# Difference between revisions of "Rms amplitude AGC"

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where ''x<sub>i</sub>'' is the trace amplitude and ''N'' is the number of samples within the gate. | where ''x<sub>i</sub>'' is the trace amplitude and ''N'' is the number of samples within the gate. | ||

− | + | [[file:ch01_fig4-10.png|thumb|left|{{figure number|1.4-10}} A portion of a CMP stack before and after application of two different rms AGC functions. Numbers on the top indicate the window sizes in milliseconds used in computing the AGC gain function described by equation ({{EquationNote|10}}).]] | |

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Typically, we start out with a certain gate length at the shallow part of the trace. Gate length can be kept either constant or it can be increased systematically down the trace. At each gate center, the value of the gain function is computed as described above. Function ''g''(''t'') then is interpolated between the gate centers. Note that the specified time gates are stationary — they do not slide down the trace. | Typically, we start out with a certain gate length at the shallow part of the trace. Gate length can be kept either constant or it can be increased systematically down the trace. At each gate center, the value of the gain function is computed as described above. Function ''g''(''t'') then is interpolated between the gate centers. Note that the specified time gates are stationary — they do not slide down the trace. | ||

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*[[Instantaneous AGC]] | *[[Instantaneous AGC]] | ||

*[[Relative trace balancing]] | *[[Relative trace balancing]] | ||

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==External links== | ==External links== | ||

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[[Category:Fundamentals of Signal Processing]] | [[Category:Fundamentals of Signal Processing]] | ||

+ | [[Category:Gain applications]] |

## Latest revision as of 16:12, 28 August 2014

Series | Investigations in Geophysics |
---|---|

Author | Öz Yilmaz |

DOI | http://dx.doi.org/10.1190/1.9781560801580 |

ISBN | ISBN 978-1-56080-094-1 |

Store | SEG Online Store |

The rms amplitude AGC gain function is based on the rms amplitude within a specified time gate on an input trace. This gain function is computed as follows. The input trace is subdivided into fixed time gates. First, the amplitude of each sample in a gate is squared. Second, the mean of these values is computed and its square root is taken. This is the rms amplitude over that gate. The ratio of a desired rms amplitude (say 2000) to the actual rms value is assigned as the value of the gain function at the center of the gate. Hence, the scaling function *g*(*t*) at the gate center is given by

**(**)

where *x _{i}* is the trace amplitude and

*N*is the number of samples within the gate.

Typically, we start out with a certain gate length at the shallow part of the trace. Gate length can be kept either constant or it can be increased systematically down the trace. At each gate center, the value of the gain function is computed as described above. Function *g*(*t*) then is interpolated between the gate centers. Note that the specified time gates are stationary — they do not slide down the trace.

Figure 1.4-10 shows the ungained data and two rms-gained sections. The gate lengths are indicated at the top of each panel. When the gate used in the computation is kept small, say 64 ms, then strong reflections become less distinct.