Session P4: PTTI Afternoon Tutorials


Date: Wednesday, January 26, 2022
Time: 1:30 p.m. - 4:55 p.m.

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Kalman Filtering and its Use in Clock Estimation

1:30 p.m. – 2:30 p.m.

The prevalence of sequential estimation in navigation has increased over the past several years. This tutorial introduces the audience to the Kalman filter (KF), the most common sequential estimator in use today, with emphasis on timing applications. The first part of the tutorial gives a general treatment of where the KF comes from and how to use it for time estimation. We will discuss measurement and state dynamic models, how to develop stochastic error models, and the use of covariance analysis for performance prediction and filter design. The second part of the tutorial covers intermediate topics like filter initialization and observability, focusing on their implications for estimating time from an ensemble of clocks. The last section highlights current research related to Kalman filters, including clock drift monitoring for fault detection and new approaches to correlated noise modeling. Numerous examples will be used throughout the tutorial to solidify concepts.

Dr. Steven Langel, Senior Technical Staff, The MITRE Corporation
Dr. Steven Langel is a senior technical staff member at The MITRE Corporation. He leads efforts designing multisensor navigation systems and is developing new techniques to improve Kalman filter robustness.


Two-way Laser Links and Optical Clocks for Space-Time Referencing

2:35 p.m. – 3:35 p.m.

An advanced atomic clock in a well-defined orbit, combined with laser links between ground and space could serve as a Space-Time Reference frame that can provide time-transfer uncertainties of < 1 ps, range uncertainties of < 1 mm worldwide. It would enable new capabilities of high-speed data transfer with PNT referencing, secure communications, and additional atmospheric science. Potential applications include worldwide synchronization of time scales (e.g. optical clocks at national standards labs), high accuracy geodetic referencing, and perhaps added value in characterizing GNSS atomic frequency references and orbits without ionospheric uncertainties. Worldwide several new atomic clocks are being studied/developed for space and might sever in this role. We have analyzed a model system with particular focus on achievable performance of time-transfer, precise orbit determination, and ranging for two-way laser links between ground and space and addressing various limitations due to atmospheric turbulence, scintillation, beam wonder and optical group delay.

Dr. Leo Hollberg, Physics Department, Stanford University
Professor Physics (research) Stanford University. Previously CTO at AOSense, and 20+ years at NIST. PhD University of Colorado and postdoc Bell Laboratory. Research in laser-atomic physics and precision measurements.

Break: 3:35 p.m. – 3:55 p.m.

CSACs for Positioning, Navigation, and Timing in Space

3:55 p.m. – 4:55 p.m.

Most low earth orbit (LEO) satellites and some geostationary (GEO) satellites rely on GPS/GNSS for timing and positioning. This includes real-time onboard operations for scheduling ground contacts, executing mission functions, and tagging data records; as well as gathering observations for precise orbit determination. Highly stable clocks, like CSACs, are not required when using GNSS, but they can provide significant benefits in detecting invalid observations, coasting through periods of reduced GNSS visibility, and supporting navigation based on one-way ranging from ground transmitters. This tutorial will cover these applications and the expected performance of CSACs operating onboard small satellites.

Dr. Penina Axelrad, Ann and H.J. Smead Aerospace Engineering Sciences, University of Colorado Boulder
Dr. Penny Axelrad is Distinguished Professor in the Smead Aerospace Engineering Sciences Department, at the University of Colorado Boulder. Her research interests include technology and algorithms for PNT and remote sensing.