DETECTION AND PROCESSING OF LIGHTNING-SOURCED MAGNETOTELLURIC TRANSIENTS WITH THE WAVELET TRANSFORM

In audio-frequency magnetotelluric surveys, electromagnetic radiation from worldwide thunderstorm activity is used as an energy source for g eophysical exploration. Owing to its origin, such a signal is inherent ly transient and short Lived. Therefore, special care should be taken in the detection and processing of this transient signal because the i nterval of time between two successive transient events contains almos t no information as far as the audio frequency magnetotellurist is con cerned. In this paper, a wavelet transform detection, processing and a nalysis technique is developed. A complex-compactly-supported wavelet, known as the Morlet wavelet, is selected as the mother wavelet. With the Morlet wavelet, lightning transients can be easily identified in t he noisy recordings and the magnetotelluric impedance tensor can be co mputed directly in the wavelet transform domain. This scheme has been tested on real data collected in the archipelago of Svalbard, Norway a s well as on five sets of synthetic data contaminated with various kin ds of noise. The results show the superior performance of the wavelet transform transient detection and analysis technique.