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The realization of International Height Reference System (IHRS) is one of themajor tasks of the International Association of Geodesy (IAG). A main componentof the IHRS realization is the global vertical datum unification, whichrequires the connection of the existing local vertical height reference systems(VHS). However, it is difficult to estimate the offsets between two localheight systems by conventional approaches when they are far apart. In thispaper, we formulate a framework for connecting two local VHSs usingultra-precise frequency signal transmission links between satellites and groundstations, which is referred to as satellite frequency signal transmission(SFST) approach. The SFST approach can directly determine the geopotentialdifference between two ground datum stations without location restrictions, andconsequently determine the height difference of the two VHSs. Simulationresults show that the China's VHS and the US's VHS can be unified at theaccuracy of several centimeters, provided that the stability of atomic clocksused on board the satellite and on ground datum stations reach the highestlevel of current technology, about $4.8\times 10^{-17}/\sqrt{\tau}$ for anaveraging time {\tau} (in seconds). The SFST approach is promising to unify theglobal vertical height datum in centimeter level in future, and it also providea new way for the IHRS realization.

Unification of global height system at centimeter level using precise frequency signal links