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History and Advances in Directional Drilling Locating Technology

Advances in Directional Drilling Locating Technology

When it comes to directional drilling technology, many significant advances have been made since the early stages of walkover tracking systems. Over several decades, walkover locating systems created for seeking a drillhead in horizontal directional drilling (HDD) have developed from various applications and evolved to become more modern, accurate, and technologically advanced.

It is impossible to understand just how far this technology has come without first understanding the major accomplishments during this evolution. Research derived from a combination of published patents, brochures, and other literature, in addition to the author’s personal experiences with HDD, has been used to compile this review. While all efforts have been made to include the most pertinent milestones, some specialized refinements may have been omitted as their most basic functions had existed in earlier equipment. It would be impossible to include every development over the history of HDD, as it would have required an extensive book—rather than a paper—to compile them. However, the author asks that readers please excuse any efforts and advances left out either intentionally or inadvertently. Your contributions have not gone unrecognized.

A review of patent records and literature indicates that innovative efforts in tracking and locating for HDD have gone back as far as 1933. While the advances at the time were nowhere near as high tech as the systems used today, they paved the way for major steps forward.


The earliest patent reference that seems to align with today’s systems appears to be a locating system used to explore blockages in sewer lines, which was attributed to Robert Neff in 1955. Like the equipment used today, a dipole transmitting antenna was fed into the sewer line while a walkover surface receiver located that antenna underground. However, in contrast to today’s standards, the dipole antenna was oriented perpendicular to the surfacer rather than parallel, which is the most common positioning used today.

In the Neff system, the receiver relied upon volume control and headphones to guide the operator to the location directly above the antenna. One of the shortcomings of this system is that while it could determine the precise location of the antenna, it was unable to determine its depth. In place of the technologically advanced high-power transistors used today, the system relied upon vacuum tubes for the receiver and transmitter. In this system, the transmitter remained above ground—enabling it to connect to a 110-volt power source—while the antenna alone was sent down-hole.


Over the next decade, additional advances were made in the industry and related fields. In 1965, C.A. Young of Bell Laboratories published a paper in the Bell Laboratories Record that introduced a cable locator that relied upon the use of signal strength ratios measured by two horizontal antennas at different heights above the ground to calculate cable depths.

Bell Laboratories

While this was another step forward, the method was not without its shortcomings. For example, Young’s cable locator presumes that the field strength variation of the magnetic field coming from the cable is known. However, when calculating horizontal distance, this can be problematic. When working with long, straight cables, the signal strength variation is inversely proportionate to the cable's distance—double the distance, half the strength. The critical signal strength relation cannot be determined if the cable bends somewhere along its path or terminates close to the locator. It is essential to give credit where credit is due, however. Despite the challenges in using it horizontally, most boring tool locators rely upon a similar twin horizontal antenna to assess depth.

Young’s contribution was not Bell Telephone Laboratories’ only addition to the evolution of directional drilling locating technology. In the late 1960s, the company developed a unique guided impact tool.  While the guidance system is not technically a walkover tracking system and did not gain much commercial popularity, the technology was critical to advancing the industry as it was the first time a small-diameter boring device had been outfitted with its own guidance system.  The 1968 patent, filed by James Coyne of Bell Labs, explains the system as a complex arrangement of antennas—both receiving and transmitting—that generate the steering signals that can be used to control the guided device or “mole.” At the time, no one took the initiative to develop a steerable system, but the commitment to improve tracking methods of non-steerable tools did continue to grow.

As the 1960s wore on, the transistor became a crucial player in all electronics. Transistors had the unique ability to effectively manage both the power and speed demanded by transmitters.


While many significant steps forward had been taken, the 1970s focused on efforts to hone locator systems' ability to accurately determine depth. In 1970, Lester McCullough and Duane Ladine of The Goldak Co. contributed an exciting development toward this goal. By putting a transistorized dipole into a portion of an unguided boring device, they could use one or two receivers to locate the nulls in the magnetic field in front and back of the boring tool.

Per McCullough and Ladine, the distance between the two nulls could then be calibrated to relate to the depth, which allowed them to use the shape of the magnetic field to calculate depth. Unfortunately, there was little information provided by way of an explanation of precisely how to find the nulls. Instead, they simply indicated that the receiver should be moved longitudinally along the transmitter axis—assuming that it was known. While this is not a particularly detailed instruction, this description was the first of its kind to document the use of magnetic field shape to determine precise locational details.  

By the late 1970s, the Electric Power Research Institute (EPRI) realized that the typical lifetime of a buried distribution was approximately twenty years. It became frighteningly evident that the EPRI was about to face a very real and potentially catastrophic issue as many of the locations of the cables they had placed in decades prior had been developed over top of them. Replacing these cables would be enormously disruptive and challenging from several different standpoints. Acknowledging the critical importance of replacing their cables without impacting the various types of development present, they took steps to improve their technology. EPRI took the initiative to sponsor the research and development for tools and equipment that would make it possible to access and replace electric power cables without disruption to the existing structures and land.


Now, on to personal experience… In 1984, the author of this paper acted as the head of an intense effort to develop new directional drilling tools using the best possible technology to achieve new marvels in efficiency and effectiveness in drilling and locating systems. This endeavor led to the production of the GuideDril System. In developing this system, it was crucial that it could determine precisely where the boring tool head was located underground—both its depth and horizontal location. As indicated in the patent review above, by the 1980s, the tools to locate cables had already been relatively well established. Because of this, the first attempt at the GuideDril system relied upon a cable locator (Metrotech® 810) to accomplish this goal.

When using this technology, a signal was generated on the drill pipe, and the cable locator was used as in the past. Unfortunately, the locator could not locate the boring tool head because the drilled hole was not formed in a straight line. Moving forward, attempts were made to develop a dipole transmitter that fit directly into the boring tool head. Even once this had been determined as a solution, additional alterations were made to make the system function appropriately. For example, the locator was rotated 90 degrees from its original design so that it would be able to capture the dipole flux lines. Additionally, it was determined that a table would need to be constructed to relate depth readings from the Metrotech 810—which had been calibrated for cables, not the boring tool head—to the depth of the dipole transmitter located within the drillhead in the new system.

By the mid-1980s, a host of new technology was available to further foster growth in the area of locator systems for drilling endeavors. The availability and relatively low cost of microprocessors capable of performing complex calculations made them extremely popular in new electronic technologies. This also re-ignited short-lived innovations based on the possibility of including steering mechanisms and navigation directly into locator systems. UTILX added a navigational computer into its locators in 1985. With this device, the operators could type in the coordinates of the drillhead once located, and the computer would generate a steering command. Unfortunately, this extra step involved a significant amount of extra work by operators, and the computer was removed from the locator after only a short period.

While progress had been made, the need for a tool specifically designed to locate a boring tool rather than a cable was still present. It was hoped that this would be accomplished with the FlowCator® in 1986—a tool designed by the author and Albert Chau. This device relied upon an antenna array that worked together to determine the exact location of the tool head, directing the operator forward and back using a series of arrows. Once the tool arrived at the site of the tool head, the FlowCator could take measurements using the array with just the touch of a button. Together, these measurements would be used to compute the lateral offset and depth of the head. In addition, the device could provide steering commands –but yet again, the feature was not utilized as the operators felt it was not worth the time it added to the overall process.

During this stage of development, a host of new issues arose in connection with using walkover systems to locate tool heads. The concept of ghost or phantom locate points became a challenge. Essentially, phantom locate points occur at the fore and aft of the tool head and are generated by the receiver’s antennas. Many well-trained and skilled operators have been fooled by these peaks, causing them to mislocate the head or believe it to be at an incorrect depth. Even though they are not quite as powerful as the signals over the actual head, they can pose a significant problem—even for the FlowCator.

Another significant challenge that accompanied the use of walkover systems during this period stemmed from the difficulty in training operators to effectively control the depth of the drillhead. Compared to left/right steering, up and down movement was extremely difficult as there was no way to mark the locate points on the ground surface to search for trends. When placing drill pipe without these cues, operators often wound up breaking the surface with their tools due to the challenges involved with depth motion. Today, we acknowledge that including a pitch orientation of the drill head would have been an effective means of eliminating this issue. However, despite several mentions of pitch sensing technology in UTILX patents, it had not been implemented in their devices.

Another challenge was seeking out tools after bores that were difficult to use locating technology—such as under highways or bridges over bodies of water. With no means of locating a dipole transmitter in these areas, the search to uncover these tools can be complicated. The developers of the FlowCator made several attempts to determine a systematic means of locating dipole transmitters under these and similar circumstances but to no avail. Even extensive training could not solve this problem. For example, UTILX attempted to gauge and improve operators' abilities by building an 8‘ x 8’ platform then placing a transmitter beneath it at a known depth and location. Even the most well-trained operators took several minutes to determine where the transmitter was.

After FlowCator had been in operation for only a couple of years, another issue developed. As this technology had become more accepted and people knew how to use it, it became commonplace to drill horizontally for several hundred feet at a time. The drill pipe was keyed to enable the steering surface of the tool head to be fixed to a drill chuck index. However, as the drilling distance increased, the drill pipe would twist, causing the tool head orientation to become skewed from the chuck index. Skilled operators could compensate and correct this issue to some extent by assessing the strength of signals as the drill rotated. They did this using the knowledge that the signal would be the strongest when the transmitter window in the drillhead was facing upward and the drill was in the 12 o’clock position. This gave the operators a rudimentary means to correct for drill string wrap-up, assuming the wrap-up would not change with rotation.

Radiodetection RD300 Locator

UTILX had not introduced its equipment to the commercial market, so it remained void of HDD tracking systems until 1988. Finally, that year, the RD300 system was offered by a company called Radiodetection®. The product had been based on a sewer locating system they had previously developed, with some changes to make it more versatile. Not only was this the first HDD tracking system to become commercially available, but it also established a solution to one of the challenges faced by UTILX. By incorporating a gravitational switch in the sonde, Radiodetection effectively corrected the wrap-up issues faced by previous equipment. The sonde usually sent a pulsed signal; however, when in the 12 o’clock position, it became a steady signal instead, enabling operators a much more accurate way to correct for the wrap-up.

Ideas to improve the technology and develop solutions to challenges in the industry continued to emerge as the 1980s began to wind down. In 1989, Peter Flowerdew at Radiodetection came up with a new locator design that would implement pitch and roll orientation based on two rotating and one nonrotating magnetic fields. The interaction of these fields would provide a relative orientation that was reliant upon where the operator was standing relative to the drillhead. Of course, this would change as the locating receiver was moved from place to place. It was hoped that this new concept would solve both the wrap-up problem and that determining the pitch would resolve issues in connection with depth and lead to less of a need for such extensive operator training. While there was undoubtedly a need for these solutions, the technology could not be practically implemented on a large scale and therefore was not commercialized with Radiodetection’s systems.


During the early 1990s, many new manufacturers were entering the industry. With this, of course, came growing competition and significant advancement in walkover tracking systems. Some of the new products brought to market included systems by Ditch Witch® and Digital Control.

The Ditch Witch Subsite™ system combined a cable locator with a tracking system based on digital signal processing capable of operating on several different frequencies. This product made great strides by completely overcoming any wrap-up steering errors with its gravitational roll sensor capable of yielding an absolute roll orientation.

A direct competitor, Digital Control also offered a new system to market. The DigiTrak™ system was unique in that it was designed with a specific purpose from the very start. Rather than pulling technologies from other locator tools and combining them, this system originated as a boring tool locator from the very beginning. It left behind conventional cable locator technology and instead focused on its specific task. Relying upon two orthogonal antennas, it could measure the total magnetic field in the area of the locator. In accomplishing this, the formerly irritating phantom locators were removed from the equation entirely.

Additionally, this product utilized a completely new method to determine depth. It relied upon a calibration procedure centered on the fact that the transmitter in the drillhead housing was designed to produce a steady, constant signal. Depth was constantly displayed rather than only at the operator’s request via the push of a button. With this system, the display would reveal the approximate slant distance to the tool head, even when the locator was not over the transmitter. Compact in design, it accommodated operators of different heights by employing internal ultrasonic measurement of the locator height above the ground. It also provided another benefit. Separating the locator antennas from the ground dramatically reduced the negative impacts rebar in streets had on the locator device.

A pioneer in this regard, the DigiTrak was the first of the commercial walkover systems to include the roll and pitch orientation of the tool head. DigiTrak also included a weak battery warning signal in the transmitter, another first in the industry. Unaffected by roll orientation, the pitch orientation covered a range of -100% to +100% grade in grade increments of 1%. Since this system's roll and pitch orientation were based on gravity, it made no difference where the operator was standing relative to the tool head. Having the pitch orientation displayed dramatically impacted the speed with which drilling projects could move forward since fewer locate points were needed to maintain control over the depth. Having this information readily available also improved drilled accuracy—especially when projects crossed uneven terrain. When it was introduced to the market, DigiTrak boasted the ability to extend the operating depth to twenty feet, which was quite a significant improvement from all prior systems.

During the early 1990s, newcomers were still joining the race to improve the technology and systems available to the drilling industry. For example, in 1991, Cogent Technology, an independent company from the U.K., introduced a roll accessory system for the RD300. It featured highlights such as a new transmitter with a roll sensor and a remote display of the roll orientation, which enabled the operator to properly orient the tool without constantly interacting with the locating operator. When it was first released, some feared that this new technology would shift the allocation of responsibilities between the two operators and questioned whether this would hinder the drilling operation’s efficiency. Fortunately, this was not the case. Instead, it was an overwhelmingly positive addition to the standard technology within the industry.

A new technique was introduced in 1992 that overcame several issues previously encountered. Digital Control introduced new firmware in their locator that allowed for a new locating approach based on the shape of the magnetic field rather than relying on signal strength to determine location. Not only did this technique allow for the tool head to be located when both depth and position were unknown, but it also provided the first systematic procedure for determining this with a high level of accuracy and efficiency. The technique was able to pinpoint the location directly over the drillhead and indicate additional locating points in front and behind the tool head, thereby offering an accurate method for sighting the bore path heading. This technique enabled operators to track the tool while the drillhead was moving, significantly reducing the time required for the locating process. Lastly, the Digital Control firmware assisted operators drilling under obstructions and in challenging terrain by allowing them to locate the drillhead from a position off to the side.

During this decade, many of the key players in the industry recognized the importance and advantages of including remote displays. McLaughlin, who marketed a Japanese-built locator known as Takachiho, and Digital Control developed and implemented remote displays indicating roll, pitch, temperature, and battery status. Digital Control went a step further, adding a left/right steering indicator, which had the capability of guiding the drillhead if the operator was unable to physically put himself over the tool in a particular location—if it was beneath a busy street, for example.

Another important company in the grand scheme of all things drilling, Metrotech, had played a critical role in the first small-diameter HDD systems with their cable locator. However, they had not yet developed a specifically calibrated locator to determine dipole transmitter depth. They also had not released a transmitter for a boring tool. However, in 1992, Metrotech contributed their own boring tool locator to the market. Led by Bill Griffiths and in alliance with Cogent, Metrotech led the effort to create BoreHawk™, a low-cost system with a remote display. While things looked promising for Borehawk, several technical development issues, paired with the untimely death of Bill Griffiths, caused their new product sales to arrive at a standstill.

Not to be left behind, UTILX continued to improve their equipment by making significant improvements in locator system range and providing additional data to operators, such as indications of ghost signal peaks. They also developed an instrument package that allowed for non-walkover guidance of their equipment and established ways to correct position errors in a wireline system using a walkover locator. UTILX even decided to enter the consumer market and began selling some of its equipment overseas. However, they did not enter their products in the domestic market.

The mid-1990s primarily consisted of technological advances that enabled locator systems to become more sensitive and work at longer ranges. As drill rigs became more powerful, there was a growing need to increase abilities in these areas. In 1994, Digital Control released a DigiTrak transmitter with a 50-foot range that remained consistent in size with the previous, shorter-range model. Digital Control took a major step in the following year by producing a transmitter with a 0.1% grade pitch sensitivity. This, essentially, made it possible to extend the HDD process to sewer lines—a major source of potential drilling business. Later that year, they designed a cabled transmitter known as Cable Sonde™. Capable of extending the depth capability to over 100 feet, a single-wire connection generated the power necessary for a strong transmitter and displayed features such as the roll, pitch, and status information to the operator. Because the information was transmitted via the wire, it was not subject to any local interference and could even be used in certain non-walkover endeavors.

As the 90s continued, manufacturers developed new advancements while also improving the products already on the market. Radiodetection developed a new walkover locator that featured left/right steering controls and an antenna array similar to the FlowCator. Digital Control and McLaughlin both introduced bore logging capability to the market. McLaughlin’s Mole Map™ displays the bore hole profile, including depth. In contrast, the Digital Control DataLog™ provides left/right steering and features a depth and plotting package that allows depth and terrain plots to be enhanced using survey data to generate drill and terrain elevations. While the Mole Map enables data to be uploaded to a computer for additional plotting or future reference, the DataLog can be used with a laptop to generate real-time plots of the bore. This feature is particularly helpful when drilling in areas of river crossings.

In more recent years, advances have continued to improve drilling efficiency. Ditch Witch recently developed a hybrid system that combines the technology of wireline systems and walkover systems. Like conventional walkover systems, the transmitter is located in the drill head. In addition to the usual pitch and roll sensors, the transmitter also features a magnetometer. Because of this, the downhole tooling near the transmitter must be made of non-magnetic materials. In the new system, the signal from the transmitter in the drill head is picked up by a receiver on the surface that must be within range—but not directly over the transmitter itself. Instead, the receiver uses telemetry to report data such as heading, pitch, and roll back to the remote unit at the drill. Upon receipt, the remote system processes the data to compute the position in the same way conventional wireline guidance would.

DigiTrak Mark III Locator

Digital Control also developed a new system. Like in the walkover system, the transmitter is placed directly in the drill head. The system relies upon two or more antenna cells located anywhere in the general vicinity of the planned drill path. Unlike Ditch Witch’s new system, the materials included in the Digital Control downhole equipment are not as limited because no magnetometer is used in the system. The system works by cells transmitting data reported from the transmitter in the drill head to a remote base station at the drill rig. At the base station, the system computes the location of the transmitter and plots the bore path, which is shown on the remote display. A steering indication is also presented to the operator. When using this system, the operator can drill past the antenna cells, which is helpful when accessing the surface is not feasible. This can be beneficial in applications such as the stabilization of embankments, environmental installations, highway crossings, and a multitude of others.

In all fairness, the last two systems are not technically walkover systems. However, their basic evolution has come from the concept of the walkover system, and therefore they are critical to both the system history and future development. These new hybrid systems would not have been possible without the progression of transmitter sensors and data transmission techniques from prior walkover systems.


Over time, dramatic improvements have been made to transform sewer line tracers and cable locators into technologically advanced modern HDD tracking systems. From the early 1980s, with the introduction of small-diameter, guided drilling tools, to today’s models, the advances to tracking systems have been quite extraordinary. Early systems provided data that allowed operators to gauge a surface location, a rough heading, and depth ranges of less than ten feet. Today’s systems, in stark contrast, provide remote displays featuring the roll and pitch orientation, battery status, temperature, accurate heading, warnings for malfunctions or overheating, and bore path logs at depths exceeding 140 feet! The developments over several decades alone are truly mind-boggling.

Additionally, transmitters once ran for a few hours at a time due to their battery life. Now, they are capable of running for a week or more. Even looking back to 1990, there remained an obvious distinction between small-diameter utility installation equipment and massive river crossing equipment, which is not necessarily the case any longer. In 1990, bored requiring depths of more than twelve feet necessitated a wireline system in most cases. Today, drillings at depths of over 70 feet have been completed using tracking systems with battery-powered transmitters. Even runs deeper than 100 feet have utilized the same receiving system but with a transmitter supplied with power by a cable. The speed and accuracy of locating technology have improved so quickly that the HDD process has broadened its reach to new markets, compliments of reduced costs and improved capabilities.

Walkover systems are critical to the drilling industry. While they have been used almost exclusively as autonomous systems in the past, they may now play a role in other guidance systems moving forward. For example, they may generate the final guidance to wireline bores, eliminating accumulated errors and allowing the bore to be completed at the perfect target. Given the many developments over time, it is likely that future systems for guidance and tracking will yield even greater automation of the drilling process.

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