Results on Planetery Boundary Layer sounding by automatic RASS

A radio acoustic sounding system (RASS), operating at an acoustic frequency f{hook} ∼ 360 Hz, proved to be capable of measuring the vertical temperature profile in the planetary boundary layer (PBL) with an accuracy and vertical resolution comparable to those of traditional apparatus (radiothermosondes borne by tethered or disposable balloons, thermosondes borne by aircraft and so on, yet combined with the advantages typical of remote sensing techniques. Since summer 1983 the system has been running in a completely automatic way by means of a microprocessor and can provide the average thermal profile at preset time intervals (typically 0.5 h). (Previously, the acoustic sounding frequency affording the fundamental condition of Bragg resonance between acoustic and radio wavelengths had to be identified by an operator). The maximum range of measurement has been ∼ 1000 m in 50% of cases. Temperature measurements are reliable from an altitude of a few tens of meters. Results for different thermodynamic stability conditions, together with good performances achieved in adverse atmospheric conditions such as strong wind, snow, rain, etc., are presented here. Such results indicate the usefulness of the automatic RASS as a tool for meteorological purposes and for the application of air pollution control strategies. Maximum sounding range attained for different areas of the acoustic antenna is also analysed in order to evaluate the performance of an automatic mobile RASS.