  Relativistic redshift correction should be accurately considered in frequency
comparisons between frequency standards. In this study, we evaluated the
relativistic redshift at Korea Research Institute of Standards and Science
(KRISS) using three different methods, depending on whether the approach was
traditional or modern or whether the geopotential model was global or local.
The results of the three methods agreed well with one another, and the height
of an Yb optical lattice clock (KRISS-Yb1) was determined to be 75.15 m with an
uncertainty of 0.04 m with respect to the conventionally adopted equipotential
surface W0(CGPM), the value of which is defined to be 62 636 856.0 m2/s2.
Accordingly, the relativistic redshift of KRISS-Yb1 was evaluated to be
8.193(4)x10-15. These data are applicable to the frequency standards at KRISS,
one of which regularly participates in the calibration of the International
Atomic Time (TAI).
