An infrared scanning system for producing thermal contour maps of radioactive waste storage tanks is capable of detecting a 1-ft2 area on the bottom of a 75-ft-diam tank if the temperature of the scanned area exceeds the background temperature by 3°C. Representative thermal maps of storage tank bottoms with artificially-introduced target regions are illustrated. Although the scanning system is primarily intended to measure temperature differences, it can be used to make background temperature measurements in the storage tanks by the use of a calibrated target.