Mapping Underground Geological Structures Using Lightning-Induced Electromagnetic Pulses in the VLF Frequency Range

A new method for underground mapping and imaging allows the use of the underground reflections of electromagnetic pulses caused by lightning (occurring up to thousands of miles away) to be used for geologic imaging. These electromagnetic pulses, known as 'sferics,' travel between the earth and the ionosphere for great distances and scatter off of underground features- a phenomenon that can be measured with the proper equipment in order to provide sub-surface data. Stanford researchers have developed a 3-antenna array that detects the original atmospheric pulse on two channels, and the underground, scattered pulse on a third channel. This information is then stored as a 3 channel, very low frequency waveform that can then be processed to obtain an image or representation of the underground features that caused the pulse to scatter. This method can be used to find mineral, gas, or oil deposits, as well as to image man-made underground features.