10m Wind Speeds

Image Source: DTU

Product Description

Synthetic aperture radar (SAR) data can be used to derive wind speeds above the sea surface. The high resolution of SAR sensors allows mesoscale phenomena such as island wakes, atmospheric wave and wind turbine wake effects to be captured.  This information can be particularly useful for long term analysis in a particular area or numerical model validation. The normalized radar cross-section (NRCS) is the amount of backscattered signal per unit area. Wind over the ocean surface results in a type of scattering known as Bragg scattering. This is due to the induced short-gravity and capillary waves. A geophysical model function (GMF) is used to derive above surface wind speeds from SAR NRCS, radar viewing direction and wind direction.

Input Data Sources

The following satellite platforms provide SAR data at various resolutions:

• • Sentinel-1
• • TerraSAR-X

Wind direction may be input from numerical model output.

Required Processing

Wind speed above the sea-surface is retrieved from SAR data using GMFs. The NRCS, wind direction and radar viewing direction are required as inputs. The wind direction is obtained from numerical models. Examples of GMFs include CMOD5, CMOD7 and XMOD2.

Coverage and Frequency

• • Coverage: global
• • Frequency:
  • • Sentinel-1: 6-12 days
  • • TerraSAR-X: 11 days
• Temporal range:
  • • Sentinel-1: 2014 – present
  • • TerraSAR-X: 2007 – present

Resolutions

SAR-derived wind speed products are usually resampled to lower resolution to reduce artefacts and speckle noise. Sentinel-1 data may be resampled to 500 m or 1 km, whereas wind speeds from very-high resolution SAR data will be provided at higher resolution.

Accuracy and Validations

Wind speeds are validated using in-situ measurements from buoys or LiDAR campaigns.

Limitations

This product provides surface wind speeds. For wind resource assessment, 100-200m wind speeds are commonly required. Extrapolating to this height requires knowledge of atmospheric variables such as air-sea boundary conditions for which observations are sparse.

Delivery Format

• GeoTIFF

• NetCDF

Accessibility and Cost

An example of this capability is provided by the Danish Technological University (DTU) and is freely available at Global Wind Atlas Science Portal.