Global Geodetic Observing System (GGOS): Current Activities and Plans of the Bureau of Networks and Observations
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Michael Pearlman↗
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COLD MAGICS - Continuous Local Deformation Monitoring of an Arctic Geodetic Fundamental Station
We describe the experience gained in a project to continuously monitor the local tie at the Geodetic Observatory Ny-Alesund. A PC-controlled robotic total station was used to monitor survey prisms that were attached to survey pillars of the local network and the monuments used for geodetic VLBI and GNSS measurements. The monitoring lasted for seven days and had a temporal resolution of six minutes. The raw angle and distance measurements show clear sinusoidal signatures with a daily period, most strongly for a four-day period with 24 hours of sunshine. The derived topocentric coordinates of the survey prisms attached to the GNSS monument and the VLBI radio telescope act as approximation for the local tie. We detect clear signatures at the mm-level. With the current approach we cannot distinguish between real motion of the prisms and potential thermal influences on the instrument used for the observations. However, the project shows that continuous local tie monitoring is feasible today and in the future can and should be used for all geodetic co-location stations.
Haas, Ruediger↗
Proposed satellite laser ranging and very long baseline interferometry sites for crustal dynamics investigations
Recommendations are presented for a global network of 125 sites for geodetic measurements by satellite laser ranging and very long baseline interferometry. The sites were proposed on the basis of existing facilities and scientific value for investigation of crustal dynamics as related to earthquake hazards. Tectonic problems are discussed for North America peripheral regions and for the world. The sites are presented in tables and maps, with bibliographic references.
Lowman, P. D.↗
Characterization and Calibration of the 12-m Antenna in Warkworth, New Zealand
The New Zealand 12-m antenna is scheduled to start participating in regular IVS VLBI sessions from the middle of 2010. Characterization procedures and results of calibration of the New Zealand 12- m radio telescope are presented, including the main reflector surface accuracy measurement, pointing model creation, and the system equivalent flux density (SEFD) determination in both S and X bands. Important issues of network connectivity, co-located geodetic systems, and the use of the antenna in education are also discussed.
Gulyaev, Sergei↗
Update on the activities of the GGOS Bureau of Networks and Observations
The recently reorganized GGOS Bureau of Networks and Observations has many elements that are associated with building and sustaining the infrastructure that supports the Global Geodetic Observing System (GGOS) through the development and maintenance of the International Terrestrial and Celestial Reference Frames, improved gravity field models and their incorporation into the reference frame, the production of precision orbits for missions of interest to GGOS, and many other applications. The affiliated Service Networks (IVS, ILRS, IGS, IDS, and now the IGFS and the PSMSL) continue to grow geographically and to improve core and co-location site performance with newer technologies. Efforts are underway to expand GGOS participation and outreach. Several groups are undertaking initiatives and seeking partnerships to update existing sites and expand the networks in geographic areas void of coverage. New satellites are being launched by the Space Agencies in disciplines relevant to GGOS. Working groups now constitute an integral part of the Bureau, providing key service to GGOS. Their activities include: projecting future network capability and examining trade-off options for station deployment and technology upgrades, developing metadata collection and online availability strategies; improving coordination and information exchange with the missions for better ground-based network response and space-segment adequacy for the realization of GGOS goals; and standardizing site-tie measurement, archiving, and analysis procedures. This poster will present the progress in the Bureau's activities and its efforts to expand the networks and make them more effective in supporting GGOS.
Networks↗
Hartebeesthoek Radio Astronomy Observatory (HartRAO)
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.
Nickola, Marisa↗
The GPS Topex/Poseidon precise orbit determination experiment - Implications for design of GPS global networks
Topex/Poseidon, a cooperative satellite mission between United States and France, aims to determine global ocean circulation patterns and to study their influence on world climate through precise measurements of sea surface height above the geoid with an on-board altimeter. To achieve the mission science aims, a goal of 13-cm orbit altitude accuracy was set. Topex/Poseidon includes a Global Positioning System (GPS) precise orbit determination (POD) system that has now demonstrated altitude accuracy better than 5 cm. The GPS POD system includes an on-board GPS receiver and a 6-station GPS global tracking network. This paper reviews early GPS results and discusses multi-mission capabilities available from a future enhanced global GPS network, which would provide ground-based geodetic and atmospheric calibrations needed for NASA deep space missions while also supplying tracking data for future low Earth orbiters. Benefits of the enhanced global GPS network include lower operations costs for deep space tracking and many scientific and societal benefits from the low Earth orbiter missions, including improved understanding of ocean circulation, ocean-weather interactions, the El Nino effect, the Earth thermal balance, and weather forecasting.
Lindqwister, Ulf J.↗
Geodetic measurements at sea floor spreading centers
A network of 8 or more precision transponder units mounted on the sea floor and interrogated periodically from an instrument package towed near bottom through the area to provide the necessary spatial averaging could provide a practical system for observing the pattern of buildup of strain at intermediate and fast spreading centers.
Spiess, F. N.↗
The spin vector of Venus determined from Magellan data
A control network of the north polar region of Venus has been established by selecting and measuring control points on full-resolution radar strips. The measurements were incorporated into a least-squares adjustment program that improved initial estimates of the coordinates of the control points, pole direction, and rotation rate of Venus. The current dataset contains 4206 measurements of 606 points on 619 radar strips. The accuracy of the determination is driven by spacecraft ephemeris errors. An accurate estimate of the rotation period of Venus was obtained by applying an ephemeris improvement technique. The second cycle closure orbits improved ephemeris solutions for 40 orbits (376-384, 520-528, 588-592, 658-668, 1002-1010, 1408-1412, 1746-1764, and 2166-2170) are included and fixed in the geodetic control computations, thus trying the network to the J2000 coordinate system.
Davies, M. E.↗
Stochastic estimation of tropospheric path delays in global positioning system geodetic measurements
Water vapor radiometric and surface meteorological measurements taken during three GPS geodetic experiments are used to calculate process noise levels for random walk and first-order Gauss-Markov temporal models of tropospheric path delays. Entire wet and combined wet and dry zenith delays at each network site are estimated simultaneously with the geodetic parameters without prior calibration. The path delays and corresponding baseline estimates are compared to those obtained with calibrated data and stochastic residual delays. In this manner, the marginal utility of a priori tropospheric calibration is assessed given the ability to estimate the path delays directly using only the GPS data. Estimation of total zenith path delays with appropriate random walk or Gauss-Markov models yields baseline repeatabilities of a few parts in 100 million. Results suggest that GPS data alone have sufficient strength to resolve centimeter-level zenith path delay fluctuations over periods of a few minutes.
Tralli, David M.↗
The VGOS High Road: From Inception and Prototyping to Operations to Maturation and Beyond
Legacy S/X has been the production system of the IVS since the inception of the service. VGOS was declared operational in 2020 after a visionary journey that involved designing, prototyping, and demonstrating the feasibility of the new observing system to generate high-quality geodetic products. And a fledgling VGOS network of between 8 and 10 stations has been contributing IVS products operationally ever since. That VGOS network had further increased by the end of 2022 to 12 stations, and counting. Currently, the VGOS observing program encompasses the 24-hour VGOS-OPS and VGOS-RD session series; further, a weekdaily VGOS Intensive series has been established (with other VGOS Intensives being set up). In addition to the network, VGOS correlation capabilities have also expanded to try to keep pace with the increased VGOS correlation load, morphing into a multi-center distributed correlator. In this poster, we will provide a status overview of the infrastructure realization efforts of the VGOS station network and the correlation centers as well as plans for a bright VGOS future.
VLBI↗
Coordinating, Scheduling, Processing and Analyzing IYA09
The IVS scheduled a special astrometric VLBI session for the International Year of Astronomy 2009 (IYA09) commemorating 400 years of optical astronomy and 40 years of VLBI. The IYA09 session is the most ambitious geodetic session to date in terms of network size, number of sources, and number of observations. We describe the process of designing, coordinating, scheduling, pre-session station checkout, correlating, and analyzing this session.
Gipson, John↗
A proposed concept for a crustal dynamics information management network
The findings of a requirements and feasibility analysis of the present and potential producers, users, and repositories of space-derived geodetic information are summarized. A proposed concept is presented for a crustal dynamics information management network that would apply state of the art concepts of information management technology to meet the expanding needs of the producers, users, and archivists of this geodetic information.
Lohman, G. M.↗
Tracking strategies for laser ranging to multiple satellite targets
By the middle of the decade, several new Laser Geodynamic Satellites will be launched to join the current constellation comprised of the laser geodynamic satellite (LAGEOS) (US), Starlette (France), Ajisai (Japan), and Etalon I and II (USSR). The satellites to be launched, LAGEOS II and III (US & Italy), and Stella (France), will be injected into orbits that differ from the existing constellation so that geodetic and gravimetric quantities are sampled to enhance their resolution and accuracy. An examination of various possible tracking strategies adopted by the network of laser tracking stations has revealed that the recovery of precise geodetic parameters can be obtained over shorter intervals than is currently obtainable with the present constellation of satellites. This is particularly important in the planning of mobile laser tracking operations, given a network of permanently operating tracking sites. Through simulations, it is shown that laser tracking of certain satellite passes, pre-selected to provide optimal sky-coverage, provides the means to acquire a sufficient amount of data to allow the recovery of 1 cm station positions.
Robbins, J. W.↗
High-precision gravimetric survey in support of lunar laser ranging at Haleakala, Maui, 1976 - 1978
The planning, observations and adjustment of high-precision gravity survey networks established on the islands of Maui and Oahu as part of the geodetic-geophysical program in support of lunar laser ranging at Haleakala, Maui, Hawaii are described. The gravity survey networks include 43 independently measured gravity differences along the gravity calibration line from Kahului Airport to the summit of Mt. Haleakala, together with some key points close to tidal gauges on Maui, and 40 gravity differences within metropolitan Honolulu. The results of the 1976-1978 survey are compared with surveys made in 1961 and in 1964-1965. All final gravity values are given in the system of the international gravity standardization net 1971 (IGSN 71); values are obtained by subtracting 14.57 mgal from the Potsdam value at the gravity base station at the Hickam Air Force Base, Honolulu.
Schenck, B. E.↗
Observations of Global and Regional Ionospheric Irregularities and Scintillation Using GNSS Tracking Networks
The rate of TEC index (ROTI) is a measurement that characterizes ionospheric irregularities. It can be obtained from standard GNSS dual-frequency phase data collected using a geodetic type of GNSS receiver. By processing GPS data from ground-based networks of International GNSS Service and Continuously Operating Reference Station (CORS), ROTI maps have been produced to observe global and regional scintillation activities. A major mid-latitude scintillation event in the contiguous United States is reported here that was captured in ROTI maps produced using CORS GPS data collected during a space weather storm. The analyses conducted in this work and previously by another group indicate that ROTI is a good occurrence indicator of both amplitude and phase scintillations of GPS L-band signals, even though the magnitudes of ROTI, S4, and sigma(sub phi) can be different. For example, our analysis indicates that prominent ROTI and the L1 phase scintillation (sigma(sub phi)) are well correlated temporally in the polar region while L1 amplitude scintillation rarely occurs. The differences are partially attributed to physics processes in different latitude regions, such as high-speed plasma convection in the polar region that can suppress the amplitude scintillation. An analysis of the impact of ionospheric scintillation on precise positioning, which requires use of dual-frequency phase data, is also conducted. The results indicate that significant (more than an order of magnitude) positioning errors can occur under phase scintillation conditions.
ionospheric measurements↗
VLBI data, acquisition, environmental effects
During this quadrennium, very long baseline interferometry (VLBI) data acquisition and system development has focused on improving the accuracy of the system sufficiently to allow the determination of reliable estimates of height variations. Associated with this aim has been improvements in the determinations of horizontal velocity fields, monitoring water vapor delay using interferometric methods, and improvements to Earth rotation measurements. The primary aims of the improvements to height measurement accuracy have been to directly measure the contemporary magnitudes of post glacial rebound, and to determine a height reference system for measuring global sea level rise. High frequency Earth rotation studies have been carried out to better define the transformation parameters from an inertial coordinate system to an Earth fixed one, and to better understand the coupling between the components of the atmosphere-ocean-solid Earth system. Two major VLBI campaigns were carried out in support of these studies: (1) Epoch-92 in July 1992 and (2) Cont-94 in January 1994. Each of these campaigns lasted approximately two weeks and involved multiple VLBI networks operating simultaneously in addition to other space geodetic systems operating during these periods. Two major compilations of the VLBI results (and results from other space geodetic systems) have been published during this quadrennium.
Herring, Thomas A.↗
NASA's Contribution to Global Space Geodesy Networks
The NASA Space Geodesy program continues to be a major provider of space geodetic data for the international earth science community. NASA operates high performance Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) ground receivers at well over 30 locations around the world and works in close cooperation with space geodetic observatories around the world. NASA has also always been at the forefront in the quest for technical improvement and innovation in the space geodesy technologies to make them even more productive, accurate and economical. This presentation will highlight the current status of NASA's networks; the plans for partnerships with international groups in the southern hemisphere to improve the geographic distribution of space geodesy sites and the status of the technological improvements in SLR and VLBI that will support the new scientific thrusts proposed by interdisciplinary earth scientists. In addition, the expanding role of the NASA Space geodesy data archive, the CDDIS will be described.
Bosworth, John M.↗