  We performed an absolute frequency measurement of the $^1S_{0}$-$^3P_{0}$
transition in $^{87}$Sr with a fractional uncertainty of $1.2 \times 10^{-15}$,
which is less than one third that of our previous measurement. A caesium
fountain atomic clock was used as a transfer oscillator to reduce the
uncertainty of the link between a strontium optical lattice clock and the SI
second. The absolute value of the transition frequency is 429 228 004 229
873.56(49) Hz.
