Triangulation can tell you where a point is between three sources but you need four to determine elevation, because it’s not the radius of a circle but the radius of a sphere.

But at sea there’s not much to obscure satellite signals so I believe resolving buoy position was a solved problem back when gps car navigation still sucked balls because tall buildings make everything harder. You need a lot more satellites to see three or four at the same moment.

i think they monitor pressure waves somehow

here is an interactive map, looks like some of them are picking up something https://www.ndbc.noaa.gov/obs.shtml?lat=13&lon=-173&zoom=2&p...