National Report of Sweden to the NKG General ... - Lantmäteriet

16dUT1-project. This project aims atproducing low latency earth rotationresults using e-VLBI. Observations arepreformed on extended east-westoriented baselines betweenFennoscandia and Japan. The observeddata from the Fennoscandian radiotelescopes are transferred in real-timeto a Japanese correlator centre andcorrelated in near real-time togetherwith the corresponding observationaldata of the Japanese radio telescopes,and successively analyzed in near realtimeto produce low latency results onUT1. The current low-latency worldrecord was achieved in 2008 with thedetermination of final UT1 resultswithin 4 minutes after the end of a onehour long observation session. Theagreement with the final IERS 38 05EOPC04 values proved to be on theorder of 30 microseconds. This is on thesame level as the standard IERS rapidsolutions, but with a much lowerlatency. Since 2009 the project isextended to regular 24 hours IVSsessions.During 2006 to 2010 we contributedactively to the development ofVLBI2010, the next generation geodeticVLBI system, with simulations ofatmospheric propagation delays and anevaluation of the importance ofatmospheric turbulence for geodeticVLBI. The simulations are based onturbulence models and aim atproducing realistic propagation delays.Atmospheric turbulence is described byturbulence parameters Cn that can bederived e.g. from high-resolutionradiosonde profiles. Our work showsthat atmospheric turbulence is animportant limiting factor for geodetic38IERS= International Earth Rotation and Reference SystemsServiceVLBI today and also for the futureVLBI2010 system.Another approach to address the issueof atmospheric propagation delays ingeodetic VLBI data analysis is the useof external information to model theseeffects. We work on the use of datafrom Numerical Weather Models(NWM), e.g. the data provided by theEuropean Centre for Medium-rangeWeather Forecast (ECMWF), tocalculate line-of-sight corrections forgeodetic VLBI data by ray-tracing. Theaim is to use these corrections asimproved a priori data for the dataanalysis, or as a way to calibrate theVLBI data. Our focus is on theEuropean VLBI data set.In 2009 we started a collaboration withthe radio telescopes in Medicina andNoto, both Italy, and colleagues atMetsähovi (Finland) and JIVE (TheNetherlands) to develop a strategy toobserve GNSS-satelltie signals withVLBI. The idea is to do VLBIobservations with GNSS-signals and torelate these to normal geodeticobservations of natural radio sources.This could be a way to connect thesatellite orbits to the celestial referenceframe and thus a new tie of GNSS andVLBI. Several tests were performed andfirst attempts of data correlation andanalysis are promising.In 2009 we started a project togetherwith the SP Technical Research Instituteof Sweden to evaluate the potential ofgeodetic VLBI for time and frequencytransfer. Geodetic collocation sites withequipment for VLBI and GNSS that areconnected to common time andfrequency distribution by H-masers areperfect candidates for time andfrequency transfer experiments. Weused the CONT08 data set for a