  Active prominences exhibit plasma motions, resulting in difficulties with the
interpretation of spectroscopic observations. These solar features being
strongly influenced by the radiation coming from the solar disk, Doppler
dimming or brightening effects may arise, depending on which lines are observed
and on the velocity of the plasma. Interlocking between the different atomic
energy levels and non local thermodynamic equilibrium lead to non-trivial
spectral line profiles, and this calls for complex numerical modelling of the
radiative transfer in order to understand the observations. We present such a
tool, which solves the radiative transfer and statistical equilibrium for H, He
I, He II, and Ca II, in moving prominences where radial plasma motions are
taking place. It is found that for isothermal, isobaric prominence models, the
He II resonance lines are very sensitive to the Doppler effect and show a
strong Doppler dimming. The Ca II lines are not very sensitive to the Doppler
effect for the prominence models considered here. We illustrate how the code
makes it possible to retrieve the plasma thermodynamic parameters by comparing
computed and observed line profiles of hydrogen and helium resonance lines in a
quiescent prominence.
