1887
Volume 17 Number 3
  • E-ISSN: 1365-2478

Abstract

A

Numerous studies have already been carried out on the Fourier Transform and its geophysical applications. The utilisation of computers has brought with it the digitalisation of the major method, reflection shooting, and the different handling techniques for numerical data have given birth to numerous papers on the subject. Gravimetric surveying has always been a numerical method, but it is evident that for it, too, new possibilities have been opened. Consequently, gravimetric experts are becoming increasingly interested in the theory and applications based on the study of frequencies spectra using the Fourier Transform. The researches of C. A. Schwartz, W. Sokoloff and W. C. Dean have been followed by other interesting ideas concerning the data processing of gravity measurements, such as: calculation of the first vertical derivative (V. Baranov), interpretation of the anomalies with the aid of their spectra (M. E. Odegard and J. Berg Jr.), isopach reduction in gravimetric surveying (J. L. Bible), etc.

All these ideas and techniques have the same purpose: to make the interpretation easier. But, although they have the same aim and tackle the same type of difficulty, it would seem that the gravimetric and the seismic experts have developed their own tools independently of each other, with no consideration for the fact that both geophysical methods, in particular the methods of treatment of raw measurements, are, if not identical, at least very close to one another and that, consequently, any improvement in one method may be useful to the other.

The purpose of the present paper is to reconsider the philosophy of the seismic and gravimetric methods, starting with data recording, then dealing with the most important data processing systems and finally ending with the interpretation. The paper bases its approach on two points of view which are in fact complementary:

– Although digital data processing is almost always effected in the functional sphere by convolutions, it is much easier to understand and to conceive these systems if one reasons alternately in the functional and frequency spheres; this is possible by using the Fourier Transform.

– By considering the problem in frequencies, there is no fundamental difference between the seismic and gravimetric methods. A curve plotted in gravity units, as a function of the distance, and a seismic trace which represents the variations of the output of a galvanometer, as a function of the time, are identical from the point of view of the Fourier Transform.

With these ideas in mind, the following problems are dealt with:

– Seismic and gravity signals.

– The sampling problem in gravimetry (data sampling rate non‐constant).

– Presentation and discussion of spectra of some synthetic and practical examples:

•Wave number filtering.

•Frequencies filtering.

•The problem of the frequency o (horizontal and vertical derivatives).

•Continuation = deconvolution.

– Other applications of the Fourier Transform in gravimetry.

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2006-04-27
2020-05-30
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References

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