Normal Height Connection across Seas by the Geopotential-Difference Method: Case Study in Qiongzhou Strait, China

摘要

The national/regional unified height datum is of great importance for the establishment of geospatial information infrastructure and the corresponding surveying applications. The geopotential-difference method is proposed for long-distance height-datum connection across seas based on global positioning system (GPS)/leveling, global geopotential model (GGM), and satellite altimetry data sets. For a case study, the Chinese height datum 1985 (CNHD85) in the mainland was connected to the local vertical datum (LVD) in Hainan across Qiongzhou Strait up to a distance over 30km. The results show that this method is independent of the selection of virtual leveling lines. Furthermore, evaluation with an indirect approach shows that the choice of GGM affects the quality of the normal height connection, where the relative accuracies of the solutions based on the Earth Gravity Model 2008 (EGM2008), European Improved Gravity Model of the Earth by New Techniques 6C (EIGEN-6C), EIGEN-6C3STAT, and EIGEN-6C4 models are 0.012, 0.0132, 0.022, and 0.009 m, respectively. The final CNHD85 normal heights of GPS/leveling benchmarks in Hainan were computed based on the EIGEN-6C4 model, and the closure of the height difference for the computed normal heights meets the tolerance requirement of the second-order spirit leveling. Moreover, the corresponding results indicate that the vertical datum difference between CNHD85 and LVD over Hainan is approximately at the level of 0.186 m.