The International Altimetry Service 2024 (IAS2024) coastal sea level dataset and first evaluations

Abstract. A new dedicated 20 Hz coastal sea level dataset, called the International Altimetry Service 2024 (IAS2024, https://doi.org/10.5281/zenodo.13208305, Peng et al., 2024c), is presented for monitoring sea level changes along the world's coastlines. One of the reasons for generating this dataset is that the quality of coastal altimeter data has been greatly improved with advanced coastal reprocessing strategies. In this study, the Seamless Combination of Multiple Retrackers (SCMR) strategy is adopted to obtain the reprocessed Jason data from January 2002 to April 2022. The evaluation/validation results show that the IAS2024 20 Hz along-track coastal sea level dataset achieves good performance over global coastal oceans. The good consistency between IAS2024 and independent altimeter datasets, including the European Space Agency Climate Change Initiative version 2.4 (ESA CCI v2.4) 20 Hz along-track coastal sea level dataset and the Copernicus Marine Environment Monitoring Service Level-3 (CMEMS L3) 1 Hz along-track sea level dataset, is observed. The closure of sea level trend differences (0.16 ± 3.97 mm yr−1) between IAS2024 and Permanent Service for Mean Sea Level (PSMSL) tide gauge data at the global scale is also achieved. Moreover, 1548 virtual stations have been constructed using the IAS2024 coastal sea level dataset, which will contribute to the analysis of coastal sea levels for the ocean community and to risk management for the policymakers. Our study also finds that no obvious variations exist in the linear sea level trends from the offshore to the coast over the last 20 km coastal strip at the global scale. In addition, the vertical land motion (VLM) estimates from the combination of the IAS2024 dataset with the PSMSL tide gauge records agree well with the University of La Rochelle 7a (ULR7a) Global Navigation Satellite System (GNSS) solution, with the mean difference of VLM estimates being 0.12 ± 2.27 mm yr−1, suggesting that altimeter-derived VLM estimates can be used as an independent data source to validate the GNSS solutions.