Determination of tropospheric parameters within the new IVS Pilot Project

Abstract

In April 2002 the International VLBI Service for Geodesy and Astrometry (IVS) set up the Pilot Project — Tropospheric Parameters, and the Institute of Geodesy and Geophysics (IGG), Vienna, was put in charge of coordinating the project. Seven IVS Analysis Centers have joined the project and regularly submitted their estimates of tropospheric parameters (wet and total zenith delays, horizontal gradients) for all IVS-R1 and IVS-R4 sessions since January 1st, 2002. The individual submissions are combined by a two-step procedure to obtain stable, robust and highly accurate tropospheric parameter time series with one hour resolution. The zenith delays derived by Very Long Baseline Interferometry (VLBI) are compared with those provided by the International GPS Service (IGS). At sites with co-located VLBI and GPS antennas, biases are found between the Global Positioning System (GPS) and VLBI derived zenith delays, although short-term variabilities generally show a good agreement. Possible reasons for these biases are discussed. Additionally, the time series submitted by the individual Analysis Centers are compared to the combined IGS time series for the CONT02 campaign of 15 days of continuous observations in the second half of October 2002.