The Reduction of Airborne Magnetic Noise Via GPS

L. Bobb, W. Gelatka, D. DePersia, A. Salik, and S. Swyers

Abstract:	The objective of this study was to demonstrate that magnetic noises which are position related can be removed from an airborne total field magnetometer system. The system contains a helium-4 magnetometer sensor with a sensitivity of 0.003 nanoteslas (nT) in the magnetic anomaly detection (MAD) band of 0.05 to 0.5 Hz. This sensor is housed in the tip of the tailboom of a U. S. Navy P-3 Orion aircraft; this 20 foot separation of the sensor from the main fuselage helps to remove some of the platform noise which arises from the permanent, induced and eddy current moments of the platform. The GPS receiving antenna is also located on this tailboom. The antenna is connected to a single frequency all-in- view narrow correlator spacing C/A code Ll receiver. The data for this study was acquired at altitudes from 500 feet to 20,000 feet off the coast of North Carolina in the Oak Bravo test area near the latitude and longitude of 35”N and 7l”W. The magnetic noises which are position (or track) related come from the magnetic geology, the magnetic field of the earth, and the gradients in these fields. The platform magnetic noise is reduced by using the total magnetic field value and the direction cosines in a platform noise model. These parameters may be determined by the GPS and the inertial navigation system (INS). The magnetic gradient noise arises in several ways. The horizontal gradient is approximately 0.003 nT/m and the vertical gradient is approximately 0.030 nT/m. These values are higher in high magnetic geology. The horizontal gradient noise arises from aircraft track changes from a straight line and from horizontal buffeting. The vertical gradient noise comes from vertical buffeting in the vertical gradient field. Small buffets (-O.lm) give rise to magnetic noise comparable to the sensor sensitivity. The magnetic geology noise was reduced by utilizing a GEODAS map of the geologic field and the GPS to provide position on the map. The frequency of the geology noise was in general below the MAD band; however, the principle of MAD band geologic noise reduction by utilizing a map and the GPS was demonstrated.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	443 - 447
Cite this article:	Bobb, L., Gelatka, W., DePersia, D., Salik, A., Swyers, S., "The Reduction of Airborne Magnetic Noise Via GPS," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 443-447.
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