DUACS¶

SSALTO/DUACS multi-mission altimeter L4 gridded sea level (sea level anomaly, absolute dynamic topography, geostrophic currents) — Copernicus Marine SEALEVEL_GLO_PHY_L4_MY_008_047 (reprocessed) and SEALEVEL_GLO_PHY_L4_NRT_008_046 (near real time), C3S satellite-sea-level-global

Available

At a glance¶

Note on period: Latest dates as of 2026-10-12: Copernicus Marine reprocessed (MY) daily 2026-05-15, monthly 2026-04; near-real-time (NRT) 0.125° daily 2026-10-11 (dataset starts 2024-07-01); C3S vDT2024 2026-01-16 (CDS catalogue). NRT normally keeps only about the last two years online, so use MY or C3S for long-term work.

Overview¶

Altimeter satellite gridded sea level anomalies (SLA), computed with respect to a twenty-year [1993, 2012] mean, produced by merging along-track measurements from all available altimeter missions (TOPEX/Poseidon, the Jason series, Sentinel-6 MF, Sentinel-3, SARAL/AltiKa and others) into gap-free daily global maps. The products also contain absolute dynamic topography (ADT = SLA + mean dynamic topography), surface geostrophic currents and formal mapping errors. They are generated by the DUACS system at CLS and distributed in two flavours: the Copernicus Marine products, which use every available satellite on a 0.125° grid and target mesoscale applications, and the C3S product, which uses a steady two-satellite constellation on a 0.25° grid for a homogeneous, stable record of climate-scale sea level change.

What changes with the successor¶

DUACS DT-2021 → DUACS DT-2024¶

Transition: 2024-11

Full reprocessing of the 30-year altimetry record with new L2P input standards and corrections. The Copernicus Marine products switched to MIOST mapping on a 1/8° grid; the C3S product keeps 0.25° optimal interpolation but adopts the new standards. The MDT changed to MDT_CNES_CLS22.

Sources: Copernicus Marine QUID (CMEMS-SL-QUID-008-032-068) · Copernicus Marine transition information — SEALEVEL_GLO_PHY_L4_NRT_008_046 · Copernicus Marine transition information — SEALEVEL_GLO_PHY_L4_MY_008_047 · C3S Sea Level vDT2024 PUGS · Ballarotta et al. — DUACS DT-2024 (EGU25-3715)

Available variables¶

Variable names as in the Copernicus Marine dataset metadata and the C3S Product User Guide (PUGS). MY and C3S daily files have the same variables; NRT has no tpa_correction. All variables are stored as int32 with a scale_factor of 0.0001. The MDT itself is not included in the files.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Sea surface height (daily maps)¶

Geostrophic currents (daily maps)¶

Monthly means¶

Flags and corrections¶

The full variable list is in the official documentation.

How to get the data¶

• Copernicus Marine — reprocessed (SEALEVEL_GLO_PHY_L4_MY_008_047) — Web Subset and File Browser / Copernicus Marine Toolbox (copernicusmarine)
  • Free Copernicus Marine account required. Dataset IDs — daily cmems_obs-sl_glo_phy-ssh_my_allsat-l4-duacs-0.125deg_P1D, monthly cmems_obs-sl_glo_phy-ssh_my_allsat-l4-duacs-0.125deg_P1M-m (current version 202411).
• Copernicus Marine — near real time (SEALEVEL_GLO_PHY_L4_NRT_008_046) — Web Subset and File Browser / Copernicus Marine Toolbox (copernicusmarine)
  • Dataset ID cmems_obs-sl_glo_phy-ssh_nrt_allsat-l4-duacs-0.125deg_P1D (from 2024-07-01). The former 0.25° dataset (…-0.25deg_P1D) has not been updated since 2024-11-26.
• C3S Climate Data Store (satellite-sea-level-global) — Web download / CDS API (cdsapi)
  • Requires an ECMWF account and acceptance of the licence. Choose variable daily or monthly_mean and version vdt2024 (recommended), vdt2021 or vdt2018; NetCDF files are delivered in a zip archive.
• Copernicus Marine Toolbox documentation — Python / command line (CLI)

Example code¶

After pip install copernicusmarine, run copernicusmarine.login() once to store your credentials. For the C3S product, put your CDS API key in ~/.cdsapirc and use cdsapi as in the commented example below.

import copernicusmarine

# Copernicus Marine reprocessed (MY) 0.125° daily data — East Asia subset
copernicusmarine.subset(
    dataset_id="cmems_obs-sl_glo_phy-ssh_my_allsat-l4-duacs-0.125deg_P1D",
    variables=["sla", "adt", "ugos", "vgos"],
    minimum_longitude=120, maximum_longitude=150,
    minimum_latitude=20, maximum_latitude=50,
    start_datetime="2020-01-01", end_datetime="2020-12-31",
    output_filename="duacs_my_eastasia_2020.nc",
)

# C3S product (vDT2024, 0.25°, two-satellite constellation)
# import cdsapi
# cdsapi.Client().retrieve(
#     "satellite-sea-level-global",
#     {"variable": "monthly_mean", "version": "vdt2024",
#      "year": ["2020"], "month": [f"{m:02d}" for m in range(1, 13)]},
#     "c3s_sealevel_2020_monthly.zip",
# )

Practical tips¶

• The Copernicus Marine (allsat) maps use every satellite available at the time, which is best for mesoscale eddies, but the changing number of satellites makes the record less homogeneous over decades. C3S builds a separate climate product with a fixed two-satellite (twosat) constellation for long-term stability, so use C3S for global or regional mean sea level rise and long-term trends.
• The QUID states that NRT products should not be used for long-term signal analysis, because constellation changes can cause jumps or drifts. If you append recent NRT months to MY, check the differences over an overlap period first.
• DUACS L4 sea level is not corrected for glacial isostatic adjustment (GIA). Apply your own GIA correction where needed, e.g. for trends or comparisons with tide gauges or GRACE.
• Geostrophic currents derived from altimeter maps are usually weaker than in situ observations (QUID). Bear this in mind when comparing statistics such as eddy kinetic energy with other datasets.
• ADT is SLA plus the MDT, so a new MDT (MDT_CNES_CLS22 in DT-2024) also changes ADT and the absolute geostrophic currents. Do not mix files from different versions.
• Copernicus Marine datasets carry a version tag (e.g. reprocessed 202411, NRT 202506). You can pin it with the Toolbox's dataset_version argument; record the version you downloaded if reproducibility matters.

Notices and change history¶

References for your paper¶

Dataset citation¶

Copernicus Marine reprocessed product (008_047) — DOI 10.48670/moi-00148

@misc{cmems_duacs_my,
  author    = {{E.U. Copernicus Marine Service Information (CMEMS)}},
  title     = {Global Ocean Gridded {L4} Sea Surface Heights and Derived Variables Reprocessed (1993-Ongoing) ({SEALEVEL\_GLO\_PHY\_L4\_MY\_008\_047})},
  year      = {2021},
  publisher = {Mercator Ocean International},
  doi       = {10.48670/moi-00148},
  note      = {Accessed on DD-MMM-YYYY}
}

Copernicus Marine near-real-time product (008_046) — DOI 10.48670/moi-00149

@misc{cmems_duacs_nrt,
  author    = {{E.U. Copernicus Marine Service Information (CMEMS)}},
  title     = {Global Ocean Gridded {L4} Sea Surface Heights and Derived Variables {NRT} ({SEALEVEL\_GLO\_PHY\_L4\_NRT\_008\_046})},
  year      = {2017},
  publisher = {Mercator Ocean International},
  doi       = {10.48670/moi-00149},
  note      = {Accessed on DD-MMM-YYYY}
}

C3S sea level dataset (CDS) — DOI 10.24381/cds.4c328c78

@misc{c3s_sea_level_global,
  author    = {{Copernicus Climate Change Service (C3S)}},
  title     = {Sea level gridded data from satellite observations for the global ocean from 1993 to present},
  year      = {2018},
  publisher = {ECMWF, Copernicus Climate Change Service (C3S) Climate Data Store (CDS)},
  doi       = {10.24381/cds.4c328c78},
  note      = {Accessed on DD-MMM-YYYY}
}

Reference papers¶

DUACS DT2018 reprocessing paper — DOI 10.5194/os-15-1207-2019

@article{taburet2019duacs,
  author  = {Taburet, Guillaume and Sanchez-Roman, Antonio and Ballarotta, Maxime and Pujol, Marie-Isabelle and Legeais, Jean-Fran{\c{c}}ois and Fournier, Florent and Faugere, Yannice and Dibarboure, Gerald},
  title   = {{DUACS} {DT2018}: 25 years of reprocessed sea level altimetry products},
  journal = {Ocean Science},
  volume  = {15},
  number  = {5},
  pages   = {1207--1224},
  year    = {2019},
  doi     = {10.5194/os-15-1207-2019}
}

DUACS DT2014 reprocessing paper (SLA computation and reference period) — DOI 10.5194/os-12-1067-2016

@article{pujol2016duacs,
  author  = {Pujol, Marie-Isabelle and Faug{\`e}re, Yannice and Taburet, Guillaume and Dupuy, St{\'e}phanie and Pelloquin, Camille and Ablain, Michael and Picot, Nicolas},
  title   = {{DUACS} {DT2014}: the new multi-mission altimeter data set reprocessed over 20 years},
  journal = {Ocean Science},
  volume  = {12},
  pages   = {1067--1090},
  year    = {2016},
  doi     = {10.5194/os-12-1067-2016}
}

Acknowledgements¶

For the Copernicus Marine products, write "This study has been conducted using E.U. Copernicus Marine Service Information;" followed by the DOI of the product used. For the C3S product, cite the CDS dataset DOI and include the attribution required by the C3S licence. As of October 2026 no journal paper describing DT-2024 itself was found in the official documentation; CLS presented it at EGU 2025 (doi:10.5194/egusphere-egu25-3715).

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• Copernicus Marine reprocessed product page (008_047)
• Copernicus Marine NRT product page (008_046)
• Product User Manual (PUM 008-046-047-060-068)
• Quality Information Document (QUID 008-033-068)
• C3S CDS dataset page
• C3S Sea Level vDT2024 Product User Guide and Specification (PUGS)
• Copernicus Marine User Notification Service
• This site — SWOT KaRIn wide-swath sea surface height
• This site — ESA Sea State CCI significant wave height