The Moderate resolution Imaging Spectro-radiometer (MODIS) has completed its first year of data acquisition on the Terra spacecraft. MODIS is a key instrument of NASA's Earth Observing System, designed to assess global climate change in the early 21st Century. MODIS was designed to provide the high radiometric accuracy measurements necessary to detect subtle signatures of global climate change in a suite of geophysical science products in the land, ocean, and atmosphere disciplines. The accuracy of these products is a function of the radiometric accuracy of MODIS. This paper uses MODIS Airborne Simulator (MAS) and Scanning High resolution Interferometer Sounder (SHIS) radiometric data sets from the TX-2001 field experiment to compare directly to MODIS measurements. The MAS and SHIS fly on NASA's high altitude ER-2 aircraft. On the ER-2, the MAS and SHIS synergism creates a powerful IR calibration assessment tool. MAS includes 19 spectral bands similar to those on MODIS, and provides the high spatial resolution data useful for simulating the MODIS footprint. SHIS provides highly accurate (< 0.5K) fine spectral resolution infrared data. In the comparison procedure, the SHIS calibration is transferred to MAS, and the MAS fields of view are integrated to the MODIS spatial resolution. Spectral, altitude, and viewing geometry dependencies are removed. The result is a robust comparison of MAS and MODIS radiances/brightness temperatures yielding residuals that will be analyzed for insight on MODIS radiometric performance.