Abrupt noise rejection using wavelet transform for electromagnetic wave observation signals

This paper presents a method of realizing abrupt noise rejection in an observed electromagnetic (EM) wave signal by using the wavelet transform(WT) technique. Our goal is to better process the EM waves that radiate from the earth's crust in order to predict earthquakes. The proposed method involves the multi-scale wavelet transform domain with a second-order derivation property. Typical noise rejection methods that use WT set the threshold according to the noise power. Unfortunately, this approach can suppress the precursor radiation since its radiated energy and period are similar to the abrupt noise. The method proposed herein uses local maximum points on the WT coefficient (wavelet maxima), which means that no threshold is needed to suppress abrupt noise. It is shown that the proposed method can be reject abrupt noise without dropping the precursor signal.