You can also track the path of the boat, to figure out which port it came from and where it went afterwards. You can also correlate it with AIS, a mandatory tracking signal for ships (used for collision avoidance etc). Of course the ship could have turned it off, but if I owned a bunch of spy satellites I would pay very special attention to any ship that appears on satellite images but doesn't have a corresponding AIS beacon.
Of course unless you are tracking a submarine back to a submarine base all of this won't tell you exactly who it was. Any state actor can just rent a fishing ship and deploy a remote controlled submarine from it. That's where more traditional information gathering comes in.
If the ship is small enough, it wouldn't be required to have an AIS beacon. From an article someone else posted, the suspected ship is a 50-foot recreational sailboat.
> A major concern in naval intelligence is the collection of up-to-date acoustic signatures for contemporary vessels so that IUSS can correctly identify them.
Doesn’t identify the occupants but could perhaps identify the vessel, depending on how extensive these databases are. Of course that’s a massive open question and I don’t want to claim it extends to small rental vessels, but I also don’t want to claim it doesn’t!
The main thing to note is that OSINT types are working with poor quality manipulable data compared to what’s available to US/NATO, even if we focus only on larger vessels with AIS. Which is not to say US/NATO should be trusted in their public statements.
Of course unless you are tracking a submarine back to a submarine base all of this won't tell you exactly who it was. Any state actor can just rent a fishing ship and deploy a remote controlled submarine from it. That's where more traditional information gathering comes in.