Broadside Shooting: Slope Line

Figure 34 is a base map showing a portion of the survey area. Data acquisition included a long line (5 meter geophone spacings) with reverse profiles along the shoulder of the highway. Shorter, cross lines were shot in the upslope direction with nominally 1 meter geophone spacings. The narrow right-of-way and steep slope conditions prevented locating source points up the slope, and provided a severe restraint on the geophone locations in the zone of most interest. A concern was that not enough offset could be obtained in the up-slope direction.

The problem was solved in two stages. First, we did conventional reverse profile interpretations of the longer, line which paralleled the roadway (shoulder line above). Second, we used the first solution to constrain the delay time at source points used to acquire the cross-lines. In this example, we will work with just one of the cross-lines, line number 3. We will use two Bison records which were acquired with a hammer (15 fold vertical stack).

Figure 34: Base map for refraction survey (line 3 goes up hill from the roadway)
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In Figure 34 we see line 1 (along the roadway) and the cross-line (line 3). The source point for shot record 10 was located near station 24 on line 1. The source point for shot record 11 was located near station 1 on line 1. We will invoke constraints to obtain a solution by using results from the line 1 solution.



Subsections