# Vibroseis Correlation - An Example of Digital Signal Processing

Lawrence W. Braile
,
Purdue University
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#### Summary

In the vibroseis method of seismic exploration, the seismic energy source (ground vibration controlled by shaking the mass of the vibroseis truck) is distributed over a time of several seconds. To see how vibroseis recording and processing works, we will look at the mathematics of vibroseis signal processing in both the time and frequency domains and view illustrations of the recorded and processed signals.

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## Context

#### Audience

Upper level or graduate geophysics or seismology course.
Designed for a geophysics course.

#### Skills and concepts that students must have mastered

Digital signal processing, Fourier Transforms.

#### How the activity is situated in the course

In reflection seismology, describes the vibroseis method; provides an example the application of digital signal processing and Fourier transforms.

## Goals

#### Content/concepts goals for this activity

Understanding vibroseis and associated processing concepts.

#### Higher order thinking skills goals for this activity

Example of digital processing using convolution, correlation and Fourier transforms.

## Description of the activity/assignment

In the vibroseis method of seismic exploration, the seismic energy source (ground vibration controlled by shaking the mass of the vibroseis truck) is distributed over a time of several seconds. This distribution of energy over time is in sharp contrast to explosive methods of generating seismic energy in which the source is generated in a small fraction of a second. The vibroseis source is usually chosen to be a distinct signal, such as a sweep (see Figure 1; sweep movie, swmovie.m, in which the sweep is generated and moves across the screen in real time) in which the signal changes systematically from low frequency at the beginning to high frequency at the end of the source. Computer processing of the seismic signals from a vibroseis source uses the distinct characteristics of the sweep to "collapse" the energy into short duration wavelets—essentially equivalent to the seismograms that would be recorded with impulsive sources such as explosives.

To see how vibroseis recording and processing works, we will look at the mathematics of vibroseis signal processing in both the time and frequency domains and view illustrations of the recorded and processed signals. To fully explore the vibroseis method, an understanding of convolution, correlation and the Fourier Transform is needed.

## Determining whether students have met the goals

Class discussion to evaluate understanding.