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We have used microwave absorbing material in different geometries around ground-based Global Navigation Satellite System (GNSS) antennas in order to mitigate multipath effects on the estimates of station coordinates and atmospheric water vapour. The influence of a hemispheric radome - of the same type as in the Swedish GPS network SWEPOS was - also investigated. Two GNSS stations at the Onsala Space Observatory were used forming a 12 m baseline. GPS data from October 2008 to November 2009 were analyzed by the GIPSY/OASIS II software using the Precise Point Positioning (PPP) processing strategy for five different elevation cutoff angles from 5 degrees to 25 degrees. We found that the use of the absorbing material decreases the offset in the estimated vertical component of the baseline from similar to 27 mm to similar to 4 mm when the elevation cutoff angle varies from 5 degrees to 20 degrees. The horizontal components are much less affected. The corresponding offset in the estimates of the atmospheric Integrated Water Vapour (IWV) decreases from similar to 1.6 kg/m(2) to similar to 0.3kg/m(2). Changes less than 5 mm in the offsets in the vertical component of the baseline are seen for all five elevation cutoff angle solutions when the antenna was covered by a hemispheric radome. Using the radome affects the IWV estimates less than 0.4 kg/m(2) for all different solutions. IWV comparisons between a Water Vapour Radiometer (WVR) and the GPS data give consistent results. (C) 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.