Toward GPS-denied Navigation Utilizing Back Projection-based Synthetic Aperture Radar Imagery

Randall S. Christensen, Jacob Gunther, David Long

Peer Reviewed

Abstract:	This paper investigates the utilization of synthetic aperture radar (SAR) images formed from the back-projection algorithm (BPA) for absolute GPS-denied navigation from an aerial platform. A 6DOF aircraft navigation and radar simulation is de- veloped to analyze the sensitivity of small BPA-SAR image chips to varying levels of position, velocity, and attitude errors at the beginning of the synthetic aperture. As part of the developed simulation, an inertial navigation system (INS) is defined, utilizing a north, east, down, flat-earth mechanization of the navigation equations. A corresponding extended Kalman filter (EKF) is developed to process position measurements during periods of GPS availability. The BPA is presented as a method for generating small SAR image chips at the location of a point reflector in the presence of radar noise and background clutter. The normalized cross correlation (NCC) is used to quantify the similarity of the SAR image chip with an error-free SAR image chip of the same location. Simulation results demonstrate that the appearance of the SAR image chip is sensitive to all initial navigation errors considered in this study, with varying levels of image shifting and blurring. Ambiguity exists, however, in the attribution of these effects to the corresponding navigation error. In all cases, the NCC approaches one as navigation errors approach zero, suggesting that maximization of the NCC is a feasible approach to determining navigation errors.
Published in:	Proceedings of the ION 2019 Pacific PNT Meeting April 8 - 11, 2019 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	108 - 119
Cite this article:	Christensen, Randall S., Gunther, Jacob, Long, David, "Toward GPS-denied Navigation Utilizing Back Projection-based Synthetic Aperture Radar Imagery," Proceedings of the ION 2019 Pacific PNT Meeting, Honolulu, Hawaii, April 2019, pp. 108-119. https://doi.org/10.33012/2019.16797
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