Executive Summary
Side scan sonar has evolved from a military seabed reconnaissance tool into one of the most important technologies in underwater survey, mine countermeasures, offshore energy, archaeology, and critical infrastructure protection. The journey is not just about prettier sonar pictures. It is about better decisions.
The evolution is clear: single beam side scan made the seabed visible. Multi-beam side scan, represented by systems such as the Klein 5000, improved coverage, resolution, and survey efficiency. Newer high-speed multi-beam systems such as the Klein 5900 push that concept further, enabling rapid wide-area search at operationally useful speeds. Then comes the next leap: synthetic aperture sonar, with systems such as Kraken KATFISH, delivering near-photographic seabed imagery with high and consistent resolution across the swath.
The provocative truth is simple: traditional side scan still matters. But vague seabed imagery is becoming harder to defend.
The Evolution of Side Scan Sonar
Side scan sonar did not begin as a commercial survey tool. It began as a military necessity. After World War II, navies needed a better way to detect mines, inspect the seabed, and understand what was hiding in the acoustic shadows. Early systems were heavy, specialized, and built for defense laboratories rather than practical offshore crews.
But they introduced something revolutionary: an acoustic image of the seabed.
That changed everything.
[Video: Evolution of Sidescan Technology]
The classic starting point is single beam side scan sonar. It transmits one fan-shaped acoustic beam to port and one to starboard. As the towfish, hull-mounted system, or AUV moves forward, each ping paints a narrow strip of seabed. Line by line, the system builds an acoustic image. Strong returns appear bright. Shadows appear dark. Objects become visible not only because of what they reflect, but because of the shadows they cast.
This remains a powerful concept. Single beam side scan is relatively simple, robust, cost-effective, and still very useful for search operations, route surveys, archaeology, harbor work, and general seabed imaging.
But physics is not sentimental.
In traditional single beam side scan, along-track resolution is limited by beam width, range, altitude, ping rate, and platform speed. The farther out you look, the larger the acoustic footprint becomes. In plain English, the image gets softer with range. At higher speeds, ping spacing can also become a problem. Push too fast and you may lose coverage, smear details, or reduce classification confidence.
This is where multi-beam side scan entered the story.
The Klein 5000 is an important reference point. Instead of using one beam per side, the Klein 5000 V2 generates multiple adjacent, parallel sonar beams on each side while using beam steering and dynamic focusing. The result is sharper along-track resolution at higher tow speeds and full bottom coverage compared with what conventional single beam side scan can normally achieve.
That is a major distinction. Multi-beam side scan is not the same as a bathymetric multibeam echo sounder. A multibeam echo sounder is primarily designed to measure depth. A multi-beam side scan is primarily designed to create acoustic imagery, but it uses multiple side-looking beams to improve image quality, speed tolerance, and coverage efficiency.
The Klein 5000 showed that side scan could become more than a picture-making tool. It could become a high-productivity survey sensor.
Then came the next operational demand: speed.
Modern survey, defense, and mine countermeasure missions cannot always afford slow and careful lawnmower patterns. Sometimes the requirement is rapid wide-area search. Sometimes the platform is a USV. Sometimes the mission is moving faster than the survey department would prefer.
That is where systems such as the Klein 5900 become relevant. Klein describes the 5900 as an ultra-high-resolution side scan sonar with integrated gap filler sonar and co-registered bathymetry for high-speed MCM and surveillance missions. It is designed for survey speeds up to 12 knots while maintaining full bottom coverage, with embedded electronics and AI-enabled processing to support target detection and survey efficiency.
This matters because speed changes economics. It changes mission planning. It reduces vessel time. It increases area coverage. For unmanned systems, this is especially important. A USV without a productive sensor is just an expensive remote-controlled boat with good marketing.
But even high-speed multi-beam side scan still lives within the world of real aperture sonar. It is very good sonar. But the physical aperture of the array and the geometry of acoustic imaging still constrains it.
Then comes synthetic aperture sonar, or SAS.
SAS changes the processing philosophy. Instead of treating each ping as an independent image line, SAS coherently combines many overlapping pings as the platform moves forward. In effect, the motion of the vehicle creates a much larger “synthetic” array than the physical sonar itself. The benefit is dramatically improved along-track resolution, and more importantly, resolution that can remain far more consistent across the swath.
A strong practical example is Kraken KATFISH. Kraken describes KATFISH as an actively stabilized towed synthetic aperture sonar system. It uses articulated tailfins and an intelligent autopilot to compensate for towfish motion, supporting high-quality SAS data collection and large-area coverage. Kraken lists real-time constant SAS imagery resolution of 3 cm x 3 cm, post-processed resolution down to 2 cm x 2 cm, survey ranges up to 200 meters per side, and standard operating speeds of 4 to 10 knots.
That is not just a prettier sidescan image. That is a different level of seabed intelligence.
With conventional side scan, range is the enemy of clarity. With SAS, range becomes less punishing. Small objects stand out. Shadows become sharper. Mine-like contacts become easier to classify. Pipelines, cables, debris fields, seabed scars, and infrastructure features become more interpretable.
For mine countermeasures, this can reduce uncertainty. For offshore energy, it can improve route and site assessment. For critical underwater infrastructure, it can support better change detection. For autonomy, it provides the kind of sensor output that automated target recognition systems actually deserve.
But let us be clear: SAS does not make traditional sidescan obsolete. That is too simplistic.
Single beam side scan remains valuable when cost, simplicity, and robustness matter. Multi-beam side scan remains highly relevant when survey productivity, coverage, and image quality must be balanced. High-speed multi-beam systems such as the Klein 5900/Mantis are powerful tools for defense, UXO, offshore, and rapid survey missions. SAS systems such as Kraken KATFISH (or THALES TSAS), sit at the premium end, where resolution, classification confidence, and wide-area seabed intelligence justify the added complexity.
Summary
The evolution of sidescan sonar is really the evolution of underwater understanding.
First, we learned to see the seabed. Then we learned to survey it efficiently. Now we are learning to classify it with confidence.
Detection is cheap. Understanding is expensive. And in the modern underwater battlespace, vague pictures are becoming a luxury we can no longer afford.
Call-To-Action
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Originally published in the Strategic Pings ))) newsletter on LinkedIn on 2026-05-05. Subscribe there to get new editions first.