Analyze the sounds that occur in the ocean is not a simple task. This activity has even been compared to space exploration; the difference is that in space there are several companies and agencies investigating, while the ocean is still pending and subject to some unknown point. Listening underwater work currently focuses on three disciplines: marine biology, geology and geophysics, and military activity.
For this type of underwater research succeed calls are used hydrophones, also known as underwater microphones, which are devices designed to capture and locate sources of sound in water, where its complexity and its wide range of possibilities make their use key for various tasks. Today we will know a little more about them and some of its major holdings.
Hydrophones: Microphones that monitor the seabed
Broadly, a hydrophone is an electro acoustic transducer that converts sound vibrations present as pressure within water, electrical energy, i.e. in human audible spectrum, which are frequencies that can sense relatively easily for understanding and study.
The big difference between a microphone and a hydrophone, is that the former is designed to capture sound vibrations in the air under pressures rarely exceed one atmosphere (atm), while the second will be adapted to different pressures, since do not affect the risk of sounds and damage the device runs.
Although it is designed to “listen” on the water, there are a variety of hydrophones with various formats, capabilities and functions; there is even a technique for making a hydrophone home from earphones and a pair of omnidirectional microphones, as it is a device capable of performing a lot of tasks and functions.
The hydrophone is considered a passive underwater listening system, however, there are some that can also be used as transmitters of sound waves in research on marine life, but the reality is that few companies that make this type because demand is minimal and its cost is much higher.
Many of the transducers used in hydrophones are mainly made of ceramic and coated with a steel wall, but recently transducers quartz crystal thin stuck together by steel plates, which have been obtained are used resonance frequencies above 150 KHz. To this must be added a suitable housing for immersion, depending on the depth and pressure may be aluminum, steel or plastic and even glass.
The hydrophones can have a size ranging from 30 centimeters to two meters, weighing only a few grams to 40 kilograms, here again it depends on the task you want to perform, and some are to eavesdrop just below surface, while the most advanced are designed to withstand pressures to 20,000 meters deep (although so far only have reached up to 11,000 meters). To immerse recommend doing at a maximum speed of five meters per second, this to ensure that the hydrophone not burst by the pressure change.
The most complex part is to extract all the sounds picked up by the hydrophone . One of the latest solutions is the use of flash memory, but this only serves to projects where the device will within 30 days submerged, as if we are witnessing the creation of a large network of hydrophones, then the most viable solution is a fiber optic connection that goes through all devices and reaches a center where all information is stored course this is the most expensive solution and is mainly used in government agencies and for military purposes.
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The ability to listen to each hydrophone depend on the design, but the most powerful can capture sounds to a radius that can reach up to 1.3 kilometers. Its design can be omnidirectional, mainly used for marine, or directional biology, which not only captures sound but also determine the location and distance from the source by triangulation with other hydrophones, and yes, as you may have guessed its use is mostly for military tasks.
Another point that requires attention is the installation of power module of each of the hydrophones. If it is a one – time project, it will integrate a battery that will give the necessary autonomy for the duration of the project; if we are dealing with a network of underwater listening modules will be supported with backup batteries, since the energy comes from the central information using the same wiring as that of the optical fiber.
Now we know some of their most important applications.
Geology and geophysics
Thanks to its capabilities, the hydrophone has become an important tool in the study of energy and earthquakes, as it is able to report unusual geological activity on the seabed, which serves to alert various parts of a possible tsunami and even an earthquake.
The National Oceanic and Atmospheric Administration (NOAA) has installed several hydrophones in strategic areas of the Pacific Ocean, with several active projects that serve to keep track of all the activity that occurs on the seabed; this serves to provide data and forecasts, as well as have control of cyclical events to try to prevent possible disasters.
In this video we can hear part of what we recorded a hydrophone placed near Alaska seconds before the earthquake in Japan occurred in 2011, one of the deadliest in history and led to a huge tsunami. This hydrophone was located about 1440 kilometers from the epicenter and therefore was able to record much of the geological activity when the ground was delayed and compressed, later transformed into seismic energy in the form of tsunami reached.
Studying the behavior of marine fauna and alert of possible changes in the ecosystem, they are a task that begins to take relevance to the hydrophones. Here they are mainly used portable devices but also rely on the same NOAA administered by international organizations or other networks.
The objective is clear, to hear what happens at the bottom of the sea, capturing the sounds of diverse fauna and determine their environment, participation, and even location , that when it comes to protected species which almost always shrines are shipped with the in order to study further the cause of their potential demise.
We have reached the beginning of everything. The first hydrophones were manufactured during World War II by British scientists, American and French, with the aim of locating submarines and icebergs, as after the sinking of the Titanic in 1912 a priority task is to know the location of large structures that could affect the navigation.
The hydrophone is today an essential part of the radars used in submarines and warships, which also led to large and powerful networks listening as SOSUS, a huge chain of posts underwater listening spread over a line from Greenland to the UK via Iceland, known as the GIUK (Greenland-Iceland-United Kingdom) step.
The SOSUS was built in 1949 and its operation was carried out by the United States to detect Soviet submarines, in addition to positions in the GIUK step, settled more in the Atlantic and Pacific Ocean. Over the years, this network has gone through various hands, from private companies to institutions like MIT. Today is operated by Lockheed Martin Corp. who acquired more than 100 million dollars with the aim of offer it for military and geological tasks.
Data emerged recently that India was about to start with the construction of a network similar to listening SOSUS submarine, which would be located in the Indian Ocean and would aim to track the activities of Chinese submarines. An important point of this project is the participation and support of the US and Japan, who are advising India for the construction of this network, as these countries are the most advanced in this kind of development, plus they are very interested what China does.
While India, Japan and the United States come together to counter China’s activities, the country is also preparing what they call the “Great Wall under the sea”, its own network of listening beneath the sea which will be located south of the country, a point strategic where he spends 30% of world trade and will serve to keep track of what other regions close to its territory.