Seismic Processing using the RAS24 Program

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Seismic Processing using the RAS-24 Program

• Prepared by Rob Jacob
• 9-9-2002

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Locate the RAS-24 Program Icon on desktop or in
START MENU and open RAS-24.

• Rob Jacob
• 9-9-2002

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In the FILE Menu- Open Record.

• Rob Jacob
• 9-9-2002

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Now that desired file is open - Check overall
integrety of the data, including the Metadata in
the OBSERVER Menu. If there is no metadata, you
should add a text file to the directory and
include necessary information as discussed on the
lab handout.

• Rob Jacob
• 9-9-2002

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In the OPERATE Menu, select filters to determine
what filters are appropriate.

• Rob Jacob
• 9-9-2002

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Filter Options.

• Rob Jacob
• 9-9-2002

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Observe the effects of a 60Hz Notch filter
(typically used to remove background noise from
Electric sources in the US).

• Rob Jacob
• 9-9-2002

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Back to the Original Data.

• Rob Jacob
• 9-9-2002

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Now observe the effects of a 60Hz Low Cut (High
Pass) Filter.

• Rob Jacob
• 9-9-2002

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Scaling the data and Picking the first Arrivals.
In DISPLAY Menu, select Individual Trace Size.

• Rob Jacob
• 9-9-2002

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Notice that the trace in channel 1 is highlighted
in yellow and it also appears along the lower
portion of the screen. The amplitude may be
increased by using the key and decreased by
using the - key.

• Rob Jacob
• 9-9-2002

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The key was used to increase the amplitude
(gain) of the first trace.
Also notice the vertical line along this lower
portion, near the first arrivals. The vertical
line is the location of the cursor and the
numeric position is displayed at the lower right
hand corner of the screen (Bx 1 Ch 1 St 1 T 2250
Db -33). The cursor and the Time (T) can then be
used to locate the first arrival.

• Rob Jacob
• 9-9-2002

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Note that the trace previously gained is no
longer highlighted, and that the trace in channel
12 is now highlighted. The key has been used
and the change in amplitude may been seen upon
close inspection. Continue this process for each
of the other channels, the desired result is a
similar amplitude of the first breaks for each
channel.

• Rob Jacob
• 9-9-2002

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Now all Traces have been scaled
appropriately. Observe the noise near the first
breaks (high frequency - quick positive and
negative amplitudes - chatter). You may want to
filter this out prior to picking the first breaks.

• Rob Jacob
• 9-9-2002

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Notice the change in the chatter (noise) with a
High Cut filter.

• Rob Jacob
• 9-9-2002

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Seismic Processing using the RAS-24 Program

• Steps presented in demo
• . Open File
• . Check Data and Metadata
• . Increase trace size or evaluate need for
  filters.
• . Verify that all first breaks have similar
  amplitudes.
• . Filter as necessary.
• . Pick first breaks, as the time at which the
  first energy arrives at the geophone typically
  the zero-break of the signal, however be
  consistent with location of first break on the
  initial wavelet for each trace.

• Prepared by Rob Jacob
• 9-9-2002

17
Seismic Processing using the RAS-24 ProgramEnd
of PresentationUse the procedures presented in
this demo to pick your data file according to
course notes.

• Prepared by Rob Jacob
• 9-9-2002