agc

Group:

TRACES

Authors:

Igor B. Morozov, 9/95; modified 5/00, 11/00. Well-log functionality added: 07/08

Module description:

Automatic Gain Control

The module applies sliding window to the data and calculates one of the specified data amplitude norms (RMS, L1, or VariMax) within the window. The specified sample (usually - at the middle of the window!) is then divided by this norm.

VARIMAX norm measures the spikiness of the distribution of trace samples within the window and produces values typically within the range [1..2]. This option is typically used for time series analysis and not for trace normalization.

Similarly, FREQ is a measure used for trace attribute extraction. FREQ generates a norm equal to the number of zero crossiings per millisecond (or current trace time unit).

AGC allows variable-length windows shifted relative to the sample being normalized.

Module call format:

*call AGC WINDOW START END OUTPUT MODE TSHIFT

Global list parameter(s):

WINDOW

 Length of sliding AGC window (ms). This is the length of the window at the beginning of the time range (see START) below). If a window changing over time is needed, use list WINEND.
  • Format: Trace Header (table entry), name, or numerical value (8 characters)
  • Default value: Not specified

START

 Beginning of the AGC window (ms)
  • Format: Trace Header (table entry), name, or numerical value (8 characters)
  • Default value: Not specified

END

 End of of the AGC window (ms)
  • Format: Trace Header (table entry), name, or numerical value (8 characters)
  • Default value: Not specified

OUTPUT

 Type of output: the calculated trace scalar or amplitude-normalized data. If BOTH is set, an additional component is added in the trace and the gain levels are written into it.
  • Format: Selection
  • Selectable Values: (codes in parentheses)
    • Processed data (DATA)
    • AGC scalar (NORM)
    • Both (BOTH)
  • Default value: DATA

MODE

 Type of the norm (amplitude measure) employed.
  • RMS,
  • L1 (mean abs value);
  • VARIMAX;
  • FREQ (a kind of instantaneous frequency; see module description);
  • HURST or FLRANGE - the Hurst fluctuation range, difference between largest and smallest trace sample values within the window.
  • RESTORE: the AGC gain factors stored in the second component of each trace is used to restore the original amplitude. To use this mode, the traces must contain records saved by a preceding call to AGC with option OUTPUT above set as BOTH. Parameter WINDOW is ignored when using this option.
    • Format: Selection
    • Selectable Values: (codes in parentheses)
      • Rms (RMS)
      • L1 (L1)
      • Varimax (VARIMAX)
      • Frequency (FREQ)
      • Hurst (HURST)
      • Restore (RESTORE)
    • Default value: RMS

    TSHIFT

    		 Shift of the window relative to the sample to which the normalization is applied. Value of 0 corresponds to the case when the sample is normalized by the time window after it, 1 -- to the normalization using the time window before the sample. The usual choice is 0.5 -- time window centered around the sample.
    • Format: Trace Header (table entry), name, or numerical value (8 characters)
    • Default value: 0.5
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    IGeoS version 5.1
    Copyright (c) 1995-2015, I.B.Morozov
    Updated Wed Apr 1 21:42:12 2020