{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,20]],"date-time":"2026-03-20T15:42:13Z","timestamp":1774021333757,"version":"3.50.1"},"reference-count":27,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2023,10,20]],"date-time":"2023-10-20T00:00:00Z","timestamp":1697760000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"German Aerospace Center, Institute for Solar-Terrestrial Physics","award":["DLR-SO"],"award-info":[{"award-number":["DLR-SO"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Coherent observations in GNSS reflectometry are prominent in regions with smooth reflecting surfaces and at grazing elevation angles. However, within these lower elevation ranges, GNSS signals traverse a more extensive atmospheric path, and increased ionospheric effects (e.g., delay biases) are expected. These biases can be mitigated by employing dual-frequency receivers or models tailored for single-frequency receivers. In preparation for the single-frequency GNSS-R ESA \u201cPRETTY\u201d mission, this study aims to characterize ionospheric effects under variable parameter conditions: elevation angles in the grazing range (5\u00b0 to 30\u00b0), latitude-dependent regions (north, tropic, south) and diurnal changes (day and nighttime). The investigation employs simulations using orbit data from Spire Global Inc.\u2019s Lemur-2 CubeSat constellation at the solar minimum (F10.7 index at 75) on March, 2021. Changes towards higher solar activity are accounted for with an additional scenario (F10.7 index at 180) on March, 2023. The electron density associated with each reflection event is determined using the Neustrelitz Electron Density Model (NEDM2020) and the NeQuick 2 model. The results from periods of low solar activity reveal fluctuations of up to approximately 300 TECUs in slant total electron content, 19 m in relative ionospheric delay for the GPS L1 frequency, 2 Hz in Doppler shifts, and variations in the peak electron density height ranging from 215 to 330 km. Sea surface height uncertainty associated with ionospheric model-based corrections in group delay altimetric inversion can reach a standard deviation at the meter level.<\/jats:p>","DOI":"10.3390\/rs15205049","type":"journal-article","created":{"date-parts":[[2023,10,20]],"date-time":"2023-10-20T11:53:56Z","timestamp":1697802836000},"page":"5049","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Characterizing Ionospheric Effects on GNSS Reflectometry at Grazing Angles from Space"],"prefix":"10.3390","volume":"15","author":[{"given":"Mario","family":"Moreno","sequence":"first","affiliation":[{"name":"Deutsches Zentrum f\u00fcr Luft-und Raumfahrt, Institut f\u00fcr Solar-Terrestrische Physik (DLR-SO), Kalkhorstweg 53, 17235 Neustrelitz, Germany"},{"name":"Institute of Geodesy and Geoinformation Science, Department of GNSS Remote Sensing, Navigation and Positioning, Technische Universit\u00e4t Berlin (TUB), Str. des 17. Juni 135, 10623 Berlin, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Maximilian","family":"Semmling","sequence":"additional","affiliation":[{"name":"Deutsches Zentrum f\u00fcr Luft-und Raumfahrt, Institut f\u00fcr Solar-Terrestrische Physik (DLR-SO), Kalkhorstweg 53, 17235 Neustrelitz, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6757-8611","authenticated-orcid":false,"given":"Georges","family":"Stienne","sequence":"additional","affiliation":[{"name":"Laboratoire d\u2019Informatique, Signal et Image de la C\u00f4te d\u2019Opale (LISIC), Universit\u00e9 Littoral C\u00f4te d\u2019Opale (ULCO), 50 rue Ferdinand Buisson, 62228 Calais, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5134-4901","authenticated-orcid":false,"given":"Mainul","family":"Hoque","sequence":"additional","affiliation":[{"name":"Deutsches Zentrum f\u00fcr Luft-und Raumfahrt, Institut f\u00fcr Solar-Terrestrische Physik (DLR-SO), Kalkhorstweg 53, 17235 Neustrelitz, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7379-5276","authenticated-orcid":false,"given":"Jens","family":"Wickert","sequence":"additional","affiliation":[{"name":"Institute of Geodesy and Geoinformation Science, Department of GNSS Remote Sensing, Navigation and Positioning, Technische Universit\u00e4t Berlin (TUB), Str. des 17. Juni 135, 10623 Berlin, Germany"},{"name":"Deutsches GeoForschungsZentrum (GFZ), Wissenschaftpark \u201cAlbert Einstein\u201d, Telegrafenberg, 14473 Potsdam, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,10,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1016\/S0076-695X(08)60682-1","article-title":"2.1. The Ionosphere","volume":"Volume 12","author":"Meeks","year":"1976","journal-title":"Methods in Experimental Physics"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2478","DOI":"10.1016\/j.asr.2005.07.030","article-title":"Ionospheric Effects on GPS Positioning","volume":"38","author":"Dubey","year":"2006","journal-title":"Adv. Space Res."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"35","DOI":"10.3319\/TAO.2007.12.26.01(F3C)","article-title":"GPS Radio Occultation: Results from CHAMP. GRACE and FORMOSAT-3\/COSMIC","volume":"20","author":"Wickert","year":"2009","journal-title":"Terr. Atmos. Ocean. Sci."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1416","DOI":"10.1109\/LGRS.2015.2404912","article-title":"Relative Ionospheric Ranging Delay in LEO GNSS Oceanic Reflections","volume":"12","author":"Xing","year":"2015","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Ruf, C., Gleason, S., Jelenak, Z., Katzberg, S., Ridley, A., Rose, R., Scherrer, J., and Zavorotny, V. (2013, January 2\u20139). The NASA EV-2 Cyclone Global Navigation Satellite System (CYGNSS) Mission. Proceedings of the 2013 IEEE Aerospace Conference, Big Sky, MT, USA.","DOI":"10.1109\/AERO.2013.6497202"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"5851","DOI":"10.1109\/JSTARS.2016.2612542","article-title":"Ionospheric Effects in GNSS-Reflectometry From Space","volume":"9","author":"Camps","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"4525","DOI":"10.1109\/JSTARS.2016.2603846","article-title":"Spaceborne GNSS-Reflectometry on TechDemoSat-1: Early Mission Operations and Exploitation","volume":"9","author":"Unwin","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_8","first-page":"1","article-title":"Ionospheric Total Electron Content and Disturbance Observations From Space-Borne Coherent GNSS-R Measurements","volume":"60","author":"Wang","year":"2022","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_9","first-page":"1","article-title":"Arctic TEC Mapping Using Integrated LEO-Based GNSS-R and Ground-Based GNSS Observations: A Simulation Study","volume":"60","author":"Liu","year":"2022","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Roesler, C., Wang, Y., Morton, Y.J., and Nerem, R.S. (October, January 26). Coherent GPS Reflections Over Ocean Surface. Proceedings of the IGARSS 2020\u20132020 IEEE International Geoscience and Remote Sensing Symposium, Waikoloa, HI, USA.","DOI":"10.1109\/IGARSS39084.2020.9323084"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Moreno, M., Semmling, M., Stienne, G., Dalil, W., Hoque, M., Wickert, J., and Reboul, S. (2022). Airborne Coherent GNSS Reflectometry and Zenith Total Delay Estimation over Coastal Waters. Remote Sens., 14.","DOI":"10.3390\/rs14184628"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Issa, H., Stienne, G., Reboul, S., Raad, M., and Faour, G. (2021). Airborne GNSS Reflectometry for Water Body Detection. Remote Sens., 14.","DOI":"10.3390\/rs14010163"},{"key":"ref_13","unstructured":"Subirana, J.S., Zornoza, J.M.J., and Hern\u00e1ndez-Pajares, M. (2013). GNSS Data Processing, ESA Communications. Fundamentals and Algorithms."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Hoque, M.M., Jakowski, N., Osechas, O., and Berdermann, J. (2019, January 11). Fast and Improved Ionospheric Correction for Galileo Mass Market Receivers. Proceedings of the 32nd International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2019), Miami, FL, USA.","DOI":"10.33012\/2019.17106"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1856","DOI":"10.1016\/j.jastp.2008.01.015","article-title":"A New Version of the NeQuick Ionosphere Electron Density Model","volume":"70","author":"Nava","year":"2008","journal-title":"J. Atmos. Sol. Terr. Phys."},{"key":"ref_16","unstructured":"(2023, July 27). Ionospheric Correction Algorithms|European GNSS Service Centre. Available online: https:\/\/www.gsc-europa.eu\/support-to-developers\/ionospheric-correction-algorithms."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1007\/s00502-022-00993-7","article-title":"PRETTY\u2014Passive GNSS-Reflectometry for CubeSats","volume":"139","author":"Dielacher","year":"2022","journal-title":"Elektrotech. Inftech."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1051\/swsc\/2021044","article-title":"A New Climatological Electron Density Model for Supporting Space Weather Services","volume":"12","author":"Hoque","year":"2022","journal-title":"J. Space Weather Space Clim."},{"key":"ref_19","unstructured":"Nguyen, V., Jales, P., and Garbacz, H. (2023, July 20). Spire Earth Observations for NASA\u2019s CSDA Program\u2014Lunch & Learn, Available online: https:\/\/www.earthdata.nasa.gov\/s3fs-public\/2022-10\/2022%2010%2006%20Spire%20Earth%20Observations%20for%20NASA%27s%20CSDA%20Program%20-%20Lunch%20%26%20Learn_0.pdf."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"6791","DOI":"10.1109\/TGRS.2016.2591065","article-title":"A Phase-Altimetric Simulator: Studying the Sensitivity of Earth-Reflected GNSS Signals to Ocean Topography","volume":"54","author":"Semmling","year":"2016","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Hoque, M.M., Jakowski, N., and Cahuasqu\u00ed, J.A. (2020, January 23\u201324). Fast Ionospheric Correction Algorithm for Galileo Single Frequency Users. Proceedings of the 2020 European Navigation Conference (ENC), Dresden, Germany.","DOI":"10.23919\/ENC48637.2020.9317502"},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Cardellach, E., Ao, C.O., de la Torre Ju\u00e1rez, M., and Hajj, G.A. (2004). Carrier Phase Delay Altimetry with GPS-Reflection\/Occultation Interferometry from Low Earth Orbiters. Geophys. Res. Lett., 31.","DOI":"10.1029\/2004GL019775"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"4088","DOI":"10.1109\/TGRS.2018.2823316","article-title":"Global Ocean Altimetry With GNSS Reflections From TechDemoSat-1","volume":"56","author":"Mashburn","year":"2018","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"601","DOI":"10.1029\/JZ067i002p00601","article-title":"A Study of F 2-Layer Effects as Observed with a Doppler Technique","volume":"67","author":"Davies","year":"1962","journal-title":"J. Geophys. Res."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"257","DOI":"10.1002\/rds196613257","article-title":"Doppler Frequency Changes in Radio Waves Propagating Through a Moving Ionosphere","volume":"1","author":"Jacobs","year":"1966","journal-title":"Radio Sci."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Kleusberg, A., and Teunissen, P.J.G. (1996). GPS for Geodesy, Springer. Lecture Notes in Earth Sciences.","DOI":"10.1007\/BFb0117676"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"102","DOI":"10.1109\/JSTARS.2019.2952694","article-title":"First Precise Spaceborne Sea Surface Altimetry With GNSS Reflected Signals","volume":"13","author":"Cardellach","year":"2020","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/15\/20\/5049\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T21:09:24Z","timestamp":1760130564000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/15\/20\/5049"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,10,20]]},"references-count":27,"journal-issue":{"issue":"20","published-online":{"date-parts":[[2023,10]]}},"alternative-id":["rs15205049"],"URL":"https:\/\/doi.org\/10.3390\/rs15205049","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,10,20]]}}}