Modeling azimuthal asymmetries of the troposphere delay during a 14-days typhoon period in Tsukuba

A. Pany1, J. Böhm1, T. Hobiger2, R. Ichikawa2 and H. Schuh1

1Institute of Geodesy and Geophysics, Vienna University of Technology, Austria
2National Institute of Information and Communications Technology, Toyo, Japan

Oral presentation

The Monte Carlo simulations carried out within the IVS to design the next generation VLBI system, VLBI2010, have revealed that the troposphere delay is the most limiting factor in VLBI analyses. The simulation studies have shown that state-of-the-art modeling of the troposphere might be insufficient to reach VLBI2010’s demanding goal of sub-mm accuracy. To exploit existing and to discover new strategies of modeling the troposphere, we computed ray-traced delays around the VLBI site in Tsukuba using KARAT, the Kashima Ray-Tracing Tools. Tsukuba is very well suited for studies of this kind because of its rather turbulent troposphere and because it is covered by high resolution numerical weather models provided by the Japanese Meteorological Agency (JMA). For our investigations we chose a 14-days typhoon period in September 2007. The ray-traced delays are given with a resolution of 1° in both azimuth and elevation down to an outgoing elevation angle of 3°. We show that the residual delays after removing the mapping function exhibit significant elevation dependent systematics as well as azimuthal asymmetries, that can only partly be modeled with gradients. Finally, we fit different functions (e.g. spherical harmonic functions) to these residual delays.