Magnetometer

A magnetometer is a sensor that measures magnetic fields, and in defense it is used to detect the magnetic disturbances that large metal objects create, finding things that are hard to detect by other means. A submarine, a naval mine, a buried weapon, all contain metal that subtly disturbs the earth's magnetic field, and a sensitive magnetometer can detect these disturbances, the magnetic anomalies that reveal the presence of the metal object, so magnetometers provide a way to find metal objects, particularly submerged or buried ones, that other sensors struggle with. This magnetic anomaly detection is a specialized but valuable capability, used most notably in anti-submarine warfare to detect submerged submarines and in the detection of mines and other buried metal, exploiting the magnetic signature of metal to find objects that are otherwise hard to detect.

How magnetic detection works and where it is used

Magnetic anomaly detection works by sensing the disturbance that a large metal object creates in the earth's magnetic field, allowing the detection of the object through its magnetic signature. The earth has a magnetic field, and a large metal object, like a submarine, disturbs this field locally, creating a magnetic anomaly, a small deviation in the field caused by the metal, and a sensitive magnetometer can detect this anomaly, sensing the presence of the metal object through the disturbance it creates, even when the object itself is hidden, submerged, or buried. This capability is used most prominently in anti-submarine warfare, where magnetic anomaly detection is a means of detecting submerged submarines, since a submarine, a large metal object underwater, creates a magnetic anomaly that a magnetometer can detect, providing a way to find submarines that complements the acoustic detection of sonar, and anti-submarine aircraft have carried magnetic anomaly detectors, often in a boom extending from the aircraft to keep the sensor away from the aircraft's own magnetic influence, using them to detect the magnetic signature of a submarine as the aircraft passes over it. Magnetic detection is also used to find mines and other buried or submerged metal, since these too create magnetic anomalies that a magnetometer can detect, so magnetometers help in the detection of naval mines, buried weapons and ordnance, and other metal objects, exploiting their magnetic signatures to find them. The value of magnetic detection is that it can find metal objects that other sensors struggle with, particularly submerged submarines and buried metal, providing a means of detection that complements the other sensors, filling gaps that acoustic, radar, and other detection leave, so magnetometers contribute to the detection of the hard-to-find metal objects, submarines and mines especially, that their magnetic signatures reveal.

Magnetic anomaly detection has significant limitations that confine it to particular uses, principally its short range, which requires the sensor to be close to the object it detects. The magnetic anomaly that an object creates weakens rapidly with distance, so a magnetometer must be relatively close to the object to detect it, giving magnetic detection a short range compared to other sensors, which limits its use to situations where the sensor can get close to the object, and which means magnetic detection is more a means of confirming and localizing an object that is already roughly located than of searching a large area, since the short range makes searching a wide area with magnetic detection slow and difficult. In anti-submarine warfare, this short range means that magnetic anomaly detection is typically used to confirm and pinpoint a submarine whose approximate location is already known, as the aircraft flies over the suspected position to detect the magnetic anomaly, rather than to search a large area for a submarine, since the short range makes area search impractical, so magnetic detection complements the longer-range acoustic detection that finds and tracks the submarine over a wider area, with the magnetometer used to confirm and localize once the submarine is roughly located. This limitation, the short range, is the main constraint on magnetic detection, confining it to the confirmation and localization of objects that are already roughly located rather than the wide-area search that longer-range sensors provide, so magnetometers are used as a complementary sensor for their specific value in detecting metal objects at short range rather than as a primary means of searching for them. Despite this limitation, magnetic detection retains its value for the specific capability it provides, detecting the magnetic signatures of metal objects, particularly submerged submarines and buried metal, that other sensors struggle with, a capability that complements the other sensors and contributes to the detection of the hard-to-find metal objects, within the constraint of the short range that confines it to close-range detection and confirmation.

Magnetometers in the broader sensing picture

Magnetometers are one specialized sensor among the many that militaries use to detect and find objects, valued for their specific capability to detect metal by its magnetic signature and used alongside the other sensors in the overall effort to find what needs to be found. In anti-submarine warfare, the magnetometer is one of several sensors used to find submarines, complementing the acoustic detection of sonar and sonobuoys, the primary means of detecting submarines over a wide area, with the magnetometer providing the short-range detection and confirmation of the submarine's magnetic signature, so the sensors work together, the acoustic sensors searching and tracking over a wide area and the magnetometer confirming and localizing at short range, combining their capabilities in the hunt for submarines. In mine detection and the detection of buried metal, magnetometers similarly work alongside other sensors and means, contributing their specific capability to detect the magnetic signatures of the metal objects, so that magnetometers are part of the broader sensing effort, used for their specific value in the detection of metal by its magnetic signature. The development of magnetic detection continues, with more sensitive magnetometers and better techniques for detecting and interpreting magnetic anomalies, seeking to improve the capability within its inherent constraints, and magnetometers remain a valuable specialized sensor for the detection of metal objects, particularly submerged submarines and buried metal, that their magnetic signatures reveal. So magnetometers occupy a specific place in the sensing capabilities of militaries, valued for detecting the magnetic signatures of metal objects that other sensors struggle with, used alongside the other sensors in the overall detection effort, and contributing their specific short-range capability to the detection of the hard-to-find metal objects, submarines and mines especially, that their magnetic signatures reveal, a specialized but valuable sensing capability within the broader array of sensors that militaries use to find what they need to find, exploiting the magnetic disturbances that metal objects create to detect them when other means of detection fall short.

Why not just use sonar to find submarines instead of magnetometers?

Sonar is the primary means of finding submarines, and magnetometers complement rather than replace it, since each has different strengths and the magnetometer's magnetic detection adds a capability that sonar lacks, particularly a means of confirming and localizing a submarine independent of the acoustic detection that sonar provides. Sonar detects submarines acoustically, by the sound they make or by the reflection of sound off them, and it is the primary means of detecting submarines because it can search and track over a wide area, detecting submarines at longer ranges than magnetic detection, so sonar is the main sensor for finding and tracking submarines over the wide areas of the ocean where they must be found. But magnetic detection adds a complementary capability, since it detects the submarine's magnetic signature independent of the acoustic detection, providing a different means of confirming and localizing a submarine that does not depend on the acoustic conditions that can complicate sonar, so the magnetometer can confirm a submarine's presence and pinpoint its location through its magnetic anomaly, adding certainty and precision to the detection, particularly useful for confirming and localizing a submarine whose approximate position sonar has established. The two sensors thus work together, sonar searching and tracking over the wide area and the magnetometer confirming and localizing at short range, combining the acoustic and magnetic detection to find and pinpoint submarines more effectively than either alone, since the magnetic detection adds a confirmation independent of the acoustic detection that can be valuable when the acoustic conditions are difficult or when independent confirmation is wanted. So magnetometers are used alongside sonar rather than instead of it, complementing the primary acoustic detection with the additional capability of magnetic detection, which adds an independent means of confirming and localizing submarines, particularly valuable for the confirmation and precise localization that the magnetic signature provides, so the answer to why not just use sonar is that sonar is indeed the primary means but that magnetometers add a valuable complementary capability, the independent magnetic detection that confirms and localizes submarines, enhancing the overall ability to find and pinpoint them beyond what sonar alone provides, which is why both sensors are used together in the hunt for submarines, each contributing its strengths to the difficult problem of finding the submarines that are among the hardest targets to detect.