There were four flights of the NASA C-130 aircraft carrying the Push Broom Microwave Radiometer (PBMR) over the Konza Prairie Research Natural Area in eastern Kansas in 1985. Their objective was to observe surface soil moisture variations with the PBMR. The radiometer operates at the 21-cm wavelength and has four beams that sweep out a swath of about 1.2 times the aircraft altitude. The resolution of each beam is 0.3 times the altitude. At the time of the flights the soil conditions ranged from very wet to moist and the microwave emission expressed as brightness temperatures for the burned watersheds ranged from below 200 to about 245 K. The brightness temperatures were correlated (r2 = 0.5) with surface moisture measurements and the slope of the regression is in good agreement with prior results over other grasslands. However, for the unburned watersheds the brightness temperatures were around 270 K and roughly independent of the soil moisture conditions. In these unburned watersheds, a buildup of a thatch layer serves as highly emissive layer above the soil, causing high brightness, especially when wet