Magnetic anomaly detector
（重定向自Magnetic anomaly detection）
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![The SH-60B Seahawk helicopter carries a yellow and red towed MAD array known as a ‘MAD bird’, seen on the aft fuselage](/Images/godic/202501/25/SH-60B_Seahawk4518.jpg")
A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the Earth's magnetic field. The term refers specifically to magnetometers used by military forces to detect submarines (a mass of ferromagnetic material creates a detectable disturbance in the magnetic field); military MAD equipment is a descendent of geomagnetic survey or aeromagnetic survey instruments used to search for minerals by detecting their disturbance of the normal earth-field.