Geophysical Survey Systems, Inc.
SIR® 4000
Manual
MN72-433 Rev F
99
3
Edit Gain Curve:
If portions of the signal are under- or over-gained after using Auto Gain Mode, try
increasing or decreasing the number of gain points. Gain points are evenly distributed along the scan
trace; adjusting the number of points can change where amplification occurs.
•
Select Edit Gain Curve.
•
Add or erase points to modify the gain curve.
•
Save and Exit to return to the Collect Setup screen.
4
IIR Stacking:
IIR Stacking is a high-frequency noise reduction filter
operating in the horizontal direction. Each new scan has a 1/n
influence in the data, so this filter has a tendency to smooth high
frequency targets and accentuate low frequency horizontal features,
such as layers. As the number of scans you stack (n) increases, the
influence of each new scan drops.
•
The IIR Stacking filter input is in number of scans. Pressing IIR
Stacking with either the Control Knob or Enter button will allow
you to select a number of scans.
•
High frequency noise generally has a ‘snowy’ appearance. The
larger the number you put in here, the smoother the data will be.
It is possible to over-smooth and ‘smudge’ out real data. With
larger numbers the system is performs many extra calculations
and this may reduce data collection speed. The maximum value is
1023 scans.
5
IIR BG Removal:
This filter removes horizontal bands of noise. These bands are occasionally caused
by ‘real’ horizontal reflectors, but they are also caused by low frequency noise such as antenna
ringing. These layers can obscure other ‘real’ horizontal or point source reflectors.
•
Filter length should be set to the number of scans equal to the feature length to be removed. Be
careful to not filter out desired reflectors.
•
The IIR Background Removal filter input is in number of scans. Determine the length in scans of
the feature or noise that you want to remove from the data and input that number. Features, or
horizontal reflections, of this size or larger will be removed.
•
The Background Removal filter maximum value is 1023 scans.
•
It is recommended that this filter be set last. When Background Removal is turned on the
previewed linescan data and individual scan will gradually be averaged out by the filter and only
noise will be visible.
6
Signal Floor:
When Signal Floor is turned on it overlays a green field on the Linescan display. This
green field is an estimate of the effective depth of each scan based on an analysis of the noise to
signal loss (attenuation). Real reflectors may still be located beneath the Signal Floor if they are
strong enough.
•
Press the Control Knob or Enter key to toggle Signal Floor On or Off.
•
This process does not affect the data being collected. It is a visual indication only.
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