Undersea magnetic noise reduction

This paper deals with oceanic natural magnetic noise. Many records were achieved in the Mediterranean and in the Atlantic Ocean with drifting magnetometric buoys, using nuclear magnetic resonance (NMR) sensors. The aim of the survey was to cancel noises recorded by buoys (geomagnetic, geologic, swell, gyromagnetic, anisotropic noises) in order to quantify the residual noise for detection purposes. Sea tests were conducted in many configurations: different sea conditions, varied geomagnetic activities, different buoys pattern geometries and distances between two buoys, drifting buoys and moored buoys. A processing system design to subtract as much noise as possible was applied to these records. It comprises a bandpass filter, an undersampler and a noise cancellation filter. The numerous sea tests gave a good knowledge of the magnetic oceanic environment and a quantification of the noise level after processing