correl

Group:

TRACES

Authors:

Igor B.Morozov, 1/97; modified 04/02 (removed the confusing time-shift option). 11/2015: added mode WAVELET

Module description:

Auto- and cross-correlation.

Calculates auto- and cross-correlations of specified traces. Auto-correlations are calculated on a trace-by-trace basis; cross-correlations are performed within each ensemble.

The program can also be used to measure the time of the second zero crossing of the autocorrelation function, or cross-correlation lags. These values can be put into trace headers for further editing or for use as DECON parameters. The measuremenbt can be carried out without changes to the input traces, or along with the changes to them. See list MEASURE.

In place of the input traces, the module outputs cross- or autocorrelation traces of lengths equal 2*(TEND-TSTART) (see the time gate parameters in the main module call line). The time starts of the output traces are set so that theie middles correspond to zero cross- (auto-) correlation lag values. Positive lags mean a delay of the cross-correlated trace relative to the reference trace (specified by the value of header INDEX=INDVAL; see the module call format).

Module call format:

*call CORREL MODE TSTART TEND INDEX INDVAL ALL

Global list parameter(s):

MODE

 Processing mode:
  • AUTO or ACORR: compute autocorrelation.
  • CROSS or CCORR: compute crosscorrelation of one or multiple traces with one reference trace, and the autpcorrelation of the reference trace.
  • COHER : compute spectral coherence of one or multiple traces with one reference trace). In this case, the output traces become two-component (first containing the absolute value and second-phase of coherence) and sampled in frequency. The reference trace is filled with values (1,0)
  • WAVELET : Compute zero-phase wavelet from autocorrelation.
    •
    • Format: Selection
    • Selectable Values: (codes in parentheses)
      • Autocorrelation (AUTO)
      • Crosscorrelation (CROSS)
      • Coherence|COHER
    • Default value: AUTO

    TSTART

    		 Beginning of the correlation time window, ms. Note that for cross-correlation, the TSTART-TEND window may be different in the two correlated traces. This can be achieved by using trace headers to parameterize TSTART and TEND. See EXAMPLES.
    • Format: Trace Header (table entry), name, or numerical value (8 characters)
    • Default value: First trace sample

    TEND

    		 End of correlation time window, ms. Note that for cross-correlation, the TSTART-TEND window may be different in the two correlated traces. This can be achieved by using trace headers to parameterize TSTART and TEND. See EXAMPLES.
    • Format: Trace Header (table entry), name, or numerical value (8 characters)
    • Default value: Last trace sample

    INDEX

    		 For CROSS option only: Name of integer header entry specifying the component with which the cross-correlationa are performed.
    • Format: Character (8 characters)
    • Default value: Not specified

    INDVAL

    		 For CROSS option only: Value of INDEX for the component cross-correlated with those indicated in Repeat list. This component is replaced by its autocorrelation.
    • Format: INTEGER
    • Default value: Not specified

    ALL

    		 Put ALL here to cross-correlate all ensemble traces with the selected one. If ALL is not set, the components are selected using the Repeat list below.
    • Format: Character (8 characters)
    • Default value: Select components from Repeat list below

    10 groups of 1 REPEAT parameter per line:

    This Repeat group is used only if MODE=CROSS. The list of components which need to be crosscorrelated with the component specified in the GLOBAL list.

    IND

    		 Value of INDEX for the cross-correlated component. This trace is replaced by the resulting cross-correlation with the component specified by the INDVAL value above
    • Format: INTEGER
    • Default value: Not specified
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    IGeoS version 5.1
    Copyright (c) 1995-2015, I.B.Morozov
    Updated Wed Apr 1 21:42:29 2020