analysis software OCCAM (Titov et al. 2004) was adapted. Random walk processes with power spectrum densities of 0.7 and 0.1 psec2/sec are used for the simulation of wet zenith delays. The clocks are simulated with Allan Standard Deviations of 1*10^-14 @ 50 min and 2*10^-15 @ 15 min and three levels of white noise, 4 psec, 8 psec and, 16 psec, are added to the artificial observations. The variations of the power spectrum densities of the clocks and wet zenith delays, and the application of different white noise levels show clearly that the wet delay is the critical factor for the improvement of the geodetic VLBI system. At GSFC the software CalcSolve is used for the VLBI analysis, therefore a comparison between the software packages OCCAM and CalcSolve was done with simulated data. For further simulations the wet zenith delay was modeled by a turbulence model. This data was provided by Nilsson T. and was added to the simulation work. Different schedules have been run.

The Southern Hemisphere VLBI experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Preston, R.A.; Meier, D.L.; Louie, A.P.

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.

Application of Raytracing Through the High Resolution Numerical Weather Model HIRLAM for the Analysis of European VLBI

NASA Technical Reports Server (NTRS)

Garcia-Espada, Susana; Haas, Rudiger; Colomer, Francisco

2010-01-01

An important limitation for the precision in the results obtained by space geodetic techniques like VLBI and GPS are tropospheric delays caused by the neutral atmosphere, see e.g. [1]. In recent years numerical weather models (NWM) have been applied to improve mapping functions which are used for tropospheric delay modeling in VLBI and GPS data analyses. In this manuscript we use raytracing to calculate slant delays and apply these to the analysis of Europe VLBI data. The raytracing is performed through the limited area numerical weather prediction (NWP) model HIRLAM. The advantages of this model are high spatial (0.2 deg. x 0.2 deg.) and high temporal resolution (in prediction mode three hours).

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

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;

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.

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.

Tropospheric Parameters Determined by VLBI Within the IVS

NASA Astrophysics Data System (ADS)

Schuh, H.; Boehm, J.

2003-12-01

In April 2002 the IVS (International VLBI Service for Geodesy and Astrometry) set up the Pilot Project - Tropospheric Parameters, and the Institute of Geodesy and Geophysics (IGG), Vienna, was put in charge of coordinating the project. Seven IVS Analysis Centers have joined the project and regularly submitted their estimates of tropospheric parameters (wet and total zenith delays, horizontal gradients) for all IVS-R1 and IVS-R4 sessions since January 1st, 2002. The individual submissions are combined by a two-step procedure to obtain stable, robust and highly accurate tropospheric parameter time series with one hour resolution. The internal accuracy of the combined wet zenith delays is between 2 and 4 mm. The zenith delays derived by VLBI are compared with those provided by the International GPS Service (IGS). At sites with co-located VLBI and GPS antennas the short-term variabilities of the GPS and VLBI derived zenith delays generally show a good agreement but biases are found between the results of the two techniques. Possible reasons for these biases are discussed. Since July 1st, 2003, within the IVS the tropospheric parameters are determined as operational products. The presentation also includes the VLBI CONT02 campaign of 15 days of continuous observing in the second half of October 2002.

IVS Working Group 4: VLBI Data Structures

NASA Astrophysics Data System (ADS)

Gipson, J.

2012-12-01

I present an overview of the "openDB format" for storing, archiving, and processing VLBI data. In this scheme, most VLBI data is stored in NetCDF files. NetCDF has the advantage that there are interfaces to most common computer languages including Fortran, Fortran-90, C, C++, Perl, etc, and the most common operating systems including Linux, Windows, and Mac. The data files for a particular session are organized by special ASCII "wrapper" files which contain pointers to the data files. This allows great flexibility in the processing and analysis of VLBI data. For example it allows you to easily change subsets of the data used in the analysis such as troposphere modeling, ionospheric calibration, editing, and ambiguity resolution. It also allows for extending the types of data used, e.g., source maps. I present a roadmap to transition to this new format. The new format can already be used by VieVS and by the global mode of solve. There are plans in work for other software packages to be able to use the new format.

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.

Establishing a celestial VLBI reference frame. 1: Searching for VLBI sources

NASA Technical Reports Server (NTRS)

Preston, R. A.; Morabito, D. D.; Williams, J. G.; Slade, M. A.; Harris, A. W.; Finley, S. G.; Skjerve, L. J.; Tanida, L.; Spitzmesser, D. J.; Johnson, B.

1978-01-01

The Deep Space Network is currently engaged in establishing a new high-accuracy VLBI celestial reference frame. The present status of the task of finding suitable celestial radio sources for constructing this reference frame is discussed. To date, 564 VLBI sources were detected, with 166 of these lying within 10 deg of the ecliptic plane. The variation of the sky distribution of these sources with source strength is examined.

Tropospheric Delay from VLBI and GNSS Measurements

NASA Astrophysics Data System (ADS)

Gubanov, V. S.

2018-02-01

Using an updated version of the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences, we have processed the VLBI observations within the international CONT14 program (May 6-20, 2014), in which a global network of 17 stations was involved (a total of 250 000 observations). The package update concerned the optimization of data structure and the refinement of stochastic models for the random variations in wet tropospheric delay and atomic clock difference. The main goal of this paper is to compare the VLBI determinations of the tropospheric delay with its independent determinations using global navigation satellite systems (GNSS). We show that both these determinations agree well between themselves only in the case of a global analysis of the VLBI observations, where the VLBI station coordinates are also refined, along with the tropospheric delay and the clock synchronization and Earth orientation parameters. If, alternatively, the station coordinates are insufficiently accurate and are not refined from VLBI observations, then it is appropriate not to determine the tropospheric delay from these observations, but to take it from the publicly accessible independent GNSS data. However, this requires that the VLBI and GNSS techniques operate simultaneously at a common observing site. We have established the shortcomings of the universally accepted method of stabilizing the global solution associated with the absence of a criterion for choosing reference stations and radio sources. Two ways of their elimination are proposed: (i) introducing a coordinated list of weight factors for the errors in the coordinates of such stations and sources into the stabilization algorithm and (ii) adopting a coordinated list of stations and sources the refinement of whose coordinates is not required at all for a certain time.

Near real-time monitoring of UT1 with geodetic VLBI

NASA Astrophysics Data System (ADS)

Haas, R.; Hobiger, T.; Sekido, M.; Koyama, Y.; Kondo, T.; Takiguchi, H.; Kurihara, S.; Kokado, K.; Tanimoto, D.; Nozawa, K.; Wagner, J.; Ritakari, J.; Mujunen, A.; Uunila, M.

2011-07-01

processing and analysis is performed with a fully automated analysis software (Hobiger et al., 2010). We present results from the ultra-rapid UT1-sessions, both, from dedicated one-baseline sessions, as well from 24-hour ultra-rapid sessions during standard IVS-experiments. The near real-time UT1 results are compared to corresponding post-processing results, and results from independent analyses and techniques. Refrences: Sekido et al. (2008) Ultra-rapid UT1 measurements by e-VLBI, Earth Planets and Space, Vol. 60, 865-870. Matsuzaka et al. (2008) Ultra Rapid UT1 Experiment with e-VLBI, In: Proc. 5th IVS General Meeting, 68-71. Haas R et al. (2010) Ultra-Rapid DUT1-Observations with E-VLBI. Artificial Satellites, 45, 75-79. Hobiger et al. (2010) Fully automated VLBI analysis with c5++ for ultra-rapid determination of UT1, Earth Planets Space.

Determination of Galactic Aberration from VLBI Measurements and Its Effect on VLBI Reference Frames and Earth Orientation Parameters.

NASA Astrophysics Data System (ADS)

MacMillan, D. S.

2014-12-01

Galactic aberration is due to the motion of the solar system barycenter around the galactic center. It results in a systematic pattern of apparent proper motion of radio sources observed by VLBI. This effect is not currently included in VLBI analysis. Estimates of the size of this effect indicate that it is important that this secular aberration drift be accounted for in order to maintain an accurate celestial reference frame and allow astrometry at the several microarcsecond level. Future geodetic observing systems are being designed to be capable of producing a future terrestrial reference frame with an accuracy of 1 mm and stability of 0.1 mm/year. We evaluate the effect galactic aberration on attaining these reference frame goals. This presentation will discuss 1) the estimation of galactic aberration from VLBI data and 2) the effect of aberration on the Terrestrial and Celestial Reference Frames and the Earth Orientation Parameters that connect these frames.

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.

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.

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.

New Uses for the VLBI Network

NASA Technical Reports Server (NTRS)

Clark, Tom

2000-01-01

This paper suggests some potential new uses for the existing VLBI network. It seems that every VLBI group in the world faces some common problems: We do not have enough money to operate! We do not have enough money to make improvements!! In this contribution I discuss several possibilities for new business that might help to support the network stations without causing serious impacts on the primary VLBI programs.

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.

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.

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.

VLBI tracking of GNSS satellites: recent achievements

NASA Astrophysics Data System (ADS)

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

2014-05-01

While the ITRF (International Terrestrial Reference Frame) is realized by the combination of the various space geodetic techniques, VLBI (Very Long Baseline Interferometry) is the only technique for determining the ICRF (International Celestial Reference Frame) through its observations of extragalactic radio sources. Therefore, small inconsistencies between the two important frames do exist. According to recent comparisons of parameters derived by GNSS (Global Navigation Satellite Systems) and VLBI (e.g. troposphere delays, gradients, UT1-UTC), evidences of discrepancies obtained by the vast amounts of data become obvious. Terrestrial local ties can provide a way to interlink the otherwise independent technique-specific reference frames but only to some degree. It is evident that errors in the determination of the terrestrial ties, e.g. due to the errors when transforming the locally surveyed coordinates into global Cartesian three dimensional coordinates, introduce significant errors in the combined analysis of space geodetic techniques. A new concept for linking the space geodetic techniques might be to introduce celestial ties, e.g. realized by technique co-location on board of satellites. A small satellite carrying a variety of space geodetic techniques is under investigation at GFZ. Such a satellite would provide a new observing platform with its own additional unknowns, such as the orbit or atmospheric drag parameters. A link of the two techniques VLBI and GNSS might be achieved in a more direct way as well: by VLBI tracking of GNSS satellites. Several tests of this type of observation were already successfully carried out. This new kind of hybrid VLBI-GNSS observation would comprise a new direct inter-technique tie without the involvement of surveying methods and would enable improving the consistency of the two space geodetic techniques VLBI and GNSS, in particular of their celestial frames. Recently the radio telescopes Wettzell and Onsala have

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.

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.

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.

Geodetic VLBI observations at Simeiz station

NASA Astrophysics Data System (ADS)

Volvach, A.; Petrov, L.; Nesterov, N.

Very long baseline interferometry (VLBI) observations under international geodetic programs are carried out at Simeiz station since June 1994. 22-m radiotelescope is equipped by dual-band S/X receivers, hydrogen maser CH-70 and data acquisition terminal Mark-IIIA. Observations are conducted by 24 hours sessions scheduled 6-15 times per year. Observational programs are a part of common efforts for maintenance of terrestrial reference frame, celestial reference frame and monitoring Earth orientation parameters carried out by international community under the auspices of International VLBI Service (IVS). Data are recorded on magnetic tapes which are shipped to correlator centers for further correlation and fringing. Fringed data are archived and are freely available via Internet for scientific analysis after 1-2 months after observations.

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).

Six-hourly time series of horizontal troposphere gradients in VLBI analyis

NASA Astrophysics Data System (ADS)

Landskron, Daniel; Hofmeister, Armin; Mayer, David; Böhm, Johannes

2016-04-01

Consideration of horizontal gradients is indispensable for high-precision VLBI and GNSS analysis. As a rule of thumb, all observations below 15 degrees elevation need to be corrected for the influence of azimuthal asymmetry on the delay times, which is mainly a product of the non-spherical shape of the atmosphere and ever-changing weather conditions. Based on the well-known gradient estimation model by Chen and Herring (1997), we developed an augmented gradient model with additional parameters which are determined from ray-traced delays for the complete history of VLBI observations. As input to the ray-tracer, we used operational and re-analysis data from the European Centre for Medium-Range Weather Forecasts. Finally, we applied those a priori gradient parameters to VLBI analysis along with other empirical gradient models and assessed their impact on baseline length repeatabilities as well as on celestial and terrestrial reference frames.

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.

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.

VLBI observations to the APOD satellite

NASA Astrophysics Data System (ADS)

Sun, Jing; Tang, Geshi; Shu, Fengchun; Li, Xie; Liu, Shushi; Cao, Jianfeng; Hellerschmied, Andreas; Böhm, Johannes; McCallum, Lucia; McCallum, Jamie; Lovell, Jim; Haas, Rüdiger; Neidhardt, Alexander; Lu, Weitao; Han, Songtao; Ren, Tianpeng; Chen, Lue; Wang, Mei; Ping, Jinsong

2018-02-01

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10 cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1 s integration time of the correlator output is on the level of 0.1 ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.

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.

Post-Correlation Processing for the VLBI2010 Proof-of-Concept System

NASA Technical Reports Server (NTRS)

Beaudoin, Christopher; Niell, Arthur

2010-01-01

For the past three years, the MIT Haystack Observatory and the broadband team have been developing a proof-of-concept broadband geodetic VLBI microwave (2-12 GHz) receiver. Also on-going at Haystack is the development of post-correlation processing needed to extract the geodetic observables. Using this processing, the first fully-phase-calibrated geodetic fringes have been produced from observations conducted with the proof-of-concept system. The results we present show that the phase-calibrated phase residuals from four 512 MHz bands spanning 2 GHz have an RMS phase variation of 8deg which corresponds to a delay uncertainty of 12 ps.

VLBI astrometry and the Hipparcos link to the extragalactic reference frame

NASA Technical Reports Server (NTRS)

Lestrade, J.-F.; Preston, R. A.; Gabuzda, D. C.; Phillips, R. B.

1991-01-01

Intermediate results are reported from a program of VLBI radio observations designed to establish a link between the rotating reference frame of the ESA Hipparcos astrometric satellite and the extragalactic VLBI frame being developed by the International Earth Rotation Service. A group of 12 link stars have been observed at various epochs since 1982, and more observations are being undertaken during the 3-yr Hipparcos mission (1989-1992). Analysis of data on Algol indicates that phase-reference VLBI can determine an expected sky displacement of 4 marcsec with an uncertainty of 0.5 marcsec, even when the activity is only a few mJy.

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

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).

First steps of processing VLBI data of space probes with VieVS

NASA Astrophysics Data System (ADS)

Plank, L.; Böhm, J.; Schuh, H.

2011-07-01

Since 2008 the VLBI group at the Institute of Geodesy and Geophysics (IGG) of the Vienna University of Technology has developed the Vienna VLBI Software VieVS which is capable to process geodetic VLBI data in NGS format. Constantly we are working on upgrading the new software, e.g. by developing a scheduling tool or extending the software from single session solution to a so-called global solution, allowing the joint analysis of many sessions covering several years. In this presentation we report on first steps to enable the processing of space VLBI data with the software. Driven by the recently increasing number of space VLBI applications, our goal is the geodetic usage of such data, primarily concerning frame ties between various reference frames, e. g. by connecting the dynamic reference frame of a space probe with the kinematically defined International Celestial Reference Frame (ICRF). Main parts of the software extension w.r.t. the existing VieVS are the treatment of fast moving targets, the implementation of a delay model for radio emitters at finite distances, and the adequate mathematical model and adjustment of the particular unknowns. Actual work has been done for two mission scenarios so far: On the one hand differential VLBI (D-VLBI) data from the two sub-satellites of the Japanese lunar mission Selene were processed, on the other hand VLBI observations of GNSS satellites were modelled in VieVS. Besides some general aspects, we give details on the calculation of the theoretical delay (delay model for moving sources at finite distances) and its realization in VieVS. First results with real data and comparisons with best fit mission orbit data are also presented.'

VLBI-based Products - Naval Oceanography Portal

Science.gov Websites

section Advanced Search... Sections Home Time Earth Orientation Astronomy Meteorology Oceanography Ice You are here: Home › USNO › Earth Orientation › VLBI-based Products USNO Logo USNO Navigation Earth determine Earth Orientation Parameters (EOP) is Very Long Baseline Interferometry (VLBI). USNO provides both

Vienna VLBI and Satellite Software (VieVS) for Geodesy and Astrometry

NASA Astrophysics Data System (ADS)

Böhm, Johannes; Böhm, Sigrid; Boisits, Janina; Girdiuk, Anastasiia; Gruber, Jakob; Hellerschmied, Andreas; Krásná, Hana; Landskron, Daniel; Madzak, Matthias; Mayer, David; McCallum, Jamie; McCallum, Lucia; Schartner, Matthias; Teke, Kamil

2018-04-01

The Vienna VLBI and Satellite Software (VieVS) is state-of-the-art Very Long Baseline Interferometry (VLBI) analysis software for geodesy and astrometry. VieVS has been developed at Technische Universität Wien (TU Wien) since 2008, where it is used for research purposes and for teaching space geodetic techniques. In the past decade, it has been successfully applied on Very Long Baseline Interferometry (VLBI) observations for the determination of celestial and terrestrial reference frames as well as for the estimation of celestial pole offsets, universal Time (UT1-UTC), and polar motion based on least-squares adjustment. Furthermore, VieVS is equipped with tools for scheduling and simulating VLBI observations to extragalactic radio sources as well as to satellites and spacecraft, features which proved to be very useful for a variety of applications. VieVS is now available as version 3.0 and we do provide the software to all interested persons and institutions. A wiki with more information about VieVS is available at http://vievswiki.geo.tuwien.ac.at/.

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.

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.

Effects of the 2011 Tohoku Earthquake on VLBI Geode- tic Measurements

NASA Astrophysics Data System (ADS)

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

2012-12-01

The VLBI antenna TSUKUB32 at Tsukuba, Japan 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-hr Intensive Int2 sessions observed on the weekends for the determination of UT1. TSUKUB32 returned to normal operational observing one month after the earthquake. The antenna is 160 km west and 240 km south of the epicenter of the Tohoku earthquake. 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 relative to the long-term rate prior to the earthquake was about 20 cm/yr four months after the earthquake and 9 cm/yr after one year. The VLBI series agrees closely with the corresponding JPL (Jet Propulsion Laboratory) GPS series measured by the co-located GPS antenna TSUK. The co-seismic UEN displacement at Tsukuba as determined by VLBI was (-90 mm, 640 mm, 44 mm). We examined the effect of the variation of the TSUKUB32 position on EOP estimates and then used the GPS data to correct its position for the estimation of UT1 in the Tsukuba-Wettzell Int2 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 the UT1 estimates from these weekend sessions and the USNO (United States Naval Observatory) combination series were used to validate the GPS correction to the TSUKUB32 position.

(abstract) A VLBI Test of Tropospheric Delay Calibration with WVRs

NASA Technical Reports Server (NTRS)

Linfield, R. P.; Teitelbaum, L. P.; Keihm, S. J.; Resch, G. M.; Mahoney, M. J.; Treuhaft, R. N.

1994-01-01

Dual frequency (S/X band) very long baseline interferometry (VLBI) observations were used to test troposphere calibration by water vapor radiometers (WVRs). Comparison of the VLBI and WVR measurements show a statistical agreement (specifically, their structure functions agree) on time scales less than 700 seconds. On longer time scales, VLBI instrumental errors become important. The improvement in VLBI residual delays from WVR calibration was consistent with the measured level of tropospheric fluctuations.

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.

Continental hydrology loading observed by VLBI measurements

NASA Astrophysics Data System (ADS)

Eriksson, David; MacMillan, D. S.

2014-07-01

Variations in continental water storage lead to loading deformation of the crust with typical peak-to-peak variations at very long baseline interferometry (VLBI) sites of 3-15 mm in the vertical component and 1-2 mm in the horizontal component. The hydrology signal at VLBI sites has annual and semi-annual components and clear interannual variations. We have calculated the hydrology loading series using mass loading distributions derived from the global land data assimilation system (GLDAS) hydrology model and alternatively from a global grid of equal-area gravity recovery and climate experiment (GRACE) mascons. In the analysis of the two weekly VLBI 24-h R1 and R4 network sessions from 2003 to 2010 the baseline length repeatabilities are reduced in 79 % (80 %) of baselines when GLDAS (GRACE) loading corrections are applied. Site vertical coordinate repeatabilities are reduced in about 80 % of the sites when either GLDAS or GRACE loading is used. In the horizontal components, reduction occurs in 70-80 % of the sites. Estimates of the annual site vertical amplitudes were reduced for 16 out of 18 sites if either loading series was applied. We estimated loading admittance factors for each site and found that the average admittances were 1.01 0.05 for GRACE and 1.39 0.07 for GLDAS. The standard deviations of the GRACE admittances and GLDAS admittances were 0.31 and 0.68, respectively. For sites that have been observed in a set of sufficiently temporally dense daily sessions, the average correlation between VLBI vertical monthly averaged series and GLDAS or GRACE loading series was 0.47 and 0.43, respectively.

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

2001 GPS and Classical Survey at Medicina Observatory: Local Tie and VLBI Antenna's Reference Point Determination

NASA Astrophysics Data System (ADS)

Vittuari, Luca; Sarti, Pierguido; Tomasi, Paolo

2001-12-01

During a 6 days campaign in June 2001, we have performed a local survey at Medicina Observatory using classical geodesy and GPS techniques in order to determine the effects of an undergone track repair. We have determined the position of the reference point P within a local and ITRF2000 (epoch 1997.0) reference frames using trilateration and triangulation: Pclas_{loc}^{2001}=(21.580pm0.001,45.536pm0.001,17.699pm0.001) Pclas_{loc}^{2001}=(21.580pm0.001,45.536pm0.001,17.699pm0.001) Pclas_{ITRF2000}^{1997.0}=(4461369.982pm0.001,919596.818pm0.001,4449559.207pm0.001) Kinematic GPS has also given interesting results:VLBI-GPS ex-centre vector has been possible.

Analysis of the DORIS, GNSS, SLR, VLBI and gravimetric time series at the GGOS core sites

NASA Astrophysics Data System (ADS)

Moreaux, G.; Lemoine, F. G.; Luceri, V.; Pavlis, E. C.; MacMillan, D. S.; Bonvalot, S.; Saunier, J.

2017-12-01

Since June 2016 and the installation of a new DORIS station in Wettzell (Germany), four geodetic sites (Badary, Greenbelt, Wettzell and Yarragadee) are equipped with the four space geodetic techniques (DORIS, GNSS, SLR and VLBI). In line with the GGOS (Global Geodetic Observing System) objective of achieving a terrestrial reference frame at the millimetric level of accuracy, the combination centers of the four space techniques initiated a joint study to assess the level of agreement among these space geodetic techniques. In addition to the four sites, we will consider all the GGOS core sites including the seven sites with at least two space geodetic techniques in addition to DORIS. Starting from the coordinate time series, we will estimate and compare the mean positions and velocities of the co-located instruments. The temporal evolution of the coordinate differences will also be evaluated with respect to the local tie vectors and discrepancies will be investigated. Then, the analysis of the signal content of the time series will be carried out. Amplitudes and phases of the common signals among the techniques, and eventually from gravity data, will be compared. The first objective of this talk is to describe our joint study: the sites, the data, and the objectives. The second purpose is to present the first results obtained from the GGAO (Goddard Geophysical and Astronomic Observatory) site of Greenbelt.

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.

TIGO: a geodetic observatory for the improvement of the global reference frame

NASA Astrophysics Data System (ADS)

Schlueter, Wolfgang; Hase, Hayo; Boeer, Armin

1999-12-01

The Bundesamt fuer Kartographie und Geodaesie (BKG) will provide a major contribution to the improvement and maintenance of the global reference frames: ICRF (International Celestial Reference Frame), ITRF (International Terrestrial Reference Frame) with the operation of TIGO (Transportable Integrated Geodetic Observatory). TIGO is designed as a transportable geodetic observatory which consists of all relevant geodetic space techniques for a fundamental station (including VLBI, SLR, GPS). The transportability of the observatory enables to fill up gaps in the International Space Geodetic Network and to optimize the contribution to the global reference frames. TIGO should operate for a period of 2 to 3 years (at minimum) at one location. BKG is looking for a cooperation with countries willing to contribute to the ITRF and to support the operation of TIGO.

Global Velocities from VLBI

NASA Technical Reports Server (NTRS)

Ma, Chopo; Gordon, David; MacMillan, Daniel

1999-01-01

Precise geodetic Very Long Baseline Interferometry (VLBI) measurements have been made since 1979 at about 130 points on all major tectonic plates, including stable interiors and deformation zones. From the data set of about 2900 observing sessions and about 2.3 million observations, useful three-dimensional velocities can be derived for about 80 sites using an incremental least-squares adjustment of terrestrial, celestial, Earth rotation and site/session-specific parameters. The long history and high precision of the data yield formal errors for horizontal velocity as low as 0.1 mm/yr, but the limitation on the interpretation of individual site velocities is the tie to the terrestrial reference frame. Our studies indicate that the effect of converting precise relative VLBI velocities to individual site velocities is an error floor of about 0.4 mm/yr. Most VLBI horizontal velocities in stable plate interiors agree with the NUVEL-1A model, but there are significant departures in Africa and the Pacific. Vertical precision is worse by a factor of 2-3, and there are significant non-zero values that can be interpreted as post-glacial rebound, regional effects, and local disturbances.

Beyond the usual mapping functions in GPS, VLBI and Deep Space tracking.

NASA Astrophysics Data System (ADS)

Barriot, Jean-Pierre; Serafini, Jonathan; Sichoix, Lydie

2014-05-01

We describe here a new algorithm to model the water contents of the atmosphere (including ZWD) from GPS slant wet delays relative to a single receiver. We first make the assumption that the water vapor contents are mainly governed by a scale height (exponential law), and secondly that the departures from this decaying exponential can be mapped as a set of low degree 3D Zernike functions (w.r.t. space) and Tchebyshev polynomials (w.r.t. time.) We compare this new algorithm with previous algorithms known as mapping functions in GPS, VLBI and Deep Space tracking and give an example with data acquired over a one day time span at the Geodesy Observatory of Tahiti.

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

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.

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.

Optimized scheduling of VLBI UT1 intensive sessions for twin telescopes employing impact factor analysis

NASA Astrophysics Data System (ADS)

Leek, Judith; Artz, Thomas; Nothnagel, Axel

2015-09-01

Daily Very Long Baseline Interferometry (VLBI) intensive measurements make an important contribution to the regular monitoring of Earth rotation variations. Since these variations are quite rapid, their knowledge is important for navigation with global navigation satellite system and for investigations in Earth sciences. Unfortunately, the precision of VLBI intensive observations is 2-3 times worse than the precision of regular 24h-VLBI measurements with networks of 5-10 radio telescopes. The major advancement of research in this paper is the improvement of VLBI intensive results by (a) using twin telescopes instead of single telescopes and (b) applying an entirely new scheduling concept for the individual observations. Preparatory investigations of standardintensive sessions suggest that the impact factors of the observations are well suited for the identification of the most influential observations which are needed for the determination of certain parameters within the entire design of a VLBI session. Based on this experience, the scheduling method is designed for optimizing the observations' geometry for a given network of radio telescopes and a predefined set of parameters to be estimated. The configuration of at least two twin telescopes, or one twin and two single telescopes, offers the possibility of building pairwise sub-nets that observe two different sources simultaneously. In addition to an optimized observing plan, a special parametrization for twin telescopes leads to an improved determination of Earth rotation variations, as it is shown by simulated observations. In general, an improvement of about 50 % in the formal errors can be realized using twin radio telescopes. This result is only due to geometric improvements as higher slew rates of the twin telescopes are not taken into account.

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

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.

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.

VLBI clock synchronization tests performed via the ATS-1 and ATS-3 satellites

NASA Technical Reports Server (NTRS)

Ramasastry, J.; Rosenbaum, B.; Michelini, R. D.; Kuegler, G.

1971-01-01

Clock synchronization experiments were carried out May 10 to June 10, 1971, by the NASA/Goddard Space Flight Center and the Smithsonian Astrophysical Observatory via the ATS-1 and 3 geostationary satellites at the NASA tracking stations Rosman and Mojave, during a VLBI (Very Long Baseline Interferometer) experiment in order to determine the clock-offset between the two stations. Ten microsecond pulses at C-band with very sharp risetime were exchanged by the two stations through the dual transponders of the satellites. At each station, a time-interval counter was started by the transmitted pulse and stopped by the received pulse. The probable error of the difference in the mean values of the clock-offset is 10 nanoseconds.

Terrestrial reference frame solution with the Vienna VLBI Software VieVS and implication of tropospheric gradient estimation

NASA Astrophysics Data System (ADS)

Spicakova, H.; Plank, L.; Nilsson, T.; Böhm, J.; Schuh, H.

2011-07-01

The Vienna VLBI Software (VieVS) has been developed at the Institute of Geodesy and Geophysics at TU Vienna since 2008. In this presentation, we present the module Vie_glob which is the part of VieVS that allows the parameter estimation from multiple VLBI sessions in a so-called global solution. We focus on the determination of the terrestrial reference frame (TRF) using all suitable VLBI sessions since 1984. We compare different analysis options like the choice of loading corrections or of one of the models for the tropospheric delays. The effect of atmosphere loading corrections on station heights if neglected at observation level will be shown. Time series of station positions (using a previously determined TRF as a priori values) are presented and compared to other estimates of site positions from individual IVS (International VLBI Service for Geodesy and Astrometry) Analysis Centers.

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.

Navigating highly elliptical earth orbiters with simultaneous VLBI from orthogonal baseline pairs

NASA Technical Reports Server (NTRS)

Frauenholz, Raymond B.

1986-01-01

Navigation strategies for determining highly elliptical orbits with VLBI are described. The predicted performance of wideband VLBI and Delta VLBI measurements obtained by orthogonal baseline pairs are compared for a 16-hr equatorial orbit. It is observed that the one-sigma apogee position accuracy improves two orders of magnitude to the meter level when Delta VLBI measurements are added to coherent Doppler and range, and the simpler VLBI strategy provides nearly the same orbit accuracy. The effects of differential measurement noise and acquisition geometry on orbit accuracy are investigated. The data reveal that quasar position uncertainty limits the accuracy of wideband Delta VLBI measurements, and that polar motion and baseline uncertainties and offsets between station clocks affect the wideband VLBI data. It is noted that differential one-way range (DOR) has performance nearly equal to that of the more complex Delta DOR and is recommended for use on spacecraft in high elliptical orbits.

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.

Vienna SAC-SOS: Analysis of the European VLBI Sessions

NASA Astrophysics Data System (ADS)

Ros, C. T.; Pavetich, P.; Nilsson, T.; Böhm, J.; Schuh, H.

2012-12-01

The Institute of Geodesy and Geophysics (IGG) of the Vienna University of Technology as an IVS Special Analysis Center for Specific Observing Sessions (SAC-SOS) has analyzed the European VLBI sessions using the software VieVS. Between 1990 and 2011, 115 sessions have been carried out. The analyzed baselines have lengths ranging from approximately 445 to 4580 km, and they show good repeatabilities, apart from the ones containing station Simeiz. The station velocities have also been investigated. The stations situated in the stable part of Europe have not shown significant relative movements w.r.t. Wettzell, whereas the stations located in the northern areas have the largest vertical motions as a result of the post glacial isostatic rebound of the zone. The stations placed in Italy, around the Black Sea, in Siberia, and near the Arctic Circle show the largest relative horizontal motions because they belong to different geodynamical units.

Improved UT1 Predictions through Low-Latency VLBI Observations

DTIC Science & Technology

2010-03-14

J Geod (2010) 84:399–402 DOI 10.1007/s00190-010-0372-8 SHORT NOTE Improved UT1 predictions through low-latency VLBI observations Brian Luzum · Axel...polar motion and nutation on UT1 determinations from VLBI Intensive obser- vations. J Geod 82(12):863. doi:10.1007/s00190-008-0212-2 Ray JR, Carter WE...Behrend D (2007) The International VLBI Service for Geodesy and Astrometry (IVS): current capabilities and future prospects. J Geod 81(6–8):479. doi

Comparison of observation level versus 24-hour average atmospheric loading corrections in VLBI analysis

NASA Astrophysics Data System (ADS)

MacMillan, D. S.; van Dam, T. M.

2009-04-01

Variations in the horizontal distribution of atmospheric mass induce displacements of the Earth's surface. Theoretical estimates of the amplitude of the surface displacement indicate that the predicted surface displacement is often large enough to be detected by current geodetic techniques. In fact, the effects of atmospheric pressure loading have been detected in Global Positioning System (GPS) coordinate time series [van Dam et al., 1994; Dong et al., 2002; Scherneck et al., 2003; Zerbini et al., 2004] and very long baseline interferometery (VLBI) coordinates [Rabble and Schuh, 1986; Manabe et al., 1991; van Dam and Herring, 1994; Schuh et al., 2003; MacMillan and Gipson, 1994; and Petrov and Boy, 2004]. Some of these studies applied the atmospheric displacement at the observation level and in other studies, the predicted atmospheric and observed geodetic surface displacements have been averaged over 24 hours. A direct comparison of observation level and 24 hour corrections has not been carried out for VLBI to determine if one or the other approach is superior. In this presentation, we address the following questions: 1) Is it better to correct geodetic data at the observation level rather than applying corrections averaged over 24 hours to estimated geodetic coordinates a posteriori? 2) At the sub-daily periods, the atmospheric mass signal is composed of two components: a tidal component and a non-tidal component. If observation level corrections reduce the scatter of VLBI data more than a posteriori correction, is it sufficient to only model the atmospheric tides or must the entire atmospheric load signal be incorporated into the corrections? 3) When solutions from different geodetic techniques (or analysis centers within a technique) are combined (e.g., for ITRF2008), not all solutions may have applied atmospheric loading corrections. Are any systematic effects on the estimated TRF introduced when atmospheric loading is applied?

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.

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

Simulations of VLBI observations of a geodetic satellite providing co-location in space

NASA Astrophysics Data System (ADS)

Anderson, James M.; Beyerle, Georg; Glaser, Susanne; Liu, Li; Männel, Benjamin; Nilsson, Tobias; Heinkelmann, Robert; Schuh, Harald

2018-02-01

We performed Monte Carlo simulations of very-long-baseline interferometry (VLBI) observations of Earth-orbiting satellites incorporating co-located space-geodetic instruments in order to study how well the VLBI frame and the spacecraft frame can be tied using such measurements. We simulated observations of spacecraft by VLBI observations, time-of-flight (TOF) measurements using a time-encoded signal in the spacecraft transmission, similar in concept to precise point positioning, and differential VLBI (D-VLBI) observations using angularly nearby quasar calibrators to compare their relative performance. We used the proposed European Geodetic Reference Antenna in Space (E-GRASP) mission as an initial test case for our software. We found that the standard VLBI technique is limited, in part, by the present lack of knowledge of the absolute offset of VLBI time to Coordinated Universal Time at the level of microseconds. TOF measurements are better able to overcome this problem and provide frame ties with uncertainties in translation and scale nearly a factor of three smaller than those yielded from VLBI measurements. If the absolute time offset issue can be resolved by external means, the VLBI results can be significantly improved and can come close to providing 1 mm accuracy in the frame tie parameters. D-VLBI observations with optimum performance assumptions provide roughly a factor of two higher uncertainties for the E-GRASP orbit. We additionally simulated how station and spacecraft position offsets affect the frame tie performance.

Earth Orientation Effects on Mobile VLBI Baselines

NASA Technical Reports Server (NTRS)

Allen, S. L.

1984-01-01

Improvements in data quality for the mobile VLBI systems have placed higher accuracy requirements on Earth orientation calibrations. Errors in these calibrations may give rise to systematic effects in the nonlength components of the baselines. Various sources of Earth orientation data were investigated for calibration of Mobile VLBI baselines. Significant differences in quality between the several available sources of UT1-UTC were found. It was shown that the JPL Kalman filtered space technology data were at least as good as any other and adequate to the needs of current Mobile VLBI systems and observing plans. For polar motion, the values from all service suffice. The effect of Earth orientation errors on the accuracy of differenced baselines was also investigated. It is shown that the effect is negligible for the current mobile systems and observing plan.

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.

Providing hydrogen maser timing stability to orbiting VLBI radio telescope observations by post-measurement compensation of linked frequency standard imperfections

NASA Astrophysics Data System (ADS)

Springett, James C.

1994-05-01

Orbiting VLBI (OVLBI) astronomical observations are based upon measurements acquired simultaneously from ground-based and earth-orbiting radio telescopes. By the mid-1990s, two orbiting VLBI observatories, Russia's Radioastron and Japan's VSOP, will augment the worldwide VLBI network, providing baselines to earth radio telescopes as large as 80,000 km. The challenge for OVLBI is to effectuate space to ground radio telescope data cross-correlation (the observation) to a level of integrity currently achieved between ground radio telescopes. VLBI radio telescopes require ultrastable frequency and timing references in order that long term observations may be made without serious cross-correlation loss due to frequency source drift and phase noise. For this reason, such instruments make use of hydrogen maser frequency standards. Unfortunately, space-qualified hydrogen maser oscillators are currently not available for use on OVLBI satellites. Thus, the necessary long-term stability needed by the orbiting radio telescope may only be obtained by microwave uplinking a ground-based hydrogen maser derived frequency to the satellite. Although the idea of uplinking the frequency standard intrinsically seems simple, there are many 'contaminations' which degrade both the long and short term stability of the transmitted reference. Factors which corrupt frequency and timing accuracy include additive radio and electronic circuit thermal noise, slow or systematic phase migration due to changes of electronic circuit temporal operating conditions (especially temperature), ionosphere and troposphere induced scintillations, residual Doppler-incited components, and microwave signal multipath propagation. What is important, though, is to realize that ultimate stability does not have to be achieved in real-time. Instead, information needed to produce a high degree of coherence in the subsequent cross-correlation operation may be derived from a two-way coherent radio link, recorded and later

Providing hydrogen maser timing stability to orbiting VLBI radio telescope observations by post-measurement compensation of linked frequency standard imperfections

NASA Technical Reports Server (NTRS)

Springett, James C.

1994-01-01

Orbiting VLBI (OVLBI) astronomical observations are based upon measurements acquired simultaneously from ground-based and earth-orbiting radio telescopes. By the mid-1990s, two orbiting VLBI observatories, Russia's Radioastron and Japan's VSOP, will augment the worldwide VLBI network, providing baselines to earth radio telescopes as large as 80,000 km. The challenge for OVLBI is to effectuate space to ground radio telescope data cross-correlation (the observation) to a level of integrity currently achieved between ground radio telescopes. VLBI radio telescopes require ultrastable frequency and timing references in order that long term observations may be made without serious cross-correlation loss due to frequency source drift and phase noise. For this reason, such instruments make use of hydrogen maser frequency standards. Unfortunately, space-qualified hydrogen maser oscillators are currently not available for use on OVLBI satellites. Thus, the necessary long-term stability needed by the orbiting radio telescope may only be obtained by microwave uplinking a ground-based hydrogen maser derived frequency to the satellite. Although the idea of uplinking the frequency standard intrinsically seems simple, there are many 'contaminations' which degrade both the long and short term stability of the transmitted reference. Factors which corrupt frequency and timing accuracy include additive radio and electronic circuit thermal noise, slow or systematic phase migration due to changes of electronic circuit temporal operating conditions (especially temperature), ionosphere and troposphere induced scintillations, residual Doppler-incited components, and microwave signal multipath propagation. What is important, though, is to realize that ultimate stability does not have to be achieved in real-time. Instead, information needed to produce a high degree of coherence in the subsequent cross-correlation operation may be derived from a two-way coherent radio link, recorded and later

SAND: an automated VLBI imaging and analysing pipeline - I. Stripping component trajectories

NASA Astrophysics Data System (ADS)

Zhang, M.; Collioud, A.; Charlot, P.

2018-02-01

We present our implementation of an automated very long baseline interferometry (VLBI) data-reduction pipeline that is dedicated to interferometric data imaging and analysis. The pipeline can handle massive VLBI data efficiently, which makes it an appropriate tool to investigate multi-epoch multiband VLBI data. Compared to traditional manual data reduction, our pipeline provides more objective results as less human interference is involved. The source extraction is carried out in the image plane, while deconvolution and model fitting are performed in both the image plane and the uv plane for parallel comparison. The output from the pipeline includes catalogues of CLEANed images and reconstructed models, polarization maps, proper motion estimates, core light curves and multiband spectra. We have developed a regression STRIP algorithm to automatically detect linear or non-linear patterns in the jet component trajectories. This algorithm offers an objective method to match jet components at different epochs and to determine their proper motions.

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.

New VLBI2010 scheduling strategies and implications on the terrestrial reference frames

NASA Astrophysics Data System (ADS)

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

2014-05-01

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.

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.

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

VLBI Phase-Referenced Observations on Southern Hemisphere HIPPARCOS Radio Start

NASA Technical Reports Server (NTRS)

Guirado, J. C.; Preston, R. A.; Jones, D. L.; Lestrade, J. F.; Reynolds, J. E.; Jauncey, D. L.; Tzioumis, A. K.; Ferris, R. H.; King, E. A.; Lovell, J. E. J.;

Connecting kinematic and dynamic reference frames by D-VLBI

NASA Astrophysics Data System (ADS)

Schuh, Harald; Plank, Lucia; Madzak, Matthias; Böhm, Johannes

2012-08-01

In geodetic and astrometric practice, terrestrial station coordinates are usually provided in the kinematic International Terrestrial Reference Frame (ITRF) and radio source coordinates in the International Celestial Reference Frame (ICRF), whereas measurements of space probes such as satellites and spacecrafts, or planetary ephemerides rest upon dynamical theories. To avoid inconsistencies and errors during measurement and calculation procedures, exact frame ties between quasi - inertial, kinematic and dynamic reference frames have to be secured. While the Earth Orientation Parameters (EOP), e.g. measured by VLBI, link the ITRF to the ICRF, the ties with the dynamic frames can be established with the differential Very Long Baseline Interferometry (D - VLBI) method. By observing space probes alternately t o radio sources, the relative position of the targets to each other on the sky can be determined with high accuracy. While D - VLBI is a common technique in astrophysics (source imaging) and deep space navigation, just recently there have been several effort s to use it for geodetic purposes. We present investigations concerning possible VLBI observations to satellites. This includes the potential usage of available GNNS satellites as well as specifically designed missions, as e.g. the GRASP mission proposed b y JPL/NASA and an international consortium, where the aspect of co - location in space of various techniques (VLBI, SLR, GNSS, DORIS) is the main focus.

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).

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.

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.

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.

Status of the test phase of K-3 VLBi system developed in RRL

NASA Astrophysics Data System (ADS)

Saburi, Y.; Yoshimura, K.; Kawajiri, N.; Kawano, N.; Takahashi, F.

An account is given of the last phase of a five-year plan to develop the K-3 system - a high precision VLBI system for applications in a wide variety of fields, such as geodesy, astrometry, and radio astronomy. At the end of 1983, the hardware and software of the K-3 system, were almost completed, and tests were undertaken to demonstrate compatibility with the Mark III system. Topics covered include: Characteristics of the 26-m antenna receiving system, the first U.S.-Japan test observations, and experiments to be conducted for the period up through 1989 at least. Precise time comparison experiments between atomic clocks at the Radio Research Laboratories and the U.S. Naval Observatory were to begin in 1985 and produce data at least once a month for several years.

VLBI2010 and the Westford Station - The Path Forward

NASA Astrophysics Data System (ADS)

Beaudoin, C.; Wilson, K.; Whittier, B.; Whitney, A.; McWhirter, R.; Smythe, J. SooHoo, D.; Ruszczyk, C.; Rogers, A.; Poirier, M.; Niell, A.; Corey, B.; Cappallo, R.; Byford, J.; Bolis, P.

2012-12-01

For the past three years the role of the Westford antenna in geodetic VLBI has been two-fold. Over this time its primary purpose has been to participate in standard S/X-band geodetic VLBI observations. In its secondary role the Westford antenna has been converted into a research instrument, facilitating the development of the broadband geodetic VLBI observing technique. As a research instrument, the Westford antenna incorporates a commercially-available ETS-Lindgren 3164 quadridge antenna as a radio telescope feed. The system also uses the VLBI2010 data acquisition system that incorporates digital backends (DBEs) implementing a polyphase filter bank processor. The process of converting the station from its mode of operations to a research instrument often introduces subtle anomalies that must be diagnosed prior to broadband observing. Furthermore, this bifurcation of the station's role is not in line with the goals of the VLBI2010 specifications. Until recently it has not been possible for the Westford station to serve as both an operational and research instrument without conversion for two reasons: poor sensitivity and incompatibility of backend baseband filter bandwidths. The poor sensitivity of the Westford antenna as a broadband radio telescope is in large part due to the commercial broadband feed which was readily available when the proof-of-concept VLBI2010 observations were initiated. However, with the materialization of the quadridge flared horn (QRFH) by the California Institute of Technology and with the improvements in the DiFX software correlator, the necessary components are now available to upgrade the Westford station to full-broadband capability while adhering to the mandate to maintain backwards compatibility with the legacy S/X systems. In this paper we will present the path forward for upgrading the Westford site to full-broadband capability while maintaining S/X compatibility.

THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dodson, R.; Rioja, M.; Imai, H.

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 mmore » 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.« less

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.

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.

Plans for the New Korean VLBI Network (kvn)

NASA Astrophysics Data System (ADS)

Fletcher, Andre B.

The new Korean VLBI Network construction project started in 2001. Currently funds have been allocated until 2007. Three new 20m diameter fast-slewing high-precision radio antennae will be built in South Korea at Seoul Tamna and Ulsan. These will be exclusively for VLBI astronomy astrometry and geodesy with a focus on developing millimeter-wave VLBI. First 2/8 22 43 and 86 GHz HEMT receivers will be used; 100/150 GHz SIS receivers will be installed later. The KVN Data Acquisition System (DAS) is being designed to realize a multi-band dual-circular polarization wide-bandwidth system. Very-high-speed digital samplers will generate data streams at rates of at least 1 Gigabit/s and a digital filter system will select the recorded frequency channels according to several observation modes one or more of which would be compatible with the VLBA and VERA DASs. The data will be transmitted by optical fibers to the new MIT Mark 5B hard-disk recorders. The KVN correlator will be designed with new technological concepts in mind. The observational capabilities and science goals of KVN are outlined. International scientific and technical collaborations with VLBI institutes will be essential for the ultimate success of the KVN project

Radio observations of active galactic nuclei with mm-VLBI

NASA Astrophysics Data System (ADS)

Boccardi, B.; Krichbaum, T. P.; Ros, E.; Zensus, J. A.

2017-11-01

Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the formation of the plasma flow, as well as those driving its exceptional radiative output up to TeV energies, remain to be clarified. Most likely, these physical processes take place at short separations from the supermassive black hole, on scales which are inaccessible to VLBI observations at centimeter wavelengths. Due to their high synchrotron opacity, the dense and highly magnetized regions in the vicinity of the central engine can only be penetrated when observing at shorter wavelengths, in the millimeter and sub-millimeter regimes. While this was recognized already in the early days of VLBI, it was not until the very recent years that sensitive VLBI imaging at high frequencies has become possible. Ongoing technical development and wide band observing now provide adequate imaging fidelity to carry out more detailed analyses. In this article, we overview some open questions concerning the physics of AGN jets, and we discuss the impact of mm-VLBI studies. Among the rich set of results produced so far in this frequency regime, we particularly focus on studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also presented.

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.

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

2018-01-01

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.

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.

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

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.

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.

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.

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.

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.

Hartebeesthoek Radio Astronomy Observatory (HartRAO)

NASA Technical Reports Server (NTRS)

Nickola, Marisa; Gaylard, Mike; Quick, Jonathan; Combrinck, Ludwig

2013-01-01

HartRAO provides the only fiducial geodetic site in Africa, and it participates in global networks for VLBI, GNSS, SLR, and DORIS. This report provides an overview of geodetic VLBI activities at HartRAO during 2012, including the conversion of a 15-m alt-az radio telescope to an operational geodetic VLBI antenna.

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

Empirical Corrections to Nutation Amplitudes and Precession Computed from a Global VLBI Solution

NASA Astrophysics Data System (ADS)

Schuh, H.; Ferrandiz, J. M.; Belda-Palazón, S.; Heinkelmann, R.; Karbon, M.; Nilsson, T.

2017-12-01

The IAU2000A nutation and IAU2006 precession models were adopted to provide accurate estimations and predictions of the Celestial Intermediate Pole (CIP). However, they are not fully accurate and VLBI (Very Long Baseline Interferometry) observations show that the CIP deviates from the position resulting from the application of the IAU2006/2000A model. Currently, those deviations or offsets of the CIP (Celestial Pole Offsets - CPO), can only be obtained by the VLBI technique. The accuracy of the order of 0.1 milliseconds of arc (mas) allows to compare the observed nutation with theoretical prediction model for a rigid Earth and constrain geophysical parameters describing the Earth's interior. In this study, we empirically evaluate the consistency, systematics and deviations of the IAU 2006/2000A precession-nutation model using several CPO time series derived from the global analysis of VLBI sessions. The final objective is the reassessment of the precession offset and rate, and the amplitudes of the principal terms of nutation, trying to empirically improve the conventional values derived from the precession/nutation theories. The statistical analysis of the residuals after re-fitting the main nutation terms demonstrates that our empirical corrections attain an error reduction by almost 15 micro arc seconds.

Simulation of Twin Telescopes at Onsala and Wettzell for the VLBI Global Observing System

NASA Astrophysics Data System (ADS)

Schönberger, Caroline; Gnilsen, Paul; Böhm, Johannes; Haas, Rüdiger

2015-04-01

The VLBI2010 committee of the International VLBI Service for Geodesy and Astrometry (IVS) developed a concept to achieve an improvement of the accuracy of geodetic Very Long Baseline Interferometry (VLBI) to 1 mm for station positions and 0.1 mm/yr for station velocities. This so-called VLBI2010 concept includes broadband observations with fast slewing telescopes and proposes twin telescopes to improve the handling of atmospheric turbulence that has been identified as a limiting factor for geodetic VLBI. There are several VLBI sites that have projects to install a Twin Telescope. The Wettzell Twin Telescope in Germany has already been constructed, and Twin Telescopes will be installed in the coming years at Onsala (Sweden), Ny-Ålesund (Spitsbergen, Norway) and Kazan (Russia). In this study, the Vienna VLBI Software (VieVS) is used to schedule and simulate a global VLBI network following the example of the CONT11 campaign, with and without the Twin Telescopes in Onsala and Wettzell. Different scheduling approaches (e.g., source-based scheduling, Twin Telescope observing in multidirectional mode, Twin Telescopes in continuous mode) were compared by evaluating the numbers of observations and scans as well as baseline length repeatabilities, station positions, Earth orientation parameters, atmospheric parameters and clock estimates. Comparison of the results show an improvement in estimated parameters with Twin Telescopes, especially with the Onsala Twin Telescope in a continuous observing mode and a strategy with four sources observed simultaneously.

Crustal movements in Europe observed with EUROPE and IVS-T2 VLBI networks

NASA Astrophysics Data System (ADS)

Zubko, N.; Poutanen, M.

2011-07-01

The comparative analysis of the EUROPE and IVS-T2 geodetic VLBI sessions has been performed. The main purpose of both campaigns is to observe and accurately determine the VLBI station coordinates and their time evolution. In this analysis our interest is to understand the influence of network configuration on the estimated parameters and, also, how much the results of these two campaigns are consistent. We have used the VieVS software developing at Vienna University of Technology to analyze the EUROPE and IVS-T2 sessions of 2002-2009. We have analyzed the difference of crustal movements obtained with these two networks and the effect of network configuration and station selection. The EPN (EUREF permanent GNSS Network) and IGS (International GNSS Service) networks can be used to compare the results.

Early science with the Korean VLBI network: evaluation of system performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sang-Sung; Byun, Do-Young; Kim, Jongsoo

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 observationsmore » 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.« less

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.

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

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.

MK3TOOLS & NetCDF - storing VLBI data in a machine independent array oriented data format

NASA Astrophysics Data System (ADS)

Hobiger, T.; Koyama, Y.; Kondo, T.

2007-07-01

In the beginning of 2002 the International VLBI Service (IVS) has agreed to introduce a Platform-independent VLBI exchange format (PIVEX) which permits the exchange of observational data and stimulates the research across different analysis groups. Unfortunately PIVEX has never been implemented and many analysis software packages are still depending on prior processing (e.g. ambiguity resolution and computation of ionosphere corrections) done by CALC/SOLVE. Thus MK3TOOLS which handles MK3 databases without CALC/SOLVE being installed has been developed. It uses the NetCDF format to store the data and since interfaces exist for a variety of programming languages (FORTRAN, C/C++, JAVA, Perl, Python) it can be easily incorporated in existing and upcoming analysis software packages.

Goddard Geophysical and Astronomical Observatory

NASA Technical Reports Server (NTRS)

Covey, Rawland; Kodak, Charles

1999-01-01

This report summarizes the technical parameters and the technical staff of the VLBI system at GGAO. It also gives an overview of VLBI activities during the previous year. The outlook lists the tasks planned for 1999.

Possible systematics in the VLBI catalogs as seen from Gaia

NASA Astrophysics Data System (ADS)

Liu, N.; Zhu, Z.; Liu, J.-C.

2018-01-01

Aims: In order to investigate the systematic errors in the very long baseline interferometry (VLBI) positions of extragalactic sources (quasars) and the global differences between Gaia and VLBI catalogs, we use the first data release of Gaia (Gaia DR1) quasar positions as the reference and study the positional offsets of the second realization of the International Celestial Reference Frame (ICRF2) and the Goddard VLBI solution 2016a (gsf2016a) catalogs. Methods: We select a sample of 1032 common sources among three catalogs and adopt two methods to represent the systematics: considering the differential orientation (offset) and declination bias; analyzing with the vector spherical harmonics (VSH) functions. Results: Between two VLBI catalogs and Gaia DR1, we find that: i) the estimated orientation is consistent with the alignment accuracy of Gaia DR1 to ICRF, of 0.1 mas, but the southern and northern hemispheres show opposite orientations; ii) the declination bias in the southern hemisphere between Gaia DR1 and ICRF2 is estimated to be +152 μas, much larger than that between Gaia DR1 and gsf2016a which is +34 μas. Between two VLBI catalogs, we find that: i) the rotation component shows that ICRF2 and gsf2016a are generally consistent within 30 μas; ii) the glide component and quadrupole component report two declination-dependent offsets: dipolar deformation of +50 μas along the Z-axis, and quadrupolar deformation of -50 μas that would induce a pattern of sin2δ. Conclusions: The significant declination bias between Gaia DR1 and ICRF2 catalogs reported in previous studies is possibly attributed to the systematic errors of ICRF2 in the southern hemisphere. The global differences between ICRF2 and gsf2016a catalogs imply that possible, mainly declination-dependent systematics exit in the VLBI positions and need further investigations in the future Gaia data release and the next generation of ICRF.

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.;

A Fast Radio Burst Search Method for VLBI Observation

NASA Astrophysics Data System (ADS)

Liu, Lei; Tong, Fengxian; Zheng, Weimin; Zhang, Juan; Tong, Li

2018-02-01

We introduce the cross-spectrum-based fast radio burst (FRB) search method for Very Long Baseline Interferometer (VLBI) observation. This method optimizes the fringe fitting scheme in geodetic VLBI data post-processing, which fully utilizes the cross-spectrum fringe phase information and therefore maximizes the power of single-pulse signals. Working with cross-spectrum greatly reduces the effect of radio frequency interference compared with using auto-power spectrum. Single-pulse detection confidence increases by cross-identifying detections from multiple baselines. By combining the power of multiple baselines, we may improve the detection sensitivity. Our method is similar to that of coherent beam forming, but without the computational expense to form a great number of beams to cover the whole field of view of our telescopes. The data processing pipeline designed for this method is easy to implement and parallelize, which can be deployed in various kinds of VLBI observations. In particular, we point out that VGOS observations are very suitable for FRB search.

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.

VizieR Online Data Catalog: 4yr 1.3mm VLBI observations of SgrA* with EHT (Fish+, 2016)

NASA Astrophysics Data System (ADS)

Fish, V. L.; Johnson, M. D.; Doeleman, S. S.; Broderick, A. E.; Psaltis, D.; Lu, R.-S.; Akiyama, K.; Alef, W.; Algaba, J. C.; Asada, K.; Beaudoin, C.; Bertarini, A.; Blackburn, L.; Blundell, R.; Bower, G. C.; Brinkerink, C.; Cappallo, R.; Chael, A. A.; Chamberlin, R.; Chan, C.-K.; Crew, G. B.; Dexter, J.; Dexter, M.; Dzib, S. A.; Falcke, H.; Freund, R.; Friberg, P.; Greer, C. H.; Gurwell, M. A.; Ho, P. T. P.; Honma, M.; Inoue, M.; Johannsen, T.; Kim, J.; Krichbaum, T. P.; Lamb, J.; Leon-Tavares, J.; Loeb, A.; Loinard, L.; MacMahon, D.; Marrone, D. P.; Moran, J. M.; Moscibrodzka, M.; Ortiz-Leon, G. N.; Oyama, T.; Ozel, F.; Plambeck, R. L.; Pradel, N.; Primiani, R. A.; Rogers, A. E. E.; Rosenfeld, K.; Rottmann, H.; Roy, A. L.; Ruszczyk, C.; Smythe, D. L.; Soohoo, J.; Spilker, J.; Stone, J.; Strittmatter, P.; Tilanus, R. P. J.; Titus, M.; Vertatschitsch, L.; Wagner, J.; Wardle, J. F. C.; Weintroub, J.; Woody, D.; Wright, M.; Yamaguchi, P.; Young, A.; Young, K. H.; Zensus, J. A.; Ziurys, L. M.

2016-06-01

The Event Horizon Telescope (EHT) obtained detections of Sgr A* on closed triangles of baselines among stations in Arizona, California, and Hawaii in 2009, 2011, 2012, and 2013. In all cases, two 480MHz bands, centered at 229.089GHz and 229.601GHz (hereafter, low and high bands, respectively), were observed. One or more telescopes from each of three sites in Arizona, California, and Hawaii participated in each set of observations. The Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) on Mt. Graham, Arizona, was used in all cases. Over the years of data analyzed here, the configuration of VLBI recording at these sites evolved as described in section 2.1. (1 data file).

VLBI phase-referencing for observations of weak radio sources

NASA Technical Reports Server (NTRS)

Lestrade, J.-F.

1991-01-01

Phase-referencing is a technique used in VLBI to extend the signal coherence time from a few minutes to a few hours in order to enhance significantly its sensitivity. With this technique, VLBI observations of milliJansky radio sources can be conducted for high-accuracy differential astrometry as well as imaging. We describe the technique in some details and present, as an example, a submilliarcsecond differential astrometric experiment design to identify the star responsible for the weak radio emission in the binary system Algol.

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.

Engineering processes for the African VLBI network

NASA Astrophysics Data System (ADS)

Thondikulam, Venkatasubramani L.; Loots, Anita; Gaylard, Michael

2013-04-01

The African VLBI Network (AVN) is an initiative by the SKA-SA and HartRAO, business units of the National Research Foundation (NRF), Department of Science and Technology (DST), South Africa. The aim is to fill the existing gap of Very Long Baseline Interferometry (VLBI)-capable radio telescopes in the African continent by a combination of new build as well as conversion of large redundant telecommunication antennas through an Inter-Governmental collaborative programme in Science and Technology. The issue of human capital development in the Continent in the techniques of radio astronomy engineering and science is a strong force to drive the project and is expected to contribute significantly to the success of Square Kilometer Array (SKA) in the Continent.

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;

Goddard Geophysical and Astronomical Observatory

NASA Technical Reports Server (NTRS)

Redmond, Jay; Kodak, Charles

2004-01-01

This report summarizes the technical parameters and the technical staff of the VLBI system at the fundamental station GGAO. It also gives an overview about the VLBI activities during the previous year. The outlook lists the outstanding tasks to improve the performance of GGAO.

Multi-technique approach for deriving a VLBI signal extra-path variation model induced by gravity: the example of Medicina

NASA Astrophysics Data System (ADS)

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

2009-09-01

During the measurement sessions gravity might induce significant deformations in large VLBI telescopes. If neglected or mismodelled, these deformations might bias the phase of the incoming signal thus corrupting the estimate of some crucial geodetic parameters (e.g. the height component of VLBI Reference Point). This paper describes a multi-technique approach implemented for measuring and quantifying the gravity-dependent deformations experienced by the 32-m diameter VLBI antenna of Medicina (Northern Italy). Such an approach integrates three different methods: Terrestrial Triangulations and Trilaterations (TTT), Laser Scanning (LS) and a Finite Element Model (FEM) of the antenna. The combination of the observations performed with these methods allows to accurately define an elevation-dependent model of the signal path variation which appears to be, for the Medicina telescope, non negligible. In the range [0,90] deg the signal path increases monotonically by almost 2 cm. The effect of such a variation has not been introduced in actual VLBI analysis yet; nevertheless this is the task we are going to pursue in the very next future.

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.

Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter-VLBI Observations of Sagittarius A*

NASA Astrophysics Data System (ADS)

Broderick, Avery E.; Fish, Vincent L.; Doeleman, Sheperd S.; Loeb, Abraham

2011-07-01

Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging spectral and polarization information as well as accretion theory, it is possible to extract accretion-model parameters (including black hole spin) from mm-VLBI experiments containing only a handful of telescopes. Here we repeat this analysis with the most recent mm-VLBI data, considering a class of aligned, radiatively inefficient accretion flow (RIAF) models. We find that the combined data set rules out symmetric models for Sgr A*'s flux distribution at the 3.9σ level, strongly favoring length-to-width ratios of roughly 2.4:1. More importantly, we find that physically motivated accretion flow models provide a significantly better fit to the mm-VLBI observations than phenomenological models, at the 2.9σ level. This implies that not only is mm-VLBI presently capable of distinguishing between potential physical models for Sgr A*'s emission, but further that it is sensitive to the strong gravitational lensing associated with the propagation of photons near the black hole. Based upon this analysis we find that the most probable magnitude, viewing angle, and position angle for the black hole spin are a = 0.0+0.64 + 0.86, \\theta ={68^\\circ }^{+5^\\circ +9^\\circ }_{-20^\\circ -28^\\circ }, and \\xi ={-52^\\circ }^{+17^\\circ +33^\\circ }_{-15^\\circ -24^\\circ } east of north, where the errors quoted are the 1σ and 2σ uncertainties.

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.

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.

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.

Rigorous Combination of GNSS and VLBI: How it Improves Earth Orientation and Reference Frames

NASA Astrophysics Data System (ADS)

Lambert, S. B.; Richard, J. Y.; Bizouard, C.; Becker, O.

2017-12-01

Current reference series (C04) of the International Earth Rotation and Reference Systems Service (IERS) are produced by a weighted combination of Earth orientation parameters (EOP) time series built up by combination centers of each technique (VLBI, GNSS, Laser ranging, DORIS). In the future, we plan to derive EOP from a rigorous combination of the normal equation systems of the four techniques.We present here the results of a rigorous combination of VLBI and GNSS pre-reduced, constraint-free, normal equations with the DYNAMO geodetic analysis software package developed and maintained by the French GRGS (Groupe de Recherche en GeÌodeÌsie Spatiale). The used normal equations are those produced separately by the IVS and IGS combination centers to which we apply our own minimal constraints.We address the usefulness of such a method with respect to the classical, a posteriori, combination method, and we show whether EOP determinations are improved.Especially, we implement external validations of the EOP series based on comparison with geophysical excitation and examination of the covariance matrices. Finally, we address the potential of the technique for the next generation celestial reference frames, which are currently determined by VLBI only.

The Observatory as Laboratory: Spectral Analysis at Mount Wilson Observatory

NASA Astrophysics Data System (ADS)

Brashear, Ronald

2018-01-01

This paper will discuss the seminal changes in astronomical research practices made at the Mount Wilson Observatory in the early twentieth century by George Ellery Hale and his staff. Hale’s desire to set the agenda for solar and stellar astronomical research is often described in terms of his new telescopes, primarily the solar tower observatories and the 60- and 100-inch telescopes on Mount Wilson. This paper will focus more on the ancillary but no less critical parts of Hale’s research mission: the establishment of associated “physical” laboratories as part of the observatory complex where observational spectral data could be quickly compared with spectra obtained using specialized laboratory equipment. Hale built a spectroscopic laboratory on the mountain and a more elaborate physical laboratory in Pasadena and staffed it with highly trained physicists, not classically trained astronomers. The success of Hale’s vision for an astronomical observatory quickly made the Carnegie Institution’s Mount Wilson Observatory one of the most important astrophysical research centers in the world.

ON THE CONNECTION OF THE APPARENT PROPER MOTION AND THE VLBI STRUCTURE OF COMPACT RADIO SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moor, A.; Frey, S.; Lambert, S. B.

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 themore » 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.« less

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.

Love numbers for the long-period tides estimated by VLBI

NASA Astrophysics Data System (ADS)

Krásná, Hana; Böhm, Johannes; Haas, Rüdiger; Schuh, Harald

2013-04-01

Love and Shida numbers are proportionality factors characterizing the deformation of the anelastic Earth which arises as a response to external forces from the Moon and Sun. The increasing precision and quality of the Very Long Baseline Interferometry (VLBI) measurements allow determining those parameters. In particular, the long history of the VLBI data enables the estimation of Love and Shida numbers at the low frequencies of the tidal waves including the periods from 14 days to 18.6 years. In this study we analyse 27 years of VLBI measurements (1984.0 - 2011.0) following the recent IERS Conventions 2010. In several global solutions, we estimate the complex Love and Shida numbers of the solid Earth tides for the main long-period tidal waves. Furthermore, we determine the Love and Shida numbers of the rotational deformation due to polar motion, the so-called pole tide. We also focus on station displacement where still some deficiencies in the long-period signal modelling can be seen.

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.

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.

VLBI-based Products - Naval Oceanography Portal

Science.gov Websites

section Advanced Search... Sections Home Time Earth Orientation Astronomy Meteorology Oceanography Ice You terrestrial reference frames and to predict the variable orientation of the Earth in three-dimensional space antennas that define a VLBI-based Terrestrial Reference Frame (TRF) and the Earth Orientation Parameters

Monte Carlo simulations of the impact of troposphere, clock and measurement errors on the repeatability of VLBI positions

NASA Astrophysics Data System (ADS)

Pany, A.; Böhm, J.; MacMillan, D.; Schuh, H.; Nilsson, T.; Wresnik, J.

2011-01-01

Within the International VLBI Service for Geodesy and Astrometry (IVS) Monte Carlo simulations have been carried out to design the next generation VLBI system ("VLBI2010"). Simulated VLBI observables were generated taking into account the three most important stochastic error sources in VLBI, i.e. wet troposphere delay, station clock, and measurement error. Based on realistic physical properties of the troposphere and clocks we ran simulations to investigate the influence of the troposphere on VLBI analyses, and to gain information about the role of clock performance and measurement errors of the receiving system in the process of reaching VLBI2010's goal of mm position accuracy on a global scale. Our simulations confirm that the wet troposphere delay is the most important of these three error sources. We did not observe significant improvement of geodetic parameters if the clocks were simulated with an Allan standard deviation better than 1 × 10-14 at 50 min and found the impact of measurement errors to be relatively small compared with the impact of the troposphere. Along with simulations to test different network sizes, scheduling strategies, and antenna slew rates these studies were used as a basis for the definition and specification of VLBI2010 antennas and recording system and might also be an example for other space geodetic techniques.

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.

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

2016-03-01

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.

International VLBI Service for Geodesy and Astrometry 2005 Annual Report

NASA Technical Reports Server (NTRS)

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

2006-01-01

This volume of reports is the 2005 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 2005 Annual Report documents the work of these IVS components over the period January 1, 2005 through December 31, 2005. 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/ar2005.

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.

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.

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.

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.

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

Astrometry VLBI in Space (AVS

NASA Technical Reports Server (NTRS)

Altunin, V.; Alekseev, V.; Akim, E.; Eubanks, M.; Kingham, K.; Treuhaft, R.; Sukhanov, K.

1995-01-01

A proposed new space radio astronomy mission for astrometry is described. The Astrometry VLBI (very long baseline) in Space (AVS) nominal mission includes two identical spacecraft, each with a 4-m antenna sending data to a 70-m ground station. The goals of AVS are improving astrometry accuracy to the microarcsecond level and improving the accuracy of the transformation between the inertial radio and optical coordinate reference frames.

VLBI Observations of ALSEP Transmitters

NASA Technical Reports Server (NTRS)

Counselman, C. C.

1977-01-01

The technique of differential very-long-baseline inteferometry (VLBI) Apollo Lunar Surface Experiments Package was used to measure the relative positions of the (ALSEP) transmitters at the Apollo 12, 14, 15, 16, and 17 lunar landing sites with uncertainties less than 0.005 sec of the geocentric arc. These measurements yielded improved determinations of the selenodetic coordinates of the Apollo landing sites, and of the physical libration of the moon.

Crustal dynamics project data analysis, 1991: VLBI geodetic results, 1979 - 1990

NASA Technical Reports Server (NTRS)

Ma, C.; Ryan, J. W.; Caprette, D. S.

1992-01-01

The Goddard VLBI group reports the results of analyzing 1412 Mark II data sets acquired from fixed and mobile observing sites through the end of 1990 and available to the Crustal Dynamics Project. Three large solutions were used to obtain Earth rotation parameters, nutation offsets, global source positions, site velocities, and baseline evolution. Site positions are tabulated on a yearly basis from 1979 through 1992. Site velocities are presented in both geocentric Cartesian coordinates and topocentric coordinates. Baseline evolution is plotted for 175 baselines. Rates are computed for earth rotation and nutation parameters. Included are 104 sources, 88 fixed stations and mobile sites, and 688 baselines.

Decision Analysis Tools for Volcano Observatories

NASA Astrophysics Data System (ADS)

Hincks, T. H.; Aspinall, W.; Woo, G.

2005-12-01

Staff at volcano observatories are predominantly engaged in scientific activities related to volcano monitoring and instrumentation, data acquisition and analysis. Accordingly, the academic education and professional training of observatory staff tend to focus on these scientific functions. From time to time, however, staff may be called upon to provide decision support to government officials responsible for civil protection. Recognizing that Earth scientists may have limited technical familiarity with formal decision analysis methods, specialist software tools that assist decision support in a crisis should be welcome. A review is given of two software tools that have been under development recently. The first is for probabilistic risk assessment of human and economic loss from volcanic eruptions, and is of practical use in short and medium-term risk-informed planning of exclusion zones, post-disaster response, etc. A multiple branch event-tree architecture for the software, together with a formalism for ascribing probabilities to branches, have been developed within the context of the European Community EXPLORIS project. The second software tool utilizes the principles of the Bayesian Belief Network (BBN) for evidence-based assessment of volcanic state and probabilistic threat evaluation. This is of practical application in short-term volcano hazard forecasting and real-time crisis management, including the difficult challenge of deciding when an eruption is over. An open-source BBN library is the software foundation for this tool, which is capable of combining synoptically different strands of observational data from diverse monitoring sources. A conceptual vision is presented of the practical deployment of these decision analysis tools in a future volcano observatory environment. Summary retrospective analyses are given of previous volcanic crises to illustrate the hazard and risk insights gained from use of these tools.

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.

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.

Seasonal station variations in the Vienna VLBI terrestrial reference frame VieTRF16a

NASA Astrophysics Data System (ADS)

Krásná, Hana; Böhm, Johannes; Madzak, Matthias

2017-04-01

The special analysis center of the International Very Long Baseline Interferometry (VLBI) Service for Geodesy and Astrometry (IVS) at TU Wien (VIE) routinely analyses the VLBI measurements and estimates its own Terrestrial Reference Frame (TRF) solutions. We present our latest solution VieTRF16a (1979.0 - 2016.5) computed with the software VieVS version 3.0. Several recent updates of the software have been applied, e.g., the estimation of annual and semi-annual station variations as global parameters. The VieTRF16a is determined in the form of the conventional model (station position and its linear velocity) simultaneously with the celestial reference frame and Earth orientation parameters. In this work, we concentrate on the seasonal station variations in the residual time series and compare our TRF with the three combined TRF solutions ITRF2014, DTRF2014 and JTRF2014.

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.

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

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.

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.

Report On Fiducial Points At The Space Geodesy Based Cagliari Astronomical Observatory

NASA Astrophysics Data System (ADS)

Banni, A.; Buffa, F.; Falchi, E.; Sanna, G.

At the present time two research groups are engaged to space-geodesy activities in Sardinia: a staff belonging to the Stazione Astronomica of Cagliari (SAC) and the To- pography Section of the Dipartimento di Ingegneria Strutturale (DIST) of the Cagliari University. The two groups have a share in international campaigns and services. The local structure, consists of permanent stations of satellite observation both on radio and laser techniques. Particularly in the Cagliari Observatory a Satellite Laser Ranging system runs with nearly daily, low, medium and high orbit satellite tracking capability (e. g. Topex, Ajisai, Lageos1/2, Glonass); up to this time the Cagliari laser station has contributed towards the following international campaigns/organizations. Besides in the Observatory's site a fixed GPS system, belonging the Italian Space Agency GPS- Network and to the IGS-Network; and a GPS+GLONASS system, acquired by DIST and belonging to the IGLOS are installed and managed. All the above stations are furnished with meteorological sensors with RINEX format data dissemination avail- ability. Moreover a new 64 meters dish radio telescope (Sardinian Radio Telescope), geodetic VLBI equipped, is under construction not long away from the Observatory. The poster fully shows the facilities and furnishes a complete report on the mark- ers eccentricities, allowing co-location of the different space techniques operating in Sardinia.

The Potential for a Ka-band (32 GHz) Worldwide VLBI Network

NASA Astrophysics Data System (ADS)

Jacobs, C. S.; Bach, U.; Colomer, F.; Garcá-Miró, C.; Gómez-González, J.; Gulyaev, S.; Horiuchi, S.; Ichikawa, R.; Kraus, A.; Kronschnabl, G.; López-Fernández, J. A.; Lovell, J.; Majid, W.; T; Natusch; Neidhardt, A.; Phillips, C.; Porcas, R.; Romero-Wolf, A.; Saldana, L.; Schreiber, U.; Sotuela, I.; Takeuchi, H.; Trinh, J.; Tzioumis, A.; de Vincente, P.; Zharov, V.

2012-12-01

Ka-band (32 GHz, 9 mm) 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.

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.;

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.

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.

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].

The performance of differential VLBI delay during interplanetary cruise

NASA Technical Reports Server (NTRS)

Moultrie, B.; Wolff, P. J.; Taylor, T. H.

1984-01-01

Project Voyager radio metric data are used to evaluate the orbit determination abilities of several data strategies during spacecraft interplanetary cruise. Benchmark performance is established with an operational data strategy of conventional coherent doppler, coherent range, and explicitly differenced range data from two intercontinental baselines to ameliorate the low declination singularity of the doppler data. Employing a Voyager operations trajectory as a reference, the performance of the operational data strategy is compared to the performances of data strategies using differential VLBI delay data (spacecraft delay minus quasar delay) in combinations with the aforementioned conventional data types. The comparison of strategy performances indicates that high accuracy cruise orbit determination can be achieved with a data strategy employing differential VLBI delay data, where the quantity of coherent radio metric data has been greatly reduced.

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.

Atmospheric Delay Reduction Using KARAT for GPS Analysis and Implications for VLBI

NASA Technical Reports Server (NTRS)

Ichikawa, Ryuichi; Hobiger, Thomas; Koyama, Yasuhiro; Kondo, Tetsuro

2010-01-01

We have been developing a state-of-the-art tool to estimate the atmospheric path delays by raytracing through mesoscale analysis (MANAL) data, which is operationally used for numerical weather prediction by the Japan Meteorological Agency (JMA). The tools, which we have named KAshima RAytracing Tools (KARAT)', are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. The KARAT can estimate atmospheric slant delays by an analytical 2-D ray-propagation model by Thayer and a 3-D Eikonal solver. We compared PPP solutions using KARAT with that using the Global Mapping Function (GMF) and Vienna Mapping Function 1 (VMF1) for GPS sites of the GEONET (GPS Earth Observation Network System) operated by Geographical Survey Institute (GSI). In our comparison 57 stations of GEONET during the year of 2008 were processed. The KARAT solutions are slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. Our results imply that KARAT is a useful tool for an efficient reduction of atmospheric path delays in radio-based space geodetic techniques such as GNSS and VLBI.

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.

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

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

Real-time Data Streams from ``e-RemoteCtrl'' to Central VLBI Network Status Monitoring Services Like IVS Live

NASA Astrophysics Data System (ADS)

Neidhardt, Alexander; Collioud, Arnaud

2014-12-01

A central VLBI network status monitoring can be realized by using online status information about current VLBI sessions, real-time, and status data directly from each radio telescope. Such monitoring helps to organize sessions or to get immediate feedback from the active telescopes. Therefore the remote control software for VLBI radio telescopes ``e-RemoteCtrl'' (http://www.econtrol-software.de), which enables remote access as extension to the NASA Field System, realizes real-time data streams to dedicated data centers. The software has direct access to the status information about the current observation (e.g., schedule, scan, source) and the telescope (e.g., current state, temperature, pressure) in real-time. This information are directly sent to ``IVS Live''. ``IVS Live'' (http://ivslive.obs.u-bordeaux1.fr/) is a Web tool that can be used to follow the observing sessions, organized by the International VLBI Service for Geodesy and Astrometry (IVS), navigate through past or upcoming sessions, or search and display specific information about sessions, sources (like VLBI images), and stations, by using an Internet browser.

Source positions from VLBI combined solution

NASA Astrophysics Data System (ADS)

Bachmann, S.; Thaller, D.; Engelhardt, G.

2014-12-01

The IVS Combination Center at BKG is primarily responsible for combined Earth Orientation Parameter (EOP) products and the generation of a terrestrial reference frame based on VLBI observations (VTRF). The procedure is based on the combination of normal equations provided by six IVS Analysis Centers (AC). Since more and more ACs also provide source positions in the normal equations - beside EOPs and station coordinates - an estimation of these parameters is possible and should be investigated. In the past, the International Celestial Reference Frame (ICRF) was not generated as a combined solution from several individual solutions, but was based on a single solution provided by one AC. The presentation will give an overview on the combination strategy and the possibilities for combined source position determination. This includes comparisons with existing catalogs, quality estimation and possibilities of rigorous combination of EOP, TRF and CRF in one combination process.

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.

Long-Term Stability of Radio Sources in VLBI Analysis

NASA Technical Reports Server (NTRS)

Engelhardt, Gerald; Thorandt, Volkmar

2010-01-01

Positional stability of radio sources is an important requirement for modeling of only one source position for the complete length of VLBI data of presently more than 20 years. The stability of radio sources can be verified by analyzing time series of radio source coordinates. One approach is a statistical test for normal distribution of residuals to the weighted mean for each radio source component of the time series. Systematic phenomena in the time series can thus be detected. Nevertheless, an inspection of rate estimation and weighted root-mean-square (WRMS) variations about the mean is also necessary. On the basis of the time series computed by the BKG group in the frame of the ICRF2 working group, 226 stable radio sources with an axis stability of 10 as could be identified. They include 100 ICRF2 axes-defining sources which are determined independently of the method applied in the ICRF2 working group. 29 stable radio sources with a source structure index of less than 3.0 can also be used to increase the number of 295 ICRF2 defining sources.

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

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.

EARLY SCIENCE WITH THE KOREAN VLBI NETWORK: THE QCAL-1 43 GHz CALIBRATOR SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrov, Leonid; Lee, Sang-Sung; Kim, Jongsoo

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 ofmore » 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.« less

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.

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.

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.

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.

The Cross-Wavelet Transform and Analysis of Quasi-periodic Behavior in the Pearson-Readhead VLBI Survey Sources

NASA Astrophysics Data System (ADS)

Kelly, Brandon C.; Hughes, Philip A.; Aller, Hugh D.; Aller, Margo F.

2003-07-01

We introduce an algorithm for applying a cross-wavelet transform to analysis of quasi-periodic variations in a time series and introduce significance tests for the technique. We apply a continuous wavelet transform and the cross-wavelet algorithm to the Pearson-Readhead VLBI survey sources using data obtained from the University of Michigan 26 m paraboloid at observing frequencies of 14.5, 8.0, and 4.8 GHz. Thirty of the 62 sources were chosen to have sufficient data for analysis, having at least 100 data points for a given time series. Of these 30 sources, a little more than half exhibited evidence for quasi-periodic behavior in at least one observing frequency, with a mean characteristic period of 2.4 yr and standard deviation of 1.3 yr. We find that out of the 30 sources, there were about four timescales for every 10 time series, and about half of those sources showing quasi-periodic behavior repeated the behavior in at least one other observing frequency.

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.

The second Caltech-Jodrell Bank VLBI survey. 1: Observations of 91 of 193 sources

NASA Technical Reports Server (NTRS)

Taylor, G. B.; Vermeulen, R. C.; Pearson, T. J.; Readhead, A. C. S.; Henstock, D. R.; Browne, I. W. A.; Wilkinson, P. N.

1994-01-01

We define the sample for the second Caltech-Jodrell Bank very long base interferometry (VLBI) survey. This is a sample of 193 flat- or gigahertz-peaked-spectrum sources selected at 4850 MHz. This paper presents images of 91 sources with a resolution of approximately 1 mas, obtained using VLBI observations at 4992 MHz with a global array. The remaining images and the integrated radio spectra will be presented in a forthcoming paper by Henstock et al.

Geodetic measurement of deformation in the Loma Prieta, California earthquake with Very Long Baseline Interferometry (VLBI)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, T.A.; Ma, C.; Sauber, J.M.

Following the Loma Prieta earthquake, two mobile Very Long Baseline Interferometry (VLBI) systems operated by the NASA Crustal Dynamics Project and the NOAA National Geodetic Survey were deployed at three previously established VLBI sites in the earthquake area: Fort Ord (near Monterey), the Presidio (in San Francisco) and Point Reyes. From repeated VLBI occupations of these sites since 1983, the pre-earthquake rates of deformation have been determined with respect to a North American reference frame with 1{sigma} formal standard errors of {approximately}1 mm/yr. The VLBI measurements immediately following the earthquake showed that the Fort Ord site was displaced 49 {plusmore » minus} 4 mm at an azimuth of 11 {plus minus} 4{degree} and that the Presidio site was displaced 12 {plus minus} 5 mm at an azimuth of 148 {plus minus} 13{degree}. No anomalous change was detected at Point Reyes with 1{sigma} uncertainty of 4 mm. The estimated displacements at Fort Ord and the Presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment is shallower than slip on the more northern segment of the fault rupture. The authors also give the Cartesian positions at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the vicinity of the earthquake.« less

Arcsecond positions for milliarcsecond VLBI nuclei of extragalactic radio sources. IV - Seventeen sources

NASA Technical Reports Server (NTRS)

Morabito, D. D.; Preston, R. A.; Linfield, R. P.; Slade, M. A.; Jauncey, D. L.

1986-01-01

VLBI measurements of time delay and delay rate at 2.29 and 8.42 GHz on baselines of 10,000 km have been used to determine the positions of the milliarcsecond nuclei in 17 extragalactic radio sources with estimated accuracies of 0.1 to 0.3 arcsec. The observed sources are part of an all-sky VLBI catalog of milliarcsecond radio sources. In addition, slightly improved positions are presented for 101 sources originally reported by Morabito et al. (1983). Arcsecond positions have now been determined for 836 sources.

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.

Digital Base Band Converter As Radar Vlbi Backend / Dbbc Kā Ciparošanas Sistēma Radara Vlbi Novērojumiem

NASA Astrophysics Data System (ADS)

Tuccari, G.; Bezrukovs, Vl.; Nechaeva, M.

2012-12-01

A digital base band converter (DBBC) system has been developed by the Istituto di Radioastronomia (Noto, Italy) for increasing the sensitivity of European VLBI Network (EVN) by expanding the full observed bandwidth using numerical methods. The output data rate of this VLBI-backend is raised from 1 to 4 Gbps for each radiotelescope. All operations related to the signal processing (frequency translation, amplification, frequency generation with local oscillators, etc.) are transferred to the digital domain, which allows - in addition to well-known advantages coming from digital technologies - achieving better repeatability, precision, simplicity, etc. The maximum input band of DBBC system is 3.5 GHz, and the instantaneous bandwidth is up to 1 GHz for each radio frequency/intermediate frequency (RF/IF) out of the eight possible. This backend is a highly powerful platform for other radioastronomy applications, and a number of additional so-called personalities have been developed and used. This includes PFB (polyphase filter bank) receivers and Spectra for high resolution spectroscopy. An additional new development with the same aim - to use the DBBC system as a multi-purpose backend - is related to the bi-static radar observations including Radar VLBI. In such observations it is possible to study the population of space debris, with detection of even centimetre class fragments. A powerful transmitter is used to illuminate the sky region to be analyzed, and the echoes coming from known or unknown objects are reflected to one or more groundbased telescopes thus producing a single-dish or interferometric detection. The DBBC Radar VLBI personality is able to realize a high-resolution spectrum analysis, maintaining in the central area the echo signal at the expected frequency including the Doppler shift of frequency. For extremely weak signals a very large integration time is needed, so for this personality different input parameters are provided. The realtime information

NASA Space Geodesy Program: GSFC data analysis, 1993. VLBI geodetic results 1979 - 1992

NASA Technical Reports Server (NTRS)

Ma, Chopo; Ryan, James W.; Caprette, Douglas S.

1994-01-01

The Goddard VLBI group reports the results of analyzing Mark 3 data sets acquired from 110 fixed and mobile observing sites through the end of 1992 and available to the Space Geodesy Program. Two large solutions were used to obtain site positions, site velocities, baseline evolution for 474 baselines, earth rotation parameters, nutation offsets, and radio source positions. Site velocities are presented in both geocentric Cartesian and topocentric coordinates. Baseline evolution is plotted for the 89 baselines that were observed in 1992 and positions at 1988.0 are presented for all fixed stations and mobile sites. Positions are also presented for quasar radio sources used in the solutions.

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.

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.

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.

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.

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.

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.

Earth's core and inner-core resonances from analysis of VLBI nutation and superconducting gravimeter data

NASA Astrophysics Data System (ADS)

Rosat, S.; Lambert, S. B.; Gattano, C.; Calvo, M.

2017-01-01

Geophysical parameters of the deep Earth's interior can be evaluated through the resonance effects associated with the core and inner-core wobbles on the forced nutations of the Earth's figure axis, as observed by very long baseline interferometry (VLBI), or on the diurnal tidal waves, retrieved from the time-varying surface gravity recorded by superconducting gravimeters (SGs). In this paper, we inverse for the rotational mode parameters from both techniques to retrieve geophysical parameters of the deep Earth. We analyse surface gravity data from 15 SG stations and VLBI delays accumulated over the last 35 yr. We show existing correlations between several basic Earth parameters and then decide to inverse for the rotational modes parameters. We employ a Bayesian inversion based on the Metropolis-Hastings algorithm with a Markov-chain Monte Carlo method. We obtain estimates of the free core nutation resonant period and quality factor that are consistent for both techniques. We also attempt an inversion for the free inner-core nutation (FICN) resonant period from gravity data. The most probable solution gives a period close to the annual prograde term (or S1 tide). However the 95 per cent confidence interval extends the possible values between roughly 28 and 725 d for gravity, and from 362 to 414 d from nutation data, depending on the prior bounds. The precisions of the estimated long-period nutation and respective small diurnal tidal constituents are hence not accurate enough for a correct determination of the FICN complex frequency.

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.

Cutting-Edge Science from Arecibo Observatory: Introduction

NASA Astrophysics Data System (ADS)

Schmelz, Joan T.

2017-01-01

The Arecibo Observatory is home to the largest radio telescope in the world operating above 2 GHz, where molecule emission pertaining to the origins of life proliferate. It also houses the most powerful radar system on the planet, providing crucial information for the assessment of impact hazards of near-Earth asteroids (NEA). It was built to study the ionosphere with a radar system that can also monitor the effects of Space Weather and climate change. Arecibo has a proven track record for doing excellent science, even after 50 years of operations. This talk will include brief summaries of several Arecibo astronomy topics including the (1) latest attempts to resolve the Pleiades distance controversy, which include VLBI and Gaia; (2) galactic and extragalactic molecules; and (3) Arecibo 3D orbit determinations of potentially hazardous asteroids, and the crucial observation required to select Bennu as the target for the recently launched NASA OSIRIS-REx mission. This introduction will set the stage for the invited talks in this session, which include such topics as Fast Radio Bursts, galactic and extragalactic HI results, the pulsar emission problem, and NANOGrav. This work is supported by NSF and NASA.

Spectral Analysis within the Virtual Observatory: The GAVO Service TheoSSA

NASA Astrophysics Data System (ADS)

Ringat, E.

2012-03-01

In the last decade, numerous Virtual Observatory organizations were established. One of these is the German Astrophysical Virtual Observatory (GAVO) that e.g. provides access to spectral energy distributions via the service TheoSSA. In a pilot phase, these are based on the Tübingen NLTE Model-Atmosphere Package (TMAP) and suitable for hot, compact stars. We demonstrate the power of TheoSSA in an application to the sdOB primary of AA Doradus by comparison with a “classical” spectral analysis.

Impact of the galactic acceleration on the terrestrial reference frame and the scale factor in VLBI

NASA Astrophysics Data System (ADS)

Krásná, Hana; Titov, Oleg

2017-04-01

The relative motion of the solar system barycentre around the galactic centre can also be described as an acceleration of the solar system directed towards the centre of the Galaxy. So far, this effect has been omitted in the a priori modelling of the Very Long Baseline Interferometry (VLBI) observable. Therefore, it results in a systematic dipole proper motion (Secular Aberration Drift, SAD) of extragalactic radio sources building the celestial reference frame with a theoretical maximum magnitude of 5-7 microarcsec/year. In this work, we present our estimation of the SAD vector obtained within a global adjustment of the VLBI measurements (1979.0 - 2016.5) using the software VieVS. We focus on the influence of the observed radio sources with the maximum SAD effect on the terrestrial reference frame. We show that the scale factor from the VLBI measurements estimated for each source individually discloses a clear systematic aligned with the direction to the Galactic centre-anticentre. Therefore, the radio sources located near Galactic anticentre may cause a strong systematic effect, especially, in early VLBI years. For instance, radio source 0552+398 causes a difference up to 1 mm in the estimated baseline length. Furthermore, we discuss the scale factor estimated for each radio source after removal of the SAD systematic.

Comparison of the calibration of ionospheric delay in VLBI data by the methods of dual frequency and Faraday rotation

NASA Technical Reports Server (NTRS)

Scheid, J. A.

1985-01-01

When both S-band and X-band data are recorded for a signal which has passed through the ionosphere, it is possible to calculate the ionospheric contribution to signal delay. In Very Long Baseline Interferometry (VLBI) this method is used to calibrate the ionosphere. In the absence of dual frequency data, the ionospheric content measured by Faraday rotation, using a signal from a geostationary satellite, is mapped to the VLBI observing direction. The purpose here is to compare the ionospheric delay obtained by these two methods. The principal conclusions are: (1) the correlation between delays obtained by these two methods is weak; (2) in mapping Faraday rotation measurements to the VLBI observing direction, a simple mapping algorithm which accounts only for changes in hour angle and elevation angle is better than a more elaborate algorithm which includes solar and geomagnetic effects; (3) fluctuations in the difference in total electron content as seen by two antennas defining a baseline limit the application of Faraday rotation data to VLBI.

VLBI geodesy - 2 parts-per-billion precision in length determinations for transcontinental baselines

NASA Technical Reports Server (NTRS)

Davis, J. L.; Herring, T. A.; Shapiro, I. I.

1988-01-01

VLBI was to make twenty-two independent measurements, between September 1984 and December 1986, of the length of the 3900-km baseline between the Mojave site in California and the Haystack/Westford site in Massachusetts. These experiments differ from the typical geodetic VLBI experiments in that a large fraction of observations is obtained at elevation angles between 4 and 10 deg. Data from these low elevation angles allow the vertical coordinate of site position, and hence the baseline length, to be estimated with greater precision. For the sixteen experiments processed thus far, the weighted root-mean-square scatter of the estimates of the baseline length is 8 mm.

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.

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.

Demonstration of intercontinental DSN clock synchronization by VLBI

NASA Technical Reports Server (NTRS)

Hurd, W. J.

1973-01-01

The prototype system for Deep Space Network clock synchronization by VLBI has been demonstrated to operate successfully over intercontinental baselines in a series of experiments between Deep Space Stations at Madrid, Spain, and Goldstone, California. As predicted by analysis and short baseline demonstration, the system achieves reliable synchronization between 26m and 64m antenna stations with 17 and 37K nominal system temperatures using under one million bits of data from each station. Semi-real-time operation is feasible since this small amount of data can be transmitted to JPL and processed within minutes. The system resolution is 50 to 400ns, depending on the amount of data processed and the source intensity. The accuracy is believed to be comparable to the resolution, although it could be independently confirmed to only about 5 microseconds using LORAN C.

The First VLBI Detection of a Spiral DRAGN Core

NASA Astrophysics Data System (ADS)

Mao, Minnie Y.; Blanchard, Jay M.; Owen, Frazer; Sjouwerman, Loránt O.; Singh, Vikram; Scaife, Anna; Paragi, Zsolt; Norris, Ray P.; Momjian, Emmanuel; Johnson, Gia; Browne, Ian

2018-05-01

We present the first observation of 0313-192, the archetypal spiral DRAGN, at VLBI resolutions. Spiral DRAGNs are Double Radio Sources Associated with Galactic Nuclei (DRAGNs) that are hosted by spiral galaxies. 0313-192 is an edge-on spiral galaxy that appears to host a 360 kpc double-lobed radio source. The core of this galaxy is clearly detected at L, S, and X-bands using the VLBA, signifying an ongoing active nucleus in the galaxy. This rules out the possibility that the spiral DRAGN is merely a chance alignment. The radio core has L1.4 GHz ˜ 3.0 × 1023 W Hz-1. Radio components are detected to the South-West of the core, but there are no detections of a counterjet. Assuming a symmetric, relativistic jet, we estimate an upper limit to the inclination angle of θ ≲ 72 degrees. The VLBI-detected radio jet components are extremely well-aligned with the larger-scale radio source suggested little to no jet disruption or interaction with the ISM of the host galaxy.

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.

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.

A complete VLBI delay model for deforming radio telescopes: the Effelsberg case

NASA Astrophysics Data System (ADS)

Artz, T.; Springer, A.; Nothnagel, A.

2014-12-01

Deformations of radio telescopes used in geodetic and astrometric very long baseline interferometry (VLBI) observations belong to the class of systematic error sources which require correction in data analysis. In this paper we present a model for all path length variations in the geometrical optics of radio telescopes which are due to gravitational deformation. The Effelsberg 100 m radio telescope of the Max Planck Institute for Radio Astronomy, Bonn, Germany, has been surveyed by various terrestrial methods. Thus, all necessary information that is needed to model the path length variations is available. Additionally, a ray tracing program has been developed which uses as input the parameters of the measured deformations to produce an independent check of the theoretical model. In this program as well as in the theoretical model, the illumination function plays an important role because it serves as the weighting function for the individual path lengths depending on the distance from the optical axis. For the Effelsberg telescope, the biggest contribution to the total path length variations is the bending of the main beam located along the elevation axis which partly carries the weight of the paraboloid at its vertex. The difference in total path length is almost 100 mm when comparing observations at 90 and at 0 elevation angle. The impact of the path length corrections is validated in a global VLBI analysis. The application of the correction model leads to a change in the vertical position of mm. This is more than the maximum path length, but the effect can be explained by the shape of the correction function.

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

Geodetic Results from Mark 4 VLBI

NASA Technical Reports Server (NTRS)

MacMillan, Daniel; Petrov, Leonid; Ma, Chopo

2002-01-01

We present geodetic results of a series of 30 VLBI experiments recorded in Mark 4 mode at rates of 128 and 256 Mbps. The formal uncertainties of UT1, polar motion, and nutation offsets derived from these experiments are better than the corresponding uncertainties from NEOS-A experiments by a factor of 1.3-2. Baseline length repeatability for the series of 32 experiments over a period of one year is about 0.9 ppb. For comparison, NEOS-A length repeatability is about 1.4 ppb. We will discuss optimal use of Mark 4 in the design of future observing networks.

Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022

NASA Astrophysics Data System (ADS)

Giroletti, M.; Paragi, Z.; Bignall, H.; Doi, A.; Foschini, L.; Gabányi, K. É.; Reynolds, C.; Blanchard, J.; Campbell, R. M.; Colomer, F.; Hong, X.; Kadler, M.; Kino, M.; van Langevelde, H. J.; Nagai, H.; Phillips, C.; Sekido, M.; Szomoru, A.; Tzioumis, A. K.

2011-04-01

Context. There is growing evidence of relativistic jets in radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies. Aims: We constrain the observational properties of the radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN J0948+0022, i.e., its flux density and structure in both total intensity and polarization, its compactness, and variability. Methods: We performed three real-time e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including telescopes in Europe, East Asia, and Australia. These are the first e-VLBI science observations ever carried out with a global array, reaching a maximum baseline length of 12 458 km. The observations were part of a large multiwavelength campaign in 2009. Results: The source is detected at all three epochs. The structure is dominated by a bright component, more compact than 55 μas, with a fainter component at a position angle θ ~ 35°. Relativistic beaming is required by the observed brightness temperature of 3.4 × 1011 K. Polarization is detected at a level of about 1%. Conclusions: The parameters derived by the VLBI observations, in addition to the broad-band properties, confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global e-VLBI is a reliable and promising technique for future studies.

Combination of Vlbi, GPS and Slr Observations At The Observation Level For The Realization of Terrestrial and Celestial Reference Frames

NASA Astrophysics Data System (ADS)

Andersen, P. H.

Forsvarets forskningsinstitutt (FFI, the Norwegian Defence Research Establishment) has during the last 17 years developed a software system called GEOSAT, for the analysis of any type of high precision space geodetic observations. A unique feature of GEOSAT is the possibility of combining any combination of different space geode- tic data at the observation level with one consistent model and one consistent strategy. This is a much better strategy than the strategy in use today where different types of observations are processed separately using analysis software developed specifically for each technique. The results from each technique are finally combined a posteriori. In practice the models implemented in the software packages differ at the 1-cm level which is almost one order of magnitude larger than the internal precision of the most precise techniques. Another advantage of the new proposed combination method is that for example VLBI and GPS can use the same tropospheric model with common parameterization. The same is the case for the Earth orientation parameters, the geo- center coordinates and other geodetic or geophysical parameters where VLBI, GPS and SLR can have a common estimate for each of the parameters. The analysis with GEOSAT is automated for the combination of VLBI, SLR and GPS observations. The data are analyzed in batches of one day where the result from each daily arc is a SRIF array (Square Root Information Filter). A large number of SRIF arrays can be combined into a multi-year solution using the CSRIFS program (Com- bination Square Root Information Filter and Smoother). Four parameter levels are available and any parameter can, at each level, either be represented as a constant or a stochastic parameter (white noise, colored noise, or random walk). The batch length (i.e. the time interval between the addition of noise to the SRIF array) can be made time- and parameter dependent. GEOSAT and CSRIFS have been applied in the analysis of selected

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)

First Local Ties from Data of the Wettzell Triple Radio Telescope Array

NASA Astrophysics Data System (ADS)

Schüler, T.; Plötz, C.; Mähler, S.; Klügel, T.; Neidhardt, A.; Bertarini, A.; Halsig, S.; Nothnagel, A.; Lösler, M.; Eschelbach, C.; Anderson, J.

2016-12-01

The Geodetic Observatory Wettzell features three radio telescopes. Local ties between the reference points are available from terrestrial precision surveying with an expected accuracy below 0.7 mm. In addition, local VLBI data analysis is currently investigated to provide independent vectors and to provide quality feedback to the engineers. The preliminary results presented in this paper show a deviation from the local survey at the level of one millimeter with a clear systematic component. Sub-millimeter precision is reached after removal of this bias. This systematic effect is likely caused by omission of thermal expansion and gravity deformation, which is not yet implemented in our local VLBI analysis software.

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.

Application of space technology to crustal dynamics and earthquake research

NASA Technical Reports Server (NTRS)

1979-01-01

In cooperation with other Federal government agencies, and the governments of other countries, NASA is undertaking a program of research in geodynamics. The present program activities and plans for extension of these activities in the time period 1979-1985 are described. The program includes operation of observatories for laser ranging to the Moon and to artificial satellites, and radio observatories for very long baseline microwave interferometry (VLBI). These observatories are used to measure polar motion, earth rotation, and tectonic plate movement, and serve as base stations for mobile facilities. The mobile laser ranging and VLBI facilities are used to measure crustal deformation in tectonically active areas.

The first VLBI detection of a spiral DRAGN core

NASA Astrophysics Data System (ADS)

Mao, Minnie Y.; Blanchard, Jay M.; Owen, Frazer; Sjouwerman, Loránt O.; Singh, Vikram; Scaife, Anna; Paragi, Zsolt; Norris, Ray P.; Momjian, Emmanuel; Johnson, Gia; Browne, Ian

2018-07-01

We present the first observation of 0313-192, the archetypal spiral DRAGN, at very long baseline interferometry (VLBI) resolutions. Spiral DRAGNs are Double-lobed Radio sources Associated with Galactic Nuclei (DRAGNs) that are hosted by spiral galaxies. 0313-192 is an edge-on spiral galaxy that appears to host a 360 kpc double-lobed radio source. The core of this galaxy is clearly detected at L, S, and X bands using the Very Long Baseline Array, signifying an ongoing active nucleus in the galaxy. This rules out the possibility that the spiral DRAGN is merely a chance alignment. The radio core has L1.4 GHz ˜ 3.0 × 1023 W Hz-1. Radio components are detected to the south-west of the core, but there are no detections of a counterjet. Assuming a symmetric, relativistic jet, we estimate an upper limit to the inclination angle of θ ≲ 72 deg. The VLBI-detected radio jet components are extremely well aligned with the larger scale radio source suggesting little to no jet disruption or interaction with the interstellar medium of the host galaxy.

The First Geodetic VLBI Field Test of LIFT: A 550-km-long Optical Fiber Link for Remote Antenna Synchronization

NASA Astrophysics Data System (ADS)

Perini, Federico; Bortolotti, Claudio; Roma, Mauro; Ambrosini, Roberto; Negusini, Monia; Maccaferri, Giuseppe; Stagni, Matteo; Nanni, Mauro; Clivati, Cecilia; Frittelli, Matteo; Mura, Alberto; Levi, Filippo; Zucco, Massimo; Calonico, Davide; Bertarini, Alessandra; Artz, Thomas

2016-12-01

We present the first field test of the implementation of a coherent optical fiber link for remote antenna synchronization realized in Italy between the Italian Metrological Institute (INRIM) and the Medicina radio observatory of the National Institute for Astrophysics (INAF). The Medicina VLBI antenna participated in the EUR137 experiment carried out in September 2015 using, as reference systems, both the local H-maser and a remote H-maser hosted at the INRIM labs in Turin, separated by about 550 km. In order to assess the quality of the remote clock, the observed radio sources were split into two sets, using either the local or the remote H-maser. A system to switch automatically between the two references was integrated into the antenna field system. The observations were correlated in Bonn and preliminary results are encouraging since fringes were detected with both time references along the full 24 hours of the session. The experimental set-up, the results, and the perspectives for future radio astronomical and geodetic experiments are presented.

On an Allan variance approach to classify VLBI radio-sources on the basis of their astrometric stability

NASA Astrophysics Data System (ADS)

Gattano, C.; Lambert, S.; Bizouard, C.

2017-12-01

In the context of selecting sources defining the celestial reference frame, we compute astrometric time series of all VLBI radio-sources from observations in the International VLBI Service database. The time series are then analyzed with Allan variance in order to estimate the astrometric stability. From results, we establish a new classification that takes into account the whole multi-time scales information. The algorithm is flexible on the definition of ``stable source" through an adjustable threshold.

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.

An accuracy assessment of Magellan Very Long Baseline Interferometry (VLBI)

NASA Technical Reports Server (NTRS)

Engelhardt, D. B.; Kronschnabl, G. R.; Border, J. S.

1990-01-01

Very Long Baseline Interferometry (VLBI) measurements of the Magellan spacecraft's angular position and velocity were made during July through September, 1989, during the spacecraft's heliocentric flight to Venus. The purpose of this data acquisition and reduction was to verify this data type for operational use before Magellan is inserted into Venus orbit, in August, 1990. The accuracy of these measurements are shown to be within 20 nanoradians in angular position, and within 5 picoradians/sec in angular velocity. The media effects and their calibrations are quantified; the wet fluctuating troposphere is the dominant source of measurement error for angular velocity. The charged particle effect is completely calibrated with S- and X-Band dual-frequency calibrations. Increasing the accuracy of the Earth platform model parameters, by using VLBI-derived tracking station locations consistent with the planetary ephemeris frame, and by including high frequency Earth tidal terms in the Earth rotation model, add a few nanoradians improvement to the angular position measurements. Angular velocity measurements were insensitive to these Earth platform modelling improvements.

Comparison of VLBI TRF solutions based on Kalman filtering and recent ITRS realizations

NASA Astrophysics Data System (ADS)

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

2016-04-01

Compared to previous prominent global terrestrial reference frames (TRF) solutions, such as the ITRF2008 or DTRF2008, the current accuracy requirements demand among other things extended parameterization to account for various non-linear signals present in the time series of station coordinates. The next generation of TRFs, built upon geodetic data until the end of 2014, employs different approaches to tackle in particular seasonal variations and post-seismic deformations. The ITRF2014, developed at the International Earth Rotation and Reference Systems Service (IERS) Combination Center (CC) at Institut Géographique National, introduces harmonic, exponential and logarithmic functions to take into account aforementioned effects. In contrast, the ITRS realization of the IERS CC at Jet Propulsion Laboratory is based on Kalman filtering, which allows coordinate variations to be modeled in a stochastic sense besides the parameterized linear and seasonal signals. In our study, we compare these multi-technique TRFs with solutions solely based on VLBI data, including 104 radio telescopes and 4239 VLBI sessions, covering a time span of 34 years. We calculated a VLBI TRF based on the traditional least-squares adjustment of session-wise normal equations, and an ensemble of Kalman filter and smoother solutions with different parameterizations and stochastic models. In particular, we investigate the impact of different process noise levels for station coordinates, the choice of stochastic processes, e.g. random walks, and the application of time- and station-dependent noise models. For instance, we find that the estimation of seasonal signals, while important for predictions, does not affect the filtered coordinate time series when observational data is available. Furthermore, post-seismic deformations after major earthquakes require the process noise to be scaled accordingly. For instance, we detected coordinate differences of up to 5 cm immediately after the Chile 2010

High-frequency VLBI Imaging of Sgr A* and VX Sgr

NASA Astrophysics Data System (ADS)

Lu, R.-S.; Krichbaum, T. P.; Zensus, A. J.

VLBI observations at millimeter wavelengths provide unprecedented high angular resolution and allow to image regions, which are self-absorbed at longer wavelengths. Here we present new results from a multi-frequency VLBA monitoring of SgrA* at 22, 43, and 86 GHz performed on 10 consecutive days in May 2007. We discuss the source structure of Sgr A* through the analysis of the closure phase and closure amplitude, of which the latter improves the calibration accuracy and shows indications of a non-Gaussian brightness distribution at the highest frequency. We also present preliminary maps of the maser emission lines (v=1, J=1-0, and J=2-1) in the circumstellar SiO maser of VX Sgr. This will put new constraints on the kinematics and the pumping mechanisms of SiO masers.

Lunar Gravity Field Determination Using SELENE Same-Beam Differential VLBI Tracking Data

NASA Technical Reports Server (NTRS)

Goossens, S.; Matsumoto, K.; Liu, Q.; Kikuchi, F.; Sato, K.; Hanada, H.; Ishihara, Y.; Noda, H.; Kawano, N.; Namiki, N.;

VizieR Online Data Catalog: Parallaxes of high mass star forming regions (Reid+, 2014)

NASA Astrophysics Data System (ADS)

Reid, M. J.; Menten, K. M.; Brunthaler, A.; Zheng, X. W.; Dame, T. M.; Xu, Y.; Wu, Y.; Zhang, B.; Sanna, A.; Sato, M.; Hachisuka, K.; Choi, Y. K.; Immer, K.; Moscadelli, L.; Rygl, K. L. J.; Bartkiewicz, A.

2016-04-01

Table1 lists the parallaxes and proper motions of 103 regions of high-mass star formation measured with Very Long Baseline Interferometry (VLBI) techniques, using the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA), the Japanese VLBI Exploration of Radio Astrometry (VERA; http://veraserver.mtk.nao.ac.jp) project, and the European VLBI Network (EVN). We have include three red supergiants (NML Cyg, S Per, VY CMa) as indicative of high-mass star forming regions. (2 data files).

Solar Dynamics Observatory On-Orbit Jitter Testing, Analysis, and Mitigation Plans

NASA Technical Reports Server (NTRS)

Liu, Kuo-Chia; Blaurock, Carl A.; Bourkland, Kristin L.; Morgenstern, Wendy M.; Maghami, Peiman G.

2011-01-01

The recently launched Solar Dynamics Observatory (SDO) has two science instruments onboard that required sub-arcsecond pointing stability. Significant effort has been spent pre-launch to characterize the disturbances sources and validating jitter level at the component, sub-assembly, and spacecraft levels. However, an end-to-end jitter test emulating the flight condition was not performed on the ground due to cost and risk concerns. As a result, the true jitter level experienced on orbit remained uncertain prior to launch. Based on the pre-launch analysis, several operational constraints were placed on the observatory aimed to minimize the instrument jitter levels. If the actual jitter is below the analysis predictions, these operational constraints can be relaxed to reduce the burden of the flight operations team. The SDO team designed a three-day jitter test, utilizing the instrument sensors to measure pointing jitter up to 256 Hz. The test results were compared to pre-launch analysis predictions, used to determine which operational constraints can be relaxed, and analyzed for setting the jitter mitigation strategies for future SDO operations.

Comparison of ITRF2014 station coordinate input time series of DORIS, VLBI and GNSS

NASA Astrophysics Data System (ADS)

Tornatore, Vincenza; Tanır Kayıkçı, Emine; Roggero, Marco

2016-12-01

In this paper station coordinate time series from three space geodesy techniques that have contributed to the realization of the International Terrestrial Reference Frame 2014 (ITRF2014) are compared. In particular the height component time series extracted from official combined intra-technique solutions submitted for ITRF2014 by DORIS, VLBI and GNSS Combination Centers have been investigated. The main goal of this study is to assess the level of agreement among these three space geodetic techniques. A novel analytic method, modeling time series as discrete-time Markov processes, is presented and applied to the compared time series. The analysis method has proven to be particularly suited to obtain quasi-cyclostationary residuals which are an important property to carry out a reliable harmonic analysis. We looked for common signatures among the three techniques. Frequencies and amplitudes of the detected signals have been reported along with their percentage of incidence. Our comparison shows that two of the estimated signals, having one-year and 14 days periods, are common to all the techniques. Different hypotheses on the nature of the signal having a period of 14 days are presented. As a final check we have compared the estimated velocities and their standard deviations (STD) for the sites that co-located the VLBI, GNSS and DORIS stations, obtaining a good agreement among the three techniques both in the horizontal (1.0 mm/yr mean STD) and in the vertical (0.7 mm/yr mean STD) component, although some sites show larger STDs, mainly due to lack of data, different data spans or noisy observations.

SN 2014C: VLBI images of a supernova interacting with a circumstellar shell

NASA Astrophysics Data System (ADS)

Bietenholz, Michael F.; Kamble, Atish; Margutti, Raffaella; Milisavljevic, Danny; Soderberg, Alicia

2018-04-01

We report on very long baseline interferometry (VLBI) measurements of supernova 2014C at several epochs between t = 384 and 1057 d after the explosion. SN 2014C was an unusual supernova that initially had Type Ib optical spectrum, but after t = 130 d it developed a Type IIn spectrum with prominent Hα lines, suggesting the onset of strong circumstellar interaction. Our first VLBI observation was at t = 384 d, and we find that the outer radius of SN 2014C was (6.40 ± 0.26) × 1016 cm (for a distance of 15.1 Mpc), implying an average expansion velocity of 19 300 ± 790 km s-1 up to that time. At our last epoch, SN 2014C was moderately resolved and shows an approximately circular outline but with an enhancement of the brightness on the W side. The outer radius of the radio emission at t = 1057 d is (14.9 ± 0.6) × 1016 cm. We find that the expansion between t = 384 and 1057 d is well described by a constant velocity expansion with v = 13 600 ± 650 km s-1. SN 2014C had clearly been substantially decelerated by t = 384 d. Our measurements are compatible with a scenario where the expanding shock impacted upon a shell of dense circumstellar material during the first year, as suggested by the observations at other wavelengths, but had progressed through the dense shell by the time of the VLBI observations.

Integration of space geodesy: A US National Geodetic Observatory

NASA Astrophysics Data System (ADS)

Yunck, Thomas P.; Neilan, Ruth E.

2005-11-01

In the interest of improving the performance and efficiency of space geodesy a diverse group in the US, in collaboration with IGGOS, has begun to establish a unified National Geodetic Observatory (NGO). To launch this effort an international team will conduct a multi-year program of research into the technical issues of integrating SLR, VLBI, and GPS geodesy to produce a unified set of global geodetic products. The goal is to improve measurement accuracy by up to an order of magnitude while lowering the cost to current sponsors. A secondary goal is to expand and diversify international sponsorship of space geodesy. Principal benefits will be to open new vistas of research in geodynamics and surface change while freeing scarce NASA funds for scientific studies. NGO will proceed in partnership with, and under the auspices of, the International Association of Geodesy (IAG) as an element of the Integrated Global Geodetic Observation System project. The collaboration will be conducted within, and will make full use of, the IAG's existing international services: the IGS, IVS, ILRS, and IERS. Seed funding for organizational activities and technical analysis will come from NASA's Solid Earth and Natural Hazards Program. Additional funds to develop an integrated geodetic data system known as Inter-service Data Integration for Geodetic Operations (INDIGO), will come from a separate NASA program in Earth science information technology. INDIGO will offer ready access to the full variety of NASA's space geodetic data and will extend the GPS Seamless Archive (GSAC) philosophy to all space geodetic data types.

Mission definition study for a VLBI station utilizing the Space Shuttle

NASA Technical Reports Server (NTRS)

Burke, B. F.

1982-01-01

The uses of the Space Shuttle transportation system for orbiting VeryLong-Baseline Interferometry (OVLBI) were examined, both with respect to technical feasibility and its scientific possibilities. The study consisted of a critical look at the adaptability of current technology to an orbiting environment, the suitability of current data reduction facilities for the new technique, and a review of the new science that is made possible by using the Space Shuttle as a moving platform for a VLBI terminal in space. The conclusions are positive in all respects: no technological deficiencies exist that would need remedy, the data processing problem can be handled easily by straightforward adaptations of existing systems, and there is a significant new research frontier to be explored, with the Space Shuttle providing the first step. The VLBI technique utilizes the great frequency stability of modern atomic time standards, the power of integrated circuitry to perform real-time signal conditioning, and the ability of magnetic tape recorders to provide essentially error-free data recording, all of which combine to permit the realization of radio interferometry at arbitrarily large baselines.

VLBI observations of the nucleus of Centaurus A

NASA Technical Reports Server (NTRS)

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

1983-01-01

VLBI observations of the nucleus of Centaurus A made at 2.3 GHz on baselines with minimum fringe spacings of 0.15 and 0.0027 arcsec are presented. Results show that the nuclear component is elongated with a maximum extent of approximately 0.05 arcsec which is equivalent to a size of approximately 1 pc at the 5 Mpc distance of Centaurus A. The position angle of the nucleus is found to be 30 + or - 20 degrees, while the ratio of nuclear jet length to width is less than or approximately equal to 20. The nuclear flux density is determined to be 6.8 Jy, while no core component is found with an extent less than or approximately equal to 0.001 (less than or approximately equal to 0.02 pc) with a flux density of greater than or approximately equal to 20 mJy. A model of the Centaurus A nucleus composed of at least two components is developed on the basis of these results in conjunction with earlier VLBI and spectral data. The first component is an elongated source of approximately 0.05 arcsec (approximately 1 pc) size which contains most of the 2.3 GHz nuclear flux, while the second component is a source of approximately 0.0005 arcsec (approximately 0.01 pc) size which is nearly completely self-absorbed at 2.3 GHz but strengthens at higher frequencies.

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.

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.

Long-term millimeter VLBI monitoring of M 87 with KVN at milliarcsecond resolution: nuclear spectrum

NASA Astrophysics Data System (ADS)

Kim, Jae-Young; Lee, Sang-Sung; Hodgson, Jeffrey A.; Algaba, Juan-Carlos; Zhao, Guang-Yao; Kino, Motoki; Byun, Do-Young; Kang, Sincheol

2018-02-01

We study the centimeter- to millimeter-wavelength synchrotron spectrum of the core of the radio galaxy M 87 at ≲0.8 mas 110Rs spatial scales using four years of fully simultaneous, multi-frequency VLBI data obtained by the Korean VLBI Network (KVN). We find a core spectral index α of ≳‑0.37 (S ∝ ν+α) between 22 and 129 GHz. By combining resolution-matched flux measurements from the Very Long Baseline Array (VLBA) at 15 GHz and taking the Event Horizon Telescope (EHT) 230 GHz core flux measurements in epochs 2009 and 2012 as lower limits, we find evidence of a nearly flat core spectrum across 15 and 129 GHz, which could naturally connect the 230 GHz VLBI core flux. The extremely flat spectrum is a strong indication that the jet base does not consist of a simple homogeneous plasma, but of inhomogeneous multi-energy components, with at least one component with the turn-over frequency ≳ 100 GHz. The spectral shape can be qualitatively explained if both the strongly (compact, optically thick at >100 GHz) and the relatively weakly magnetized (more extended, optically thin at <100 GHz) plasma components are colocated in the footprint of the relativistic jet.

The Acceleration of the Barycenter of Solar System Obtained from VLBI Observations and Its Impact on the ICRS

NASA Astrophysics Data System (ADS)

Xu, M. H.

2016-03-01

Since 1998 January 1, instead of the traditional stellar reference system, the International Celestial Reference System (ICRS) has been realized by an ensemble of extragalactic radio sources that are located at hundreds of millions of light years away (if we accept their cosmological distances), so that the reference frame realized by extragalactic radio sources is assumed to be space-fixed. The acceleration of the barycenter of solar system (SSB), which is the origin of the ICRS, gives rise to a systematical variation in the directions of the observed radio sources. This phenomenon is called the secular aberration drift. As a result, the extragalactic reference frame fixed to the space provides a reference standard for detecting the secular aberration drift, and the acceleration of the barycenter with respect to the space can be determined from the observations of extragalactic radio sources. In this thesis, we aim to determine the acceleration of the SSB from astrometric and geodetic observations obtained by Very Long Baseline Interferometry (VLBI), which is a technique using the telescopes globally distributed on the Earth to observe a radio source simultaneously, and with the capacity of angular positioning for compact radio sources at 10-milliarcsecond level. The method of the global solution, which allows the acceleration vector to be estimated as a global parameter in the data analysis, is developed. Through the formal error given by the solution, this method shows directly the VLBI observations' capability to constrain the acceleration of the SSB, and demonstrates the significance level of the result. In the next step, the impact of the acceleration on the ICRS is studied in order to obtain the correction of the celestial reference frame (CRF) orientation. This thesis begins with the basic background and the general frame of this work. A brief review of the realization of the CRF based on the kinematical and the dynamical methods is presented in Chapter 2

VLBI Monitoring of the Nucleus of Centaurus A

NASA Technical Reports Server (NTRS)

Preston, Robert

1995-01-01

A series of 8.4 GHz VLBI images of the nucleus of Centaurus A have been made with a Southern Hemisphere array over more than a 3-year time span. The nuclear radio jet is approximately 50 mas in length, or about 1 pc at the 3.5 Mpc distance of Centaurus A. Sub-luminal motion is seen and structural changes observed on time-scales shorter than four months. Observations at both 4.8 and 8.4 GHz at one epoch allow identification of the core at the southwestern end of the jet.

Terrestrial Planet Finder Coronagraph Observatory summary

NASA Technical Reports Server (NTRS)

Ford, Virginia; Levine-Westa, Marie; Kissila, Andy; Kwacka, Eug; Hoa, Tim; Dumonta, Phil; Lismana, Doug; Fehera, Peter; Cafferty, Terry

2005-01-01

Creating an optical space telescope observatory capable of detecting and characterizing light from extra-solar terrestrial planets poses technical challenges related to extreme wavefront stability. The Terrestrial Planet Finder Coronagraph design team has been developing an observatory based on trade studies, modeling and analysis that has guided us towards design choices to enable this challenging mission. This paper will describe the current flight baseline design of the observatory and the trade studies that have been performed. The modeling and analysis of this design will be described including predicted performance and the tasks yet to be done.

International mission planning for space Very Long Baseline Interferometry

NASA Technical Reports Server (NTRS)

Ulvestad, James S.

1994-01-01

Two spacecraft dedicated to Very Long Baseline Interferometry (VLBI) will be launched in 1996 and 1997 to make observations using baselines between the space telescopes and many of the world's ground radio telescopes. The Japanese Institute of Space and Astronautical Science (ISAS) will launch VSOP (VLBI Space Observatory Program) in September 1996, while the Russian Astro Space Center (ASC) is scheduled to launch RadioAstron in 1997. Both spacecraft will observe radio sources at frequencies near 1.7, 4.8, and 22 GHz; RadioAstron will also observe at 0.33 GHz. The baselines between space and ground telescopes will provide 3-10 times the resolution available for ground VLBI at the same observing frequencies. Ground tracking stations on four continents will supply the required precise frequency reference to each spacecraft measure the two-way residual phase and Doppler on the ground-space link, and record 128 Megabit/s of VLBI data downlinked from the spacecraft. The spacecraft data are meaningless without cross-correlation against the data from Earth-bound telescopes, which must take place at special-purpose VLBI correlation facilities. Therefore, participation by most of the world's radio observatories is needed to achieve substantial science return from VSOP and RadioAstron. The collaboration of several major space agencies and the ground observatories, which generally follow very different models for allocation of observing time and for routine operations, leads to great complexity in mission planning and in day-to-day operations. This paper describes some of those complications and the strategies being developed to assure productive scientific missions.

Dual-Frequency VLBI Study of Centaurus A on Sub-Parsec Scales: The Highest-Resolution View of an Extragalactic Jet

NASA Technical Reports Server (NTRS)

Mueller, C.; Kadler, M.; Ojha, R.; Wilms, J.; Boeck, M.; Edwards, P.; Fromm, C. M.; Hase, H.; Horiuchi, S.; Katz, U.;

A test of water vapor radiometer-based troposphere calibration using VLBI observations on a 21-kilometer baseline

NASA Technical Reports Server (NTRS)

Linfield, R. P.; Teitelbaum, L. P.; Skjerve, L. J.; Keihm, S. J.; Walter, S. J.; Mahoney, M. J.; Treuhaft, R. N.

1995-01-01

Simultaneous very long baseline interferometry (VLBI) and water vapor radiometer (WVR) measurements on a 21 km baseline showed that calibration by WVRs removed a significant fraction of the effect of tropospheric delay fluctuations for these experiments. From comparison of the residual delay variations within scans and between scans, the total tropospheric contribution t the delay residuals for each of the three 5 to 20 hour sessions was estimated as 1, 17, and 10%, with the first value being uncertain. The observed improvement in rms residual delay from WVR calibration during these three sessions was 4, 16, and 2%, respectively. The improvement is consistent with the estimated 2 to 3 mm path delay precision of current WVRs. The VLBI measurements, of natural radio sources, were conducted in April and May 1993 at Goldstone, California. Dual-frequency (2.3 and 8.4 GHz) observations were employed to remove the effects of charged particles from the data. Measurements with co-pointed WVRs, located within 50 m of the axis of each antenna, were performed to test the ability of the WVRs to calibrate line-of-sight path delays. Factors that made WVR performance assessment difficult included (1) the fact that the level of tropospheric fluctuations was smaller than is typical for Goldstone during these experiments and (2) VLBI delay variations on longer time scales (i.e., over multiple scans) contained uncalibrated instrumental effects (probably a result of slow temperature variations in the VLBI hardware) that were larger than the tropospheric effects.

A complete sample of double-lobed radio quasars for VLBI tests of source models - Definition and statistics

NASA Technical Reports Server (NTRS)

Hough, D. H.; Readhead, A. C. S.

1989-01-01

A complete, flux-density-limited sample of double-lobed radio quasars is defined, with nuclei bright enough to be mapped with the Mark III VLBI system. It is shown that the statistics of linear size, nuclear strength, and curvature are consistent with the assumption of random source orientations and simple relativistic beaming in the nuclei. However, these statistics are also consistent with the effects of interaction between the beams and the surrounding medium. The distribution of jet velocities in the nuclei, as measured with VLBI, will provide a powerful test of physical theories of extragalactic radio sources.

Estimating Accurate Relative Spacecraft Angular Position from DSN VLBI Phases Using X-Band Telemetry or DOR Tones

NASA Technical Reports Server (NTRS)

Bagri, Durgadas S.; Majid, Walid

2009-01-01

At present spacecraft angular position with Deep Space Network (DSN) is determined using group delay estimates from very long baseline interferometer (VLBI) phase measurements employing differential one way ranging (DOR) tones. As an alternative to this approach, we propose estimating position of a spacecraft to half a fringe cycle accuracy using time variations between measured and calculated phases as the Earth rotates using DSN VLBI baseline(s). Combining fringe location of the target with the phase allows high accuracy for spacecraft angular position estimate. This can be achieved using telemetry signals of at least 4-8 MSamples/sec data rate or DOR tones.

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

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.

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.

Running a distributed virtual observatory: U.S. Virtual Astronomical Observatory operations

NASA Astrophysics Data System (ADS)

McGlynn, Thomas A.; Hanisch, Robert J.; Berriman, G. Bruce; Thakar, Aniruddha R.

2012-09-01

Operation of the US Virtual Astronomical Observatory shares some issues with modern physical observatories, e.g., intimidating data volumes and rapid technological change, and must also address unique concerns like the lack of direct control of the underlying and scattered data resources, and the distributed nature of the observatory itself. In this paper we discuss how the VAO has addressed these challenges to provide the astronomical community with a coherent set of science-enabling tools and services. The distributed nature of our virtual observatory-with data and personnel spanning geographic, institutional and regime boundaries-is simultaneously a major operational headache and the primary science motivation for the VAO. Most astronomy today uses data from many resources. Facilitation of matching heterogeneous datasets is a fundamental reason for the virtual observatory. Key aspects of our approach include continuous monitoring and validation of VAO and VO services and the datasets provided by the community, monitoring of user requests to optimize access, caching for large datasets, and providing distributed storage services that allow user to collect results near large data repositories. Some elements are now fully implemented, while others are planned for subsequent years. The distributed nature of the VAO requires careful attention to what can be a straightforward operation at a conventional observatory, e.g., the organization of the web site or the collection and combined analysis of logs. Many of these strategies use and extend protocols developed by the international virtual observatory community. Our long-term challenge is working with the underlying data providers to ensure high quality implementation of VO data access protocols (new and better 'telescopes'), assisting astronomical developers to build robust integrating tools (new 'instruments'), and coordinating with the research community to maximize the science enabled.

NASA Space Geodesy Program: GSFC data analysis, 1992. Crustal Dynamics Project VLBI geodetic results, 1979 - 1991

NASA Technical Reports Server (NTRS)

Ryan, J. W.; Ma, C.; Caprette, D. S.

1993-01-01

The Goddard VLBI group reports the results of analyzing 1648 Mark 3 data sets acquired from fixed and mobile observing sites through the end of 1991, and available to the Crustal Dynamics Project. Two large solutions were used to obtain Earth rotation parameters, nutation offsets, radio source positions, site positions, site velocities, and baseline evolution. Site positions are tabulated on a yearly basis for 1979 to 1995, inclusive. Site velocities are presented in both geocentric Cartesian and topocentric coordinates. Baseline evolution is plotted for 200 baselines, and individual length determinations are presented for an additional 356 baselines. This report includes 155 quasar radio sources, 96 fixed stations and mobile sites, and 556 baselines.

Going Digital - The Transition from Mark IV to DBBC at Onsala

NASA Astrophysics Data System (ADS)

Kareinen, Niko; Haas, Rüdiger; La Porta, Laura; Bertarini, Alessandra

2014-12-01

The Onsala Space Observatory is currently equipped with both a VLBI Mark IV rack and a digital BBC (DBBC). The Mark IV rack at Onsala has been used operationally for both astronomical and geodetic VLBI for more than 40 years. In 2011, Onsala purchased a DBBC and we started to test it and to gain experience with the new device, both for astronomical and geodetic VLBI. The DBBC was upgraded several times and the Field System (FS) interface was implemented. We did parallel recordings, with both the old Mark IV/Mark 5A system and the new DBBC/Mark 5B+ system, during numerous geodetic VLBI sessions. Several R1, T2, and Euro sessions were correlated during the last two years by the Bonn correlator with Onsala being included both as an analog station (two-letter code On) and as a digital station (two-letter code Od). We present results from these parallel sessions, both results from the original correlation and results from the analysis of the corresponding databases.

Griffith Observatory: Hollywood's Celestial Theater

NASA Astrophysics Data System (ADS)

Margolis, Emily A.; Dr. Stuart W. Leslie

2018-01-01

The Griffith Observatory, perched atop the Hollywood Hills, is perhaps the most recognizable observatory in the world. Since opening in 1935, this Los Angeles icon has brought millions of visitors closer to the heavens. Through an analysis of planning documentation, internal newsletters, media coverage, programming and exhibition design, I demonstrate how the Observatory’s Southern California location shaped its form and function. The astronomical community at nearby Mt. Wilson Observatory and Caltech informed the selection of instrumentation and programming, especially for presentations with the Observatory’s Zeiss Planetarium, the second installed in the United States. Meanwhile the Observatory staff called upon some of Hollywood’s best artists, model makers, and scriptwriters to translate the latest astronomical discoveries into spectacular audiovisual experiences, which were enhanced with Space Age technological displays on loan from Southern California’s aerospace companies. The influences of these three communities- professional astronomy, entertainment, and aerospace- persist today and continue to make Griffith Observatory one of the premiere sites of public astronomy in the country.

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.

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.

A possible space VLBI constellation utilizing the stable orbits around the TLPs in the Earth-Moon system.

NASA Astrophysics Data System (ADS)

Liu, Bin; Tang, Jingshi; Hou, Xiyun

2016-07-01

Current studies indicate that there are stable orbits around but far away from the triangular libration points .Two special quasi-periodic orbits around each triangular libration points L4 , L5 in the Earth-Moon sys-tem perturbed by Sun are gain , and the stable orbits discussed in this work are ideal places for space colonies because no orbit control is needed. These stable orbits can also be used as nominal orbits for space VLBI (Very Long Baseline Interferometry) stations. The two stations can also form baselines with stations on the Earth and the Moon, or with stations located around another TLP. Due to the long distance between the stations, the observation precision can be greatly enhanced compared with the VLBI stations on the Earth. Such a VLBI constellation not only can advance the radio astronomy, but also can be used as a navigation system for human activities in the Earth-Moon system and even in the solar system. This paper will focus on the navigation constellation coverage issues, and the orbit determination accuracy problems within the Earth-Moon sys-tem and interplanetary space.

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.'

Automated and dynamic scheduling for geodetic VLBI - A simulation study for AuScope and global networks

NASA Astrophysics Data System (ADS)

Iles, E. J.; McCallum, L.; Lovell, J. E. J.; McCallum, J. N.

2018-02-01

As we move into the next era of geodetic VLBI, the scheduling process is one focus for improvement in terms of increased flexibility and the ability to react with changing conditions. A range of simulations were conducted to ascertain the impact of scheduling on geodetic results such as Earth Orientation Parameters (EOPs) and station coordinates. The potential capabilities of new automated scheduling modes were also simulated, using the so-called 'dynamic scheduling' technique. The primary aim was to improve efficiency for both cost and time without losing geodetic precision, particularly to maximise the uses of the Australian AuScope VLBI array. We show that short breaks in observation will not significantly degrade the results of a typical 24 h experiment, whereas simply shortening observing time degrades precision exponentially. We also confirm the new automated, dynamic scheduling mode is capable of producing the same standard of result as a traditional schedule, with close to real-time flexibility. Further, it is possible to use the dynamic scheduler to augment the 3 station Australian AuScope array and thereby attain EOPs of the current global precision with only intermittent contribution from 2 additional stations. We thus confirm automated, dynamic scheduling bears great potential for flexibility and automation in line with aims for future continuous VLBI operations.

Impact of quasar proper motions on the alignment between the International Celestial Reference Frame and the Gaia reference frame

NASA Astrophysics Data System (ADS)

Liu, J.-C.; Malkin, Z.; Zhu, Z.

2018-03-01

The International Celestial Reference Frame (ICRF) is currently realized by the very long baseline interferometry (VLBI) observations of extragalactic sources with the zero proper motion assumption, while Gaia will observe proper motions of these distant and faint objects to an accuracy of tens of microarcseconds per year. This paper investigates the difference between VLBI and Gaia quasar proper motions and it aims to understand the impact of quasar proper motions on the alignment of the ICRF and Gaia reference frame. We use the latest time series data of source coordinates from the International VLBI Service analysis centres operated at Goddard Space Flight Center (GSF2017) and Paris observatory (OPA2017), as well as the Gaia auxiliary quasar solution containing 2191 high-probability optical counterparts of the ICRF2 sources. The linear proper motions in right ascension and declination of VLBI sources are derived by least-squares fits while the proper motions for Gaia sources are simulated taking into account the acceleration of the Solar system barycentre and realistic uncertainties depending on the source brightness. The individual and global features of source proper motions in GSF2017 and OPA2017 VLBI data are found to be inconsistent, which may result from differences in VLBI observations, data reduction and analysis. A comparison of the VLBI and Gaia proper motions shows that the accuracies of the components of rotation and glide between the two systems are 2-4 μas yr- 1 based on about 600 common sources. For the future alignment of the ICRF and Gaia reference frames at different wavelengths, the proper motions of quasars must necessarily be considered.

The Determination of Earth Orientation by VLBI and GNSS: Principles and Results

NASA Astrophysics Data System (ADS)

Capitaine, Nicole

2017-10-01

The Earth Orientation Parameters (EOP) connect the International Terrestrial Reference System (ITRS) to the Geocentric Celestial Reference System (GCRS). These parameters, i.e., Universal Time, UT1, and pole coordinates in the ITRS and in the GCRS, describe the irregularities of the Earth's rotation. They are mainly determined by two modern astro-geodetic techniques, VLBI (Very Long Baseline Radio Interferometry) on extragalactic radio sources, which is used to realize and maintain the International Celestial Reference System (ICRS), and Global Navigation Satellite System (GNSS), especially GPS (Global Positioning System), which has an important contribution to the realization of the ITRS. The aim of this presentation is twofold: to present the modern bases for the consider- ation of Earth orientation and to discuss how the principles of VLBI and GPS give access to the measure of different components of the EOP variations, especially UT1. The accuracy that can be achieved is based on the improved concepts, definitions, and models that have been adopted by IAU/IUGG resolutions on reference systems and Earth's rotation, as well as on the refined strategy of the observations.

The new 64m Sardinia Radio Telescope and VLBI facilities in Italy

NASA Astrophysics Data System (ADS)

Giovannini, Gabriele; Feretti, Luigina; Prandoni, Isabella; Giroletti, Marcello

2015-08-01

The Sardinia Radio Telescope (SRT) is a new major radio astronomical facility available in Italy for single dish and interferometric observations. It represents a flexible instrument for Radio Astronomy, Geodynamical studies and Space Science, either in single dish or VLBI mode. The SRT combines a 64m steerable collecting area, one of the largest all over the World with state-of-the-art technology (including an active surface) to enable high efficiency observations up to the 3-mm band.This new radio telescope together with the two 32m antennas in Noto and Medicina can be used for VLBI observations on a national basis (VLBIT). Data can be correlated in a short time (in real time soon) thanks to fiber-optics connection among the radio telescopes and the software correlator installed at the Radio Astronomy Institute in Bologna (IRA/INAF). In the poster I will present capabilities of the SRT telescope as well as the VLBIT project and I will shortly discuss the scientific prospects of the VLBIT.

OSO-6 Orbiting Solar Observatory

NASA Technical Reports Server (NTRS)

1972-01-01

The description, development history, test history, and orbital performance analysis of the OSO-6 Orbiting Solar Observatory are presented. The OSO-6 Orbiting Solar Observatory was the sixth flight model of a series of scientific spacecraft designed to provide a stable platform for experiments engaged in the collection of solar and celestial radiation data. The design objective was 180 days of orbital operation. The OSO-6 has telemetered an enormous amount of very useful experiment and housekeeping data to GSFC ground stations. Observatory operation during the two-year reporting period was very successful except for some experiment instrument problems.

R&D at JIVE: transforming the way VLBI is done

NASA Astrophysics Data System (ADS)

Szomoru, Arpad; van Langevelde, Huib

2015-08-01

Arpad Szomoru, Huib van Langevelde and the JIVE staffFor many years, the heart of operations at JIVE has been the MkIV hardware correlator, a custom-built high-performance data processor. At this time the MkIV has been replaced by the locally developed EVN software correlator (SFXC).This development has vastly improved the science capacity of the EVN, by providing higher spectral resolution and polarization accuracy, but most notably, by enabling completely new observing modes. Observing multiple simultaneous field centers has enabled wide-field imaging, while a phased-array mode has made it possible to do pulsar time series with the EVN. New algorithms have been developed for near-field VLBI, making it possible to focus on objects within our solar system. This has been used to track the RadioAstron satellite, and by applying the derived orbital parameters to improve subsequent space VLBI observations.New digital baseband convertors will allow higher observing bandwidths in the EVN. In anticipation of this, and of the even higher bandwidths of future mm-VLBI observations, added to the deployment of much larger arrays (including the AVN, the SKA precursors and the SKA itself), we are investigating more powerful and economical solutions. The JIVE UniBoard Correlator is the first FPGA-based EVN correlator; its scalability and flexibility are now under assessment. The new UniBoard2 project, also sponsored by the EC, will skip two generations of FPGA technology and deliver enormous processing power at lower power consumption.Maybe just as importantly, research is ongoing into software tools to enable the efficient handling of the vast data sets that the EVN and other current and future instruments will produce. New data processing pipelines are being designed that will be able to cache intermediate products, and upon changing parameters only re-calculate what is needed, as opposed to re-starting every time from scratch.Finally, we will discuss the development of time

Development of Very Long Baseline Interferometry (VLBI) techniques in New Zealand: Array simulation, image synthesis and analysis

NASA Astrophysics Data System (ADS)

Weston, S. D.

2008-04-01

This thesis presents the design and development of a process to model Very Long Base Line Interferometry (VLBI) aperture synthesis antenna arrays. In line with the Auckland University of Technology (AUT) Institute for Radiophysics and Space Research (IRSR) aims to develop the knowledge, skills and experience within New Zealand, extensive use of existing radio astronomical software has been incorporated into the process namely AIPS (Astronomical Imaging Processing System), MIRIAD (a radio interferometry data reduction package) and DIFMAP (a program for synthesis imaging of visibility data from interferometer arrays of radio telescopes). This process has been used to model various antenna array configurations for two proposed New Zealand sites for antenna in a VLBI array configuration with existing Australian facilities and a passable antenna at Scott Base in Antarctica; and the results are presented in an attempt to demonstrate the improvement to be gained by joint trans-Tasman VLBI observation. It is hoped these results and process will assist the planning and placement of proposed New Zealand radio telescopes for cooperation with groups such as the Australian Long Baseline Array (LBA), others in the Pacific Rim and possibly globally; also potential future involvement of New Zealand with the SKA. The developed process has also been used to model a phased building schedule for the SKA in Australia and the addition of two antennas in New Zealand. This has been presented to the wider astronomical community via the Royal Astronomical Society of New Zealand Journal, and is summarized in this thesis with some additional material. A new measure of quality ("figure of merit") for comparing the original model image and final CLEAN images by utilizing normalized 2-D cross correlation is evaluated as an alternative to the existing subjective visual operator image comparison undertaken to date by other groups. This new unit of measure is then used ! in the presentation of the

VizieR Online Data Catalog: VLBI Ecliptic Plane Survey: VEPS-1 (Shu+, 2017)

NASA Astrophysics Data System (ADS)

Shu, F.; Petrov, L.; Jiang, W.; Xia, B.; Jiang, T.; Cui, Y.; Takefuji, K.; McCallum, J.; Lovell, J.; Yi, S.-O.; Hao, L.; Yang, W.; Zhang, H.; Chen, Z.; Li, J.

2017-08-01

We began observations in the search mode in 2015 February. The participating stations included the three core stations of the Chinese VLBI Network (CVN): seshan25, kunming, and urumqi. Depending on the participating stations, the longest baseline length in each session can be varied from 3200km to 9800km. Our observations were performed at a 2048Mbps data rate, with 16 Intermediate Frequency (IF) channels and 2-bit sampling. The first eight IFs of 32MHz bandwidth were distributed in the range of [8.188, 8.444]GHz, and the remaining eight IFs of 32MHz bandwidth were in the range of [8.700, 8.956]GHz. Table 1: Summary of the VLBI Ecliptic Plane Survey (VEPS) observations in search mode: --------------------------------------------------- Date Dur. Code Stations Number of (Y/M/D) (h) Targets --------------------------------------------------- 2015 Feb 13 24 VEPS01 ShKmUr 293 2015 Feb 14 24 VEPS02 ShKmUr 338 2015 Apr 23 24 VEPS03 UrKv 300 2015 Apr 24 24 VEPS04 ShKmUrKv 400 2015 Aug 10 25 VEPS05 ShKmKvHo 252 2015 Aug 19 25 VEPS06 ShKmKvHo 277 2016 Mar 02 24 VEPS07 ShKmUrKb 333 2016 Mar 11 24 VEPS08 ShKmUrKb 477 2016 May 13 24 VEPS09 ShUrHo 291 2016 May 14 22 VEPS10 ShUrKv 322 2016 Jul 06 24 VEPS11 ShUrKb 307 2016 Sep 02 23 VEPS12 ShUr 424 2016 Sep 03 23 VEPS13 ShKmUr 344 --------------------------------------------------- Sh=Seshan25; Km=Kunming; Ur=Urumqi; Kv=Sejong; Kb=Kashim34; Ho=Hobart26. --------------------------------------------------- We ran two absolute astrometry dual-band VLBA programs that targeted ecliptic plane compact radio sources: the dedicated survey of weak ecliptic plane calibrators with the VLBA BS250 program in 2016 March-May, and the VLBA Calibrator Survey 9 (VCS-9) in 2015 August-2016 September. The International VLBI Service for Geodesy and Astrometry (IVS) runs a number of VLBI observing programs. We made an attempt to improve the coordinates of some VEPS sources detected in the search mode and provide additional measurements of telescope

Daily variation characteristics at polar geomagnetic observatories

NASA Astrophysics Data System (ADS)

Lepidi, S.; Cafarella, L.; Pietrolungo, M.; Di Mauro, D.

2011-08-01

This paper is based on the statistical analysis of the diurnal variation as observed at six polar geomagnetic observatories, three in the Northern and three in the Southern hemisphere. Data are for 2006, a year of low geomagnetic activity. We compared the Italian observatory Mario Zucchelli Station (TNB; corrected geomagnetic latitude: 80.0°S), the French-Italian observatory Dome C (DMC; 88.9°S), the French observatory Dumont D'Urville (DRV; 80.4°S) and the three Canadian observatories, Resolute Bay (RES; 83.0°N), Cambridge Bay (CBB; 77.0°N) and Alert (ALE, 87.2°N). The aim of this work was to highlight analogies and differences in daily variation as observed at the different observatories during low geomagnetic activity year, also considering Interplanetary Magnetic Field conditions and geomagnetic indices.

Report for 2012 from the Bordeaux IVS Analysis Center

NASA Technical Reports Server (NTRS)

Charlot, Patrick; Bellanger, Antoine; Bouffet, Romuald; Bourda, Geraldine; Collioud, Arnaud; Baudry, Alain

2013-01-01

This report summarizes the activities of the Bordeaux IVS Analysis Center during the year 2012. The work focused on (i) regular analysis of the IVS-R1 and IVS-R4 sessions with the GINS software package; (ii) systematic VLBI imaging of the RDV sessions and calculation of the corresponding source structure index and compactness values; (iii) investigation of the correlation between astrometric position instabilities and source structure variations; and (iv) continuation of our VLBI observational program to identify optically-bright radio sources suitable for the link with the future Gaia frame. Also of importance is the 11th European VLBI Network Symposium, which we organized last October in Bordeaux and which drew much attention from the European and International VLBI communities.

VizieR Online Data Catalog: The VLBA Extragalactic Proper Motion Catalog (Truebenbach+, 2017)

NASA Astrophysics Data System (ADS)

Truebenbach, A. E.; Darling, J.

2017-11-01

We created our catalog of extragalactic radio proper motions using the 2017a Goddard VLBI global solution. The 2017a solution is computed from more than 30 years of dual-band VLBI observations --1979 August 3 to 2017 March 27. We also observed 28 objects with either no redshift or a "questionable" Optical Characteristic of Astrometric Radio Sources (OCARS; Malkin 2016ARep...60..996M) redshift at the Apache Point Observatory (APO) 3.5m telescope and/or at Gemini North. We conducted observations on the 3.5m telescope at Apache Point Observatory with the Dual Imaging Spectrograph (DIS) from 2015 April 18 to 2016 June 30. We chose two objects for additional observations with the Gemini Multi-Object Spectrograph-North (GMOS-N) at Gemini North Observatory. 2021+317 was observed on 2016 June 26 and 28, while 0420+417 was observed on 2016 November 8 and 26. We also observed 42 radio sources with the Very Long Baseline Array (VLBA) in the X-band (3.6cm/8.3GHz). Our targets had all been previously observed by VLBI. Our VLBA observations were conducted in two campaigns from 2015 September to 2016 January and 2016 October to November. The final extragalactic proper motion catalog (created primarily from archival Goddard VLBI data, with redshifts obtained from OCARS) contains 713 proper motions with average uncertainties of 24μas/yr. (5 data files).

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.

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

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.

Improvement of VLBI EOP Accuracy and Precision

NASA Technical Reports Server (NTRS)

MacMillan, Daniel; Ma, Chopo

2000-01-01

In the CORE program, EOP measurements will be made with several different networks, each operating on a different day. It is essential that systematic differences between EOP derived by the different networks be minimized. Observed biases between the simultaneous CORE-A and NEOS-A sessions are about 60-130 micro(as) for PM, UT1 and nutation parameters. After removing biases, the observed rms differences are consistent with an increase in the formal precision of the measurements by factors ranging from 1.05 to 1.4. We discuss the possible sources of unmodeled error that account for these factors and the biases and the sensitivities of the network differences to modeling errors. We also discuss differences between VLBI and GPS PM measurements.

Single baseline GLONASS observations with VLBI: data processing and first results

NASA Astrophysics Data System (ADS)

Tornatore, V.; Haas, R.; Duev, D.; Pogrebenko, S.; Casey, S.; Molera Calvés, G.; Keimpema, A.

2011-07-01

Several tests to observe signals transmitted by GLONASS (GLObal NAvigation Satellite System) satellites have been performed using the geodetic VLBI (Very Long Baseline Interferometry) technique. The radio telescopes involved in these experiments were Medicina (Italy) and Onsala (Sweden), both equipped with L-band receivers. Observations at the stations were performed using the standard Mark4 VLBI data acquisition rack and Mark5A disk-based recorders. The goals of the observations were to develop and test the scheduling, signal acquisition and processing routines to verify the full tracking pipeline, foreseeing the cross-correlation of the recorded data on the baseline Onsala-Medicina. The natural radio source 3c286 was used as a calibrator before the starting of the satellite observation sessions. Delay models, including the tropospheric and ionospheric corrections, which are consistent for both far- and near-field sources are under development. Correlation of the calibrator signal has been performed using the DiFX software, while the satellite signals have been processed using the narrow band approach with the Metsaehovi software and analysed with a near-field delay model. Delay models both for the calibrator signals and the satellites signals, using the same geometrical, tropospheric and ionospheric models, are under investigation to make a correlation of the satellite signals possible.

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.

Planetary research at Lowell Observatory

NASA Technical Reports Server (NTRS)

Baum, William A.

1988-01-01

Scientific goals include a better determination of the basic physical characteristics of cometary nuclei, a more complete understanding of the complex processes in the comae, a survey of abundances and gas/dust ratios in a large number of comets, and measurement of primordial (12)C/(13)C and (14)N/(15)N ratios. The program also includes the observation of Pluto-Charon mutual eclipses to derive dimensions. Reduction and analysis of extensive narrowband photometry of Comet Halley from Cerro Tololo Inter-American Observatory, Perth Observatory, Lowell Observatory, and Mauna Kea Observatory were completed. It was shown that the 7.4-day periodicity in the activity of Comet Halley was present from late February through at least early June 1986, but there is no conclusive evidence of periodic variability in the preperihelion data. Greatly improved NH scalelengths and lifetimes were derived from the Halley data which lead to the conclusion that the abundance of NH in comets is much higher than previously believed. Simultaneous optical and thermal infrared observations were obtained of Comet P/Temple 2 using the MKO 2.2 m telescope and the NASA IRTF. Preliminary analysis of these observations shows that the comet's nucleus is highly elongated, very dark, and quite red.

NASA Extends Chandra X-ray Observatory Contract with the Smithsonian Astrophysical Observatory

NASA Astrophysics Data System (ADS)

2002-07-01

NASA NASA has extended its contract with the Smithsonian Astrophysical Observatory in Cambridge, Mass. to August 2003 to provide science and operational support for the Chandra X- ray Observatory, one of the world's most powerful tools to better understand the structure and evolution of the universe. The contract is an 11-month period of performance extension to the Chandra X-ray Center contract, with an estimated value of 50.75 million. Total contract value is now 298.2 million. The contract extension resulted from the delay of the launch of the Chandra X-ray Observatory from August 1998 to July 1999. The revised period of performance will continue the contract through Aug. 31, 2003, which is 48 months beyond operational checkout of the observatory. The contract type is cost reimbursement with no fee. The contract covers mission operations and data analysis, which includes both the observatory operations and the science data processing and general observer (astronomer) support. The observatory operations tasks include monitoring the health and status of the observatory and developing and distributing by satellite the observation sequences during Chandra's communication coverage periods. The science data processing tasks include the competitive selection, planning, and coordination of science observations with the general observers and the processing and delivery of the resulting scientific data. Each year, there are on the order of 200 to 250 observing proposals selected out of about 800 submitted, with a total amount of observing time about 20 million seconds. X-ray astronomy can only be performed from space because Earth's atmosphere blocks X-rays from reaching the surface. The Chandra Observatory travels one-third of the way to the Moon during its orbit around the Earth every 64 hours. At its highest point, Chandra's highly elliptical, or egg-shaped, orbit is 200 times higher than that of its visible-light- gathering sister, the Hubble Space Telescope. NASA

PMD IVS Analysis Center

NASA Technical Reports Server (NTRS)

Tornatore, Vincenza

2013-01-01

The main activities carried out at the PMD (Politecnico di Milano DIIAR) IVS Analysis Center during 2012 are briefly higlighted, and future plans for 2013 are sketched out. We principally continued to process European VLBI sessions using different approaches to evaluate possible differences due to various processing choices. Then VLBI solutions were also compared to the GPS ones as well as the ones calculated at co-located sites. Concerning the observational aspect, several tests were performed to identify the most suitable method to achieve the highest possible accuracy in the determination of GNSS (GLOBAL NAVIGATION SATELLITE SYSTEM) satellite positions using the VLBI technique.

Multi-Epoch 8.4GHz VLBI Observations of the Nucleus of Centaurus A

NASA Technical Reports Server (NTRS)

Meier, David L.

1992-01-01

We present the results of several 8.4 GHz VLBI observations of the nucleus of Centaurus A. We fing that the source possesses a classical core-jet structure with the inner portion of the jet expanding at a proper motion of 4.o mas yr or an apparet velocity of 0.26c along the jet.

Toward the ICRF3: Astrometric Comparison of the USNO 2016A VLBI Solution with ICRF2 and Gaia DR1

NASA Astrophysics Data System (ADS)

Frouard, Julien; Johnson, Megan C.; Fey, Alan; Makarov, Valeri V.; Dorland, Bryan N.

2018-06-01

The VLBI USNO 2016A (U16A) solution is part of a work-in-progress effort by USNO toward the preparation of the ICRF3. Most of the astrometric improvement with respect to the ICRF2 is due to the re-observation of the VCS sources. Our objective in this paper is to assess U16A’s astrometry. A comparison with ICRF2 shows statistically significant offsets of size 0.1 mas between the two solutions. While Gaia DR1 positions are not precise enough to resolve these offsets, they are found to be significantly closer to U16A than ICRF2. In particular, the trend for typically larger errors for southern sources in VLBI solutions is decreased in U16A. Overall, the VLBI-Gaia offsets are reduced by 21%. The U16A list includes 718 sources not previously included in ICRF2. Twenty of those new sources have statistically significant radio-optical offsets. In two-thirds of the cases, these offsets can be explained from PanSTARRS images.

Two-Component Structure of the Radio Source 0014+813 from VLBI Observations within the CONT14 Program

NASA Astrophysics Data System (ADS)

Titov, O. A.; Lopez, Yu. R.

2018-03-01

We consider a method of reconstructing the structure delay of extended radio sources without constructing their radio images. The residuals derived after the adjustment of geodetic VLBI observations are used for this purpose. We show that the simplest model of a radio source consisting of two point components can be represented by four parameters (the angular separation of the components, the mutual orientation relative to the poleward direction, the flux-density ratio, and the spectral index difference) that are determined for each baseline of a multi-baseline VLBI network. The efficiency of this approach is demonstrated by estimating the coordinates of the radio source 0014+813 observed during the two-week CONT14 program organized by the International VLBI Service (IVS) in May 2014. Large systematic deviations have been detected in the residuals of the observations for the radio source 0014+813. The averaged characteristics of the radio structure of 0014+813 at a frequency of 8.4 GHz can be calculated from these deviations. Our modeling using four parameters has confirmed that the source consists of two components at an angular separation of 0.5 mas in the north-south direction. Using the structure delay when adjusting the CONT14 observations leads to a correction of the average declination estimate for the radio source 0014+813 by 0.070 mas.

Nobeyama Radio Observatory

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

Nobeyama Radio Observatory has telescopes at millimeter and submillimeter wavelengths. It was established in 1982 as an observatory of Tokyo Astronomical Observatory (NATIONAL ASTRONOMICAL OBSERVATORY, JAPAN since 1987), and operates the 45 m telescope, Nobeyama Millimeter Array, and Radioheliograph. High-resolution images of star forming regions and molecular clouds have revealed many aspects of...

A two-level approach to VLBI terrestrial and celestial reference frames using both least-squares adjustment and Kalman filter algorithms

NASA Astrophysics Data System (ADS)

Soja, B.; Krasna, H.; Boehm, J.; Gross, R. S.; Abbondanza, C.; Chin, T. M.; Heflin, M. B.; Parker, J. W.; Wu, X.

2017-12-01

The most recent realizations of the ITRS include several innovations, two of which are especially relevant to this study. On the one hand, the IERS ITRS combination center at DGFI-TUM introduced a two-level approach with DTRF2014, consisting of a classical deterministic frame based on normal equations and an optional coordinate time series of non-tidal displacements calculated from geophysical loading models. On the other hand, the JTRF2014 by the combination center at JPL is a time series representation of the ITRF determined by Kalman filtering. Both the JTRF2014 and the second level of the DTRF2014 are thus able to take into account short-term variations in the station coordinates. In this study, based on VLBI data, we combine these two approaches, applying them to the determination of both terrestrial and celestial reference frames. Our product has two levels like DTRF2014, with the second level being a Kalman filter solution like JTRF2014. First, we compute a classical TRF and CRF in a global least-squares adjustment by stacking normal equations from 5446 VLBI sessions between 1979 and 2016 using the Vienna VLBI and Satellite Software VieVS (solution level 1). Next, we obtain coordinate residuals from the global adjustment by applying the level-1 TRF and CRF in the single-session analysis and estimating coordinate offsets. These residuals are fed into a Kalman filter and smoother, taking into account the stochastic properties of the individual stations and radio sources. The resulting coordinate time series (solution level 2) serve as an additional layer representing irregular variations not considered in the first level of our approach. Both levels of our solution are implemented in VieVS in order to test their individual and combined performance regarding the repeatabilities of estimated baseline lengths, EOP, and radio source coordinates.

Revealing the Nature of Blazar Radio Cores through Multifrequency Polarization Observations with the Korean VLBI Network

NASA Astrophysics Data System (ADS)

Park, Jongho; Kam, Minchul; Trippe, Sascha; Kang, Sincheol; Byun, Do-Young; Kim, Dae-Won; Algaba, Juan-Carlos; Lee, Sang-Sung; Zhao, Guang-Yao; Kino, Motoki; Shin, Naeun; Hada, Kazuhiro; Lee, Taeseok; Oh, Junghwan; Hodgson, Jeffrey A.; Sohn, Bong Won

2018-06-01

We study the linear polarization of the radio cores of eight blazars simultaneously at 22, 43, and 86 GHz with observations obtained by the Korean VLBI Network (KVN) in three epochs between late 2016 and early 2017 in the frame of the Plasma-physics of Active Galactic Nuclei project. We investigate the Faraday rotation measure (RM) of the cores; the RM is expected to increase with observing frequency if core positions depend on frequency owing to synchrotron self-absorption. We find a systematic increase of RMs at higher observing frequencies in our targets. The RM–ν relations follow power laws with indices distributed around 2, indicating conically expanding outflows serving as Faraday rotating media. Comparing our KVN data with contemporaneous optical polarization data from the Steward Observatory for a few sources, we find indications that the increase of RM with frequency saturates at frequencies of a few hundred gigahertz. This suggests that blazar cores are physical structures rather than simple τ = 1 surfaces. A single region, e.g., a recollimation shock, might dominate the jet emission downstream of the jet-launching region. We detect a sign change in the observed RMs of CTA 102 on a timescale of ≈1 month, which might be related to new superluminal components emerging from its core undergoing acceleration/deceleration and/or bending. We see indications for quasars having higher core RMs than BL Lac objects, which could be due to denser inflows/outflows in quasars.

Next-Generation A/D Sampler ADS3000+ for VLBI2010

NASA Technical Reports Server (NTRS)

Takefuji, Kazuhiro; Takeuchi, Hiroshi; Tsutsumi, Masanori; Koyama, Yasuhiro

2010-01-01

A high-speed A/D sampler, called ADS3000+, has been developed in 2008, which can sample one analog signal up to 4 Gbps to versatile Linux PC. After A/D conversion, the ADS3000+ can perform digital signal processing such as real-time DBBC (Digital Base Band Conversion) and FIR filtering such as simple CW RFI filtering using the installed FPGAs. A 4 Gsps fringe test with the ADS3000+ has been successfully performed. The ADS3000+ will not exclusively be used for VLBI but will also be employed in other applications.

MDM Observatory

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

MDM Observatory was founded by the University of Michigan, Dartmouth College and the Massachusetts Institute of Technology. Current operating partners include Michigan, Dartmouth, MIT, Ohio State University and Columbia University. The observatory is located on the southwest ridge of the KITT PEAK NATIONAL OBSERVATORY near Tucson, Arizona. It operates the 2.4 m Hiltner Telescope and the 1.3 m McG...

WIYN Observatory

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

Located at Kitt Peak in Arizona. The WIYN Observatory is owned and operated by the WIYN Consortium, which consists of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatories (NOAO). Most of the capital costs of the observatory were provided by these universities, while NOAO, which operates the other telescopes of the KITT PEAK NATIONAL OBS...

Private Observatories in South Africa

NASA Astrophysics Data System (ADS)

Rijsdijk, C.

2016-12-01

Descriptions of private observatories in South Africa, written by their owners. Positions, equipment descriptions and observing programmes are given. Included are: Klein Karoo Observatory (B. Monard), Cederberg Observatory (various), Centurion Planetary and Lunar Observatory (C. Foster), Le Marischel Observatory (L. Ferreira), Sterkastaaing Observatory (M. Streicher), Henley on Klip (B. Fraser), Archer Observatory (B. Dumas), Overbeek Observatory (A. Overbeek), Overberg Observatory (A. van Staden), St Cyprian's School Observatory, Fisherhaven Small Telescope Observatory (J. Retief), COSPAR 0433 (G. Roberts), COSPAR 0434 (I. Roberts), Weltevreden Karoo Observatory (D. Bullis), Winobs (M. Shafer)

SN 1986J VLBI. IV. The Nature of the Central Component

NASA Astrophysics Data System (ADS)

Bietenholz, Michael F.; Bartel, Norbert

2017-12-01

We report on Very Large Array measurements between 1 and 45 GHz of the evolving radio spectral energy distribution (SED) of SN 1986J, made in conjunction with very long baseline interferometry (VLBI) imaging. The SED of SN 1986J is unique among supernovae, and shows an inversion point and a high-frequency turnover. Both are due to the central component seen in the VLBI images, and both are progressing downward in frequency with time. The optically thin spectral index of the central component is almost the same as that of the shell. We fit a simple model to the evolving SED consisting of an optically thin shell and a partly absorbed central component. The evolution of the SED is consistent with that of a homologously expanding system. Both components are fading, but the shell is fading more rapidly. We conclude that the central component is physically inside the expanding shell, and not a surface hotspot central only in projection. Our observations are consistent with the central component being due to interaction of the shock with the dense and highly structured circumstellar medium that resulted from a period of common-envelope evolution of the progenitor. However, a young pulsar-wind nebula or emission from an accreting black hole can also not be ruled out at this point.

The Russian-Ukrainian Observatories Network for the European Astronomical Observatory Route Project

NASA Astrophysics Data System (ADS)

Andrievsky, S. M.; Bondar, N. I.; Karetnikov, V. G.; Kazantseva, L. V.; Nefedyev, Y. A.; Pinigin, G. I.; Pozhalova, Zh. A.; Rostopchina-Shakhovskay, A. N.; Stepanov, A. V.; Tolbin, S. V.

2011-09-01

In 2004,the Center of UNESCO World Heritage has announced a new initiative "Astronomy & World Heritage" directed for search and preserving of objects,referred to astronomy,its history in a global value,historical and cultural properties. There were defined a strategy of thematic programme "Initiative" and general criteria for selecting of ancient astronomical objects and observatories. In particular, properties that are situated or have significance in relation to celestial objects or astronomical events; representations of sky and/or celestial bodies and astronomical events; observatories and instruments; properties closely connected with the history of astronomy. In 2005-2006,in accordance with the program "Initiative", information about outstanding properties connected with astronomy have been collected.In Ukraine such work was organized by astronomical expert group in Nikolaev Astronomical Observatory. In 2007, Nikolaev observatory was included to the Tentative List of UNESCO under # 5116. Later, in 2008, the network of four astronomical observatories of Ukraine in Kiev,Crimea, Nikolaev and Odessa,considering their high authenticities and integrities,was included to the Tentative List of UNESCO under # 5267 "Astronomical Observatories of Ukraine". In 2008-2009, a new project "Thematic Study" was opened as a successor of "Initiative". It includes all fields of astronomical heritage from earlier prehistory to the Space astronomy (14 themes in total). We present the Ukraine-Russian Observatories network for the "European astronomical observatory Route project". From Russia two observatories are presented: Kazan Observatory and Pulkovo Observatory in the theme "Astronomy from the Renaissance to the mid-twentieth century".The description of astronomical observatories of Ukraine is given in accordance with the project "Thematic study"; the theme "Astronomy from the Renaissance to the mid-twentieth century" - astronomical observatories in Kiev,Nikolaev and Odessa; the

4-station ultra-rapid EOP experiment with e-VLBI technique and automated correlation/analysis

NASA Astrophysics Data System (ADS)

Kurihara, S.; Nozawa, K.; Haas, R.; Lovell, J.; McCallum, J.; Quick, J.; Hobiger, T.

2013-08-01

Since 2007, the Geospatial Information Authority of Japan (GSI) and the Onsala Space Observatory (OSO) have performed the ultra-rapid dUT1 experiments, which can provide us with near real-time dUT1 value. Its technical knowledge has already been adopted for the regular series of the Tsukuba-Wettzell intensive session. Now we tried some 4-station ultra-rapid EOP experiments in association with Hobart and HartRAO so that we can estimate not only dUT1 but also the two polar motion parameters. In this experiment a new analysis software c5++ developed by the National Institute of Information and Communications Technology (NICT) was used. We describe past developments and an overview of the experiment, and conclude with its results in this report.

Observatories and Telescopes of Modern Times

NASA Astrophysics Data System (ADS)

Leverington, David

2016-11-01

Preface; Part I. Optical Observatories: 1. Palomar Mountain Observatory; 2. The United States Optical Observatory; 3. From the Next Generation Telescope to Gemini and SOAR; 4. Competing primary mirror designs; 5. Active optics, adaptive optics and other technical innovations; 6. European Northern Observatory and Calar Alto; 7. European Southern Observatory; 8. Mauna Kea Observatory; 9. Australian optical observatories; 10. Mount Hopkins' Whipple Observatory and the MMT; 11. Apache Point Observatory; 12. Carnegie Southern Observatory (Las Campanas); 13. Mount Graham International Optical Observatory; 14. Modern optical interferometers; 15. Solar observatories; Part II. Radio Observatories: 16. Australian radio observatories; 17. Cambridge Mullard Radio Observatory; 18. Jodrell Bank; 19. Early radio observatories away from the Australian-British axis; 20. The American National Radio Astronomy Observatory; 21. Owens Valley and Mauna Kea; 22. Further North and Central American observatories; 23. Further European and Asian radio observatories; 24. ALMA and the South Pole; Name index; Optical observatory and telescope index; Radio observatory and telescope index; General index.

Science Priorities of the RadioAstron Space VLBI Mission

NASA Astrophysics Data System (ADS)

Langston, Glen; Kardashev, N.; International Space VLBI Collaboration

2006-12-01

The main scientific goal of the RadioAstron Space VLBI mission is study of Active Galactic Nuclei (AGN), Masers and other astronomical objects with unprecedented angular resolution, up to few millionths of an arc-second. The resolution achieved with RadioAstron will allow study the following phenomena and problems: * Central engine of AGN and physical processes near super massive black holes providing an acceleration of cosmic rays size, velocity and shape of emitting region in the core, spectrum, polarization and variability of emitting components; * Cosmological models, dark matter and dark energy by studying dependence of above mentioned AGN's parameters with redshift, and by observing gravitational lensing; * Structure and dynamics of star and planets forming regions in our Galaxy and in AGN by studying maser and Mega maser radio emission; * Neutron (quark?) stars and black holes in our Galaxy, their structure and dynamics by VLBI and measurements of visibility scintillations, proper motions and parallaxes; * Structure and distribution of interstellar and interplanetary plasma by fringe visibility scintillations of pulsars; The RadioAstron mission uses the satellite SPECTR (astrophysical module), developed by Lavochkin Association of Russian Aviation and Space Agency (RASA). This module will be used in several other scientific missions. The total mass of the scientific payload is about 2500 kg, of which the unfolding parabolic 10-m radio astronomy antenna's mass is about 1500 kg, and scientific package holding the receivers, power supply, synthesizers, control units, frequency standards and data transmission radio system. The mass of the whole system (satellite and scientific payload) to be carried into orbit by the powerful "Zenit-2SB"-"Fregat-2CB" launcher is about 5000 kg. The RadioAstron project is an international collaboration between RASA and ground radio telescope facilities around the world.

The Malaysian Robotic Solar Observatory (P29)

NASA Astrophysics Data System (ADS)

Othman, M.; Asillam, M. F.; Ismail, M. K. H.

2006-11-01

Robotic observatory with small telescopes can make significant contributions to astronomy observation. They provide an encouraging environment for astronomers to focus on data analysis and research while at the same time reducing time and cost for observation. The observatory will house the primary 50cm robotic telescope in the main dome which will be used for photometry, spectroscopy and astrometry observation activities. The secondary telescope is a robotic multi-apochromatic refractor (maximum diameter: 15 cm) which will be housed in the smaller dome. This telescope set will be used for solar observation mainly in three different wavelengths simultaneously: the Continuum, H-Alpha and Calcium K-line. The observatory is also equipped with an automated weather station, cloud & rain sensor and all-sky camera to monitor the climatic condition, sense the clouds (before raining) as well as to view real time sky view above the observatory. In conjunction with the Langkawi All-Sky Camera, the observatory website will also display images from the Malaysia - Antarctica All-Sky Camera used to monitor the sky at Scott Base Antarctica. Both all-sky images can be displayed simultaneously to show the difference between the equatorial and Antarctica skies. This paper will describe the Malaysian Robotic Observatory including the systems available and method of access by other astronomers. We will also suggest possible collaboration with other observatories in this region.

Okayama Astrophysical Observatory

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

The Okayama Astrophysical Observatory (OAO) is a branch Observatory of the NATIONAL ASTRONOMICAL OBSERVATORY, JAPAN. Its main facilities are 188 cm and 91 cm telescopes, equipped with newly built instruments with CCD/IR cameras (e.g. OASIS). OAO accepts nearly 300 astronomers a year, according to the observation program scheduled by the committee....

Gravitational effects from a series of IVS R&D VLBI-sessions with observations close to the Sun

NASA Astrophysics Data System (ADS)

Heinkelmann, R.; Soja, B.; Schuh, H.

2015-08-01

In 2011 and 2012 the IVS observed twelve VLBI research and development (R&D) sessions that include successful observations as angularly close as 3.9° from the heliocenter. Among others, one purpose of these IVS-R&D sessions was to achieve an improvement in the determination of the PPN parameter γ . Besides, by analyzing this specific set of IVS sessions, it was for the first time possible to measure the dispersive effect of the Solar corona with VLBI (Soja et al., 2014). In this work we assess the formal error of the γ-parameter and the contributions of the various terms to the partial derivative of the γ-parameter. Furthermore, we investigate the size of the gravitational delays caused by: (i) Solar monopole field at rest and with approximately linear translation, (ii) rotation of the Solar monopole field, (iii) Solar gravitational field quadrupole expansion, and (iv) Solar higher order term.

Detection of Intrinsic Source Structure at ∼3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*

NASA Astrophysics Data System (ADS)

Lu, Ru-Sen; Krichbaum, Thomas P.; Roy, Alan L.; Fish, Vincent L.; Doeleman, Sheperd S.; Johnson, Michael D.; Akiyama, Kazunori; Psaltis, Dimitrios; Alef, Walter; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, Lindy; Blundell, Ray; Bower, Geoffrey C.; Brinkerink, Christiaan; Broderick, Avery E.; Cappallo, Roger; Crew, Geoffrey B.; Dexter, Jason; Dexter, Matt; Falcke, Heino; Freund, Robert; Friberg, Per; Greer, Christopher H.; Gurwell, Mark A.; Ho, Paul T. P.; Honma, Mareki; Inoue, Makoto; Kim, Junhan; Lamb, James; Lindqvist, Michael; Macmahon, David; Marrone, Daniel P.; Martí-Vidal, Ivan; Menten, Karl M.; Moran, James M.; Nagar, Neil M.; Plambeck, Richard L.; Primiani, Rurik A.; Rogers, Alan E. E.; Ros, Eduardo; Rottmann, Helge; SooHoo, Jason; Spilker, Justin; Stone, Jordan; Strittmatter, Peter; Tilanus, Remo P. J.; Titus, Michael; Vertatschitsch, Laura; Wagner, Jan; Weintroub, Jonathan; Wright, Melvyn; Young, Ken H.; Zensus, J. Anton; Ziurys, Lucy M.

2018-05-01

We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N–S direction, and leads to a spatial resolution of ∼30 μas (∼3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of ∼4%–13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of ∼3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.

Solar Dynamics Observatory On-Orbit Jitter Testing, Analysis, and Mitigation Plans

NASA Technical Reports Server (NTRS)

Liu, Kuo-Chia (Alice); Blaurock, Carl A.; Bourkland, Kristin L.; Morgenstern, Wendy M.; Maghami, Peiman G.

2011-01-01

The Solar Dynamics Observatory (SDO) was designed to understand the Sun and the Sun s influence on Earth. SDO was launched on February 11, 2010 carrying three scientific instruments: the Atmospheric Imaging Assembly (AIA), the Helioseismic and Magnetic Imager (HMI), and the Extreme Ultraviolet Variability Experiment (EVE). Both AIA and HMI are sensitive to high frequency pointing perturbations and have sub-arcsecond level line-of-sight (LOS) jitter requirements. Extensive modeling and analysis efforts were directed in estimating the amount of jitter disturbing the science instruments. To verify the disturbance models and to validate the jitter performance prior to launch, many jitter-critical components and subassemblies were tested either by the mechanism vendors or at the NASA Goddard Space Flight Center (GSFC). Although detailed analysis and assembly level tests were performed to obtain good jitter predictions, there were still several sources of uncertainties in the system. The structural finite element model did not have all the modes correlated to test data at high frequencies (greater than 50 Hz). The performance of the instrument stabilization system was not known exactly but was expected to be close to the analytical model. A true disturbance-to-LOS observatory level test was not available due to the tight schedule of the flight spacecraft, the cost in time and manpower, difficulties in creating gravity negation systems, and risks of damaging flight hardware. To protect the observatory jitter performance against model uncertainties, the SDO jitter team devised several on-orbit jitter reduction plans in addition to reserve margins on analysis results. Since some of these plans severely restricted the capabilities of several spacecraft components (e.g. wheels and High Gain Antennas), the SDO team performed on-orbit jitter tests to determine which jitter reduction plans, if any, were necessary to satisfy science LOS jitter requirements. The SDO on

VLBI imaging of a flare in the Crab nebula: more than just a spot

NASA Astrophysics Data System (ADS)

Lobanov, A. P.; Horns, D.; Muxlow, T. W. B.

2011-09-01

We report on very long baseline interferometry (VLBI) observations of the radio emission from the inner region of the Crab nebula, made at 1.6 GHz and 5 GHz after a recent high-energy flare in this object. The 5 GHz data have provided only upper limits of 0.4 milli-Jansky (mJy) on the flux density of the pulsar and 0.4 mJy/beam on the brightness of the putative flaring region. The 1.6 GHz data have enabled imaging the inner regions of the nebula on scales of up to ≈ 40''. The emission from the inner "wisps" is detected for the first time with VLBI observations. A likely radio counterpart (designated "C1") of the putative flaring region observed with Chandra and HST is detected in the radio image, with an estimated flux density of 0.5 ± 0.3 mJy and a size of 0.2 arcsec - 0.6 arcsec. Another compact feature ("C2") is also detected in the VLBI image closer to the pulsar, with an estimated flux density of 0.4 ± 0.2 mJy and a size smaller than 0.2 arcsec. Combined with the broad-band SED of the flare, the radio properties of C1 yield a lower limit of ≈ 0.5 mG for the magnetic field and a total minimum energy of 1.2 × 1041 erg vested in the flare (corresponding to using about 0.2% of the pulsar spin-down power). The 1.6 GHz observations provide upper limits for the brightness (0.2 mJy/beam) and total flux density (0.4 mJy) of the optical Knot 1 located at 0.6 arcsec from the pulsar. The absolute position of the Crab pulsar is determined, and an estimate of the pulsar proper motion (μα = -13.0 ± 0.2 mas/yr, μδ = + 2.9 ± 0.1 mas/yr) is obtained.

Ten years of the Spanish Virtual Observatory

NASA Astrophysics Data System (ADS)

Solano, E.

2015-05-01

The main objective of the Virtual Observatory (VO) is to guarantee an easy and efficient access and analysis of the information hosted in astronomical archives. The Spanish Virtual Observatory (SVO) is a project that was born in 2004 with the goal of promoting and coordinating the VO-related activities at national level. SVO is also the national contact point for the international VO initiatives, in particular the International Virtual Observatory Alliance (IVOA) and the Euro-VO project. The project, led by Centro de Astrobiología (INTA-CSIC), is structured around four major topics: a) VO compliance of astronomical archives, b) VO-science, c) VO- and data mining-tools, and d) Education and outreach. In this paper I will describe the most important results obtained by the Spanish Virtual Observatory in its first ten years of life as well as the future lines of work.

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.

A Model of Relation between Fluctuation of Double Differential Total Ionospheric Electron Content and Angular Distance of the Two Satellites Observed by Same-beam VLBI

NASA Astrophysics Data System (ADS)

Xiao, Yao; Qing-hui, Liu

2018-01-01

Time delay and phase fluctuation are produced when the signals of a spacecraft are transmitted through the ionosphere of the earth, which give rise to a great influence on the measurement precision of VLBI (Very Long Baseline Interferometry). Using the 1-year same-beam VLBI data of 2 satellites (Rstar and Vstar) in the Japanese lunar exploration project SELENE, we obtained a model of the relation between the fluctuation of double differential total electron content in the ionosphere and the angular distance of the two satellites. For the 6 baselines, the root mean square r of fluctuation (in units of TECU) and the angular distance of the two satellites θ (in units of ∘) has a relation of r = 0.773θ + 0.562, and for the 4 VLBI stations, the relation is r = 0.554θ + 0.399 from the baselines inversion. The results can serve as a reference for the derivation of differential phase delay and for the occultation observation and study of planetary ionospheres.

The Little Thompson Observatory

NASA Astrophysics Data System (ADS)

Schweitzer, A.; Melsheimer, T.; Sackett, C.

1999-05-01

The Little Thompson Observatory is believed to be the first observatory built as part of a high school and accessible to other schools remotely, via the Internet. This observatory is the second member of the Telescopes in Education (TIE) project. Construction of the building and dome has been completed, and first light is planned for spring 1999. The observatory is located on the grounds of Berthoud High School in northern Colorado. Local schools and youth organizations will have prioritized access to the telescope, and there will also be opportunities for public viewing. After midnight, the telescope will be open to world-wide use by schools via the Internet following the model of the first TIE observatory, the 24" telescope on Mt. Wilson. Students remotely connect to the observatory over the Internet, and then receive the images on their local computers. The observatory grew out of grassroots support from the local community surrounding Berthoud, Colorado, a town of 3,500 residents. TIE has provided the observatory with a Tinsley 18" Cassegrain telescope on a 10-year loan. The facility has been built with tremendous support from volunteers and the local school district. We have received an IDEAS grant to provide teacher training workshops which will allow K-12 schools in northern Colorado to make use of the Little Thompson Observatory, including remote observing from classrooms.

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.

McDonald Observatory

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

McDonald Observatory, located in West Texas near Fort Davis, is the astronomical observatory of the University of Texas at Austin. Discoveries at McDonald Observatory include water vapor on Mars, the abundance of rare-earth chemical elements in stars, the discovery of planets circling around nearby stars and the use of the measurements of rapid oscillations in the brightness of white dwarf stars ...

Astronomical observatories

NASA Technical Reports Server (NTRS)

Ponomarev, D. N.

1983-01-01

The layout and equipment of astronomical observatories, the oldest scientific institutions of human society are discussed. The example of leading observatories of the USSR allows the reader to familiarize himself with both their modern counterparts, as well as the goals and problems on which astronomers are presently working.

NASA'S Great Observatories

NASA Technical Reports Server (NTRS)

1998-01-01

Why are space observatories important? The answer concerns twinkling stars in the night sky. To reach telescopes on Earth, light from distant objects has to penetrate Earth's atmosphere. Although the sky may look clear, the gases that make up our atmosphere cause problems for astronomers. These gases absorb the majority of radiation emanating from celestial bodies so that it never reaches the astronomer's telescope. Radiation that does make it to the surface is distorted by pockets of warm and cool air, causing the twinkling effect. In spite of advanced computer enhancement, the images finally seen by astronomers are incomplete. NASA, in conjunction with other countries' space agencies, commercial companies, and the international community, has built observatories such as the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory to find the answers to numerous questions about the universe. With the capabilities the Space Shuttle provides, scientist now have the means for deploying these observatories from the Shuttle's cargo bay directly into orbit.

The Compton Observatory Science Workshop

NASA Technical Reports Server (NTRS)

Shrader, Chris R. (Editor); Gehrels, Neil (Editor); Dennis, Brian (Editor)

1992-01-01

The Compton Observatory Science Workshop was held in Annapolis, Maryland on September 23-25, 1991. The primary purpose of the workshop was to provide a forum for the exchange of ideas and information among scientists with interests in various areas of high energy astrophysics, with emphasis on the scientific capabilities of the Compton Observatory. Early scientific results, as well as reports on in-flight instrument performance and calibrations are presented. Guest investigator data products, analysis techniques, and associated software were discussed. Scientific topics covered included active galaxies, cosmic gamma ray bursts, solar physics, pulsars, novae, supernovae, galactic binary sources, and diffuse galactic and extragalactic emission.

The Little Thompson Observatory

NASA Astrophysics Data System (ADS)

Schweitzer, A.; Melsheimer, T.; Rideout, C.; Vanlew, K.

1998-12-01

The Little Thompson Observatory is believed to be the first observatory built as part of a high school and accessible to other schools remotely, via the Internet. This observatory is the second member of the Telescopes in Education (TIE) project. Construction is nearly completed and first light is planned for fall 1998. The observatory is located on the grounds of Berthoud High School in northern Colorado. Local schools and youth organizations will have prioritized access to the telescope, and there will also be opportunities for public viewing. After midnight, the telescope will be open to world-wide use by schools via the Internet following the model of the first TIE observatory, the 24" telescope on Mt. Wilson. That telescope has been in use for the past four years by up to 50 schools per month. Students remotely connect to the observatory over the Internet, and then receive the images on their local computers. The observatory grew out of grassroots support from the local community surrounding Berthoud, Colorado, a town of 3,500 residents. TIE has provided the observatory with a Tinsley 18" Cassegrain telescope on a 10-year loan. The facility has been built with tremendous support from volunteers and the local school district. We have applied for an IDEAS grant to provide teacher training workshops which will allow K-12 schools in northern Colorado to make use of the Little Thompson Observatory, including remote observing from classrooms.

NMA Analysis Center

NASA Technical Reports Server (NTRS)

Kierulf, Halfdan Pascal; Andersen, Per Helge

2013-01-01

The Norwegian Mapping Authority (NMA) has during the last few years had a close cooperation with Norwegian Defence Research Establishment (FFI) in the analysis of space geodetic data using the GEOSAT software. In 2012 NMA has taken over the full responsibility for the GEOSAT software. This implies that FFI stopped being an IVS Associate Analysis Center in 2012. NMA has been an IVS Associate Analysis Center since 28 October 2010. NMA's contributions to the IVS as an Analysis Centers focus primarily on routine production of session-by-session unconstrained and consistent normal equations by GEOSAT as input to the IVS combined solution. After the recent improvements, we expect that VLBI results produced with GEOSAT will be consistent with results from the other VLBI Analysis Centers to a satisfactory level.

Interactive 3D visualization for theoretical virtual observatories

NASA Astrophysics Data System (ADS)

Dykes, T.; Hassan, A.; Gheller, C.; Croton, D.; Krokos, M.

2018-06-01

Virtual observatories (VOs) are online hubs of scientific knowledge. They encompass a collection of platforms dedicated to the storage and dissemination of astronomical data, from simple data archives to e-research platforms offering advanced tools for data exploration and analysis. Whilst the more mature platforms within VOs primarily serve the observational community, there are also services fulfilling a similar role for theoretical data. Scientific visualization can be an effective tool for analysis and exploration of data sets made accessible through web platforms for theoretical data, which often contain spatial dimensions and properties inherently suitable for visualization via e.g. mock imaging in 2D or volume rendering in 3D. We analyse the current state of 3D visualization for big theoretical astronomical data sets through scientific web portals and virtual observatory services. We discuss some of the challenges for interactive 3D visualization and how it can augment the workflow of users in a virtual observatory context. Finally we showcase a lightweight client-server visualization tool for particle-based data sets, allowing quantitative visualization via data filtering, highlighting two example use cases within the Theoretical Astrophysical Observatory.

The Carl Sagan solar and stellar observatories as remote observatories

NASA Astrophysics Data System (ADS)

Saucedo-Morales, J.; Loera-Gonzalez, P.

In this work we summarize recent efforts made by the University of Sonora, with the goal of expanding the capability for remote operation of the Carl Sagan Solar and Stellar Observatories, as well as the first steps that have been taken in order to achieve autonomous robotic operation in the near future. The solar observatory was established in 2007 on the university campus by our late colleague A. Sánchez-Ibarra. It consists of four solar telescopes mounted on a single equatorial mount. On the other hand, the stellar observatory, which saw the first light on 16 February 2010, is located 21 km away from Hermosillo, Sonora at the site of the School of Agriculture of the University of Sonora. Both observatories can now be remotely controlled, and to some extent are able to operate autonomously. In this paper we discuss how this has been accomplished in terms of the use of software as well as the instruments under control. We also briefly discuss the main scientific and educational objectives, the future plans to improve the control software and to construct an autonomous observatory on a mountain site, as well as the opportunities for collaborations.

WNCC Observatory

NASA Astrophysics Data System (ADS)

Snyder, L. F.

2003-05-01

Western Nevada Community College (WNCC), located in Carson City, Nevada, is a small two year college with only 6,000 students. Associate degrees and Cer- tificates of Achievement are awarded. The college was built and started classes in 1971 and about 12 years ago the chair of the physics department along with a few in administration had dreams of building a small observatory for education. Around that time a local foundation, Nevada Gaming Foundation for Education Excellence, was looking for a beneficiary in the education field to receive a grant. They decided an observatory at the college met their criteria. Grants to the foundation instigated by Senators, businesses, and Casinos and donations from the local public now total $1.3 million. This paper will explain the different facets of building the observatory, the planning, construction, telescopes and equipment decisions and how we think it will operate for the public, education and research. The organization of local volunteers to operate and maintain the observatory and the planned re- search will be explained.

``Route of astronomical observatories'' project: Classical observatories from the Renaissance to the rise of astrophysics

NASA Astrophysics Data System (ADS)

Wolfschmidt, Gudrun

2016-10-01

Observatories offer a good possibility for serial transnational applications. For example one can choose groups like baroque or neoclassical observatories, solar physics observatories or a group of observatories equipped with the same kind of instruments or made by famous firms. I will discuss what has been achieved and show examples, like the route of astronomical observatories, the transition from classical astronomy to modern astrophysics. I will also discuss why the implementation of the World Heritage & Astronomy initiative is difficult and why there are problems to nominate observatories for election in the national tentative lists.

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.

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.

VLBI observations of the 0957 + 561 gravitational lens system

NASA Technical Reports Server (NTRS)

Gorenstein, M. V.; Falco, E. E.; Shapiro, I. I.; Bartel, N.; Bonometti, R. J.; Cohen, N. L.; Rogers, A. E. E.; Marcaide, J. M.; Clark, T. A.

1988-01-01

A series of VLBI observations of the gravitational lens system 0957 + 561 at a wavelength of 13 cm has yielded the positions of the A and B images, the relative magnification of their largest discernible radio structures, and the time variability of their smallest discernible radio structures. These observations have also allowed upper limits to be placed on the flux density of an expected third image. The positions and relative magnification of the A and B images provide new information with which to constrain models of the lens that forms the images. The detection of variations in the flux densities of the cores of A and B suggests that observations at shorter wavelengths may reveal superluminal motion, which may in turn provide a means to measure the relative time delay.

A Regional Groundwater Observatory to Enhance Analysis and Management of Water Resources

NASA Astrophysics Data System (ADS)

Yoder, A. M.; Maples, S.; Hatch, N. R.; Fogg, G. E.

2017-12-01

Timely, effective management of groundwater often does not happen because timely information on the state of the groundwater system is seldom available. A groundwater observatory for monitoring real-time groundwater level fluctuations is being developed in the American-Cosumnes groundwater system of Sacramento County, California. The observatory records the consequences of complex interplay between pumpage, recharge, drought, and floods in the context of a heterogeneous stratigraphic framework that has been extensively characterized with more than 1,100 well logs. Preliminary results show increases in recharge caused by removal of flood control levees to allow more frequent floodplain inundation as well as consequences of the 2012-16 drought followed by the wet winter of 2016-17. Comparison of recharge rates pre- and post-levee breach restoration show significant increases in recharge, despite the presence of fine-grained floodplain soils. Estimated total recharge corresponded closely with the frequency and magnitude of flood events in any given water year. The lowest value calculated for estimated recharge was from 2012-2013, 490 +/- 220 ac-ft (0.65 +/- 0.29 ac-ft per acre). The highest estimated recharge value calculated was for the 2015-2016 water year and was 3180 +/- 1430 ac-ft (2.83 +/- 1.27 ac-ft per acre). These preliminary numbers will be updated with more comprehensive estimates based on a full analysis of the 2016-17 data. The increase in data transfer efficiency afforded by the observatory can be widely used by the many parties reliant on Central Valley groundwater and can serve as a model for real-time data collection in support of California's Sustainable Groundwater Management Act, passed in 2014.

A National Solar Digital Observatory

NASA Astrophysics Data System (ADS)

Hill, F.

2000-05-01

The continuing development of the Internet as a research tool, combined with an improving funding climate, has sparked new interest in the development of Internet-linked astronomical data bases and analysis tools. Here I outline a concept for a National Solar Digital Observatory (NSDO), a set of data archives and analysis tools distributed in physical location at sites which already host such systems. A central web site would be implemented from which a user could search all of the component archives, select and download data, and perform analyses. Example components include NSO's Digital Library containing its synoptic and GONG data, and the forthcoming SOLIS archive. Several other archives, in various stages of development, also exist. Potential analysis tools include content-based searches, visualized programming tools, and graphics routines. The existence of an NSDO would greatly facilitate solar physics research, as a user would no longer need to have detailed knowledge of all solar archive sites. It would also improve public outreach efforts. The National Solar Observatory is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation.

Astronomical publications of Melbourne Observatory

NASA Astrophysics Data System (ADS)

Andropoulos, Jenny Ioanna

2014-05-01

During the second half of the 19th century and the first half of the 20th century, four well-equipped government observatories were maintained in Australia - in Melbourne, Sydney, Adelaide and Perth. These institutions conducted astronomical observations, often in the course of providing a local time service, and they also collected and collated meteorological data. As well, some of these observatories were involved at times in geodetic surveying, geomagnetic recording, gravity measurements, seismology, tide recording and physical standards, so the term "observatory" was being used in a rather broad sense! Despite the international renown that once applied to Williamstown and Melbourne Observatories, relatively little has been written by modern-day scholars about astronomical activities at these observatories. This research is intended to rectify this situation to some extent by gathering, cataloguing and analysing the published astronomical output of the two Observatories to see what contributions they made to science and society. It also compares their contributions with those of Sydney, Adelaide and Perth Observatories. Overall, Williamstown and Melbourne Observatories produced a prodigious amount of material on astronomy in scientific and technical journals, in reports and in newspapers. The other observatories more or less did likewise, so no observatory of those studied markedly outperformed the others in the long term, especially when account is taken of their relative resourcing in staff and equipment.

Keele Observatory

NASA Astrophysics Data System (ADS)

Theodorus van Loon, Jacco; Albinson, James; Bagnall, Alan; Bryant, Lian; Caisley, Dave; Doody, Stephen; Johnson, Ian; Klimczak, Paul; Maddison, Ron; Robinson, StJohn; Stretch, Matthew; Webb, John

2015-08-01

Keele Observatory was founded by Dr. Ron Maddison in 1962, on the hill-top campus of Keele University in central England, hosting the 1876 Grubb 31cm refractor from Oxford Observatory. It since acquired a 61cm research reflector, a 15cm Halpha solar telescope and a range of other telescopes. Run by a group of volunteering engineers and students under directorship of a Keele astrophysicist, it is used for public outreach as well as research. About 4,000 people visit the observatory every year, including a large number of children. We present the facility, its history - including involvement in the 1919 Eddington solar eclipse expedition which proved Albert Einstein's theory of general relativity - and its ambitions to erect a radio telescope on its site.

The Little Thompson Observatory

NASA Astrophysics Data System (ADS)

Schweitzer, A. E.; VanLew, K.; Melsheimer, T.; Sackett, C.

1999-12-01

The Little Thompson Observatory is the second member of the Telescopes in Education (TIE) project. Construction of the dome and the remote control system has been completed, and the telescope is now on-line and operational over the Internet. The observatory is located on the grounds of Berthoud High School in northern Colorado. Local schools and youth organizations have prioritized access to the telescope, and there are monthly opportunities for public viewing. In the future, the telescope will be open after midnight to world-wide use by schools following the model of the first TIE observatory, the 24" telescope on Mt. Wilson. Students remotely connect to the observatory over the Internet, and then receive the images on their local computers. The observatory grew out of grassroots support from the local community surrounding Berthoud, Colorado, a town of 3,500 residents. TIE has provided the observatory with a Tinsley 18" Cassegrain telescope on a 10-year loan. The facility has been built with tremendous support from volunteers and the local school district. With funding from an IDEAS grant, we have begun teacher training workshops which will allow K-12 schools in northern Colorado to make use of the Little Thompson Observatory, including remote observing from classrooms.

Observation VLBI Session RAPL02. the Results of the Data Processing

NASA Astrophysics Data System (ADS)

Chuprikov, A. A.

Results of processing of data of a VLBI experiment titled RAPL02 are presented. These observations were made in 2011 February with 5 antennas. All 3 antennas of Petersberg's Institute of Applied Astronomy (IAA) were used in this session. These were antennae in Svetloe, in Zelenchuck, and in Badary. Additionally, a 22-m antenna in Puschino as well as a 32-m antenna in Medicina (Italy) were also included into observations. The raw data correlation was made at the software correlator of Astro Space Center. The secondary data processing was made for 3 quasars, 3C273, 3C279, and 3C286.

Reliability culture at La Silla Paranal Observatory

NASA Astrophysics Data System (ADS)

Gonzalez, Sergio

2010-07-01

The Maintenance Department at the La Silla - Paranal Observatory has been an important base to keep the operations of the observatory at a good level of reliability and availability. Several strategies have been implemented and improved in order to cover these requirements and keep the system and equipment working properly when it is required. For that reason, one of the latest improvements has been the introduction of the concept of reliability, which implies that we don't simply speak about reliability concepts. It involves much more than that. It involves the use of technologies, data collecting, data analysis, decision making, committees concentrated in analysis of failure modes and how they can be eliminated, aligning the results with the requirements of our internal partners and establishing steps to achieve success. Some of these steps have already been implemented: data collection, use of technologies, analysis of data, development of priority tools, committees dedicated to analyze data and people dedicated to reliability analysis. This has permitted us to optimize our process, analyze where we can improve, avoid functional failures, reduce the failures range in several systems and subsystems; all this has had a positive impact in terms of results for our Observatory. All these tools are part of the reliability culture that allows our system to operate with a high level of reliability and availability.

On the Automation of the MarkIII Data Analysis System.

NASA Astrophysics Data System (ADS)

Schwegmann, W.; Schuh, H.

1999-03-01

A faster and semiautomatic data analysis is an important contribution to the acceleration of the VLBI procedure. A concept for the automation of one of the most widely used VLBI software packages the MarkIII Data Analysis System was developed. Then, the program PWXCB, which extracts weather and cable calibration data from the station log-files, was automated supplementing the existing Fortran77 program-code. The new program XLOG and its results will be presented. Most of the tasks in the VLBI data analysis are very complex and their automation requires typical knowledge-based techniques. Thus, a knowledge-based system (KBS) for support and guidance of the analyst is being developed using the AI-workbench BABYLON, which is based on methods of artificial intelligence (AI). The advantages of a KBS for the MarkIII Data Analysis System and the required steps to build a KBS will be demonstrated. Examples about the current status of the project will be given, too.

Gravity-dependent signal path variation in a large VLBI telescope modelled with a combination of surveying methods

NASA Astrophysics Data System (ADS)

Sarti, Pierguido; Abbondanza, C.; Vittuari, L.

2009-11-01

The very long baseline interferometry (VLBI) antenna in Medicina (Italy) is a 32-m AZ-EL mount that was surveyed several times, adopting an indirect method, for the purpose of estimating the eccentricity vector between the co-located VLBI and Global Positioning System instruments. In order to fulfill this task, targets were located in different parts of the telescope’s structure. Triangulation and trilateration on the targets highlight a consistent amount of deformation that biases the estimate of the instrument’s reference point up to 1 cm, depending on the targets’ locations. Therefore, whenever the estimation of accurate local ties is needed, it is critical to take into consideration the action of gravity on the structure. Furthermore, deformations induced by gravity on VLBI telescopes may modify the length of the path travelled by the incoming radio signal to a non-negligible extent. As a consequence, differently from what it is usually assumed, the relative distance of the feed horn’s phase centre with respect to the elevation axis may vary, depending on the telescope’s pointing elevation. The Medicina telescope’s signal path variation Δ L increases by a magnitude of approximately 2 cm, as the pointing elevation changes from horizon to zenith; it is described by an elevation-dependent second-order polynomial function computed as, according to Clark and Thomsen (Techical report, 100696, NASA, Greenbelt, 1988), a linear combination of three terms: receiver displacement Δ R, primary reflector’s vertex displacement Δ V and focal length variations Δ F. Δ L was investigated with a combination of terrestrial triangulation and trilateration, laser scanning and a finite element model of the antenna. The antenna gain (or auto-focus curve) Δ G is routinely determined through astronomical observations. A surprisingly accurate reproduction of Δ G can be obtained with a combination of Δ V, Δ F and Δ R.

International Ultraviolet Explorer Observatory operations

NASA Technical Reports Server (NTRS)

1985-01-01

This volume contains the final report for the International Ultraviolet Explorer IUE Observatory Operations contract. The fundamental operational objective of the International Ultraviolet Explorer (IUE) program is to translate competitively selected observing programs into IUE observations, to reduce these observations into meaningful scientific data, and then to present these data to the Guest Observer in a form amenable to the pursuit of scientific research. The IUE Observatory is the key to this objective since it is the central control and support facility for all science operations functions within the IUE Project. In carrying out the operation of this facility, a number of complex functions were provided beginning with telescope scheduling and operation, proceeding to data processing, and ending with data distribution and scientific data analysis. In support of these critical-path functions, a number of other significant activities were also provided, including scientific instrument calibration, systems analysis, and software support. Routine activities have been summarized briefly whenever possible.

Prospect of Continuous VLBI Measurement of Earth Rotation in Monitoring Geophysical Fluids

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.; Ma, Chopo; Clark, Thomas

1998-01-01

Large-scale mass transports in the geophysical fluids of the Earth system excite Earth's rotational variations in both length-of-day and polar motion. The excitation process is via the conservation of angular momentum. Therefore Earth rotation observations contain information about the integrated angular momentum (consisting of both the mass term and the motion term) of the geophysical fluids, which include atmosphere, hydrosphere, mantle, and the outer and inner cores. Such global information is often important and otherwise unattainable depending on the nature of the mass transport, its magnitude and time scale. The last few years have seen great advances in VLBI measurement of Earth rotation in precision and temporal resolution. These advances have opened new. areas in geophysical fluid studies, such as oceanic tidal angular momentum, atmospheric tides, Earth librations, and rapid atmospheric angular momentum fluctuations. Precision of 10 microseconds in UTI and 200 microarcseconds in polar motion can now be achieved on hourly basis. Building upon this heritage, the multi-network geodetic VLBI project, Continuous Observation of the Rotation of the Earth (CORE), promises to further these studies and to make possible studies on elusive but tell-tale geophysical processes such as oscillatory modes in the core and in the atmosphere. Currently the early phase of CORE is underway. Within a few years into the new mellinnium, the upcoming space gravity missions (such as GRACE) will measure the temporal variations in Earth's gravitational field, thus providing complementary information to that from Earth rotation study for a better understanding of global geophysical fluid processes.

The Global GNSS, SLR, VLBI, and DORIS Networks and their Support of GGOS: IGS+ILRS+IVS+IDS

NASA Technical Reports Server (NTRS)

Noll, Carey

2008-01-01

The global network of the International GNSS Service (IGS), the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS), and the International DORIS Service (IDS) are part of the ground-based infrastructure for GGOS. The observations obtained from these global networks provide for the determination and maintenance of the International Terrestrial Reference Frame (ITRF), an accurate set of positions and velocities that provides a stable coordinate system allowing scientists ts to link measurements over space and time. Many of these sites offer co-location of two or more techniques. Co-location provides integration of technique-specific networks into the ITRF as well as an assessment/validation of the quality and accuracy of the resulting measurements. As of fall 2008, these networks consisted of 410 GNSS sites, 42 laser ranging sites, 45 VLBI sites, and 58 DORIS sites. This poster will illustrate the global coverage of these networks, highlighting inter-technique co-locations, and show the importance of these networks 60 the underlying goals of GGOS including providing the observational basis to maintain a stable, accurate, global reference frame.

VLBI observations of 6 GHz OH masers in three ultra-compact H Ii regions

NASA Astrophysics Data System (ADS)

Desmurs, J. F.; Baudry, A.

1998-12-01

Following our successful analysis of VLBI observations of the (2) Pi_ {3/ 2}, J={5/ 2}, F=3-3 and F=2-2 excited OH emission at 6035 and 6031 MHz in W3(OH), we have analyzed the same transitions in three other ultra-compact HII regions, M17, ON1, and W51. The restoring beams were in the range 6 to 30 milliarc sec. The F=3-3 and 2-2 hyperfine transitions of OH were both mapped in ON1. Seven 6035 MHz LCP or RCP maser components were identified in ON1. They are distributed over a region whose diameter is similar to that of the compact HII region, namely ~ 0.4 - 0.5 arc sec. In contrast with the F=3-3 line emission, the F=2-2 transition at 6031 MHz is nearly an order of magnitude weaker than the peak 6035 MHz emission. In M17, we observed fringes only in the 6035 MHz line. The detected OH components appear to be projected on to the compact HII region. We report also on weak VLBI detection of the 6035 MHz emission from W51. This emission seems to be located between two active ultra-compact HII regions in a complex area which deserves further investigation. The 5 cm OH minimum brightness temperatures range from about 3 10(7) K in W51 to 8 10(9) K in ON1. Variability of the 6035 or 6031 MHz emission is well established and suggests that the 5 cm OH masers are not fully saturated. The high spectral and spatial resolutions achieved in this work allowed us to identify Zeeman pairs and hence to derive the magnetic field strength. In ON1 and W51 the field lies in the range 4 to 6 mG with a trend for higher field at 6031 MHz than at 6035 MHz in ON1. In M17 no Zeeman splitting was observed and the magnetic field appears to be weaker than 1 mG.

Tools for Coordinated Planning Between Observatories

NASA Technical Reports Server (NTRS)

Jones, Jeremy; Fishman, Mark; Grella, Vince; Kerbel, Uri; Maks, Lori; Misra, Dharitri; Pell, Vince; Powers, Edward I. (Technical Monitor)

2001-01-01

With the realization of NASA's era of great observatories, there are now more than three space-based telescopes operating in different wavebands. This situation provides astronomers with a unique opportunity to simultaneously observe with multiple observatories. Yet scheduling multiple observatories simultaneously is highly inefficient when compared to observations using only one single observatory. Thus, programs using multiple observatories are limited not due to scientific restrictions, but due to operational inefficiencies. At present, multi-observatory programs are conducted by submitting observing proposals separately to each concerned observatory. To assure that the proposed observations can be scheduled, each observatory's staff has to check that the observations are valid and meet all the constraints for their own observatory; in addition, they have to verify that the observations satisfy the constraints of the other observatories. Thus, coordinated observations require painstaking manual collaboration among the observatory staff at each observatory. Due to the lack of automated tools for coordinated observations, this process is time consuming, error-prone, and the outcome of the requests is not certain until the very end. To increase observatory operations efficiency, such manpower intensive processes need to undergo re-engineering. To overcome this critical deficiency, Goddard Space Flight Center's Advanced Architectures and Automation Branch is developing a prototype effort called the Visual Observation Layout Tool (VOLT). The main objective of the VOLT project is to provide visual tools to help automate the planning of coordinated observations by multiple astronomical observatories, as well as to increase the scheduling probability of all observations.

Verification of the astrometric performance of the Korean VLBI network, using comparative SFPR studies with the VLBA AT 14/7 mm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rioja, María J.; Dodson, Richard; Jung, TaeHyun

The Korean VLBI Network (KVN) is a new millimeter VLBI dedicated array with the capability to simultaneously observe at multiple frequencies, up to 129 GHz. The innovative multi-channel receivers present significant benefits for astrometric measurements in the frequency domain. The aim of this work is to verify the astrometric performance of the KVN using a comparative study with the VLBA, a well-established instrument. For that purpose, we carried out nearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, in 2013 April. The KVN observations consisted of simultaneous dual frequency observations, while the VLBA used fast frequency switchingmore » observations. We used the Source Frequency Phase Referencing technique for the observational and analysis strategy. We find that having simultaneous observations results in superior compensation for all atmospheric terms in the observables, in addition to offering other significant benefits for astrometric analysis. We have compared the KVN astrometry measurements to those from the VLBA. We find that the structure blending effects introduce dominant systematic astrometric shifts, and these need to be taken into account. We have tested multiple analytical routes to characterize the impact of the low-resolution effects for extended sources in the astrometric measurements. The results from the analysis of the KVN and full VLBA data sets agree within 2σ of the thermal error estimate. We interpret the discrepancy as arising from the different resolutions. We find that the KVN provides astrometric results with excellent agreement, within 1σ, when compared to a VLBA configuration that has a similar resolution. Therefore, this comparative study verifies the astrometric performance of the KVN using SFPR at 14/7 mm, and validates the KVN as an astrometric instrument.« less

VLBI observations at 2.3 GHz of the compact galaxy 1934-638

NASA Technical Reports Server (NTRS)

Tzioumis, Anastasios K.; Jauncey, David L.; Preston, Robert A.; Meier, David L.; Morabito, David D.; Skjerve, Lyle; Slade, Martin A.; Nicolson, George D.; Niell, Arthur E.; Wehrle, Ann E.

1989-01-01

VLBI observations of the strong radio source 1934-638 show it to be a binary with a component separation of 42.0 + or - 0.2 mas, a position angle of 90.5 + or - 1 deg, and component sizes of about 2.5 mas. The results imply the presence of an additional elongated component aligned with, and between, the compact double components. The sources's almost equal compact double structure, peaked spectrum, low variability, small polarization, and particle-dominated radio lobes suggests that it belongs to the class of symmetric compact double sources identified by Phillips and Mutel (1980, 1981, 1982).

VLBI observations of 23 hot spots in the starburst galaxy M82

NASA Technical Reports Server (NTRS)

Bartel, Norbert; Ratner, Michael I.; Shapiro, Irwin I.; Rogers, Alan E. E.; Preston, Robert A.

1987-01-01

The simultaneous 2.3 and 8.4 GHz VLBI observations of 23 hot spots in the nuclear region of M82 presented indicate the presence of six hot spots at 2.3 GHz, but only one at 8.4 GHz. Attention is given to a mapping of the brightest hot spot, 41.9+58, at 2.3 GHz, which exhibits a complex brightness distribution whose angular width in the NE-SW direction is 45 mas at the 10-percent contour. These data are consistent with the hot spots in M82 being powerful SNRs, with ages between about 10 and 300 yr.

Optimizing fixed observational assets in a coastal observatory

NASA Astrophysics Data System (ADS)

Frolov, Sergey; Baptista, António; Wilkin, Michael

2008-11-01

Proliferation of coastal observatories necessitates an objective approach to managing of observational assets. In this article, we used our experience in the coastal observatory for the Columbia River estuary and plume to identify and address common problems in managing of fixed observational assets, such as salinity, temperature, and water level sensors attached to pilings and moorings. Specifically, we addressed the following problems: assessing the quality of an existing array, adding stations to an existing array, removing stations from an existing array, validating an array design, and targeting of an array toward data assimilation or monitoring. Our analysis was based on a combination of methods from oceanographic and statistical literature, mainly on the statistical machinery of the best linear unbiased estimator. The key information required for our analysis was the covariance structure for a field of interest, which was computed from the output of assimilated and non-assimilated models of the Columbia River estuary and plume. The network optimization experiments in the Columbia River estuary and plume proved to be successful, largely withstanding the scrutiny of sensitivity and validation studies, and hence providing valuable insight into optimization and operation of the existing observational network. Our success in the Columbia River estuary and plume suggest that algorithms for optimal placement of sensors are reaching maturity and are likely to play a significant role in the design of emerging ocean observatories, such as the United State's ocean observation initiative (OOI) and integrated ocean observing system (IOOS) observatories, and smaller regional observatories.

First mm-VLBI Observations between the TRAO 14-m and the NRO 45-m Telescopes: Observations of 86 GHz SiO Masers in VY Canis Majoris

NASA Astrophysics Data System (ADS)

Shibata, Katsunori M.; Chung, Hyung-Soo; Kameno, Seiji; Roh, Duk-Gyoo; Umemoto, Tomofumi; Kim, Kwang-Dong; Asada, Keiichi; Han, Seog-Tae; Mochizuki, Nanako; Cho, Se-Hyung; Sawada-Satoh, Satoko; Kim, Hyun-Goo; Bushimata, Takeshi; Minh, Young Chol; Miyaji, Takeshi; Kuno, Nario; Mikoshiba, Hiroshi; Sunada, Kazuyoshi; Inoue, Makoto; Kobayashi, Hideyuki

2004-06-01

We have made VLBI observations at 86GHz using a 1000-km baseline between Korea and Japan with successful detections of SiO v = 1, J = 2 - 1 maser emissions from VY CMa and Orion KL in 2001 June. This was the first VLBI result for this baseline and the first astronomical VLBI observation for the Korean telescope. Since then, we observed SiO v = 1, J = 2 - 1 maser emission in VY CMa in 2002 January and 2003 February and derived the distributions of the maser emissions. Our results show that the maser emissions extend over 2-4 stellar radii, and were within the inner radius of the dust shell. We observed other SiO maser sources and continuum sources, and 86-GHz continuum emissions were detected from three continuum sources. It was verified that this baseline has a performance comparable to the most sensitive baseline in the VLBA and the CMVA, and is capable of investigating the proper motions of maser features in circumstellar envelopes using monitoring observations.

The Boulder magnetic observatory

USGS Publications Warehouse

Love, Jeffrey J.; Finn, Carol A.; Pedrie, Kolby L.; Blum, Cletus C.

2015-08-14

The Boulder magnetic observatory has, since 1963, been operated by the Geomagnetism Program of the U.S. Geological Survey in accordance with Bureau and national priorities. Data from the observatory are used for a wide variety of scientific purposes, both pure and applied. The observatory also supports developmental projects within the Geomagnetism Program and collaborative projects with allied geophysical agencies.

International time and frequency comparison using very long baseline interferometer

NASA Astrophysics Data System (ADS)

Hama, Shinichi; Yoshino, Taizoh; Kiuchi, Hitoshi; Morikawa, Takao; Sato, Tokuo

VLBI time comparison experiments using the Kashima station of the Radio Research Laboratory and the Richmond and Maryland Point stations of the U.S. Naval Observatory have been performed since April 1985. A precision of 0.2 ns for the clock offset and 0.2 ps/s for the clock rate have been achieved, and good agreement has been found with GPS results for clock offset. Much higher precision has been found for VLBI time and frequency comparison than that possible with conventional portable clock or Loran-C methods.

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

NASA Technical Reports Server (NTRS)

Diehl, R.; Bennett, K.; Collmar, W.; Connors, A.; Denherder, J. W.; Hermsen, W.; Lichti, G. G.; Lockwood, J. A.; Macri, J.; Mcconnell, M.

1992-01-01

The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied.

Australian radio observations of SN1987A - A progress report

NASA Technical Reports Server (NTRS)

Reynolds, John E.; Jauncey, David L.; Preston, Robert A.; Mutel, Robert L.; Livermore, R. W.

1987-01-01

Regular monitoring of SN 1987A in the radio spectrum is being conducted at a number of Australian observatories. Although no emission is detectable at present, a VLBI network has been established to map a possible major outburst at high resolution.

"Route of astronomical observatories'' project: classical observatories from the Renaissance to the rise of astrophysics

NASA Astrophysics Data System (ADS)

Wolfschmidt, Gudrun

2015-08-01

Observatories offer a good possibility for serial transnational applications. A well-known example for a thematic programme is the Struve arc, already recognized as World Heritage.I will discuss what has been achieved and show examples, like the route of astronomical observatories or the transition from classical astronomy to modern astrophysics (La Plata, Hamburg, Nice, etc.), visible in the architecture, the choice of instruments, and the arrangement of the observatory buildings in an astronomy park. This corresponds to the main categories according to which the ``outstanding universal value'' (UNESCO criteria ii, iv and vi) of the observatories have been evaluated: historic, scientific, and aesthetic. This proposal is based on the criteria of a comparability of the observatories in terms of the urbanistic complex and the architecture, the scientific orientation, equipment of instruments, authenticity and integrity of the preserved state, as well as in terms of historic scientific relations and scientific contributions.Apart from these serial transnational applications one can also choose other groups like baroque or neo-classical observatories, solar physics observatories or a group of observatories equipped with the same kind of instruments and made by the same famous firm. I will also discuss why the implementation of the Astronomy and World Heritage Initiative is difficult and why there are problems to nominate observatories for election in the national Tentative Lists

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.

The Virtual Observatory: I

NASA Astrophysics Data System (ADS)

Hanisch, R. J.

2014-11-01

The concept of the Virtual Observatory arose more-or-less simultaneously in the United States and Europe circa 2000. Ten pages of Astronomy and Astrophysics in the New Millennium: Panel Reports (National Academy Press, Washington, 2001), that is, the detailed recommendations of the Panel on Theory, Computation, and Data Exploration of the 2000 Decadal Survey in Astronomy, are dedicated to describing the motivation for, scientific value of, and major components required in implementing the National Virtual Observatory. European initiatives included the Astrophysical Virtual Observatory at the European Southern Observatory, the AstroGrid project in the United Kingdom, and the Euro-VO (sponsored by the European Union). Organizational/conceptual meetings were held in the US at the California Institute of Technology (Virtual Observatories of the Future, June 13-16, 2000) and at ESO Headquarters in Garching, Germany (Mining the Sky, July 31-August 4, 2000; Toward an International Virtual Observatory, June 10-14, 2002). The nascent US, UK, and European VO projects formed the International Virtual Observatory Alliance (IVOA) at the June 2002 meeting in Garching, with yours truly as the first chair. The IVOA has grown to a membership of twenty-one national projects and programs on six continents, and has developed a broad suite of data access protocols and standards that have been widely implemented. Astronomers can now discover, access, and compare data from hundreds of telescopes and facilities, hosted at hundreds of organizations worldwide, stored in thousands of databases, all with a single query.

Creating Griffith Observatory

NASA Astrophysics Data System (ADS)

Cook, Anthony

2013-01-01

Griffith Observatory has been the iconic symbol of the sky for southern California since it began its public mission on May 15, 1935. While the Observatory is widely known as being the gift of Col. Griffith J. Griffith (1850-1919), the story of how Griffith’s gift became reality involves many of the people better known for other contributions that made Los Angeles area an important center of astrophysics in the 20th century. Griffith began drawing up his plans for an observatory and science museum for the people of Los Angeles after looking at Saturn through the newly completed 60-inch reflector on Mt. Wilson. He realized the social impact that viewing the heavens could have if made freely available, and discussing the idea of a public observatory with Mt. Wilson Observatory’s founder, George Ellery Hale, and Director, Walter Adams. This resulted, in 1916, in a will specifying many of the features of Griffith Observatory, and establishing a committee managed trust fund to build it. Astronomy popularizer Mars Baumgardt convinced the committee at the Zeiss Planetarium projector would be appropriate for Griffith’s project after the planetarium was introduced in Germany in 1923. In 1930, the trust committee judged funds to be sufficient to start work on creating Griffith Observatory, and letters from the Committee requesting help in realizing the project were sent to Hale, Adams, Robert Millikan, and other area experts then engaged in creating the 200-inch telescope eventually destined for Palomar Mountain. A Scientific Advisory Committee, headed by Millikan, recommended that Caltech Physicist Edward Kurth be put in charge of building and exhibit design. Kurth, in turn, sought help from artist Russell Porter. The architecture firm of John C. Austin and Fredrick Ashley was selected to design the project, and they adopted the designs of Porter and Kurth. Philip Fox of the Adler Planetarium was enlisted to manage the completion of the Observatory and become its

Current Technology Development Efforts on the International X-Ray Observatory

NASA Technical Reports Server (NTRS)

Robinson, David

2011-01-01

The International X-ray Observatory (IXO) is a collaboration between NASA, ESA, and JAXA which is under study for launch in 2021. IXO will be a large 6600 kilogram Great Observatory-class mission which will build upon the legacies of the Chandra and XMM-Newton X-ray observatories. There is an extensive ongoing effort to raise the technology readiness level of the X-ray mirror from TRL 3 to TRL 6 in the next decade. Improvements have recently been made in the area of positioning and bonding mirrors on the nanometer scale and developing metals and composites with a matching coefficient of thermal expansion to the glass X-ray mirrors. On the mission systems side, the NASA reference design has been through a preliminary coupled loads analysis and a STOP analysis of the flight mirror assembly has been initiated. An impact study was performed comparing launching IXO on an Ariane 5 or a U.S. EELV. This paper will provide a snapshot of NASA's current observatory configuration and summarize the progress of these various technology and design efforts.

High Energy Astronomy Observatory (HEAO)

NASA Image and Video Library

1978-01-01

Managed by the Marshall Space Flight Center and built by TRW, the second High Energy Astronomy Observatory was launched November 13, 1978. The observatory carried the largest X-ray telescope ever built and was renamed the Einstein Observatory after achieving orbit.

The Little Thompson Observatory

NASA Astrophysics Data System (ADS)

Schweitzer, A.; VanLew, K.; Melsheimer, T.; Sackett, C.

2000-12-01

The Little Thompson Observatory is the second member of the Telescopes in Education (TIE) project. The observatory is located on the grounds of Berthoud High School in northern Colorado. The telescope is operational over the Internet, and we are now debugging the software to enable schools to control the telescope from classroom computers and take images. Local schools and youth organizations have prioritized access to the telescope, and there are monthly opportunities for public viewing. In the future, the telescope will be open after midnight to world-wide use by schools following the model of the first TIE observatory, the 24" telescope on Mt. Wilson. The observatory grew out of grassroots support from the local community surrounding Berthoud, Colorado, a town of 3,500 residents. TIE has provided the observatory with a Tinsley 18" Cassegrain telescope on a 10-year loan. The facility has been built with tremendous support from volunteers and the local school district. With funding from an IDEAS grant, we have completed the first teacher training workshops to allow K-12 schools in northern Colorado to make use of the Little Thompson Observatory, including remote observing from classrooms. The workshops were accredited by the school district, and received very favorable reviews.

The Penllergare Observatory

NASA Astrophysics Data System (ADS)

Birks, J. L.

2005-12-01

This rather picturesque and historically important Victorian observatory was built by the wealthy John Dillwyn Llewelyn near to his mansion, some four miles north-west of Swansea, Wales. He had many scientific interests, in addition to astronomy, and was a notable pioneer of photography in Wales. Together with his eldest daughter, Thereza, (who married the grandson of the fifth Astronomer Royal, Nevil Maskelyne), he took some early photographs of the Moon from this site. This paper describes the construction of the observatory, and some of those primarily involved with it. Despite its having undergone restoration work in 1982, the state of the observatory is again the cause for much concern.

Comprehension and retrieval of failure cases in airborne observatories

NASA Technical Reports Server (NTRS)

Alvarado, Sergio J.; Mock, Kenrick J.

1995-01-01

This paper describes research dealing with the computational problem of analyzing and repairing failures of electronic and mechanical systems of telescopes in NASA's airborne observatories, such as KAO (Kuiper Airborne Observatory) and SOFIA (Stratospheric Observatory for Infrared Astronomy). The research has resulted in the development of an experimental system that acquires knowledge of failure analysis from input text, and answers questions regarding failure detection and correction. The system's design builds upon previous work on text comprehension and question answering, including: knowledge representation for conceptual analysis of failure descriptions, strategies for mapping natural language into conceptual representations, case-based reasoning strategies for memory organization and indexing, and strategies for memory search and retrieval. These techniques have been combined into a model that accounts for: (a) how to build a knowledge base of system failures and repair procedures from descriptions that appear in telescope-operators' logbooks and FMEA (failure modes and effects analysis) manuals; and (b) how to use that knowledge base to search and retrieve answers to questions about causes and effects of failures, as well as diagnosis and repair procedures. This model has been implemented in FANSYS (Failure ANalysis SYStem), a prototype text comprehension and question answering program for failure analysis.

Comprehension and retrieval of failure cases in airborne observatories

NASA Astrophysics Data System (ADS)

Alvarado, Sergio J.; Mock, Kenrick J.

1995-05-01

This paper describes research dealing with the computational problem of analyzing and repairing failures of electronic and mechanical systems of telescopes in NASA's airborne observatories, such as KAO (Kuiper Airborne Observatory) and SOFIA (Stratospheric Observatory for Infrared Astronomy). The research has resulted in the development of an experimental system that acquires knowledge of failure analysis from input text, and answers questions regarding failure detection and correction. The system's design builds upon previous work on text comprehension and question answering, including: knowledge representation for conceptual analysis of failure descriptions, strategies for mapping natural language into conceptual representations, case-based reasoning strategies for memory organization and indexing, and strategies for memory search and retrieval. These techniques have been combined into a model that accounts for: (a) how to build a knowledge base of system failures and repair procedures from descriptions that appear in telescope-operators' logbooks and FMEA (failure modes and effects analysis) manuals; and (b) how to use that knowledge base to search and retrieve answers to questions about causes and effects of failures, as well as diagnosis and repair procedures. This model has been implemented in FANSYS (Failure ANalysis SYStem), a prototype text comprehension and question answering program for failure analysis.

Ancient "Observatories" - A Relevant Concept?

NASA Astrophysics Data System (ADS)

Belmonte, Juan Antonio

It is quite common, when reading popular books on astronomy, to see a place referred to as "the oldest observatory in the world". In addition, numerous books on archaeoastronomy, of various levels of quality, frequently refer to the existence of "prehistoric" or "ancient" observatories when describing or citing monuments that were certainly not built with the primary purpose of observing the skies. Internet sources are also guilty of this practice. In this chapter, the different meanings of the word observatory will be analyzed, looking at how their significances can be easily confused or even interchanged. The proclaimed "ancient observatories" are a typical result of this situation. Finally, the relevance of the concept of the ancient observatory will be evaluated.

The Virtual Solar Observatory and the Heliophysics Meta-Virtual Observatory

NASA Technical Reports Server (NTRS)

Gurman, Joseph B.

2007-01-01

The Virtual Solar Observatory (VSO) is now able to search for solar data ranging from the radio to gamma rays, obtained from space and groundbased observatories, from 26 sources at 12 data providers, and from 1915 to the present. The solar physics community can use a Web interface or an Application Programming Interface (API) that allows integrating VSO searches into other software, including other Web services. Over the next few years, this integration will be especially obvious as the NASA Heliophysics division sponsors the development of a heliophysics-wide virtual observatory (VO), based on existing VO's in heliospheric, magnetospheric, and ionospheric physics as well as the VSO. We examine some of the challenges and potential of such a "meta-VO."

On the Modeling of the Residual Effects of the Clock Behavior and the Atmosphere Effects in the Analysis of VLBI Data

NASA Astrophysics Data System (ADS)

Bo, Zhang; Li, Jin-Ling; Wang, Guan-Gli

2002-01-01

We checked the dependence of the estimation of parameters on the choice of piecewise interval in the continuous piecewise linear modeling of the residual clock and atmosphere effects by single analysis of 27 VLBI experiments involving Shanghai station (Seshan 25m). The following are tentatively shown: (1) Different choices of the piecewise interval lead to differences in the estimation of station coordinates and in the weighted root mean squares ( wrms ) of the delay residuals, which can be of the order of centimeters or dozens of picoseconds respectively. So the choice of piecewise interval should not be arbitrary . (2) The piecewise interval should not be too long, otherwise the short - term variations in the residual clock and atmospheric effects can not be properly modeled. While in order to maintain enough degrees of freedom in parameter estimation, the interval can not be too short, otherwise the normal equation may become near or solely singular and the noises can not be constrained as well. Therefore the choice of the interval should be within some reasonable range. (3) Since the conditions of clock and atmosphere are different from experiment to experiment and from station to station, the reasonable range of the piecewise interval should be tested and chosen separately for each experiment as well as for each station by real data analysis. This is really arduous work in routine data analysis. (4) Generally speaking, with the default interval for clock as 60min, the reasonable range of piecewise interval for residual atmospheric effect modeling is between 10min to 40min, while with the default interval for atmosphere as 20min, that for residual clock behavior is between 20min to 100min.

NASA's Great Observatories: Paper Model.

ERIC Educational Resources Information Center

National Aeronautics and Space Administration, Washington, DC.

This educational brief discusses observatory stations built by the National Aeronautics and Space Administration (NASA) for looking at the universe. This activity for grades 5-12 has students build paper models of the observatories and study their history, features, and functions. Templates for the observatories are included. (MVL)

Everyday astronomy @ Sydney Observatory

NASA Astrophysics Data System (ADS)

Parello, S. L.

2008-06-01

Catering to a broad range of audiences, including many non-English speaking visitors, Sydney Observatory offers everything from school programmes to public sessions, day care activities to night observing, personal interactions to web-based outreach. With a history of nearly 150 years of watching the heavens, Sydney Observatory is now engaged in sharing the wonder with everybody in traditional and innovative ways. Along with time-honoured tours of the sky through two main telescopes, as well as a small planetarium, Sydney Observatory also boasts a 3D theatre, and offers programmes 363 days a year - rain or shine, day and night. Additionally, our website neversleeps, with a blog, YouTube videos, and night sky watching podcasts. And for good measure, a sprinkling of special events such as the incomparable Festival of the Stars, for which most of northern Sydney turns out their lights. Sydney Observatory is the oldest working observatory in Australia, and we're thrilled to be looking forward to our 150th Anniversary next year in anticipation of the International Year of Astronomy immediately thereafter.

Stratospheric Observatory for Infrared Astronomy

NASA Astrophysics Data System (ADS)

Hamidouche, M.; Young, E.; Marcum, P.; Krabbe, A.

2010-12-01

We present one of the new generations of observatories, the Stratospheric Observatory For Infrared Astronomy (SOFIA). This is an airborne observatory consisting of a 2.7-m telescope mounted on a modified Boeing B747-SP airplane. Flying at an up to 45,000 ft (14 km) altitude, SOFIA will observe above more than 99 percent of the Earth's atmospheric water vapor allowing observations in the normally obscured far-infrared. We outline the observatory capabilities and goals. The first-generation science instruments flying on board SOFIA and their main astronomical goals are also presented.

The Montsec Observatory and the Gaia science alerts

NASA Astrophysics Data System (ADS)

Carrasco, J. M.; Burgaz, U.; Vilardell, F.; Jordi, C.

2017-03-01

The continuous and reiterative scan of the whole sky performed by Gaia ESA's mission during its (at least) 5 years of mission allows to detect transient events (e.g., supernovae, microlensing events, cataclysmic variables, etc) almost in real time among the daily millions of observations. The pipeline in charge to discover these alerts does a quick look analysis of the daily data stream, identify those sources increasing their brightness with respect to previous Gaia observations and also analyse their spectrophotometry to decide if those sources are good candidates to be published as a Gaia Photometric Science Alerts. These events are publicly announced for follow-up observations (both photometric and spectroscopic are needed). Observatories around the world confirm, classify and study them in detail. Observations are put in common and analysed together in a common interface in order to get a single analysis as detailed and precise as possible. Our team in Barcelona contributes to this Gaia science alerts follow-up programme with the 0.8 m robotic telescope Joan Oró (TJO), at the Montsec Observatory (OAdM), located at Sant Esteve de la Sarga (Lleida, Spain) performing photometric observations to derive the lightcurves of the most interesting alerts accessible from the observatory. Until now we have contributed with about 4500 images in multicolour Johnson-Cousins passbands obtained with TJO for a total of 38 Gaia science alerts, becoming the third most contributing observatory in the programme. Here we summarise the procedure to select new targets to be observed by TJO, submit follow-up observations and we explain the analysis we did for some interesting obtained lightcurves.

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.

Effects of illumination functions on the computation of gravity-dependent signal path variation models in primary focus and Cassegrainian VLBI telescopes

NASA Astrophysics Data System (ADS)

Abbondanza, Claudio; Sarti, Pierguido

2010-08-01

This paper sets the rules for an optimal definition of precise signal path variation (SPV) models, revising and highlighting the deficiencies in the calculations adopted in previous studies and improving the computational approach. Hence, the linear coefficients that define the SPV model are rigorously determined. The equations that are presented depend on the dimensions and the focal lengths of the telescopes as well as on the feed illumination taper. They hold for any primary focus or Cassegrainian very long baseline interferometry (VLBI) telescope. Earlier investigations usually determined the SPV models assuming a uniform illumination of the telescope mirrors. We prove this hypothesis to be over-simplistic by comparing results derived adopting (a) uniform, (b) Gaussian and (c) binomial illumination functions. Numerical computations are developed for AZ-EL mount, 32 m Medicina and Noto (Italy) VLBI telescopes, these latter being the only telescopes which possess thorough information on gravity-dependent deformation patterns. Particularly, assuming a Gaussian illumination function, the SPV in primary focus over the elevation range [0°, 90°] is 10.1 and 7.2 mm, for Medicina and Noto, respectively. With uniform illumination function the maximal path variation for Medicina is 17.6 and 12.7 mm for Noto, thus highlighting the strong dependency on the choice of the illumination function. According to our findings, a revised SPV model is released for Medicina and a model for Noto is presented here for the first time. Currently, no other VLBI telescope possesses SPV models capable of correcting gravity-dependent observation biases.

VLBI-resolution radio-map algorithms: Performance analysis of different levels of data-sharing on multi-socket, multi-core architectures

NASA Astrophysics Data System (ADS)

Tabik, S.; Romero, L. F.; Mimica, P.; Plata, O.; Zapata, E. L.

2012-09-01

A broad area in astronomy focuses on simulating extragalactic objects based on Very Long Baseline Interferometry (VLBI) radio-maps. Several algorithms in this scope simulate what would be the observed radio-maps if emitted from a predefined extragalactic object. This work analyzes the performance and scaling of this kind of algorithms on multi-socket, multi-core architectures. In particular, we evaluate a sharing approach, a privatizing approach and a hybrid approach on systems with complex memory hierarchy that includes shared Last Level Cache (LLC). In addition, we investigate which manual processes can be systematized and then automated in future works. The experiments show that the data-privatizing model scales efficiently on medium scale multi-socket, multi-core systems (up to 48 cores) while regardless of algorithmic and scheduling optimizations, the sharing approach is unable to reach acceptable scalability on more than one socket. However, the hybrid model with a specific level of data-sharing provides the best scalability over all used multi-socket, multi-core systems.

Distributed Observatory Management

NASA Astrophysics Data System (ADS)

Godin, M. A.; Bellingham, J. G.

2006-12-01

A collection of tools for collaboratively managing a coastal ocean observatory have been developed and used in a multi-institutional, interdisciplinary field experiment. The Autonomous Ocean Sampling Network program created these tools to support the Adaptive Sampling and Prediction (ASAP) field experiment that occurred in Monterey Bay in the summer of 2006. ASAP involved the day-to-day participation of a large group of researchers located across North America. The goal of these investigators was to adapt an array of observational assets to optimize data collection and analysis. Achieving the goal required continual interaction, but the long duration of the observatory made sustained co-location of researchers difficult. The ASAP team needed a remote collaboration tool, the capability to add non-standard, interdisciplinary data sets to the overall data collection, and the ability to retrieve standardized data sets from the collection. Over the course of several months and "virtual experiments," the Ocean Observatory Portal (COOP) collaboration tool was created, along with tools for centralizing, cataloging, and converting data sets into common formats, and tools for generating automated plots of the common format data. Accumulating the data in a central location and converting the data to common formats allowed any team member to manipulate any data set quickly, without having to rely heavily on the expertise of data generators to read the data. The common data collection allowed for the development of a wide range of comparison plots and allowed team members to assimilate new data sources into derived outputs such as ocean models quickly. In addition to the standardized outputs, team members were able to produce their own specialized products and link to these through the collaborative portal, which made the experimental process more interdisciplinary and interactive. COOP was used to manage the ASAP vehicle program from its start in July 2006. New summaries were

Robust Ambiguity Estimation for an Automated Analysis of the Intensive Sessions

NASA Astrophysics Data System (ADS)

Kareinen, Niko; Hobiger, Thomas; Haas, Rüdiger

2016-12-01

Very Long Baseline Interferometry (VLBI) is a unique space-geodetic technique that can directly determine the Earth's phase of rotation, namely UT1. The daily estimates of the difference between UT1 and Coordinated Universal Time (UTC) are computed from one-hour long VLBI Intensive sessions. These sessions are essential for providing timely UT1 estimates for satellite navigation systems. To produce timely UT1 estimates, efforts have been made to completely automate the analysis of VLBI Intensive sessions. This requires automated processing of X- and S-band group delays. These data often contain an unknown number of integer ambiguities in the observed group delays. 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 minimization). We implement the robust L1-norm with an alternative estimation method in c5++. The implemented method is used to automatically estimate the ambiguities in VLBI Intensive sessions for the Kokee-Wettzell baseline. The results are compared to an analysis setup where the ambiguity estimation is computed using the L2-norm. Additionally, we investigate three alternative weighting strategies for the ambiguity estimation. The results show that in automated analysis the L1-norm resolves ambiguities better 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.

Studying the Light Pollution around Urban Observatories: Columbus State University’s WestRock Observatory

NASA Astrophysics Data System (ADS)

O'Keeffe, Brendon Andrew; Johnson, Michael

2017-01-01

Light pollution plays an ever increasing role in the operations of observatories across the world. This is especially true in urban environments like Columbus, GA, where Columbus State University’s WestRock Observatory is located. Light pollution’s effects on an observatory include high background levels, which results in a lower signal to noise ratio. Overall, this will limit what the telescope can detect, and therefore limit the capabilities of the observatory as a whole.Light pollution has been mapped in Columbus before using VIIRS DNB composites. However, this approach did not provide the detailed resolution required to narrow down the problem areas around the vicinity of the observatory. The purpose of this study is to assess the current state of light pollution surrounding the WestRock observatory by measuring and mapping the brightness of the sky due to light pollution using light meters and geographic information system (GIS) software.Compared to VIIRS data this study allows for an improved spatial resolution and a direct measurement of the sky background. This assessment will enable future studies to compare their results to the baseline established here, ensuring that any changes to the way the outdoors are illuminated and their effects can be accurately measured, and counterbalanced.

Permanent Monitoring of the Reference Point of the 20m Radio Telescope Wettzell

NASA Technical Reports Server (NTRS)

Neidhardt, Alexander; Losler, Michael; Eschelbach, Cornelia; Schenk, Andreas

2010-01-01

To achieve the goals of the VLBI2010 project and the Global Geodetic Observing System (GGOS), an automated monitoring of the reference points of the various geodetic space techniques, including Very Long Baseline Interferometry (VLBI), is desirable. The resulting permanent monitoring of the local-tie vectors at co-location stations is essential to obtain the sub-millimeter level in the combinations. For this reason a monitoring system was installed at the Geodetic Observatory Wettzell by the Geodetic Institute of the University of Karlsruhe (GIK) to observe the 20m VLBI radio telescope from May to August 2009. A specially developed software from GIK collected data from automated total station measurements, meteorological sensors, and sensors in the telescope monument (e.g., Invar cable data). A real-time visualization directly offered a live view of the measurements during the regular observation operations. Additional scintillometer measurements allowed refraction corrections during the post-processing. This project is one of the first feasibility studies aimed at determining significant deformations of the VLBI antenna due to, for instance, changes in temperature.

LAGO: The Latin American giant observatory

NASA Astrophysics Data System (ADS)

Sidelnik, Iván; Asorey, Hernán; LAGO Collaboration

2017-12-01

The Latin American Giant Observatory (LAGO) is an extended cosmic ray observatory composed of a network of water-Cherenkov detectors (WCD) spanning over different sites located at significantly different altitudes (from sea level up to more than 5000 m a.s.l.) and latitudes across Latin America, covering a wide range of geomagnetic rigidity cut-offs and atmospheric absorption/reaction levels. The LAGO WCD is simple and robust, and incorporates several integrated devices to allow time synchronization, autonomous operation, on board data analysis, as well as remote control and automated data transfer. This detection network is designed to make detailed measurements of the temporal evolution of the radiation flux coming from outer space at ground level. LAGO is mainly oriented to perform basic research in three areas: high energy phenomena, space weather and atmospheric radiation at ground level. It is an observatory designed, built and operated by the LAGO Collaboration, a non-centralized collaborative union of more than 30 institutions from ten countries. In this paper we describe the scientific and academic goals of the LAGO project - illustrating its present status with some recent results - and outline its future perspectives.

A comparative study of amplitude calibrations for the East Asia VLBI Network: A priori and template spectrum methods

NASA Astrophysics Data System (ADS)

Cho, Ilje; Jung, Taehyun; Zhao, Guang-Yao; Akiyama, Kazunori; Sawada-Satoh, Satoko; Kino, Motoki; Byun, Do-Young; Sohn, Bong Won; Shibata, Katsunori M.; Hirota, Tomoya; Niinuma, Kotaro; Yonekura, Yoshinori; Fujisawa, Kenta; Oyama, Tomoaki

2017-12-01

We present the results of a comparative study of amplitude calibrations for the East Asia VLBI Network (EAVN) at 22 and 43 GHz using two different methods of an "a priori" and a "template spectrum", particularly on lower declination sources. Using observational data sets of early EAVN observations, we investigated the elevation-dependence of the gain values at seven stations of the KaVA (KVN and VERA Array) and three additional telescopes in Japan (Takahagi 32 m, Yamaguchi 32 m, and Nobeyama 45 m). By comparing the independently obtained gain values based on these two methods, we found that the gain values from each method were consistent within 10% at elevations higher than 10°. We also found that the total flux densities of two images produced from the different amplitude calibrations were in agreement within 10% at both 22 and 43 GHz. By using the template spectrum method, furthermore, the additional radio telescopes can participate in KaVA (i.e., EAVN), giving a notable sensitivity increase. Therefore, our results will constrain the detailed conditions in order to measure the VLBI amplitude reliably using EAVN, and discuss the potential of possible expansion to telescopes comprising EAVN.

High Energy Astronomy Observatory (HEAO)

NASA Image and Video Library

1978-11-13

The launch of an Atlas/Centaur launch vehicle is shown in this photograph. The Atlas/Centaur, launched on November 13, 1978, carried the High Energy Astronomy Observatory (HEAO)-2 into the required orbit. The second observatory, the HEAO-2 (nicknamed the Einstein Observatory in honor of the centernial of the birth of Albert Einstein) carried the first telescope capable of producing actual photographs of x-ray objects.

Science Initiatives of the US Virtual Astronomical Observatory

NASA Astrophysics Data System (ADS)

Hanisch, R. J.

2012-09-01

The United States Virtual Astronomical Observatory program is the operational facility successor to the National Virtual Observatory development project. The primary goal of the US VAO is to build on the standards, protocols, and associated infrastructure developed by NVO and the International Virtual Observatory Alliance partners and to bring to fruition a suite of applications and web-based tools that greatly enhance the research productivity of professional astronomers. To this end, and guided by the advice of our Science Council (Fabbiano et al. 2011), we have focused on five science initiatives in the first two years of VAO operations: 1) scalable cross-comparisons between astronomical source catalogs, 2) dynamic spectral energy distribution construction, visualization, and model fitting, 3) integration and periodogram analysis of time series data from the Harvard Time Series Center and NASA Star and Exoplanet Database, 4) integration of VO data discovery and access tools into the IRAF data analysis environment, and 5) a web-based portal to VO data discovery, access, and display tools. We are also developing tools for data linking and semantic discovery, and have a plan for providing data mining and advanced statistical analysis resources for VAO users. Initial versions of these applications and web-based services are being released over the course of the summer and fall of 2011, with further updates and enhancements planned for throughout 2012 and beyond.

Hawaiian Volcano Observatory

USGS Publications Warehouse

Venezky, Dina Y.; Orr, Tim R.

2008-01-01

Lava from Kilauea volcano flowing through a forest in the Royal Gardens subdivision, Hawai'i, in February 2008. The Hawaiian Volcano Observatory (HVO) monitors the volcanoes of Hawai'i and is located within Hawaiian Volcanoes National Park. HVO is one of five USGS Volcano Hazards Program observatories that monitor U.S. volcanoes for science and public safety. Learn more about Kilauea and HVO at http://hvo.wr.usgs.gov.

Determination of tidal h Love number parameters in the diurnal band using an extensive VLBI data set

NASA Technical Reports Server (NTRS)

Mitrovica, J. X.; Davis, J. L.; Mathews, P. M.; Shapiro, I. I.

1994-01-01

We use over a decade of geodetic Very Long Baseline Interferometry (VLBI) data to estimate parameters in a resonance expansion of the frequency dependence of the tidal h(sub 2) Love number within the diurnal band. The resonance is associated with the retrograde free core nutation (RFCN). We obtain a value for the real part of the resonance strength of (-0.27 +/- 0.03) x 10(exp -3); a value of -0.19 x 10(exp -3) is predicted theoretically. Uncertainties in the VLBI estimates of the body tide radial displacement amplitudes are approximately 0.5 mm (1.1 mm for the K1 frequency), but they do not yield sufficiently small Love number uncertainties for placing useful constraints on the frequency of the RFCN, given the much smaller uncertainties obtained from independent analyses using nutation or gravimetric data. We also consider the imaginary part of the tidal h(sub 2) Love number. The estimated imaginary part of the resonance strength is (0.00 +/- 0.02) x 10(exp -3). The estimated imaginary part of the nonresonant component of the Love number implies a phase angle in the diurnal tidal response of the Earth of 0.7 deg +/- 0.5 deg (lag).

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

Astronomical virtual observatory and the place and role of Bulgarian one

NASA Astrophysics Data System (ADS)

Petrov, Georgi; Dechev, Momchil; Slavcheva-Mihova, Luba; Duchlev, Peter; Mihov, Bojko; Kochev, Valentin; Bachev, Rumen

2009-07-01

Virtual observatory could be defined as a collection of integrated astronomical data archives and software tools that utilize computer networks to create an environment in which research can be conducted. Several countries have initiated national virtual observatory programs that combine existing databases from ground-based and orbiting observatories, scientific facility especially equipped to detect and record naturally occurring scientific phenomena. As a result, data from all the world's major observatories will be available to all users and to the public. This is significant not only because of the immense volume of astronomical data but also because the data on stars and galaxies has been compiled from observations in a variety of wavelengths-optical, radio, infrared, gamma ray, X-ray and more. In a virtual observatory environment, all of this data is integrated so that it can be synthesized and used in a given study. During the autumn of the 2001 (26.09.2001) six organizations from Europe put the establishment of the Astronomical Virtual Observatory (AVO)-ESO, ESA, Astrogrid, CDS, CNRS, Jodrell Bank (Dolensky et al., 2003). Its aims have been outlined as follows: - To provide comparative analysis of large sets of multiwavelength data; - To reuse data collected by a single source; - To provide uniform access to data; - To make data available to less-advantaged communities; - To be an educational tool. The Virtual observatory includes: - Tools that make it easy to locate and retrieve data from catalogues, archives, and databases worldwide; - Tools for data analysis, simulation, and visualization; - Tools to compare observations with results obtained from models, simulations and theory; - Interoperability: services that can be used regardless of the clients computing platform, operating system and software capabilities; - Access to data in near real-time, archived data and historical data; - Additional information - documentation, user-guides, reports

Observatory Improvements for SOFIA

NASA Technical Reports Server (NTRS)

Peralta, Robert A.; Jensen, Stephen C.

2012-01-01

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint project between NASA and Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), the German Space Agency. SOFIA is based in a Boeing 747 SP and flown in the stratosphere to observe infrared wavelengths unobservable from the ground. In 2007 Dryden Flight Research Center (DFRC) inherited and began work on improving the plane and its telescope. The improvements continue today with upgrading the plane and improving the telescope. The Observatory Verification and Validation (V&V) process is to ensure that the observatory is where the program says it is. The Telescope Status Display (TSD) will provide any information from the on board network to monitors that will display the requested information. In order to assess risks to the program, one must work through the various threats associate with that risk. Once all the risks are closed the program can work towards improving the observatory.

Iranian National Observatory

NASA Astrophysics Data System (ADS)

Khosroshahi, H. G.; Danesh, A.; Molaeinezhad, A.

2016-09-01

The Iranian National Observatory is under construction at an altitude of 3600m at Gargash summit 300km southern Tehran. The site selection was concluded in 2007 and the site monitoring activities have begun since then, which indicates a high quality of the site with a median seeing of 0.7 arcsec through the year. One of the major observing facilities of the observatory is a 3.4m Alt-Az Ritchey-Chretien optical telescope which is currently under design. This f/11 telescope will be equipped with high resolution medium-wide field imaging cameras as well as medium and high resolution spectrographs. In this review, I will give an overview of astronomy research and education in Iran. Then I will go through the past and present activities of the Iranian National Observatory project including the site quality, telescope specifications and instrument capabilities.

The role of geomagnetic observatory data during the Swarm mission

NASA Astrophysics Data System (ADS)

Ridley, Victoria; Macmillan, Susan; Beggan, Ciaran

2014-05-01

The scientific use of Swarm magnetic data and Swarm-derived products is greatly enhanced through combination with observatory data and indices. The strength of observatory data is their long-term accuracy, with great care being taken to ensure temperature control and correction, platform stability and magnetic cleanliness at each site. Observatory data are being distributed with Swarm data as an auxiliary product. We describe the preparation of the data set of ground observatory hourly mean values, including procedures to check and select observatory data spanning the modern magnetic survey satellite era. Existing collaborations, such as INTERMAGNET and the World Data Centres for Geomagnetism, are proving invaluable for this. We also discuss how observatory measurements are being used to ground-truth Swarm data as part of the Calibration/Validation effort. Recent efforts to improve the coverage and timeliness of observatory data have been encouraged and now over 60 INTERMAGNET observatories and several other high-quality observatories are providing close-to-definitive data within 3 months of measurement. During the Calibration/Validation period these data are gathered and homogenised on a regular basis by BGS. We then identify measurements collected during overhead passes of the Swarm satellites. For each pass, we remove an estimate of the main field from both the data collected at altitude and that collected on the ground. Both sets of data are then normalised relative to the data variance during all passes in the Calibration/Validation period. The absolute differences of the two sets of normalised data can be used as a metric of satellite data quality relative to observatory data quality. This can be examined by universal time, local time, disturbance level and geomagnetic latitude, for example. A preliminary study of CHAMP data, using definitive minute mean observatory data, has shown how this approach can provide a baseline for detecting abnormalities at all

International lunar observatory / power station: from Hawaii to the Moon

NASA Astrophysics Data System (ADS)

Durst, S.

Astronomy's great advantages from the Moon are well known - stable surface, diffuse atmosphere, long cool nights (14 days), low gravity, far side radio frequency silence. A large variety of astronomical instruments and observations are possible - radio, optical and infrared telescopes and interferometers; interferometry for ultra- violet to sub -millimeter wavelengths and for very long baselines, including Earth- Moon VLBI; X-ray, gamma-ray, cosmic ray and neutrino detection; very low frequency radio observation; and more. Unparalleled advantages of lunar observatories for SETI, as well as for local surveillance, Earth observation, and detection of Earth approaching objects add significant utility to lunar astronomy's superlatives. At least nine major conferences in the USA since 1984 and many elsewhere, as well as ILEWG, IAF, IAA, LEDA and other organizations' astronomy-from-the-Moon research indicate a lunar observatory / power station, robotic at first, will be one of the first mission elements for a permanent lunar base. An international lunar observatory will be a transcending enterprise, highly principled, indispensable, soundly and broadly based, and far- seeing. Via Astra - From Hawaii to the Moon: The astronomy and scie nce communities, national space agencies and aerospace consortia, commercial travel and tourist enterprises and those aspiring to advance humanity's best qualities, such as Aloha, will recognize Hawaii in the 21st century as a new major support area and pan- Pacific port of embarkation to space, the Moon and beyond. Astronomical conditions and facilities on Hawaii's Mauna Kea provide experience for construction and operation of observatories on the Moon. Remote and centrally isolated, with diffuse atmosphere, sub-zero temperature and limited working mobility, the Mauna Kea complex atop the 4,206 meter summit of the largest mountain on the planet hosts the greatest collection of large astronomical telescopes on Earth. Lunar, extraterrestrial

Automatic system of collection of parameters and control of receiving equipment of the radiotelescope of VLBI complex "Quasar "

NASA Astrophysics Data System (ADS)

Syrovoy, Sergey

At present the radiointerferometry with Very Long Bases (VLBI) is more and more globalized, turning into the world network of observation posts. So the inclusion of the developing Russian system "Quasar" into the world VLBI community has a great importance to us. The important role in the work of radiotelescope as a part of VLBI network belongs to a question of ensuring the optimal interaction of the its sub-systems, which can only be done by means of automation of the whole process of observation. The possibility of participation of RTF-32 in the international VLBI sessions observation is taken into account in the system development. These observations have the stable technology of experiments on the base Mark-IV Field System. In this paper the description, the structured and the functional schemes of the system of automatic collection of parameters and control of receiving complex of radiotelescope RTF-32 are given. This system is to solve the given problem. The most important tasks of the system being developed are the ensuring of distant checking and control of the following systems of the radiotelescope: 1. the receivers system, which consists of the five dual-channel radiometers 21-18 sm, 13 sm, 6 sm, 3.5 sm, 1.35 sm brands; 2. the radiotelescope pointing system; 3. the frequency-time synchronizing system, which consists of the hydrogen standard of frequency, the system of ultrahigh frequency oscillators and the generators of picosecond impulses; 4. the signal transformation system; 5. the signal registration system; 6. the system of measurement of electrical features of atmosphere; 7. the power supply system. The part of the automatic system, ensuring the distant checking and control of the radiotelescope pointing system both in the local mode and in the state of working under control the Field System computer, was put into operation and is functioning at this moment. Now the part of the automatic system ensuring the checking and control of receiving system

Astrometria diferencial de precision con VLBI el triangulo de Draco (y estudios de SN1993J)

NASA Astrophysics Data System (ADS)

Ros, E.

1997-11-01

The Very Long Baseline Interferometry (VLBI) technique provides unprecedented resolutions in astronomy. In this PhD we show progress in the study of high precision phase-delay differential astrometry through observations of the radio source triangle formed by the BL-Lac objects 1803+784 and 2007+777, and the QSO 1928+738, in the Northern constellation of Draco (the Dragon), from observations carried out on 20/21 November 1991 with an intercontinental interferometric array simultaneously at the frequencies of 2.3 and 8.4 GHz. We have determined the angular separations among the three radio sources with submilliarcsecond accuracy from a weighted least squares analysis of the differential phase delay from the three celestial bodies. Our present work introduces important advances with respect to previous astrometric studies, carried out over radio source pairs separated by smaller angular distances. We have consistently modeled the parameters involved in an astrometric VLBI observation, in order to reproduce the differential phase observed for radio sources separated by almost 7o on the sky. We have demonstrated the possibility of phase-connection over these angular distances at 8.4 GHz, even at an epoch of a maximum in the solar activity. After the phase-connection we have corrected the effects of the extended structure of the radio source and of the ionosphere. This last correction is one of the main technical achievements of this thesis: it is possible to remove the ionospheric contribution with independent measurements of the ionosphere total electron content obtained at Global Positioning Systems (GPS) sites the VLBI observing stations. The triangular geometry introduces constraints in parameter space that allow a better estimation of the angular separations among the radio sources. It is possible to test the consistency of the astrometric results through the Sky-Closure, defined as the circular sum of the angular separations of the three radio sources, determined

Spectroscopic analysis in the virtual observatory environment with SPLAT-VO

NASA Astrophysics Data System (ADS)

Škoda, P.; Draper, P. W.; Neves, M. C.; Andrešič, D.; Jenness, T.

2014-11-01

SPLAT-VO is a powerful graphical tool for displaying, comparing, modifying and analysing astronomical spectra, as well as searching and retrieving spectra from services around the world using Virtual Observatory (VO) protocols and services. The development of SPLAT-VO started in 1999, as part of the Starlink StarJava initiative, sometime before that of the VO, so initial support for the VO was necessarily added once VO standards and services became available. Further developments were supported by the Joint Astronomy Centre, Hawaii until 2009. Since end of 2011 development of SPLAT-VO has been continued by the German Astrophysical Virtual Observatory, and the Astronomical Institute of the Academy of Sciences of the Czech Republic. From this time several new features have been added, including support for the latest VO protocols, along with new visualization and spectra storing capabilities. This paper presents the history of SPLAT-VO, its capabilities, recent additions and future plans, as well as a discussion on the motivations and lessons learned up to now.

Observatory data and the Swarm mission

NASA Astrophysics Data System (ADS)

Macmillan, S.; Olsen, N.

2013-11-01

The ESA Swarm mission to identify and measure very accurately the different magnetic signals that arise in the Earth's core, mantle, crust, oceans, ionosphere and magnetosphere, which together form the magnetic field around the Earth, has increased interest in magnetic data collected on the surface of the Earth at observatories. The scientific use of Swarm data and Swarm-derived products is greatly enhanced by combination with observatory data and indices. As part of the Swarm Level-2 data activities plans are in place to distribute such ground-based data along with the Swarm data as auxiliary data products. We describe here the preparation of the data set of ground observatory hourly mean values, including procedures to check and select observatory data spanning the modern magnetic survey satellite era. We discuss other possible combined uses of satellite and observatory data, in particular those that may use higher cadence 1-second and 1-minute data from observatories.

A new estimator for VLBI baseline length repeatability

NASA Astrophysics Data System (ADS)

Titov, O.

2009-11-01

The goal of this paper is to introduce a more effective technique to approximate for the “repeatability-baseline length” relationship that is used to evaluate the quality of geodetic VLBI results. Traditionally, this relationship is approximated by a quadratic function of baseline length over all baselines. The new model incorporates the mean number of observed group delays of the reference radio sources (i.e. estimated as global parameters) used in the estimation of each baseline. It is shown that the new method provides a better approximation of the “repeatability-baseline length” relationship than the traditional model. Further development of the new approach comes down to modeling the repeatability as a function of two parameters: baseline length and baseline slewing rate. Within the framework of this new approach the station vertical and horizontal uncertainties can be treated as a function of baseline length. While the previous relationship indicated that the station vertical uncertainties are generally 4-5 times larger than the horizontal uncertainties, the vertical uncertainties as determined by the new method are only larger by a factor of 1.44 over all baseline lengths.

The Space Telescope Observatory

NASA Technical Reports Server (NTRS)

Bahcall, J. N.; Odell, C. R.

1979-01-01

A convenient guide to the expected characteristics of the Space Telescope Observatory for astronomers and physicists is presented. An attempt is made to provide enough detail so that a professional scientist, observer or theorist, can plan how the observatory may be used to further his observing programs or to test theoretical models.

Orbiting Carbon Observatory Briefing

NASA Image and Video Library

2009-01-29

Anna Michalak, an Orbiting Carbon Observatory science team member from the University of Michigan, Ann Arbor, speaks during a media briefing to discuss the upcoming Orbiting Carbon Observatory mission, the first NASA spacecraft dedicated to studying carbon dioxide, Thursday, Jan. 29, 2009, at NASA Headquarters in Washington. Photo Credit: (NASA/Paul E. Alers)

Virtual hydrology observatory: an immersive visualization of hydrology modeling

NASA Astrophysics Data System (ADS)

Su, Simon; Cruz-Neira, Carolina; Habib, Emad; Gerndt, Andreas

2009-02-01

The Virtual Hydrology Observatory will provide students with the ability to observe the integrated hydrology simulation with an instructional interface by using a desktop based or immersive virtual reality setup. It is the goal of the virtual hydrology observatory application to facilitate the introduction of field experience and observational skills into hydrology courses through innovative virtual techniques that mimic activities during actual field visits. The simulation part of the application is developed from the integrated atmospheric forecast model: Weather Research and Forecasting (WRF), and the hydrology model: Gridded Surface/Subsurface Hydrologic Analysis (GSSHA). Both the output from WRF and GSSHA models are then used to generate the final visualization components of the Virtual Hydrology Observatory. The various visualization data processing techniques provided by VTK are 2D Delaunay triangulation and data optimization. Once all the visualization components are generated, they are integrated into the simulation data using VRFlowVis and VR Juggler software toolkit. VR Juggler is used primarily to provide the Virtual Hydrology Observatory application with fully immersive and real time 3D interaction experience; while VRFlowVis provides the integration framework for the hydrologic simulation data, graphical objects and user interaction. A six-sided CAVETM like system is used to run the Virtual Hydrology Observatory to provide the students with a fully immersive experience.

NASA Awards Chandra X-Ray Observatory Follow-On Contract

NASA Astrophysics Data System (ADS)

2003-08-01

NASA has awarded a contract to the Smithsonian Astrophysical Observatory in Cambridge, Mass., to provide science and operational support for the Chandra X-ray Observatory, one of the world's most powerful tools to better understand the structure and evolution of the universe. The contract will have a period of performance from August 31, 2003, through July 31, 2010, with an estimated value of 373 million. It is a follow-on contract to the existing contract with Smithsonian Astrophysical Observatory that has provided science and operations support to the Observatory since its launch in July 1999. At launch the intended mission life was five years. As a result of Chandra's success, NASA extended the mission from five to 10 years. The value of the original contract was 289 million. The follow-on contract with the Smithsonian Astrophysical Observatory will continue through the 10-year mission. The contract type is cost reimbursement with no fee. The contract covers mission operations and data analysis, which includes the observatory operations, science data processing and the general and guaranteed time observer (astronomer) support. The observatory operations tasks include monitoring the health and status of the observatory and developing and up linking the observation sequences during Chandra's communication coverage periods. The science data processing tasks include the competitive selection, planning, and coordination of science observations with the general observers and processing and delivery of the resulting scientific data. There are approximately 200 to 250 observing proposals selected annually out of about 800 submitted, with a total amount of observing time of about 20 million seconds. Chandra has exceeded expectations of scientists, giving them unique insight into phenomena light years away, such as exotic celestial objects, matter falling into black holes, and stellar explosions. X-ray astronomy can only be performed from space because Earth's atmosphere

INTERMAGNET and magnetic observatories

USGS Publications Warehouse

Love, Jeffrey J.; Chulliat, Arnaud

2012-01-01

A magnetic observatory is a specially designed ground-based facility that supports time-series measurement of the Earth’s magnetic field. Observatory data record a superposition of time-dependent signals related to a fantastic diversity of physical processes in the Earth’s core, mantle, lithosphere, ocean, ionosphere, magnetosphere, and, even, the Sun and solar wind.

International VLBI Service for Geodesy and Astrometry. Delivering high-quality products and embarking on observations of the next generation

NASA Astrophysics Data System (ADS)

Nothnagel, A.; Artz, T.; Behrend, D.; Malkin, Z.

2017-07-01

The International VLBI Service for Geodesy and Astrometry (IVS) regularly produces high-quality Earth orientation parameters from observing sessions employing extensive networks or individual baselines. The master schedule is designed according to the telescope days committed by the stations and by the need for dense sampling of the Earth orientation parameters (EOP). In the pre-2011 era, the network constellations with their number of telescopes participating were limited by the playback and baseline capabilities of the hardware (Mark4) correlators. This limitation was overcome by the advent of software correlators, which can now accommodate many more playback units in a flexible configuration. In this paper, we describe the current operations of the IVS with special emphasis on the quality of the polar motion results since these are the only EOP components which can be validated against independent benchmarks. The polar motion results provided by the IVS have improved continuously over the years, now providing an agreement with IGS results at the level of 20-25 μas in a WRMS sense. At the end of the paper, an outlook is given for the realization of the VLBI Global Observing System.

Astronomical Archive at Tartu Observatory

NASA Astrophysics Data System (ADS)

Annuk, K.

2007-10-01

Archiving astronomical data is important task not only at large observatories but also at small observatories. Here we describe the astronomical archive at Tartu Observatory. The archive consists of old photographic plate images, photographic spectrograms, CCD direct--images and CCD spectroscopic data. The photographic plate digitizing project was started in 2005. An on-line database (based on MySQL) was created. The database includes CCD data as well photographic data. A PHP-MySQL interface was written for access to all data.

WFIRST Observatory Performance

NASA Technical Reports Server (NTRS)

Kruk, Jeffrey W.

2012-01-01

The WFIRST observatory will be a powerful and flexible wide-field near-infrared facility. The planned surveys will provide data applicable to an enormous variety of astrophysical science. This presentation will provide a description of the observatory and its performance characteristics. This will include a discussion of the point spread function, signal-to-noise budgets for representative observing scenarios and the corresponding limiting sensitivity. Emphasis will be given to providing prospective Guest Observers with information needed to begin thinking about new observing programs.

Archive interoperability in the Virtual Observatory

NASA Astrophysics Data System (ADS)

Genova, Françoise

2003-02-01

Main goals of Virtual Observatory projects are to build interoperability between astronomical on-line services, observatory archives, databases and results published in journals, and to develop tools permitting the best scientific usage from the very large data sets stored in observatory archives and produced by large surveys. The different Virtual Observatory projects collaborate to define common exchange standards, which are the key for a truly International Virtual Observatory: for instance their first common milestone has been a standard allowing exchange of tabular data, called VOTable. The Interoperability Work Area of the European Astrophysical Virtual Observatory project aims at networking European archives, by building a prototype using the CDS VizieR and Aladin tools, and at defining basic rules to help archive providers in interoperability implementation. The prototype is accessible for scientific usage, to get user feedback (and science results!) at an early stage of the project. ISO archive participates very actively to this endeavour, and more generally to information networking. The on-going inclusion of the ISO log in SIMBAD will allow higher level links for users.

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 S sa with 1.07 ± 0.19 mm.

The extension of the parametrization of the radio source coordinates in geodetic VLBI and its impact on the time series analysis

NASA Astrophysics Data System (ADS)

Karbon, Maria; Heinkelmann, Robert; Mora-Diaz, Julian; Xu, Minghui; Nilsson, Tobias; Schuh, Harald

2017-07-01

The radio sources within the most recent celestial reference frame (CRF) catalog ICRF2 are represented by a single, time-invariant coordinate pair. The datum sources were chosen mainly according to certain statistical properties of their position time series. Yet, such statistics are not applicable unconditionally, and also ambiguous. However, ignoring systematics in the source positions of the datum sources inevitably leads to a degradation of the quality of the frame and, therefore, also of the derived quantities such as the Earth orientation parameters. One possible approach to overcome these deficiencies is to extend the parametrization of the source positions, similarly to what is done for the station positions. We decided to use the multivariate adaptive regression splines algorithm to parametrize the source coordinates. It allows a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. The algorithm finds the ideal knot positions for the splines and, thus, the best number of polynomial pieces to fit the data autonomously. With that we can correct the ICRF2 a priori coordinates for our analysis and eliminate the systematics in the position estimates. This allows us to introduce also special handling sources into the datum definition, leading to on average 30 % more sources in the datum. We find that not only the CPO can be improved by more than 10 % due to the improved geometry, but also the station positions, especially in the early years of VLBI, can benefit greatly.

Seeing Double Old and New: Observations and Lightcurve Analysis at the Palmer Divide Observatory of Six Binary Asteroids

NASA Astrophysics Data System (ADS)

Warner, Brian D.

2013-04-01

Results of the analysis of lightcurves of six binary asteroids obtained at the Palmer Divide Observatory are reported. Of the six, three were previously known to be binary: 9069 Hovland, (26471) 2000 AS152, and 1994 XD. The remaining three are new confirmed or probable binary discoveries made at PDO: 2047 Smetana, (5646) 1990 TR, and (52316) 1992 BD.

Onsala Space Observatory: IVS Network Station

NASA Technical Reports Server (NTRS)

Haas, Ruediger; Elgered, Gunnar; Loefgren, Johan; Ning, Tong; Scherneck, Hans-Georg

2013-01-01

During 2012 we participated in 40 IVS sessions. As in the previous four years, we used the majority of the sessions that involved both Onsala and Tsukuba to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. We observed one four-station ultra-rapid EOP session together with Tsukuba, Hobart, and HartRAO. We also observed the RadioAstron satellite and several GLONASS satellites using the Onsala 25-m telescope. The highlight in 2012 was that our proposal to the Knut and Alice Wallenberg Foundation to establish a twin-telescope system at Onsala in accordance with the VLBI2010 recommendations was accepted.

Long-term mass variations from SLR, VLBI and GPS data

NASA Astrophysics Data System (ADS)

Luceri, Vincenza; Sciarretta, Cecilia; Bianco, Giuseppe

2013-04-01

The second-degree geopotential coefficients reflect the behaviour of the Earth's inertia tensor of order 2 which describes the main mass variations of our planet impacting polar motion and length of day (EOP). SLR, VLBI and GPS allow the estimation of those variations, either directly in the case of SLR through its dynamics, and indirectly, for all the three geodetic techniques, by deriving excitation functions from the EOP estimations. The geodetic estimates include the influence of the Earth's atmosphere and oceans, both from their mass and motion components, which can be modelled using the atmospheric and oceanic angular momenta variations. The different C21, S21 and C20 geodetic time series are compared in order to evaluate their coherence and their response to the mass variations after the removal of the motion terms. Moreover, the residual signal contents of the geodetic values, deprived by the atmospheric and oceanic mass and motion components, will be investigated.

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.

The Virtual Astronomical Observatory: Re-engineering access to astronomical data

NASA Astrophysics Data System (ADS)

Hanisch, R. J.; Berriman, G. B.; Lazio, T. J. W.; Emery Bunn, S.; Evans, J.; McGlynn, T. A.; Plante, R.

2015-06-01

The US Virtual Astronomical Observatory was a software infrastructure and development project designed both to begin the establishment of an operational Virtual Observatory (VO) and to provide the US coordination with the international VO effort. The concept of the VO is to provide the means by which an astronomer is able to discover, access, and process data seamlessly, regardless of its physical location. This paper describes the origins of the VAO, including the predecessor efforts within the US National Virtual Observatory, and summarizes its main accomplishments. These accomplishments include the development of both scripting toolkits that allow scientists to incorporate VO data directly into their reduction and analysis environments and high-level science applications for data discovery, integration, analysis, and catalog cross-comparison. Working with the international community, and based on the experience from the software development, the VAO was a major contributor to international standards within the International Virtual Observatory Alliance. The VAO also demonstrated how an operational virtual observatory could be deployed, providing a robust operational environment in which VO services worldwide were routinely checked for aliveness and compliance with international standards. Finally, the VAO engaged in community outreach, developing a comprehensive web site with on-line tutorials, announcements, links to both US and internationally developed tools and services, and exhibits and hands-on training at annual meetings of the American Astronomical Society and through summer schools and community days. All digital products of the VAO Project, including software, documentation, and tutorials, are stored in a repository for community access. The enduring legacy of the VAO is an increasing expectation that new telescopes and facilities incorporate VO capabilities during the design of their data management systems.

The Pearson-Readhead Survey of Compact Extragalactic Radio Sources from Space. I. The Images

NASA Astrophysics Data System (ADS)

Lister, M. L.; Tingay, S. J.; Murphy, D. W.; Piner, B. G.; Jones, D. L.; Preston, R. A.

2001-06-01

We present images from a space-VLBI survey using the facilities of the VLBI Space Observatory Programme (VSOP), drawing our sample from the well-studied Pearson-Readhead survey of extragalactic radio sources. Our survey has taken advantage of long space-VLBI baselines and large arrays of ground antennas, such as the Very Long Baseline Array and European VLBI Network, to obtain high-resolution images of 27 active galactic nuclei and to measure the core brightness temperatures of these sources more accurately than is possible from the ground. A detailed analysis of the source properties is given in accompanying papers. We have also performed an extensive series of simulations to investigate the errors in VSOP images caused by the relatively large holes in the (u,v)-plane when sources are observed near the orbit normal direction. We find that while the nominal dynamic range (defined as the ratio of map peak to off-source error) often exceeds 1000:1, the true dynamic range (map peak to on-source error) is only about 30:1 for relatively complex core-jet sources. For sources dominated by a strong point source, this value rises to approximately 100:1. We find the true dynamic range to be a relatively weak function of the difference in position angle (P.A.) between the jet P.A. and u-v coverage major axis P.A. For regions with low signal-to-noise ratios, typically located down the jet away from the core, large errors can occur, causing spurious features in VSOP images that should be interpreted with caution.

Sofia Observatory Performance and Characterization

NASA Technical Reports Server (NTRS)

Temi, Pasquale; Miller, Walter; Dunham, Edward; McLean, Ian; Wolf, Jurgen; Becklin, Eric; Bida, Tom; Brewster, Rick; Casey, Sean; Collins, Peter;

In Brief: Deep-sea observatory

NASA Astrophysics Data System (ADS)

Showstack, Randy

2008-11-01

The first deep-sea ocean observatory offshore of the continental United States has begun operating in the waters off central California. The remotely operated Monterey Accelerated Research System (MARS) will allow scientists to monitor the deep sea continuously. Among the first devices to be hooked up to the observatory are instruments to monitor earthquakes, videotape deep-sea animals, and study the effects of acidification on seafloor animals. ``Some day we may look back at the first packets of data streaming in from the MARS observatory as the equivalent of those first words spoken by Alexander Graham Bell: `Watson, come here, I need you!','' commented Marcia McNutt, president and CEO of the Monterey Bay Aquarium Research Institute, which coordinated construction of the observatory. For more information, see http://www.mbari.org/news/news_releases/2008/mars-live/mars-live.html.

An astronomical observatory for Peru

NASA Astrophysics Data System (ADS)

del Mar, Juan Quintanilla; Sicardy, Bruno; Giraldo, Víctor Ayma; Callo, Víctor Raúl Aguilar

2011-06-01

Peru and France are to conclude an agreement to provide Peru with an astronomical observatory equipped with a 60-cm diameter telescope. The principal aims of this project are to establish and develop research and teaching in astronomy. Since 2004, a team of researchers from Paris Observatory has been working with the University of Cusco (UNSAAC) on the educational, technical and financial aspects of implementing this venture. During an international astronomy conference in Cusco in July 2009, the foundation stone of the future Peruvian Observatory was laid at the top of Pachatusan Mountain. UNSAAC, represented by its Rector, together with the town of Oropesa and the Cusco regional authority, undertook to make the sum of 300,000€ available to the project. An agreement between Paris Observatory and UNSAAC now enables Peruvian students to study astronomy through online teaching.

Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode

NASA Astrophysics Data System (ADS)

Egron, E.; Pellizzoni, A.; Giroletti, M.; Righini, S.; Stagni, M.; Orlati, A.; Migoni, C.; Melis, A.; Concu, R.; Barbas, L.; Buttaccio, S.; Cassaro, P.; De Vicente, P.; Gawroński, M. P.; Lindqvist, M.; Maccaferri, G.; Stanghellini, C.; Wolak, P.; Yang, J.; Navarrini, A.; Loru, S.; Pilia, M.; Bachetti, M.; Iacolina, M. N.; Buttu, M.; Corbel, S.; Rodriguez, J.; Markoff, S.; Wilms, J.; Pottschmidt, K.; Cadolle Bel, M.; Kalemci, E.; Belloni, T.; Grinberg, V.; Marongiu, M.; Vargiu, G. P.; Trois, A.

2017-11-01

In 2016 September, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 d with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on an hourly scale, covering six frequency ranges from 1.5 to 25.6 GHz. The radio emission reached a maximum of 13.2 ± 0.7 Jy at 7.2 GHz and 10 ± 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: α steepened from 0.3 to 0.6 (with Sν ∝ ν-α) within 5 h. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), very long baseline interferometry (VLBI) observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2 h duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core 10 d before the onset of the giant flare. From the latest VLBI observation we infer that 4 d after the flare peak the jet emission was extended over 30 mas.

The Most Remote Point Method for the Site Selection of the Future VGOS Network

NASA Astrophysics Data System (ADS)

Hase, Hayo; Pedreros, Felipe

2014-12-01

The VLBI Global Observing System (VGOS) will be part of the Global Geodetic Observing System (GGOS) and will consist of globally well distributed geodetic observatories. The most remote point (MRP) method is used to identify gaps in the network geometry. In each iteration step the identified most remote points are assumed to become new observatory sites improving the homogeneity of the global network. New locations for VGOS observatories have been found in La Plata, Tahiti, O'Higgins, Galapagos, Colombo, and Syowa. This contribution is an excerpt of a work published in Journal of Geodesy (DOI: 10.1007/s00190-014-0731-y) covering the site selection for the GGOS.%

New Opportunities for Cabled Ocean Observatories

NASA Astrophysics Data System (ADS)

Duennebier, F. K.; Butler, R.; Karl, D. M.; Roger, L. B.

2002-12-01

With the decommissioning of transoceanic telecommunications cables as they become obsolete or uneconomical, there is an opportunity to use these systems for ocean observatories. Two coaxial cables, TPC-1 and HAW-2 are currently in use for observatories, and another, ANZCAN, is scheduled to be used beginning in 2004 to provide a cabled observatory at Station ALOHA, north of Oahu. The ALOHA observatory will provide several Mb/s data rates and about 1 kW of power to experiments installed at Station ALOHA. Sensors can be installed either by wet mateable connection to a junction box on the ocean floor using an ROV, or by acoustic data link to the system. In either case real-time data will be provided to users over the Internet. A Small Experiment Module, to be first installed at the Hawaii-2 Observatory, and later at Station ALOHA, will provide relatively cheap and uncomplicated access to the observatories for relatively simple sensors. Within the next few years, the first electro-optical cables installed in the 1980's will be decommissioned and could be available for scientific use. These cables could provide long "extension cords" (thousands of km) with very high bandwidth and reasonable power to several observatories in remote locations in the ocean. While they could be used in-place, a more exciting scenario is to use cable ships to pick up sections of cable and move them to locations of higher scientific interest. While such moves would not be cheap, the costs would rival the cost of installation and maintenance of a buoyed observatory, with far more bandwidth and power available for science use.

Observatories of Sawai Jai Singh II

NASA Astrophysics Data System (ADS)

Johnson-Roehr, Susan N.

Sawai Jai Singh II, Maharaja of Amber and Jaipur, constructed five observatories in the second quarter of the eighteenth century in the north Indian cities of Shahjahanabad (Delhi), Jaipur, Ujjain, Mathura, and Varanasi. Believing the accuracy of his naked-eye observations would improve with larger, more stable instruments, Jai Singh reengineered common brass instruments using stone construction methods. His applied ingenuity led to the invention of several outsize masonry instruments, the majority of which were used to determine the coordinates of celestial objects with reference to the local horizon. During Jai Singh's lifetime, the observatories were used to make observations in order to update existing ephemerides such as the Zīj-i Ulugh Begī. Jai Singh established communications with European astronomers through a number of Jesuits living and working in India. In addition to dispatching ambassadorial parties to Portugal, he invited French and Bavarian Jesuits to visit and make use of the observatories in Shahjahanabad and Jaipur. The observatories were abandoned after Jai Singh's death in 1743 CE. The Mathura observatory was disassembled completely before 1857. The instruments at the remaining observatories were restored extensively during the nineteenth and twentieth centuries.

The Pierre Auger Cosmic Ray Observatory

DOE PAGES

Aab, Alexander

2015-07-08

The Pierre Auger Observatory, located on a vast, high plain in western Argentina, is the world's largest cosmic ray observatory. The objectives of the Observatory are to probe the origin and characteristics of cosmic rays above 1017 eV and study the interactions of these, the most energetic particles observed in nature. The Auger design features an array of 1660 water Cherenkov particle detector stations spread over 3000 km 2 overlooked by 24 air fluorescence telescopes. Additionally, three high elevation fluorescence telescopes overlook a 23.5 km 2, 61-detector infilled array with 750 m spacing. The Observatory has been in successful operationmore » since completion in 2008 and has recorded data from an exposure exceeding 40,000 km 2 sr yr. This paper describes the design and performance of the detectors, related subsystems and infrastructure that make up the Observatory.« less

Asteroid Lightcurve Analysis at Elephant Head Observatory: 2013 August- October