# First In-Orbit Validation of Interferometric GNSS-R Altimetry: Mission Overview and Initial Results
## 5 Conclusions  
The first spaceborne demonstration of iGNSS-R altimetry via the 2023 Chinese satellite mission has validated its operational feasibility for global ocean monitoring. Our crossover validation with Jason-3 and Sentinel-6 reveals an unprecedented altimetric accuracy of 17.2 cm at 40 km resolution, representing a breakthrough improvement over previous GNSS-R missions and establishing a new benchmark for GNSS-R altimetry. Compared to traditional altimeters and SWOT's single-pass performance, iGNSS-R technology shows clear disadvantages in measurement precision. However, the successful demonstration of the iGNSS-R technology opens up new possibilities for cost-effective, wide-swath sea level monitoring; its unique advantages--including an observation swath exceeding 1000 km and rapid global coverage/revisit capability--present opportunities for complementary use with existing altimetry systems and enhance our understanding of global sea surface dynamics. Future work will focus on further refining the SSH retrieval model and error correction methods presented in this study in order to achieve optimal performance, and on validating the impacts of ionospheric delay and sea state bias. Notably, iGNSS-R has also demonstrated strong coherent characteristics over polar ice surfaces, where its altimetric accuracy and spatial resolution are expected to surpass those over ocean surfaces. Exploring iGNSS-R's applications in polar ice detection will be an important focus of future research. Conceptualization, Y.S. ([PERSON]), [PERSON] ([PERSON]) and J.X. ; methodology, [PERSON] ([PERSON]), J.X., Q.D., W.B. and L.D. ; software, L.H., J.X., X.W., D.W., L.D., Z.H. and S.L. ; validation, [PERSON] ([PERSON]), J.X., L.H., Z.Z. and B.G. ; investigation, [PERSON] ([PERSON]) and J.X. ; resources, [PERSON] ([PERSON]), J.X., L.H., Q.D. and W.B. ; data curation, [PERSON] ([PERSON]), J.X., L.H., F.H., C.Y. and R.L. ; writing--[PERSON]. ([PERSON]), J.X. and L.H. ; writing--review and editing, Y.S. ([PERSON]), Y.S. ([PERSON]), J.X., L.H., Q.D., W.B., L.D., X.W., D.W., Y.C., Z.Z., B.G., Z.H., S.L., F.H., C.Y. and R.L. ; funding acquisition, Y.S. ([PERSON]), Q.D. and W.B. All authors have read and agreed to the published version of the manuscript. This research was funded by the Youth Innovation Promotion Association, CAS, grant number 2020152; the National Natural Science Foundation of China, grant number 42104032 and 42074042; the Youth Cross Team Scientific Research Project of the Chinese Academy of Sciences, grant number JCTD-2021-10; the FengYun Application Pioneering Project, grant number FY-APP-2022.0108; and the State Key Laboratory of Spatial Datum, grant number SKLGIE2024-ZZ-3 and SKLGIE2023-ZZ-5. The Jason-3 and Sential-6 datasets used in this study can be downloaded individually from ftp-access.aviso.altimetry.fr and [[https://data.eumetsat.int/](https://data.eumetsat.int/)]([https://data.eumetsat.int/](https://data.eumetsat.int/)) (accessed on 1 April 2025). The iGNSS-R datasets used in this study are not readily available because the data are part of ongoing research, and interested readers may contact the authors for updates on data accessibility. DTU21 MSS can be found at [[https://ftp.space.dtu.dk/pub/](https://ftp.space.dtu.dk/pub/)]([https://ftp.space.dtu.dk/pub/](https://ftp.space.dtu.dk/pub/)) (accessed on 1 April 2025). The final GNSS precise ephemeris can be downloaded from [[ftp://igs.gnsswhu.cn/pub/gnss/products/mgex/](ftp://igs.gnsswhu.cn/pub/gnss/products/mgex/)]([ftp://igs.gnsswhu.cn/pub/gnss/products/mgex/](ftp://igs.gnsswhu.cn/pub/gnss/products/mgex/)) (accessed on 1 April 2025). The ECMWF reanalysis temperature and humidity can be found at [[https://cds.climate.copernicus.eu/datasets](https://cds.climate.copernicus.eu/datasets)]([https://cds.climate.copernicus.eu/datasets](https://cds.climate.copernicus.eu/datasets)) (accessed on 1 April 2025).