GSSI 200 HS, Руководство пользователя

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Geophysical Survey Systems, Inc. GS Series
200 HS Antenna
MN27-151 Rev A 12
Stacking:
This is a horizontal filtering method that works to smooth horizontal random noise. Often this
noise looks like static in the deeper time ranges. Since each new scan that is recorded is made up of some
amount of random noise as well as actual information, this process works by relying more heavily on data
already collected. For each new scan, the amount of information from that point that you are on will be
1/n where n is the value in scans you input. The rest of the information making up that scan will be from
the previously collected data according to (n-1)/n. This means that larger n’s will smooth out small
changes in the data, potentially erasing what you are trying to find. As a result, this value is usually small,
typically 3-11 scans.
Backgr(ound) Removal:
This is a horizontal filtering method that removes horizontal bands, sometimes
called ringing, from the data. Perfectly flat, horizontal bands are unlikely to be real features in the
subsurface but are more often the result of system noise or lower frequency interference. Background
removal works by averaging together n scans and then subtracting that averaged scan from each scan. The
averaged scan should only have signals which are present in all n scans and thus should only remove
horizontal bands with a length of n scans or greater. Care must be taken here to not remove real horizontal
features, so n should be a large number. Values of 100+ scans are usually enough. Note that any value
you enter will remove the direct wave since this is a signal which is present in all scans.
Noise Band Removal:
Toggles On/Off a horizontal band filter. This filter is designed to downplay
horizontal noise artifacts resulting from wet or clayey conditions and is weighted to not impact hyperbolic
features as much. This filter will also remove the direct wave from the top of the screen.
Signal Floor:
This is an information tool designed to display the effective limit of your penetration. It
uses a specialized algorithm to analyze the signal to noise ratio. Once a threshold is crossed, the software
will overlay a green shade on the noisy data. Large, highly reflective targets may still be visible in this
region, but lower or mid amplitude targets may not be seen. RADAN will display the signal floor
information if the data were collected with the tool turned on.
Gain
Gain is signal amplification, basically “turning up the
volume” on the received signal. GPR energy gets
absorbed by the soils or sediments as it moves though
the subsurface. The term for this absorption is
“attenuation.” Different materials attenuate GPR
energy at different rates. Highly attenuative materials
are sometimes called “lossy.” While it is very difficult
to know exactly how lossy a material is before
surveying, more highly conductive materials such as
wet clays, soils with agricultural runoff, and high salt
areas are typically more lossy. Gain counters the
effects of attenuation by adding more amplification at different depths. No additional energy is sent from
the antenna however; gain works strictly with the received signal.
Gain operates on a number of points which are evenly distributed along the time scale. Deeper (later)
areas will require more gain than shallower (earlier) ones. Since the amount of gain added varies with the
point’s position on the time scale, this process is often called “time variable gain” or TVG. Furthermore,
the software only changes the gain amount at the gain points, so it is important to set an adequate number
of points. In an area with complex stratigraphy, you may want more points than in an area with
homogenous conditions. Opening the O-scope display will show the gain curve as a red line
superimposed on the scan trace. The location of each point is represented by a small dot along the curve.
Each successive gain point should be equal to or greater than the previous point.