Effects and disturbances on GPS-derived zenith tropospheric delay during the CONT08 campaign

The zenith total delay (ZTD) can be retrieved from space geodetic techniques, e.g., Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI), which plays a key role in climatological and atmospheric sciences. However, ZTD estimates still have lots of effects and uncertainties, particularly in GPS model errors. The continuous VLBI observations provide an opportunity to assess GPS ZTD estimates during the Continuous VLBI Campaign 2008 (CONT08) at 11 co-located stations from August 12 to 26, 2008. In this paper, the effects on GPS ZTD estimate and its disturbances are investigated using different mapping function models (GMF, NMF, and VMF1), Phase Center Variation (PCV) models (AZEL and ELEV) and Ocean Tide Loading (OTL) models (FES2004, CSR4.0 and GOT00). It has shown that the ZTDs from VLBI and GPS have an agreement in -3.88-3.74 mm with correlation coefficients of higher than 0.87. For mapping function models, there are no obvious differences, while the PCV model of ELEV is always a little better than AZEL for large scale network with mixed antenna types. For stations near to the coastlines, ocean loading effects must be corrected. While for short period, the effects with OTL models of FFES2004, CSR4.0 and GOT00 are always at the same level. In addition, significant diurnal cycles S-1 (24 h period) and semidiurnal cycles S-2 (12 h period) of GPS ZTD are found with amplitudes between 0.82 and 13.84 mm and 0.30 and 5.23 mm, respectively, which are closer to VLBI ZTD estimates. The correlation coefficients between VLBI and GPS ZTD are 0.85 and 0.95 in S-1 and S-2, respectively. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.