Summary: With Global Navigation Satellite System (GNSS) positioning integrated with GPR, you can interpret utility locations in the field while capturing geo-referenced positions as you work. Export your findings to mapping and GIS software for flexible, “Map It Your Way™” visualization. Whether you’re tracking multiple utilities or surveying complex sites, GPR can help you create, customize, and share digital utility maps that align with your workflow.
Regardless of the utility locating technology you’re using – whether it’s an electromagnetic (EM) precision locator or a GPR – capturing the position of detected utilities is an important part of the locating workflow.
One way to document a locate is to paint the ground as an immediate visual reference of what was located underground. Locators may now produce a long(er)-term record of their work, for example in the form of a digital utility map (Figure 1).
One option to obtain this digital map is to send a surveyor with a high-accuracy* GNSS to the site to digitize the location of the paint marks on the ground.
Another option is to map while you locate, using an onboard high-accuracy GNSS on your locator. The Radiodetection® RD8200®SG Survey-Grade Precision Locator has offered this capability for years (Figure 2, left). With the release of the GPR-SG accessory, Sensors & Software™ GPR systems now also have a plug-and-play, high-accuracy GNSS solution available (Figure 2, right).
Just like the RD8200SG, any Sensors & Software GPR system fitted with a high-accuracy GNSS can provide geo-referenced, breadcrumb paths of interpreted utilities.
GPR users can locate and track one or multiple utilities simultaneously by scanning the area of interest in what we call a “pseudo-grid”. The idea is to survey with GPR by zigzagging back and forth across the area, similar to “cutting the lawn”. This workflow may be performed using the SplitView screen, which shows both the GPR cross-section of the subsurface and a map view of your path (Figure 3).
The SplitView screen (Figure 3) shows the GPR cross-section view on the left. This example has 10 meters of data horizontally and 3 meters of data vertically. You can see a hyperbola from our targets, which are interpreted as utilities.
On the right is the bird’s eye view, or map view, of the survey area. You can see that the survey was a pseudo-grid, with the operator zigzagging back and forth over the targets. The apparent accuracy of pseudo-grid path depends on the accuracy of the GNSS used with the GPR system – generally improved GNSS accuracy can result in a more precisely rendered GPR path.
Each square of the grid on the map view image is 0.5 meters wide, so the total length of the zigzagging path is several tens of meters long. It is important to understand that the cross-section on the left is only a 10-meter-long section of the total GPR line length. The part of the cross-section displayed is indicated by the orange line on the map view display.
Therefore, when looking at the SplitView screen, note the orange line because it indicates the part of the cross-section being shown on the left. You can move the orange line to view a different part of the cross-section using the arrow keys, allowing you to quickly line up hyperbolas from the same utility.
In Figure 3, two utilities are tracked simultaneously by adding field interpretations with different colors (yellow and red, in this example) to the top of the hyperbolas.
Figure 3b shows an animation of how field interps are added by scrolling through the cross-section on the left (indicated on the right by the orange line moving), finding the hyperbola that lines up with others from the same utility and adding the colored field interp to it.
The high-accuracy GNSS positions of the field interpretations (colored dots) and the GPR path can be mapped after transferring the data from the GPR system. When the GPR data is exported from Sensors & Software GPR systems, a Google Earth® KMZ file and a Comma Separated Values (CSV) file are automatically generated. These file types are commonly supported by third-party locator mapping software.
Figure 4 shows examples of KMZ files plotted in different mapping software: Figure 4a – Google Earth, Figure 4b – PointMan®, and Figure 4c – Subsurface Maps™. The zigzagging GPR collection path and the field interpretations are shown on each map.
GPR results can also be displayed in GIS (Geographical Information Systems) Software, such as ArcGIS® and QGIS. GIS software typically reads CSV or spreadsheet files.
Figure 5 shows the CSV file data (from Figure 3) plotted in QGIS; the field interpretations are displayed indicating the breadcrumb of the buried utility location.
Moving from GPR data collected in the field to a digital utility map in your chosen mapping software can help streamline utility-locating workflows. For more information about how the new LMX®-SG bundles and GPR-SG accessory packages can support mapping utilities with GPR, contact us.
Sensors & Software, Radiodetection, RD8200SG, and RD8200 are either trademarks or registered trademarks of Radiodetection in the United States and / or other countries. Google Earth is a trademark of Google LLC. QGIS is a free and open-source Geographic Information System developed by the QGIS community and QGIS.ORG. ArcGIS is a trademark of Esri, used here for identification purposes only. PointMan and ProStar are registered as trademarks owned by ProStar Geocorp, Inc. SubsurfaceMaps is by Subsurface Solutions (trademark pending).
The positioning performance described in this article reflects typical capabilities of high-accuracy GNSS solutions such as the GPR-SG system paired with a pre-configured Juniper Geode GNSS receiver and applicable correction services. Standards and specification materials covering geodetic control and professional GNSS surveys include accuracy classifications that range from sub-centimeter up to about 10 cm at typical confidence levels (e.g., 95%) for professional work. Actual results may vary based on field conditions, GNSS signal quality, availability of correction sources (e.g., RTK or SBAS), environmental factors (e.g., multipath, canopy, urban canyons), and how the equipment is deployed and operated. Use of GNSS-integrated GPR for utility mapping should be combined with appropriate surveying practices and quality control procedures; it is the responsibility of the user to verify the accuracy and suitability of the data for their specific application. Sensors & Software and associated technology providers do not guarantee specific positioning accuracy in all conditions, and users should consult product documentation and local standards when interpreting GNSS-referenced GPR data.
