SAC Command Reference Manual

RGLITCHES

SUMMARY

Removes glitches and timing marks.

SYNTAX

RGLITCHES options

where options are one or more of the following:

THRESHOLD v
TYPE LINEAR|ZERO
WINDOW ON|OFF|pdw
METHOD ABSOLUTE|POWER|RUNAVG

INPUT

THRESHOLD v:Set onset threshold level to v. Data points whose absolute values are greater than or equal to v are corrected.
TYPE LINEAR:Correct data points above the threshold by linearly interpolating between the data points on each side of the bad data.
TYPE ZERO:Correct data points above the threshold by setting them to zero.
METHOD ABSOLUTE:
 Corrects data points having absolute values >= the threshold v.
METHOD POWER:Corrects data points where the power of the signal computed using a backward difference method exceeds the threshold v.
METHOD RUNAVG:Corrects data points by calculating a running average and standard deviation in a window SWINLEN seconds long that moves from the end of the trace to the beginning of the trace in 1-point increments. Each new point is compared to the average, and if it differs by more than THRESH2 times the current standard deviation, and if the difference is greater than MINAMP counts, it is replaced by the current mean. This method is always applied to the entire seismogram.

There are three options associated with the RUNAVG method. These are

SWINLEN v:Set length in seconds of running average window.
THRESH2 v:Set the threshold value for glitches.
MINAMP v:Set the minimum amplitude for glitches.
WINDOW ON:Only correct data points within the previously defined pdw.
WINDOW OFF:Correct data points within the entire data file.
WINDOW pdw:Only correct data points within the defined pdw. A pdw consists of a starting and a stopping value of the independent variable, usually time, which defines the desired window of data that you wish to make measurements on. See the CUT command for a complete explanation of how to define and use a pdw. Some examples are given below.

DEFAULT VALUES

RGLITCHES THRESHOLD 1.0E+10 TYPE LINEAR WINDOW OFF METHOD ABSOLUTE SWINLEN 0.5
    THRESH2 5.0 MINAMP 50

DESCRIPTION

This command can be used to smooth out irregularities caused by "glitches" in the data acquistion system and by timing marks produced by some data acquistion systems. It checks each data point to see if it's value is greater than or equal to the requested "onset threshold level". It then zeros out these bad data points or linearly interpolates between the data point just before and the data point just after the bad ones. You can have it remove glitches in the entire file or select a smaller portion of the file by setting the window. Using this option lets you remove glitches that are smaller than the maximum in the entire data file.

EXAMPLES

Some examples of pdw are given below:

B 0 30:      First 30 secs of the file.
T3 -1 T7:    From 1 sec before T3 time pick to T7 time pick.
30.2 48:     30.2 to 48 secs relative to file zero.

HEADER CHANGES

DEPMIN, DEPMAX, DEPMEN

ERROR MESSAGES

  • 1301: No data files read in.
  • 1306: Illegal operation on unevenly spaced file
  • 1307: Illegal operation on spectral file

LATEST REVISION

March, 1997 (Version 00.53a)