A study of the effects of melting snow on communications links in Scotland

Melting snow, or sleet, is recognised as a potentially serious form of impairment on communications links in cooler temperate climates. Current models neglect sleet, and base their precipitation-related fade depth solely on rain. To develop an improved understanding of the potential effects of sleet, the Radio Communications Research Unit at RAL has developed a 3 GHz fully scanning polarimetric Doppler radar and deployed it at the University of St Andrews in south-east Scotland. It is designed for long-term, statistical observations of rainfall spatial structure and melting layer effects in Scotland. Data from the radar will augment measurements of precipitation-induced attenuation along operational microwave and millimetre wave communication links in the radar coverage area. Results are presented of a continuing study to quantify the annual statistics of the radar-derived melting layer height and its vertical extent and the correlation with ground temperature and raingauge measurements. Comparisons are made between radar-measured parameters and theoretical predictions from a melting layer model, developed at the University of Essex, UK, in an attempt to impose constraints on the model parameters. Once this is achieved, more confidence can be gained in the ability of the model to describe the additional attenuation to be expected in the melting layer. Finally, examples are shown where radar measurements support the idea that observed enhancements in link attenuation are related to a descent of the melting layer to intersect the link path.