Computer Assisted Radar Tomography Starting to Take Off
When Witten Technologies CEO Robert Green met Alan Witten in 1992, it was acollision of two worlds: hard knocks and hard science. Robert Green was asecond-generation utility contractor who recognized a glaring need that Alan’sWitten’s technology could solve.
Green was tired of hitting unmarked ormismarked underground utilities. He was tired of the delays and lostproductivity. He was tired of risking his and his employees’ safety, as well asall the extra costs incurred across entire projects’ lives by the risks of the“unknownderground.” He recognized the twofold root of all his problems: utilitymapping/as-built information that was either bad or non-existent, and there wasno way to efficiently and accurately characterize the subsurface (or accuratelymark the surface, for that matter) in the absence of good maps.
Enter Dr.Alan Witten. Witten, one of the world’s most prominent geophysicists who passedaway in February, had been working for the last several years on a techniqueinvented by his college roommate a decade earlier while working forSchlumberger: geophysical diffraction tomography (GDT). Simply stated, GDT is away to generate 3D imagery of the subsurface and all the “stuff” containedtherein by using an array of antennae to measure how signals pass through it.
By this time, Witten had achieved significant results using an acousticsound as the signal source version of GDT. Whether it was banging on a steelplate with a hammer, blasting with a specially modified sawed-off shotgun ortrolling with hydrophones off Madagascar…acoustic GDT was used to 3D-imageeverything from pirate ships, to ancient caves, to enemy tunnels, to dinosaursand (most importantly) the oil reserves they had become. The vast quantity ofpreviously unknown reserves found using acoustic GDT actually caused oil pricesto level off at the time, although that’s tough to recall given the recentskyrocketing trend.
Green, recognizing the possible application of GDT to hisindustry, asked the burning question: “What if we could take this geophysicaltelescope (deep/low-resolution) and convert it to a geophysical microscope(shallow/high resoluton)?” Witten’s answer was to use ground-penetrating radar(GPR), instead of acoustics, as the signal source. Seven years, thousands ofhours (including a few hundred at the bottom of Kingsley Lake), hiringSchlumberger’s research staff, and $5 million later, Computer Assisted RadarTomography (CART, or RT for short) was born.
Fast-forward to September2001, where Witten Technologies found itself helping sort out the subsurfacespaghetti left in the wake of the 9/11 tragedy. Having just finished working inthe vicinity of the WTC for ConEd, the company was able to provide before/afterimagery that was used in recovery and rebuilding efforts. Fast-forward again toApril 2005, and you find the company finishing up a roughly 2 million-sq ftproject for the Florida Department of Transportation (FDOT). Finally, thetechnology is reaching the mainstream.
The technology itself is both simpleand complicated in the same breath. Simply stated, it’s a big, 6-ft swath ofground-penetrating radar antennae, a laser survey station and some software. Onthe hardware side, a closer look reveals 17 antennae (nine transmitters/eightreceivers) in a pooltable-sized box, which are rapidly fired by a control boxnestled in a thick patch of wiring spaghetti as the array moves across theground. While the array is either pushed or pulled across the ground, it istracked by a robotic laser for x/y positional accuracy. The result of this datacollection process is a large volume of multi-aspect (that is: samespot-multiple shots from multiple angles) 2D, GPR imagery … 60,000 sq ft perday, on average.
The software component is basically twofold. In thefirst stage, the raw 2D imagery is focused by Witten’s patented software intofull-motion, virtual excavation videos. In these movies ( as the company callsthem), the viewer virtually descends through the earth seeing utilities, etc.(sometimes the “etc.” is more important) appearing at various depths. Althoughthe movies are quite striking, especially in busy downtown areas, they are butan interim step. From them, utility lines are extracted and rendered inplan/profile CAD drawings.
The CAD drawings go through two iterations.The first iteration typically contains many unknowns (i.e. lines not shown onmaps, anomalies), so it is used for precisely targeted vacuum excavation to putfaces on those unknowns. The second, fully verified version, showing allutilities (etc.) color-coded by type is provided to project designers, who usethe data to create conflict-free construction plans. The end result:conflict-free construction, a concept few believe is even possible. Taken a stepfurther, individual facilities can be extracted from the CAD files and convertedto GIS format for utility clients to import.
Conflict-free constructionis the primary reason that FDOT is embracing Witten’s technology. Faced withever-increasing construction and corresponding change order (conflict = changeorder in FDOTese) activity to keep pace with explosive growth, they were seekingnew ways to reduce costs and speed up the process of roadway improvements withutility accommodation requirements. FDOT found Witten.
The Florida Pilot Project
In the firstFDOT pilot project in West Palm Beach, Fla., RT was employed at the start of theconstruction phase, and the data were not shared with the road contractors. Thebenefits derived from proper design-phase integration were not realized, so itwas possible to accurately track the impact RT could have had.
The end resultwas a double-blind study that revealed two important things. First, FDOT wouldhave done two-thirds less vacuum excavation and seen a cost-savings of $9 forevery $1 spent on radar tomography, had it been employed at the correct time.For every change order FDOT processed, the cause was shown in the RT data.
Second, Witten Technologies had proven that RT worked. Craig A. Smithand Associates, Witten’s Florida’s licensee, dove in headfirst, teaching WittenTechnologies and FDOT how to work cutting-edge science into a usable engineeringproduct. Craig Smith has since helped improve the technology with real-world,expert feedback. Much to the delight of the field crew, they’ve even replacedthe first John Deere commercial-mower-chassis unit with an all-wheel-turningair-conditioned ToolCat by Bobcat (hence the name BobCART) with XM radio.
Cut to the second pilot project, which is nearing its conclusion as ofthe writing of this article. In short, FDOT is (or rather, will be in three tofour years) widening state Route 688 (Ulmerton Road), an extremely congestedeast-west artery in Pinellas County, from four to six lanes. FDOT is employingRT on about 1.5 miles of primary roadbed, inclusive of four intersections andall accessible rights of way.
The project entailed almost 2 million sqft and this one was done by the numbers.
RT was provided during the earlystages of design, at roughly 70 percent of the survey phase and delivered byCraig A. Smith and Associates (which was subcontracted by the prime designcontractor) in the context of the full subsurface utility engineering (SUE)process. All the available mapping and as-built data were assembled (andcompared to RT data on the back end), and all the surface features were surveyedin. Vacuum excavation was employed after RT to identify the unknowns.
Although the full benefit will not be derived for several years, there aresome early benefits that will be realized. Besides the reduction of vacuumexcavation, FDOT will see increased speed of design and the happy demise of the“30 percent plan” phase, in which FDOT sends its plans to all the utilities formark-up. The design contractor was heard to say: “This will be great … I cantell the utilities where they are instead of asking them.”
As a show ofsupport of FDOT’s damage prevention efforts, Sunshine State One Call of Florida(SSOCOF, Florida’s legally mandated call-before-you-dig center) contributed$50,000 toward application of the technology. As one of the more proactiveone-call centers in the United States, it has evolved well beyond “take the call— send the ticket,” and has funded numerous damage preventioninitiatives.
Besides FDOT’s RT pilot projects, it has been sponsoringlocal damage prevention symposiums across the state to educate and encouragecommunication between various stakeholder groups, it has funded a program totarget trouble spots with off-duty law enforcement officers, and has evencreated a citation form that looks just like a standard traffic ticket tofacilitate participation among law enforcement agencies statewide.
Theproactive natures of both FDOT and SSOCOF were a few of the main reasons Wittenchose Florida as a beachhead for the technology. That and the state is mostlysand, which is GPR/RT-friendly…so it’s a literal beachhead, too.
Earlystudies of SUE have already revealed some powerful cost-savings andreturn-on-investment numbers. Proper integration of RT can result in furtherconstruction cost reductions, improved damage prevention and more substantialROI. Perhaps someday, when the industry fully embraces SUE and relatedtechnologies like RT, conflict and damage during underground construction willno longer be accepted as “givens.”