Estimation of peak return stroke currents, current time derivatives and return stroke velocities from measured fields

Eighteen subsequent return stroke fields from triggered lightning flashes, observed at 5.16 km were used to test the ability of a return stroke model to predict the return stroke peak currents, peak current time derivatives and return stroke velocities from the measured fields. In each example, the parameters of this previously published model were changed until a best fit was obtained for the first few microseconds of the measured field and the final static field change. Once a best fit had been obtained, the corresponding peak current, the peak current time derivative and the return stroke velocity were all compared with the measured values. The mean percentage error (MPE) and the mean absolute percentage error (MAPE) of the predicted current peaks are 6.9 and 11.3%, respectively. The MPE and MAPE corresponding to the predicted current time derivatives are 13.0 and 13.8%, respectively. The model predicted velocities of these eighteen strokes had a MPE of 19.6% and a MAPE of 20.3%. The results show that the method outlined in this paper can be used to extract the return stroke current parameters from the measured electromagnetic fields. (C) 1998 Elsevier Science B.V. All rights reserved.