Metop ASCAT Surface Soil Moisture Near Real Time 12.5 km sampling

The Surface Soil Moisture (SSM) product (H29) is derived from the ASCAT Level 1b full-resolution radar backscatter product. It maps the soil moisture content in the topmost surface layer (<5 cm) expressed in degree of saturation on a fixed-earth grid with a spatial sampling of about 12.5km.

• Coverage: Global, provided as strips of swaths representing 3 minutes of data acquisition (~1200 km)
• Resolution: 25 km x 25 km, sampled at 12.5 km
• Timeliness: Metop B: <70 min, Metop C: <110min
• Dissemination: H SAF FTP and EUMETCast
• Formats: NetCDF4 and BUFR

The ASCAT Surface Soil Moisture (SSM) products are based on the ASCAT Level 1b full-resolution product containing geolocated radar backscatter observation along each of the six ASCAT beams. The individual beam measurement is not collocated on a regular swath grid and therefore provided in their original observation geometry. The spatial resolution of the backscatter observation per beam varies slightly depending on the incidence angle, but is approximately 10 km (along-beam direction) x 25 km (across-beam direction. The full-resolution backscatter observation are resampled to a fixed Earth grid using a spatial filter (Hamming window) with a search radius of approximately 24 km. Resampled backscatter observation are merged into triplets (Fore, Mid, Aft beam) for overlapping beams. These backscatter triplets are used as input to the EUMETSAT H SAF TU Wien soil moisture retrieval algorithm, computing the ASCAT SSM product.