First Operational Implementation of SAR Winds at NOAA

With the launch of Seasat in 1978, it was noticed that the high-resolution (25 m) synthetic aperture radar (SAR) revealed signatures of ocean wind variability. Changes in wind speed induced changes in sea surface roughness which in turn changed radar cross section. Features such as gap flows, convection, and hurricane eye structure were observed. In the intervening years, the relationship between the near-surface marine vector and the radar cross section has become better understood. In 1999, NOAA and the Johns Hopkins University Applied Physics Laboratory began the Alaska SAR Demonstration Program. SAR data from the Radarsat-1 satellite were downloaded and processed into SAR imagery at the Alaska Satellite Facility in Fairbank, AK. The imagery were then transmitted to NOAA in Maryland. There the SAR imagery was converted in near real-time into wind speed estimates. Comparisons with buoys, models, and other satellite measurements indicated a measurement accuracy for wind speed (corrected to 10-m height) of better than 2 m/s at a horizontal resolution of 500 m. Radarsat-1 SAR wind images from the Alaska SAR Demo demonstrated the ability to visualize gap flows in coastal regions, barrier jets, wind shadowing, and even the presence of atmospheric internal waves. In addition, SAR winds have also been used for guidance in the assessment of offshore wind power turbine locations. Radar scatterometer measurements from QuikSCAT and ASCAT can measure winds on a global scale at about 25 km resolution. SAR winds at almost two-orders of magnitude higher resolution represent complimentary measurements suited for coastal regions. The next step from research to operations was to convert a research-based approach into a comprehensive APL/NOAA SAR Wind Speed Retrieval System (ANSWRS). ANSWRS is a set of software and protocols that can processes SAR imagery in near real time. Data from the available SAR satellites are ingested and converted to a common format. From there, the SAR radar cross sections are mated with NOAA National Weather Service GFS (Global Forecast System) wind directions to initiate the wind speed retrieval. Wind speeds are computed and stored into a NOAA-standard netCDF format. In addition, color-coded wind speed images are provided in PNG, KMZ, and GeoTIFF formats. On May 1, 2013, this wind speed product became operational within NOAA's National Environmental Satellite, Data, and Information Service (NESDIS). At present, SAR data from Radarsat-2 via the U.S. National Ice Center is used as the operational source of SAR data. Although ANSWRS can process TerraSAR-X and COSMO-SkyMed SAR imagery, Radarsat-2 is the operational data source. We anticipate free and open data availability from the Sentinel-1a satellite to be launched in early 2014. When available, Sentinel-1 data will become the principal source of SAR data for operational NOAA winds, augmented with data expected to continue to be obtained from Radarsat-2 In this presentation, we will summarize the physical relationship between radar cross section and wind speed that is exploited in the wind speed retrieval, outline the ANSWRS processing procedures and data flow, explain how these data can be obtained in near real-time, and describe likely future applications of these winds. On May 1, 2013, this wind speed product became operational at NOAA. At present SAR data from Radarsat-2 via the National Ice Center is used as the operational source of SAR data. Although ANSWRS can process TerraSAR-X and Cosmo-SkyMed SAR imagery, Radarsat-2 is the operational data source. We anticipate free and open data availability from the Sentinel-1 satellite to be launched in early 2014. When available, Sentinel-1 data will augment the In this presentation, we will summarize the physical relationship between radar cross section and wind speed that is exploited in the wind speed retrieval, outline the ANSWRS processing procedures and data flow, explain how these data can be obtained in near real-time, and describe likely future applications of these winds. The attached figure show a sample wind speed product off the southern coast of Alaska acquired 2013 Jan 15 03:40:43 UTC. The views, opinions, and findings contained here are those of the authors and should not be construed as an official NOAA or U.S. Government position, policy, or decision