Hydrography has always been about one thing. Reducing uncertainty before uncertainty becomes expensive.
The Egyptians understood that. Long before sonar, they were already measuring water levels and restoring order after the Nile floods wiped out boundaries and infrastructure. Their tools were simple, but the principle was powerful. Measure carefully. Repeat consistently. Turn water from chaos into something you can manage.
That, in essence, is still hydrography.
[Video: Evolution of Hydrographic]
For centuries, the lead line was the main tool of the trade. A weighted rope lowered to the bottom. One depth point. One moment in time. If you were lucky, a little tallow on the lead would also bring up mud or sand, giving you a clue about bottom type. It worked. Sort of. But it was painfully slow, highly manual, and left enormous gaps between soundings. In other words, it gave you information directly under the vessel and a healthy amount of optimism everywhere else.
Then came the fathometer.
In the 1920s, echo sounding changed the game by allowing surveyors to measure depth acoustically while underway. This was a major step forward. No more dropping a line over the side every few minutes. Now we could collect a continuous depth profile along track. Productivity jumped. Confidence improved. But there was still a problem. A single-beam echo sounder only looks straight down. It tells you what is below the keel, not what is waiting a few meters off to port. Or starboard. Or directly in the gap between survey lines where nasty surprises like to hide.
That is why multibeam mattered so much.
Multibeam did not just improve hydrography. It changed the question. We stopped asking, “What is the depth under me?” and started asking, “What does the entire seabed look like across my swath?” That is a very different level of ambition. And it is the reason hydrography moved from sparse measurement to true seafloor mapping.
One of the important commercial milestones in that transition was the SeaBat 9001. It helped bring multibeam out of the realm of specialist systems and into practical survey operations. Compact. Commercial. Usable. It made it possible for more operators to move from isolated soundings to real swath bathymetry. That was a big deal. Once people saw proper coverage, going back to sparse data felt a bit like going from radar to binoculars and calling it progress.
Then came the systems I know personally.
I had the privilege of helping to lead the development of the SeaBat 8125 and, later, the 7125 as R&D Manager for RESON Inc. The SeaBat 8125 was based on Jens Steenstrup’s (co-founder of RESON) brilliant ideas, with Mark and Kirk as lead engineers. This was a major leap in shallow-water hydrography. It delivered extremely high resolution, using focused beamforming, and helped redefine what surveyors expected from multibeam performance in ports, harbors, and coastal approaches. It was not just about measuring depth better. It was about seeing the seabed with a level of clarity that changed operational standards.
The 7125 took that further. Dual-frequency capability. Greater flexibility. Better coverage. More productivity. Better data in more conditions. This is where multibeam matured from a clever sonar into a true survey system. When operators can reduce infill lines, maintain data quality, and get cleaner results faster, that is not a small engineering improvement. That is commercial and operational leverage.
And then we arrive at the SeaBat T20 & T50.
The T20 & T50 represent the next stage in the evolution. Frequency agility. Advanced beamforming and better sidelobe suppression, resulting in cleaner bathymetry.
Better integration with inertial navigation. Higher data density. Less time fighting artifacts in post-processing. In simple terms, it reflects where hydrography has been heading all along. Not just toward more data, but toward better data. Data you can trust. Data that shortens the path from acquisition to decision.
That is really the story here.
The evolution of hydrographic survey is not just a story of better sensors. It is the story of reducing ambiguity. From Egyptian measurement staffs to lead lines. From lead lines to fathometers. From fathometers to multibeam. From multibeam to agile, high-resolution systems like the SeaBat T50/T51.
I give the examples of SeaBat sonar family, as that is what I’m most familiar with. Similar MBES to T50/T51 would be Norbit Winghead or Kongsberg EM 2042, all excellent MBES systems
We no longer just sample the seabed. We model it. We interpret it. We operationalize it.
And that is a very good thing.
Because the ocean has always been unforgiving to people who confuse limited data with real understanding.
Call-To-Action
Please comment and provide insight so we all can learn from each other. Did you ever used any of the older SeaBat MBES systems?
Originally published in the Strategic Pings ))) newsletter on LinkedIn on 2026-03-31. Subscribe there to get new editions first.