The speed of sound in water is proportional to temperature and conductivity — which are approximately dynamic functions of water column depth and temperature (and time depending on the properties of the region you are in — the tenperature can change a lot over short time scales). You need to measure to measure these properties in order to obtain a sufficiently accurate sound speed profile to be able to trace the path taken by acoustic energy projected from the transceiver, off the sea floor and back to the transceiver. Inaccurate sound velocity quickly becomes one of the largest error terms in measurement accuracy. We computed sound speed profiles as often as we reasonably could — sometimes the science objective involved measuring these properties and we’d use data from those measurements but sometimes we were just transiting along and would draw from a supply of expendable bathy thermographs that we could use to make sound speed profiles periodically (but certainly not often enough to maintain accurate calibration all the time.)
The ship is moving and the orientation of the array needs to be accurately calibrated — shipboard MRUs are expensive and imperfect.
The water column is rising and falling and vertical position measurement accuracy is very low from systems like gps compared to horizontal measurement accuracy.
The ship is pitching and with many ship designs this can create bubbles which can be swept beneath the ship — a small amount of bubbles close to the transceiver head can absolutely overwhelm the noise budget of these systems.
I’d be curious to know how much data from ship mounted sonar systems are actually useable for large scale high resolution mapping. I believe the best teams that build high resolution global sea floor maps rely on satellite gravimetric measurements for baselines — and use very sophisticated algorithms to fuse shipboard datasets with the global gravimetry — which im guessing probably have to throw away huge amounts of information from the higher resolution shipboard systems ...
I don't have the first clue about sonar, but as someone who crunches data for environmental assessments, stratification occasionally plays hell with a lot of chemical & biological models.
Only 6% of the ocean floor has been mapped. People at the Seabed 2030 project plan to map the ocean floor in high res by 2030.
Reasons to do this include navigation safety, ability to lay fiber optic wire and pipelines, because we don't know what's there, weather forecasts since water/temperature flows along ocean floor contours affect atmospheric flows, tsunami predictions, we could find sea wrecks.
Another thing that fascinates me are seamounts: volcanoes that either didn't reach the surface or that did but later eroded and subsided. With sea levels 100-150 ft lower in the last ice age, many eroded to that level, leaving a flat-topped mountain that far beneath the surface. It's too deep for normal scuba, but amateur underwater drones could easily explore them.
Secondly, no scuba diver is about to dive on the ocean floor. Maybe you're thinking of deep sea divers, who dive in a submarine or other deep sea vessel?
Low-resolution sonar: https://www.gannett-cdn.com/presto/2019/10/21/USAT/ecaf19d4-...
Enhanced with a manual pass: https://www.gannett-cdn.com/presto/2019/10/21/USAT/0a89e2ce-...
Best guess they used the Remus 6000 to find the ship. It looks like a torpedo.
- 3.8 meters long
- 9 km/h speed
- 22 hour 'charge'
- 6000 meter max. diving depth
- EdgeTech 2205 sidescan array (best guess)
Logistical support alone for this AUV is incredible: crew of 20, four two thousand horsepower diesel engines eating 54 gallons of diesel per hour each at low throttle. Like 216 - 283 gallons of diesel per hour on average, and not counting electric generators on that vessel. The engines have to be overhauled every 4,000 hours. In other words, this effort would be a massive undertaking under current conditions, and there's not enough diesel on the planet to make it happen.
I don't see why that data should be held classified, at least make this project a little bit easier.
Really, you don't see why the military would want to keep the strategic advantage of keeping what they know about the sea floor secret?
It's all about to be "de-classified" anyway once the first of these sort of projects kicks off.
Not possible, period.
Note that minimizing harm and preventing it are different things.
"with the sonar switched on, having first ensured no marine wildlife is nearby that would be distressed by the sonar"
> As part of its post-prize impact work, XPRIZE announced a partnership with Seabed 2030, a collaborative project between The Nippon Foundation and The General Bathymetric Chart of the Oceans (GEBCO) to inspire the complete mapping of the world’s ocean by 2030 and to compile all bathymetric data into the freely-available GEBCO Ocean Map.
Imagining you could dive into any spot at any time kinda gives the feeling of having an entire alien planet to explore.
Our always-connected society gives us the illusion that we've discovered everything there is to discover, but apparently most of the world is uninhabited (by humans) and as this says, many parts aren't even mapped.