{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,31]],"date-time":"2025-10-31T08:00:20Z","timestamp":1761897620962,"version":"build-2065373602"},"reference-count":63,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2021,10,19]],"date-time":"2021-10-19T00:00:00Z","timestamp":1634601600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100011033","name":"Agencia Estatal de Investigaci\u00f3n","doi-asserted-by":"publisher","award":["RTI2018-099008-B-C21\/AEI\/10.13039\/501100011033","MDM-2016-060"],"award-info":[{"award-number":["RTI2018-099008-B-C21\/AEI\/10.13039\/501100011033","MDM-2016-060"]}],"id":[{"id":"10.13039\/501100011033","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Altimetric performance of Global Navigation Satellite System - Reflectometry (GNSS-R) instruments depends on receiver\u2019s bandwidth and signal-to-noise ratio (SNR). The altimetric delay is usually computed from the time difference between the peak of the direct signal waveform and the maximum of the derivative of the reflected signal waveform. Dual-frequency data gathered by the airborne Microwave Interferometric Reflectometer (MIR) in the Bass Strait, between Australia and Tasmania, suggest that this approach is only valid for flat surfaces and large bandwidth receivers. This work analyses different methods to compute the altimetric observables using GNSS-R. A proposed novel method, the Peak-to-Minimum of the 3rd Derivative (P-Min3D) for narrow-band codes (e.g., L1 C\/A), and the Peak-to-Half Power (P-HP) for large bandwidth codes (e.g., L5 or E5a codes) show improved performance when using real data. Both methods are also compared to the Peak-to-Peak (P-P) and Peak-to-Maximum of the 1st Derivative (P-Max1D) methods. The key difference between these methods is the determination of the delay position in the reflected signal waveform in order to compute the altimetric observable. Airborne experimental results comparing the different methods, bands and GNSS-R processing techniques show that centimeter level accuracy can be achieved.<\/jats:p>","DOI":"10.3390\/rs13204186","type":"journal-article","created":{"date-parts":[[2021,10,20]],"date-time":"2021-10-20T21:31:26Z","timestamp":1634765486000},"page":"4186","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Improved GNSS-R Altimetry Methods: Theory and Experimental Demonstration Using Airborne Dual Frequency Data from the Microwave Interferometric Reflectometer (MIR)"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8899-6911","authenticated-orcid":false,"given":"Oriol Cervell\u00f3 i","family":"Nogu\u00e9s","sequence":"first","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6441-6676","authenticated-orcid":false,"given":"Joan Francesc","family":"Munoz-Martin","sequence":"additional","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0031-0802","authenticated-orcid":false,"given":"Hyuk","family":"Park","sequence":"additional","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9514-4992","authenticated-orcid":false,"given":"Adriano","family":"Camps","sequence":"additional","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6636-1587","authenticated-orcid":false,"given":"Raul","family":"Onrubia","sequence":"additional","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8517-2415","authenticated-orcid":false,"given":"Daniel","family":"Pascual","sequence":"additional","affiliation":[{"name":"CommSensLab\u2014UPC, Universitat Polit\u00e8cnica de Catalunya\u2014BarcelonaTech, and IEEC\/CTE-UPC, 08034 Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4375-4446","authenticated-orcid":false,"given":"Christoph","family":"R\u00fcdiger","sequence":"additional","affiliation":[{"name":"Science and Innovation Group\/Research, Bureau of Meteorology, Docklands, VIC 3008, Australia"},{"name":"Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4817-2712","authenticated-orcid":false,"given":"Jeffrey P.","family":"Walker","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9186-6867","authenticated-orcid":false,"given":"Alessandra","family":"Monerris","sequence":"additional","affiliation":[{"name":"Department of Infrastructure Engineering, The University of Melbourne, Parkville, VIC 3010, Australia"}]}],"member":"1968","published-online":{"date-parts":[[2021,10,19]]},"reference":[{"key":"ref_1","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_2","doi-asserted-by":"crossref","first-page":"4343","DOI":"10.1029\/2001GL013815","article-title":"2-cm GPS altimetry over Crater Lake","volume":"28","author":"Treuhaft","year":"2001","journal-title":"Geophys. 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