The mean dynamic height of the ocean surface is estimated along a subsatell
ite track of TOPEX/Poseidon crossing the East Auckland Current system north
east of New Zealand. Repeated hydrographic surveys along the track, togethe
r with surface elevation anomalies deduced from TOPEX altimeter data, enabl
e four independent estimates of the mean dynamic height. From these estimat
es a more stable mean is calculated in which the uncertainty is estimated a
s less than 5 cm. The result can be applied as a reference profile for cali
brating a long series of TOPEX passes so that cross-track geostrophic curre
nts can be calculated. The scatter in the individual estimates indicates su
fficient sampling variability to caution against using single hydrographic
surveys as a basis for calibrating the satellite data.