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Requirement | Target | C3S Soil Moisture Products | Comment | Status |
|---|---|---|---|---|
Product Specification | ||||
Parameter of interest | Surface Soil Moisture (SSM) | Surface Soil Moisture | In addition to Surface Soil Moisture, GCOS provides requirements for Root-zone soil moisture, which is currently not included in C3S Soil Moisture. | Achieved |
Unit | Volumetric (m³/m³) | Volumetric [m³/m³] passive merged product, combined active +passive merged product; [% of saturation] active merged product | Conversion between volumetric units and % saturation is possible using soil porosity information. | Achieved |
Product aggregation | L2 single sensor and L3 merged products | L3 merged active, merged passive, and combined active + passive products | C3S Soil Moisture aims to provide merged products only. | Achieved |
Horizontal resolution | 10 km | 0.25° (~25 km) | Current spatial resolution is within the 50 km “Threshold” requirement from GCOS, but below the 10 km “Breakthrough” and 1 km "Target" requirement. C3S Soil moisture is provided on a regular lat/lon grid. Pixel size in kilometers, therefore, varies with latitude. | Approached |
Record length | >30-35 years | >43 years (1978/11 - present) | Not strictly required by CMUG. CMUG only states that datasets of that length cover a period long enough for climate monitoring. | Achieved |
Revisit time | Daily | Daily | CMUG is highlighting the added value of sub-daily observations for special process studies but also states that monthly observations are sufficient for some applications (e.g. trend monitoring). | Achieved |
Product accuracy | 0.04 m³/m³ | Variable (0.04-0.10 m³/m³), depending on land cover and climate (current assessment for various climates, land covers, and texture classes based on in-situ data shows accuracy to be < 0.1 m³/m³) | Relative to (in situ) reference data. Based on estimates of unbiased root-mean-square-difference (see Gruber et al. (2020) and [RD10]). The GCOS "Breakthrough" requirement (0.04 m³/m³) is met at ~85% of all relevant ground stations, in all other cases the 0.1 m³/m³ requirement is met. | Approached |
Product stability | 0.01 m³/m³/decade | 0.01 m³/m³/decade | No formal guidelines exist yet on how to best validate the stability of merged soil moisture products over time. | Achieved, but no formal guidelines followed |
Quality flags | Should be provided with observations | Quality flags provided: Frozen soils, dense vegetation, no convergence in retrieval, physical bounds exceeded, weights of measurements below the threshold, all datasets unreliable, barren ground | C3S soil moisture is not provided when quality flags are raised (flagging of deserts as an exception). Most, flags are therefore only informational. This is to simplify using the data. | Achieved |
Uncertainty | Daily estimate, per pixel | Daily estimate, per pixel | Uncertainty estimates are derived from triple collocation and gap-filled using vegetation density information. | Achieved |
Format Specification | ||||
Product spatial coverage | Global | Global | Only land points, Antarctica excluded, permanent gaps for tropical forests. | Achieved |
Product update frequency / Timeliness | 6 hours (GCOS) Monthly to annually (CMUG) | 10-20 days (ICDR), and 12 monthly (CDR) | 10-daily chunks are processed with a 10-day delay (ICDR). Monthly averages are only computed for completed months. Sub-daily update frequencies for merged products are currently not targeted. | Achieved |
Product format | Daily images, Monthly mean images | Daily images, dekadal (10-day) mean, monthly mean images | No threshold for minimum number of observations per dekad / month is set. | Achieved |
Grid definition | 0.25° | 0.25° | Regularly sampled grid in latitude and longitude dimensions. | Achieved |
Projection or reference system | Projection: Geographic lat/lon Reference system: WGS84 | Projection: Geographic lat/lon Reference system: WGS84 | Achieved | |
Data format | NetCDF | NetCDF 4 | Each timestamp (day/dekad/month) is provided as an individual file. | Achieved |
Data distribution system | FTP, WMS, WCF, WFS, OpenDAP | Data is distributed through the Climate Data Store (CDS) at https://cds.climate.copernicus.eu/cdsapp#!/dataset/10.24381/cds.d7782f18 | Programmatic access via CDS API is possible (see https://cds.climate.copernicus.eu/api-how-to6) | Achieved |
Metadata standards | CF, obs4mips | NetCDF Climate and Forecast (CF 1.7) Metadata Conventions; ISO 19115, obs4mips (distributed separately through ESGF) | Achieved | |
Quality standards | QA4ECV | QA4ECV and QA4SM standards and best practices implemented and verified. | Following best practice guidelines (Gruber et al. (2020) and [RD10]). | Achieved |
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