Hybrid models for operational EM forecasting with EEMS

Electromagnetic sensors are affected by refractive effects in the troposphere and by diffraction and reflection due to terrain. Defence applications require fast and accurate propagation models for operational EM forecasting. The TERPEM propagation package has been commissioned by the Royal Navy for inclusion in its electromagnetic forecasting tool EEMS (environmental electromagnetic modelling system). The TERPEM propagation models are based on the hybrid model approach, which provides fast computation while retaining high fidelity of the results. The simple sine transform approach used in the vertical parabolic equation (VPE) region is adequate for microwave propagation over smooth surfaces, but more sophisticated methods are needed for the modelling of rough surfaces and for HF applications. Current work focuses on the rigorous treatment of finite impedance and rough surfaces with generalised impedance techniques