Development of an Ellipsoid Based Chart Datum Around the China Seas

Establishing a continuous chart datum (CD) surface is essential for marine navigation and geodetic applications. In China, the theoretical lowest tide (TLT) surface is adopted as the CD, calculated using 13 specific tidal constituents. This study outlines a comprehensive methodology for constructing a continuous TLT surface referenced to the Chinese Geodetic Coordinate System 2000 (CGCS2000) ellipsoid around the China Seas. A high-precision hybrid tide model was developed by integrating global tide models with satellite altimetry data to ensure a reliable CD. Accuracy evaluations of four global tide models, based on 72 tide gauge observations, identified EOT20 as the optimal model. The hybrid tide model incorporates eleven short-period constituents from EOT20 and FES2014, and two long-period constituents empirically derived from along-track satellite data. Using this hybrid tide model, we first constructed a mean sea surface (MSS) based TLT model. By integrating the HYBRID2023MSS model, this study further established a CGCS2000-based TLT model. Validation against measurements from the 72 tide gauge stations revealed that the ellipsoid based TLT model produces ellipsoid heights ranging from −53.44 to 74.50 m, exhibiting significant spatial variation. The MSS based TLT model achieved a standard deviation of 14.68 cm, confirming its high accuracy and reliability for practical applications.