{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:02:28Z","timestamp":1760241748581,"version":"build-2065373602"},"reference-count":38,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2018,8,1]],"date-time":"2018-08-01T00:00:00Z","timestamp":1533081600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>GNSS-R (Global Navigation Satellite System-Reflectometry) has been demonstrated to be a new and powerful tool to sense soil moisture in recent years. Multi-antenna pattern and single-antenna pattern have been proposed regarding how to receive and process reflected signals. Great efforts have been made concerning ground-based and air-borne observations. Meanwhile, a number of satellite-based missions have also been implemented. For the in-depth study of soil moisture remote sensing by the technique of GNSS-R, regardless of the extraction methods of the reflected signals or the types of the observation platform, three key issues have to be determined: The specular reflection point, the spatial resolution and the detection depth in the soil. However, in current literatures, there are no comprehensive explanations of the above three key issues. This paper conducts theoretical analysis and formula derivation, aiming to systematically and quantitatively determine the extent of soil moisture being detected in three dimensions from the above-mentioned aspects. To further explain how the three factors behave in the specific application, the results of two application scenarios are shown: (1) a ground-based GPS measurement in Marshall, Colorado, US from the Plate Boundary Observatory, corresponding to single-antenna pattern. The relative location of the specular reflection points, the average area of the First Fresnel Ellipse Clusters and the sensing depth of the time-series soil moisture are analyzed, and (2) an aviation experiment conducted in Zhengzhou to retrieve soil moisture content, corresponding to the multi-antenna pattern. The spatial distribution of soil moisture estimation with a certain resolution based on the flight tracks and the relevant sensing depth are manifested. For remote sensing using GNSS reflected signals, BeiDou is different from GPS mainly in the carrier frequency. Therefore, the results of this study can provide references for China\u2019s future development of the BeiDou-R technique.<\/jats:p>","DOI":"10.3390\/s18082498","type":"journal-article","created":{"date-parts":[[2018,8,1]],"date-time":"2018-08-01T11:22:34Z","timestamp":1533122554000},"page":"2498","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Analysis of Key Issues on GNSS-R Soil Moisture Retrieval Based on Different Antenna Patterns"],"prefix":"10.3390","volume":"18","author":[{"given":"Fei","family":"Li","sequence":"first","affiliation":[{"name":"Institute of Remote Sensing and GIS, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China"}]},{"given":"Xuefeng","family":"Peng","sequence":"additional","affiliation":[{"name":"Institute of Remote Sensing and GIS, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China"}]},{"given":"Xiuwan","family":"Chen","sequence":"additional","affiliation":[{"name":"Institute of Remote Sensing and GIS, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3319-6284","authenticated-orcid":false,"given":"Maolin","family":"Liu","sequence":"additional","affiliation":[{"name":"Institute of Remote Sensing and GIS, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China"}]},{"given":"Liwen","family":"Xu","sequence":"additional","affiliation":[{"name":"Institute of Remote Sensing and GIS, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China"}]}],"member":"1968","published-online":{"date-parts":[[2018,8,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"461","DOI":"10.3724\/SP.J.1300.2013.13080","article-title":"The current status of research on GNSS-R remote sensing technology in China and future development","volume":"2","author":"Li","year":"2013","journal-title":"J. Radars"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Jia, Y., and Savi, P. (2016, January 10\u201315). Polarimetric GNSS-R measurements for soil moisture and vegetation sensing. Proceedings of the 2016 IEEE International Geoscience and Remote Sensing Symposium, Beijing, China.","DOI":"10.1109\/IGARSS.2016.7730370"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2110","DOI":"10.1109\/LGRS.2014.2320852","article-title":"An algorithm for sea-surface wind field retrieval from GNSS-R delay-doppler map","volume":"11","author":"Li","year":"2014","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"4817","DOI":"10.1109\/JSTARS.2016.2560763","article-title":"Estimation of snow depth from GLONASS SNR and phase-based multipath reflectometry","volume":"9","author":"Qian","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"4795","DOI":"10.1109\/JSTARS.2016.2582690","article-title":"Spaceborne GNSS-R sea ice detection using delay-doppler maps: First results from the U.K. TechDemoSat-1 mission","volume":"9","author":"Yan","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1363","DOI":"10.1109\/TGRS.2015.2478776","article-title":"Weak tsunami detection using GNSS-R-based sea surface height measurement","volume":"54","author":"Yu","year":"2016","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"3317","DOI":"10.1002\/2016GL068189","article-title":"Demonstrating soil moisture remote sensing with observations from the UK TechDemoSat-1 satellite mission","volume":"43","author":"Chew","year":"2016","journal-title":"Geophys. Res. Lett."},{"key":"ref_8","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":"2017","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Ruf, C., Gleason, S., Ridley, A., Rose, R., and Scherrer, J. (2017, January 23\u201328). The nasa cygnss mission: Overview and status update. Proceedings of the 2017 IEEE International Geoscience and Remote Sensing Symposium, Fort Worth, TX, USA.","DOI":"10.1109\/IGARSS.2017.8127537"},{"key":"ref_10","unstructured":"Wickert, J., Andersen, O.B., Beyerle, G., Chapron, B., Cardellach, E., D\u2019Addio, S., Foerste, C., Gommenginger, C., Gruber, T., and Helm, A. (2013). GEROS-ISS: Innovative GNSS Reflectometry\/Occultation Payload Onboard the International Space Station for the Global Geodetic Observing System, American Geophysical Union."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1436","DOI":"10.1109\/JSTARS.2014.2320873","article-title":"Optimization and performance analysis of interferometric GNSS-R altimeters: Application to the PARIS IoD mission","volume":"7","author":"Camps","year":"2014","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Buchanan, M., and O\u2019Brien, A. (2017, January 23\u201328). Investigation of spaceborne polarimetric GNSS-R using the SMAP radar instrument. Proceedings of the 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2017), Fort Worth, TX, USA.","DOI":"10.1109\/IGARSS.2017.8127901"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Cosh, M.H., Ochsner, T., and Mckee, L. (2016). Early conclusions of the soil moisture active passive marena Oklahoma in situ sensor testbed (SMAP-MOISST). Vadose Zone J., 15.","DOI":"10.2136\/vzj2015.09.0122"},{"key":"ref_14","unstructured":"Masters, D., Zavorotny, V., Katzberg, S., and Emery, W. (2000, January 24\u201328). GPS signal scattering from land for moisture content determination. Proceedings of the IEEE 2000 International Geoscience and Remote Sensing Symposium, 2000 (IGARSS 2000), Honolulu, HI, USA."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"507","DOI":"10.1016\/j.rse.2004.05.016","article-title":"Initial results of land-reflected GPS bistatic radar measurements in SMEX02","volume":"92","author":"Masters","year":"2004","journal-title":"Remote Sens. Environ."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2356","DOI":"10.3390\/rs4082356","article-title":"Global navigation satellite systems reflectometry as a remote sensing tool for agriculture","volume":"4","author":"Egido","year":"2012","journal-title":"Remote Sens."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1522","DOI":"10.1109\/JSTARS.2014.2322854","article-title":"Airborne GNSS-R polarimetric measurements for soil moisture and above-ground biomass estimation","volume":"7","author":"Egido","year":"2014","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Alonso-Arroyo, A., Camps, A., Monerris, A., R\u00fcdiger, C., Walker, J.P., Forte, G., Pascual, D., Park, H., and Onrubia, R. (2014, January 13\u201318). The light airborne reflectometer for GNSS-R observations (LARGO) instrument: Initial results from airborne and Rover field campaigns. Proceedings of the 2014 IEEE Geoscience and Remote Sensing Symposium, Quebec City, QC, Canada.","DOI":"10.1109\/IGARSS.2014.6947376"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Alonso-Arroyo, A., Forte, G., Camps, A., Park, H., Pascual, D., Onrubia, R., and Jove-Casulleras, R. (2013, January 21\u201326). Soil Moisture mapping using forward scattered GPS L1 signals. Proceedings of the 2013 IEEE Geoscience and Remote Sensing Symposium, Melbourne, VIC, Australia.","DOI":"10.1109\/IGARSS.2013.6721165"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Alonsoarroyo, A., Torrecilla, S., Querol, J., Camps, A., Pascual, D., Park, H., and Onrubia, R. (2015, January 26\u201331). Two dedicated soil moisture experiments using the scatterometric properties of GNSS-reflectometry. Proceedings of the 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Milan, Italy.","DOI":"10.1109\/IGARSS.2015.7326682"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1016\/j.rse.2017.06.020","article-title":"SMAP radar receiver measures land surface freeze\/thaw state through capture of forward-scattered L-band signals","volume":"198","author":"Chew","year":"2017","journal-title":"Remote Sens. Environ."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"91","DOI":"10.1109\/JSTARS.2009.2033612","article-title":"GPS multipath and its relation to near-surface soil moisture content","volume":"3","author":"Larson","year":"2010","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2755","DOI":"10.1109\/TGRS.2014.2364513","article-title":"Vegetation sensing using GPS-interferometric reflectometry: Theoretical effects of canopy parameters on signal-to-noise ratio data","volume":"53","author":"Chew","year":"2015","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"28287","DOI":"10.3390\/s151128287","article-title":"Prototyping a GNSS-based passive radar for UAVs: An instrument to classify the water content feature of lands","volume":"15","author":"Gamba","year":"2015","journal-title":"Sensors"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"4781","DOI":"10.1109\/JSTARS.2016.2537847","article-title":"Detection of soil moisture variations using gps and GLONASS SNR data for elevation angles ranging from 2\u00b0 to 70\u00b0","volume":"9","author":"Roussel","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_26","first-page":"1134","article-title":"SVRM-assisted soil moisture retrieval method using reflected signal from BeiDou GEO satellites","volume":"42","author":"Lei","year":"2016","journal-title":"J. Beijing Univ. Aeronaut. Astronaut."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Wei, W., Huang, L.I., Yang, H., Chen, X., and Peng, X. (2015). Definition and application of GNSS-R observation patterns. J. Remote Sens.","DOI":"10.11834\/jrs.20154304"},{"key":"ref_28","unstructured":"Kaplan, E.D., and Hegarty, C.J. (2006). Understanding GPS: Principles and Applications, Artech House Inc."},{"key":"ref_29","unstructured":"Torres, O. (2004). Analysis of Reflected Global Positioning System Signals as a Method for the Determination of Soil Moisture. [Master\u2019s Thesis, University of Texas]."},{"key":"ref_30","unstructured":"Katzberg, S.J., and Garrison, J.J.L. (1996). Utilizing GPS to Determine Ionospheric Delay over the Ocean."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"4700","DOI":"10.1109\/JSTARS.2016.2543301","article-title":"Reconstruction of the radar image from actual DDMs collected by TechDemoSat-1 GNSS-R mission","volume":"9","author":"Schiavulli","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1016\/j.rse.2005.09.015","article-title":"Utilizing calibrated GPS reflected signals to estimate soil reflectivity and dielectric constant: Results from SMEX02","volume":"100","author":"Katzberg","year":"2006","journal-title":"Remote Sens. Environ."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1573","DOI":"10.1109\/JSTARS.2014.2301019","article-title":"Reconstruction of the normalized radar cross section field from GNSS-R delay-doppler map","volume":"7","author":"Schiavulli","year":"2014","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_34","unstructured":"Ulaby, F.T., Moore, R.K., and Fung, A.K. (1986). Microwave Remote Sensing Active and Passive-Volume III: From Theory to Applications, Artech House Inc."},{"key":"ref_35","unstructured":"Ulaby, F.T., Moore, R.K., and Fung, A.K. (1982). Microwave Remote Sensing Active and Passive-Volume II: Radar Remote Sensing and Surface Scattering and Enission Theory, Artech House Inc."},{"key":"ref_36","first-page":"2711","article-title":"Dual-frequency synthetic aperture radar for deep soil moisture estimation","volume":"29","author":"Zhang","year":"2007","journal-title":"J. Electron. Inf. Technol."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1109\/TGRS.1985.289497","article-title":"Microwave dielectric behavior of wet soil-part 1: Empirical models and experimental observations","volume":"GE-23","author":"Hallikainen","year":"2007","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"803","DOI":"10.1109\/36.387598","article-title":"Dielectric properties of soils in the 0.3-1.3-GHz range","volume":"33","author":"Peplinski","year":"1995","journal-title":"IEEE Trans. Geosci. Remote Sens."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/8\/2498\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T15:15:48Z","timestamp":1760195748000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/18\/8\/2498"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,8,1]]},"references-count":38,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2018,8]]}},"alternative-id":["s18082498"],"URL":"https:\/\/doi.org\/10.3390\/s18082498","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2018,8,1]]}}}