Development of radio acoustic sounding system (RASS) with Gadanki MST radar – first results

摘要

A high-power acoustic exciter was designed and developed for the Gadanki MST Radarto facilitate observations in the Radio Acoustic Sounding System (RASS) mode. Sweeprange of acoustic signal frequencies was set to 94–125 Hz so as to satisfy Bragg matchingcondition for temperature range of −90°–40°C between surface and the tropopause(about 17 km). Raytracing of acoustic wave propagation was used to predict the antennabeam directions along which optimum RASS echoes could be obtained. During theRASS observation period of about 18 h on 23–24 July 2006 height profiles ofatmospheric virtual temperature were obtained between 1.5 km and 10 km andoccasionally up to 14 km. In comparison with the three simultaneous radiosondelaunches, RASS derived temperature profiles had the r.m.s. discrepancy of about 1 K,although deviation of the RASS results sometimes appeared when the radial windvelocity was not fully available for the correction of apparent sound speed. This study hassuccessfully demonstrated capability of the RASS application with the Gadanki MSTradar, which will be used for continuous monitoring of the temperature profiles in thetroposphere and lower stratosphere region in the tropics.