1. A method for extracting a target signal from measured signal including the steps of: a) measuring a target signal and background noise to obtain measurement data; b) using a computer to extract coherent structure from the measurement data using wavelets and corresponding wavelet coefficients; c) comparing the wavelet coefficients of the wavelets with a threshold with the computer; d) eliminating the wavelet coefficients of the wavelets that are less than the threshold with the computer; e) determining approximation coefficients at a selected scale m after said steps a)-d) based upon the wavelet coefficients at scale m; f) determining a wavelet vector at scale m based upon the approximation coefficients; and g) extracting information at scale m based upon the wavelet vector with all wavelet coefficients set to zero except those at the scale m.