For purposes of completing the initial calibration and validation work for the Special Sensor Microwave Imager/Sounder (SSMIS) serial number 2 instrument, we have implemented a comprehensive radiative transfer model (RTM) in order to verify on-orbit upper air brightness temperature measurements for SSMIS channels 19--24. Rigorous computational treatment of the effects of the Earth's magnetic field on absorption by oxygen in the stratosphere and mesosphere provides us a solid baseline for comparison of theoretically based forward RTM calculations with the satellite observations. With the inclusion of flexibility in our model to account for departures from perfect instrument behavior, initial results provide us a reasonable measure of confidence that the agreement of our model with the observations should make the SSMIS-derived data products sufficiently reliable.