Improving Celestial AltPNT Availability and Performance: Full Sky Polarization Tracking Algorithms for Challenging Conditions

Laura M. Eshelman and Adam Smith

Peer Reviewed

Abstract:	Inspired by nature, the Sky Position and Azimuth Sensing System (SkyPASS) utilizes the polarization patterns of the sky to achieve highly accurate heading determination (0.1125º RMS) in conditions where traditional sun and star sensors fail to operate. By tracking sky polarization, SkyPASS offers improved performance under cloud cover, beneath canopies, in urban environments, and during civil and nautical twilight, as well as at sunrise and sunset. Polarization, a fundamental property of light, enhances conventional sensing methods that typically measure brightness and color. The Rayleigh scattering of light creates a distinct sky polarization pattern that can be leveraged for navigation. Polaris has recently developed advanced full-image algorithms that enhance the sensor's capability and availability, particularly when the sun is high in the sky and obscured by clouds and when the sensor is physically tilted beyond 10º. These algorithms enable the determination of sun azimuth and elevation from a sky polarization image, regardless of sensor orientation, facilitating absolute position capability. A polarimeter equipped with these full-sky image algorithms can identify regions of interest (ROIs) characterized by high degrees of linear polarization (DoLP), resulting in more accurate heading and positioning solutions. When blue skies are visible, SkyPASS can reliably produce heading and position data. Additionally, Polaris's clutter rejection algorithms enhance SkyPASS’s performance by filtering out clouds from the data. The results from experimental testing on static platforms in various conditions—including clear, cloudy, and overcast skies—will be presented by Polaris. SkyPASS serves as a valuable complement to visual navigation systems that may have degraded performance over featureless terrains like open water and deserts, as well as inertial sensors that drift when GPS signals are contested. Designed for ease of integration, this plug-and-play sensor is optimized for size, weight, and power (SWaP), with specifications of 0.0762 m3 , 0.5670 kg, and 5 W. Keywords—celestial navigation sensing, ALTPNT, low SWaP
Published in:	2025 IEEE/ION Position, Location and Navigation Symposium (PLANS) April 28 - 1, 2025 Salt Lake Marriott Downtown at City Creek Salt Lake City, UT
Pages:	837 - 844
Cite this article:	Eshelman, Laura M., Smith, Adam, "Improving Celestial AltPNT Availability and Performance: Full Sky Polarization Tracking Algorithms for Challenging Conditions," 2025 IEEE/ION Position, Location and Navigation Symposium (PLANS), Salt Lake City, UT, April 2025, pp. 837-844.
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