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This PhD defense by Stig Syndergaard presents innovative methodologies in atmospheric limb sounding using GNSS radio occultation. It covers the principle of the GNSS radio occultation technique, data processing with illustrative results, and addresses challenges such as the violation of spherical symmetry assumptions and severe weather gradients. The role of Earth's oblateness and the calibration of ionosphere data is also discussed, culminating in conclusions and future prospects in atmospheric observation, emphasized by case studies like the GPS/MET occultation.

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  1. Retrieval Analysis and Methodologies in Atmospheric Limb Sounding Using the GNSS Radio Occultation Technique PhD Defence by Stig Syndergaard

  2. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  3. The GPS constellation • 24 satellites • Six 12 hour orbits • Altitude: 20200 km • Inclination: 55º • Transmit dual frequency signals

  4. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  5. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  6. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  7. Correcting for the Earth’s oblateness

  8. Earth’s oblateness Before correction After correction

  9. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  10. Model calculation of retrievals of the temperature in the case of a typical day-time, solar maximum ionosphere

  11. GPS/MET occultation no. 259, day 35, 1997

  12. Content of presentation • The GNSS radio occultation principle • Data processing and exemplar results • ----------------------------------------------- • Violation of spherical symmetry assumption • Severe weather gradients • Earth’s oblateness • Ionosphere calibration of data • Conclusion and prospects

  13. 14 days of GPS/MET occultations

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