Rain radar measurements in Papua New Guinea and their implications for slant path propagation

The Rutherford Appleton Laboratory (RAL) is engaged in an experimental program to characterise precipitation in the tropics. We have developed and built a 3 GHz vertically pointing pulsed Doppler radar capable of measuring the co-polar reflectivity (Z), cross-polar reflectivity (LDR) and the full Doppler spectrum. The system has been installed at the University of Technology (Unitech) at Lae, Papua New Guinea. The radar system began a measurement campaign in December 1995. Unitech operates a receiver for the 12.75 GHz beacon of the Australian OPTUS-B satellite. The elevation angle of the satellite receiver is 72.8/spl deg/. The experiment yields valuable data on the slant path attenuation for comparison with radar predictions. The three principal parameters which are to be extracted from the radar data are the rainfall rate, the rain height and the rain drop-size distribution. The drop-size distribution is also being measured on the ground with a Jess distrometer. The rain events recorded with the radar can generally be classified into i) those which exhibit a clear, well defined bright band caused by the presence of the melting layer in stratiform precipitation, and ii) those which are convective with rain at heights often above 10 km and the Doppler data showing severe updrafts. The linear de-polarisation ratio (LDR) parameter is an excellent indicator of the melting layer which is an effective method of determining the top of the rain.