(d) Having thus aligned the receiver mark the spot on the ground directly
below the pointer antenna Now move forward and/or backward from
that spot to locate peaks at other spots over the line As you traced the
peaks you will be tracing the course of the line
Determining Line Depth Using Triangulation
While tracing in conventional modes you may wish to determine the
approximate depth of the line being traced Because the conventional
locating modes do not provide automatic depth the user must use
triangulation based on response nulls around the line as described below
(a) During line tracing mark
the spot over the line
where you desire to
measure the depth Locate
this spot via the null or
peak method described
previously It may be most
convenient to use the
NULL mode for this entire
procedure
(b) With the
in NULL
mode angle the receiver
at about
° relative to the
ground Move the angled
receiver laterally away
from the line until the
response enters a null
While maintaining the
°
angle move the pointer toward and away from the pipe and narrow in
on the precise null location Mark this spot
(c) Measure the distance between the surface location above the line and
the
° null This distance is roughly equal to the depth of the line It is
wise to confirm this depth measurement by performing the same
procedure on the opposite side of the line If the pair of measurements
is close to each other then the determined depth is probably fairly
accurate If not then the accuracy is questionable
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Locating a Sonde by Nulls
Begin by setting the locating mode to NULL as described in Chapter of this
manual While locating hold the
Receiver vertically
(a) In the general area of signal response walk about a
to foot
diameter circle until the ANR and bar response sharply decline At the
location of decline (null) swing the pointer back a forth slowly in order
to narrow the null spot Mark the spot of the null
(b) Now walk a rough circle perhaps to feet in diameter The receiver
should detect a second null away from the first null Mark this spot
You have now located two “side nulls” so called because they are found
