Abstract：Solar prominences are very large-scale magnetic structures in the solar atmosphere. Their eruptions participate in solar events that affect the Earth's atmosphere in the context of "space weather". We analyzed an prominence eruption with a joint observation from spatial instruments (IRIS, SDO/AIA, STEREO/EUVI) and ground-based observatory (HAO/K-Cor) and focused on the observational signatures of the processes which have been put forward for explaining eruptive prominences.

   The simultaneous observations (May 28, 2014) are first analyzed in terms of plane-of-sky velocities in the Mg II k and h (IRIS) and He II (AIA) lines complemented by the STEREO/EUVI images that allow to derive the 3D geometry. The velocities along the line of sight are derived from two methods that attempt to account for the complexity of the profiles.

   The necessary determination of the densities results from an Non-Local Thermodynamic Equilibrium (NLTE) radiation transfer modeling (1D), through the comparison with the intensities of Mg II h and k lines pixel by pixel, to determine variable physical quantities in the space and in the time of the observation sequence (4 hours 30 minutes).

   The code used is PRODOP_Mg maintained at MEDOC. A remarkable result on the relationship between the intensity of the h and k lines and the emission measurement is thus obtained, a simple and useful relationship for the diagnostics of the structures observed by IRIS. Density maps (neutral hydrogen, electron) and temperature maps are thus obtained, for the first time, over time.