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CENIntegrated Climate Data Center ICDC

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Soil moisture from ESA-CCI

Volumetric soil moisture from ESA-CCI 2013
Volumetric soil moisture from ESA-CCI 2013. Copyright: UHH/CEN/S. Kern

Topics

Access

RESTRICTED: This link to the data set is only available for a restricted user group.  The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account.  Please contact ICDC if you would like to access this data from outside the network.

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Description

A unique > 40-year long soil moisture data set, version 8.1, has been generated in the framework of the ESA-CCI Soil Moisture ECV projects. For this purpose C-band scatterometer data (among others: ERS-1/2 AMI scatterometer, MetOp Advanced Scatterometer) and multi-frequency radiometer data (among others: SMAP, SMOS, SMMR, SSM/I, TMI, AMSR-E, Windsat, AMSR2) are used to compute the soil moisture. 

For the completely re-processed data set offered here, different (Level 2) soil moisture (SM) data sets are merged together. One strand of data comprises soil moisture retrieved using satellite active microwave data (C-Band scatterometers, see above); the second strand comprises soil moisture retrieved using satellite microwave radiometry. Data products from each strand are merged directly, together with a sophisticated uncertainty characterization (see ATBD in references). The approach makes best use of already established Level 2 services of ESA, EUMETSAT, NASA, JAXA, etc. for the different satellites and sensors. From the two separate strands of data two additional data products are generated. This new version v7.1 differs from the predecessors by a new processing scheme and continued updated usage of more recent relevant satellite observations.

For more information regarding retrieval schemes we refer to the ICDC web pages of ASCAT soil moisture, AMSR-E soil moisture, SMOS soil moisture as well as to the extensive number of documents created during the ESA-CCI Soil Moisture ECV project (see ESA CCI Soil Moisture website in references ).

We strongly recommend all interested users to register at the respective ESA web site (see references) to not miss information about updates of the data set. We recommend to regularly check the ESA CCI Soil Moisture website (see references) for updated information from the ESA-CCI Soil Moisture ECV project.

We are offering the daily "COMBINED" data set version v08.1. Currently, data sets "ACTIVE" and "PASSIVE" are only available on request.

Last update of data set at ICDC: July 6, 2023.

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Parameters

Parameters of the ESA-CCI soil moisture data set
NameUnitComment
Volumetric soil moisture m³ / m³ 0 ... 1
Error of Volumetric soil moisture m³ / m³ 0 ... 1
Day/Night flag -
  • 0: no data,
  • 1: day,
  • 2: night,
  • 3: day+night
Quality flag data gaps - 0 ... 31 (0 = best quality)
Frequency band flag - 0 ... 130 (L to Ka-Band, single bands and combinations)
Satellite orbit flag -
  • 0: no data,
  • 1: ascending,
  • 2: descending,
  • 3: both
Sensor flag - 0 ... 1888 (single sensors and combinations)
Time Days since 1970-01-01 00 UTC  

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Coverage, spatial and temporal resolution

Period and temporal resolution:

  • 1978-11-01 to 2022-12-31
  • Daily

Coverage and spatial resolution:

  • Global
  • Spatial resolution: 0.25° x 0.25°, cartesian grid
  • Geographic latitude: 89.875°S to 89.875°N
  • Geographic longitude: 179.875°W to 179.875°E
  • Dimension: 720 rows x 1440 columns
  • Altitude: following terrain

Format:

  • NetCDF

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Data quality

Each file of the data set contains an uncertainty estimate (when observations from at least two sensors are merged) and a set of quality flags which basically document the reason why data have been discarded from the data set (see parameters); in addition each file gives information about the sensors used. Beginning with this version v08.1 the uncertainty estimates obtained through Triple Collocation Analysis and the resulting merging weights are generated on a seasonal basis. The product uncertainty is therefore more representative of seasonal errors in the soil moisture retrieval.

The barren ground flagging strategy has been changed to a majority decision, where at least 50% + 1 of the observing sensors need to raise the flag. The flag is kept optional, i.e., the soil moisture data is not masked.

We note, that soil moisture retrieval is less reliable and/or impossible in regions of pronounced topography, in case of standing water, and in areas of dense vegetation. For snow covered areas and frozen soil a soil moisture retrieval is also not possible.

Substantial gaps occur in the data set - particularly during the initial years of the time series. These stem from the fact that the used satellite sensors only view a limited portion of the Earth's surface during their overpasses during one day.

We recommend to take a look at the documents in the references, especially Gruber et al., 2017 and 2019,  and Dorigo et al., 2017, for more details about data quality, validation, and inter-comparison studies and to regularly check the ESA CCI Soil Moisture website (see references) for updated information from the ESA-CCI Soil Moisture ECV project.

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Contact

Vienna University of Technology, Austria
Transmissitivity B.V. / VanderSat B.V. Noordwijk, The Netherlands
email: ecv_sm_contact (at) eodc.eu

Richard Kidd
Vienna University of Technology
Vienna, Austria
email: richard.kidd (at) geo.tuwien.ac.at

Stefan Kern
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de

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References

Literature: (note: as of today, July 6 2023, the updated documentation for v08.1 products is not yet available.)

Websites:

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Data citation

Please cite the data as follows:

Whenever the product, made available by the ESA CCI SM project, is used for publication, the data's origin must be acknowledged and referenced. Please use the following web page:

http://www.esa-soilmoisture-cci.org 

And the data set should be cited using the complete three references as follows:

  1. Gruber, A., et al., 2019, Evolution of the ESA CCI soil moisture climate data records and their underlying merging methodology, Earth System Science Data, 11, 717-739, http://doi.org/10.5194/essd-11-717-2019.
  2. Dorigo, W. A., et al., 2017, ESA CCI Soil Moisture for improved Earth system understanding: State-of-the art and future directions, Remote Sensing of Environment, 203, 185-215, 2017, doi:10.1016/j.rse.2017.07.001.
  3. Gruber, A., et al., 2017, Triple Collocation-Based Merging of Satellite Soil Moisture Retrievals, Transactions on Geoscience and Remote Sensing, 55(12), 1-13. doi:10.1109/TGRS.2017.2734070.
Last data accessed by ICDC from ftp.geo.tuwien.ac.at on June 16, 2023.

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