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OSTIA

Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA)

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Current status

Both the near-real-time (NRT) analysis and the reprocessed (REP) product are available as normal. Since 2025, however, the Copernicus Marine NRT product retains only the most recent two years, so use the reprocessed product (SST_GLO_SST_L4_REP_OBSERVATIONS_010_011) for long-term analyses.

At a glance

Item Details
Section Ocean › Sea surface temperature analyses
Type Observation-based analysis
Domains Ocean, Sea ice
Provider Met Office / Copernicus Marine Service (CMEMS)
Period 1981-10 ~ present
Coverage Global
Horizontal resolution 1/20° (0.05°) regular latitude-longitude grid (7200 × 3600)
Vertical resolution Sea surface only (foundation SST — the temperature free of diurnal warming)
Temporal resolution Daily mean (midnight to midnight, centred at noon)
Update frequency NRT daily (by 1200 UTC) / REP extended irregularly (once or twice a year)
Licence Copernicus Marine Service licence — free of charge, redistribution and derived products allowed, with mandatory attribution and citation of the product DOI. The PO.DAAC mirror follows the NASA Earthdata terms of use.
Account required Yes

Note on period: The reprocessed product (REP) covers 1 October 1981 to 31 March 2026 and is extended in batches, more than about six months behind real time. The NRT product is updated daily, and Copernicus Marine serves only the most recent two years of it. The full NRT record since 2007 is available from NASA PO.DAAC.

How to read the resolution
  • Horizontal resolution lists both the native model grid and the grid you download, as given in the official documentation. The same dataset can come on different grids from different providers or products, so check the grid of your downloaded file.
  • Grid spacing is not the effective resolution. A provided grid that is finer than the native one carries no extra information.
  • Intervals and whether a value is instantaneous, mean or accumulated differ between variables — see 'Available variables' below.
  • The 'provided resolution' in lists and the comparison table is a simplified km/degree value for quick comparison. Use this page for exact values.

Overview

The L4 (gap-free) output of OSTIA, the global sea surface temperature and sea ice concentration analysis run daily by the Met Office — a merged, multi-sensor L4 foundation SST product for applications requiring gap-free observational SST. Infrared and microwave satellite SSTs and in situ observations from buoys and ships are combined with NEMOVAR-based data assimilation into daily 0.05° foundation SST, and sea ice concentration is taken from EUMETSAT OSI SAF. It is widely used as a lower boundary condition for numerical weather prediction and for ocean monitoring, and a reprocessed record from 1981 produced with the same system is also provided.

Available variables

Variable names in the files, from the Copernicus Marine Product User Manual (PUM). NRT and REP have the same variables. The original REP files are packed as integers (scale_factor, add_offset), so check that your library unpacks them automatically.

Time-stamp convention — instantaneous, mean or accumulated? — click to show

One analysis is produced per day. The product user manual describes each file as a daily mean over the day (midnight to midnight UTC), centred and time-stamped at noon. The SST is a foundation SST with diurnal (daytime surface) warming removed, so it differs both from the instantaneous temperature at any time of day and from a simple daily mean that includes daytime warming.

  • File names and the time coordinate carry 12:00 UTC of the date, but the value represents the whole day (00–24 UTC), not an instantaneous value at noon.
  • Foundation SST is the temperature from which diurnal warming develops. To limit daytime warming, daytime satellite observations with wind speeds below 6 m/s are excluded; only night-time observations and daytime observations in stronger winds are used (Good et al. 2020).
  • The analysis for a given date uses SST observations received from 18 UTC the previous day to 06 UTC the next day (36 hours) (Good et al. 2020).
  • Sea ice concentration is taken directly from the OSI SAF daily sea ice concentration for that date, without blending neighbouring days (Good et al. 2020).
  • The NRT run starts at 05:50 UTC the next morning to produce the previous day's analysis; REP recomputes the past with the same definitions.

Source: Copernicus Marine PUM (SST-010-001) and Good et al. (2020)

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 temperature

Variable Short name Units Time convention Notes
Analysed sea surface temperature (foundation SST) analysed_sst K Daily mean A daily mean (00–24 UTC) according to the manual, but as a foundation SST with diurnal warming removed it differs from the true daily mean temperature including daytime warming.
Estimated error standard deviation of analysed_sst analysis_error K Daily mean Estimated error (standard deviation) of the same day's analysed_sst; follows the time definition of analysed_sst.

Sea ice and mask

Variable Short name Units Time convention Notes
Sea ice area fraction sea_ice_fraction 0–1 Daily mean Uses the OSI SAF daily sea ice concentration for that date. The internal time definition of the OSI SAF daily value is not given in this manual.
Land sea ice lake bit mask mask bit flags static The ocean/land/lake classification is fixed, but the sea ice bit (8) can change from day to day with the ice analysis.

The full variable list is in the official documentation.

How to get the data

Example code

Register your Copernicus Marine account once in a terminal with copernicusmarine login before running.

# pip install copernicusmarine xarray
import copernicusmarine

copernicusmarine.subset(
    dataset_id="METOFFICE-GLO-SST-L4-REP-OBS-SST",
    variables=["analysed_sst", "sea_ice_fraction"],
    minimum_longitude=120, maximum_longitude=135,
    minimum_latitude=30, maximum_latitude=45,
    start_datetime="2020-01-01T00:00:00",
    end_datetime="2020-01-31T23:59:59",
    output_filename="ostia_rep_korea_202001.nc",
)

Practical tips

  • The NRT product (010_001) and the reprocessed product (010_011) differ in input data and processing version, so values differ even on the same date. Use the reprocessed product throughout for climatologies and trends, and if you append recent months from NRT, check the differences over an overlap period first.
  • OSTIA SST is a foundation SST (the temperature at a depth free of diurnal variation), so it can be lower than daytime satellite skin SST or buoy measurements. Allow for this difference in definition when comparing with observations.
  • The grid is 0.05°, but the scales actually resolved are larger and depend on observation density. Check analysis_error as well, especially in persistently cloudy regions and in coastal areas with little satellite microwave coverage.
  • For climate research there is also the ESA SST CCI / C3S-based L4 analysis (CEDA, from 1980). It shares much of its input with OSTIA REP but is a separate product, so cite it and its version separately.

Notices and change history

2026-04-28 · Info · [MDSOP-377] Application of retention periods to ARCO datacubes — start dates may change

Copernicus Marine has begun applying the retention periods defined in the product manuals to ARCO-based services (web subset, Toolbox subset, MyOcean Viewer), so the start date and length of some time series may change. Original files (File Browser, copernicusmarine get) are not affected.

Read the original

2025-06-24 · Warning · NRT product (010_001) dataset length reduced to the most recent two years

The change history of the product user manual records "Updated dataset length to be the most recent two years" for the NRT dataset. For NRT data older than two years use NASA PO.DAAC (OSTIA-UKMO-L4-GLOB-v2.0); for long-term analyses use the REP product.

Read the original

2025-05-28 · Info · Ingestion of VIIRS on NOAA-21 observations (NRT)

The NRT analysis started assimilating VIIRS SST observations from NOAA-21. Small changes in the product's characteristics are possible around this date.

Read the original

References for your paper

Double-check before using in a paper

The citations below were compiled by the maintainer and may contain errors. Always double-check DOIs, authors, years and access-date formats against the provider's official dataset page and your journal's guidelines.

Dataset citation

NRT analysis product (010_001) — DOI 10.48670/moi-00165

E.U. Copernicus Marine Service Information (CMEMS). Global Ocean OSTIA Sea Surface Temperature and Sea Ice Analysis (SST_GLO_SST_L4_NRT_OBSERVATIONS_010_001). DOI: 10.48670/moi-00165 (Accessed on DD-MMM-YYYY)

Show BibTeX 
@misc{cmems_ostia_nrt,
  author    = {{E.U. Copernicus Marine Service Information (CMEMS)}},
  title     = {Global Ocean {OSTIA} Sea Surface Temperature and Sea Ice Analysis ({SST\_GLO\_SST\_L4\_NRT\_OBSERVATIONS\_010\_001})},
  publisher = {Mercator Ocean International},
  doi       = {10.48670/moi-00165},
  note      = {Accessed on DD-MMM-YYYY}
}

Reprocessed product (010_011) — DOI 10.48670/moi-00168

E.U. Copernicus Marine Service Information (CMEMS). Global Ocean OSTIA Sea Surface Temperature and Sea Ice Reprocessed (SST_GLO_SST_L4_REP_OBSERVATIONS_010_011). DOI: 10.48670/moi-00168 (Accessed on DD-MMM-YYYY)

Show BibTeX 
@misc{cmems_ostia_rep,
  author    = {{E.U. Copernicus Marine Service Information (CMEMS)}},
  title     = {Global Ocean {OSTIA} Sea Surface Temperature and Sea Ice Reprocessed ({SST\_GLO\_SST\_L4\_REP\_OBSERVATIONS\_010\_011})},
  publisher = {Mercator Ocean International},
  doi       = {10.48670/moi-00168},
  note      = {Accessed on DD-MMM-YYYY}
}

PO.DAAC NRT mirror (GHRSST) — DOI 10.5067/GHOST-4FK02

UK Met Office. GHRSST Level 4 OSTIA Global Foundation Sea Surface Temperature Analysis (GDS version 2), version 2.0. PO.DAAC, CA, USA. DOI: 10.5067/GHOST-4FK02 (Accessed on DD-MMM-YYYY)

Reference papers

Current OSTIA configuration (reference recommended in the PUM) — DOI 10.3390/rs12040720

Good, S., Fiedler, E., Mao, C., Martin, M. J., Maycock, A., Reid, R., Roberts-Jones, J., Searle, T., Waters, J., While, J., Worsfold, M. (2020): The Current Configuration of the OSTIA System for Operational Production of Foundation Sea Surface Temperature and Ice Concentration Analyses. Remote Sensing, 12(4), 720.

Show BibTeX 
@article{good2020ostia,
  author  = {Good, Simon and Fiedler, Emma and Mao, Chongyuan and Martin, Matthew J. and Maycock, Adam and Reid, Rebecca and Roberts-Jones, Jonah and Searle, Toby and Waters, Jennifer and While, James and Worsfold, Mark},
  title   = {The Current Configuration of the {OSTIA} System for Operational Production of Foundation Sea Surface Temperature and Ice Concentration Analyses},
  journal = {Remote Sensing},
  volume  = {12},
  number  = {4},
  pages   = {720},
  year    = {2020},
  doi     = {10.3390/rs12040720}
}

Original OSTIA system paper — DOI 10.1016/j.rse.2010.10.017

Donlon, C. J., Martin, M., Stark, J., Roberts-Jones, J., Fiedler, E., Wimmer, W. (2012): The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) system. Remote Sensing of Environment, 116, 140–158.

Show BibTeX 
@article{donlon2012ostia,
  author  = {Donlon, Craig J. and Martin, Matthew and Stark, John and Roberts-Jones, Jonah and Fiedler, Emma and Wimmer, Werenfrid},
  title   = {The Operational Sea Surface Temperature and Sea Ice Analysis ({OSTIA}) system},
  journal = {Remote Sensing of Environment},
  volume  = {116},
  pages   = {140--158},
  year    = {2012},
  doi     = {10.1016/j.rse.2010.10.017}
}

Reprocessed (REP) dataset paper — DOI 10.3390/rs16183358

Worsfold, M., Good, S., Atkinson, C., Embury, O. (2024): Presenting a Long-Term, Reprocessed Dataset of Global Sea Surface Temperature Produced Using the OSTIA System. Remote Sensing, 16(18), 3358.

Acknowledgements

The Copernicus Marine licence requires publications to state "This study has been conducted using E.U. Copernicus Marine Service Information" and to give the DOI of every product used. The product user manual also recommends the acknowledgement "These data were provided by GHRSST, Met Office and the Copernicus Marine Service".

If this page helped, please acknowledge the Korean Climate Data Navigator

Please add the sentence below to the Acknowledgements of your paper.

Acknowledgements

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).