The cross-calibration exercise for the Jason-2 and Envisat
missions at both calibration sites shows that the regional
method can be very useful when the in situ data are not
available at the dedicated site of a given mission. Indeed, it
enables to continue the monitoring of any mission, when it
is not possible any longer with the classical absolute methods.
Moreover, this exercise teaches that the choice of the
calibration sites is rather complicated and delicate, as it
appears that the Ajaccio tide gauge contains some very
local signals, including tidal signal, which are difficult to
model and may interfere in the comparison with the altimeter
SSH. Some errors in the high resolution mean sea surfaces
derived from GPS measurements and used to link the
in situ and altimetry datasets may also contribute to the
systematic differences observed between the two sites of
Ajaccio and Senetosa. This point will have to be further
investigated in the framework of future studies.