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Undersea Exploration

Undersea Exploration


Over the last two centuries there has been an explosion in our knowledge of the global underwater environment. This understanding of the world's oceans and seas has been accomplished by a variety of methods, including the use of both manned and unmanned (i.e., robotic) vehicles. When people use any of these modern methods to explore the undersea realm, they must, in one way or another, use a mathematical description of the under-sea environment in order to be successful. For example, scuba divers must be aware of such quantities as the depth below the surface and the total time they can remain submerged. Each of these quantities is expressed as a number: for example, depth in feet and total dive time in minutes. The use and application of mathematics is therefore an essential part of undersea exploration.

Oceanography is the branch of earth science concerned with the study of all aspects of the world's oceans, such as the direction and strength of currents, and variations in temperatures and depths. Oceanography also encompasses the study of the marine life inhabiting the oceans. As noted earlier, there are multiple ways to explore the oceans and oceanic life. When people and/or machines are sent to directly explore the ocean environment, several different properties of the oceans must be taken into account in order for the dive to be successful and safe. These properties includebut are not limited toocean depth and pressure, temperature, and illumination (visibility).

Ocean Properties

"Pressure" is a measurement related to force, and is especially useful when dealing with gases or liquids. When an object is immersed in a swimming pool, in a lake, or in the ocean, it experiences a force pushing inward over its entire surface. For instance, a balloon that is inflated, sealed, and then submerged will be pushed inward by water pressure. The pressure on the balloon is the force exerted by the water on every square inch of the balloon's surface. Pressure is therefore measured as the force-per-unit-area, such as pounds-per-square-inch. Due to Earth's atmosphere, all objects at sea level experience a pressure of approximately 14.7 pounds-per-square-inch (abbreviated 14.7 lbs/in2) over their entire surface.

Perhaps the greatest limitation to underwater exploration is water pressure, which increases with depth (i.e., the deeper one goes, the greater the pressures encountered). Moreover, the pressures within the ocean depths can be immense. A balloon lowered deeper and deeper into the ocean will continuously shrink in size as the water pressure increases. Just under the ocean's surface the water pressure is 14.7 lbs/in2, equal to one atmosphere . For every 10 meters (about 33 feet) of additional ocean depth, the pressure increases by one atmosphere.

"Visibility" refers to how well one can see through the water. As light from the Sun passes through seawater, it is both absorbed and scattered so that visibility due to sunlight decreases rapidly with increasing depth. Below about 100 meters (approximately 330 feet), most areas of the ocean appear dark.

"Temperatures" at the ocean surface vary greatly across the globe. Tropical waters can be quite comfortable to swim in, while polar waters are much colder. However, below a depth of about 250 meters most sea-water across the world hovers around the freezing point, from 3°C to 1°C.

The Development of Diving Equipment

In the past, people who wished to dive down and explore the oceans were limited by the extremes of pressure, visibility and temperature found there. Nevertheless, for thousands of years people have dove beneath the waves to exploit the sea's resources for things like pearls and sponges. However, divers without the benefit of mechanical devices are limited to the amount of air stored in their lungs, and so the duration of their dives is quite restricted. In such cases, diving depths of around 12 meters (less than 40 feet) and durations of less than two minutes are normal.

Various devices have been invented to extend the depth and duration of divers. All these devices provide an additional oxygen supply. Over 2,300 years ago Alexander the Great (356 b.c.e323 b.c.e) was supposedly lowered beneath the waves in a device that allowed him an undersea view. Alexander may have used an early form of the diving bell, which is like a barrel with one end open and the other sealed. With the closed end at the top, air becomes trapped inside the barrel, and upon being lowered into the water the occupant is able to breathe.

About 2,000 years after Alexander's undersea excursion, Englishman Edmund Halley (16561742) constructed a modified diving bell, similar to Alexander's apparatus, but with additional air supplied to the occupant through hoses. Modern diving stations, like diving bells, are containers with a bottom opening to the sea. Water is prevented from entering the station because, like a diving bell, the air pressure inside the station is equal to the water pressure outside. Researchers can live in a diving station for long periods of time, allowing them immediate access to the ocean environment at depths of up to 100 meters (328 feet).

The Emergence of Diving Suits

To allow greater freedom of movement when submerged, various under-water suits and breathing devices have been invented. In the early 1800s, diving suits were constructed, and modern versions are still in use. These suits possess a hard helmet with a transparent front for visibility; an airtight garment that keeps water out but still allows movement; and connecting hoses linked to a surface machine that feeds a continuous flow of fresh air to the suit. Over the years, additional improvements have been added to diving suits, such as telephone lines running between the surface and diver for communication.

From an exploratory point-of-view, diving suits are limited because of their bulkiness, the cumbersome connecting lines that run to the surface, and the restriction of the diver to the seafloor. Skin diving (or "free diving") overcomes the mobility problem by allowing the diver to freely swim underwater. As the name implies, most skin divers are not completely covered by a suit, but rather use minimal equipment such as a facemask, flippers, and often a snorkel for breathing. A snorkel has tubes that allow the diver to breathe surface air while underwater. This type of diving (called snorkeling) must be performed close to the surface.

As compared to snorkeling, scuba diving considerably increases the diving depth of snorkeling by employing an oxygen supply contained in tanks (scuba is derived from "s elf c ontained u nderwater b reathing a pparatus"). Varying versions of scuba gear have been invented. Probably the most popular is the aqualung, introduced by the undersea explorer Jacques Cousteau (19101997). When the diver begins to inhale, compressed air is automatically fed into her or his mouthpiece by valves designed to assure a constant airflow at a pressure that matches the outside water pressure. The compressed air is contained in cylinders that are carried on the diver's back. Using conventional mixtures of oxygen and compressed air, divers can safely submerge to around 75 meters (almost 250 feet). With special breathing mixtures, such as oxygen with helium, scuba dives of greater than 150 meters (about 500 feet) have been safely accomplished. To illuminate their surroundings, scuba divers sometimes carry battery-powered lights.

Station, suit, and scuba divers utilize compressed gases for breathing. As divers go deeper, the pressure on their lungs increases, requiring that they breathe higher-pressure air. This process forces gases such as nitrogen into the cells of the diver's body. Divers who do not follow the proper procedure upon returning to the surface risk experiencing a painful, possibly fatal condition known as "the bends." The bends are the result of the pressurized gases inside the diver's body being released quickly, like carbon dioxide being released from a shaken soda can. A diver can avoid the bends by ascending to the surface in a controlled and timed manner, so that the gas buildup inside his or her cells is slowly dissipated. This procedure is called decompression. A competent diver uses gauges to be aware at all times of the depth of the dive, and ascends to the surface in a timed manner.

It is recommended that divers ascend no faster than 30 feet per minute. For example, if a diver is at a depth of 90 feet, it should take 3 minutes to

ascend. The use of numbers and measurements are therefore of utmost importance in all types of diving.

Underseas Exploration Using Submersibles

Although scuba divers can explore some shallow parts of the ocean, especially environments such as coral reefs, submersibles allow exploration of every part of the ocean, regardless of depth. Submersibles are airtight, rigid diving machines built for underwater activities, including exploration. They may be classified as being either manned or remotely operated.

Manned submersibles require an onboard crew. Unlike scuba or suit divers, the people inside submersibles usually breathe air at sea-level pressure. Therefore, people in submersibles are not concerned with decompressing at the end of a dive. In 1960, the Trieste submersible made a record dive of 10,914 meters (35,800 feet) into an area of the Pacific Ocean known as Challenger Deep. Mathematics was essential for both the construction of Trieste and for its record-breaking dive. For instance, the maximum pressure anticipated for its dives (over 80 tons per-square-inch) had to be correctly calculated, and then the vessel walls had to be built accordingly, or the craft would be destroyed. Today there are many new and sophisticated manned submersibles possessing their own propulsion system, life support system, external lighting, mechanical arms for sampling, and various recording devices, such as video and still cameras.

Remotely operated submersibles do not need a human crew onboard and they are guided instead by a person at a different location (hence its name). These vehicles are equipped with video cameras from which the remote operator views the underwater scene. Remote submersibles can byand-large duplicate the operations of a manned submersible but without endangering human life in the case of an accident.

Philip Edward Koth with

William Arthur Atkins

Bibliography

Carey, Helen H., and Judith E. Greenberg. Under the Sea. Milwaukee, WI: Raintree Publishers, 1990.

Davies, Eryl. Ocean Frontiers. New York: Viking Press, 1980.

Oleksy, Walter G. Treasures of the Deep: Adventures of Undersea Exploration. New York: J. Messner, 1984.

Stephen, R. J. Undersea Machines. London, U.K.: F. Watts, 1986.


IS AN OCEAN DIFFERENT FROM A SEA?

The words "ocean" and "sea" are often used interchangeably to refer to any of the large bodies of salt water that together cover a majority of Earth's surface. The word "undersea" refers to everything that lies under the surface of the world's seas or oceans, down to the seafloor.



USING PROPORTIONS WHEN DIVING

Scuba divers know that the deeper the dive, the greater the pressurea direct proportion. Yet the deeper the dive, the less time they can safely stay underwater to avoid "the bends" an inverse proportion.


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Nautical Archaeology

Nautical archaeology

Nautical archaeology (pronounced NAW-tih-kul ar-kee-OL-low-jee) is the science of finding, collecting, preserving, and studying human objects that have become lost or buried under water. It is a fairly modern field of study since it depends primarily on having the technology both to locate submerged objects and to be able to remain underwater for some time to do real work. Whether it is conducted in freshwater or in the sea, and whether it finds sunken ships, submerged cities, or things deliberately thrown into the ocean, nautical archaeology is but another way of exploring and learning more about the human past.

Archaeology done underwater

Although some use the words nautical archaeology to mean a specialized branch of underwater archaeology, which is concerned only with ships and the history of seafaring, most consider the term to mean the same as the words underwater archaeology, undersea archaeology, marine archaeology, or maritime archaeology. All of these interchangeable terms mean simply that it is the study of archaeology being done underwater. Archaeology is the scientific study of the artifacts or the physical remains of past human cultures. By studying objects that ancient people have made, we can learn more about how they lived and even what they were like. In fact, studying ancient artifacts is the only way to learn anything about human societies that existed long before the invention of writing. For those later societies that are studied, being able to examine the actual objects made and used by those people not only adds to the written records they left behind, but allows us to get much closer to the reality of what life was like when they lived. Also, if we pay close attention to how the objects were made and used and what were their purposes, we begin to get a much more realistic picture of what these people were really like.

Underwater repositories of human history

Ever since the beginning of civilization and mankind's ability to move over water, the bottoms of nearly all oceans, lakes, and rivers became the final resting place for whatever those vessels were carrying. Once real trade began, it is safe to say that nearly every object made by humans was probably transported over water at some point in time, and just as frequent were mishaps and accidents of all sorts that resulted in those objects sinking to the bottom. Vessels of all typesfrom canoes, rafts, and barges to seafaring shipsbecame victims of every imaginable disaster. Vessels were sunk by severe weather and fierce storms, by construction defects and collisions, by robbery and warfare, by hidden sandbars and jagged reefs, and probably just as often by simple human error and misjudgment. Some cultures may have thrown things into the sea, perhaps to appease an angry god, while others conducted burials at sea. Finally, entire coastal cities are known to have been totally and permanently submerged as the result of an earthquake. All of these and more resulted in the creation of what might be called underwater repositories of human history.

Destroyed or preserved

Not all of these objects survived either the trip down to, or their stay on, the bottom. Their fate depended on where they landed. If an object sank near the seashore, chances are that it would have been broken by wave action. Even if it sank far below the action of waves, it still might not have survived, since it could have landed on submerged rocks and been broken by ocean currents. Sometimes underwater creatures, like snails and worms, burrowed inside and ate them, while others like coral or barnacles may have cemented themselves on the surface of an object and rotted or rusted away its inside.

Words to Know

Archaeology: The scientific study of material remains, such as fossils and relics, of past societies.

Artifact: In archaeology, any human-made item that relates to the culture under study.

Scuba: A portable device including one or more tanks of compressed air used by divers to breathe underwater.

However, besides hiding or destroying objects, the sea can also preserve them. Objects that sank into deep layers of mud were hidden from sight but were usually well-preserved. Often the saltiness of the water discouraged the growth of bacteria that can rot organic materials like wood. Other times, metals were buried in mud that allowed little or no air to get in, thus preventing them from corroding. It is not unusual, therefore, to discover ancient ships that have been deeply buried whose partsfrom their wood boards to their ropes, masts, and nailsand cargos of pottery or weapons or even leather and cloth have been perfectly preserved.

Underwater technology

People have been finding submerged objects of all sorts for as long as they have been able to get and stay below the surface. Early sponge divers were probably among the first, since they were expert at holding their breath and working underwater. Although primitive diving suits were used as early the sixteenth century, it was not until the nineteenth century that helmet diving gear was invented that allowed a person to "walk" on the bottom and explore it. Connected to the surface by an air hose and wearing what must have felt like a heavy suit of armor, the diver was clumsy and very slow and could never get very much done during his short trips to the bottom.

Nautical archaeology did not become a feasible pursuit until the invention in 1943 of an underwater breathing device by French naval officer and ocean explorer Jacques-Yves Cousteau (19101997) and Emile Gagnan, also of France. Called scuba gear for self-contained underwater breathing apparatus (and trademarked under the name Aqua-Lung), it revolutionized diving and allowed a person to swim freely down to about 180 feet (55 meters) wearing only a container of highly compressed air on his back. It was later improved by using a mixture of oxygen and helium rather than normal air (which is oxygen and nitrogen), and this allowed a diver to descend as deep as 1,640 feet (500 meters). Until this invention, actual underwater exploring had been done mostly by professional divers who were directed by archaeologists. With this new scuba gear, however, archaeologists could explore themselves. From this, modern nautical archaeology was born.

Improving technology

The first underwater site to be excavated (exposed by digging) by diving archaeologists was a Bronze Age (c. 1200 b.c.) ship wrecked off the coast of Turkey. It was explored by Americans Peter Throckmorton and George Bass, who became pioneers in the field. They and all others to follow used nearly the same techniques that archaeologists on land always

follow, although working underwater made their job one of the most difficult and demanding of all scientific activities.

Today, nautical archaeologists employ a variety of technologies and techniques that make their job easier. They sometimes use aerial photographs to get detailed pictures of shallow, clear water. They often use metal detectors or a magnetometer (pronounced mag-neh-TAH-meh-ter) to find metal objects. Sonar devices send waves of sound through the water that bounce off solid objects and return as echoes, which are recorded by electronic equipment. Underwater cameras are regularly used, as are remotely operated vehicles that can penetrate to extreme depths where severe cold, high pressure, and total darkness would prevent humans from going. Finally, before excavating, nautical archaeologists carefully study and map a site (the location of a deposit or a wreck). This is probably the most time-consuming part of the job, as each artifact is drawn on a map to note its exact location. Only after the entire site is mapped will removal begin. This is done using several different methods. Balloons or air bags are often used to raise large or heavy objects. Vacuum tubes called airlifts are used to suck up smaller objects or pieces. Certain objects brought to the surface must be properly cared for or they can fall apart in a matter of days. Nautical archaeologists must therefore have ready a thorough plan to preserve these fragile objects once they are raised.

Nautical archaeology is still a young science, but it has achieved some spectacular results. Entire ships, like the Swedish warship Vasa, which sank in 1628, and the even older English ship Mary Rose, have been raised. The Vasa took five years to raise; the Mary Rose took nearly twice that long. The wreck of the Titanic, which sunk in 1912 after hitting an iceberg, has been thoroughly explored ever since it was first located by a remote-control submarine in 1985. As technology improves, so does the ability of nautical archaeologists to explore the hidden museum under the sea that holds more clues about our human past.

[See also Archaeology ]

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