Application of Coincident Sub-Footprint Scale Winds to Observe the Effect of Sea Surface Vorticity on the RapidScat Scatterometer Ku-Band NRCS

David E Weissman, Hofstra University, Hempstead, NY, United States
This study combines very high resolution wind vectors analysis in the Gulf of Mexico with normalized radar cross section (NRCS) measurements of the sea surface. The NRCS is provided by the RapidScat Ku-band scatterometer mission on the International Space Station. One topic of interest is observing how calculations of the vorticity, using different spatial scales from this wind product, are related to the radar backscatter for each of the two radar polarizations. Vorticity is a key ocean forcing parameter. The winds in regions near atmospheric fronts, when rain is also likely to be present, usually display very large directional diversity on scales smaller than a radar footprint. One goal of this project is to assess the sensitivity of the curl of the wind to different scales of wind resolution that are used to calculate it, and to consider its relation to the behavior of the NRCS in that region. Included in these comparisons are the collocated calculations of the NRCS using the JPL Ku-band NRCS model function with this wind product, and its response to a variety of vorticity conditions. The approach here involves a study of numerous scatterometer orbits, and will include a variety of wind and weather conditions.
The sub-footprint winds are from a new high-resolution wind vector product (hourly, 2.5 km grid spacing). This product is the Real Time Mesoscale Analysis (RTMA), from NOAA-NCEP. We are comparing the PO.DAAC NRCS products (Level 2A) to the values estimated from the higher resolution wind product, transferred to backscatter, through the RapidScat geophysical model function (GMF), provided by colleagues at JPL. Coincident rain data is available through a special RScat “RadRain” product created by Remote Sensing Systems (REMSS) for this mission, using a variety of collocated, coincident satellite radiometer sensors. Higher resolution rain measurements available via the NASA IMERG data resource is provided by the NASA Precipitation Measurements Mission.