Two Antenna GPS Attitude and Integer Ambiguity Resolution for Aircraft Applications

Roger Hayward, Adam Marchick, J. David Powell

Abstract:	GPS has been used successfully for attitude determination in aircraft applications. Ultra short baselines (less than one meter between antennas) have been shown to provide the extremely high level of integrity required in aviation applications. Three antenna, two baseline, ultra short baseline systems have been shown to provide sub degree accuracy in pitch, roll and yaw when coupled with automotive grade solid state rate sensors. An alternative method of attitude determination, using only one baseline oriented along the longitudinal axis of the aircraft to determine all three Euler angles is presented. This approach uses the same method to determine yaw as used in the two baseline configuration. Roll and pitch are determined by using knowledge about acceleration in two reference frames. The key advantage of the single baseline attitude approach is that it provides for increased roll accuracy for cases in which there is limited space on the top of the fuselage. In a three antenna configuration, the accuracy of the roll angle is directly related to the lateral distance between the two antennas. This single baseline attitude method is also ideally suited as a backup mode for a more traditional two baseline attitude system. If one baseline or receiver was to fail, the system could still provide pitch, roll and yaw measurements. The approach can also be used as a further integrity check. Both the single baseline and two baseline attitude computations could be accomplished in parallel and the results compared in real time. An integrity analysis for integer ambiguity resolution is presented. Both the integrity and availability of the integer resolution process are evaluated for the single baseline method and the two baseline attitude determination method. A systematic process for bounding the integrity of the solution for both methods is also presented. The results are based on data taken from multiple flight tests with phase measurements and inertial attitude values. This allows the integer computation to be done at each epoch as opposed to only several times in a given flight. The large number of epochs tested (tens of thousands) leads to a high level of precision in the predicted integrity and availability for the integer search method.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	155 - 164
Cite this article:	Hayward, Roger, Marchick, Adam, Powell, J. David, "Two Antenna GPS Attitude and Integer Ambiguity Resolution for Aircraft Applications," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 155-164.
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