Final Report - Minnesota Local Road Research Board

Final Report - Minnesota Local Road Research Board
Incorporating GPS and Mapping
Capability into
Ground Penetrating Radar (GPR)
Operations for Pavement Thickness
Evaluations
Matthew Lebens, Primary Author
Office of Materials and Road Research
June 2010
Research Project
Final Report #2010-37
Technical Report Documentation Page
1. Report No.
2.
3. Recipients Accession No.
MN/RC 2010-37
4. Title and Subtitle
5. Report Date
Incorporating GPS and Mapping Capability into Ground
Penetrating Radar (GPR) Operations for Pavement Thickness
Evaluations
7. Author(s)
June 2010
6.
8. Performing Organization Report No.
Matthew A. Lebens, P.E.
9. Performing Organization Name and Address
10. Project/Task/Work Unit No.
Minnesota Department of Transportation
Office of Materials and Road Research
1400 Gervais Avenue
Maplewood, MN 55109-2403
11. Contract (C) or Grant (G) No.
(c)
GPSGPR
12. Sponsoring Organization Name and Address
13. Type of Report and Period Covered
Minnesota Department of Transportation
Research Services Section
395 John Ireland Boulevard, MS 330
St. Paul, MN 55155-1899
Final Report
14. Sponsoring Agency Code
15. Supplementary Notes
http://www.lrrb.org/PDF/201037.pdf
16. Abstract (Limit: 250 words)
Ground Penetrating Radar (GPR) investigations performed by Mn/DOT of pavements and other subsurface
features have been limited by an inefficient and poorly documented GPR survey process and underdeveloped
project mapping and reporting process.
The objectives of this project were; first to develop a more robust system for GPR surveying using dual aircoupled antennas to provide redundancy in data collection and to improve accuracy and completeness of the survey
results. Secondly; the addition of Global Positioning System (GPS) location data, acquired in coordination with the
GPR data, for improved project location and ArcGIS mapping capability. Thirdly; the development of a standard
format for GPR data reporting in a more user-friendly, exportable format.
After completing the other objectives, a GPR Manual was developed, describing GPR vehicle and survey
operations, GPS with GPR data collection, mapping using ArcGIS, and the new standardized reporting format. The
result was an improved and better documented subsurface data collection and reporting process that incorporates
GPS and improves the effectiveness of Mn/DOT's GPR program.
17. Document Analysis/Descriptors
18. Availability Statement
Ground Penetrating Radar, GPR, GPS for GPR, dual aircoupled antennas, Global Positioning System, GPS, ArcGIS
mapping, GPR data reporting, GPR Manual
No restrictions. Document available from:
National Technical Information Services,
Alexandria, Virginia 22312
19. Security Class (this report)
20. Security Class (this page)
21. No. of Pages
Unclassified
Unclassified
49
22. Price
Incorporating GPS and mapping capability into Ground
Penetrating Radar (GPR) operations for pavement
thickness evaluations.
Final Report
Submitted by:
Office of Materials
Minnesota Department of Transportation
Prepared by
Matthew A. Lebens
MN/DOT, OFFICE OF MATERIALS AND ROAD RESEARCH
1400 Gervais Avenue
Maplewood, Minnesota 55109-2044
June 2010
ACKNOWLEDGEMENTS
The author would like to express appreciation to the Minnesota Department of Transportation for
their support of this research. Special thanks are offered to Shongtao Dai (of the Office of Materials)
for his technical support and guidance and to Gary Wallner (of the Office of Pavement Management)
for technical assistance and collection of the data presented herein.
2
TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION............................................................................................. 4
1.1
BACKGROUND ......................................................................................... 4
1.2
OBJECTIVE ................................................................................................ 5
1.3
SCOPE ......................................................................................................... 5
CHAPTER 2 PROJECT ACCOMPLISHMENTS............................................................. 6
2.1
GPR VEHICLE ANTENNA FRONT MOUNT SYSTEM ......................... 6
2.2
INCORPORATING GPS CAPABILITY IN TO THE GPR SYSTEM ...... 8
2.3
STANDARDIZED GPR MAPPING AND REPORTING .......................... 8
2.4
DEVELOPMENT OF GPR MANUAL ..................................................... 13
CHAPTER 3 PROJECT SUMMARY ................................................................................. 13
APPENDICES
APPENDIX A TEST PROJECT FOR VEHICLE FRONT MOUNT
APPENDIX B TH96 GPS/GPR EXAMPLE REPORT
APPENDIX C GPR OPERATIONS MANUAL
LIST OF FIGURES
Figure 2.1
Previous vehicle GPR antenna mount ....................................................................... 6
Figure 2.2
New GPR vehicle antenna mount ............................................................................. 7
Figure 2.3
Mn Trunk Highway 1, test site location .................................................................... 7
Figure 2.4
Mn Trunk Highway 96 GPS/GPR mapping test ....................................................... 9
Figure 2.5
TH 96 GPS/GPR data point .................................................................................... 10
Figure 2.6
TH 96 Sample Report.............................................................................................. 11
Figure 2.7
MnDOT Basemap TH 96 Project Location............................................................. 12
Figure 2.8
MnDOT Basemap TH 96 Project Detail ................................................................. 12
3
CHAPTER 1 INTRODUCTION
1.1
BACKGROUND
Mn/DOT districts are increasingly requesting Ground Penetrating Radar (GPR) investigations
of pavement layer thickness and other subsurface investigations. Research completed to date at
Mn/DOT concerning GPR has focused on procurement of radar equipment, defining Mn/DOT GPR
operational methods, performing GPR field surveys, and development of improved methods of layer
analysis.
The ground penetrating radar equipment currently owned by Mn/DOT uses a vehicle distance
measurement Instrument (DMI) and written notes taken by the operator to define survey limits and
report on features and/or defects found. Although distance measurement instruments are commonly
used at Mn/DOT to record positions along trunk highways, the level of accuracy using reference post
data provides insufficient detail to precisely map the route of the radar survey vehicle and the features
found. Also the GPR surveys requested by Districts often involve operations in small localized areas
off the roadway, where highway reference posts are not applicable.
The antenna mounting system used by Mn/DOT previously allowed only one single air
coupled antenna to be operated, and was of poor design. A more robust system for GPR surveying
using dual air-coupled antennas was identified as a need. The simultaneous use of dual GPR antennas
provides redundancy in data collection and a comparison tool to improve accuracy and completeness
of the survey results.
The GPS positional data obtained also had be coordinated with the GPR data and made
available to the districts in a user-friendly, exportable format. The development of a standard format
for GPR data reporting at Mn/DOT was indicated as a potential improvement. Also, the accurate
coordinate data acquired with GPS system developed with this project could be used to apply ArcGIS
mapping and database capability to the GPR reporting. Incorporating GPS into this kind of pavement
management survey has been requested by Mn/DOT soils engineers and industry partners, and is
important for effective data sharing.
Because the addition of GPS equipment, data collection, and mapping to the GPR system
increases the complexity and difficulty of standard survey operations, a “GPR user manual” was
requested. The user manual would describe GPR vehicle and manual survey operations, data
collection and analysis, mapping using ArcGIS, and a standardized data reporting format.
Therefore it was determined that an additional GPR project would be beneficial in order to
accomplish the necessary tasks and to incorporate global positioning system (GPS) data collection
and mapping capability into Ground Penetrating Radar (GPR) operations for pavement evaluations.
4
1.2
OBJECTIVE
The overall objective of this project is to incorporate GPS and mapping capability into
Ground Penetrating Radar (GPR) operations for pavement thickness evaluations. At the conclusion of
this project, enhanced GPR data collection and reporting methods will be available to all Mn/DOT
users. The addition of GPS capability will allow detailed mapping of GPR survey projects and
improve the positional accuracy of subsurface locates. Defining and clarifying GPR operations with
the development of standardized reports and a user manual will benefit current and future employees
involved with the system at all levels. The analyses described herein, presents the compilation of the
projects tasks as a final report (Task 6).
1.3
SCOPE
The GPS for GPR implementation study included the following activities:
a) Upgrading the data collection vehicle to allow dual antenna GPR data collection by
installing and testing a compatible antenna mounting device on the Mn/DOT GPR vehicle.
b) Incorporating GPS capability in to the GPR system by identifying and obtaining suitable
GPS equipment, configuring the GPR system to incorporate the GPS data, and developing
a standardized GPS data transfer and collection process.
c) Developing an improved, standardized GPR project mapping capability in ArcGIS format.
d) Developing a uniform, comprehensive data reporting format for GPR projects that
includes; GPS coordinate data, Mapping of project locations and detailed mapping of
specific underground investigations, and Standardized layer thickness data.
a) Developing a GPR user operating manual which will compile operating instructions for
GPR & GPS equipment, mapping software, and reporting examples developed in other
tasks of this project.
e) Preparation of a final report describing; field testing of the new dual antenna and GPS
system and results of the subsequent analysis, documentation on the GPS and mapping
development, recommended GPR standardized reports to accompany the new equipment
enhancements, and final recommendations on full implementation of GPR equipment and
standardized reports.
5
CHAPTER 2 PROJECT ACCOMPLISHMENTS
2.1 GPR VEHICLE ANTENNA FRONT-MOUNT SYSTEM
In December of 2008, a literature and internet search was performed to determine the best system
for a vehicle mount that would allow dual antenna GPR data collection and be safer and more stable than
the in-house system built during the GPR research phase. Mn/DOT was informed that a new vehicle
mount system had recently been developed by the manufacturer of Mn/DOT's radar system; Geophysical
Survey Systems, Inc. (GSSI) of Salem, NH USA. Because the system was designed to mount the GPR
antennas that MnDOT already had and was fully compatible with the system, it was determined to be the
best option for upgrading the GPR survey vehicle mount.
The system was purchased from GSSI and installed by Mn/DOT Central Shops in April of 2009.
The vehicle was configured and proper operation of the vehicle mount took place at the Maplewood
Research Lab in May, 2009. The first field trial of the rig was done in Mn/DOT District 2, near the town
of Oslo, Mn. The work required testing of MN TH1 in an area that had recently experienced flooding.
The new vehicle front mount performed well and no problems were experienced. (See the GPR survey
report of TH1 testing in Appendix A).
The new vehicle front antenna mount system also allows simultaneous dual channel data
collection, which gives additional information and flexibility. It also provides faster, safer and more
stable vehicle survey operations, especially at highway speeds.
Figure 2.1 Previous GPR vehicle antenna mount
6
Figure 2.2 New GPR vehicle antenna mount
Vehicle Mount Test Location
Figure 2.3 Mn Trunk Highway 1, Test Site Location
7
2.2 INCORPORATING GPS CAPABILITY IN TO THE GPR SYSTEM
In January of 2009, a separate literature and internet search was performed to determine suitable
Global Positioning System (GPS) equipment for the Mn/DOT GPR vehicle and hand cart. The goal was
to acquire a GPS system that would provide an acceptable level of GPS accuracy, while functioning
during GPR data collection at highway speeds. The GPS data output format also had to be compatible
with the Radar equipment owned by Mn/DOT.
It was determined that the best GPS system for the GPR needs would be a Trimble ProXRT receiver
with GLONASS capability. The ProXRT is commonly used in Mobile GPS for GPR operations by other
users. It allows a 1 Hz re-positioning rate with uncorrected sub-meter accuracy. Higher positional
accuracy can be obtained with post processing or real-time with a correction signal. To control the
mobile receiver, a JUNO handheld device was acquired, along with processing software and vehicle
mounting hardware for the GPS equipment.
In July, 2009 the GPS equipment specified was purchased from Frontier Precision, INC, of
Bloomington, MN. This is a company that had previously supplied Mn/DOT with Trimble equipment
and had a good track record of expertise and support. In fall of 2009, training was provided by Frontier
Precision at the Maplewood research lab to familiarize the employees working with the radar equipment
with the GPS system.
2.3 STANDARDIZED GPR MAPPING AND REPORTING
To complete the standardized mapping and reporting tasks of this project, the consultant firm
American Engineering Testing (AET) was contracted in 2009. AET was tasked with creating a
standardized ARCGIS mapping and reporting format for the collected GPR/GPS data. A test section for
the new GPR/GPS system was identified on TH96, between TH61, and TH95. This section was already
scheduled to be GPR surveyed in 2010 as part of the regular GPR production work.
The TH96 test data was useful for this purpose as it represented a ‘real life’ GPR project, and had the
type of road conditions expected to be regularly encountered. The field data collection took place in
March of 2010, and GPR/GPS system performed as expected. The data, along with Mn/DOT cad
mapping, was collected and transferred to AET for reporting and mapping development.
Two different types of GPR mapping were identified as needs. First, “project level” mapping, which
shows the actual route the GPR vehicle (or hand cart) travels. This is needed because of the extreme
variability of the subsurface materials often encountered – precise positioning and mapping is needed to
properly correlate the GPR readings to points the data is taken. The second level of mapping needed is
“system level” - to show where in the state or district GPR projects have been completed. This is useful
for project tracking and provides information to Mn/DOT soils and materials engineers.
8
The process for mapping GPS/GPR data using ARCGIS was completed by in June, 2010.
Microstation mapping was acquired from Metro Design and was used along with an aerial photo to map
the test data. The process for properly configuring the equipment, transferring the GPS/GPR data, and
developing the maps needed was well defined and submitted by AET.
ArcGIS is versatile mapping software that meets the identified needs of the project, and is the
preferred (supported) mapping software for all GIS users at Mn/DOT. Both the system and project level
GPR mapping that will now be normally produced will be readily available to all interested users in
ArcGIS format. GPR data is attached to each GPS location and can be labeled, organized, and presented
in several desired mapping schemes, depending on the project requirements. Visual examples of the
mapped TH96 test section GPR data are shown in figures 2.4 and 2.5.
Figure 2.4 Mn Trunk Highway 96 GPS/GPR mapping test
9
Figure 2.5 TH 96 GPS/GPR data point
For the TH96 test project, the pavement thickness was the primary focus of study. A standard
method to report this type of GPR survey was developed. The standard report contains general project
information, a statistical thickness and length summary, and both graphical and listing representations of
pavement thickness.
The inputting and reporting spreadsheets developed with this project can be adapted to any future
GPR project. They were developed in a user-friendly checkbox format. An example of the GPR
reporting input form is shown in figure 2.6. A summary pavement thickness report for the TH96 test
project is attached in Appendix B. The process for mapping and reporting the GPR data was
documented and provided to Mn/DOT for use in creating the GPR user manual required as part of this
project.
10
SUMMARY OF PAVEMENT SURVEY
COUNTY
PROJECT NO.
PFN
STATE ROAD
MILEPOST LIMITS (SLMP)
PAVEMENT TYPE
Wahington
50204
1234-5
TH 96
0.368
Milepost
From
0.368
To
10.200
Test Date
3/8/2010
to
Date
6/11/10
10.200
Lanes
L1
R1
L2
R2
F
Legend:
F = Flexible, R = Rigid, B = Composite (HMA / PCC) and W = Composite (PCC/HMA)
SUMMARY STATISTICS & PLOT SETTINGS (Please use the menu in this block to modify the settings.)
Display:
Statistics
Data:
Thickness
Plots
for
HMA or
PCC
Cross Slope
Rut Depth
Lanes:
or
All
Limits:
x
y
L1R1
L2R2
Minimum Maximum Maj. Unit
0.368
10.200
1.0
0.0
20.0
2.0
L3R3
L4R4
Min. Unit
0.50
1.00
or
L5R5
L6R6
Initialize
SUMMARY STATISTICS
Lane #
1
Average
7.54
L-Direction
Stdev
Max.
1.56
16.93
Min.
4.45
Average
7.59
Units:
R-Direction
Stdev
Max.
1.89
21.25
in.
Min.
3
Figure 2.6 TH 96 Sample Report
At the completion of the project, certain key information will be captured from the data spreadsheet
and stored in a project history database file. The database file will contain project name, date, and GPS
positional data that will be periodically exported into an ARCGIS shapefile. The shapefile that contains
the project info will be shared with MnDOT districts and other interested people. Instructions will be
provided about how to load the shapefile into the MnDOT Interactive Basemap – located on IHUB at;
http://gisservices.dot.state.mn.us/mndot-basemap/
The TH96 test project info was exported into a shapefile and loaded into the interactive basemap as a
test of that process. Examples of how this output appears are shown in figures 2.7 and 2.8
11
Figure 2.7 MnDOT Basemap TH 96 Project Location
Figure 2.8 MnDOT Basemap TH 96 Project Detail
12
2.4 DEVELOPMENT OF GPR MANUAL
Throughout the term of this project, all aspects of the steps needed for GPR field operations data
functions were being observed, recorded and compiled for development of a GPR user manual. A
successful GPR manual would contain the essential operating instructions for GPR & GPS equipment,
field mapping software, and reporting methods and examples.
The version 1.1 GPR user manual was completed by AET and transferred to Mn/DOT in June 2010.
It is considered complete for purposes of this project, but may be updated and improved upon as future
changes to the GPR operations or reporting needs develop. It is intended that at some point the manual
created with this project will be incorporated into the Mn/DOT standard manual system, therefore the
format of the GPR manual follows the typical Mn/DOT manual format. The June, 2010 GPR Manual
(version 1.1) is attached in appendix C.
CHAPTER 3 PROJECT SUMMARY
A safer, more robust system for GPR survey operations using either single or dual air-coupled
antennas was accomplished with this project. The simultaneous use of dual GPR antennas provides
redundancy in data collection and a comparison tool to improve accuracy and completeness of the
survey results.
Incorporating GPS into GPR pavement management surveys has been requested by Mn/DOT
soils engineers and others, and is important for effective data sharing. The accurate coordinate data
obtained with the GPS system acquired for this project will be used to apply ArcGIS mapping and
project information and history capability to the GPR reports. The development of a user-friendly,
standardized format for GPR data reporting at Mn/DOT will also be a useful improvement. The GPS
positional data obtained will be precisely coordinated with the GPR data and both the layer analysis and
project locations will be made available to the districts in an easy to use, viewable and/or exportable
format.
Because the addition of GPS equipment, data collection, and mapping to the GPR system will
increase the complexity and difficulty of standard survey operations, a “GPR user manual” was
developed as part of this project. The user manual describes GPR vehicle and manual survey operations,
data collection and analysis, mapping using ArcGIS, and describes a method to standardize the GPR
data reporting. The manual was written in the proper format for potential inclusion in the Mn/DOT
standard manual series. The tasks accomplished with this project will improve the efficiency and
effectiveness of the ground penetrating radar (GPR) program at Mn/DOT.
13
APPENDIX A TEST PROJECT FOR VEHICLE FRONT MOUNT
TH 1, 2009 Red River Flooding GPR Study
Survey for voids and deterioration caused by floodwater overtopping by Red River of the North
Approximate Location: TH 1; From Milepost 0.86, to Milepost 3.56
Eastbound and Westbound traveling lanes, both wheel paths
In Oslo, MN
Mn/DOT District 2
May 2009
14
Background
The project location is along MN TH1, east of the town of Oslo, in Mn/DOT district 2. The project area is
between Milepost 0.86 and 3.56. TH1 in this area is a 2-lane rural highway, with minimal shoulders. The pavement
is Bituminous over granular base.
In spring of 2009, the Red River of the North experienced severe flooding and overtopped TH1 to a depth
of more than 1ft in this area, causing deterioration of the shoulders and some of the pavement cracks. Temporary
repairs were made when the flooding subsided to allow vehicle traffic, but the roadway was restricted to 7TON
loads at the time of the survey. The goal of the Ground Penetrating Radar (GPR) survey was to examine the area of
the floodwater overtopping for structural soundness and to attempt to detect unknown voids beneath the pavement.
TH1 Spring Flooding 2009
Surveys
The GPR survey was performed on May 5th, 2009. Ambient conditions were cloudy and dry, however
water from flooding was still standing in ditches and subsurface soils were very moist. The GPR system used was
the SIR-20, manufactured by GSSI. The antenna used was the 1-GigHz air-coupled, attached by a GSSI front
vehicle mount system.
Both Eastbound and both Westbound traveling lanes (all four wheel paths) were surveyed between
Reference posts 0.86 and 3.56. The instrument was attached to the front vehicle mount and driven at approximately
10 MPH. Traffic control in the form of GPR vehicle protection was provided by District 2 Maintenance forces.
Mn/DOT GPR Survey Vehicle with vehicle antenna mount
15
Results
Subsurface void locations that were visible in the data at the time of surveying were immediately marked in
the field for evaluation and repair. Most voids located during the GPR survey were associated with pavement cracks
that had been widened or “washed out” by the flooding. Most of the voids and damage was visible on the surface.
However, some subsurface voids appeared at crack locations where the pavement surface looked fairly sound.
The moist materials caused degradation of the radar signal below approximately 3 feet, but voids above that
depth in the wheel paths were observed with a high degree of confidence. A utility crossing visible in the radar data
during testing verified that the GPR equipment was functioning and was able to view anomalies at depths of at least
36 inches with expected resolution.
Voids visible in the radar data after post processing in the office are summarized in the spreadsheet shown
in the following pages. Note that the radar data measures conditions directly under the path of the antenna, in an
approximately 1-foot wide scan path. Voids outside the survey path will not be visible, nor will any anomalies be
visible deeper than approximately 48 inches (the maximum depth range). Cracks that had been totally washed out
and temporarily repaired at the time of GPR surveying may not appear in the following spreadsheet.
No extremely large, un-collapsed voids appeared in the GPR survey of the traveling lanes. The spreadsheet
summarizes the crack void locations at distances (in feet) going eastbound, starting from the overhead power line
crossing at MP 0.86.
16
Pavement Survey
Begin Eastbound pavement scans @ Milepost 0.86 (directly under the overhead utility line crossing)
End Eastbound pavement scans @ Centerline of Co Rd 17 (approx. Milepost 3.56)
17
Th1 Voids visible in Radar Data
milepost
0.86
0.962
0.995
1.024
1.114
1.123
1.125
1.144
1.147
1.160
1.225
1.248
1.251
1.263
1.274
1.305
1.341
1.410
1.445
1.500
1.558
1.688
1.744
1.766
1.792
1.794
1.817
1.820
1.829
1.852
1.901
1.935
1.956
1.959
2.207
2.209
2.244
2.267
2.269
2.314
2.340
2.402
2.575
2.657
2.660
2.670
2.673
2.690
2.692
dist
4540.8
5081.214
5252.963
5405.462
5883.959
5928.459
5941.375
6039.708
6056.291
6125.208
6466.372
6591.288
6606.872
6668.371
6726.871
6887.87
7079.369
7447.2
7630.865
7918.697
8226.196
8914.192
9209.024
9325.357
9459.772
9470.439
9594.105
9610.855
9658.188
9776.354
10034.69
10216.52
10327.6
10345.18
11651.93
11665.09
11847.68
11970.51
11981.01
12215.42
12353.84
12684.09
13596.17
14028.41
14046.91
14098.5
14114.83
14201.58
14211.5
dist from
power line
crossing
0.00
540.4
712.2
864.7
1343.2
1387.7
1400.6
1498.9
1515.5
1584.4
1925.6
2050.5
2066.1
2127.6
2186.1
2347.1
2538.6
2906.4
3090.1
3377.9
3685.4
4373.4
4668.2
4784.6
4919.0
4929.6
5053.3
5070.1
5117.4
5235.6
5493.9
5675.7
5786.8
5804.4
7111.1
7124.3
7306.9
7429.7
7440.2
7674.6
7813.0
8143.3
9055.4
9487.6
9506.1
9557.7
9574.0
9660.8
9670.7
File
start
WBLTVOIDPICKS
EBLTVOIDPICKS
EBRTVOIDPICKS
WBLTVOIDPICKS
WBRTVOIDPICKS
EBLTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
WBRTVOIDPICKS
WBRTVOIDPICKS
EBLTVOIDPICKS
EBLTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
WBLTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBLTVOIDPICKS
WBRTVOIDPICKS
WBRTVOIDPICKS
WBLTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBLTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBLTVOIDPICKS
WBLTVOIDPICKS
EBLTVOIDPICKS
EBLTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBLTVOIDPICKS
18
2.702
2.830
2.856
2.859
2.898
2.939
2.942
3.127
3.127
3.130
3.166
3.196
14267.5
14940.91
15080.49
15098.16
15303.74
15515.49
15532.07
16508.98
16511.4
16526.82
16713.9
16874.73
9726.7
10400.1
10539.7
10557.4
10762.9
10974.7
10991.3
11968.2
11970.6
11986.0
12173.1
12333.9
WBRTVOIDPICKS
WBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
WBLTVOIDPICKS
EBRTVOIDPICKS
WBRTVOIDPICKS
WBRTVOIDPICKS
19
APPENDIX B TH96 GPS/GPR EXAMPLE REPORT
PLOTS
Ground Penetrating Radar Pavement Thickness Survey
Washington County / Control Section 8211
SR 001 / MP 0.368 to 10.2
20.0
18.0
16.0
). 14.0
ni
( 12.0
ss
e 10.0
n
kc 8.0
i 6.0
h
T
4.0
2.0
0.0
0.368
1.368
2.368
3.368
4.368
5.368
6.368
7.368
8.368
9.368
Milepost
L1
Ground Penetrating Radar Pavement Thickness Survey
Washington County / Control Section 8211
SR 001 / MP 0.368 to 10.2
20.0
18.0
16.0
). 14.0
ni 12.0
(
sse 10.0
n 8.0
kc
i 6.0
h
T 4.0
2.0
0.0
0.368
1.368
2.368
3.368
4.368
5.368
6.368
7.368
8.368
9.368
Milepost
R1
20
Milepost
0.019
0.038
0.057
0.076
0.095
0.114
0.133
0.152
0.170
0.189
0.208
0.227
0.246
0.265
0.284
0.303
0.322
0.341
0.360
0.379
0.398
0.417
0.436
0.455
0.474
0.492
0.511
0.530
0.549
0.568
0.587
0.606
0.625
0.644
0.663
0.682
0.701
0.720
0.739
0.758
0.777
0.795
0.814
0.833
0.852
0.871
0.890
0.909
0.928
0.947
0.966
0.985
1.004
1.023
1.042
1.061
1.080
1.098
1.117
1.136
1.155
1.174
1.193
1.212
1.231
1.250
1.269
1.288
1.307
HMA Thickness
(in.)
8.8
8.1
10.2
9.6
9.2
8.5
7.7
8.5
7.0
7.6
7.1
7.6
7.4
8.3
8.5
10.6
9.7
7.2
6.1
6.5
6.9
6.1
6.5
6.3
7.6
7.0
7.7
6.8
7.1
6.4
7.5
8.2
7.4
7.7
7.3
7.6
7.3
7.7
8.3
7.8
7.0
6.9
6.7
7.4
5.9
6.8
7.3
7.5
9.1
8.2
7.6
7.8
7.6
6.6
6.6
6.9
7.3
8.8
14.0
16.1
16.9
8.7
8.3
8.3
11.3
13.3
12.5
11.2
11.3
L1
PCC Thickness
(in.)
Cross Slope
(%)
Rut Depth
(in.)
Milepost
0.019
0.038
0.057
0.076
0.095
0.114
0.133
0.152
0.171
0.189
0.208
0.227
0.246
0.265
0.284
0.303
0.322
0.341
0.360
0.379
0.398
0.417
0.436
0.455
0.474
0.492
0.511
0.530
0.549
0.568
0.587
0.606
0.625
0.644
0.663
0.682
0.701
0.720
0.739
0.758
0.777
0.796
0.814
0.833
0.852
0.871
0.890
0.909
0.928
0.947
0.966
0.985
1.004
1.023
1.042
1.061
1.080
1.099
1.117
1.136
1.155
1.174
1.193
1.212
1.231
1.250
1.269
1.288
1.307
HMA Thickness
(in.)
8.9
7.2
6.8
7.0
8.4
10.9
8.3
9.6
9.3
8.0
9.7
7.7
7.4
7.8
8.5
8.3
8.6
7.3
7.6
8.2
8.7
8.5
9.1
8.7
10.8
10.0
7.5
7.1
7.4
8.3
7.0
7.5
8.4
9.2
8.1
7.7
7.7
7.4
8.0
8.7
7.4
6.6
6.6
6.8
7.0
6.9
6.5
6.2
9.1
10.3
9.8
9.0
8.0
7.7
7.5
8.0
8.2
8.4
15.4
21.2
14.2
18.1
15.6
16.7
13.5
11.9
12.4
12.7
12.7
R1
PCC Thickness
(in.)
Cross Slope
(%)
Rut Depth
(in.)
21
APPENDIX C GPR OPERATIONS MANUAL
22
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CHAPTER 1 - GENERAL
1-1 INTRODUCTION
1-1.01 PURPOSE
The Minnesota Department of Transportation (Mn/DOT) GPR Operation Manual provides an
overview of the GPR data collecting with a GPS extension and mapping functions in the
department. This manual contains material that is of both an informational and instructional
nature. Guidelines and procedures are spelled out in detail in the hope that greater uniformity and
quality can be obtained in GPR and GPS data collecting and mapping related activities within
Mn/DOT.
The manual clarifies procedures technical and professional GPR data collecting and mapping
personnel use in their day to day work. Using these procedures should result in uniform GPR and
GPS data collecting and mapping practices.
The manual introduces procedures to work with GPR systems now being used throughout
Mn/DOT.
1-1.02 SCOPE
The manual is written for use at the Senior Highway Technician level or above.
The manual contains definitions of common GPR and GPS data collecting and mapping terms
used to communicate with colleagues and clients.
The manual also references other Mn/DOT manuals and other references as necessary for
understanding a topic.
1-2 GPR SECTION - OFFICE OF MATERIALS AND ROAD RESEARCH
1-2.01 GPR SECTION FUNCTIONS
Develop and implement GPR and GPS data collecting and mapping procedures and training.
Test and research new GPR and GPS methods and systems for Mn/DOT.
Budget, purchase and integrate these new methods and systems.
Represent Mn/DOT with governmental agencies and professional and private organizations.
Work with the District Offices to provide training to GPR and GPS data users in understanding of
the standardized reporting format.
Coordinate Mn/DOT GPR and GPS data collecting and mapping activities with each District.
Provide GPR and GPS data collecting and mapping products and services as necessary for
planning, design, construction and maintenance of the transportation system.
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1-2.02 GPR SECTION ACTIVITIES
Develop and implement GPR and GPS data collection and mapping procedures and training.
Test and research new GPS and GPS data collection and mapping methods and equipment for
Mn/DOT.
Budget, purchase and integrate these new methods and equipment.
Represent Mn/DOT with governmental agencies and professional and private organizations.
Work with the District Offices to provide training to GPR and GPS data collection and mapping
personnel in applications of pavement thickness surveys, pavement steel reinforcement and load
transfer surveys, concrete pavement defect surveys, and project mapping.
Coordinate Mn/DOT GPR and GPS data collection and mapping activities with each District
Engineer.
Provide GPR and GPS data collection and mapping products and services as necessary for
planning, design, construction and maintenance of the transportation system.
1-2.03 REQUESTS FOR SERVICES FROM THE GPR SECTION
In order to avoid duplication of work and effort on a project, requests for GPR data collecting and
mapping services should be channeled through the appropriate District Office. The District
Pavement Engineer is responsible for their GPR and GPS records and should be knowledgeable
about past and present respective district data collecting and mapping activities.
Each District submits the GPR requests along with Falling Weight Deflectometer (FWD) requests
or submits GPR requests for individual projects separately. These requests should be sent to the
GPR Section as soon as possible in order to efficiently schedule projects. A minimum of one
month’s notice is usually requested for GPR surveys.
Requests for GPR survey should include the following information:
a. Roadway ID (e.g. US 10, TH 52)
b. County Name (e.g. Ramsey)
c. Project Limits (e.g. MP 171.700 to MP 188.900)
d. Exceptional Needs (e.g. Test on shoulder, Call for distress and roughness surveys)
e. Recommended Due Date
After a request has been received, the GPR Request Tracker (an EXCEL spreadsheet) should be
updated and field work should be scheduled accordingly.
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1-3 LIMITATIONS
The most significant performance limitation of GPR is in high-conductivity materials such as clay
soils and soils that are salt contaminated or water saturated. GPR surveys should be performed in
the dry season if at all possible, especially when base and subbase layers are of interest. Soil
moisture, especially in high-clay soils, only increases the radar attenuation rates, further limiting
the radar performance.
With the noise reduction the interferences from the power lines and telecommunication can be
reduced significantly. However, spurious radar echoes (known as "clutter") can also be expected
in many test areas because of buried debris such as old rails, wire scraps, boulders, and small
metal objects. Usually a trained operator can interpret the desired radar signatures in the midst of
a moderate amount of such clutter. Performance is also limited by signal scattering in
heterogeneous conditions (e.g. rocky soils).
Interpretation of GPR records is an art as well as a science, even with the best available state of
the art radars. Interpretation of radar grams is generally non-intuitive to the novice.
Considerable expertise is necessary to effectively design, conduct, and interpret GPR surveys.
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CHAPTER 2 - SURVEY
2-1 INTRODUCTION
Road Structures are defined here as the layered asphalt or concrete paving and any geo-textiles,
base and sub-base materials. While it is sometimes possible to detect buried utility lines, that
particular application is not a focus of the RoadScan technique.
The RoadScan technique described here involves the use of a GSSI SIR-20 control unit, Model
4105, 4105NR, 4108, or 4108(F) Horn antennas, and some type of distance measure instrument
(DMI). The unit is mounted on a vehicle for high speed data acquisition. Data processing is done
with GSSI’s RADAN processing software with Road Structure Assessment module.
The RoadScan technique used for PCC pavements involves the use of a GSSI SIR-20 control unit,
Model 5100 (1.5 GHz) or Model 5100B (1.6 GHz) antenna, and some type of distance measure
instrument (DMI).
The RoadScan technique used for Utility involves the use of a GSSI SIR-20 control unit, Model
5103A (400 MHz) and Model 3207 (100 MHz) antenna, and some type of distance measure
instrument (DMI).
The current state of the art has competent practitioners review each project site for adequate
pavement and soil conditions and employ GPR when it is suitable. They use multiple frequencies
and use GPR in conjunction with other techniques. A site appropriate survey and data referencing
methods are selected.
Data can be collected in closely spaced parallel profiles and combined in a 3-D volume of data
for post-processing and time or depth-slice interpretation. While GPR is still rarely used for
conventional locating, it is becoming more common as equipment costs drop and ease of use
improves.
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2-2 EQUIPMENT
2-2.01 GPR
The GPR equipment currently used by Mn/DOT is summarized in Table 2-2. All of this
equipment has been purchased from Geophysical Survey Systems Inc. in North Salem, NH. This
equipment consists of two data collection systems (SIR-020 and SIR-2000), two data collection
and analysis software packages (RADAN and ROADDOCTOR), 3 ground-coupled (GC)
antennas (100 MHz, 400MHz, and 1.5 GHz) and 2 air-coupled (AC) antennas (1.0 GHz and 2.0
GHz).
Table 2-2 Mn/DOT GPR Antenna
Model:
Range:
Depth of penetration (ft.):
Samples per Scan:
Resolution:
Number of gain pts:
Vertical High Pass Filter:
Vertical Low Pass Filter:
Scans per second:
Transmit Rate:
Air-Coupled
1 GHz
2 GHz
4108
4105
12 ns
12 ns
3
1.5
512
512
16 bits
16 bits
5
1
250 MHz
300 MHz
3000MHz 5000 MHz
100
150
100-500
100 kHz
KHz
Ground-Coupled
1.5 GHz 400 MHz 100 MHz
5100
5103A
3207
12 ns
50 ns
500ns
1.5
8
36
512
512
512
16 bits
16 bits
16 bits
5
5
5
250 MHz 100 MHz 25 MHz
3000MHz 800MHz 300MHz
100
100
16
100 kHz
100 kHz
50 kHz
The approximate depths of penetration for each of these antennas are given in Table 2-2. In
general the depth of penetration is inversely proportional to the antenna transmission speed. In
addition, Mn/DOT maintains a vehicle totally dedicated to GPR data collection that includes an
independent power source, GPS data collection, electronic DMI device, GPS unit and a Video
camera. Also, for “off-road” projects, a baby buggy has been modified for GPR data collection,
which includes a battery power source and survey wheel.
The SIR-20 is a high-speed, powerful, multi-channel ground penetrating radar system that is ideal
for a wide variety of applications. With different installations, two same or different antennas can
be operated simultaneously with one SIR-20. The maximum number of antennas that can be
operated by one vehicle and two SIR-20 processors is four. Two DMI units are required for four
antennas, one for controlling data acquisition and one for synchronizing two SIR-20 processors.
References that should be used are:
a. SIR System-20 Manual.
b. Handbook for GPR Inspection of Road Structures.
c. RADAN Version 6.6 Manual.
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2-2.02 GPS
The Trimble ProXRT GPS receiver uses H-Star technology in real time by connecting to a realtime correction source for decimeter (10 cm) to subfoot (30 cm) positions in the field. A wireless
link to your local VRS™ network or local base station can be used for the flexibility. The
ProXRT GPS receiver is also capable of using the OmniSTAR XP (20 cm accuracy) services.
Installing the GLONASS option on GPS Pathfinder ProXRT receiver increases the number of
GNSS satellites that can be observed when working in the field. GLONASS improves the ability
to maintain lock on enough satellites to keep working when sky visibility becomes limited in
tough environments. Tracking GLONASS satellites as well as GPS satellites can also improve
productivity by reducing the time required to achieve real-time decimeter or subfoot accuracy.
The National Marine Electronics Association (NMEA, pronounced “NEE’ma”) has generated a
standard set of messages for communicating GPS information. GPR uses the NMEA 0183
version 2.1 protocol that requires the NMEA output from a Pathfinder ProXRT GPS receiver.
GPS Pathfinder® ProXRT Receiver User Manual.
To configure NMEA output on a GPS Pathfinder ProXRT receiver, the NMEA output
option must be enabled on the receiver. The following settings have been modified from
their default values on the Trimble GPS Pathfinder ProXRT receiver:
a.
b.
c.
d.
e.
f.
g.
h.
i.
Input: None
Output: NMEA
Output Baud Rate: 9600
Output Message: GGA (disable all others)
Output Rate: ASAP
GPS Configuration: (see Trimble manual)
Position Rate: 5 Hz
DGPS Configuration: (see Trimble manual)
Source: OmniStar
GPS data from the Trimble GPS Pathfinder ProXRT receiver is logged using the Acumen
Data Logger for GPR. The settings on the Acumen Data Logger shipped with the SIR-20
system are factory preset to match the baud rate of the SIR-20 Tough-book computer
serial communication port (115,200 bps). Acumen data logger settings are adjusted using
the HyperTerminal communication utility by specifying the following parameters:
a.
b.
c.
d.
e.
Bits per second: 115200
Data Bits: 8
Parity: None
Stop Bits: 1
Flow control: Hardware
The mandatory reference is Acumen Data Logger and Trimble AG132 GPS, SIR-20 System
Settings and User Notes.
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2-2.03 DMI
GSSI provides the Model 630B High Resolution Distance Measuring Instrument (DMI) with the
RoadScan system. Model 630B Distance Measuring Instrument (DMI) represents the state-ofthe-art in high-speed, high-accuracy survey control. The 630B is designed to be used on the rear
wheel of a vehicle.
The mandatory reference is Model 630B Distance Measuring Instrument (DMI) Assembly Guide.
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2-3 DATA COLLECTION
2-3.01 PROJECT RECORDS
The amount of research required will depend on the needs of the project. The following
documents may contain useful project information:
a. Construction Plans. Both State and County plans will furnish construction centerline
alignment and reference termini of the constructed highways. The plans will also furnish
pavement design that includes materials types and design thickness of pavement layers
and reinforcement and load transfer design for PCC pavements.
b. Geotechnical Reports. Geotechnical reports will furnish subgrade soils types and
moisture conditions of the constructed highways.
2-3.02 WORK PLAN
The GPR data collection is planned after the project information has been completed. The project
starting and ending locations are identified for route planning. The work plan should include the
following major components:
a. Safety.
b. Quality.
2-3.03 SYSTEM PARAMETER SETUP
The project number will be used to create the project folder to keep this data organized prior to
staring data collection program. If the project number is not available the roadway ID and staring
milepost will be used to create the project folder. A new project should be created under that
folder with a unique name. The followings are steps to define the folders previously created and
set some other parameters:
a. Start from the initial RADAN/SIR-20 screen.
b. Find the View pull-down menu at the top of the screen and click on it. Look for the
Customize options.
c. Click Customize.
d. Click Directories tab.
e. Click the Source button for a window pop-up with a list of folders that are on your
computer. Find the folder created in the previous section and click the picture of the little
folder to open it. Then click OK.
f. Click the Output button to select the same folder as Source and create a subdirectory
called “Output” under the source folder. Source and Output folders should be separated
because the SIR-20 will store different parts of data in different places. It does this so that
parts of data that won’t get overwritten by accident (like project info files) are protected
in the Source folder while the system stores other files in the Output (processed data).
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g. Click the Linear Units tab. Click the down arrow for a pull-down menu list after Vertical
button to select “INCH”. Click the down arrow for a pull-down menu list after
Horizontal button to select “FOOT” if the project length is less than 5 miles or select
“MILE” if the project length is greater than 5 miles. Click the down arrow for a pulldown menu list after GPS Units button to select “Lat Long”.
h. Click the SIRVEYOR tab to configure the GPS. Click the down arrow for a pull-down
menu list after GPS button to select “SDR Logger”. Click the down arrow for a pulldown menu list after Port button to select “COM1”. Click the down arrow for a pulldown menu list after Baud rate button to select “115200”.
i. Click OK once you are satisfied that you have set up the system to your desired
parameters.
The SIR-20 collects data with a project file system. The Project file defines settings for the whole
data collection project and then collects a series of data files with some common settings.
A new collection project is created by going to File>New with the following file convention (the
name should not be more than 8 characters because the name will be cropped after the eighth
character):
a.
b.
c.
d.
e.
First numerical digit: Computer Number
Second letter: Data Collection Direction (W – West; E – East; N – North; S – South)
Third and fourth numerical digits: Section Number
Fifth and sixth numerical digits: Pass Number
Seventh and eighth numerical digits: Processing Sequence Number
Survey wheel data collection method will be used. In this method the system is equipped with a
DMI so that the rate of data collection (scans per foot) can be controlled. These devices allow
collecting data at a specific even scan spacing so that data is collected with a linear horizontal
scale, no matter what speed of collecting data at. Survey wheel should be calibrated by laying out
a 100-foot distance with tape measure and by doing the following steps in SIR-20:
a. Enter the distance in the “Calibration Distance” window and inch the vehicle forward so
that the front wheel is at that start of the tape.
b. Click Calibrate and drive to the end of that distance.
c. Record the number of ticks.
Collecting synchronized GPS data consists of the following steps:
a. Press the Enable GPS button in the dada collection mode (There may be a delay
of several seconds before you see the GPS information appear in the window).
b. Make sure you are receiving valid GPS information. (GPS must be receiving 4 or
more satellites in order to provide a good solution).
c. Run the project and start collecting a file. (You should hear a beep within the first
several seconds of collecting a file. This beep signifies that GPS information is
synchronized with the GPR file.)
d. Upon closing the GPR file you will see a window pop up signifying that GPS data
is being downloaded from the logger. This may take anywhere from several
seconds to more than a minute depending on the length of the file.
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When the following “Configuration” window appears, the value of 512 should be selected in the
“Samp/Scan” drop down box. Also, the values for “Scans / ft” and “ft / Mark” should be changed
to 1 and 528, respectively. All GPR surveys for pavement thickness at highway speed should be
conducted in this setting unless the survey is for a special research need. The detailed settings
under different conditions are shown in Table 2-3.
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Table 2-3 Parameter Settings
Application
Configuration Type
Channels
Configuration Name
Speed (miles/hour)
Scans per second
Dielectric Constant
Scans per foot
Foot per mark
Auto Gain Level
1
H2GHz
60
400
6.25
1
528
0.5
Asphalt Concrete Pavement Thickness
Highway
1
2
2
H2GHz
H2GHz_H2GHz
H2GHz_400MHz
30
60
30
400
400
200
6.25
6.25
6.25
2
1
1
100
528
100
0.5
0.5
0.5
Next step is to open the Macro window. This window will allow for either creating a new macro,
or attaching an existing macro. If there are no pre-saved macros on the system, the new macro
should be created. Upon clicking the button for Create New Macro and clicking Finish the
antenna will initialize, clock will count a few seconds and then data will scroll across the screen.
You will need to make a few adjustments before beginning collection. The steps below should be
followed:
a. Configure Position
b. Check Gain
c. Check Filter. The correct filter settings of different antennas are listed in Table 2-2. If
the noise reduction filter has been installed in the antenna (4105NR), “Custom” filter
should be applied instead by selecting the filter which corresponds to your 4105NR’s
serial number.
d. Save Macro
After assigning the correct parameters for data collection, click the “Antenna Calibration File”
button followed by the “Next” button.
2-3.04 CALIBRATION
The Bumper Jump Antenna Calibration file (.CZT) is crucial to Horn antenna processing. A 4 ×
4 foot (1.2 × 1.2 m) minimum size sheet of metal is used for the antenna calibration. This metal
plate should be clean and smooth. A Bumper Jump file will be collected at the beginning of each
day’s data collection. If the filed work lasts longer than 6 hours an additional one will be
collected at the end of the day as well. The calibration file should have the same system
parameter setup as data files defined in Section 2-3.03.
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2-3.05 FIELD WORK
The field work is performed by a two-person crew that consists of a designated driver and a GPR
operator. The GPS receiver is attached at the center of GPR antenna mounted to the vehicle front
bumper or the GPR buggy.
Manually inserted markers are needed to assist in minimizing the error due to the starting offset in
the data. The operator should take notes of what the markers are representing. As many markers
as necessary should be inserted manually to indicate the following:
a. Starting and ending points and/or mileposts (if present) of the section under
survey.
b. Any physical objects with known milepost. (e.g., bridges, intersections, railroad
crossing and etc.)
c. Pavement changes.
After the data collection is completed, the data should be copied and pasted to the GPR data
server or hard drive. If the coring was conducted, these results should also be saved in the same
project folder. The field notes taken by the operator(s) should be scanned and saved electronically.
2-3.06 VERIFICATION CORES
The accuracy of the analyzed GPR data will be determined by correlating the computed layer
thickness values to core data which have not been used in the analysis process. Where possible,
the short scans will be selected to cover areas where cores have already been taken. Where core
data are not available for correlation, GPR data will be used to recommend locations for coring.
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CHAPTER 3 - ANALYSIS
3-1 INTRODUCTION
The Road Structure Assessment Module (RSA) in RADAN is a specialized data processing tool
used to assess thickness (depth) and physical characteristics of multiple road layers. The RSA
module can be used to process data obtained with GSSI SIR Systems using the 1 GHz (Model
4108) or 2 GHz (Model 4105) horn antennas.
The collected GPR data should be processed using GSSI’s RADAN 6.6 software. The software
allows the user to view the amplitude of the reflected waves in either stacked waveform or color
coded display as shown in Figure 5. The horizontal axis at the top shows the traveling distance of
the vehicle while the vertical axis on the left shows the two-way travel time of the radar wave.
The color coded display mode is preferred for data processing since it is easier to understand and
more convenient to use.
3-2 PAVEMENT LAYER THICKNESS
3-2.01 CALIBRATION FILE GENERATION
Each raw calibration file (*.dzt) is processed using the Calibration file generation tool in RADAN.
The default extension on the output from the Calibration Tool is *.czt. The calibration generation
tool reorganizes input data scans, performs some scan stacking, and overwrites the last 6 samples
of each output scan with specific amplitude and height information. Choose 4105HR for the 2
GHz and 4108HR for the 1 GHz. Save the .CZT file with a name that consists of the calibration
date. If more than one calibration files exist add the letter at the end of the date file name. Save
CZT file to the folder called “Horn Calibration”.
3-2.02 AUTO LOAD CALIBRATION FILE
RADAN will search for a CZT file in the Current folder selection. Check to make sure that the
calibration file displayed is correct and if not uncheck “auto load calibration file”, click “browse”
to pick the appropriate calibration file, and click ‘finish”. The data file will scroll rapidly and it
will prompt you to save the new, processed file. Give the file a unique name and click Save.
Remember to add display gain. Note that in the processed data file, the pavement surface is now
flat and Time-Zero is now at the pavement surface.
3-2.03 INTERACTIVE LAYER TRACKING
The processed antenna calibration file is used to process the raw data files in the process, called
the horn reflection picking, which eliminates the effect of bouncing of the van during data
collection. In addition, the vertical time scale is automatically adjusted such that the zero time
corresponds to the point of time the radar wave reaches the pavement surface instead of the time
the radar wave leaves the antenna.
There should be at least two markers indicating the beginning and ending locations of the section.
After the beginning and ending locations are identified in the data, the horizontal scale should be
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corrected such that those locations match the mileposts of project termini. For increasing
direction, horizontal offset can calculated as:
X offset = X actual − X RADAN
For decreasing direction, horizontal offset can calculated as:
X offset = − X actual − X RADAN
When this offset value is inputted into RADAN by selecting “edit”>”edit
database”>”regions/position, the horizontal scale will be updated.
To obtain the depth to a layer interface using RADAN, the interface under consideration should
be identified and picked from the data. The interface can be found in the data as a series of
positive or negative peaks. Whether the peaks will be positive or negative depends on the
dielectric properties of the layers above and below the layer interface. Positive peaks appear
when the radar wave passes through an interface from a material with lower dielectric
permittivity to a material with higher dielectric permittivity and vice versa for the negative peaks.
The results can be saved in a comma delimited file with an extension *.lay. This output contains
the thickness information as well as other useful information such as the propagation velocity,
reflection amplitude and two-way travel time.
3-2.04 EXPORT
Project information are stored in the header file and exported into tabular data that contains
geographic locations in the form of x,y coordinates to your map.
The GPR results can be directly exported to KML files under the conditions that the GPS
coordinate systems have be enabled prior to exporting. A KML file is a file type used to display
geographic data. KML files have a tag-based structure with names and attributes used for
specific display purposes. KML files can be imported in ArcGIS 9.2 as a line layer.
The GPR results can also be exported from the ASCII test file with the file extension of lay as a
result of picking. The test files should be imported into either Excel or Access applications to
create coma separated text files that can be imported in ArcGIS 9.2 as a point or line layer.
The output from RADAN can be imported into MS Access for further summarizing the layer
thickness at 100 ft. interval and the reported thicknesses are the averages of those from one or
both wheel paths.
3-3 STEEL TARGETS
When the antenna crosses a target (tie bar, rebar) at a right angle, the resulting image looks like a
hyperbola. In all GSSI antennas, steel target reflection is a copy of the transmit pulse that has a
certain polarity: positive peak first, then a negative peak (possibly followed by a second positive).
In a grayscale line scan, this looks like a white band followed by a black band (then possibly
another white).
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3-3.01 TIME ZERO
Time Zero function will shift the vertical scale so time zero is aligned with the surface reflection
in each scan. After opening the data file that will be processed, it is possible to run the process by
selecting Process > Infrastructure, then selecting Structure Identification to open the dialog
window. The processing parameters should be selected as follows:
a. Check “Set time Zero”
b. Select the antenna of 5100 (1.5 GHz)
c. Check “Background Removal”
3-3.02 MIGRATION
The radar antenna radiates energy with a wide bandwidth pattern such that objects several feet
away may be detected. As a consequence of this, objects of finite dimensions may appear as
hyperbolic reflectors on the radar record as the antenna detects the object from far off and is
moved over and past it. Migration is a technique that collapses hyperbolic diffractions.
The Kirchhoff method should be selected for migration by adjusting the shape of the Ghost
Hyperbola in the following steps:
a. Left-click and hold the mouse button when the cursor is over the center of the Ghost
Hyperbola to drag the Ghost Hyperbola to center it over a real hyperbola in the data.
b. Use the Shaping Handles to match the shape of the Ghost Hyperbola to a real one by
covering up the entire real hyperbola using to tails of the real hyperbola to help shaping.
c. Adjust the Width by left-clicking and holding on the Slider Bar Handle at the top or the
bottom of the profile window to make the slider bars to be wide enough to encompass the
real hyperbola, but not so wide as to include adjacent hyperbolas.
d. Click on Run 2-D Constant Velocity Migration.
3-3.03 INTERACTIVE TARGET TRACKING
Interactive Interpretation allows the user to semi-automatically locate and analyze features in
radar data by placing “picks” on the data. A “pick” is a peak of amplitude identified in a scan that
can correspond to a point target. The hyperbola becomes a point after migration that can be
picked.
If this is the first time on a GPR image file after it was processed in Time Zero and Migration,
there is no result (ASCII) file associated with it. It is possible to run the process by selecting
View > Interactive to open the dialog window. The Generate New ASCII File option should be
checked and OK clicked.
The target picking options should be specified prior to picking. All of the user options available
in Interactive Interpretation are accessed first by moving the mouse cursor so that it is within the
Interactive Interpretation data window (upper pane), then pressing the right mouse button.
Clicking on the Target Options menu item from the Main Menu opens up a list box containing the
names and properties of all of the targets. Targets are added by clicking
. The new
target properties are edited by placing the mouse cursor over the target name and double-clicking.
The following properties should be used:
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a.
b.
c.
d.
e.
f.
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Name: Steel Bar
Color: White
Size: 5
Diameter: 0
Picking Criteria: Positive Peak
Velocity Calc.: User-specified or Core Data
The target points can be picked either using single point or EZ Tracker. The pick locations,
depths, and reflection amplitudes are stored in an ASCII file (*.lay) when the user selects the
“Save Changes” option. An ASCII file can be opened and edited many times.
3-3.04 EXPORT
Project information are stored in the header file and exported into tabular data that contains
geographic locations in the form of x,y coordinates to your map.
The GPR results can be directly exported to KML files under the conditions that the GPS
coordinate systems have be enabled prior to exporting. Only depth of steel bars can be exported
in this operation. KML files can be imported in ArcGIS 9.2 as a line layer.
The GPR results can also be exported from the ASCII test file with the file extension of lay as a
result of picking. The test files should be imported into either Excel or Access applications to
create coma separated text files that can be imported in ArcGIS 9.2 as a point or line layer.
3-4 DEFECT TARGETS
A phase inversion occurs at a concrete-air interface because of the low dielectric of air. A phase
inversion is a flip-flopping of the normal polarity sequence. So instead of a
positive/negative/positive (white/black/white) peak, the phase inverted sequence is
negative/positive/negative (black/white/black). A concrete-air reflection starts with a negative
(black) peak followed by a positive (white) peak.
3-4.01 TIME ZERO
Time Zero function will shift the vertical scale so time zero is aligned with the surface reflection
in each scan. After opening the data file that will be processed, it is possible to run the process by
selecting Process > Infrastructure, then selecting Structure Identification to open the dialog
window. The processing parameters should be selected as follows:
a. Check “Set time Zero”
b. Select the antenna of 5100 (1.5 GHz)
3-4.02 FIR FILTER
RADAN contains Vertical and Horizontal FIR filters. FIR filters, when encountering a feature in
the data, are guaranteed to output a finite filtered version of that feature. The Triangular FIR
filter should be used for filtering defect features in concrete pavement. The Triangular filter
emphasizes the center of the filter more heavily than the ends of the filter. This type of filter is a
weighted moving average, with the weighting function shaped like a triangle. A portion of the
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data, determined by the filter length, is multiplied and summed by this function. The result is
output at the center of the triangle.
FIR filter settings should be the followings:
a. Background Removal (scans): 349
b. Low Pass (MHz): 500
c. Filter Type: Triangle
3-4.03 RESTORE GAIN
The Restore Gain function removes the gain applied to the data during acquisition. Restoring gain
is an important option should you wish to export your data to a forward modeling program, or
determine the dielectric permittivity, conductivity, and dispersion (approximate attenuation) of
layers. The Restore Gain function uses gain information found in the file header to remove the
gain function and normalize the gains.
3-4.04 INTERACTIVE TARGET TRACKING
Clicking on the Target Options menu item from the Main Menu opens up a list box containing the
names and properties of all of the targets. Targets are added by clicking
. The new
target properties are edited by placing the mouse cursor over the target name and double-clicking.
The following properties should be used:
a.
b.
c.
d.
e.
f.
Name: Defect
Color: Red
Size: 5
Diameter: 0
Picking Criteria: Negative Peak
Velocity Calc.: User-specified or Core Data
The target points can be picked either using single point. The pick locations, depths, and
reflection amplitudes are stored in an ASCII file (*.lay) when the user selects the “Save Changes”
option. An ASCII file can be opened and edited many times.
3-4.05 EXPORT
Project information are stored in the header file and exported into tabular data that contains
geographic locations in the form of x,y coordinates to your map.
The GPR results can be directly exported to KML files under the conditions that the GPS
coordinate systems have be enabled prior to exporting. Only depth of defects can be exported in
this operation. KML files can be imported in ArcGIS 9.2 as a line layer.
The GPR results can also be exported from the ASCII test file with the file extension of lay as a
result of picking. The test files should be imported into either Excel or Access applications to
create coma separated text files that can be imported in ArcGIS 9.2 as a point layer.
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CHAPTER 4 - MAPPING
4-1 INTRODUCTION
A standardized mapping process is developed for GPR project information and data specifically
designed to report GPR results in an ArcGIS format. The developed ArcGIS mapping process
will provide the following capability:
a. A standardized process to convert the GPR and GPS data exported by RADAN software
into an ArcGIS format will be developed and documented.
b. Data that is transferred into ArcGIS using the procedure developed in step a) will be
presented using two different mapping processes.
The standard process includes written instructions for GPR and GPS data conversion and transfer
process, a statewide Minnesota mapping process, showing the locations of GPR data collection
projects, and a method of prompting the user for the required information. The statewide map
layer (point layer) developed will display the following attributes of the GPR projects:
a.
b.
c.
d.
e.
f.
GPR project type
Mn/DOT district
Trunk Highway number
Project limits
The date the data was collected
GPR data file name.
The attributes for the projects listed above are searchable and able to be sorted and outputted into
a written report format, which will include a printed Minnesota ArcGIS project location map.
A more detailed level of project mapping developed shows the GPR vehicle track as data was
collected. At each point a GPR/GPS data point is recorded, the pavement thickness data will be
mapped by color coding the GPS locations (line layer). If there was a core taken at a certain point,
the coring information of the cores is mapped by color coded GPS locations (point layer). The
mapping system also allows the user to 'click on' individual project points on the map for the
detailed information by 'hotlink' to the color coded pavement and base layer thickness with GPS
X/Y coordinates, photos of the pavement, and GPR filename information. The mapping layers
generated are presented in ArcGIS format, and utilize the Mn/DOT GIS base map and/or county
highway GIS maps. The mapping capability developed is in a format allowing output into a
written report, which will include a printed Minnesota ArcGIS project details map.
Mn/DOT Web-based interactive basemap is used to display the GPR project information and test
results if the size of the GPR shape file is less 20 MB. Custom ArcGIS toolbars developed in the
basemap provide point-and-click data automation, enabling analysts and scientists to easily
navigate through GPR project layers and state highways, while hyperlinked features provide realtime access to project reports and GPR data.
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4-2 CONVERSION
4-2.01 FILE ORGNIZATION
GPR Project information in tabular format are supplemented or merged with the highway project
information into a project file. The GPR supporting files include the followings:
a. Report files.
b. Results files.
c. Core picture files.
4-2.02 IMPORT
Coma delimited files (.csv) are preferred for importing GPR results files into ArcGIS to create the
shape files. Both project files and results files can be converted into .cvs files using MS Excel.
During importing the MnDOT projection is needed to be specified as follows:
a. Group: UTM Nad 1983
b. Name: NAD 1983 UTM Zone 15N
Keyhole Markup Language (KML) is an XML-based language for defining the display of threedimensional spatial data. KML files have either a .kml file extension or a .kmz file extension (for
zipped KML files). Support for KML 2.0 is included in the ArcGIS 9.2 release. The purpose of
adding KML functionality to ArcGIS is to allow interoperability between ArcGIS and the Google
Earth system. ArcGIS can act as a client for KML data. It can also export KML files for sharing
with others, and serve KML content to the Google Earth browser.
In ArcGIS, KML data is represented using a KML Layer. KML layers are supported in ArcGlobe,
ArcGIS Explorer, and the ArcGIS Engine Globe control. Like other layers (such as feature or
raster layers), a KML layer is based on a data source, appears in the table of contents, has a
context menu, property sheet, and associated toolbars and tools.
The ArcGIS KML layer treats the KML document as read-only information. It does not support
functionality for interactively editing or creating new KML content. You cannot use KML
elements as input for analysis operations.
The Data Interoperability Extension allows you to add KML data formats directly to
ArcMap and ArcGlobe. The steps required for this procedure are the same as adding
Geodatabase feature classes or shapefiles as follows.
1. Start ArcMap or ArcGlobe.
2. Enable the extension if need be.
3. Click the Add Data (
) button. The Add Data dialog opens.
4. Click the Look in drop-down arrow and navigate to the folder or
Interoperability Connection that contains the external data source, as shown
below.
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5. Click the data source and click Add.
4-2.03 SERVICES
You can also use a service as a basemap to go under your local data. For example, you might use
satellite or aerial photographs or administrative boundaries from a service, and then overlay your
own data, such as parcels, land uses, or demographics.
A GIS portal provides access to a variety of data and services gathered together in one
clearinghouse. GIS portals organize content and services such as directories, search tools,
community information, support resources, data, and applications. They provide capabilities to
query metadata records for relevant data and services and link directly to the online sites that host
content services.
Another place you can find data is in a metadata service provided by an organization or agency.
These services are online catalogs of metadata that can be searched and browsed over the Internet
to find and access data. Each metadata service has a Metadata Explorer Web page that allows you
to search and browse the data that the organization or agency has made available.
A layer based on an ArcIMS feature class works the same as any other feature layer. A Feature
service layer acts like a group layer, as a container layer for child layers. These child layers are
ArcIMS Feature Classes, which reference individual feature classes residing on an ArcIMS server.
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An ArcGIS Server map service provides mapping data associated with a single data frame of an
ArcGIS map document (.mxd or .pmf) that is being served through ArcGIS Server. You can
connect to an ArcGIS Server map service over the Internet or over a local area network (LAN).
4-3 CONVERSION
4-3.01 PROJECT POINT LAYER
Creating a point feature class from x,y coordinates exported from GPR header file consists of the
following steps:
a. Right-click a table in the ArcCatalog tree that has columns containing coordinates, point
to Create Feature Class, and click From XY Table.
b. Click the X Field drop-down arrow and click the name of the column that contains the xcoordinates.
c. Click the Y Field drop-down arrow and click the name of the column that contains the ycoordinates.
d. If appropriate, click the Z Field drop-down arrow and click the name of the column that
contains the z-coordinates.
e. Click Spatial Reference of Input Coordinates and define the coordinate system for the
input values as necessary.
f. Click the Browse button.
g. Click the Save as type drop-down arrow and click the format in which to create the new
point features.
h. Navigate to the folder in which you want to store the new features.
i. Type a name for the new data source.
j. Click Save.
k. Set any Advanced Geometry Options and ArcSDE configuration keywords as necessary.
l. Click OK.
4-3.02 Project Callout Text Box
Adding text with a callout box and leader line consists of the following steps:
a. Click the Callout button
on the Draw toolbar.
b. Click a project point for the leader line and drag and release the mouse pointer
where you want the callout and text to be placed (in the image below, the start
point is the yellow dot).
c. Type the text string.
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4-3.03 HYPERLINKS
Hyperlinks let you provide additional information about the features to people who will be using
your maps with ArcMap. When you click a feature with the Hyperlink tool, a document or file is
launched using the application with which that file type is currently associated.
Accessing a feature's hyperlink consists of the following steps:
a. Make sure the layer containing the feature for which you want to access a hyperlink is
checked on (visible) in the table of contents.
b. Click the Hyperlink tool. Any visible features in the map that have hyperlinks defined
are drawn in blue, the default color, or outlined in blue in the case of polygons. When you
are over a feature for which a hyperlink exists, the mouse pointer turns into a pointing
hand and you see a pop-up tip with the name of the target.
c. Click the feature. A hyperlink is invoked. If more than one hyperlink has been defined
for the feature you clicked, a dialog box will appear from which you can select the
hyperlink you want to launch.
4-3.04 INTEGRATION
The integration of all project related files consists of two major stages: initial and expanding. The
initial stage is focused on setting up a statewide Minnesota mapping process, showing the
locations of GPR data collection projects. The expanding stage is involved in adding the new
GPR projects to the existing map with elapsing of time.
4-4 WEB APPLICATION
4-4.01 GPR PROJECTS
The GPR projects shape files should be imported into the Mn/DOT web-based interactive
basemap that can be accessed via:
http://gisservices.dot.state.mn.us/mndot-basemap/
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In the web based GIS map as shown above, there is a pulldown menu in the toolbox at
the upper left. The down arrow should be clicked to select project and then, just to the
right is “upload shapefile”. The shape files are uploaded using the following steps:
a.
b.
c.
d.
Browse for the shapefile files created in ArcGIS 9.2
Load all four of the necessary files (.shp, .shx, dbf. and .prj)
Name your new map layer
Press ”Submit” and if the points are valid they should show up as an uploaded
layer
e. Change point properties in the “symbolize layer” box
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CHAPTER 5 - REPORTING
5-1 INTRODUCTION
The reporting is in a format allowing output into a written report, which will include a printed
Minnesota ArcGIS project details map.
5-2 DATA REPORT
A spreadsheet reporting the layer thickness should be prepared and sent electronically to the
requestor. The spreadsheet contains 2 worksheets: a summary sheet and a data sheet.
5-2.01 SUMMARY
The summary sheet consists of the following separate blocks:
a. Pavement Inventory: This block describes the inventory of the project. The survey
date should also be included in this block.
b. Pavement Type: Pavement types and their limits should be provided in this block for
the viewer. Comments should be made in this block to let the engineer be aware of
any findings that may be useful for rehabilitation design or any issues with the radar
data such as presence of noise due to interferences from other sources.
c. Summary Statistics & Plot Settings: This is the only block in the summary sheet that
can be modified by the viewer. Included in this block is the menu that controls the
settings for the summary statistics and the plots provided in blocks 4 and 5.
d. Summary Statistics: Summary statistics of the data between the limiting mileposts are
shown as a table format. The statistics include average, standard deviation, minimum
and maximum values and the limiting mileposts are the x-limits in 3rd block.
e. Plots: The data is plotted and shown in this block. Using the menu in the 3rd block,
the viewer can choose to plot different data: thickness, cross slope or rut depth. The
horizontal and vertical axes can be modified for zooming in and out.
5-2.02 DATA
The data sheet consists of the actual data, including mileposts, thicknesses, and drilling data
placed under the corresponding columns and lanes. Mileposts and the thicknesses can be copied
from the excel files exported from Access and pasted into this spreadsheet.
5-3 GIS REPORT
5-3.01 MAP TEMPLATE
If the map is part of a series, you might have a template to work from, or you might create a new
template for the series. Map templates make it easy to produce maps that conform to a standard,
and they save time by letting you do the layout work for all the maps in the series at once.
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5-3.02 MAP PRINTING
In the web based GIS map as shown above, there is a pull-down menu in the toolbox at
the upper left. The down arrow should be clicked to select navigation and then, just to
the right are “in”, “out”, and “pan”. At the left, there is layer list. The map layer
created in the previous chapter should be checked. When the map is ready to print, the
down arrow should be clicked to select print and then, just to the right is “print”. The
project details map is printed using the following steps:
a.
b.
c.
d.
e.
f.
g.
Select a page size
Select an output format
Select “Show All Layers”
Type the project title
Enter the map description
Press “View”
Press “Download”
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