The temperature, salinity and pressure of the

The ocean is the driving force of planet Earth.

It covers about 70% of Earth’s surface and is 97% of the Earth’s water. Oceans produce oxygen, absorb carbon dioxide, regulate temperature, and shelter thousands of species. Although essential to life, the ocean is still a mysterious place because less than 5% of the ocean has been explored. Developing technology, such as, ocean acoustic tomography (OAT) is revealing the wonders of the ocean.  Technical Discussion    Introduced by Walter Munk and Carl Wunsch in 1979, ocean acoustic tomography is a technique for displaying a representation of the ocean using sounds.

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An acoustical approach is used because the ocean is fairly transparent to low- frequency acoustics, allowing sound to travel long distances underwater. Electromagnetic energy, such as light and radar can not be used because saltwater is an electrical conductor, making it opaque to electromagnetic energy. An advantage to acoustics is the use of remote sensing. Information can be gathered without making any physical contact, resulting in no significant biological impact. Applications Ocean acoustic tomography is used in sonar technology and to track global warming.Measuring TemperatureOcean acoustic tomography is mainly used to measure temperatures of the ocean.

The speed of sound, the time it takes for a sound signal to travel between an acoustic source and receiver, depends on the temperature, salinity and pressure of the water.  There is a direct proportion; as the speed of sound in water increases, the temperature, salinity, and pressure increases. However, most of the change in the speed of sound is due to the change in the temperature.Ocean Temperature times maps are drawn from precise measurements of acoustic travel times. Precise measures include the data from many crossing acoustic paths. In the figure above, there are four acoustic sources and five acoustic receives, mapping 20 acoustic paths.

The shaded region is warmer than its surroundings. Since sound travels faster with higher temperatures, the travel times of sound pulses traveling through the warm region will be slightly shorter than the cold regions. Combining all of the travel times, it is possible to distinguish the warm and cold regions of the ocean. Mathematical Discussion     The basic principles in ocean acoustic tomography is related to those used in computed axial tomography.

In a CAT scan, the absorption of x-rays are used to map a slice through the human body by using Beer’s Law.  Beer’s law can be described by Absorption= – ln(I/I0), where I0 is the initial intensity of the X- ray beam when it leaves the source and I is the final intensity of the beam at the receiver.In ocean acoustic tomography, the travel time of sound waves are used to map the temperature in a slice of the ocean. It can be described by The Speed of Sound= -ln (D/D0), where D0 is the initial decibel of the sound when it leaves the acoustic source and D is the final decibel of the sound at the receiver.  Global Warming Global warming is a gradual increase in the overall temperature of the Earth’s atmosphere, including the ocean’s temperature. As ocean temperatures rise, sound travels faster. Since ocean acoustic tomography uses sound to determine the temperature of the ocean, global warming can be tracked by using acoustic tomography. Climate Impacts of Global Warming     Global warming would impact the physical processes of the ocean.

The rise in temperature will result in the increase frequency and severity of storms, a rise in sea level, and changes to ocean currents. An increase of these natural disasters, such as hurricanes and tsunamis will cause damage to the coastal infrastructure, ocean habitats, housing, ect.     Changes to biological and chemical processes will also be observed. The temperature will rise and pH levels will lower. The most significant changes in temperature and pH levels have occured in the surface layers of the ocean, where the base of the marine food web is most active. Phytoplankton and plants, which live at the surface, take in carbon dioxide when they grow. Global warming would decrease the activity of phytoplanktons and plants, increasing the carbon dioxide in the atmosphere.

     Biological changes will also be an effect of global warming. Plankton production will change, resulting in the change of life cycles of their predators, such as fish. Corals, urchins, and many other species located in the surfaces of the ocean will not be able to digest, reproduce, and grow, due to the excess of carbon dioxide. A decline in the productivity at the base of the food chain will affect the food resources for other species. Global warming has serious consequences that affect the Earth as a whole. The risk of more severe storms, changes in the food chain, and the increase of carbon dioxide are all effects of global warming.

 Sonar Technology    SOund NAvigation and Ranging is used to find and identify objects in a body of water. There are two types of sonar technology, active and passive. Active Sonar TechnologyActive sonar transducers send an acoustic signal or sound into the water. An echo is produced if an object is in the path of the sound pulse because the sound bounces off the object. The transducer receives the signals and measures the strength of it. The time the sound took to hit the object can determine how far the object is. The equation, Range= (sound speed x travel time)/ 2 can be used. Passive Sonar Technology     Passive sonar transducers are used to detect noise from objects and animals.

Passive sonar does not emit its own signals and only detects sound waves coming towards it. This is useful if you do not want to be found or you want to concentrate on listening to the ocean. The range of an object cannot be measure with passive sonar technology, unless there are multiple passive listening devices, which would help triangulate the sound source easier.Applications of Sonar Technology     There are many uses for sonar technology, such as defense, bathymetric studies, pipeline inspections, and installations of wind turbines. The military uses sonar systems to detect and track enemy ships, vessels, torpedos, etc. Sonar technology is used to determine the depth of ocean floors. Oil and gas companies use sonar technology for their pipeline inspections to detect spans, rock dump integrity, and possible damage. Seabed and scour protection is checked by sonar technology for possible sites of wind turbines.

ConclusionDay by day, there are new discoveries of the ocean, yet it still remains a place full of wonder.  With the help of ocean acoustic tomography and Beer’s Law, more discoveries are successive. The use of sound measures the temperature of the ocean and is the backbone to sonar technology. In recent years, ocean acoustic tomography has become very important in the discovery of the ocean and time will only make its technology better.

 

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