The spectral line-reversal method has been applied to determine population temperatures within an (argon-calcium) plasma, generated by a reflected aerodynamic shock. The measurements have been made simultaneously on (i) normal bound-bound Ca I lines, and (ii) lines involving strongly auto-ionizing levels. The agreement of the two sets of values identifies the electron temperature with the temperature characterizing the populations of the bound excited states, giving improved confidence in the existence of local thermodynamic equilibrium in the reflected shock.