VGOS - VLBI Global Observing System
VGOS – VLBI Global Observing System - VGOS is part of the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), which integrates different geodetic techniques to provide the geodetic infrastructure necessary for monitoring the Earth system and for Global Change research. It provides observations of the three fundamental geodetic observables and their variations:
Earth's gravity field
Earth's rotational motion.
GGOS (and within it, VGOS) provides the observational basis to maintain a stable, accurate and global reference frame and in this function is crucial for all Earth observation and many practical applications.
To improve VLBI data to meet increasingly demanding requirements, an end-to-end redesign called the VLBI Global Observing System (VGOS, formerly VLBI2010) is in progress. The key concepts are a broadband signal acquisition chain (2-14 GHz) with digital electronics and fast, small antennas. By placing up to four carefully chosen RF bands in the 2–14 GHz range, Radio Frequency Interference (RFI) should be ameliorated and the requisite observation precision achieved. Fast antennas will provide many more observations. More observations support higher temporal and spatial resolution in estimating the effect of the troposphere at each station. Simulations show tropospheric effects as the largest noise source. High recording bandwidths are required to achieve the necessary sensitivity.
VGOS is being developed to be minimally staffed, remotely controllable, broadband, RFI avoiding, fully digital, fast slewing, and capable of producing VLBI delays with precision of 4 picoseconds (in 4 picoseconds light travels 1 millimeter.) The system is designed to observe continuously.
The International VLBI Service for Geodesy and Astrometry (IVS) has been gradually introducing the VGOS systems into the new broadband network as they become available. The initial provisional roll-out plan included broadband test observations in 2015, mainly on the GGAO-Westford baseline. The goal for 2016 was to have one 24-hr VGOS session every week and in 2017 to have several 1-hr sessions for Earth Orientation Parameters (EOP) each day. The pilot project for 2018 is the combination of the 2016 and 2017 observing scenarios using more than ten VGOS stations.
Some of the scientific results derived from VLBI include:
- Motion of the Earth's tectonic plates
- Regional deformation and local uplift or subsidence.
- Definition of the celestial reference frame
- Variations in the Earth's orientation and length of day
- Maintenance of the terrestrial reference frame
- Measurement of gravitational forces of the Sun and Moon on the Earth and the deep structure of the Earth
- Improvement of atmospheric models