Acoustic tomography is a powerful, non-invasive imaging and measurement technique that uses sound waves to visualize and quantify internal properties of physical mediums whether it be human tissue, the ocean, or atmospheric environments. Originally developed for geophysical and oceanographic applications, acoustic tomography has now branched into environmental sciences, medical imaging, and water resource management.

At its core, this technology measures the travel time of sound waves between multiple points. Since sound speed is affected by variables like temperature, salinity, density, or motion within a medium, these travel times can be analyzed to produce a high-resolution image or model of the medium’s internal structure and dynamic processes.

In this blog post, we’ll explore different types of acoustic tomography, how they function, their applications, and conclude with how this technology powers innovative solutions like AcouInfo‘s water measurement system.

Scanning Acoustic Tomography (SAT)

Scanning Acoustic Tomography (SAT) is widely used in non-destructive testing (NDT) and materials science. It relies on high-frequency sound waves to create a detailed image of internal structures in solid objects. The system transmits acoustic pulses through an object and records the reflections to assess flaws, density changes, and mechanical properties.

SAT is especially valuable in:

• Detecting cracks and voids in industrial components
• Mapping the elasticity or mechanical integrity of composites
• Semiconductor inspection in microelectronics

Key Advantages:

• High spatial resolution (down to micrometers)
• Safe and non-invasive
• Applicable to ceramics, polymers, and metals

According to a study published in Ultrasonics (Elsevier), SAT offers resolution advantages over X-ray in detecting micro-level delamination’s and inclusions in semiconductor wafers a key driver behind its increasing use in chip manufacturing lines.

Ocean Acoustic Tomography (OAT)

One of the earliest and most impactful uses of acoustic tomography came from the oceanographic community. Ocean Acoustic Tomography (OAT) involves measuring sound travel time across large ocean basins to map temperature variations, ocean currents, and dynamic systems such as gyres and eddies.

Since the speed of sound in seawater is affected by temperature, salinity, and pressure, any variations in the travel time of acoustic signals can be translated into precise thermal and flow maps of oceanic structures.

A well-known initiative, the Acoustic Thermometry of Ocean Climate (ATOC) project, demonstrated that acoustic signals can travel thousands of kilometers through the ocean and be used to monitor global temperature changes with sensitivity better than satellite sensors (source: National Academy of Sciences).

With oceans absorbing over 90% of the heat trapped by greenhouse gases, accurate temperature profiling through OAT is now more critical than ever for climate modeling.

Acoustic Computed Tomography (ACT)

While often confused with standard CT (Computed Tomography) scans that use X-rays, Acoustic Computed Tomography is a distinct field used in medical imaging and material science. It combines acoustic wave analysis with advanced image reconstruction algorithms to create cross-sectional images of a target area.

In medical settings, ACT can be used to:

• Examine soft tissue contrast better than ultrasound
• Detect tumors or cysts in breast tissue or liver
• Provide safe imaging without ionizing radiation

Researchers are increasingly exploring ACT for portable and affordable diagnostic imaging in under-resourced areas, as it avoids the radiation risks of CT and does not require as much infrastructure as MRI.

A 2020 study in IEEE Transactions on Medical Imaging reported that ACT provides comparable resolution to X-ray CT in phantom models, especially in detecting tissue abnormalities with varying acoustic impedance.

Acoustic Coherence Tomography (ACT or ACoT)

Acoustic Coherence Tomography, a newer frontier in the field, emphasizes high spatial coherence of acoustic sources to build extremely detailed images in complex or turbulent media. This technique excels in measuring dynamic processes where conventional sound wave imaging falls short.

It is particularly useful in:

• Biomedical imaging for real-time motion analysis
• Environmental systems like flowing water or turbulent gases
• Fluid mechanics research, including river and ocean studies

Unlike ocean acoustic tomography which works over long distances, ACoT focuses on capturing localized but complex flow patterns, including vortices, eddies, and turbulent shear zones. It’s a perfect fit for monitoring river systems, flood modeling, and hydrology applications.

 Application in Environmental Monitoring: AcouInfo’s Innovation

AcouInfo has harnessed the principles of acoustic coherence tomography and transducer-based sensing to develop a next-generation river flow measurement device.

 Product Highlights:

• Uses dual transducers on riverbanks to measure full cross-sectional flow using sound wave travel times.
• Accurately measures velocity, flow rate, temperature, and salinity in real-time.
• Works in all weather conditions, including floods, and requires no boats or bridges.
• Transmits data via Wi-Fi and Bluetooth, with cloud storage integration.
• Ideal for government agencies, environmental researchers, and flood control authorities.

Traditional devices like ADCPs or AVMs measure limited points in a river and require manual deployment. AcouInfo’s device provides a stationary, continuous, and safe alternative with better spatial accuracy and cost-efficiency.

In Canada alone, there are over 8,500 named rivers, and many lack adequate monitoring infrastructure. With a global water management market expected to reach CAD 15.5 billion by 2026 (source: Allied Market Research), the need for such innovations is both economic and ecological.

Conclusion

From industrial testing to oceanic climate monitoring, acoustic tomography is reshaping how we understand hidden systems in our environment and technology. Each subtype whether scanning, oceanic, computed, or coherence-based offers unique insights and applications.

As global challenges like climate change, water scarcity, and infrastructure monitoring demand smarter solutions, acoustic-based technologies will continue to rise in prominence. AcouInfo’s innovative application of acoustic coherence tomography to river and environmental monitoring represents just one of the many exciting directions this field is taking.

With the ability to gather real-time, full-spectrum hydrological data without invasive methods or heavy infrastructure acoustic tomography isn’t just a scientific breakthrough; it’s a practical necessity for the future.