A VHF BOUNDARY-LAYER RADAR - FIRST RESULTS

The development of a novel VHF radar designed to measure winds and tem peratures in the planetary boundary layer is described. The radar oper ates at 54.1 MHz and is compact and easily transportable. The antenna system consists of 12 Yagis grouped into three subarrays arranged in t he form of an equilateral triangle. Transmission takes place on the wh ole array, and reception takes place on the three subarrays, with wind s measured by the spaced antenna technique over a height range between 300 and 3000 m. Results from field trials conducted in southern Austr alia in a variety of meteorological conditions are presented. Comparis ons with high-resolution radiosondes launched from the radar site show excellent agreement, with rms differences between radiosonde and rada r wind components being about 1.5 m s(-1). Observations carried out in rain show that echoes from precipitation are clearly distinguishable from clear-air echoes. Unlike UHF radars, this means that vertical air velocities can be measured during precipitation, and the evolution of drop-size distributions can be studied down to low altitudes. It is s hown that temperatures derived from a radio acoustic sounding system a re measured up to heights near 2 km, depending on background wind cond itions.