How Does It Work?

Advanced Sonic Technologies uses specially-crafted sound to detect, locate and map buried pipes and cables more reliably and deeper than any other available method. The technique we use is commonly referred to as echolocation.  We send audible acoustic pulses into the ground and time how long it takes for them to return.  From that timing information, we can infer the presence and depth of structures under the ground. The animation in Figure 1 shows this process.

The pulses are carefully tailored sounds custom-designed for the soil, soil conditions and surface conditions.  The waveforms are highly structured audible acoustic sequences that allow us to separate the signals from other ambient noise, enabling the technology to work in sonically polluted environments, such as roadways and active plants. By recording the times of pulse transmission and receipt of the echos, we can estimate the depth of the structures under the surface.

By acoustically probing at multiple points, we gather returns across a survey area. We combine the precisely surveyed locations of the probe points with the depths provided by the acoustic measurement to create a 3D data set of return points within a volume of ground.  We then link up returns between multiple points to identify extended structures and create our 3D map. We then correlate the identified structures with surface features to determine the function of the detected structures and that competes the 3D representation of subsurface utilities.

The image appearing in Figure 2 shows a top-down view of a BIM model from a survey we performed in 2019.  A different perspective of the same model appears in Figure 3. On this project, we performed more than 300 individual acoustic collections across the 0.6 acre site. The geodetic survey required 5 different baselines since line-of-site within the plant was constrained.  Further complicating the collection was the variety of surface conditions, ranging from asphalt pavement, to concrete paving bricks, to open soil.  And the soil underneath was saturated, which made the traditional techniques employed by the client yield little-to-no useful data. The red areas in the model depict detected structures from the acoustic survey while the gray lines show known structures from as-built and historic reference drawings.  The acoustic structures align very well with the known structures and above-ground features, validating the accuracy and effectiveness of the acoustic method. The client was pleased with the results of the acoustic survey, and felt the knowledge gained will decrease project risk and provide a safer excavation environment.

There are two stages of processing involved with creating a 3D volumetric survey. The first stage occurs on the cart at the time of collection.  This signal processing step provides immediate feedback to the operator as to the success of the collection and to the presence of echos. The second stage of processing is done in Cartacoustics’ offices, and adds calibration calculations, determines the arrival times, and computes the depths to detected structures.  Once all individual point collections are analyzed, the acoustic depth information is combined with lateral, or geodetic, survey information to establish an integrated 3D location for all the returns in the same coordinate system.  These 3D points are then correlated to determine linear, planar or point-like features.  Once features are identified and correlated, simplified geometry is generated for the verified structures and exported for incorporation into project files.  At this point, we can add additional information about surface manifestations of the infrastructure and begin to assign a functional category to the subsurface infrastructure.

Figure 1 – The AST cart “shouts” sound pulses into the ground and times their return. From the time it takes sound to travel down and back, we can estimate the depth of the buried structures.  We then move to another position and repeat the process.

3D Subterranean CAD Map

Figure 2 – The red areas are the consolidated acoustic returns from over 300 collection points formatted as a 3D CAD file with accompanying as-built information.

Figure 3 – A different perspective on the 3D acoustic map showing good lateral positioning as well as accurate depth information.

How Does Acoustic Mapping Compare to Other Methods?

AST’s acoustic approach to locating and mapping has a number of key advantages over existing, non-invasive locating technologies that we showcase in the table below. One very important one is that sound can detect non-conducting structures made with PVC, fiberglass, plastic, concrete or vitreous clay as well as the conducting infrastructure. This means we can find all types of materials used for subterranean infrastructure.  Another is that sound is much less affected by soil types and soil conditions.  We have successfully collected in saturated soils along the gulf coast and Pacific northwest, rocky and sandy soils in the mountain west, and in high-clay content soils. The maps below compare where AST can be effective to where other approaches are suitable. We have also collected with 4 inches of snow on the ground and immediately after a hard rain.

Acoustic locating and mapping is finally here and it overcomes many of the frustrating short-comings of traditional electromagnetic methods and the time and expense associated with pot-holing and excavating.  Click on these links to learn about the key advantages for owners, engineers and contractors A summary of this information can be found on our flyer and more information plus a live demonstration of AST in action is available during one of our demo events, that you can register for below.

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