Benefits of Low-Cost INS/GPS to Augment Land Navigation

Michael K. Martin, Bruce C. Detterich, Thomas W. DeVries

Abstract:	A tactical grade inertial measurement unit (IMU) has potential to provide significant benefits in land navigation performance. When used as a tightly coupled inertial navigation system (INS) and Global Positioning System (GPS) navigator, the INS enables (via velocity aiding) enhanced GPS anti-jam (A-J) performance, and so delays the transition to a “GPS-lost” navigation mode. For relatively brief GPS outage periods, a tactical-grade INS serves to navigate with acceptable accuracy through the outage. For longer outages, INS/GPS data obtained before the outage enables on-the-fly calibration of dead reckoning (DR) sensors (such as a vehicle odometer and compass), which in turn enables better DR navigation (and pointing) performance than is obtainable with unaided DR. This type of system provides performance (and cost) midway between systems employing expensive navigation grade INS systems and those that use no INS at all. There are military vehicles for which improved GPS A-J, DR navigation, and (gun or sensor) pointing capability would be of interest, given sufficiently low system cost. The objective of the effort reported in this paper was to quantify the DR navigation performance enhancement available by fusing data from a low cost INS/GPS with auxiliary sensor data. Van testing was conducted incorporating (1) a 10-channel P(Y) code M-MIGITSä [modular miniature integrated GPS/INS tactical system], (2) a three axis magnetometer, and (3) a conventional odometer. The data showed that the magnetometer and odometer, after calibration via use of INS/GPS, could provide a land navigation circular error probable (CEP) accuracy of 0.25% of distance traveled following loss of GPS. INS/GPS data was used to calibrate the odometer to an accuracy of better than 0.2% under these circumstances. Magnetic heading bias/variation was calibrated to an accuracy of better than 0.1%. Pendulous/self leveling compasses were also tested, and showed very noisy heading outputs during vehicle motion/acceleration. This error can be smoothed and reduced with the aid of the INS, but the strap-down three-axis magnetometer is preferred for higher accuracy. Use of P(Y) code GPS or differential GPS was also preferred (versus C/A code) because of the higher resultant DR accuracy. The conclusion from this effort is that low-cost off-the-shelf INS/GPS systems in conjunction with auxiliary sensors can be used to enable (1) improved GPS anti-jam, (2) significantly improved DR navigation when GPS is lost, and (3) improved pointing performance. The combined benefits of a tactical INS/GPS could provide valuable military utility to land vehicles for which high-cost navigation-grade INS systems are not an affordable option.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1121 - 1132
Cite this article:	Martin, Michael K., Detterich, Bruce C., DeVries, Thomas W., "Benefits of Low-Cost INS/GPS to Augment Land Navigation," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1121-1132.
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