Study of Sferic Position Location Mechanisms

D. Qiu, T. Nguyen, C. Yang

Abstract:	Naturally occurring very low frequency (VLF) signals such as radio signals produced by lightning strikes (sferic) have been considered for underground navigation. The magnetic fields of VLF radio signals can penetrate into the ground much deeper than the electric counterpart. In addition, the out-band noise caused by the interference of two radio signals with their difference of frequency in the VLF band is much lower underground than above ground simply because these higher frequency signals are attenuated more than the VLF signals, leading to an increased underground signal to noise ratio (SNR). In this paper, we investigate three sferic-based position location mechanisms. The first mechanism makes use of a small local array with arbitrarily distributed sferic detectors, which cannot determine the location of a lightning source but its angle of arrival (AOA). The AOA can be estimated using the total least squares (TLS) fitting of TDOA measurements. Then the location of an unknown user relative to this array can be determined given two or more non-collinear signals. Dual hyperbolic positioning is the second mechanism to be presented in the paper wherein a large scale network of sferic detectors at known locations is used to detect a lightning strike and calculate its time difference of arrival (TDOA) measurements between various sferic detectors. This is the first hyperbolic positioning, which determines the lightning source explicitly. The same lightning event is also detected by a user at an unknown location. The TDOA measurements between this unknown user and other detectors form the second hyperbolic positioning. The second hyperbolic positioning yields a solution for the unknown user. The last mechanism also relies on a network of sferic detectors but in a smaller scale. The method assumes the lightning wavefront is linear, and solves the slope and yintercept of the wavefront in two dimensions. Unknown user’s position is calculated based on the geometry and estimated lightning wavefronts. Simulation results will be presented to illustrate the three sferic-based position location mechanisms where digitalized waveforms from real data are used to perform signal detection and correlation for TOA estimation. Positioning accuracy of the two algorithms will be evaluated as a function of scenario geometry, array configuration, clock precision, and noise level among others. Future work will also be outlined to consider more realistic atmospheric and underground conditions.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2241 - 2250
Cite this article:	Qiu, D., Nguyen, T., Yang, C., "Study of Sferic Position Location Mechanisms," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 2241-2250.
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