Magnetic anomaly detector
Overview
 
A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

. The term refers specifically to magnetometer
Magnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

s used by military forces to detect submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s (a mass of ferromagnetic material creates a detectable disturbance in the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

); the military MAD gear is a descendent of geomagnetic survey
Geological survey
The term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information....

 instruments used to search for mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s by the disturbance of the normal earth-field.
Geoexploration by measuring and studying variations in the Earth's magnetic field has been conducted by scientists since 1843.
Encyclopedia
A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

. The term refers specifically to magnetometer
Magnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

s used by military forces to detect submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s (a mass of ferromagnetic material creates a detectable disturbance in the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

); the military MAD gear is a descendent of geomagnetic survey
Geological survey
The term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information....

 instruments used to search for mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s by the disturbance of the normal earth-field.

History

Geoexploration by measuring and studying variations in the Earth's magnetic field has been conducted by scientists since 1843. The first uses of magnetometers were for the location of ore deposits. Thalen's 'The Examination of Iron Ore Deposits by Magnetic Measurements', published in 1879, was the first scientific treatise describing this practical use.

Magnetic anomaly detectors employed to detect submarines during World War II harnessed the fluxgate magnetometer, an inexpensive and easy to use technology developed in the 1930s by Victor Vacquier
Victor Vacquier
Victor Vacquier, Sr. was a professor of geophysics at the Scripps Institution of Oceanography at the University of California, San Diego.Vacquier was born in St. Petersburg, Russia...

 of Gulf Oil
Gulf Oil
Gulf Oil was a major global oil company from the 1900s to the 1980s. The eighth-largest American manufacturing company in 1941 and the ninth-largest in 1979, Gulf Oil was one of the so-called Seven Sisters oil companies...

 for finding ore deposits. MAD gear was used by both Japanese and U.S. anti-submarine forces, either towed by ship or mounted in aircraft to detect shallow submerged enemy submarines. The Japanese called the technology jikitanchiki(磁気探知機, "Magnetic Detector"). After the war, the U.S. Navy continued to develop MAD gear as a parallel development with sonar detection technologies.

Satellite, near-surface and oceanic data from detectors was used to create the World Digital Magnetic Anomaly Map published by the Commission for the Geological Map of the World (CGMW) in July 2007.

Operation

To reduce interference from electrical equipment or metal in the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

 of the aircraft, the MAD sensor is placed at the end of a boom or a towed aerodynamic device. Even so, the submarine must be very near the aircraft's position and close to the sea surface for detection of the change or anomaly. The size of the submarine and its hull composition determine the detection range. MAD devices are usually mounted on aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

.

Function

There is some misunderstanding of the mechanism of detection of submarines in water using the MAD boom system. Magnetic moment
Magnetic moment
The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it...

 displacement is ostensibly the main disturbance, yet submarines are detectable even when oriented parallel to the Earth's magnetic field, despite construction with non-ferromagnetic hulls. For example, the Soviet-Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n Alfa class submarine
Alfa class submarine
The Soviet Union/Russian Navy Project 705 was a class of hunter/killer nuclear powered submarines. The class is also known by the NATO reporting name of Alfa...

, whose hull is constructed out of titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 to give dramatic submerged performance and protection from detection by MAD sensors, is still detectable.

This is due in part to the fact that even submarines with titanium hull will still have a substantial content of ferromagnetic materials as the nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

, steam turbines, auxiliary diesel engines and numerous other systems will be manufactured from steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 and nickel alloys.

Other uses

For geomagnetic survey work the detector can be mounted on a long probe in front of the aircraft or be a towed device. A chart is produced that geologists can study to determine the location and extent of mineral deposits.

During the Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 the original AC-130A Spectre gunships and the A-6C Intruder
A-6 Intruder
The Grumman A-6 Intruder was an American, twin jet-engine, mid-wing attack aircraft built by Grumman Aerospace. In service with the U.S. Navy and U.S. Marine Corps between 1963 and 1997, the Intruder was designed as an all-weather medium attack aircraft to replace the piston-engined A-1 Skyraider...

 employed the "Pave Mace"/"Black Crow" magnetic anomaly detection system to detect truck ignition coil
Ignition coil
An ignition coil is an induction coil in an automobile's ignition system which transforms the battery's 12 volts to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel...

s in vehicles hidden under heavy jungle canopies. When the electric current flowing through such a coil changes it produces a magnetic flux, which is, in simplest terms, a change in the magnetic field over a given area. In particular, when the trucks were turned on the current flowing through the coils went from zero to some maximum, producing a large and easily detectable flux.
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