  The phase observable measured by an atomic gravimeter built up on stimulated
Raman transitions is discussed in a fully relativistic context. It is written
in terms of laser phases which are invariant under relativistic gauge
transformations. The dephasing is the sum of light and atomic contributions
which are connected to one another through their interplay with conservation
laws at the interaction vertices. In the case of a closed geometry, a compact
form of the dephasing is written in terms of a Legendre transform of the laser
phases. These general expressions are illustrated by discussing two techniques
used for compensating the Doppler shift, one corresponding to chirped
frequencies and the other one to ramped variations.
