What Technique Could Be Used to Figure Out How Deep the Ocean Is?

Abstract

Did yous know that we have meliorate maps of the moon, Mars, and Venus than we do of the seafloor on Earth? Since oceans cover 71% of the Earth's surface, understanding what the seafloor looks like, and where dissimilar processes, such every bit ocean currents are agile, is hugely of import. Mapping the seafloor helps us to piece of work out things like where different types of fish live, where we might detect resources, such as rare metals and fossil fuels, and whether there is a hazard of underwater landslides happening that might cause a tsunami. Mapping the seafloor is very challenging, because we cannot employ the same techniques that we would use on land. To map the deep body of water, nosotros utilise a tool called a multibeam repeat-sounder, which is fastened to a transport or a submarine vessel.

Why Do Nosotros Need to Map the Seafloor?

Over 96.5% of the Earth's water is constitute in the oceans, while the remaining 3.5% is found in lakes and rivers [1]. In this article, we are going to talk about how nosotros map the seafloor of the oceans, but the same engineering science is besides used on a slightly smaller calibration in lakes and rivers, to map the land under these bodies of h2o.

Merely why do nosotros need maps of the seafloor? The nigh obvious answer is to assist ships find their style around. Although well-nigh vessels travel along at the sea surface, they need to be enlightened of hazards nether the water, like rocks and shallow banks where they might run ashore. For vessels that travel nether the water, similar submarines, information technology is even more of import to have accurate maps, so they can navigate and avoid hazards. It is likewise of import to know where these hazards are when nosotros plan to build offshore structures, such every bit piers and current of air turbines, then that we know they will be congenital on suitable foundations. Seafloor maps assistance us understand processes, such as ocean currents. Ocean currents are huge conveyor belts of fast-moving h2o, driven by differences in ocean temperature and salinity (saltiness) [2]. The strongest electric current system is called the Antarctic Circumpolar Electric current, which is the merely current to link all the major oceans as it flows all the manner around the world [2]. Features under the h2o, such every bit submarine volcanoes and canyons, tin influence where these currents menstruum. So, if nosotros know where these underwater features are, nosotros can more accurately predict where the currents volition get and how they will acquit. Bounding main currents are likewise very important because they aid command our weather and climate. Maps of the seafloor are also useful tools for answering a wide range of other scientific questions, such as finding out where certain types of fish similar to live, how new volcanoes can form at the bottom of the ocean, and where nosotros might find natural resource, such as oil and gas.

How Do We Map the Seafloor?

On country, nosotros tin can map the landscape quickly and efficiently using satellite-based engineering. This technology works by sending a betoken from a satellite that is orbiting the World, which then bounces off the Earth's surface and returns to the satellite. Satellites use various types of signals for mapping the landscape, simply basically all the signals are some grade of lite. The length of time it takes for the signal to return to the satellite tells the satellite how far abroad the Earth is, and the satellite can then use that information to map out the features of the landscape. While some satellite-based applied science that we use to map the country surface tin can be used in shallow water, these technologies do not work once for the deeper parts of the ocean, because the water stops the signals from reaching the seafloor. This is why nosotros have such good maps of the moon, Mars and Venus—they practise not take oceans, then we can use satellite technology to map them in keen item.

Early seafarers measured water depths using a lead-line. This was a very simple tool, made up of a heavy weight covered in something glutinous (usually grease) on the end of a rope. The weight was lowered over the side of the ship until it striking the bottom then information technology was pulled back up. The seafarers could tell the weight had hit the seafloor because some sediment would be stuck to the grease, so they could mensurate the length of rope that was lowered down, in club to effigy out the water'due south depth. The position where the measurement was taken then had to exist calculated using compass bearings and other instruments, such every bit a sextant. This was not a very accurate method and took a very long time.

During World War II, new technology was developed that allowed ships to accurately measure water depths every bit they sailed across the oceans [3]. These were single beam echo-sounders , instruments that could be attached to the hulls of ships. An echo-sounder works by sending out a sound signal, or "ping," into the h2o. This sound travels through the h2o until it reaches the seafloor. When information technology reaches the seafloor, information technology bounces off and reflects support to the ship, where the echo-sounder records the reflected signal. So, the name "repeat-sounder" actually tells yous how it works—it sends out a "sound" (sounder) and listens for the reflected audio, or "echo." This is basically the same thing that happens when you lot stand in a big empty room and make a dissonance—the audio bounces off the walls because they are a hard surface, and you lot hear the repeat of the noise that gets reflected back toward you. The time information technology takes for the signal to achieve the seafloor and return to the ship can be used to calculate the water depth. This is done by halving the time between when the sound was generated and when the reflected sound returned and multiplying that time by the speed of audio in water (usually around i,500 meters per second). Well-nigh ships, including small fishing boats, have an echo-sounder on board.

Unmarried beam echo-sounders were a huge improvement in seafloor mapping, simply they only allow us to map a line of points across the seafloor. These points tin then be used to make basic maps of the seafloor, but at that place might be big rocks or holes in between the mapped lines that we would not see. In 1964, a company called SeaBeam developed a new technology chosen multibeam echo-sounders [four]. This system allows the echo-sounder to ship out a "fan" of pings (chosen a swath) into the water, which allows us to accurately map a broad strip of the seafloor every bit the ship travels forth (Effigy 1). We tin can change the frequency of the audio that is emitted by the echo-sounder; in order to wait for certain features in the water. For example, we can place smaller targets, such equally schools of fish and areas where gas is seeping out of the seafloor to grade plumes of bubbles, or flares (Figure ii).

• Figure 1 - Ship mapping the seafloor using a multibeam repeat-sounder.
• The echo-sounder works by sending a sound signal into the water. The sound waves travel downwards through the water column until they hit the seafloor where they are reflected back up to the repeat-sounder. By recording the fourth dimension it takes for the audio to travel down to the seafloor and back again, nosotros can calculate the depth of the water as we know how fast the sound travels.

• Figure 2 - Also as mapping the water depth, repeat-sounders can give us other information well-nigh what the seafloor is like, and what is happening in the water in a higher place the seafloor.
• (a) Hither we can see an case of backscatter information from a multibeam repeat-sounder showing ripples in a channel on the seafloor. Backscatter data records how much of the sound waves that the echo-sounder sends out become reflected back again. The calorie-free colors stand for to difficult surfaces which reflect a lot of the sound, like gravel and sand, while the dark colors correspond to soft surfaces, similar mud, which absorbs some of the sound waves. (b) Echo-sounders can as well show us what is in the water above the seafloor, such as these flares of bubbles that have been imaged in 3D using repeat-sounder data.

Underwater Discoveries and Records

Mount Everest is the highest mountain on World, reaching 8,848 m. This is technically true, as it is the highest mountain when you start measuring from sea level. Even so, if you get-go measuring from the seafloor, in that location are some much higher mountains on globe. The highest of these is Mauna Loa in Hawai'i, which reaches ~9,170 one thousand above the seafloor. But 4,170 chiliad of this is exposed above the body of water surface. The average depth of the world'due south oceans is iii,682 k, with the deepest areas found in oceanic trenches. The deepest of these is the Marianas Trench, which reaches ten,994 m below the sea surface. You could submerge Mount Everest in the trench and nevertheless have space for Mount Washington or Tongariro every bit well. Y'all could likewise fit thirteen buildings the height of the Burj al Khalifa, the tallest building in the earth, in the trench, stacked end to finish (Effigy iii).

• Figure 3 - Did y'all know that you lot could hide Mountain Everest underwater?
• And that in that location are even higher mountains if you measure them from the seafloor? To explore the deepest parts of the ocean we take to use technology, such as submersible vehicles. Even the deepest scuba divers accept but reached 332 thou beneath the ocean surface. Sperm whales tin become much deeper than this, reaching around iii,000 m. But we can use repeat-sounders to map all of this without even leaving the send!

Surprisingly, you can also find some of the hottest places on earth at the seafloor. Black smokers are vents found to a higher place submarine volcanoes, where very hot fluids generated in the Earth'due south crust reach the seafloor. These tin reach temperatures of 400°C and are home to incredibly unique animals, such as clams and tube worms that are not found anywhere else in the world [5]. Many of these interesting underwater features have merely been identified and studied in the concluding few decades, because we did not have the technology available to find them before this.

New improvements to repeat-sounder technology mean that multibeam echo-sounders can also be used to find shipwrecks on the seafloor [3]. This technology allows us to image the seafloor in such high resolution that we tin can actually produce images that evidence the outline of a shipwreck, down to the pocket-sized details like the mast.

What Do We Need to Practise Next?

Although there have been huge improvements in the maps nosotros have of the seafloor, there are still vast areas of the body of water for which we have hardly whatever information. In 2018, a group of research organizations, universities, and companies launched a project called Oceans 2030 [i]. The aim of this project is to map all of the oceans to a reasonable level of item by 2030. This is a huge project that will need a lot of work, but with all these new areas to explore, who knows what we might find! The seafloor is constantly irresolute as sediment is moved around by the currents and as earthquakes and faults shift the seafloor and volcanic eruptions occur. Information technology is incommunicable to constantly map these changes, but we do endeavour to return to key locations afterwards large events like earthquakes to see what has changed on the seafloor. Mapping all of the ocean floor might seem similar a huge task, but in just the terminal few decades we have made some massive changes in the engineering that we use. This means we can become much more accurate maps, and we can do this relatively quickly. But there are still big areas to explore, who knows what nosotros might discover?

Glossary

Map: ↑ A representation, normally on a apartment surface, of the whole or a function of an expanse

Echo-Sounder: ↑ An instrument for determining the depth of water below the surface using sound waves

Conflict of Involvement Statement

The author declares that the enquiry was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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References

[one] ↑ Mayer, L., Jakobsson, M., Allen, K., Dorschel, B., Falconer, R., Ferrini, 5., et al. 2018. The Nihon Foundation—GEBCO Seabed 2030 Project: the quest to meet the world's oceans completely mapped by 2030. Geosciences 8:63. doi: 10.3390/geosciences8020063

[ii] ↑ National Oceanic and Atmospheric Administration. 2011. Ocean Currents. Available online at: https://world wide web.noaa.gov/resource-collections/ocean-currents

[three] ↑ Dierssen, H. M., and Theberge, A. E. 2014. "Bathymetry: history seafloor mapping," in Encyclopedia of Natural Resource: Volume II–H2o and Air, ed Y. Wang (Didcot: Taylor & Francis Group), 644–eight. Bachelor online at: https://colors.uconn.edu/wp-content/uploads/sites/1423/2015/09/Dierssen_2014_ENRHistory.pdf

[4] ↑ Fifty-3 Communications SeaBeam Instruments. 2000. Multibeam Sonar Theory of Operation. E Walpole. Available online at: https://www3.mbari.org/data/mbsystem/sonarfunction/SeaBeamMultibeamTheoryOperation.pdf

[v] ↑ National Oceanic and Atmospheric Administration. 2018. What is a Hydrothermal Vent? Available online at: https://oceanservice.noaa.gov/facts/vents.html

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Source: https://www.frontiersin.org/articles/437704

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