Corrections to Scatterometer Wind Vectors During Hurricane Dennis Using High Resolution NEXRAD Radar Rain Corrections

Scatterometer wind measurements in Hurricanes have excellent potential for studying ocean forcing and the forecasting of coastal storm surges and flooding potential. These observations have the advantages of wide coverage, high resolution and accuracy. However, significant errors can occur when rain causes attenuation and backscatter of the Scatterometer´s microwave pencil-beam. For most of the rain conditions existing in Hurricanes, the signal returned to the satellite is larger than that reflected by the sea surface resulting in erroneously high estimates of the wind speed. One consequence can be large errors in estimates of the coastal storm surge. This study shows how NEXRAD measurements of the rain within each Scatterometer cell can be used, with a physically based electromagnetics model, to correct the affected radar cross section data. Hurricane Dennis made landfall in the Gulf of Mexico on July 10, 2005, not far from the Florida/Alabama border. There was a serious impact on the Apalachee Bay and Cedar Key region because of a anomalously high storm surge. Heavy precipitation affected the ability of the QuikSCAT Scatterometer to accurately predict this phenomena. The precipitation in this storm was continuously monitored by the NWS Tallahassee NEXRAD (S-band) radar. The mode of this instrument is to collect radar reflectivity data using conical scans at a sequence of elevations, resulting in a 3-D volume with 2 km spatial scales. This example studies herein underscores the necessity of correcting the Scatterometer´s normalized radar cross section (NRCS) measurements to remove the excess backscatter and attenuation provided by rain areas that exist within the 25-by-35 km antenna footprint. High resolution NWS-NEXRAD techniques are especially useful because of the wide variability of the rain intensity, both horizontally and vertically across each Scatterometer footprint and along the incident beam