what range of altitudes do you envisage operating at above the seabed? 5-10m? If this is so, we’ve just brought out a new laser altimeter that operates to 3000m depth and is extremely useful for pipeline survey work. Its’ accurate to 1.0mm and takes around 1000 readings/second.
tested yes, but made it better accuracy at <2m range in the end. it’s more of an appropriate tool for maintaining altitude for things like pipeline survey rather than mid-water depths, where frankly you’re better with an IMGEX.