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IOVWST Meeting
Portland, Maine, USA, 2019

Combined Active and Passive Microwave Remote Sensing of High Ocean Winds

Presenting Author: Dr. Simon Yueh

To assess the capability of combined active and passive remote sensing for high ocean winds, we analyzed the data from WindSAT, ASCAT, and QuikSCAT for several Atlantic Hurricanes in 2003-2008. The WindSAT data from 20 hurricanes were collocated with the NOAA HWind analyses. The WindSat 6-GHz brightness temperatures (TB) were less affected by rain than the high frequency channels, and were mostly far from saturation near the hurricanes. The differences between vertical and horizontal polarizations were quite significant, indicating the characteristics of surface emissions, rather than rain attenuation. The excess surface emissivity at the C-band frequency appears to be consistent with the SFMR model with about 0.5K-1K change in TB for 1 m/s change in wind speed. For ASCAT backscatter analysis, 30 revs of ASCAT data were collocated with the HWind analyses. The ASCAT data at 50-60 degree incidence angles showed weak wind speed response, about 1 dB change from 30 m/s to 50 m/s. The comparisons show that the ASCAT backscatter levels are in good agreement with the CMOD5 model function for < 15 m/s, but can be below the CMOD5 model by 1-2 dB for 15-50 m/s wind speeds. From the analysis of microwave propagation through rain, we determined that the 1-2 dB discrepancy is within the attenuation range of precipitation near hurricanes. It is suggested that the C-band ASCAT backscatter, although less sensitive to precipitation than Ku-band, will still require rain attenuation correction to reduce the wind speed bias. We evaluate the synergism of combining active and passive data through the wind retrievals using the QuikSCAT data only and the addition of WindSAT data. We find that including the WindSAT polarimetric data in the retrieval allows the reduction of wind solution ambiguities, improvement in directional accuracy and consequently improvement in wind speed accuracy for high ocean winds.

2019 International OVWST Meeting
May 29-31 in Portland, Maine, USA
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