An improved method for broadband interferometric lightning location using wavelet transforms

Abstract

The principle of VHF broadband interferometer for lightning observations is to extract the phase differences between a pair of RF signals at different frequency components, and thereafter, to compute the direction of the radiation source. However, the phase difference spectra are usually distorted by random noise, which directly affects the location accuracy and reliability. In order to suppress phase interference effectively, a phase filtering algorithm which combines circular correlation with translation-invariant denoising is proposed. Application of the algorithm to a segment of observational data shows that the proposed algorithm does a much better job in recovering the phase spectra than other techniques. Simulated data distorted by the addition of random noise are also used to illustrate the improvements of the method in resolving incident angle, which is compared with other wavelet-based thresholding techniques and the conventional Fourier transform-based cross-correlation method. Finally, this phase filtering algorithm is applied to mapping two natural lightning processes. Contrast analysis reveals that this algorithm could be utilized to retrieve well-defined paths which are not discerned by conventional method, and depict the branches more clearly and precisely. Copyright 2009 by the American Geophysical Union.