Quality Control of Sea Clutter and Constant Power Function Artifacts for Operational U.S. Navy Shipboard Radar Data Assimilation
Authors: Harasti Paul 
Published: March 2020

&lt;p&gt;The Marine Meteorology Division of the U.S. Naval Research Laboratory (NRL) has developed and transitioned a 3DVAR reflectivity data assimilation (DA) system into operations at Fleet Numerical Meteorology and Oceanography Center (FNMOC), located in Monterey, California.&amp;#160; The system assimilates hourly, volumetric, radar reflectivity data into the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS&lt;sup&gt;&amp;#174;&lt;/sup&gt;)&lt;sup&gt;1&lt;/sup&gt; high-resolution NWP model within the ship-following COAMPS &amp;#8211; On demand System (COAMPS-OS&lt;sup&gt;&amp;#174;&lt;/sup&gt;)&lt;sup&gt;1&lt;/sup&gt;.&amp;#160; Both Next-Generation Radar (NEXRAD) land-based radar data and U.S. Navy shipboard SPS-48/Hazardous Weather Detection and Display Capability (HWDDC) radar data are assimilated depending on their data coverage provided to the COAMPS&lt;sup&gt;&amp;#174;&lt;/sup&gt; nested grids. The SPS-48/HWDDC units are installed on eighteen U.S. Navy aircraft carriers and amphibious assault ships, and when underway on a mission, the available units automatically transmit compressed, radar data files to FNMOC near the top of the hour.&amp;#160; Through previously reported NRL and FNMOC demonstrations, and more recent operationally testing at FNMOC, the COAMPS-OS&lt;sup&gt;&amp;#174; &lt;/sup&gt;radar DA system&amp;#8217;s nowcasting products have demonstrated their ability to provide improved predictions of precipitation events out to at least 6 hour forecasts compared to 3DVAR conventional DA into COAMPS&lt;sup&gt;&amp;#174;&lt;/sup&gt; alone.&amp;#160; Shipboard SPS-48/HWDDC radar data and their assimilation into COAMPS-OS&lt;sup&gt;&amp;#174;&lt;/sup&gt; at FNMOC provide critical environmental awareness in the data sparse oceanic regions of the world that the Navy warfighter encounters.&lt;/p&gt;&lt;p&gt;The SPS-48 radar is a S-band, phased-array, azimuthally scanning, air-search radar that scans electronically in elevation and completes a volume scan in four seconds. The HWDDC combines the volume scans into motion-compensated, one-minute composites with limited clutter filtering applied. The SPS-48 beams are combined to yield full PPI scans at 22 different elevation angles ranging from 0.1&amp;#176; to 24&amp;#176;. The azimuthal resolution of the data is 1&amp;#176; and the range resolution is 1 km. The maximum range for reflectivity (radial velocity) data is 250 (81) km. &amp;#160;The Doppler data are only produced for the lowest three elevation scans whereas reflectivity data are produced for all elevation scans; all these data are archived in Universal Format and compressed before dissemination to FNMOC.&amp;#160; &amp;#160;Owing to the limited HWDDC Doppler data both in range and elevation, and the single-polarization of the SPS-48 radar waveform, reflectivity data quality control is particularly challenging.&amp;#160; New algorithms have been developed to handle sea clutter and constant power function artifacts, such as bullseyes and sun strobes.&amp;#160; There are two algorithms for sea clutter; the first one deals with anomolus propagation sea clutter caused by sea-water evaporation into the atmospheric surface layer, and the second one deals with the more widespread and distant sea clutter due to surface-based and elevated electromagnetic ducts resulting from trapped moist air under temperature inversions often encountered off the coasts of California and the Arabian Gulf region.&amp;#160; An overview of the ship-following COAMPS-OS&lt;sup&gt;&amp;#174; &lt;/sup&gt;radar data quality control and assimilation system will be presented along with examples of quality controlled SPS-48/HWDDC radar data and the impact on COAMPS&lt;sup&gt;&amp;#174;&lt;/sup&gt; forecast skill scores.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; COAMPS and COAMPS-OS are registered trademarks of the U.S. Naval Research Laboratory&lt;/p&gt;