Course 338: Ionospheric Effects, Monitoring, and Mitigation Techniques

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Course 338: Ionospheric Effects, Monitoring, and Mitigation Techniques

Instructor: Dr. Jade Morton, University of Colorado Boulder
This course is available for private group training. | 1.8 CEUs CEUs
Onsite onlyALL of our courses can be taught onsite at your location. Most onsite courses can be customized for your group.

Course Description

Ionospheric effects are major threats to the availability, continuity, and accuracy of GNSS solutions and other satellite-based radio systems. Models, global networks of GNSS stations, and LEO satellite-based radio occultation constellations have been established to monitor and predict the ionospheric effects. This course will present the current state-of-art understanding of the various ionospheric effects on GNSS-based navigation systems and their mitigation techniques. The course consists of five lectures. The first lecture introduces the fundamental properties of the ionosphere that impact satellite navigation signals and PVT solutions, discusses the ionospheric refractive effects, broadcast models from various GNSS service provides, and the Total Electron Content (TEC) estimation techniques for single, dual-, and multi-frequency GNSS receivers. The second lecture focuses on ionospheric error correction methods, including IGS TEC products, network-based TEC mapping techniques, low-cost ionospheric monitoring system, and the latest developing in using cell phone measurements to map ionosphere. Higher order refraction errors and correction techniques will also be covered. Lecture 3 covers ionospheric scintillation effect, with a focus on the concepts, theory, modeling, and indicators for monitoring. Scintillation signal models for current GNSS L-band signals and potential future LEO satellite-based navigation systems at multiple bands ranging from VHF to S band will be discussed. Lecture 4 takes a deeper look into GNSS receiver signal processing algorithms designed to combat ionospheric scintillation effects. Part 5 will provide an update on the latest development in ionospheric effects monitoring and forecasting using machine learning algorithms, worldwide ground-based and space-based GNSS observations, the ionospheric effects on signals transmitted from LEO satellites. We will finish the course with an outlook for outstanding challenges in the field.

Objectives

To provide a comprehensive review of fundamentals of ionospheric effects on GNSS
To present ionospheric correction techniques to improve GNSS measurement accuracy
To showcase the latest receiver signal processing techniques to mitigate ionospheric scintillation effects
To highlight recent advances in ground and spaceborne ionospheric monitoring systems, machine learning algorithms, and simulation models to improve current and future navigation systems performance.

Who Should Attend?

This course is designed for students, engineers, researchers, and managers interested in satellite navigation and remote sensing technologies and applications.

Materials You Will Keep

A color electronic copy of all course notes provided in advance on a USB drive or CD-ROM.
Ability to use Adobe Acrobat sticky notes on electronic course notes.
NavtechGPS Glossary of GNSS Acronyms.
A black and white hard copy of the course notes.
A textbook from the list below.

Course Fee Entitles You to One of the Following Books

GPS Basics for Technical Professionals, P. Misra, 2019, OR
Introduction to GPS: The Global Positioning System, 2nd ed., Ahmed El-Rabbany, Artech House, 2006., OR
Global Positioning System: Signals, Measurement and Performance, P. Misra and P. Enge, 2nd ed., 2011.

Agenda - Day 1

Lecture 1: Introduction to ionospheric effects (R1: p879-894; R2)

Fundamental properties of ionosphere impacting satellite navigation
- Ionosphere electron density profiles
- Ionospheric refractive index: Appleton-Hartree equation and linear expansions
  - Plasma frequency and electron gyrofrequency
  - Refractive index for L band signals
  - Carrier refractive index vs code refractive index
  - Comparison between ionosphere and troposphere refractive index

Ionospheric refraction effects in GNSS measurements: code delay, carrier advance, and total electron content (TEC)
TEC broadcast models for single-frequency receivers
- Klobuchar model
- BDGIM
- NeQuick G
- Performance comparison of broadcast models
TEC estimation using dual-frequency receiver measurements
- General approach
- Code multipath and noise estimation
- Differential code bias (DCB) estimation
TEC estimation using multi-frequency receiver measurements
TEC estimation using single-frequency receiver measurements

Lecture 2: Ionospheric effects correction method (R1: p894-906; R3)

Vertical TEC (VTEC) and mapping function
IGS VTEC products
Network-based VTEC mapping methods
- Triangular tile method
- Spherical harmonics basis function method
- Tomography-based method
- Other network-based TEC mapping methods
TEC estimation using low-cost receivers
TEC estimation using cell phone measurements
Higher-order ionospheric errors
- Estimation method
- Higher-order error impact on position solution accuracy

Agenda - Day 2

Lecture 3: Ionospheric Scintillation – Concepts, theory, modeling, and monitoring (R1: p906-914; R4; R5)

Distinctions between refraction and diffraction effects
Scintillation theory: phase screen models
GNSS signal scintillation indicators
- Amplitude scintillation index
- Phase scintillation index
- Frequency scintillation index
- Decorrelation time
- Rate of TEC index
Scintillation model for GPS-like signals transmitted from LEO satellites
- Phase screen model adaption for LEO satellite signals
- Simulated scintillation effects on LEO satellite-transmitted GPS-like signals at L1, L2, and L5 bands
Scintillation model for VHF, UHF, L, C, and S band signals transmitted from LEO satellites
- Phase screen model adaption for LEO satellite signals at VHF, UHF, L, C, and S bands
- Simulated scintillation effects on LEO satellite-transmitted signals at VHF, UHF, L, C, and S bands.
- Scintillation observations of real VHF and L band signals transmitted from LEO satellites

Lecture 4: Ionospheric scintillation effects and mitigation techniques (R1: p914 - 928; R6, R7,R8, R9, R10, R11)

Scintillation effects
- Scintillation effects on carrier phase measurements
- Scintillation effects on position solution accuracy and availability
- High latitude scintillation
- Equatorial scintillation
- Mid-latitude scintillation
- Scintillation climatology
Scintillation signal tracking algorithms: architecture, implementations, and performance assessment
- Ionospheric scintillation monitoring (ISM) receivers: conventional architecture, implementation, and measurements
- Challenges of scintillation signals on carrier tracking
- Semi-open loop tracking
- Open loop tracking
- State-based GNSS carrier tracking
- Optimized inter-carrier aiding algorithm
- Vector processing

Agenda - Day 3

Lecture 5: Recent advances in ionospheric effects monitoring and forecasting (R12: p971-994; R13; R14; R15; R16)

GNSS radio occultation
- Fundamentals of radio occultation (RO)
- GNSS-RO TEC retrieval
  - Dual-frequency retrieval
  - Single frequency retrieval
- Electron density retrieval
- RO measurement error sources
- Scintillation observations using GNSS-RO measurements
- Case studies using COSMIC-2
GNSS reflectometry
- Fundamentals of GNSS-reflectometry (GNSS-R)
- Scintillation observations through delay-Doppler maps
- Carrier phase-based GNSS-R range measurements
- Ionospheric TEC retrieval through coherent carrier phase measurements
- Real GNSS-R ionospheric TEC and scintillation retrieval using low cost CubeSats measurements
Ionospheric effects on signals transmitted from LEO satellites
- Controlled ionospheric disturbance experiments
- Ionospheric effects frequency dependence
- Ionospheric orbit dependence
Machine learning (ML) for ionospheric disturbance detection, classification, and forecasting.
- Similarities and difference among ionospheric disturbances, satellite oscillator anomalies, and radio frequency interference
- ML architecture and feature engineering for event detection/classificaiton
- ML for global TEC forecasting
- ML for ionospheric disturbance prediction

Lecture Reference Materials

R1. Morton, Y., Z. Yang, B. Breitsch, H. Borne, C. Rino, Chapter 31: Ionospheric Effects, Monitoring, and Mitigation Techniques, in Position, Navigation, and Timing Technologies in the 21st Century, edt. Y. J. Morton, F. van Diggelen, J. J., Spilker, B. Parkinson, Wiley-IEEE Press, 2020.
R2. Evans, M., B. Breitsch, J. Morton, Ionospheric TEC estimations using singal-frequency wideband low elevation GNSS signals, Proc. ION GNSS+, 2024.
R3. Morton, Y., F. van Graas, Q. Zhou, J. Herdtner, Assessment of the higher order ionosphere error on position solutions, Navigation, J. Institute of Navigation, 56(3), 185-193, Fall 2009.
R4. Morton. Y. J., D. Xu, Y. Jiao, Ionospheric scintillation effects on signals transmitted from LEO satellites, Proc. ION GNSS+, DOI: 10.33012/2022.18341, 2022.
R5. Sun, A., Y. J. Morton, C. Rino, J. Lee, Ionospheric scintillation effects across multiple carrier frequency bands transmitted from LEO satellites, submitted to AFRL for public release approval, 2024.
R6. Xu D., Y. Morton, Semi-open loop estimation of GPS carrier phase variations during deep amplitude fading of equatorial ionospheric scintillation, IEEE Trans. Aero. Elec. Sys., DOI: 10.1109/TAES.2017.2764778, PP(99), 2017.
R7. Van Graas, F., Soloviev, A., de Haag, M. U., & Gunawardena, S. Closed-loop sequential signal processing and open-loop batch processing approaches for GNSS receiver design. IEEE Journal of Selected Topics in Signal Processing, 3(4), 571-586, 2009.
R8. Yang, R., Y. Morton, K. Ling, E. Poh, Generalized GNSS signal carrier tracking in challenging environments: part II - optimization and implementation, IEEE Trans. Aero. Elec. Sys., 53(4):1798-1811, DOI:10.1109/TAES.2017.2674198, 2017.
R9. Yang, R., D. Xu, Y. Morton, Generalized multi-frequency GPS carrier tracking architecture: design and performance analysis, IEEE Trans. Aero. Elec. Sys., DOI: 10.1109/TAES.2019.2948535, 2019.
R10. Lashley, M., S. Martin, J. Sennott, Chapter 16: Vector Processing, in Position, Navigation, and Timing Technologies in the 21st Century, edt. Y. J. Morton, F. van Diggelen, J. J., Spilker, B. Parkinson, Wiley-IEEE Press, 2020.
R11. Morton, Y., R. Yang, B. Breitsch, Chapter 15: GNSS Receiver Signal Tracking, in Position, Navigation, and Timing Technologies in the 21st Century, edt. Y. J. Morton, F. van Diggelen, J. J., Spilker, B. Parkinson, Wiley-IEEE Press, 2020.
R12. Mannucci, A., J., W. Williamson, Chapter 33: GNSS Radio Occultation, in Position, Navigation, and Timing Technologies in the 21st Century, edt. Y. J. Morton, F. van Diggelen, J. J., Spilker, B. Parkinson, Wiley-IEEE Press, 2020.
R13. Wang, Y., Y. J. Morton, Ionospheric total electron content and disturbance observations from space borne coherent GNSS-R measurements, IEEE Trans. Geosci. Remote Sensing, DOI: 10.1109/TGRS.2021.3093328, 2021.
R14. Morton, Y. J., H. Bourne, S. Taylor, C. Yang, M. Naudeau, A controlled experiment of ionospheric effects on VHF signals transmitted from a NOAA weather satellite. Proc. ION GNSS+, 2024.
R15. Wu, K., Y. J. Morton, S. T. Dittmann, H. Chang, GNSS Signal Disturbance Detection and Classification Based on LEO Satellite Measurements, Proc. ION ITM, 2024.
R16. Liu, Y., Z. Yang, Y. J. Morton, R. Li, Spatiotemporal deep learning network for high-latitude ionospheric phase scintillation forecasting, Navigation, J. of ION, 70(4), 2023.
R17. Liu, L., Y. J. Morton, Y. Liu, ML Prediction of Global Ionospheric TEC Maps, Space Weather, DOI:10.1029/2022SW003135, 2022.
R18. Liu, L., Y. J. Morton, Y. Liu, Machine learning prediction of storm-time high latitude ionospheric irregularities from GNSS-derived ROTI maps, Geophy. Res. Lett., DOI: 10.1029/2021GL095561, 2021.