With this approach the energy of a particle is related to a maximum range that this particle can travel in air. The range is defined in terms of number of ambient molecules encountered before all of the particle's initial energy is consumed. Given a density model, this range can be related to altitude or pressure level. In addition, an energy dissipation function is given that describes the rate of energy loss along the path to the maximum range as a function of the initial energy of the precipitating electron. For precipitating electrons below 32 keV, the energy dissipation function is independent of the energy of the incident particle.
Theoretical calculations extend the energy dissipation function to relativistic particles.
Figure 11 shows the energy dissipation functions for electrons with energies between 25 keV and 10 MeV as a function of fractional range. The largest effect of a changing angular distribution occurs at high altitudes, in the first half of the fractional range. The PEM particle instruments sample the incident spectra at a number of energies to give a good energy resolution of the spectra. At each energy step the pitch angle distribution is characterized. The energy step and resulting peaking parameter are used to look up the appropriate energy deposition profile.