A bottom-mounted, circularly scanning sonar operating at 40 kHz has been used to map changes in water sound speed over a circular region 150 m in diameter. If it is assumed that the salinity remains constant, the change in sound sped can be converted to a change in temperature. For the present system, the spatial resolution is 7.5 m and the temperature resolution is 0.05 ¿C. The technique is based on comparison of successive sonar scans by means of a correlation algorithm. The algorithm is illustrated using data from the Sediment Transport Events on Slopes and Shelves (STRESS) experiment. ¿ American Geophysical Union 1991