Surveying Colocated GNSS, VLBI, and SLR Stations in China

Abstract

The local tie vectors between different space geodesy instruments in colocated sites, such as the global navigation satellite system (GNSS), very long baseline interferometry (VLBI), and satellite laser ranging (SLR), are essential for combination with the international terrestrial reference frame (ITRF). This paper introduces the surveying method and data processing model for determining the tie vectors in the seven colocated sites in Shanghai, Wuhan, Kunming, Beijing, Xian, Changchun, and Urumqi, and presents the values and full variance-covariance of these local ties. The surveying methodology and data processing method of the current work are rigorously determined to guarantee the relative positional precision of reference points (RPs) of different instruments in each colocation site to be a few millimeters. This paper compares the new tie vectors with those derived from ITRF 2008 products to consider the discrepancies at tie epoch. By comparing the new results to the previous results by other organizations, the new tie vector at the Wuhan site is in good agreement, but the vertical coordinate difference of the tie vector at the Shanghai site is as large as 2.24 cm. Therefore, the tie vector at the Shanghai site may have changed about 2 cm from 2003 to 2011.