Detection of ducts by wind profiler radar

Abstract

Propagation of radar signals through the atmosphere is strongly dependent on local meteorological conditions, especially in the atmospheric boundary layer. A rapid change in air temperature and humidity with height leads to the generation of tropospheric ducts. Electromagnetic energy can propagate over large distances within a duct and can cause interference on terrestrial and satellite communication links. Duct detection is therefore desirable to predict such interference and influence on radar coverage. Anomalous variations in radiosonde measured temperature and humidity gradient, yield negative values of modified refractive index, M, gradient profiles. These profiles are indicators of ducting conditions in the lower troposphere. However, radiosonde measurements are sparsely distributed in time. Autonomous systems such as wind profiler radars, which operate continuously 24 hours a day could provide continuous monitoring of duct occurrence with height. The 915 MHz wind profiler (operated by the UK Meteorological Office at Camborne) and radiosonde data from Camborne were analysed for the month of June 2000. The data analyses showed that the wind profiler is able to detect ducting conditions through (i) strong correlation of increase in the turbulence structure function parameter, Cn2, with negative values of dM/dz and (ii) agreement in increase in potential refractive index (estimated from radar data) with increase in potential refractive index obtained from radiosonde data, within the duct region.