BFIT
Vertical times correct for the source horizontal offset. If the vertical distance between the source and the geophone is , if the horizontal offset of the source from the bore hole is , and if the straight line slant distance from source to geophone is , then the cosine of the angle, , between the vertical and the slant is
. The slant time is
where is the interval velocity. Typically we don't measure , but do measure . So the angle,
. The vertical time is then:
|
(3) |
where is the observed arrival time. Except in large horizontal offsets, the correction is modest. This program computes a straight line fit to vertical times, . A similar program in OCTAVE is VFITW 8.2.3. The command line arguments are:
bfit infile emin emax labl
infile = input file name (4char minimum)
emin =minimum elevation for interval
emax =maximum elevation for interval
labl =2 character ID label for interval
Example for the X5 borehole: bfit twave.seg 820. 840. X5
Figure 24:
BFIT: Straight line fit yields interval velocity by least squares. Title has the value of the velocity, 479 m/s.
|