A Simulation of Height Datum Transfer from the Mainland to an Island Using the Optical Clock Frequency Comparison Method

Abstract

Orthometric height (H) is an important geophysical parameter widely applied in scientific research, civil planning, and engineering projects. However, when oceans separate the two points or the measurement points are on islands, it is not easy to connect the heights between them using classical measurement methods (such as spirit levelling combined with gravimetry). This study aimed to simulate the transfer of height datum from the mainland to an island using the Optical Fiber Frequency Transfer (OFFT) method, based on the principles of relativistic geodesy. A simulation was performed with two points approximately 200 km apart: one on the mainland (Hanoi station) and one on an island (Bach Long Vi Station). The optical clock Ca⁺ with a stability of 3.0 × 10^-18 was placed at each point, and the two clocks were connected by an optical fiber. The main purpose of the simulation was to determine the geopotential difference, and consequently the orthometric height difference, between the stations from the measured relativistic frequency shift, providing an alternative to classical methods. The simulation utilized geopotential data and existing height control points as input data for the model setup. Besides, errors that affect the frequency difference measurement results have been added to the model. Through a numerical simulation, the obtained orthometric height for the Bach Long Vi island station was 13.968 m ± 0.022 m (its true height is 13.965 m). The simulation results presented in this study demonstrate the potential of the OFFT method for transmitting height datum from the mainland to an island or for connecting height systems between islands. However, real-world implementation faces practical challenges related to connecting the optical fibers and deploying ultra-stable optical clocks.