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6.6.5 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 a linear target (e.g. pipe) at a 90 degree angle or a localized object (e.g. box) will
produce 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 6-13). 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)
•
Soil Cal – allows you to use hyperbola-fitting to determine a more accurate Soil Cal.
The options are slightly different, depending on whether or not you are in backup mode.
If the backup indicator is on the screen when you press Soil Cal, then you can only
adjust the vertical position of the horizontal scroll bar, since it is presumed you have
backed-up so that the system is right over the hyperbola in question. The scroll bar can
Figure 6-12: Varying the Gain
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