Vienna VLBI Simulations

This paper gives an overview about the progress of the simulation work, carried out at the Institute of Geodesy and Geophysics (IGG), with the goal to design a new geodetic Very Long Baseline Interferometry (VLBI) system. Influences of the schedule, the network geometry and the main stochastic processes on the geodetic results are investigated. For this purpose temporally very dense schedules are prepared with the software package SKED (Vandenberg 1999), which are then compared in terms of baseline length repeatabilities. For the simulation of VLBI observations a Monte Carlo Simulator was set up which creates artificial observations by randomly simulating zenith wet delay and clock values as well as additive white noise representing the antenna errors. For this purpose the VLBI analysis software OCCAM (Titov et al. 2004) was adapted to run the simulator and analyze the simulated observations. Random walk processes with power spectral densities of 0.7 and 0.1 psec(2)/sec are used for the simulation of zenith wet delays. The clocks are simulated with Allan Standard Deviations of 1.10(-14)@50min and 2.10(-15)@15min and three levels of white noise, 4 psec, 8 psec and, 16 psec are added to the artificial observations. The variations of the power spectrum densities of the clocks and zenith wet delays and the application of different white noise levels show clearly that the wet delay is the critical factor for the improvement of the geodetic VLBI system.