BRED Example Flow

Using BRED to flatten the refracted arrivals in time is not necessary, but can make it easier to pick first breaks. See BVEL 8.2.2 for the down-hole version. That is, it aids in identification of the refracted arrival (if the reduction velocity is approximately equal to the apparent horizontal velocity of the refracted arrival). It can also get the refracted arrival in a more confined time window, and this permits scaling the display for better resolution of the first arrivals. Here is an example flow. The situation is sandy soil over bedrock. The bedrock velocity is about 3000 m/s. See figure 14 for the original and reduced in time data plot.

 bred k008.seg 1 3000. .05
 
 octave
    segpic
      bredk008.seg (input file prompt answer)
      3 for clip, 0.15 for maximum time
      use mouse to pic first major down deflection
      (this produces output file bredk008.pic )
      exit
 
 picrestore bredk008.dat bredk008.pic > out.pic
 
 bpic k008.seg 1 out.pic 0.
 
 mv bpick008.seg k008.seg
 
 bshf k008.seg 0  1  .05

First, the data are reduced by a 3000 m/s velocity, bulk shift of .05 seconds to make picking easier. An octave session is started and the segpic program is run (requires segpic.m, segyinfo.m, bsegin.m files be in the directory. Exit octave, and note that file bredk008.pic contains the picks as two column text file (channel, pic time). Picks are corrected for the reduction velocity by running picrestore (see 8.4.1). The picks are then uploaded to file k008.seg by program BPIC 8.4.3. This produces file bpick008.seg which is then renamed k008.seg using the move command. A quality control (QC) check is done by using program BSHF 12.1.1, static shifting the data to align on .05 seconds using the header values uploaded during the BPIC step. Figure 37 shows the data aligned on .05 seconds (red arrow). Now file k008.seg is ready for further refraction analysis.

Figure 37: BSHF: After picks uploaded to headers with BPIC, data are static shifted to align on .05 seconds using header values. This is a quality control step. See example flow, section 8.4.0.1.
\includegraphics[scale=0.6]{Figure33.pdf}