A commercially available Doppler-SODAR and a sonic anemometer-thermometer have been operated during June and July 1990 at the Nuclear Research Center Karlsruhe to mesure backscattered echo, the wind vector, the standard deviation of the vertical wind speed and sonic data like the heat flux. Other meteorological parameters have additionally been measured by the SODAR, the sonic instrument at 100 m AGL, and at a 200 m high tower at which the sonic instrument was installed. Temperature structure parameters derived from SODAR backscattering echo and from sonic anemometer-thermometer data using mixed layer similarity relationship are compared and show fairly good correlation. Measurements of the SODAR backscattered echo and standard deviation of the vertical wind speed are each used to estimate the sensible heat flux in the convective Planetary Boundary Layer. Comparison with simultaneous point measurement by the eddy correlation method shows good agreement between the two instruments. (orig.).