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White Paper On The Pig-In-A-Pipeline Tunnel Detector

An automatic Tunnel Detection System for roughly 1,600 miles of the U.S. southern border with Mexico may be among DSI’s first products with installation commencing in 2022. DSI hopes to be under contract near the end of 2020 and through 2021 during which we will complete the basic design and development of the Tunnel Detection System. The Test and Evaluation phases for these products will culminate in Proof-of-Concept testing and prototype development.

Frederick L. Newton
Chairman, D-fence Solutions, Inc.

Background and Objectives

An automatic Tunnel Detection System for roughly 1,600 miles of the U.S. southern border with Mexico may be among DSI’s first products with installation commencing in 2022.  DSI hopes to be under contract near the end of 2020 and through 2021 during which we will complete the basic design and development of the Tunnel Detection System.  The Test and Evaluation phases for these products will culminate in Proof-of-Concept testing and prototype development.

In late 2020 and 2021, a one-year contract will be proposed to DHS, who is working with the U.S. Army Engineer Research and Development Center (ERDC) and U.S. Law Enforcement Agencies (LEAs) to develop and test tunnel detection systems.

ERDC and LEAs have studied and tested over 17 methods of detecting either existing tunnels or the manmade sounds of constructing new tunnels.  The most effective detectors were:

  • Near-Surface Active Seismic Sensors to Detect Tunnel-Building Activities
  • Passive Seismic Detectors of Tunnel-Building Activities
  • Multi-Frequency EM Gradiometers that may detect tunnels but also some false targets
  • Borehole Fluxgate Magnetic Gradiometers to detect nearby tunnel steel reinforcements.

Even the best-performing sensors were negatively affected by anomalies or only detected active tunnel building.  DHS in cooperation with ERDC and LEAs may have tested other systems in the past few years that may not have been published.  In any case, these federal organizations have effectively evaluated a remarkably wide array of technologies to solve a never-ending threat from well-funded cartels and foreign government adversaries.  Evildoers at our southern border will always attempt to thwart our defensive measures to stop the flow of narcotics, human trafficking, illegal entry and every form of trafficking contraband.

DSI’s Tunnel Detection System is currently in “Patent Pending” status with a Non-Provisional Patent filed in June, 2020 following the original Provisional Patent filed in June, 2019.  DSI will propose one early contract to complete the DDT&E for the Pig-in-a-Pipeline Tunnel Detector™ and an optional follow-on contract to construct a pipeline test bed with water storage tanks at each end.  The test bed built by DSI could be located within the existing tunnel detection test bed facility at Otay Mesa, CA near San Diego.  A pipeline test bed would detect any existing tunnels along its length as well as any new tunnel that reaches a point beneath the pipeline.

The purposes of the testbed are to (1) evaluate several optional subsystems and acoustic sub-bottom profiler frequencies through on-site testing, (2) exercise the data collection system and computer-based “change-detection” software that will be used to rapidly, and almost automatically, detect new tunnels being dug under the fence/wall, (3) train the Tunnel Detection System operators and technicians and (4) provide live demos to Government personnel or others who would like to become more familiar with the Tunnel Detector’s full benefits and capabilities. It is envisioned that this testbed will remain in operation for similar purposes and to evaluate new technologies involving pipelines for many years.

Tunnel Detector Features and Functions

Pipelines have been very effectively used by those familiar with their construction and utility to accomplish unusual objectives quickly, reliably and less expensively.  A prime example is the use of old oil or gas pipelines to carry fiberoptic cable long distances throughout the United States without spending a decade securing easements and fighting for the right of eminent domain.

I was fortunate to work under Roy Wilkens at Continental Pipeline (a Conoco company) in 1968 and, in this tunnel detection application, I have tried to follow his example for yet another use of well-engineered pipeline technology.  Roy applied his expertise in pipeline engineering to run fiberoptic cable as the CEO of Williams Pipeline Company in 1982.  In 1985, he started WilTel as a unit of The Williams Companies and has now retired after more than 20 years of incredible success applying pipelines to the most modern telecom applications.  He was pleased to hear of our adaptation of pipelines for border security.  Roy has already offered technical advice that will improve the system’s lifecycle and survivability to threats.  We hope to consult with Roy Wilkens for his expertise in pipeline technology as we engineer this important application.

Spanning the decades of pipeline engineering, electromechanical devices called “Pigs” are routinely placed in pipelines to separate different products moving down the line.  They are also used to clean the inner walls of pipelines and to inspect signs of wear.  Sometimes, pigs are outfitted with electronic sensors — hence the term, “instrumented pigs”.  In DSI’s proposal, the electronic instruments could include a Ground-Penetrating Radar (GPR) although we are far more likely to use an Acoustic Sub-Bottom Profiler (SBP).  In either case, the pipeline would not be made of steel nor supported by any metal framework except for a few valves and supports at pumping stations.  Fortunately, high-density polyethylene (HDPE) pipelines are now commonplace and they are excellent for transmitting either GPR or acoustic SBP beams through the pipeline wall to image lithology including voids such as tunnels.

When the geological material consists of clay or salts with high-water content, GPR is rapidly attenuated to the point that ranges of up to 100 feet are unachievable.  And the difference in electromagnetic impedance of many sediments as compared to air is not always dramatic enough for high target (tunnel) detection probability.

Acoustic signals, however, depending upon frequency and power level, are able to reach such ranges with sufficient power to produce backscatter intensity for detecting changes in the lithology.  And few changes in lithology are more pronounced than the presence of air such as in a tunnel.  In fact, the sudden change in acoustic impedance from rock, clay, sand or loam to air could not be greater than when using acoustic imaging at selected frequencies.  The illustration below provides DSI’s general proposal of buried pipelines near border fences or walls and the instrumented pig and acoustic SBP as it interdicts a partly completed tunnel.

Tunnel detector schematic

DSI has considered a wide range of acoustic SBP systems.  Owing to a number of special features for this unique application, any acoustic instrumented pig will have to be repackaged.  The acoustic system will be dual frequency.  Typical frequencies may be near 15 KHz and 45 KHz but these frequencies may change for a best fit to local geology and seasonal moisture.

On average, pipeline lengths will reach approximately 80 miles for each section — some longer or shorter.  At our southern border with Mexico, roughly 1,600 miles of the 1,954 miles of border are expected to be considered possible candidates for tunnel crossings beneath the fence, wall or river representing the border.  Therefore, the total number of pipeline sections is expected to be roughly 20.  A large welded steel tank will be connected to each end of every pipeline segment to store the working fluid.  The instrumented pig may travel eastward one day and westward the next in the same pipeline.  The tanks will normally service two pipeline segments and the pig will reverse its direction for its next transit.

The cost of storage tanks is far less than the cost of adding a second “return” pipeline for each segment just so that the working fluid can always flow in the same direction.  Two pipelines in each section is not a reasonable requirement given its higher cost.

Pigs will travel at roughly 10 fps.  The average transit time over an 80-mile section is just under 12 hours.  Let us assume that the HDPE pipeline has an inside diameter of 11 to 12 inches.  The instrumented pig with its acoustic T/R transducer, amplifier, signal processor, data storage, lithium battery, waypoint sensor and data transceiver will all fit within a 300-psi pressure housing (and possibly as high as 400 to 500 psi) as illustrated below.

The lifecycle cost of the HDPE pipeline is very low since its expected life exceeds 100 years as long as it is buried or has a protective coating where short lengths at pump stations must be exposed to sunlight.  Maintenance costs are primarily limited to valves, pumps and pigs.

Finally, the working fluid could be chosen from many possibilities.  However, we should recall that 7,216 border crossers died in the 20 years of crossings between 1998 and 2017.  3,221 were rescued in 2017 alone and dehydration often caused death or critical calls for help.  Such tragedies can be avoided if fresh water is the working fluid in the Tunnel Detector pipeline.  DSI proposes that fresh water be used and that outlets be available for border patrol and other government workers every two miles on both sides of the fence or wall and visitors on the southern side should have access to fresh water fountains.  While the Tunnel Detector guards against the illegal trafficking of drugs, contraband and humans, it does so in a moral way.

While border visitors and law enforcement on both sides are provided safe drinking water 24 hours a day, U.S. authorities can also utilize the fountains on the south side of the border to collect high-quality fingerprints, 3D near-infrared facial recognition and voice prints in some cases to support the Artificial Intelligence database.  Data collection helps CBP, ICE and local LEA’s manage large numbers of visitors with their individual needs and objectives.

The average speed of the instrumented pig in the pipeline will be 10 fps as driven by water pumps at an average pressure of 300 psi.  Since frictional losses accumulate over miles of pipeline (even through smooth HDPE pipelines), a third pump station located midway at approximately 40 miles from each end of a typical pipeline segment may be proposed.

Data Processing to Identify Existing or New Tunnels

As the pig moves through the pipeline, it passes waypoint stations that have coded magnetic markers on the pipeline specifying the mile marker that was surveyed using GPS during pipeline installation.  Between these waypoints, dead reckoned position is very accurate and small corrections in position of every acoustic trace can be made to the collected data.

When the pig passes a transceiver attached to the pipeline, collected data over the past 8 or 9 minutes will be uploaded to a transceiver, passed to a 5G or AppleFi satellite system transceiver at the border fence or wall and sent to the central processing station for the whole border fence.  Data is processed and automatically analyzed through change detection within 10 minutes of the pig’s data collection.  If the pig is run every day end-to-end, border officials will be notified of any new tunnel within one day of its presence beneath the pipeline.  Therefore, all new tunnels can be interdicted well before they are completed and brought into service.  Adequate time is assured for mobilization of manpower.

Those of us who are experienced in target detection and identification are very familiar with the principle of “change detection”.   As mentioned above, air has an acoustic impedance that is far different from lithology consisting of dirt, sand, clay, rock, etc.  Acoustic imaging of an air-filled tunnel is relatively easy to identify and classify.  A new tunnel reaching a point directly below the pipeline may show an anomaly for the first pass that represents a small change from the average of many previous scans.  But subsequent passes will quickly cause the new feature to be positively identified as a new tunnel under construction.

When a new tunnel is detected, the processing center will alert ICE (HSI) personnel to ensure a plan is developed to interdict the new tunnel.  Scanning passes can be increased by inserting a second pig or by catching a pig at a mid-station and reversing the water flow to complete another pass in the same day.  Ordinarily, whenever a new tunnel is detected, an acoustician should also review the new acoustic record for verification of the target, mensuration of its size, and logging of any special characteristics.

Overall, the Pig-in-a-Pipeline Tunnel Detector utilizes proven technologies in acoustics and image processing to detect targets based on change detection.  The pipeline itself along with storage tanks, pump stations, pig catchers, etc. are all comprised of standard equipment and construction methods that ensure the result conforms with pipeline industry standards.  Construction of the pipeline, pump stations and welded tanks will be subcontracted to leading companies in the pipeline industry.  DSI managers are experienced in large contracts (>$100M).

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