From above, the Daugava reveals very little. The water is uneven and rusty, the depths changing suddenly, and the surface reveals very little about what is underneath. When most people stand at the mouth of the river close to Riga, they see nothing more than brown water flowing toward the Baltic. The hydrographers at LVR Flote have been reading this puzzle for twenty years.
The puzzle gave them something unexpected last summer. A shape that didn’t belong on the screen appeared during what was meant to be a routine survey. Bicycles, fallen trees, broken pieces of breakwater, and the occasional sunken vessel are among the clutter that surveyors are accustomed to seeing down there. None of those things applied here. Four meters of something that appeared to have been deliberately placed in the murk was neat, well-defined, and nearly flawless. “The clarity of the sonar image immediately told us this was not a typical object,” stated Liga Cerusa, the chief surveyor for the company. The hesitancy in that statement is audible. Even before they realized what it was, they could tell it was odd.
As it happened, it was an anchor. An old one, about four tonnes in weight and four by two and a half meters in size, admiral-style, the kind that hung off tall ships and traditional sailing vessels in the early twentieth century. It had not been reported missing. There was absolutely no record of it. For what seemed like decades, it had just been sitting there, untouched.
A piece of fishing net wrapped around the shank was the detail that transformed a curiosity into a minor mystery. It included the name of a net-weaving factory in Riga that closed at some point in the 1940s. Observing that piece gives one the impression that time is folding in on itself; it is a functional artifact from a long-gone industrial world that has been snagged, dragged down, and forgotten while the city above it has repeatedly rebuilt itself.
The part that continues to garner attention is what made the discovery possible. Teledyne RESON’s SeaBat T51-R multibeam sonar, which operates at 800 kHz—an exceptionally high frequency that most survey work doesn’t bother with—was the system on board. Range and resolution are traded off, and in a river this murky, resolution prevails. Before a single diver entered the water, the team could see what they were looking at thanks to the sharp display of the anchor’s geometry. These surveys typically don’t work that way. Typically, you have suspicions, check, and then confirm.
The engineers themselves frequently sound a little taken aback by what their instruments are now capable of. “Even in difficult turbid river environments, operators can resolve small and complex features with remarkable clarity at high frequencies like 800 kHz, according to Pim Kuus, a senior hydrographer at Teledyne Marine. Put simply, they are able to see objects in contaminated water that would have remained invisible a short time ago. The darkness that concealed that anchor for more than a century ceased to be a barrier.
That change is more significant than a single fortunate finding. In order to track unmanned vehicles sneaking into and out of a busy port, Teledyne recently installed a forward-looking sonar on a seabed frame in Gothenburg. This is just one example of how Teledyne has been pushing the same imaging logic into other areas of the marine world. There are security-related questions, not historical ones. However, the fundamental concept remains the same. The water has changed from being a curtain.
For its part, LVR Flote has standardized a large portion of its fleet around RESON systems, in part due to their confidence in the image. Cerusa stated, “With Teledyne RESON systems, we know that what we see on screen accurately represents what’s on the seabed.” This statement is more subdued than it might seem because it eliminates the need for repeat surveys and second guesses.
Meanwhile, the anchor is on its way to dry land. This summer, the company intends to install it outside its headquarters, carefully repainting it to preserve the original texture. No one is yet certain whether it ended up in the river due to a storm, an accident, or slow abandonment. Perhaps no one will ever do so. For the time being, it serves as a reminder that the riverbed conceals its mysteries until something eventually learns to look.
