  SI-traceable measurements of optical frequencies using International Atomic
Time (TAI) do not require a local primary frequency reference, but suffer from
an uncertainty in tracing to the SI second. For the measurement of the
$^{87}$Sr lattice clock transition, we have reduced this uncertainty to low
$10^{-16}$ level by averaging three sets of ten-day intermittent measurements,
in which we operated the lattice clock for $10^4$ s on each day. Moreover, a
combined oscillator of two hydrogen masers was employed as a local flywheel
oscillator (LFO) in order to mitigate the impact of sporadic excursion of LFO
frequency. The resultant absolute frequency with fractional uncertainty of
$4.3\times10^{-16}$ agrees with other measurements based on local
state-of-the-art cesium fountains.
