{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:35:06Z","timestamp":1760146506610,"version":"build-2065373602"},"reference-count":17,"publisher":"MDPI AG","issue":"22","license":[{"start":{"date-parts":[[2024,11,9]],"date-time":"2024-11-09T00:00:00Z","timestamp":1731110400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"French Space Agency (CNES)"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The Surface Water and Ocean Topography (SWOT) mission was launched on 16 December 2022 to measure water levels over both open ocean and inland waters. To achieve these objectives, the SWOT Payload contains an innovative Ka-band radar interferometer, called KaRIn, completed with a nadir altimeter called POSEIDON-3C that was switched on a month after launch and a few days before KaRIn. POSEIDON-3C measurements provide a link between large-scale phenomena and high resolution. The POSEIDON-3C design is based on POSEIDON-3B, its predecessor on board JASON-3. It is also a dual-frequency radar altimeter operating in C- and Ku-bands, but with some improvements to enhance its performance. Even though it is a Low Resolution Mode altimeter, its performance over open ocean, inland waters and coastal zones are indeed excellent. This paper first describes the POSEIDON-3C design and its modes with a focus on its new features and the Digital Elevation Model that drives its open-loop tracking mode. Then, we assess the in-flight performances of the altimeter from an instrumental point of view. For that purpose, special and routine calibrations have been realized. They show the good performance and stability of the radar. In-flight assessments thus provide confidence when it comes to ensuring excellent altimeter measurement stability throughout the mission duration.<\/jats:p>","DOI":"10.3390\/rs16224183","type":"journal-article","created":{"date-parts":[[2024,11,11]],"date-time":"2024-11-11T11:34:11Z","timestamp":1731324851000},"page":"4183","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Description and In-Flight Assessment of the POSEIDON-3C Altimeter of the SWOT Mission"],"prefix":"10.3390","volume":"16","author":[{"given":"Alexandre","family":"Gu\u00e9rin","sequence":"first","affiliation":[{"name":"Centre National d\u2019Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2049-9120","authenticated-orcid":false,"given":"Fanny","family":"Piras","sequence":"additional","affiliation":[{"name":"Collecte Localisation Satellites (CLS), 11 Rue Herm\u00e8s, Parc Technologique du Canal, 31520 Ramonville-Saint-Agne, France"}]},{"given":"Nicolas","family":"Cuvillon","sequence":"additional","affiliation":[{"name":"Centre National d\u2019Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France"}]},{"given":"Alexandre","family":"Homerin","sequence":"additional","affiliation":[{"name":"NOVELTIS, 153 Rue du Lac, 31670 Lab\u00e8ge, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4933-2706","authenticated-orcid":false,"given":"Sophie","family":"Le Gac","sequence":"additional","affiliation":[{"name":"Centre National d\u2019Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France"}]},{"given":"Claire","family":"Maraldi","sequence":"additional","affiliation":[{"name":"Centre National d\u2019Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France"}]},{"given":"Fran\u00e7ois","family":"Bignalet-Cazalet","sequence":"additional","affiliation":[{"name":"Centre National d\u2019Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France"}]},{"given":"Marta","family":"Alves","sequence":"additional","affiliation":[{"name":"Collecte Localisation Satellites (CLS), 11 Rue Herm\u00e8s, Parc Technologique du Canal, 31520 Ramonville-Saint-Agne, France"}]},{"given":"Laurent","family":"Rey","sequence":"additional","affiliation":[{"name":"Thales Alenia Space (TAS), 26 Avenue Jean Fran\u00e7ois Champollion, 31100 Toulouse, France"}]}],"member":"1968","published-online":{"date-parts":[[2024,11,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"407","DOI":"10.1175\/1520-0426(1989)006<0407:PCASLT>2.0.CO;2","article-title":"Pulse Compression and Sea Level Tracking in Satellite Altimetry","volume":"6","author":"Chelton","year":"1989","journal-title":"J. Atmos. Ocean. Technol."},{"key":"ref_2","unstructured":"(2024, October 18). Jason-3 Products Handbook, Aviso; 2021. Available online: https:\/\/www.aviso.altimetry.fr\/fileadmin\/documents\/data\/tools\/hdbk_j3.pdf."},{"key":"ref_3","unstructured":"Bignalet-Cazalet, F., Roinard, H., Pirotte, T., Picard, B., Homerin, A., Kientz, N., Nouvel de la Fl\u00e8che, A., Maraldi, C., Raynal, M., and Picot, N. (Remote Sens., 2024). Calibration and validation performance assessment for SWOT\u2019s nadir altimeter, Remote Sens., submitted."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1080\/01490419.2010.488970","article-title":"POSEIDON-3 Radar Altimeter: New Modes and In-Flight Performances","volume":"33","author":"Carayon","year":"2010","journal-title":"Mar. Geod."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"843","DOI":"10.1016\/j.asr.2019.10.031","article-title":"Benefits of the Open-Loop Tracking Command (OLTC): Extending conventional nadir altimetry to inland waters monitoring","volume":"68","author":"Boy","year":"2021","journal-title":"Adv. Space Res."},{"key":"ref_6","unstructured":"Hernandez, F., and Schaeffer, P. (2001). The CLS01 Mean Sea Surface: A Validation with the GSFC00.1 Surface, CLS."},{"key":"ref_7","unstructured":"Smith, R.G., and Berry, P.A.M. (2010). ACE2: Global Digital Elevation Model, EAPRS Laboratory, De Montfort University."},{"key":"ref_8","unstructured":"Wessel, P., and Smith, W.H.F. (2024, October 18). GSHHG-A Global Self-Consistent, Hierarchical, High-resolution Geography Database, version 2.3.7; 2017. Available online: https:\/\/www.soest.hawaii.edu\/pwessel\/gshhg\/."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"67","DOI":"10.1109\/TAP.1977.1141536","article-title":"The average impulse response of a rough surface and its applications","volume":"25","author":"Brown","year":"1977","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1007\/s10712-008-9051-1","article-title":"Monitoring continental surface waters by satellite altimetry","volume":"29","author":"Calmant","year":"2008","journal-title":"Surv. Geophys."},{"key":"ref_11","unstructured":"Vallado, D.A. (2007). Fundamentals of Astrodynamics and Applications, Springer. [3rd ed.]."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"337","DOI":"10.1109\/TGRS.2022.3216595","article-title":"Sentinel-6 MF POSEIDON-4 Radar Altimeter In-Flight Calibration and Performances Monitoring","volume":"60","author":"Dinardo","year":"2022","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"256","DOI":"10.1080\/01490419.2010.487794","article-title":"Jason-1\/Jason-2. Metocean Comparisons and Monitoring","volume":"33","author":"Quartly","year":"2010","journal-title":"Mar. Geod."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3244","DOI":"10.1109\/TGRS.2018.2796630","article-title":"Investigating the 59-Day Error Signal in the Mean Sea Level Derived From TOPEX\/Poseidon, Jason-1, and Jason-2 Data With FES and GOT Ocean Tide Models","volume":"56","author":"Zawadzki","year":"2018","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Thibaut, P., Piras, F., Roinard, H., Guerou, A., Boy, F., Maraldi, C., and Picot, N. (2021, January 11\u201316). Benefits of the \u201cAdaptive Retracking Solution\u201d for the JASON-3 GDR-F Reprocessing Campaign. Proceedings of the 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, Brussels, Belgium.","DOI":"10.1109\/IGARSS47720.2021.9553647"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"9927","DOI":"10.1109\/TGRS.2021.3064236","article-title":"Benefits of the adaptive algorithm for retracking altimeter nadir echoes: Results from simulations and CFOSAT\/SWIM observations","volume":"59","author":"Tourain","year":"2021","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1080\/01490410490465210","article-title":"Improving the Jason-1 ground retracking to better account for attitude effects","volume":"27","author":"Amarouche","year":"2004","journal-title":"Mar. Geod."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/16\/22\/4183\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T16:29:27Z","timestamp":1760113767000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/16\/22\/4183"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,11,9]]},"references-count":17,"journal-issue":{"issue":"22","published-online":{"date-parts":[[2024,11]]}},"alternative-id":["rs16224183"],"URL":"https:\/\/doi.org\/10.3390\/rs16224183","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2024,11,9]]}}}