107 points by dnetesn 5 days ago
I used to operate multibeam sonar system on an oceanographic research ship. Getting good data from those kinds of systems is an interesting challenge.
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 used to do this as well except we were transitioning from ship mounted multibeams to AUVs carrying multibeams and subsurface arrays. Simrad EM3000's IIRC. The difference in the amount of necessary data processing was quite a bit. Just the noise from the ship could be quite distorting and then the sea life would hear you and come try to play.
Does multibeam sonar function well in the presence of temperature/salinity stratification layers in the water column?
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.
Those layers are why you need to measure the sound speed profile -- speed of sound as a function of depth. The variation in sound speed in the water column affects not only the travel time of acoustic energy -- but also the path -- (snell's law).
I worked on USNS Maury. The T-AGS ships are incredible. The amount of technology packed on to them is bewildering. Glorified spy ships if you ask me :)
Here are "high frequency" sonar images of the Japanese WWII aircraft carrier Akagi, sunk in the Battle of Midway. They were supposedly taken by an AUV.
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.
We're working on a cheaper way to do it:
A quick summary:
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.
I hadn't thought about the possibility of sunken ships and sea wrecks until you mentioned it. I wonder how many mysteries this sea-floor mapping endeavor will put to rest? If they can put even one big mystery (something like finding Malaysia Airlines Flight 370) to bed, they'd get a lot of great publicity.
Imagine finding a Roman galley out in the Atlantic, or even more than one. I'm always amazed Madeira and the Azores weren't colonized before the Portuguese arrived in the early 1400's, even though there are possible Roman, Viking, and Genovese references or evidence.
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.
They mapped a pretty large area of the ocean floor looking for that wreckage
Yeah on the one hand it's cool possibility for historians and stuff, on the other it kind of ruins the adventurous scuba diver studying old maps and stuff searching for lost treasure.
Firstly, who still does this? Nobody I know in the scuba diving community "[studies] old maps and stuff searching for lost treasure". That'd be a good way to not have a dive plan and end up in trouble.
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?
Imagine all the gold and treasure there waiting for other people to lay claim on! Forget those conniving explorers they only found it but its not theirs.
We only have a few years to bring back Sealab 2021.
Take some more pills, pillhead.
I would rather have an international law (if such laws exist) that force fiber optic and pipeline companies to share their underwater map data to everyone, essentially force an open source data for it. No need for governments to spend money when private companies can do it because they need to.
In the UK this information is already published. They don't want fisherman accidentally damaging their assets.
What about: https://earthlymission.com/world-ocean-floor-map/
You mean a mostly artistic rendition based on rough known features?
Based on soundings. Which is at some resolution, not based simply on what pokes above the surface.
There is no way that the nuclear submarine fleets of the world's countries haven't mapped a significant portion of the seabed since the 1980s when the advanced techniques were invented.
I don't see why that data should be held classified, at least make this project a little bit easier.
> 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?
I think it should be all be declassified for the public good, but I can understand why they would want to keep it classified: by revealing where they've mapped, they reveal where they've been. Quality variations in different parts of the map could also reveal where they spend more time, or at what depths. But I'm skeptical that it really matters.
Or they awoke eldritch leviathans who now command them.
Nothing is Beyond Their Reach
Reference to https://en.wikipedia.org/wiki/USA-247
> 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.
Subs don't typically dive that deep only a few hundred (US Los Angeles class) to 2000 or so (US Seawolf class) (of course this is stated depth but speculation gets us nowhere). The ocean averages over 3.5 km deep so most of it is beyond the range of subs so they probably have pretty good maps of up to the continental shelf but beyond that it gets less useful.
Yep. The Navy already has an extensive map of the ocean floor
I thought woods hole "serpedipitously discovered" a lot of stuff.
Does this scanning with sonar harm whales? I'm surprised they are not mentioned in the article.
I believe that the sonar they are talking about here is much "quieter" and directional than the type which they is harming sea life. The "harmful" type is either the intense omni directional sonar used to locate other ships, and the extremely loud sounds used by the petroleum industry to map subsurface deposits of oil and gas.
Indeed. It's also possible to further minimize harm by not transmitting when marine mammals can be seen or heard nearby.
With the speed of sound and its characteristic attenuation in the sea water and marine mammals' general stealthiness this is just not possible.
Not possible, period.
Interesting conjecture! I have seen whales with my eyes and heard them on sonar, and disagree with you.
Note that minimizing harm and preventing it are different things.
I recently read an article on a UK navy ship on a mission of seafloor mapping (https://www.theregister.co.uk/2018/11/21/hms_enterprise_roya...) and apparently they still make sure that there's no wildlife nearby.
"with the sonar switched on, having first ensured no marine wildlife is nearby that would be distressed by the sonar"
This will most benefit the deep sea mining industry.
I'm surprised no one has mentioned the XPrize foundation: https://oceandiscovery.xprize.org/prizes/ocean-discovery
> 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.
Just gotta say, nothing quite drives home the point of how much water there is on Earth, like even a short oceanic flight and looking out the window.
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.
Doesn't the ocean floor change often due to currents? Sediment consistently is moved from point A to point B similar to sand dunes?
Even if this is related to just 'bedrock' or whatever more solid mass is down there, doesn't that get impacted by the faults a lot? Or is that around just the fault lines?
It's probably a lot like trying to document the internet. Once you've begun you have to start over because of how much will have changed.
Raising money for such a project should be easy. What investors would not want to partake in a treasure hunt?
What benefit has come from mapping the ocean floor when they searched for Malaysia Airlines Flight 370?
Anyway, it's science so should be done.
I'd suggest to see if there is anyway for it to be done by normal sail boats, crowd sourcing it.
I reckon people crossing a ocean would find it fun to map a location on the way.
Get the price to $1000 for something then people would suck themselves into paying more for better systems. Boats just chew money anyway.
Not until we finish raking the forest floors.