Sensors & Software LMX200 Series, User Manual

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6.7.6 Soil Cal
The Soil Cal (also known as velocity) is a parameter used to ensure that measured depths are
accurate. The best way to ensure this is by using the hyperbola-fitting method, since it is based
on data collected in the area.
Crossing linear targets like pipes or cables at a 90 degree angle produces a hyperbola suitable
for soil calibration. The Soil Cal value obtained will be used to compute a depth estimate of a
target. These depths will be
incorrect if the soil type is calibrated on a target hyperbola
produced at an oblique angle, rather than 90 degrees.
Once you have a hyperbola on the screen from a subsurface target, press Soil Cal . The menu
at the bottom of the screen will change, giving you the option of specifying a Soil Type or
adjusting the Soil Cal using the hyperbola-fitting method (Figure 6-18). These options are
explained below:
•
Soil Types
– If there are no targets to calibrate to, and you know the type of soil, press
this button to vary between the following mediums, with the pre-set Soil Cal value shown
in brackets:
o
very wet soil (60)
o
wet soil (80)
o
moist soil (100)
o
dry soil (120)
o
very dry soil (150)
o
air (300)
– this value can be used to check for air waves, but it cannot be applied
as a Soil Cal value
•
Soil Cal
– allows you to use hyperbola-fitting to determine a more accurate Soil Cal.
The options are slightly different, depending whether or not you are in backup mode.
If the back-up indicator is on screen, it is presumed you have backed up the LMX100
and you’re right over the hyperbola. Move the horizontal line to the align with the top of
the hyperbola by touching and dragging it. Pressing Soil Cal will display a hyperbola
that is locked to the position where the back-up indicator meets the horizontal line
(Figure 6-18).