{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T01:52:55Z","timestamp":1760233975706,"version":"build-2065373602"},"reference-count":34,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2021,3,9]],"date-time":"2021-03-09T00:00:00Z","timestamp":1615248000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000270","name":"Natural Environment Research Council","doi-asserted-by":"publisher","award":["NE\/L002566\/1"],"award-info":[{"award-number":["NE\/L002566\/1"]}],"id":[{"id":"10.13039\/501100000270","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>GNSS Reflectometry (GNSS-R), a method of remote sensing using the reflections from satellite navigation systems, was initially envisaged for ocean wind speed sensing. In recent times there has been significant interest in the use of GNSS-R for sensing land parameters such as soil moisture, which has been identified as an Essential Climate Variable (ECV). Monitoring objectives for ECVs set by the Global Climate Observing System (GCOS) organisation include a reduction in data gaps from spaceborne sources. GNSS-R can be implemented on small, relatively cheap platforms and can enable the launch of constellations, thus reducing such data gaps in these important datasets. However in order to realise operational land sensing with GNSS-R, adaptations are required to existing instrumentation. Spaceborne GNSS-R requires the reflection points to be predicted in advance, and for land sensing this means the effect of topography must be considered. This paper presents an algorithm for on-board prediction of reflection points over the land, allowing generation of DDMs on-board as well as compression and calibration. The algorithm is tested using real satellite data from TechDemoSat-1 in a software receiver with on-board constraints being considered. Three different resolutions of Digital Elevation Model are compared. The algorithm is shown to perform better against the operational requirements of sensing land parameters than existing methods and is ready to proceed to flight testing.<\/jats:p>","DOI":"10.3390\/rs13051031","type":"journal-article","created":{"date-parts":[[2021,3,9]],"date-time":"2021-03-09T06:22:32Z","timestamp":1615270952000},"page":"1031","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Towards a Topographically-Accurate Reflection Point Prediction Algorithm for Operational Spaceborne GNSS Reflectometry\u2014Development and Verification"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3758-7688","authenticated-orcid":false,"given":"Lucinda","family":"King","sequence":"first","affiliation":[{"name":"Surrey Space Centre, University of Surrey, Guildford GU2 7HX, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6143-8944","authenticated-orcid":false,"given":"Martin","family":"Unwin","sequence":"additional","affiliation":[{"name":"Surrey Satellite Technology Ltd., Guildford GU2 7YE, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4277-4894","authenticated-orcid":false,"given":"Jonathan","family":"Rawlinson","sequence":"additional","affiliation":[{"name":"Surrey Satellite Technology Ltd., Guildford GU2 7YE, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9041-4244","authenticated-orcid":false,"given":"Raffaella","family":"Guida","sequence":"additional","affiliation":[{"name":"Surrey Space Centre, University of Surrey, Guildford GU2 7HX, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7001-5510","authenticated-orcid":false,"given":"Craig","family":"Underwood","sequence":"additional","affiliation":[{"name":"Surrey Space Centre, University of Surrey, Guildford GU2 7HX, UK"}]}],"member":"1968","published-online":{"date-parts":[[2021,3,9]]},"reference":[{"key":"ref_1","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_2","doi-asserted-by":"crossref","first-page":"4730","DOI":"10.1109\/JSTARS.2016.2588467","article-title":"Sensitivity of GNSS-R Spaceborne Observations to Soil Moisture and Vegetation","volume":"9","author":"Camps","year":"2016","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote. Sens."},{"key":"ref_3","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_4","unstructured":"Jales, P. (2012). Spaceborne Receiver Design for Scatterometric GNSS Reflectometry. [Ph.D. Thesis, University of Surrey]."},{"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","unstructured":"DMA WGS84 Development Committee (1991). Department of Defense World Geodetic System 1984, Its Definition and Relationships with Local Geodetic Systems, Technical Report 8350.2."},{"key":"ref_7","first-page":"331","article-title":"PARIS: Application to Ocean Altimetry","volume":"17","year":"1993","journal-title":"ESA J."},{"key":"ref_8","unstructured":"Fraczek, W. (2003). Mean Sea Level, GPS, and the Geoid, ArcUser."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2990","DOI":"10.1109\/TGRS.2018.2879059","article-title":"Quality Control of Delay-Doppler Maps for Stare Processing","volume":"57","author":"Grieco","year":"2019","journal-title":"IEEE Trans. Geosci. Remote. Sens."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"King, L., Unwin, M., Rawlinson, J., Guida, R., and Underwood, C. (October, January 26). A Topographically-Accurate GNSS-R Reflection Point Predictor For On-Board Operational Processing. Proceedings of the IGARSS 2020\u20142020 IEEE International Geoscience and Remote Sensing Symposium, Waikoloa, HI, USA.","DOI":"10.1109\/IGARSS39084.2020.9324677"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Gleason, S. (2019). A Real-Time On-Orbit Signal Tracking Algorithm for GNSS Surface Observations. Remote. Sens., 11.","DOI":"10.3390\/rs11161858"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1740","DOI":"10.1109\/JSTARS.2020.2981570","article-title":"Modeling the Effects of Topography on Delay-Doppler Maps","volume":"13","author":"Campbell","year":"2020","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote. Sens."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Gleason, S., O\u2019Brien, A., 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_14","unstructured":"Global Climate Observing System (GCOS) (2010). Essential Climate Variables, GCOS."},{"key":"ref_15","unstructured":"Global Climate Observing System (GCOS) (2010). The GCOS Story, GCOS."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Brocca, L., Ciabatta, L., Massari, C., Camici, S., and Tarpanelli, A. (2017). Soil moisture for hydrological applications: Open questions and new opportunities. Water, 9.","DOI":"10.3390\/w9020140"},{"key":"ref_17","unstructured":"Global Climate Observing System (GCOS) (2003). GCOS Monitoring Principles, GCOS."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Camps, A., Vall\u00b7Llossera, M., Park, H., Portal, G., and Rossato, L. (2018). Sensitivity of TDS-1 GNSS-R Reflectivity to Soil Moisture: Global and Regional Differences and Impact of Different Spatial Scales. Remote. Sens., 11.","DOI":"10.3390\/rs10111856"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Pierdicca, N., Mollfulleda, A., Costantini, F., Guerriero, L., Dente, L., Paloscia, S., Santi, E., and Zribi, M. (2018, January 22\u201327). Spaceborne GNSS Reflectometry Data For Land Applications: An Analysis Of TechDemoSat Data. Proceedings of the IGARSS 2018\u20142018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain.","DOI":"10.1109\/IGARSS.2018.8517987"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2996","DOI":"10.1109\/JSTARS.2020.2986859","article-title":"Monitoring Freeze-Thaw State by Means of GNSS Reflectometry: An Analysis of TechDemoSat-1 Data","volume":"13","author":"Comite","year":"2020","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote. Sens."},{"key":"ref_21","unstructured":"Surrey Satellite Technology Ltd (2019). MERRByS Product Manual\u2014GNSS Reflectometry on TDS-1 with the SGR-ReSI, Surrey Satellite Technology Ltd.. [7th ed.]."},{"key":"ref_22","unstructured":"Eakins, B.W., and Sharman, G.F. (2012). Hypsographic Curve of Earth\u2019s Surface from ETOPO1."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"7.1","DOI":"10.1175\/AMSMONOGRAPHS-D-15-0018.1","article-title":"Impacts of the Tibetan Plateau on Asian Climate","volume":"56","author":"Wu","year":"2016","journal-title":"Meteorol. Monogr."},{"key":"ref_24","unstructured":"Gleason, S. (2018). Algorithm Theoretical Basis Document\u2014Level 1B DDM Calibration."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/sdata.2018.40","article-title":"A suite of global, cross-scale topographic variables for environmental and biodiversity modeling","volume":"5","author":"Amatulli","year":"2018","journal-title":"Sci. Data"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Danielson, J., and Gesch, D. (2011). Global Multi-Resolution Terrain Elevation Data 2010 (GMTED2010), U.S. Geological Survey Open-File Report 2011-1073.","DOI":"10.3133\/ofr20111073"},{"key":"ref_27","unstructured":"Jarvis, A., Reuter, H., and Nelson, A. (2008). Hole-Filled Seamless SRTM Data V4, International Centre for Tropical Agriculture (CIAT)."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"49","DOI":"10.1016\/j.rse.2016.04.018","article-title":"A multi-sensor approach towards a global vegetation corrected SRTM DEM product","volume":"182","author":"Paiva","year":"2016","journal-title":"Remote. Sens. Environ."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"111825","DOI":"10.1016\/j.rse.2020.111825","article-title":"Analysis of scattering characteristics from inland bodies of water observed by CYGNSS","volume":"245","author":"Loria","year":"2020","journal-title":"Remote. Sens. Environ."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Al-Khaldi, M.M., Johnson, J.T., Gleason, S., Loria, E., O\u2019Brien, A.J., and Yi, Y. (2020). An Algorithm for Detecting Coherence in Cyclone Global Navigation Satellite System Mission Level-1 Delay-Doppler Maps. IEEE Trans. Geosci. Remote. Sens., 1\u201310.","DOI":"10.1109\/TGRS.2020.3009784"},{"key":"ref_31","unstructured":"SSTL, and NOC (2015). Measurement of Earth Reflected Radio-Navigation Signals By Satellite, SSTL."},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"De Vos Van Steenwijk, R., Unwin, M., and Jales, P. (2010, January 8\u201310). Introducing the SGR-ReSI: A next generation spaceborne GNSS receiver for navigation and remote-sensing. Proceedings of the Programme and Abstract Book\u20145th ESA Workshop on Satellite Navigation Technologies and European Workshop on GNSS Signals and Signal Processing, NAVITEC 2010, Noordwijk, The Netherlands.","DOI":"10.1109\/NAVITEC.2010.5708063"},{"key":"ref_33","unstructured":"Kwan, P. (2019). NAVSTAR GPS Space Segment\/User Segment Interfaces, GPS Directorate, Space & Missile Systems Center (SMC). IS-GPS-200."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"2119","DOI":"10.1109\/TGRS.2009.2036721","article-title":"Altimetric Analysis of the Sea-Surface GPS-Reflected Signals","volume":"48","author":"Rius","year":"2010","journal-title":"IEEE Trans. Geosci. Remote Sens."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/5\/1031\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:35:21Z","timestamp":1760160921000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/5\/1031"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,3,9]]},"references-count":34,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2021,3]]}},"alternative-id":["rs13051031"],"URL":"https:\/\/doi.org\/10.3390\/rs13051031","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2021,3,9]]}}}