{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T14:47:31Z","timestamp":1773931651236,"version":"3.50.1"},"reference-count":55,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2020,10,20]],"date-time":"2020-10-20T00:00:00Z","timestamp":1603152000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"the National Key R&amp;D Program of China","award":["2016YFC1401005"],"award-info":[{"award-number":["2016YFC1401005"]}]},{"name":"the National Science Foundation of China","award":["61931025"],"award-info":[{"award-number":["61931025"]}]},{"name":"the National Science Foundation of China","award":["61501130"],"award-info":[{"award-number":["61501130"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The rain-free normalized radar cross-section (NRCS) measurements from the Ku-band precipitation radars (PRs) aboard the tropical rainfall measuring mission (TRMM) and the global precipitation measurement (GPM) mission, along with simultaneous sea surface wind truth from buoy observations, stepped-frequency microwave radiometer (SFMR) measurements, and H*Wind analyses, are used to investigate the abilities of the quasi-specular scattering models, i.e., the physical optics model (PO) and the classical and improved geometrical optics models (GO and GO4), to reproduce the Ku-band NRCS at low incidence angles of 0\u201318\u00b0 over the wind speed range of 0\u201345 m\/s. On this basis, the limitations of the quasi-specular scattering theory and the effects of wave breaking are discussed. The results show that the return caused by quasi-specular reflection is affected significantly by the presence of background swell waves at low winds. At moderate wind speeds of 5\u201315 m\/s, the NRCS is still dominated by the quasi-specular reflection, and the wave breaking starts to work but its contribution is very small, thus, the models are found in excellent agreement with the measurements. With wind speed increasing, the impact of wave breaking increases, whereas the role of standard quasi-specular reflection decreases. The wave breaking impact on NRCS is first visible at incidence angles near 18\u00b0 as wind speed exceeds about 20 m\/s, then it becomes dominant when wind speed exceeds about 37 m\/s where the NRCS is insensitive to wind speed and depends linearly on incidence angle, which cannot be explained by the standard quasi-specular scattering theory.<\/jats:p>","DOI":"10.3390\/rs12203445","type":"journal-article","created":{"date-parts":[[2020,10,20]],"date-time":"2020-10-20T09:28:23Z","timestamp":1603186103000},"page":"3445","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models"],"prefix":"10.3390","volume":"12","author":[{"given":"Qiushuang","family":"Yan","sequence":"first","affiliation":[{"name":"College of Oceanography and Space Informatics, China University of Petroleum, Qingdao 266580, China"},{"name":"Oceanic Telemetry Engineering and Technology Research Center, Ministry of Natural Resources, Qingdao 266061, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chenqing","family":"Fan","sequence":"additional","affiliation":[{"name":"Oceanic Telemetry Engineering and Technology Research Center, Ministry of Natural Resources, Qingdao 266061, China"},{"name":"First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jie","family":"Zhang","sequence":"additional","affiliation":[{"name":"College of Oceanography and Space Informatics, China University of Petroleum, Qingdao 266580, China"},{"name":"Oceanic Telemetry Engineering and Technology Research Center, Ministry of Natural Resources, Qingdao 266061, China"},{"name":"First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Junmin","family":"Meng","sequence":"additional","affiliation":[{"name":"Oceanic Telemetry Engineering and Technology Research Center, Ministry of Natural Resources, Qingdao 266061, China"},{"name":"First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3000","DOI":"10.1109\/TGRS.2017.2658672","article-title":"SWIM: The first spaceborne wave scatterometer","volume":"55","author":"Hauser","year":"2017","journal-title":"IEEE Trans. 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