Bare-Augmented Integrity Monitoring (BAIM)

Karl L. Kovach and Patricia A. Alexander

Abstract:	With GPS full operational capability just around the corner, system integrity continues to be a major concern for aircraft GPS applications. A variety of techniques to assure GPS integrity have been proposed. These techniques are categorized as either being receiver internal or receiver external. Receiver autonomous integrity monitoring (RAIM) includes the class of techniques that come under the receiver internal category, while GPS integrity channel (GIC) and DGPS are examples of the latter group. This paper presents a variation on the RAIM theme which relies on another sensor on board the aircraft--the barometric (baro) altimeter--as an integrity augmenter. This technique, dubbed baro-augmented integrity monitoring (BAIM), is an example of a “platform-internal” integrity technique. In the BAIM technique, the altitude provided by the baro altimeter provides a redundant measurement which is compared against the vertical component of the GPS- derived aircraft position in space. The principle behind BAIM is that a large GPS error in the vertical direction will indicate a large error in the horizontal direction as well. Comparing the vertical GPS position against the altitude provided by the baro altimeter provides a means to flag potential errors as indicated by a large mismatch between the vertical positions given by the two systems. An algorithm for comparing the baro altimeter measurement against a simple four-satellite GPS position solution to provide this integrity check is described in this paper. Conditions under which this “BAIM algorithm” can meet the integrity requirements given in the Technical Standard Order for Using GPS as Airborne Supplemental Navigation Equipment (TSO- C129) are also discussed.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	555 - 566
Cite this article:	Kovach, Karl L., Alexander, Patricia A., "Bare-Augmented Integrity Monitoring (BAIM)," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 555-566.
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