Estimating ground conductivity and improving lightning location goodness of fit by compensating propagation effects

Abstract

Propagation effects were noticed in lightning ground waves received at the five stations of a 10-km-baseline time-of-arrival lightning location system at Kennedy Space Center, Florida, on 10 September 1992. The ground waves were nonuniformly smoothed, and that caused the tagged points in time on the pulses to be nonuniformly delayed. Lightning location chi-squares were 2 orders of magnitude worse for ground wave propagation than for line-of-sight propagation, but 0.3 of an order of magnitude was recovered by compensating the time tags for propagation effects. Effective ground conductivity, associated time tag delay, effective source height, and station gain were estimated by applying the method of least squares to a nonlinear objective function. The geometric mean ground conductivity was 0.0059 S/m, and the geometric standard deviation was 1.83 for 384 propagation paths of 78 lightning sources, in line with accepted values. The geometric standard deviation of conductivity for a subset of 122 paths, including consecutive lightning sources having nearly identical propagation paths, was 1.86. The geometric standard deviation derived from 68 ratios of consecutive conductivity estimates having nearly identical propagation paths was 1.38; thus the geometric standard deviation of conductivity among paths was 1.71. Copyright 2006 by the American Geophysical Union.