EUMETSAT Support to Operational Hydrology and Water Management

Small scale surface soil moisture by radar scatterometer (SSM ASCAT NRT D)

The disaggregated Surface Soil Moisture (SSM) product (H08) derived from the global ASCAT NRT product (H16) is limited to the H SAF area (Europe) and maps the soil moisture content in the surface layer (0-2 cm) at spatial sampling of 1 km.

• Coverage: Strips of 1000 km swath crossing the H SAF area [25-75°N lat, 25°W-45°E long]
• Cycle: 36 hours
• Resolution: Basic 25 km, constant through the field of view; sampling 1 km
• Accuracy: 0.05 m³ m-³, degrading in dependence of the presence of vegetation, topographic complexity
• Timeliness: 135 min (potentially 35 min using the EARS service)
• Dissemination: By dedicated lines to centres connected by GTS - By EUMETCast to most other users, especially scientific ones
• Formats: Values in grid points in the orbital projection or fixed latitude-longitude grid (BUFR) and NetCDF

Short description of the basic principles for product generation

The product is derived by disaggregating the global ASCAT NRT product (H16), which is generated at the EUMETSAT H/Q and disseminated via EUMETCast. The disaggregation process is performed based on a pre-computed fine-mesh scaling layer derived from statistical analysis of C-band SAR imagery. A linear relationship is established between the local (fine-scale) and the regional (coarse-scale) backscatter information and derived from a multi-annual image-analysis. The downscaling parameter database is then used to disaggregate the scatterometer pixels to the fine mesh in near real-time. The SAR imagery used for generating the database is ENVISAT ASAR in ScanSAR Global Mode (years 2004-2012) and, planned for future, imagery from the upcoming Sentinel-1. The disaggregated product, sampled at km-scale, enables better fitting of local information to better suite hydrological requirements.