Comparison of 3-D and 2-D Cylindrical Symmetry FDTD Simulation Results of a Lightning Strike to Gaisberg With ALDIS Sensor Measurements

In this article, numerical computations applying the finite-difference time-domain (FDTD) method are performed. Lightning electromagnetic fields radiated by a lightning strike to the Gaisberg Tower in Salzburg, Austria, and propagating over irregular terrain are calculated. The field propagation is computed with a three-dimensional (3-D) FDTD and, for comparison, a 2-D cylindrical symmetry FDTD. With topographic height maps, seven different propagation paths for a selected lightning strike to the Gaisberg tower are simulated and the resulting magnetic field (H-field) is compared with the received signal strength at seven sensors of the ALDIS sensor network for that event. The return stroke is represented by a transmission line model and the current waveform recorded at the top of the Gaisberg tower was used. The results of the 3D-FDTD simulation correlate well with H-fields registered at sensor sites in mountainous environments. Hence, 3D-FDTD can represent complex local reflection phenomena correctly, which the 2D-FDTD cannot. The results of recent studies, which show that a lightning strike to a mountain gives rise to a field enhancement at the sensor site for a relatively flat propagation path, could be verified by comparing the FDTD results with a set of existing sensor measurements. For the, otherwise, very hilly terrain conditions in Austria, the field enhancement caused by the mountain is attenuated along the paths to the respective sensors.