Detecting Wave-Induced Magnetic Signals with an Airborne Magnetometer


  1. Nelson, J.B.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN)
"Swell noise" is a common phenomenon observed by Magnetic Anomaly Detection (MAD) operators flying at low altitudes during anti-submarine patrols, and it has been reported by aeromagnetic survey companies during low-altitude offshore surveys the magnetic fields are generated from electrical currents induced in the conducting seawater by the vertical motion of the water particles, in the presence of the Earth's magnetic field. Most MAD operators simply fly higher to reduce swell noise. However, next-generation military MAD systems have significantly more signal-processing capability than do earlier systems and it is conceivable that instead of reducing the swell noise by flying higher, and thereby also reducing the amlitude of the submarine's MAD signature, it may be possible to measure the wave parameters (amplitude, frequency, and direction), and relay that information to the aircraft in real time. Then from the known aircraft parameters (altitude, heading, speed and position relative to the wave sensor), it may be possible to model the wave-induced noise and remove it from the raw MAD signal. This concept was tested by flying an aeromagnetic system near a directional wavebuoy in October 2002. Post-processing was used to eliminate other sources of magnetic noise and focus on only the frequency band where wave-induced noise was expected. Forward modeling of the wave-induced magnetic fields, based on the wave characteristics measured with the buoy and aircraft flight parameter

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Sea swells;Wave-induced magnetic fields;Swell noise
Report Number
DRDC-ATLANTIC-TM-2002-209 — Technical Memorandum
Date of publication
01 Dec 2002
Number of Pages

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