  According to general relativity theory (GRT), the clock at a position with
lower geopotential ticks slower than an identical one at a position with higher
geopotential. Here, we provide a geopotential comparison using a
non-transportable hydrogen clock and a transportable hydrogen clock for
altitude transmission based on the two-way satellite time and frequency
transfer (TWSTFT) technique. First, we set one hydrogen clock on the fifth
floor and another hydrogen clock on the ground floor, with their height
difference of 22.8 m measured by tape, and compared the time difference between
these two clocks by TWSTFT for 13 days. Then, we set both clocks on the ground
floor and compared the time difference between the two clocks for 7 days for
zero-baseline calibration (synchronization). Based on the measured time
difference between the two clocks at different floors, we obtained the height
difference of $28 \pm 05.4$ m, which coincides well with the tape-measured
result. This experiment provides a method of height propagation using precise
clocks based on the TWSTFT technique.
