Taiwan: Gain-Filter, Filter-Gain
We now have 5 seconds of Taiwan data and we zeroed the bad hydrophones. In this chapter we will
apply spherical divergence correction, then band-pass filter the data. We will also
apply a band-pass filter, then apply spherical divergence correction. We will compare gathers from these two paths and consider whether one path is better.
To determine which exponential gain to apply to the line of CMPs, we will apply gain to two shot gathers: 820 and 930̤ We window them from the 2-D line:
We will determine a tpow value for sugain by using script igain (Section 10.5), option T. Below is the user area of igain.sh changed for the Taiwan data.
The script creates three displays:
a wiggle plot of the file,
a decibel (dB) ximage plot of the user-selected trace(s), and
an amplitude graph of the user-selected trace(s). Remember:
The script applies gain to the entire file, but only the user-selected trace or traces are used to create the second and third displays.
The user is asked to supply the name of a key (offset, tracr, etc.) and corresponding key minimum and key maximum values for the second and third displays.
We selected key tracf and supplied tracf values 92 93 for both shot gathers, based on our displays in Chapter 12.
After several trials, we decide to use a spherical divergence correction of 1.8 (Figures 13.1 and 13.2).
We apply spherical divergence correction with the command below.
To select frequencies