Schematic to describe the methodology pursued in this work. First, the expansion of the metal vapour in the background atmosphere and the consequent hyperthermal collisions are computed using the DSMC-Boltzmann method (i). Second, the long trail evolution is simulated by means of a Lagrangian diffusive reactor marching along the streamlines, which takes advantage of the parabolised nature of the equations. This solver accounts for ionic chemical reactions and radial diffusion (ii). Then, the diffusion coefficient and electron line density are retrieved from the simulations (iii). Finally, the radio echo reflected by an underdense meteor is reconstructed at the receiver (iv).