Showing papers on "Wavelet published in 1975"

Homomorphic filtering — theory and practice*

Abstract: The application of homomorphic filtering in marine seismic reflection work is investigated with the aims to achieve the estimation of the basic wavelet, the wavelet deconvolution and the elimination of multiples. Each of these deconvolution problems can be subdivided into two parts: The first problem is the detection of those parts in the cepstrum which ought to be suppressed in processing. The second part includes the actual filtering process and the problem of minimizing the random noise which generally is enhanced during the homomorphic procedure. The application of homomorphic filters to synthetic seismograms and air-gun measurements shows the possibilities for the practical application of the method as well as the critical parameters which determine the quality of the results. These parameters are: a) the signal-to-noise ratio (SNR) of the input data b) the window width and the cepstrum components for the separation of the individual parts c) the time invariance of the signal in the trace. In the presence of random noise the power cepstrum is most efficient for the detection of wavelet arrival times. For wavelet estimation, overlapping signals can be detected with the power cepstrum up to a SNR of three. In comparison with this, the detection of long period multiples is much more complicated. While the exact determination of the water reverberation arrival times can be realized with the power cepstrum up to a multiples-to-primaries ratio of three to five, the detection of the internal multiples is generally not possible, since for these multiples this threshold value of detectibility and arrival time determination is generally not realized. For wavelet estimation, comb filtering of the complex cepstrum is most valuable. The wavelet estimation gives no problems up to a SNR of ten. Even in the presence of larger noise a reasonable estimation can be obtained up to a SNR of five by filtering the phase spectrum during the computation of the complex cepstrum. In contrast to this, the successful application of the method for the multiple reduction is confined to a SNR of ten, since the filtering of the phase spectrum for noise reduction cannot be applied. Even if the threshold results are empirical, they show the limits for the successful application of the method.

Techniques for the deconvolution of seismic signals

Abstract: It is commonly assumed that a reflected seismic signal consists, at least in part, of a convolution of the earth reflectivity function with a propagating "wavelet". The purpose of "deconvolution" is to separate the wavelet from the reflectivity function, or to at least change the form of the wavelet to one which is more desirable. This paper describes methods which have been applied or proposed for the deconvolution of seismic signals recorded for geophysical exploration purposes.