The absolute in situ calibration of the altimeter missions
insures the regular and long-term control of the altimeter
sea surface height (SSH) time series with independent measurements.
In this paper, the absolute calibration of an
altimeter means the estimation of a bias of the SSH derived
from the altimeter with respect to an external ground truth.
Complementary to the global estimates of the relative
altimeter biases and drifts performed with global tide gauge
databases