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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 7, issue 2 | Copyright
Atmos. Meas. Tech., 7, 437-449, 2014
https://doi.org/10.5194/amt-7-437-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Feb 2014

Research article | 07 Feb 2014

Retrieving hurricane wind speeds using cross-polarization C-band measurements

G.-J. van Zadelhoff1, A. Stoffelen1, P. W. Vachon2, J. Wolfe2, J. Horstmann3,4, and M. Belmonte Rivas5 G.-J. van Zadelhoff et al.
  • 1Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
  • 2Defence R&D Canada, Ottawa, Ontario, Canada
  • 3Center for Maritime Research and Experimentation, La Spezia, Italy
  • 4Institute of Coastal Research, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany
  • 5Geoscience and Remote sensing, Technical University Delft, Delft, the Netherlands

Abstract. Hurricane-force wind speeds can have a large societal impact and in this paper microwave C-band cross-polarized (VH) signals are investigated to assess if they can be used to derive extreme wind-speed conditions. European satellite scatterometers have excellent hurricane penetration capability at C-band, but the vertically (VV) polarized signals become insensitive above 25 m s−1. VV and VH polarized backscatter signals from RADARSAT-2 SAR imagery acquired during severe hurricane events were compared to collocated SFMR wind measurements acquired by NOAA's hurricane-hunter aircraft. From this data set a geophysical model function (GMF) at strong-to-extreme/severe wind speeds (i.e., 20 m s−1 < U10 < 45 m s−1) is derived. Within this wind speed regime, cross-polarized data showed no distinguishable loss of sensitivity and as such, cross-polarized data can be considered a good candidate for the retrieval of strong-to-severe wind speeds from satellite instruments. The upper limit of 45 m s−1 is defined by the currently available collocated data. The validity of the derived relationship between wind speed and VH backscatter has been evaluated by comparing the cross-polarized signals to two independent wind-speed data sets (i.e., short-range ECMWF numerical weather prediction (NWP) model forecast winds and the NOAA best estimate 1-minute maximum sustained winds). Analysis of the three comparison data sets confirm that cross-polarized signals from satellites will enable the retrieval of strong-to-severe wind speeds where VV or horizontal (HH) polarization data has saturated. The VH backscatter increases exponentially with respect to wind speed (linear against VH [dB]) and a near-real-time assessment of maximum sustained wind speed is possible using VH measurements. VH measurements thus would be an extremely valuable complement on next-generation scatterometers for hurricane forecast warnings and hurricane model initialization.

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