GSSI SIR 4000, Руководство пользователя

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Geophysical Survey Systems, Inc. SIR® 4000
Manual
MN72-433 Rev F 24
Filter length should be set to the
number of scans equal to the feature
length to be removed. Any continuous
feature within the data, such as a
water table reflector or a stratigraphic
boundary between two soil types, may
also be filtered out by performing
Background Removal. Be careful; it is
easy to filter out desired reflectors.
The FIR Background Removal filter
input is in number of scans. Pressing
FIR BG Removal with either the
Control Knob or Enter button will
allow you to select a 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. This makes it impossible to preview the effects of other filters.
Custom Filter
This filter overrides the FIR Low/High Pass filters with a custom filter provided with an antenna. Custom
Filters are only available with certain antennas and are sent with the antenna when it is purchased.
IIR Low Pass and IIR High Pass
IIR filters (Infinite Impulse Response) are a holdover from analog circuits. It is a simpler and potentially
cruder type of filter than the FIR filter. The IIR filter is used to remove noise, but may change the
waveform shape. When an IIR filter encounters a feature in the radar data, it produces an output that
decays exponentially towards zero but never reaches it, hence the name “infinite.” IIR filters are not
necessarily symmetrical and while they achieve excellent amplitude response, their phase response is non-
linear and so they can cause slight phase shifts in the data.
By setting these at different ends of the antenna’s bandwidth, you are determining the range of
frequencies that the antenna is filtering out. Pressing IIR Low/High Pass with either the Control Knob or
Enter button will allow you to scroll through different frequencies.
•
IIR Filters should not be used with 4096 samples/scan or higher.
•
The maximum Low and High Pass filter values are 5000 MHz.
•
Select Off to disable either filter.
IIR Low Pass:
The selected frequency in MHz is the upper limit of the filter. Any frequency lower than
selected Low Pass frequency will be allowed to pass through the filter and be recorded by the system.
IIR High Pass:
The selected frequency in MHz is the lower limit of the filter. Any frequency higher than
selected High Pass frequency will be allowed to pass through the filter and be recorded by the system.
IIR Stacking
In addition to IIR frequency filters, another option is Stacking. Stacking is a high-frequency noise
reduction filter which operates 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
Horizontal Noise to be
Removed