You are correct. I assume it is some sort of sea floor scanning sonar. Do you have any idea how incredibly long it takes to cover even a small area with one of those?
The past few weeks have been strictly a "narrowing down" operation. Looking for debris and listening for pings.
Now that they've heard pings and localized it to an area roughly similar in size to a major city they can use the scanning sonar sub. Meter by meter they will scan the sea floor for a man made object.
Even knowing exactly where to look it could take another month or two if long ladder pattern dredging with that sub.
Then if they find something. An ROV will be sent to check it out. Maybe even retrieve black boxes.
I think this jet is largely in one piece down there
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