Location Accuracy Improvements using Propagation Corrections: A Case Study of the U.S. National Lightning Detection Network

A number of applications that employ information from Lightning Locating Systems (LLSs) require accurate estimates of the ground-strike location of return strokes in Cloud-to-Ground (CG) flashes. A study by Schulz and Diendorfer (2000) has shown that the primary factors limiting accurate geo-location of these strokes are (1) the delay of arrival-time of the return-stroke radiation field produced by variations in terrain elevation, and (2) frequencydependent delay and attenuation of the ground-wave radiation field produced by propagation over finiteconductivity soil. It has been found that both of these propagation effects can be addressed by applying location-specific corrections to the arrival times measured by LLS sensors. This paper provides an overview of Vaisala’s propagation correction methodology as applied to the NLDN, and includes performance-related analyses using both natural and rocket-triggered lightning (RTL) from 2008-9. Both theoretical and experimental analyses indicate that these corrections produce approximately a factor-of-two improvement in location accuracy, with typical median values in the range of 200 m. A preliminary unpublished study of corrected and uncorrected location accuracy for the NLDN was carried out by one of the authors (A. Nag) using RTL data from the summers of 2003-4. Results from this study are consistent with the findings reported by Nag, and are from a more-recent time period. Networks with closer-spaced sensors (<~150 km) typically experience less improvement from the use of propagation corrections, but they also normally start out with RMS timing errors well under one μs.