Gain; Filter - Sensors & Software LMX100 User Manual

6.2.1

Gain

Since the material being scanned absorbs the GPR signal, deeper targets return weaker
signals. Gain acts like an audio volume control, amplifying signals and making deeper targets
appear stronger in the image. Gain values vary from 1 to 9 where 1 means a minimal
amplification has been applied and 9 means that maximum amplification has been applied.
Pressing this button increments the gain; once you reach 9 it cycles back to 1. Avoid over-
gaining the data as it can make interpretation difficult (Figure 6-9). In general, soils that are
more electrically conductive (e.g. clays) will require a higher gain compared to soils that are less
electrically conductive (e.g. sand).
6.2.2

Filter

The Filter is a background subtraction filter used for removing flat-lying responses in the data.
Filtering helps identify shallow targets that might be masked by the strong signals at the top of
the image, as well as possibly enhancing the visibility of hyperbolas further down in the data.
However, it will also filter out other flat-lying responses, such as soil boundaries, so be careful
when using this option if your target is flat.
It works by applying a running-average background subtraction to the data set, defined by the
filter width or a window. This window "moves" across the data and the result is subtracted for
every trace in the data set. The Filter is variable and pressing this button cycles between OFF
and values 1 to 5. Variable filter lengths are shown in Figure 6-10.
The lower the number, the longer the filter width, and the more "relaxed" the filter. Only the
longer flat-lying features get removed.
Figure 6-9: Varying the Gain
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Data Collection