Investigations into the initial refractivity gradients and signal strengths over the english channel

Refractive conditions in the lowest portions of atmosphere influence the propagation of radio waves passing through them. Previous studies into initial refractive conditions (i.e. lowest 100m of atmosphere) are either old or based on estimates from global isopleths. A radio propagation study in English Channel carried out in 2006 observed super-refractive conditions, correlated to signal strengths received on different over sea paths. The current research uses meteorological information from the weather stations in the English Channel, based on the assumption of horizontal homogeneity. Signal level enhancements on two trans-horizon, co-linear paths operating on 2 GHz and 240 MHz frequencies can be attributed to super-refractive/ducting refractive conditions within the lowest 100m of atmosphere, particularly those within the 52m to 84m height interval. The refractivity gradient between 52m and 84m height interval is maximum (in magnitude) in summers, correlating with enhanced signal strengths received in summer. Based on signature comparison, the propagation mechanism for most of signal enhancement events is ducting.