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Abstract

So far, the complexities of the seismic source and receiver have been discussed. Once a seismic signal is transmitted and received, it must be recorded. The different types of signals discussed in this chapter are defined as follows:

  • (1)

    Source signal—The pressure field created by the seismic source.

  • (2)

    Reflectivity signal—The earth's reflection sequence convolved with the source wavelet.

  • (3)

    Seismic signal—Everything received as a result of the source firing. The seismic signal includes the reflectivity signal as well as ground roll, refractions, diffractions, sideswipe, channel waves, etc.

  • (4)

    Received signal—The electrical output of the receiver group. This is the seismic signal plus all environmental noise.

  • (5)

    Recorded signal—The data, that is the instrument-filtered signal plus any additive instrument noise, which go on tape.

The information contained in a signal can be characterized by three quantities: signal-to-noise ratio, bandwidth, and duration. Signal-to-noise ratio can have different meanings depending on the circumstances. For example, diffractions from out of the reflection plane are noise on 2-D data but are part of the signal in 3-D surveys. In seismic exploration, the recorded signal bandwidth is usually 0–250 Hz or lower. Often, data are processed in a narrower band, say 5–80 Hz, even though they may be recorded in a broader band. The duration of recorded signals depends on the nature of the source and target depth. Impulsive sources, such as land dynamite or marine air guns, create a source signal with a duration of a few

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