Wide Swath Radar Altimeter for real-time reporting of hurricane wave height and Directional Wave Spectra

The NOAA airborne Wide Swath Radar Altimeter (WSRA) was developed by ProSensing with funding from the NOAA SBIR and JHT programs, with additional support from the University of Massachusetts and DARPA. The WSRA system provides continuous real-time reporting of several data products: (1) directional ocean wave spectra, (2) significant wave height, (3) rain rate, and (4) the mean square slope of the ocean surface. All the data products are transmitted in real-time from the NOAA P-3 aircraft to the National Hurricane Center (NHC) through a satellite data link. Development of the WSRA prototype was completed in 2007. Its design was based on the previous experience from the NASA Scanning Radar Altimeter system led by Ed Walsh, but with the incorporation of new technologies which have significantly improved the performance of the instrument. Implementation of the digital beam-forming technique allowed for (1) implementation of a more reliable microstrip antenna that does not require any mechanically moving parts, and (2) lower transmitting frequency, which improved the system's performance in the heavy precipitation conditions often found in hurricanes. In short, the Wide Swath Radar Altimeter is a downward looking radar with 80 narrow beams spread over ±30° from nadir in the cross-track direction. From the radar return of all 80 beams it generates at a 10 Hz rate raster lines of sea surface topography, seen in Figure 1, from which sea surface directional wave spectra and significant wave height are calculated. The WSRA was installed in the fuselage of the NOAA hurricane reconnaissance aircraft WP-3D during the 2007 hurricane season when the first test flight was successfully conducted. During the next three years (2008, 2009, 2010) effort was focused on transitioning the WSRA system from a prototype to operation. Raw WSRA radar data were collected over a wide range of ocean surface conditions, from calm seas up to CAT 3 hurricanes. Post-flight analysis of WSRA data were critical for the development of the processing algorithm, improving its efficiency, robustness, and output data product quality. During flights into Hurricane Irene on August 24, 25 and 26, 2011, the WSRA generated in-flight and real-time maps of sea surface topography, processed the topography into directional wave spectra, and for the first time transmitted the spectra and extracted parameters to a public FTP site at the NOAA Aircraft Operations Center, from which it was automatically extracted by the Joint Hurricane Testbed (JHT) server at the National Hurricane Center. The JHT computer automatically converted the spatial distribution of wave height into a NAWIPS format that forecasters could superimpose on their other displays. After the successful 2011 hurricane season WSRA system was upgraded by NOAA to operational use. Continued development on the WSRA software led to the fully-automated and unattended operation of the WSRA system. WSRA data products, besides being transmitted in real-time to NHC, are also displayed on a web page that was specifically developed for this system (www.prosensing.com/wsradisplay). During the 2013 hurricane season WSRA operated on all NOAA's recon flights (TS Gabriel, TS Ingrid, and Hurricane Karen). The figure 2 below shows the WSRA web page for the flight 201331004H on October 4th, 2013 into Hurricane Karen that was at CAT1 strength.