ESA CCI Soil Moisture¶

ESA Soil Moisture Climate Change Initiative (Soil_Moisture_cci) v09.2 — ACTIVE, PASSIVE and COMBINED (multi-satellite microwave surface soil moisture climate record, 0.25°, daily)

Available

At a glance¶

Note on period: PASSIVE and COMBINED cover 1978-11-01 to 2024-12-31, and ACTIVE 1991-08-05 to 2024-12-31 (v09.2). Until about 1987 SMMR is the only sensor, so observations are sparse and orbit stripes are visible; for PASSIVE and COMBINED the uncertainty variable starts on 1987-07-09 (per the v09.1 user guide).

Overview¶

The ESA Climate Change Initiative merges microwave soil moisture retrievals from many satellites flown since 1978 into a single global surface soil moisture climate record. There are three products — ACTIVE (merged scatterometer data), PASSIVE (merged radiometer data) and COMBINED (both) — all provided as daily 0.25° images. ESA recommends COMBINED for most applications, and the v09 series is the first to include an end-to-end, error-propagation-based uncertainty. C3S produces a near-real-time version with the same algorithm on the CDS.

What changes with the successor¶

ESA CCI SM v08.1 → ESA CCI SM v09.x (v09.1 → v09.2)¶

v09.1 introduced the first end-to-end, error-propagation-based uncertainty, a new way of combining multiple SMOS incidence angles and an updated COMBINED rescaling, and extended the record to end-2023. v09.2 extends v09.1 to end-2024 without algorithm changes. C3S version v202505 corresponds to this 'CCI algorithm version 9'.

Sources: ESA CCI Soil Moisture project page · ESA news — v09.1 release · CEDA — COMBINED v09.2 catalogue record

Available variables¶

Variables per the CEDA v09.2 catalogue and the v09.1 Product User Guide (PUG). All three products share the same variables; only the units of sm differ. Files are named ESACCI-SOILMOISTURE-L3S-SSMV--000000-fv.nc and stored in yearly folders.

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

Soil moisture (observed that day)¶

Observation information and quality (per observation that day)¶

The full variable list is in the official documentation.

How to get the data¶

• CEDA Archive (official ESA CCI SM distribution) — HTTP download / anonymous FTP / OPeNDAP
  • All versions can be downloaded without registration. Under daily_files the layout is ACTIVE/PASSIVE/COMBINED → version (v09.2) → year. The anonymous FTP path is ftp://anon-ftp.ceda.ac.uk/neodc/esacci/soil_moisture/data/daily_files/.
• ESA CCI Open Data Portal — Web search and download
  • A single portal for all ESA CCI variables.
• Copernicus Climate Data Store — C3S soil moisture (near real time, monthly) — Web download / CDS API (cdsapi)
  • The C3S product built with the ESA CCI SM algorithm (v202505 = CCI algorithm version 9). It offers daily, 10-day and monthly means, a CDR updated annually and an ICDR appended every 10 days, plus root-zone soil moisture (RZSM) and freeze/thaw (F/T) products. Requires an ECMWF account.
• esa_cci_sm Python package (TU Wien) — pip install esa_cci_sm
  • Converts the daily image files into per-grid-point time series for fast point analyses.

Example code¶

Downloads one month of COMBINED v09.2 from CEDA's anonymous FTP and computes an area mean over the Korean Peninsula (no account needed). The file naming follows the v09.1 user guide and the esa_cci_sm examples, so check the folder listing before downloading.

from ftplib import FTP
import xarray as xr

base = "/neodc/esacci/soil_moisture/data/daily_files/COMBINED/v09.2/2024"
ftp = FTP("anon-ftp.ceda.ac.uk"); ftp.login()
ftp.cwd(base)
names = [n for n in ftp.nlst() if "202407" in n]   # July 2024 files
for n in names:
    with open(n, "wb") as f:
        ftp.retrbinary(f"RETR {n}", f.write)
ftp.quit()

ds = xr.open_mfdataset(sorted(names), combine="by_coords")
sm = ds["sm"].sel(lat=slice(39, 33), lon=slice(124, 132))  # latitude runs north to south
good = sm.where(ds["flag"].sel(lat=slice(39, 33), lon=slice(124, 132)) == 0)
print(good.mean(["lat", "lon"]).values)   # daily area mean (m3 m-3)

Practical tips¶

• Exclude non-zero flag values (snow/frozen soil, dense vegetation, values outside physical bounds, etc.). Bit 64 (barren ground) is advisory only and does not mask values. Flags are summed bits, so decode them in binary.
• Dense vegetation (tropical forest), mountains, ice and snow, large water fractions and extreme deserts are masked. Averages over regions with many gaps are prone to seasonal sampling bias.
• COMBINED absolute values are rescaled to a common model-based climatology and are not an independent measure of absolute soil moisture. Use them for anomalies and variability, and be careful comparing absolute values.
• Each new version recomputes the past. Do not mix v09.1 and v09.2, and state the version and product (ACTIVE/PASSIVE/COMBINED) in your paper.
• Breaks can occur when the sensor mix changes. COMBINED is homogenized, but for long-term trend analysis check when sensors were added or retired.
• The C3S soil moisture product (CDS) uses the same algorithm but is a separate product with its own version names (e.g. v202505), input streams and update cycle. Check the differences over an overlap period before splicing CCI v09.2 and C3S.
• Some evapotranspiration and reanalysis products (e.g. GLEAM4) assimilate ESA CCI SM, so comparisons against them are not independent validation.

Notices and change history¶

References for your paper¶

Dataset citation¶

COMBINED v09.2 (CEDA) — DOI 10.5285/d4e66299f5054129b8076fb7502949e1

@misc{esacci_sm_combined_v092,
  author    = {Dorigo, W. and Preimesberger, W. and Hahn, S. and Van der Schalie, R. and De Jeu, R. and Kidd, R. and Rodriguez-Fernandez, N. and Hirschi, M. and Stradiotti, P. and Frederikse, T. and Gruber, A. and Duchemin, D.},
  title     = {{ESA} Soil Moisture Climate Change Initiative ({Soil\_Moisture\_cci}): {COMBINED} product, Version 09.2},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2026},
  doi       = {10.5285/d4e66299f5054129b8076fb7502949e1}
}

PASSIVE v09.2 (CEDA) — DOI 10.5285/c93c99588d5848b1ac7833e3bc6d5c2d

@misc{esacci_sm_passive_v092,
  author    = {Dorigo, W. and Preimesberger, W. and Hahn, S. and Van der Schalie, R. and De Jeu, R. and Kidd, R. and Rodriguez-Fernandez, N. and Hirschi, M. and Stradiotti, P. and Frederikse, T. and Gruber, A. and Duchemin, D.},
  title     = {{ESA} Soil Moisture Climate Change Initiative ({Soil\_Moisture\_cci}): {PASSIVE} product, Version 09.2},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2026},
  doi       = {10.5285/c93c99588d5848b1ac7833e3bc6d5c2d}
}

ACTIVE v09.2 (CEDA) — DOI 10.5285/2600f842cfeb481bb21f032a5741c353

@misc{esacci_sm_active_v092,
  author    = {Dorigo, W. and Preimesberger, W. and Hahn, S. and Van der Schalie, R. and De Jeu, R. and Kidd, R. and Rodriguez-Fernandez, N. and Hirschi, M. and Stradiotti, P. and Frederikse, T. and Gruber, A. and Duchemin, D.},
  title     = {{ESA} Soil Moisture Climate Change Initiative ({Soil\_Moisture\_cci}): {ACTIVE} product, Version 09.2},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2026},
  doi       = {10.5285/2600f842cfeb481bb21f032a5741c353}
}

C3S soil moisture (CDS, near-real-time version of the same algorithm) — DOI 10.24381/cds.d7782f18

@misc{c3s_soil_moisture,
  author    = {{Copernicus Climate Change Service}},
  title     = {Soil moisture gridded data from 1978 to present},
  year      = {2018},
  publisher = {ECMWF},
  doi       = {10.24381/cds.d7782f18},
  note      = {Accessed on DD-MMM-YYYY}
}

Reference papers¶

ESA CCI SM merging methodology and version history — DOI 10.5194/essd-11-717-2019

@article{gruber2019esacci,
  author  = {Gruber, Alexander and Scanlon, Tracy and van der Schalie, Robin and Wagner, Wolfgang and Dorigo, Wouter},
  title   = {Evolution of the {ESA CCI} Soil Moisture climate data records and their underlying merging methodology},
  journal = {Earth System Science Data},
  volume  = {11},
  number  = {2},
  pages   = {717--739},
  year    = {2019},
  doi     = {10.5194/essd-11-717-2019}
}

ESA CCI SM overview — DOI 10.1016/j.rse.2017.07.001

@article{dorigo2017esacci,
  author  = {Dorigo, Wouter and Wagner, Wolfgang and Albergel, Clement and Albrecht, Franziska and Balsamo, Gianpaolo and Brocca, Luca and Chung, Daniel and Ertl, Martin and Forkel, Matthias and Gruber, Alexander and Haas, Eva and Hamer, Paul D. and Hirschi, Martin and Ikonen, Jaakko and de Jeu, Richard and Kidd, Richard and Lahoz, William and Liu, Yi Y. and Miralles, Diego and Mistelbauer, Thomas and Nicolai-Shaw, Nadine and Parinussa, Robert and Pratola, Chiara and Reimer, Christoph and van der Schalie, Robin and Seneviratne, Sonia I. and Smolander, Tuomo and Lecomte, Pascal},
  title   = {{ESA CCI} Soil Moisture for improved Earth system understanding: State-of-the art and future directions},
  journal = {Remote Sensing of Environment},
  volume  = {203},
  pages   = {185--215},
  year    = {2017},
  doi     = {10.1016/j.rse.2017.07.001}
}

COMBINED break homogenization (when using COMBINED) — DOI 10.1109/TGRS.2020.3012896

@article{preimesberger2021homogenization,
  author  = {Preimesberger, Wolfgang and Scanlon, Tracy and Su, Chun-Hsu and Gruber, Alexander and Dorigo, Wouter},
  title   = {Homogenization of Structural Breaks in the Global {ESA CCI} Soil Moisture Multisatellite Climate Data Record},
  journal = {IEEE Transactions on Geoscience and Remote Sensing},
  volume  = {59},
  number  = {4},
  pages   = {2845--2862},
  year    = {2021},
  doi     = {10.1109/TGRS.2020.3012896}
}

Acknowledgements¶

ESA asks users to cite the CEDA dataset DOI of the product used together with Gruber et al. (2019) and Dorigo et al. (2017), plus Preimesberger et al. (2021) when using COMBINED. Using the citation given on the CEDA catalogue record is a condition of the terms of use. If you used the C3S (CDS) product, cite the C3S DOI and access date separately.

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¶

• ESA CCI Soil Moisture project page
• CEDA catalogue — v09.2 data collection
• Product User Guide (PUG) v09.2 (Zenodo)
• Product User Guide (PUG) v09.1 (variable and flag tables)
• ESA CCI SM frequently asked questions
• C3S soil moisture (CDS)