Building a model of a fi eld sweep signal complicated by harmonics in a problem of seismic data spectrum broadening

Background. The excitation of elastic waves in Vibroseis is accompanied by the appearance of harmonics, i.e. waves with multiple with respect to the fundamental one frequencies. Traditionally they have been regarded as noise and many efforts have been made to suppress them. However, over time it became clear that harmonics can be used to expand the signal spectrum. The corresponding technique is a two-stage procedure, the first step of which is the prediction of the harmonics. In the second step, this field is subtracted from the correlogram in an adaptive manner. It is possible to provide the algorithm with the desired statistical stability property in the presence of intensive random noise in case the adaptation filters have certain qualities. Here, using a real ground force signal as an example, we study the features of the adaptation filters and show that they have the required properties. This allows using them to solve the problem of broadening the seismic data spectrum by involving harmonics.

Aim. The aim of the work is not only to study the properties of the adaptation operators, including their efficient length, but also to develop an algorithm for broadening the spectrum of a vibroseis signal by involving harmonics.

Materials and methods. In the course of the study, a filed ground force signal recorded during a seismic experiment was used, as well as two raw vibroseis gathers acquired at two diff erent locations. Methods for its study involve the use of various digital filtering techniques. The method of optimal recursive filtering is also used, which makes it possible to separate the wavefield associated with the main sweep signal from the wavefields associated with harmonics.

Results. The main result of the work is the conclusion about the small efficient length of the adaptation filters, which allows them to be used to solve the problem of broadening the seismic data spectrum.

Conclusions. The separation of the seismic data associated with the main sweep signal from the data associated with the harmonics is possible due to the fact that the adaptation filters have a simple shape and a small efficient length. After separation of the wavefields, it becomes possible to use harmonics to broaden the signal spectrum to increase the resolution of the seismic data, as well as to refine the depth images.

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