{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T18:55:58Z","timestamp":1773255358930,"version":"3.50.1"},"reference-count":21,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2023,3,3]],"date-time":"2023-03-03T00:00:00Z","timestamp":1677801600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"EUMETSAT","award":["EUM\/CO\/21\/4600002530\/RN"],"award-info":[{"award-number":["EUM\/CO\/21\/4600002530\/RN"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The radio occultation (RO) measurements of the Global Navigation Satellite System\u2019s (GNSS\u2019s) signals onboard a Low Earth Orbiting (LEO) satellite enable the computation of the vertical electron density profile from the LEO satellite\u2019s orbit height down to the Earth\u2019s surface. The ionospheric extension experiment performed by the GNSS Receiver for Atmospheric Sounding (GRAS) receiver on board MetOp-A provides opportunities for ionospheric sounding but with the RO measurements only taken with an impact parameter height below 600 and 300 km within two different experiments, although MetOp-A was flying at an orbit height of about 800 km. Here, we present a model-assisted RO inversion technique for electron density retrieval from such kind of truncated data. The topside ionosphere and plasmasphere above the LEO orbit height are modelled by a Chapman layer function superposed with an exponential decay function representing the plasmasphere. Our investigation shows that the model-assisted technique is stable and robust and can successfully be used to retrieve the electron density values up to the LEO height from the truncated MetOp-A data, in particular when observations are available until 600 km. Moreover, this model-assisted technique is also successful with the availability of a small number of observations of the topside above the peak density height. For observations available only up to 300 km, the accuracy of the retrieved profile is comparable to the one obtained by the data truncated at a 600 km height only when the peak electron density lies below the 250 km altitude level.<\/jats:p>","DOI":"10.3390\/rs15051424","type":"journal-article","created":{"date-parts":[[2023,3,6]],"date-time":"2023-03-06T01:35:30Z","timestamp":1678066530000},"page":"1424","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["A New Method of Electron Density Retrieval from MetOp-A\u2019s Truncated Radio Occultation Measurements"],"prefix":"10.3390","volume":"15","author":[{"given":"M. Mainul","family":"Hoque","sequence":"first","affiliation":[{"name":"German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics, Kalkhorstweg 53, 17235 Neustrelitz, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6711-107X","authenticated-orcid":false,"given":"Liangliang","family":"Yuan","sequence":"additional","affiliation":[{"name":"German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics, Kalkhorstweg 53, 17235 Neustrelitz, Germany"}]},{"given":"Fabricio S.","family":"Prol","sequence":"additional","affiliation":[{"name":"German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics, Kalkhorstweg 53, 17235 Neustrelitz, Germany"},{"name":"Department of Navigation and Positioning, Finnish Geospatial Research Institute (FGI), National Land Survey of Finland (NLS), Vuorimiehentie 5, 02150 Espoo, Finland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9687-5850","authenticated-orcid":false,"given":"Manuel","family":"Hern\u00e1ndez-Pajares","sequence":"additional","affiliation":[{"name":"Department of Mathematics, Universitat Polit\u00e8cnica de Catalunya\u2014IOnospheric Determination and Navigation Based on Satellite and Terrestrial Systems (UPC-IonSAT), E08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7403-0208","authenticated-orcid":false,"given":"Riccardo","family":"Notarpietro","sequence":"additional","affiliation":[{"name":"European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Eumetsat Allee 1, 64295 Darmstadt, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3174-2624","authenticated-orcid":false,"given":"Norbert","family":"Jakowski","sequence":"additional","affiliation":[{"name":"German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics, Kalkhorstweg 53, 17235 Neustrelitz, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9604-6753","authenticated-orcid":false,"given":"German","family":"Olivares Pulido","sequence":"additional","affiliation":[{"name":"Department of Mathematics, Universitat Polit\u00e8cnica de Catalunya\u2014IOnospheric Determination and Navigation Based on Satellite and Terrestrial Systems (UPC-IonSAT), E08034 Barcelona, Spain"}]},{"given":"Axel","family":"Von Engeln","sequence":"additional","affiliation":[{"name":"European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Eumetsat Allee 1, 64295 Darmstadt, Germany"}]},{"given":"Christian","family":"Marquardt","sequence":"additional","affiliation":[{"name":"European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Eumetsat Allee 1, 64295 Darmstadt, Germany"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,3]]},"reference":[{"key":"ref_1","first-page":"2743","article-title":"Improving the Abel inversion by adding ground data LEO radio occultations in the ionospheric sounding","volume":"27","author":"Juan","year":"2000","journal-title":"Geophys. 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