Did You Know?
1822 Daniel Colloden used an underwater bell to find the calculations of
the speed of sound underwater in Switzerland.
Sonar is a system that detects sound wave echoes to measure distances of
submerged objects and relay communication. Sonar is useful in submarine and mine
detection, commercial fishing, diving safety and communication at sea. The sonar
systems send sound waves and listens for a returning echo before relaying data to
a human operator or a computer monitor.
1906 Lewis Nixon invented the first sonar type listening device to detect
1915 Paul Langevin invented first device for submarines.
1918 Both Britain and the U.S. had active sonar systems.
Americans coined sonar as an acronym of sorts for SOund, NAvigation,
and Ranging because of its use in In World War II. Similarly, the British use ASDICS because
it stands for Anti-Submarine Detection Investigation Committee Survey. There have
also been less specific titles assigned to sonar such as echo sounders, depth finders,
rapid-scanning sonar, side-scan sonar, and WPESS (within-pulse electronic sector-scanning)
There are two different kinds of sonar: active and passive.
- Active sonar sends a pulse of sound also known as a “ping” and then listens for the reflection.
For long distances, the active sonar uses lower frequencies. The receivers measure
the distance of an object by taking the time from emission of the pulse to the reception
- Passive sonar listens without transmitting anything. This sonar is usually used
for military purposes. The systems usually have large sonic database to identify
classes of ships, actions, and particular ships.
A fish finder or a depth sounder is one of the simplest sonar devices. They send out a narrowly focused
pulse. The information that it transmutes determines the distance and the objects
density. These devices are used to locate fish, to determine sea-floor depth, and
More sophisticated devices employ side-scan sonar
. They are encased in a torpedo-shaped tube
and are “towed” behind and below the boat. Everything in a 180-degree range is the field
of view. The more sound pulses that are received from an object, the stronger
they return, and the clearer the sound picture is. Usually rough surfaces return strong
echoes while smooth surfaces return little energy. The side-scan sonar devices are
very detailed, 3-D pictures of objects through computer analysis of the returning
sound waves. These devices are used in many different ways such as to map features,
including hills and valleys on the ocean floor, locating submarines, mines, and
shipwrecks, and to inspect pipelines, cables, and bridge foundations.
Transponders are a form of wireless communication. They
monitor or control a device by detecting and responding to a signal. Transponders
can also be either passive or active.
- Passive transponders allow a computer to identify an object
and must be used in conjunction with an active sensor to decode and transmit its
data. They can be very small and their information can be detected at a distance
of several feet. An example would be the magnetic strip on a credit card.
- Simple active transponders are used in location, identification, and
navigation systems for commercial and private aircraft. With input and output frequencies
determined beforehand, radio frequency transponders can be tracked and constantly
monitored over distances of thousands of miles. Very sophisticated active transponders can operate on an interplanetry scale and
are commonly used in communications satellites and on board space vehicles.
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