A two-step methodology is presented for extracting ground state population distributions from I+i resonance enhanced multiphoton ionization (REMPI) spectra. In the first step the ion signal is corrected for variation with laser intensity as it is collected, generating an iso-power spectrum. In the second step populations and alignments are derived from the iso-power spectrum by correcting for the interdependent effects of saturation and intermediate state alignment. This procedure is applied to

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... a room temperature thermal distribution of nitric oxide using the i+i REMPI process in which lines of the NO A~Z--X2H (0,0) band constitute the resonant transition. The present treatment is able to recover the known rovibrational population distribution, independent of branch choice, over a wide range of practical operating conditions.