On validation of FCCFs for lightning striking tall objects considering propagation effect of finitely conducting earth

In this paper we have studied the accuracy of field-to-current conversion factors (FCCFs) presented by Baba and Rakov for currents inferred from electromagnetic field produced by lightning strike to tall objects, considering the perfectly and finitely conducting ground, respectively. For the perfectly conducting ground, the different FCCFs for the peak currents have different accuracy ranging from about underestimation of 18% to overestimation of 10% for the reflection coefficients at the two ends of object ρ
t
=−0.5 and π
b
=1.0, and from about underestimation of 25% to overestimation of 10% for π
t
=−0.5 and π
b
=0.7, and their accuracy decreases with the increase of current risetime RT. For the finite conductivity with 0.01 S/m and 0.001 S/m, FCCFs will cause many errors if we do not take into account the propagation effect along the finitely conducting ground, and their errors obviously increase with the decrease of the conductivity. For example, for π
t
=−0.5 and π
b
=1.0, the errors are about 20% when the conductivity is 0.01 S/m while the errors are about 55% when the conductivity is 0.001 S/m for lightning strike to the 168-m-high object. Therefore, we revised FCCFs by considering the propagation effect of finite conductivity on the electromagnetic field radiated by lightning strike to tall objects, and found that our revised FCCFs have much better accuracy for the lossy ground than that presented by Baba and Rakov.