OSI SAF (sea ice concentration)¶

EUMETSAT OSI SAF Global Sea-Ice Concentration Climate Data Record (OSI-450-a1 and related products)

Available

At a glance¶

Note on period: The SSMIS-series CDR (OSI-450-a1) covers 1978-10-25 to 2020-12-31, and its extension OSI-430-a covers 2021-01-01 to 2025-10-16, where it stopped. The AMSR series continues with the CDR OSI-458 (2002-06 to 2020-12, gap 2011-10 to 2012-07) and the ICDRs OSI-438 (from 2021-01, AMSR2) and OSI-438-a (from 2026-09, AMSR3). Before July 1987 (SMMR) the temporal sampling is 48 hours.

Overview¶

Global (Northern and Southern Hemisphere) sea-ice concentration from EUMETSAT OSI SAF, derived from SMMR, SSM/I, SSMIS and AMSR-E/AMSR2/AMSR3 passive microwave observations. Atmospheric effects are corrected with ERA5, tie-points are dynamic, and every grid cell comes with an uncertainty estimate. Use the CDR and its interim extension (ICDR) for long-term climate analyses, and the near-real-time products (OSI-401-d, OSI-408) for current conditions. The algorithms are shared with the ESA CCI Sea Ice project, and the records are redistributed by Copernicus Marine and the C3S CDS.

What changes with the successor¶

OSI SAF SSMIS series → OSI SAF AMSR series¶

Transition: 2025-10

As DMSP SSMIS data became intermittent, OSI SAF moved the extension (ICDR) of its sea-ice concentration climate record from the SSMIS series to the AMSR series. The SSMIS ICDR OSI-430-a was suspended on 2025-10-17, the AMSR2-based OSI-438 was declared operational on 2026-05-04, and from 2026-09-01 the AMSR3-based OSI-438-a provides the fast-track updates. Grid and latency are unchanged, but the AMSR record starts only in 2002, so treat it separately from the single long record starting in 1978.

Sources: OSI SAF — Implications of the end of SSMIS data on OSI SAF products · OSI SAF — Implications of AMSR2 being replaced by AMSR3 on OSI SAF products · OSI SAF Service Message · OSI-430-a product page · OSI-438 product page · OSI-458 product page · Sea-ice concentration CDR/ICDR Product User Manual (PUM v3.4)

OSI-450-a v3.0 → OSI-450-a1 v3.1¶

Transition: 2025-06

A bug was found in the land spill-over correction of the SSMIS-series CDR OSI-450-a, and a corrected release, OSI-450-a1, was issued with a new DOI. Period, grid and variables are unchanged.

Sources: OSI-450-a1 product page · OSI-450-a product page (superseded) · Sea-ice concentration CDR/ICDR Product User Manual (PUM v3.4)

Available variables¶

Variables in the daily climate-record (CDR/ICDR) files, following the Product User Manual (PUM v3.4). Monthly and yearly files have no uncertainty variables, and monthly/yearly means below 10% are removed from ice_conc and moved to raw_ice_conc_values. The near-real-time files (OSI-401-d, OSI-408) contain a different set of variables.

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-ice concentration¶

Uncertainty (one standard deviation)¶

Quality information¶

The full variable list is in the official documentation.

How to get the data¶

• OSI SAF product page — OSI-450-a1 (SSMIS-series CDR v3.1) — Product information / FTP (ice/conc/v3p1 under ftp://osisaf.met.no/reprocessed/) No login needed
  • Each product page lists the FTP directory, DOI, citation text and documentation.
• MET Norway THREDDS — sea-ice concentration climate data record catalogue — THREDDS / OPeNDAP / HTTP download No login needed
  • No account needed; OPeNDAP lets you read only the region and period you need.
• OSI SAF product page — OSI-438 (AMSR2-based ICDR) — FTP (ice/conc-cont-reproc-amsr/ under ftp://osisaf.met.no/reprocessed/) / THREDDS / EUMETSAT Data Store No login needed
  • The recommended extension for 2021 onwards. From 2026-09-01 only the nominal (16-day latency) files continue, at a new FTP location.
• OSI SAF product page — OSI-438-a (AMSR3-based ICDR) — FTP / THREDDS / EUMETSAT Data Store No login needed
  • Operational since 2026-09-01. Use this product for fast-track files with about 2 days latency.
• Copernicus Marine — SEAICE_GLO_SEAICE_L4_REP_OBSERVATIONS_011_009 — Web download / copernicusmarine toolbox
  • Redistribution of the OSI SAF climate records. Requires a Copernicus Marine account.
• C3S Climate Data Store — Sea ice concentration from 1978 to present derived from satellite observations — Web download / CDS API
  • Requires an ECMWF account. The SSMIS-based product spans 1979–2025 and is not updated; only the AMSR-based product is updated operationally.
• OSI SAF product page — OSI-408-a (AMSR2 near-real-time, 10 km) — FTP (ftp://osisaf.met.no/prod/ last 31 days, /archive/ full record) / THREDDS / EUMETCast No login needed
  • Operational near-real-time product with a different algorithm and grid from the climate records. From 2026-09-01 the AMSR3-based OSI-408-g is the main product.

Example code¶

Assumes a daily file downloaded via FTP or THREDDS from the product page. File names follow ice_conc_ease2-250_1200.nc.

import xarray as xr

# e.g. OSI-450-a1 Northern Hemisphere daily file (product ID cdr-v3p1)
ds = xr.open_dataset("ice_conc_nh_ease2-250_cdr-v3p1_201909011200.nc")
sic = ds["ice_conc"].squeeze()                       # units: % (0–100), one day's 2-D grid
unc = ds["total_standard_uncertainty"].squeeze()     # units: % (one standard deviation)

# EASE2 grid is equal-area 25 km x 25 km -> cell area 625 km²
area_km2 = float((sic.where(sic >= 15) / 100 * 625).sum())
print(f"Sea-ice area (cells with concentration >= 15%): {area_km2:,.0f} km²")

Practical tips¶

• The SSMIS series (OSI-450-a1 + OSI-430-a) and the AMSR series (OSI-458 + OSI-438 + OSI-438-a) are separate records. When extending beyond 2020, use the ICDR from the same series as your CDR. OSI-430-a ended at 2025-10-16, so if you need ongoing updates, move to the AMSR series.
• The earlier OSI-450-a (DOI 10.15770/EUM_SAF_OSI_0013) had a land spill-over correction bug affecting 343 days and was replaced in 2025 by the corrected OSI-450-a1 (DOI 10.15770/EUM_SAF_OSI_0023). The affected dates are listed in PUM Appendix B.
• In summer, melt ponds look like open water to microwave radiometers, so concentration is underestimated. This error is not included in the uncertainty variables, so take care with Arctic concentrations in June–August. Thin ice at the edge below about 10% can also be removed to 0% by the weather filter.
• The polar observation hole differs by sensor (poleward of 84°N for SMMR, 87°N for SSM/I, 89°N for SSMIS). In the climate records it is filled by interpolation, so check interpolated cells with status_flag and state how you treat this area when computing your own area or extent series.

Notices and change history¶

References for your paper¶

Dataset citation¶

SSMIS-series CDR — OSI-450-a1 (v3.1) — DOI 10.15770/EUM_SAF_OSI_0023

@misc{osisaf450a1,
  author    = {{EUMETSAT Ocean and Sea Ice Satellite Application Facility}},
  title     = {Global sea ice concentration climate data record 1978-2020 (v3.1, 2025), {OSI-450-a1}},
  year      = {2025},
  publisher = {EUMETSAT OSI SAF},
  doi       = {10.15770/EUM_SAF_OSI_0023}
}

SSMIS-series ICDR — OSI-430-a (v3.0, 2021-01 to 2025-10) — DOI 10.15770/EUM_SAF_OSI_0014

AMSR-series CDR — OSI-458 (v3.0) — DOI 10.15770/EUM_SAF_OSI_0015

AMSR2 ICDR — OSI-438 (v3.0) — DOI 10.15770/EUM_SAF_OSI_0024

AMSR3 ICDR — OSI-438-a (v3.0) — DOI 10.15770/EUM_SAF_OSI_0027

Reference papers¶

Algorithm and version 2 climate record paper (methodology carried into v3) — DOI 10.5194/tc-13-49-2019

@article{lavergne2019osisaf,
  author  = {Lavergne, Thomas and S{\o}rensen, Atle Macdonald and Kern, Stefan and Tonboe, Rasmus and Notz, Dirk and Aaboe, Signe and Bell, Louisa and Dybkj{\ae}r, Gorm and Eastwood, Steinar and Gabarro, Carolina and Heygster, Georg and Killie, Mari Anne and Brandt Kreiner, Matilde and Lavelle, John and Saldo, Roberto and Sandven, Stein and Pedersen, Leif Toudal},
  title   = {Version 2 of the {EUMETSAT} {OSI SAF} and {ESA} {CCI} sea-ice concentration climate data records},
  journal = {The Cryosphere},
  volume  = {13},
  number  = {1},
  pages   = {49--78},
  year    = {2019},
  doi     = {10.5194/tc-13-49-2019}
}

First EUMETSAT sea ice concentration climate record paper (optional) — DOI 10.5194/tc-10-2275-2016

Acknowledgements¶

Under CC BY 4.0, credit "EUMETSAT OSI SAF" as the source and give the DOI of each product you used (OSI-450-a1, OSI-438, etc.). If you downloaded from Copernicus Marine or the CDS, fill in the distributor and download date in the citation text.

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¶

• OSI SAF sea-ice concentration CDR/ICDR v3 description
• Product User Manual (PUM v3.4)
• Algorithm Theoretical Basis Document (ATBD v3.2)
• Implications of AMSR2 being replaced by AMSR3 (2026-04-24)
• OSI SAF list of service messages
• This site — AMSR2 ASI 6.25 km sea ice concentration