| 20 Apr 2026
A multi-year dataset of integrated water vapor derived from shipborne GNSS observations collected aboard eight French research vessels during oceanographic campaigns (2015–2024)
Abstract. In the context of climate change and the growing need for improved observations of the atmospheric water cycle, measurements of atmospheric water vapor over the global ocean remain scarce compared with those available over land. This observational gap can be addressed using Integrated Water Vapor (IWV) derived from shipborne Global Navigation Satellite System (GNSS) observations, which provide a robust and well-established method for monitoring atmospheric moisture over the oceans.
This study presents a shipborne IWV dataset obtained from the processing of raw data collected by GNSS antennas installed on research vessels. The dataset benefits from substantial support and data access provided by Genavir, the operator of the French Oceanographic Fleet (FOF), and the Ifremer archive department SISMER. It is based on oceanographic campaigns conducted worldwide by eight vessels over a ten-year period (2015–2024), representing a total of 6,427 campaign days in both offshore and coastal regions.
After describing the methodology used to derive IWV from raw GNSS observations and to remove spurious measurements through a screening procedure, the dataset is evaluated through comparisons with the ERA5 reanalysis and satellite radiometer measurements from Remote Sensing Systems. These comparisons yield mean differences of (0.3 ± 2.0) kg m−2 and (−0.4 ± 1.8) kg m−2, respectively.
To further quantify the inherent uncertainty of the shipborne IWV retrieval, the dataset is cross-validated using instances where two vessels were within 50 km of each other. This comparison results in an estimated uncertainty of 0.96 kg m−2, demonstrating the suitability of the dataset for climate studies.
Local discrepancies identified in these comparisons are discussed, highlighting limitations in each dataset considered.
The GNSS-derived IWV dataset is intended to be updated annually to support long-term monitoring of atmospheric water vapor over the global ocean.
The IWV estimates are available at https://doi.org/10.25326/876 (Panetier and Bosser, 2026) through the AERIS data center (https://en.aeris-data.fr/, last access: 20 March 2026), and currently span the period from 2015 to the end of 2024.
The manuscript presents a valuable multi-year dataset of integrated water vapor (IWV) derived from shipborne GNSS observations collected aboard eight French research vessels during oceanographic campaigns between 2015 and 2024. The topic is timely and relevant, as observations of atmospheric water vapor over the oceans remain sparse compared with land areas, while such measurements are essential for climate studies, numerical weather prediction, satellite validation, and the investigation of ocean–atmosphere interactions.
The main strength of the manuscript is the systematic construction of a long-term and geographically extensive IWV dataset from opportunistic shipborne GNSS observations. The authors provide a clear description of the GNSS processing strategy, the screening procedure, and the conversion from ZTD/ZWD to IWV. The dataset is carefully evaluated using independent reference data, including ERA5 reanalysis, satellite microwave radiometer products, and inter-vessel comparisons when two ships were located within 50 km of each other. The reported agreement with ERA5 and RSS radiometer products, as well as the internal consistency shown by vessel-crossing comparisons, demonstrates the overall quality and usefulness of the dataset.
I particularly appreciate that the authors do not limit the validation to global statistics, but also investigate specific outlier cases in detail. The discussion of discrepancies related to island/coastal regions, ERA5 interpolation limitations, latitude-dependent differences, cloud-cover-dependent radiometer biases, and occasional vessel-specific GNSS issues provides useful insight into both the strengths and limitations of the dataset. This makes the manuscript more informative and increases confidence in the data product.
Overall, I find the dataset scientifically useful and well suited for publication in Earth System Science Data. It provides an important contribution to oceanic water vapor observations and has clear potential for applications in satellite product validation, reanalysis assessment, climate monitoring, and future data assimilation studies. I therefore support publication of the manuscript after minor revisions. Some points could be further clarified to improve the manuscript and enhance the usability of the dataset.
Specific comments
1. It would be useful if the authors could clarify the availability of the original GNSS observation data, preferably in RINEX/RNXO format, if these data are publicly accessible. Although the derived IWV product is the main dataset of this paper, access to the original GNSS observations would further improve reproducibility and would be valuable for users interested in reprocessing the data with alternative strategies.
2. I suggest that uncertainty information for the GNSS-derived PWV/IWV product, or at least for the intermediate ZWD/ZTD estimates, be included in the dataset. If this is not feasible for the current release, the authors could consider adding such information in future updates. This would be helpful for data assimilation, validation studies, and quantitative comparison with other water vapor products.
3. The authors may also check whether the comparison datasets or collocated comparison results used in the manuscript, for example the interpolated ERA5 IWV values and the matched RSS radiometer values, can be made available together with the GNSS-IWV product. This is not essential, since ERA5 and RSS are already available from their respective providers, but providing the collocated comparison data would facilitate reproducibility of the validation results and make the dataset more convenient for users.