Dear Colleagues. Apologies for any cross-posting. The XXXVIth URSI General Assembly and Scientific Symposium (URSI GASS 2026) will be held in Krakow, Poland, August 15 to 22, 2026. We cordially invite you to submit contributions to the Session G06 - LEO topside and radio occultation measurements for ionosphere and plasmasphere estimation and modelling (see description below). URSI-GASS accepts three types of submissions: (a) Summary paper, of length between 2 and 4 pages (b) An extended abstract of 1 page maximum (c) A full paper for the student paper competition, prepared as submission to the Radio Science Letters All information about GASS 2026 including paper submission, student paper competition, and young scientist awards can be found at URSI-GASS 2026 | URSI-GASS 2026<https://www.ursi-gass2026.pl/>. SUBMISSION DEADLINE: Paper/abstract submission deadline is: January 25, 2026 Best regards, Mainul Hoque, Riccardo Notarpietro, Manuel Hernandez-Pajares, Marjolijn Adolfs ______________________________________________________________________ G06: LEO topside and radio occultation measurements for ionosphere and plasmasphere estimation and modelling Organizers/Convenors: Mainul Hoque, Riccardo Notarpietro, Manuel Hernandez-Pajares, Marjolijn Adolfs Session Description: The availability of numerous medium Earth orbit (MEO) satellites deployed by GPS, Galileo, GLONASS, and BeiDou systems allows continuous and reliable monitoring of the Earth's ionosphere and neutral atmosphere by tracking GNSS multifrequency signals from Low Earth orbiting (LEO) satellites. From the proof-of-concept GPS/MET experiment on Microlab-1, flown within the years 1995 -1997, till the today's EUMETSAT's Metop-B and Metop-C, the FORMOSAT-5/COSMIC-2, the numerous CubeSats operated by commercial entrepreneurs (e.g., Spire, PlanetIQ) and the recently launched Metop-SGA1, they all have demonstrated a huge potential of the limb sounding technique on LEO satellites for atmosphere/ionosphere sounding. In addition, the LEO onboard navigation and in-situ measurements can be used to derive the topside total electron content (TEC) and electron density at orbit heights. However, improved inversion techniques, assimilation methods including high-resolution tomography and powerful processing systems need to be developed for improved space weather monitoring, forecasting and modelling. Long term RO and topside data obtained by combining multi-instrument multi-satellite data has a large potential for climate related assessments. With more than 3 decades, i.e. almost 3 solar cycles of continuous LEO observations being available now, together with advanced machine learning techniques we have the unprecedented opportunity to model the ionosphere and plasmasphere with greater accuracy and detail. In this session, contributions on new techniques to estimate the electron density and TEC distribution, ionospheric gradients and irregularities using onboard LEO data, and their ingestion into data assimilation models for supporting space weather applications are welcome. Any email message from EUMETSAT is sent in good faith but shall neither be binding nor construed as constituting a commitment by EUMETSAT, except where provided for in a written agreement or contract or if explicitly stated in the email. Please note that any views or opinions presented in this email are solely those of the sender and do not necessarily represent those of EUMETSAT. This message and any attachments are intended for the sole use of the addressee(s) and may contain confidential and privileged information. Any unauthorised use, disclosure, dissemination or distribution (in whole or in part) of its contents is not permitted. If you received this message in error, please notify the sender and delete it from your system.