{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,11]],"date-time":"2026-04-11T13:21:20Z","timestamp":1775913680006,"version":"3.50.1"},"reference-count":26,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2021,9,3]],"date-time":"2021-09-03T00:00:00Z","timestamp":1630627200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000844","name":"European Space Agency","doi-asserted-by":"publisher","award":["4000130560\/20\/NL\/FF\/gp"],"award-info":[{"award-number":["4000130560\/20\/NL\/FF\/gp"]}],"id":[{"id":"10.13039\/501100000844","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Global Navigation Satellite System Reflectometry (GNSS-R) is a rapidly developing Earth observation technology that makes use of signals of opportunity from Global Navigation Satellite Systems that have been reflected off the Earth\u2019s surface. The Cyclone Global Navigation Satellite System (CyGNSS) is a constellation of eight small satellites launched by NASA in 2016, carrying dedicated GNSS-R payloads to measure ocean surface wind speed at low latitudes (\u00b135\u00b0 North\/South). The ESA ECOLOGY project evaluated CyGNSS v3.0 products, which were recently released following various calibration updates. This paper examines the performance of the new calibration by evaluating CyGNSS v3.0 Level-1 Normalised Bistatic Radar Cross Section (NBRCS) and Leading Edge Slope (LES) data from individual CyGNSS units and different GPS transmitters under constant ocean wind conditions. Results indicate that L1 NBRCS from individual CyGNSS units are well inter-calibrated and remarkably stable over time, a significant improvement over previous versions of the products. However, prominent geographical biases reaching over 3 dB are found in NBRCS, linked to factors including the choice of GPS transmitter and the bistatic geometry. L1 LES shows similar anomalies as well as a secondary geographical pattern of biases. These findings provide a basis for further improvement of CyGNSS Level-2 wind products and have wider applicability to improving the calibration of GNSS-R sensors for the remote sensing of non-ocean Earth surfaces.<\/jats:p>","DOI":"10.3390\/rs13173500","type":"journal-article","created":{"date-parts":[[2021,9,6]],"date-time":"2021-09-06T13:18:26Z","timestamp":1630934306000},"page":"3500","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["An Assessment of CyGNSS v3.0 Level 1 Observables over the Ocean"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8918-2351","authenticated-orcid":false,"given":"Matthew Lee","family":"Hammond","sequence":"first","affiliation":[{"name":"National Oceanography Centre, Southampton SO14 3ZH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1507-2133","authenticated-orcid":false,"given":"Giuseppe","family":"Foti","sequence":"additional","affiliation":[{"name":"National Oceanography Centre, Southampton SO14 3ZH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6941-1671","authenticated-orcid":false,"given":"Christine","family":"Gommenginger","sequence":"additional","affiliation":[{"name":"National Oceanography Centre, Southampton SO14 3ZH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7347-7411","authenticated-orcid":false,"given":"Meric","family":"Srokosz","sequence":"additional","affiliation":[{"name":"National Oceanography Centre, Southampton SO14 3ZH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,9,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Hall, C.D., and Cordey, R.A. (1988, January 12\u201316). Multistatic Scatterometry. Proceedings of the International Geoscience and Remote Sensing Symposium, \u2019Remote Sensing: Moving toward the 21st Century, Edinburgh, UK.","DOI":"10.1109\/IGARSS.1988.570200"},{"key":"ref_2","first-page":"331","article-title":"A passive reflectometry and interferometry system (PARIS): Application to ocean altimetry","volume":"17","year":"1993","journal-title":"ESA J."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1229","DOI":"10.1109\/TGRS.2005.845643","article-title":"Detection and Processing of Bistatically Reflected GPS Signals from Low Earth Orbit for the Purpose of Ocean Remote Sensing","volume":"43","author":"Gleason","year":"2005","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"5435","DOI":"10.1002\/2015GL064204","article-title":"Spaceborne GNSS reflectometry for ocean winds: First results from the UK TechDemoSat-1 mission","volume":"42","author":"Foti","year":"2015","journal-title":"Geophys. Res. Lett."},{"key":"ref_5","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_6","doi-asserted-by":"crossref","first-page":"8782","DOI":"10.1038\/s41598-018-27127-4","article-title":"A New Paradigm in Earth Environmental Monitoring with the CYGNSS Small Satellite Constellation","volume":"8","author":"Ruf","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"4678","DOI":"10.1109\/JSTARS.2016.2602703","article-title":"The GNSS Reflectometry Response to the Ocean Surface Winds and Waves","volume":"9","author":"Soisuvarn","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"12358","DOI":"10.1002\/2017GL076166","article-title":"First Spaceborne GNSS-Reflectometry Observations of Hurricanes From the UK TechDemoSat-1 Mission","volume":"44","author":"Foti","year":"2017","journal-title":"Geophys. Res. Lett."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2009","DOI":"10.1175\/BAMS-D-18-0337.1","article-title":"In-Orbit Performance of the Constellation of CyGNSS Hurricane Satellites","volume":"100","author":"Ruf","year":"2019","journal-title":"Am. Meteorol. Soc."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"5801","DOI":"10.1029\/2019JC015327","article-title":"Sea Ice Detection Using GNSS-R Data From TechDemoSat-1","volume":"124","author":"Cartwright","year":"2019","journal-title":"J. Geophys. Res. Ocean."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"4049","DOI":"10.1029\/2018GL077905","article-title":"Soil Moisture Sensing Using Spaceborne GNSS Reflections: Comparison of CyGNSS Reflectivity to SMAP Soil Moisture","volume":"45","author":"Chew","year":"2018","journal-title":"Geophys. Res. Lett."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1109\/MGRS.2014.2374220","article-title":"Tutorial on remote sensing using GNSS bistatic radar of opportunity","volume":"2","author":"Zavorotny","year":"2014","journal-title":"IEEE Geosci. Remote Sens. Mag."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Ruf, C., Gleason, S., Jelenak, Z., Katzberg, S., Ridley, S., 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_14","doi-asserted-by":"crossref","first-page":"9336","DOI":"10.1038\/s41598-018-27673-x","article-title":"CyGNSS data map flood inundation during the 2017 Atlantic hurricane season","volume":"8","author":"Chew","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Sa\u00efd, F., Jelenak, Z., Park, J., and Chang, P.S. (2021). The NOAA Track-Wise Wind Retrieval Algorithm and Product Assessment for CyGNSS. IEEE Trans. Geosci. Remote Sens., 1\u201324.","DOI":"10.1109\/TGRS.2021.3087426"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Wang, T., Ruf, C., Gleason, S., Block, B., Mckague, D., and Brien, A.O. (August, January 28). A Real-Time EIRP Level 1 Calibration Algorithm for the CYGNSS Mission Using the Zenith Measurements. Proceedings of the IGARSS 2019\u20142019 IEEE International Geoscience and Remote Sensing Symposium, Yokohama, Japan.","DOI":"10.1109\/IGARSS.2019.8900456"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Wang, T., Ruf, C., Block, B., and McKague, D. (2018, January 22\u201327). Characterization of the Transmit Power and Antenna Pattern of the GPS Constellation for the CYGNSS Mission. Proceedings of the IGARSS 2018\u20142018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain.","DOI":"10.1109\/IGARSS.2018.8518531"},{"key":"ref_18","unstructured":"Gleason, S. (2021, August 20). Level 1B DDM Calibration Algorithm Theoretical Basis Document rev. 3, CyGNSS Project Document 148-0137, Available online: https:\/\/podaac-tools.jpl.nasa.gov\/drive\/files\/allData\/cygnss\/L1\/docs\/148-0137-3_ATBD_L1B_v3.0_DDMCalibration_Release.pdf."},{"key":"ref_19","unstructured":"Hersbach, H., De Rosnay, P., Bell, B., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Balmaseda, A., Balsamo, G., and Bechtold, P. (2021, August 20). Operational Global Reanalysis: Progress, Future Directions and Synergies with NWP Including Updates on the ERA5 Production Status. Available online: https:\/\/www.ecmwf.int\/en\/elibrary\/18765-operational-global-reanalysis-progress-future-directions-and-synergies-nwp."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"831","DOI":"10.5194\/os-15-831-2019","article-title":"Characterizing ERA-interim and ERA5 surface wind biases using ASCAT","volume":"15","author":"Stoffelen","year":"2019","journal-title":"Ocean Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"50","DOI":"10.1109\/JSTARS.2018.2849323","article-title":"An Assessment of CYGNSS Normalized Bistatic Radar Cross Section Calibration","volume":"12","author":"Said","year":"2019","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1029\/2011JB008916","article-title":"The development and evaluation of the Earth Gravitational Model 2008 (EGM2008)","volume":"117","author":"Pavlis","year":"2012","journal-title":"J. Geophys. Res. Solid Earth"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Gleason, S., Brien, A.O., Russel, A., Al-khaldi, M.M., and Johnson, J.T. (2020). Geolocation, Calibration and Surface Resolution of CyGNSS GNSS-R Land Observations. Remote Sens., 12.","DOI":"10.3390\/rs12081317"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"66","DOI":"10.1109\/JSTARS.2018.2833075","article-title":"Development of the CYGNSS Geophysical Model Function for Wind Speed","volume":"12","author":"Ruf","year":"2019","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"951","DOI":"10.1109\/36.841977","article-title":"Scattering of GPS Signals from the Ocean with Wind Remote Sensing Application","volume":"38","author":"Zavorotny","year":"2000","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_26","unstructured":"Clarizia, M.P., Zavorotny, V., and Ruf, C. (2021, August 20). Level 2 Wind Speed Retrieval Algorithm Theoretical Basis Document rev. 6, CyGNSS Project Document 148-0138, Available online: https:\/\/podaac-tools.jpl.nasa.gov\/drive\/files\/allData\/cygnss\/L2\/docs\/148-0138-6_ATBD_L2_v3.0_Wind_Speed_Retrieval.pdf."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/17\/3500\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:55:52Z","timestamp":1760165752000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/17\/3500"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,9,3]]},"references-count":26,"journal-issue":{"issue":"17","published-online":{"date-parts":[[2021,9]]}},"alternative-id":["rs13173500"],"URL":"https:\/\/doi.org\/10.3390\/rs13173500","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,9,3]]}}}