Ocean mapping consists of different techniques and resolutions of quality all of which have benefits. 100% of the ocean seafloor has been mapped with a horizonal resolution of 1 to 12 kilometres by the Geosat and ERS-1 spacecraft (Smith and Sandwell 1997). However less than 10% of the global ocean has been mapped by sonar technology (NOAA 2018). Although the knowledge of the ocean floors terrain and its depths are known, the detail of the floor its self is vague.
The information taken from ocean mapping can give a lot of insight into the biological and geological history and the change in sea levels. It can also help provide information on volcanic rifts and seamounts. It can benefit in the construction of sea structures such as wind farms by providing information as to where is best to build them. Changes to the Oceans climate can be monitored to help provide data towards climate change. It can also help with assessing an area and help coastal management preserve and protect the oceans ecosystem.
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The ocean was first mapped in 1957 (Maxwell 2013) and published in 1968 by Marie Tharp and Bruce Charles Heezen using echo sounding which is a type of sonar. Sonar stands for sound, navigation and ranging and was first used in world war one (Bellis 2017). This is where high frequency sounds are sent out and the time delay of the returning echo is recorded, the data is then plotted to record a profile of the sea floor (Mason 2017). It was at this time noticed that the floor had many rift valleys which supported the continental drift claim.
Sonar continued to advance and there are now many different types and ways of using sonar to map the ocean, even some fishermen use sonar to locate large schools of fish. Swath-sounding/multibeam echo sounders is one type which was developed in 1960 by the Royal Navy (Vilming 1998). One of the more updated versions of this is the Tangaroa’s Kongsberg EM302 multibeam system (Pallentin 2016), upgraded in 2010, which is mounted on to the hull of the boat and it sends out a signal which is divided into 288 separate beams forming a swath on the seafloor. The width of the swath is increased with water depth and can map depths of up to 8000 metres with a width of up to 7 kilometres. This is then reflected off the seafloor and sent back to the ship’s receiver. This then provides the distance from the bottom of the ocean giving the reader the depth. There is also a similar high-resolution shallow water multibeam system called Kongsberg EM3002D (Kongsberg 2006) which has a max of 508 beams and covers a range of 1-200m. Most simple sonar echosounders transmit sound at 12 kiloHertz to discover the depth. Whereas some use a lower frequency of 3.5 kiloHertz, which are used to penetrate the sea floor and see the layers of sediment below (Dive and Discover N/A).
Another modern sonar technique is the side-looking sonar. This sonar is towed behind a water vehicles and ships and although works similar to a multibeam echo sounder, it focuses more on intensity of the return echo. This means it is better for finding objects in the sea such as ship wrecks and providing information on the sea beds makeup. They also work well in varying water conditions and can measure the ocean floor with up to 10cm of resolution (Pennstate N/A).
To then turn the information received by the multibeam system and the side-looking sonar into a map the data must be analysed. The seafloors denseness is provided by the strength of a returning signal, for example; weak returning signals indicate soft mud while strong returning signals suggest rock (NIWA 2016). Also, louder echo’s suggest a darker area in comparison to quiet echo’s suggesting it to lighter. This data is then combined with satellite data to produce a picture of the seafloor.
Benthic habitat mapping is a combination of satellite imagery, underwater photos, data from samples and acoustic surveys. All of which give a picture of what the bottom of the ocean is like in certain areas. Benthic is a term which refers to anything at the bottom of the ocean on or in the sea bed. It is mainly shallow waters which have been mapped in this way, mainly due to it being easier to map than the open ocean but also for management and preservation reasons. An example of using benthic habitat mapping is the mapping of the Florida coral reef ecosystem, in which a 9-year project was done to map 3000 square kilometres of shallow water which was less than 25 metres deep. This particular coral reef is important because of the endangered and threatened marine life which live within, the vital fishery which generates and estimated $4 billion in total revenue, and it provides protection from hurricane driven waves and storms.
There are many ways of exploring the ocean with technology but to get the best view of the sea floor you must view it with human eyes. One way this is possible is by scuba diving, which can be done in shallows of up to 40 metres. Divers can take photos or videos of the routes they take which can be used to provide a data base of the area. Another way that humans can view the oceans depths is by using a submersible, an example being Alvin. This particular vessel can submerge 2 humans into depths of up to 4500 metres for up to 10 hours (WHOI 2018). Alvin has two robotic arms which can obtain samples and with its current dive depth it can reach around 2/3rds of the oceans floor. Scientists also believe they can improve this depth to 6500 metres, meaning it would have access to around 98% of the ocean floor. Although this procedure can provide a lot of information about the sea floor it can be very time consuming and very expensive.
All the techniques discussed have their benefits and disadvantages, however, to map the ocean in the highest revolution it would be best to use all methods simultaneously. Satellite mapping provides an all-round good view of the ocean topography, however, it leaves out the details. Sonars many different techniques and uses can fill in most of the blanks that the satellite misses out. Echosounders and side scan sonar are often used together to provide as much information possible. Then submersibles can be used on areas of interest given by other methods. These along with benthic habitat mapping technique it can produce a high-resolution profile of the sea floors, which can be used to provide lots of information for future science and help explain the environments history.
Ocean mapping is a great scientific advantage towards learning more about the environment. One group of scientists aim to map 100% of the topography of the ocean by 2030 (GEBCO 2017) to help understand the oceans circulation, tides, tsunamis, forecasting, fishing resources and lots more. There are doubts behind this project however due to the fact it would aid mining industries that could try to mine discovered spots for profit (Frischkorn 2017). It has been 61 years since the first map of the ocean was produced and although still only a small percentage of it has been mapped in any sort of detail, the interest in the subject has increased, meaning more is now being done to find out more. If by 2030 the entire ocean floor has been analysed, many doors into exploring science will be opened and much more can be learned about the planet.
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