Numerical modelling of propagation effects

Efficient spectrum planning requires models to account for the effects of the atmosphere and terrain on radio systems. One requirement is for statistical models based on as few, readily available, parameters as possible; these tend to be empirical or semi-empirical in nature. A second type of requirement is the modelling of the performance of a specific communication or radar system; real-time forecasts are of particular interest to military users. This requires more accurate propagation models and more detailed environmental information than the statistical approach. RAL have developed several numerical propagation models that account for the effects of the atmosphere and terrain on radio systems at frequencies from VHF to millimetric. Some of these are discussed. As well as being useful simulation and forecasting tools, the models have provided insight into the propagation mechanisms and can be a basis for improved statistical models