Estimation of Lightning Current Waveforms from Far‐Field Waveforms Generated by Lightning Strikes to a Tall Structure Using the z ‐Transform

The relationship between FDTD‐computed far vertical electric‐field waveforms over perfectly conducting ground and those over lossy ground, generated by a lightning strike to flat ground, is formulated using a transfer function in the z ‐domain. In the FDTD simulations, a lightning current propagates upward along a vertical channel. Using the derived transfer function, far vertical electric‐field waveforms over lossy ground for lightning strikes to both flat ground and a tall structure are transformed into the corresponding waveforms over perfectly conducting ground. The lightning current waveforms are then estimated from the transformed far‐field waveforms. © 2026 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.