The Microwave Sounding Unit (MSU) aboard the NOAA series of polar orbiting satellites (TIROS-N to NOAA-11) have provided stable, precise measurements of vertically integrated, atmospheric temperature since December 1978. In this study, comparisons are made between the MSU channel measurements and those derived from the Global Data Assimilation System (GDAS) at the National Meteorological Center (NMC) over the period 1979 to 1990. Land areas rich in Radiosonde Observations (RAOBS) showed similar magnitudes of spatial variability between the NMC GDAS and the MSU temperatures. Excessive spatial variability can be noted in the GDAS over land areas where conventional data is poor. Over the ocean, however, the assimilation of satellite data into the model improves the spatial variability detected by the GDAS.