Application of Improved Cross Power Spectrum Phase Method to Acoustic Source Localization of Thunder

The thunder sound source is located by using single station lightning channel three-dimensional imaging system. Different time delaying estimation method is used, among which the cross correlation function method and the cross power spectrum phase method are mainly introduced. Considering the high frequency noise produced by the lightning process, reflection reverberation caused when the thunder reaches the ground, all kinds of noise is superimposed on the thunder signal (such as collection circuit itself noise), and an improved cross power spectrum phase delay estimation method is raised.Station imaging system is composed of microphone array and data acquisition card. A large amount of reliable data is collected by the system on the roof of Guangdong Provincal Meteorological Bureau building since 2009. Two thunder processing records in Guangzhou are selected, combined with the high speed camera data, and the cross correlation function method and the improvement cross power spectrum phase method are compared in the application of acoustic localization of thunder. First, the time difference of thunder signal reaching the different microphones is calculated by using the cross correlation function method and the improved cross power spectrum phase method. Then, the sound source azimuth and elevation angle information are solved by the array geometry. Comparing with the two-dimensional photographs observed by high speed camera, the imaging result is in good agreement, showing good reliability. As the cross correlation function method algorithm is based on the amplitude correlation, it can't distinguish the array arriving simultaneously from different sound source. Because its noise immunity is weak, the discrete imaging point can't depict the channel shape better. Instead, the improved cross power spectrum phase method calculates time delay by phase difference, and it has strong noise immunity and intensive imaging point, so it does better in discerning the branch channel. The contrast result indicates that the improved cross power spectrum phase method is better than the cross correlation function method for the low signal to noise ratio environments and multi-forked lightning. Finally, three-dimensional thunder source is obtained through the direction information and distance of thunder calculated with improved cross power phase method.The application of single station microphone array imaging system reduces the environmental requirements and costs. Although the accuracy of results is low, for close range, multi-branch, multi-ground lightning, the single station microphone array provides a simple and practical three-dimensional observation programs, and it has application prospects for small scale lightning monitoring, early warning and research. A real-time processing of three-dimensional imaging thunder sound source system is in plan, based on a single station of microphone array, and it will play its unique role in the three-dimensional structure of the lightning research.