Absolute frequency measurement of the 87Sr optical lattice clock at NTSC using international atomic time

We report the absolute frequency measurement of the $5s^{2}{}^{1}S_{0}\rightarrow 5s5p{}^{3}P_{0}$ transition in ⁸⁷Sr optical lattice clock (Sr1) at National Time Service Center. Its systematic frequency shifts are evaluated carefully with a total relative uncertainty of $5.1\times10^{-17}$ . The measured absolute frequency is 429 228 004 229 872.91(18) Hz with a relative uncertainty of $4.1\times10^{-16}$ , with reference to the ensemble of primary and secondary frequency standards published in the Circular T bulletin by BIPM through a global navigation satellite system link.