How can parameters of the ionosphere be calculated?
Answer to that one: What you describe is a measurment, not a calculation.
The measurment you describe varies the potential difference at a satellites Langmuir probe. The potential difference then attracts or deflects ions, and deflects or attracts electrons. Those electrons and ions are the current being picked up by the Langmuir probe.
Then follows a translation of current into local ion or electron densities. Different ion species can be distinguished w.r.t each other because they have different inertia, and thus different arrival times. I'm not sure how many ion species one can distinguish however in this way.