Efficient calculation of the lightning generated underground electric field

When studying electromagnetic field problems like lightning phenomena, the efficiency of the adopted model relies on the accurate and rapid calculation of Sommerfeld type Integrals (SI). In the present work we propose an efficient method for calculating them, based on their numerical evaluation along a deformed path of integration. The method is combined with an interpolation technique in order to reduce the number of frequencies required in the Fourier synthesis of the time domain electric field. The result is a fast and straightforward tool for the calculation of underground lightning field, without the use of specially developed numerical algorithms or analytical approximations.