VLBI measurements for time transfer between time and frequency laboratories

In the usual geodetic VLBI analysis, clock offsets and their rates of change at participating stations except for the reference station are estimated. The averaged formal error (1σ) of the clock offsets is typically about 20 picoseconds in the geodetic VLBI experiments regularly conducted by the International VLBI Service for Geodesy and Astrometry (IVS). This accuracy is better than other techniques like GPS time transfer and TWSTFT (Two-way Satellite Time and Frequency Transfer) which are used to maintain Coordinated Universal Time (UTC). It will become possible to use the geodetic VLBI technique for accurate time transfer if we can collocate the VLBI radio telescopes at Time and Frequency laboratories. For this purpose, we started to develop a compact and transportable VLBI system. In this study, to confirm the potential of VLBI time transfer aiming at the practical use of VLBI time transfer in the future, we compared the results of VLBI time transfer and the results of GPS time transfer (Carrier Phase) by using Kashima-Koganei baseline (109 km). The averaged formal error (1σ) of the clock offsets when they are estimated every one hour was 29 picoseconds. The results of VLBI time transfer were consistent with the results of GPS time transfer. The difference of both results was about ±500 picoseconds and it is considered to be dominated by the uncertainty of the GPS time transfer. In terms of frequency stability, the Allan deviation was evaluated and it showed that VLBI time transfer is more stable than GPS time transfer in the time range from 2000 seconds to 60000 seconds. Based on these results, we will discuss about the possible improvements to the time transfer between Time and Frequency laboratories by collocating the compact VLBI system at the laboratorie

Current status of the IAG working group 4.3.7 on geodetic GNSS-R

Presentación realizada online en el Scientific Assembly of the International Association of Geodesy (2021) celebrado del 28 de junio al 2 de julio en Beijing

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

A study of VLB 2010 potential for source structure corrections

International audienceIn October 2003, the International VLBI Service for Geodesy and Astrometry (IVS) in- stalled Working Group 3 ‘VLBI2010' to examine current and future requirements for geodetic/astrometric VLBI including all components from antennas to analysis, and to create recommendations for a new gen- eration of VLBI systems. Some important recommendations include: the use of larger networks; the use of smaller faster slewing antennas; the use of very high data rates; and, the use of multiple (e.g. 4) widely spaced bands to resolve RF phase ambiguities. When taken together, these recommendations result in a many-fold increase in the number of observations per session. UV coverage improves to the point where precise VLBI images of the ICRF sources can be constructed on a daily basis directly from the geodetic observations, therefore enabling source structure corrections to be calculated. Simulations are currently underway to evaluate the potential of this approach