Abstract
Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is quickly maturing toward the objective of becoming a viable alternative for operational coastal sea-level (SL) altimetry in a geocentric reference frame. SL has immense societal implications related to climate change. Of particular interest is the exploitation of existing coastal GNSS sites for reflectometry by means of signal-to-noise ratio (SNR) observables. We report results from the first inter-comparison campaign on SNR-based GNSS-R. The goal was to cross-validate retrieval solutions from independent research groups under comparable conditions. This action was an initiative of the International Association of Geodesy working group 4.3.9 (2015–2019 term). Data collected at the Onsala Space Observatory for a 1-year period (2015–2016) were compared to a co-located tide gauge (TG). SNR data for the GPS L1-C/A signal were processed by four groups, in Sweden, Luxembourg/Brazil, Germany, and the UK. Semidiurnal tidal constituents showed good agreement between TG and all GNSS-R groups. SL variations at diurnal and longer periods were also well captured by all series. Most GNSS-R solutions exhibited spurious tones at integer fractions of one sidereal day, the satellite revisit time of the particular GNSS constellation employed (GPS). Band-pass filtering between 3 h and 30 h confirmed that the dominant tidal components were well captured by most GNSS-R solutions. Higher-frequency SL variations (periods < 3 h) are poorly represented by GNSS-R as a consequence of its low temporal resolution. The solution with the worst agreement neglects a correction associated with the rate of change in sea level and uses narrower satellite elevation ranges per retrieval. Overall, there was excellent agreement, with correlation coefficients exceeding 0.9 and RMSE smaller than 5 cm.
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Data availability
The input and output datasets analyzed in the present study are available openly at the Zenodo repository, at https://doi.org/10.5281/zenodo.2924308 and https://doi.org/10.5281/zenodo.2925042 respectively.
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Acknowledgements
The tide gauge and GNSS-R data were provided by the Onsala Space Observatory, Chalmers University of Technology, Sweden, which is funded by Vetenskapsrådet, the Swedish Research Council. The Adlerbert Research Foundation partially funded the GNSS tide gauge project at the Onsala Space Observatory. The receivers and antennas were purchased through the Leica Geosystems ATHENA program. FGN acknowledges funding from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico; 457530/2014-6, 433099/2018-6) and Fapergs (Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul; 26228.414.42497.26062017). WL thanks for the sponsorship from Shanghai Pujiang Program (No. 18PJD017) and Shanghai Natural Science Foundation (18ZR1417100, 19ZR1422800).
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FGN and TH helped in project administration and provided statement based on the Contributor Roles Taxonomy (CRediT) and conceptualization. JS, RH, and TH contributed to data curation. All coauthors performed formal analysis, investigation, validation, and writing—review & editing and provided software. FGN, TH, JS, and ST contributed to methodology and visualization. FGN performed writing—original draft.
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T. Hobiger: Previously at Chalmers University of Technology.
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Geremia-Nievinski, F., Hobiger, T., Haas, R. et al. SNR-based GNSS reflectometry for coastal sea-level altimetry: results from the first IAG inter-comparison campaign. J Geod 94, 70 (2020). https://doi.org/10.1007/s00190-020-01387-3
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DOI: https://doi.org/10.1007/s00190-020-01387-3