We will present results obtained during the Joint Airborne IASI Validation Experiment (JAIVEx). The JAIVEx is an international calibration/validation campaign in support of the NPOESS and MetOp series of operational satellites. One of the instruments that flew onboard the WB-57 aircraft is the NPOESS Airborne Sounder Testbed Interferometer (NAST I). It has a similar spectral resolution (0.25 cm^-1) and spectral coverage (645-2760 cm^-1) as the Infrared Atmospheric Sounding Interferometer (IASI), which is onboard the MetOp-A satellite. Both the NAST-I and the IASI ultra-spectral sensors have more than eight thousand spectral channels. We will describe a physical inversion algorithm, which includes all available channels for the atmospheric temperature and moisture retrievals. Due to the spectral properties of the Fourier Transform Spectrometer, data taken from these sensors can be accurately transformed into proxy data for the NPOESS Cross-track Infrared Sounder (CrIS) and can be used to test advanced retrieval algorithms.