Establishment of Chart Datum and Conversion of Land–Sea Vertical Datum in the Guangdong Province, China

As the demand for marine development along the South China Coast continues to grow, the absence of a unified land–sea vertical reference datum system in this region has become an important problem to be solved. The establishment of a seamless chart datum and its separation/conversion model with other vertical data is crucial for unifying vertical reference measurements across land and sea. In this paper, a comprehensive study is conducted, involving the collection of 78 tide gauges, 846 satellite altimetry points, and leveling connections from the coastal Guangdong Province (20°–25° N, 105°–120° E) over a period of 19 years (2003–2021). Through the application of a national tidal datum epoch and an algorithmic approach, a seamless chart datum model, a topography of sea surface model, a mean sea level model, and a separation/conversion model were established. Model accuracy assessment and validation results indicate that the sea surface topography model exhibits a root mean square error (RMSE) of 3.2 cm. The mean difference between the mean sea level height and observed values is found to be 4.45 cm. Further, the separation/conversion model achieves an accuracy of 6.5 cm. When tide gauge and satellite altimetry data are incorporated into the accuracy statistics, the overall RMSE for the seamless chart datum model is 7.93 cm. However, when only the data from the tide gauge station are used to evaluate, the accuracy of the unified land–sea vertical datum and conversion is determined to be better than 7 cm.