A Kalman Filter Mechanization for the Baro-Inertial Vertical Channel

J. Stanley Ausman

Abstract:	Traditionally, the vertical channel in an inertial system has been stabilized with barometric altitude feedback loops employing conventional second- or third-order feedback with constant, time varying, or trajectory dependent gains. With the increasing availability of GPS for altitude updating. it becomes more attractive to go to a Kalman filter mechanization of the vertical channel. Previous Kalman filter mechanizations have used either four or five state variables which are: inertial altitude error, vertical velocity error, vertical acceleration error. baromeaic bias error, and sometimes barometric scale factor error for the fifth state. In these mechanizations, both the barometric bias and scale factor errors are assumed to be altitude independent. These mechanizations have been reasonably successful. but can be further improved through better modeling of the barometric scale factor error. In the actual atmosphere. scale factor deviations (errors) from the Standard Atmosphere tend to reverse sign at about 26,C00-ft altitude. Hence, a more realistic error model for scale factor error is one which varies linearly with altitude, passing through zero at 26,OCO ft. This paper develops a Kalman filter vertical channel mechanization based upon this linear error model for scale factor variation with altitude. Simulations of the resulting vertical channel performance show it to be much superior to either the conventional mechanizations or to Kalman filter mechanizations with altitude independent bar0 scale factor error models.
Published in:	Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991) June 10 - 12, 1991 Williamsburg Hilton and National Conference Center Williamsburg, VA
Pages:	153 - 159
Cite this article:	Ausman, J. Stanley, "A Kalman Filter Mechanization for the Baro-Inertial Vertical Channel," Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991), Williamsburg, VA, June 1991, pp. 153-159.
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