GSSI SIR 4000, Manual

Page: 124 / 163

Geophysical Survey Systems, Inc. SIR® 4000
Manual
MN72-433 Rev F 118
7.5: Collecting Digital 3D Data
Step 1: Position Antenna
Once in the 3D Collection screen (after
pressing the green Start button) you will
see a grid layout in the center of the
screen. The grid coordinates are displayed
at the bottom left and top right corners of
the grid. The X and Y line lengths appear
on the bottom and left side of the grid. At
the top of the screen the total number of
lines is displayed along with the number
in both the X and Y directions.
The estimated file size for the grid is also
displayed at the top. A yellow line and red
box appear at your starting coordinate.
Position the center of the antenna over the
starting coordinate for your grid.
Typically that will be at (0,0), where the
center of the antenna is centered over both the X and Y baseline at the same time.
Step 2: Adjusting Settings in the Process, Output, and System Menus
Process Menu:
This menu allows you to adjust Gain settings and apply filters for data collection.
• Gain Mode:
Choose between Auto and Manual Gain. Auto Gain Mode will automatically
manage Gain settings based on the number of Gain Curve points.
• Edit Gain Curve:
Opens a window where you can add or delete Gain Points, and increase or
decrease the Gain for each point.
• IIR Stacking:
IIR Stacking is a high-frequency noise reduction filter operating in the horizontal
direction. 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 increases, the
influence of each new scan drops.
o
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.
o
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.
• 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.
o
The IIR Background Removal filter input is in number of scans, with a maximum value of
1023 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.