Advances in GPR Array Data Processing a Boost to AR

It was not many years ago the first ads ran on television broadcasts for persons donning headsets for gaming and other activities. For some of us of a certain stature (euphemism for a bit older than many), it reminds us of how futuristic the “Jetsons” and other entertainment from our youth really were. It is also a reminder that if it is dreamed it can be become a reality-virtually!

Today the range of visualization tools is expanding and what seemed out of reach for most consumers, products such as HoloLens and Google Glasses, are not as cost prohibitive as one would think. In addition, visualization tools for both the above and below ground are now available for platforms such as smart phones and tablets in Android, IOs, and Windows. All of these are equally capable to display subsurface utility data with the aid of GIS and other software platforms. This coincides as well to accessibility and affordability of GPS systems and integration of GPS into several devices either directly or through NTRIP or VRS correction services as well as GNSS. Without real time positioning to sub-meter to sub-centimeter, the ability to point the device and traverse the site while tracking the subsurface image superimposed into the real world would be prohibitive.

The real issue discussed in one of my previous articles is that the data displayed must be obtained at some point in the field through the SUE standard of care or through an accurate asbuilt drawing. As-builts are often akin to a Unicorn most of the time and verification as to the accuracy is usually unknown or suspect at best. It is imperative that the data quality be known by the end user as these tools continue to become more mainstream. James Anspach, Distinguished Member of ASCE, Chair of ASCE 38-22 (the update to the SUE standard 38-02) poses the risk this way, “These visualizations have tretremendous value but false assurances in the data will outweigh the One Call statutes to control it. It is all about the fidelity of the data and if you don’t own the providence of the data… you are relying on data that could ultimately hurt you in some way.” There is no doubt it is human nature to accept a reality that looks like just that reality. However, in the future perhaps there will be a method to qualify these visualizations in real time so there are no misperceptions of the accuracy of the information.

Over time the acceptance and pervasive use of the new “As-Built” standard, ASCE 75 Standard Guideline for Recording and Exchanging Utility Infrastructure Data, will add value to the information obtained through a QLD records search in terms of assured accuracy from a survey at the time of installation. This will be over years due to the magnitude of projects and the time necessary to incorporate the data for many corridors project-by-project. The standard can only address parts of the corridor that are in the scope of the project, moreover participation may also be limited unless there is a mandate for the installed documentation survey by the governing authority of the project willing to pay for it. One would hope, over time, the standard is universally embraced and these data become part of the mix in the AR solution of the future. The existing and emerging tech for capture of installed utilities from LiDAR and 3D photogrammetry and a combination thereof are exciting and may eventually replace traditional survey instruments.

Figure 1. Raptor OspreyView Data Courtesy of GEL Solutions LLC and David Evans &b Associates, 2nd Ave Spokane WA. Image of utilities from surface to approximate depth of three meters.

Perhaps by the time of this article publication of 38-22, the Standard Guideline for Investigating and Documenting Existing Utilities will officially be released as the updated version of 38-02.

The updated “22” incorporates 3D MCGPR or GPR arrays and provides guidance on 3D models perfectly timed for the advances in AR and GPR arrays.

The updated SUE is a leap forward and will be instrumental in qualifying the data downstream to the AR world. Processing and visualization of array data in of itself is also approaching the AR realm at least as a QLB representation. Last year, ImpulseRadar developed and released Osprey View software for treatment of data collected with the Raptor high-speed GPR array. Processed GPR array data can be viewed as a complete range of data from the surface to the detection limits of the radar energy. The visualization is a virtual image as if one were looking at a street corridor vacuum excavated in its entirety in favorable GPR soil conditions. Figure 1 clearly illustrates how this visualization tool mimics AR from the manholes down to the maximum array penetration depth of close to three meters. One could argue this is reality, but not physically contacting these utilities qualifies them as QLB regardless under the SUE standard. Remarkably, these data were collected at posted city speed limits.

Figure 2. Raptor OspreyView Data courtesy of Central Florida Locating, Bushnell FL.

Figure 2 illustrates the high resolution achievable with MCGPR arrays clearly disseminating the numerous of conduits installed as well as other underground assets through a major intersection in Bushnell, Florida. Until recently, visualization of this clarity was not achievable for the SUE professional and certainly not achievable with 2D GPR systems.

Utility Mapping Services, Inc., a Montana-based subsurface utility engineering firm, provides advanced utility mapping services primarily throughout the western U.S. The soils in this vast region range from ideal to poor for GPR.

However, according to Clifford Meis, PE and project lead on many Raptor array subsurface mapping projects, “Even in the most difficult conditions the use of OspreyView visualization enhances trench lines previously or until now not as clearly distinguished in the data volume.” According to Mr. Meis, this was clear on a recent project as access into manholes for the gravity sewer system does not guarantee the ability to discern the alignment. He explained that “They attempted to note the relative pipe projections visually, but as nonconductive pipes, we are limited in practical methods to map them (we did not run rodder or a sonde due to traffic considerations) and the difference of a few degrees is difficult to visually discern.”

Figure 3. Raptor OspreyView Data courtesy of Utility Mapping Services, Inc., Clancy, MT. Imaging tool clearly shows unanticipated route of sewer line not manhole-to-manhole, which is a reasonable professional judgement as a QLC segment.

Based on the limited information from a visual inspection from the surface due to the inability to invasively enter the sewer system, the assumed QLC segment assigned transected manhole-to-manhole, a reasonable professional judgement call in most circumstances. However, it became clear from the array data processed with OspreyView that the segment was not as one would have judged. In Figure 3 the pink dashed line is the prescribed QLC segment prior to the array imaging. Based on the processed subsurface image, it is clear that a QLB segment should follow the unanticipated indirect route of this line. Mr. Meis adds that, “In this business we see a lot of creative field engineering and plumbing and this is no exception.”

Seeing is believing as they say, but all stakeholders in the subsurface utility investigation business need to make sure we have a firm grip on reality when peering through the virtual or augmented lenses of whatever device is used. The future is now, and it is truly exciting to be living in the burgeoning age of digital visualizations of both the above- and below-ground world.

Matthew J. Wolf is President of ImpulseRadar USA, Inc. He can be reached at matthew.wolf@impulseradar.se

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