Key Words:
GSSI get XY
Mala Mira Multi-Channel
Follow horizon
ABSOLUTE normalization
Interpolation + 3D file
Newsletter - September 2008
GPR-SLICE Users,
I would like to welcome the following people:

Professor Mahmut G. Drahor and Meric A. Berge, Center for Near
Surface Geophysics and Archaeological Prospection, Dokuz Eylul
University, Turkey

Dr. William J Scott and Dr. Tom Loader, GeoScott Exploration
Consultants, Newfoundland Canada, (www.GeoScott.nf.ca)

Jason Herrmann, Environmental Dynamics Program, University of
Arkansas Fayetteville

Erhan Aydiner, CET Engineering and Trading Ltd, Istanbul, Turkey

Christophe Norgoet, Responsible Development MDS, Paris, France

Dr. Brenda Franey and Dr. John Wozniak, Lytewrks Productions LLC,
Houston, Texas

Terry Cole, Historic Preservation Department, Choctaw Nation of
Oklahoma

Dr. Goran Bekic, Dr Beton d.o.o., Zagreb, Croatia
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Also, recently Jurgen Neiben’s GeoRail Group from Wiebe in Germany
took a total of 4 subscriptions to expand their multi-channel surveying work
using GPR-SLICE.
Amzie Wenning from the Indiana Geological Survey
returned to the GPR-SLICE community after a one year hiatus after locating
budgets to re-instate their subscription. Also, Paul Gibson from the National
University of Ireland recently acquired a license to GPRSIM v3.0 Ground
Penetrating Radar Simulation Software.
Updates:
1)
2)
3)
4)
5)
6)
7)
8)
GSSI Get XY
Mala Mira Multi-Channel Support
Interpolation + 3D compilation streamlined
ABSOLUTE normalization options
Auto Horizon Follow and Detect
Topography net plots
Speed enhancements
Miscellaneous additions
1) GSSI Get XY
An option to extract the survey wheel measurement for GSSI equipment
is available in the Edit Info File menu. The GSSI Get XY button reads the
GSSI survey wheel calibration in the header and the total number of scans of
the profile to calculate the survey wheel length (Figure 1). On import, the
user can decide if they want to round off the measured range to the nearest
integer value, or to keep the fractional line lengths that are recorded. A
message box will appear asking the user how to import with rounding or not.
If you decide to use the exact (fractional) line lengths, remember you need
to use the “ang” survey definition for the information file. The GSSI get XY
button will place the length into either the x1 or y1 slot in the information
file depending on whether the profile is an x or y line. If the start locations
of the profiles are other than 0, you will need to adjust the files by editing
them.
In order to effectively use the GSSI Get XY button, or the same buttons
from other manufacturers, you will need to accurately calibrate your survey
wheel in the field for these imported ranges to be correct.
Note: Even with an accurately calibrated survey wheel there is slippage on
most sites other than very clean and smooth surfaces.
In these areas,
using the exact fractional line length from the survey wheel may be off from
the actual length. If you are collecting the data to the nearest integral
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distance unit, e.g. meter or feet in the field, then rounding the survey wheel
will most likely predict the correct length for short lines. However, for longer
lines the slippage on some sites can be larger than a half a unit distance and
rounding may give the incorrect length of the line. It is always good to keep
a field notebook to write the line location recorded.
Remember, for
navigation with survey wheels to use the simple Artificial Marker process to
account for survey wheel slippage.
2) Mala Mira Multi-Channel Support
For those with multi-channel extended licenses in GPR-SLICE, there is
now support for processing Mala’s new Mira multi-channel system. File
naming conventions in the Create Info File menu and new buttons to extract
and read Mira *.pos GPS or total station navigation files are available in the
Edit Info File menu. This equipment has unique naming conventions for
extracted channels and navigation files.
The names may look like
gps_000_a000.rd3 where the first 000 is the track number followed the
a000 which is the channel number in the track.
The new naming
conventions for this equipment can be automatically generated in the Edit
Info File menus for multi-channel licenses (Figure 1). For multi-channel
operations 2 information files are needed when random GPS or total station
surveying is used:
1) Create an information file of the first channel name for each track, e.g.
info.dat (Figure 1)
2) Create another information file for all the extracted track names, e.g.
infomain.dat. This can be easily done by setting the N channels to 16
(Figure 2)
3) In the Edit Info File menu insert the info.dat file and click the Mira to
Nav button to generate the GPS track from the *.g01.pos file
associated with the Mira track. (Figure 3)
4) Edit the GPS track if desired.
5) Click GPS Get List to update the number of listings.
6) In the Edit Info File menu insert the info main.dat file and click the
Array to Nav button to generate the individual GPS tracks taking into
consideration the track movement as well as the offsets in the
infomain.dat file. (Figure 4)
7) To make time slice proceed as usual using the GPS Trace # in
the Navigation menu etc. Example time slices for the Mala Mira multichannel system are shown in Figure 5.
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Note: Mala’s naming convention for the navigation file which is now called a
*.pos file may change. I would recommend that the *.pos file have the
same extension name as the first radar track as is done with other multichannel systems.
3) Interpolation + 3D File Compilation
A new streamlined process to generate a 3D file is now available in the
Pixel Map menu. The new process called “Interpolate + 3D File” (Figure 6)
will interpolate the time slices and then compile them to the defined 3D
filename in the menu. This new process eliminates the need to have to
return to the Grid menu in order to generate a 3D file after interpolation.
The original interpolate button is left in the menu if this is the only process
that one wants to complete. 3D file compilation can also be accessed as
before in the Grid menu if users want to do this.
4) ABSOLUTE Normalization
For displaying time slices, a new option exists for the normalization. This
new option is called ABSOLUTE. At the request of researchers Dr. Henry Lin
and his graduate student Jun Zhuang at Penn State University, we have
provided this new option for data normalization. Henry and Jun are actively
involved in 4D measurements with GPR and they need to compare times
slices made at different times. They asked if the color table that is applied
to the data be referenced to the binary resolution in the time slice grids.
This colorization would then allow them to compare the absolute reflection
returns from an area which was measured at different times to see the
changes at a site. They are involved in 4D hydropedologic studies and are
examining changes in soil conditions after injecting a site with fluid.
To provide this new option, a new radio button called “ABSOLUTE” was
developed in the Pixel Map menu (Figure 7). When ABSOLUTE is chosen for
the normalization the software will generate a color table based on the either
2^31 or 2^15 depending upon whether the time slices were generated from
16 bit or 8 bit radargrams. 2^31 comes from using 16 bit radargrams and
then using the squared pulse amplitude as the cut parameter in the
Slice/Resample menu. To see the color legend one can turn this on in the
Options menu.
“Absolute” (not capitalized radio button) normalization
which has been provided in GPR-SLICE since its inception back with GPRSLICE for DOS in 1994, this will simply reference the highest/lowest
response of just those time slices displayed to the screen and provide
colorization using these local max/min. “Relative” normalization of course
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independently colorizes each map based on its own maximum and minimum
data in that individual grid. Absolute and ABSOLUTE are sensitive to the
actual gain in the raw radar pulses. For poorly gained radargrams Absolute
and ABSOLUTE time slice displays will show weakly gained areas where the
pulse is not gained well, and likewise emphasize time slice levels where the
gain is too much.
The color legend is placed onto the time slices when this is turned on will
give a relative numbers for 0,.25,.5,.75,1, Absolute number from the hi/lo
response of the N time slices displayed to the screen, or ABSOLUTE numbers
following the set binary resolution in the generated time slices grids. The
actual numbers for Absolute and ABSOLUTE are quite large – in excess of
several tens of millions - and indicate that there is more resolution in the
grid maps (then we have colors to apply).
For most subsurface applications with GPR I recommend that relative
normalization be used.
GPR-SLICE effectively handles automatic gain
control for GPR data in the time slice grid mode with relative normalization.
Rather than trying to discover an optimum gain curve to apply to the raw
radargram pulses, the auto gaining is easier and more useful to do with the
constructed time slice images.
5) Follow Horizon
Larry Conyers at the University of Denver who is evaluating GPR-SLICE,
asked for an option to have a horizon detection operation that will follow a
horizon from an initial starting location. Currently, the Auto Detect or Auto
Detect Batch in the Horizon menu will discover the peak response between a
set horizontal band given by the sample start and sample end locations.
These options are probably best for looking at horizontally layered structures
such as from road bed stratigraphy where layering thickness are reasonably
known within limits. For a dipping horizon which fluctuates dramatically in
scan depth, these Auto detect options cannot “follow” below or above a set
horizontal band. Using the Follow Horizon option, the user can trace a
dipping horizon or fluctuating horizon. An example is shown in Figure 9.
The new Follow Horizon option in the Horizon menu will begin searching a
horizon in the radargram between the start and end sample settings. The
channel thickness to search over is the difference between the end and start
sample. In this example, the channel to search over is 50 samples. The
newly found horizon will then be detected and the sample that this is
detected at will then be the center of the channel to look at the next scan in
radargram.
The Follow Horizon can also have the filter engaged to
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compare a running average of the detected horizon with the local horizon.
When the difference between the running average and the local horizon is
larger than the user set threshold, the running average will be used to define
the local horizon.
Note: If the horizon to be detected is not well defined in areas, the Follow
Horizon detection may not be able to work optimally.
Also, as an
interpretation pitfall reminder, it may be incorrect to say that the undulating
surfaces that are detected by the horizon processes are changes in layer
thickness. The changes in apparent “thickness” of a layer may simply be
related to changes in velocity of the overburden layers.
6) Topography Net Plots
The topography used in the Static Correction menu can be used in Open
GL Volume displays via a new option to show net plots of the topography at
various line densities. Shown in Figure 10 is a Open GL Volume screen shot
with a netplot of the topography along with a topography+tilt corrected
radargram, as well as some x, y, z fence plots. Clicking the Net button in
the Open GL Volume menu will generate alternate topography net plots
where the number of lines used in the topography grid is decimated up to 5
lines from the original grid length. The Horizon button can also be clicked to
show the solid plot of the topography.
If this is done however, the
topography is drawn opaquely and deeper graphic elements cannot be seen.
With the Net function, some “transparency” to deeper graphic elements can
be achieved.
7) Speed enhancements
The announcement made in May regarding the speed enhancements to
the Convert menu, Slice/Resample and the Filter menu have been
documented by many users that have sent information in. Most of the
processing operations in these menus are between 5 to 21 times faster
compared to older versions of the software!!! This has had a very positive
effect on the total time to process datasets which can be reduced now
significantly.
8) Miscellaneous additions
GPR_Slice V5.0 www.gpr-survey.com
A variety of additions and bug fixes have been added to GPR-SLICE over
the last 2 months. Some of the more important additions are:
A. GPS XYpoints for multi-radar displays corrected.
B. Reading any radargram via the listbox in Open GL Volume added (in
addition to line-by-line scrolling with step +/- button)
C. Help Set added to Open GL Volume x,y,z start/end list boxes.
D. Plot+/- added to the GPS grid plot.
E. Show markers available for all radargrams.
F. Resample scans/mark setting shown in the Slice/Resample menu for
easy lookup.
G. ERA Radar – UK data conversion support added to the Convert Data
menu.
Recent Events:
Dr Henrique Lorenzo from the University of Vigo sponsored a GPR-SLICE
advanced workshop on June 23-24. We are very grateful to him to open up
his University to GPR-SLICE users and to also host some very nice dinners in
Pontevedra. Also, it was great that Spain was always doing well in the
Eurocup while we were there so everyone was very happy. I cannot wait to
have some more Pimiento de Padron on the next trip to Vigo!
A total of 11 users came to the Los Angeles 2 day advanced workshop
here on Gypsy Ln. Komex from Canada sent 2 users, GeoVision in California
sent 4 people, Spectrum Geophysics in Burbank sent 2 people and California
State University in Long Beach had 2 users come. Also, Justin Klein who
was the developer of GPR-SLICE VIEW came to the workshop. As our
revenues have improved over the last few years, Justin just started working
2 weeks per month beginning on June 30. What this means is we are reinvesting our revenues to make GPR-SLICE even better and it will get better
much faster for the future. There are numerous requests in for GPR-SLICE
developments. Among one of the top priorities that Justin will be assisting in
developing is a scrollable radargram menu for super long profiles that are 50
kilometers or longer for radar data and to make these displays run
instantaneously.
Operational Notes:
Dave Taylor from Spectrum Geophysics pointed out at our recent
workshop that it is possible to measure staggering noises in images using
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the XYpoints option by right clicking your mouse over the time slice images.
Choosing points between adjacent lines in the image where staggering can
be seen, then one can subtract the XYpoints values that are tabulated in the
on-line dialog to get an estimate of the staggering amount.
A recent survey made by Dan Casto from Technos in Miami involved
using a mixture of hand markers and random navigation. Dan had recorded
a site that had hand markers placed into long radargram transects at 50 ft
intervals. He had several lines however, that did not end on a 50 ft multiple.
Hand markers also did not exist at the end of lines that had ranges less than
some multiple of 50ft. Dan asked if there was a way to process and
navigate this dataset. It is possible! To use a dataset like this which is
rather uncommon, one can generate an “artificial” GPS navigation file for
each radargram and then do the processing. The *.*.gps file would have
the typical 5 column navigation file of x,y,z,”time”,scan #.
When the x,y
(and z) of the data are known, having the scan numbers really completes
the necessary navigation for random (GPS or Total Station) navigation. To
get the scan numbers, one can first use the Edit submenu in the Navigation
menu to place in a marker on the very last scan of each file. The next step
is to run the Field Marker navigation. Running the Field Marker navigation
will generate *.mrk files in the \marker\ folder which simply tabulates the
scan number for each hand marker existing in the radargram header for
each scan. These scan #’s in the *.mrk files can be inserted (manually) into
the *.*.gps file and then typical GPS imaging can be done. Note, that a fake
“z” and “time” column need to be generated.
As a reminder for new VISTA users, you need to shut off the User
Account controls in the Control Panel. The reason this is needed is that
VISTA controls the Program Files directory and unless you are the
administrator of your own computer, you cannot run GPR-SLICE in that
folder. GPR-SLICE is currently programmed only to run out of the Program
Files and needs writing access to this folder to operate. In 2009, we will be
moving GPR-SLICE to a separate folder to accommodate the movement of
users to VISTA that cannot easily be the administrator of their own computer
particularly at large organizations.
Upcoming Events:
I will be traveling in Japan, Mongolia and China from Aug 9-Sept 9. In
Japan, there are several surveys at the newly established branch of the
Geophysical Archaeometry Laboratory Saito. After this work, I have 2 weeks
of surveys in Mongolia with Professor Yasuyuki Murakami of Ehime
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University in search of campsites/crypts of Genghis Khan and will be unable
to access the internet from August 18-30th. If you need any assistance with
the software or technical support during these times, Dr. Kent Schneider
(krschne@bellsouth.net) or Bryan Haley of the University of Mississippi
(bshaley@olemiss.edu) can help out.
This newsletter is also available on the Subscribers Only page of the
www.GPR-SURVEY.com website for download.
Cheers, Dean
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Figure 1. GSSI get XY button added to Edit Info File menu to read survey
wheel range. Two options to either round the range to the nearest integral
distance or to keep the fractional range are prompted in the message box.
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Figure 2. The first step to process Mira multi-channel data is to generate a
file containing the names of the first antenna pair for all tracks.
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Figure 3. The 2nd step in handling Mira multi-channel data for GPS imaging
is to generate another information file containing all the offsets with the total
number of channels and tracks.
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Figure 4. The information file with only the first channel profiles names have
the GPS tracks named with the Mala extension *.g01.pos. To generate the
*.*.rd3.gps GPR-SLICE standard GPS files the button Mira to Nav is
available. The GPS Get List button will update the list of the total number of
listing for each GPS track for the first channel.
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Figure 5.
The information file containing the channel offsets and all the
names for extracted channel names and tracks is set active in the Edit Info
File menu. Clicking the Array to Nav button will read the corrected gps
tracks for the first channel and generate all the individual GPS tracks for
each of the offset channels in the Mira system.
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Figure 6. An example of Mira multi-channel time slices is shown below (data
courtesy of Helder Teraco, GeoSurveys, Portugal).
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Figure 7. A new streamlined button is provided in the Pixel Map menu which
will generate interpolated time slices and then automatically create the 3D
filename. This new button eliminates the need to return to the Grid menu to
generate a 3D file from interpolated and normalized time slices.
GPR_Slice V5.0 www.gpr-survey.com
Figure 8. ABSOLUTE normalization option was added to the Pixel Map menu
to allow for time slice comparisons based on the absolute binary resolution
in the time slice grid maps. A comparison showing displays with different
normalization options is given.
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Figure 9. The new Follow Horizon option in the Horizon menu will begin
searching a horizon in the radargram between the start and end sample
settings.
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Figure 10. Topography net plots can be added to any Open GL Volume
display using the new Net button.
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