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.
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