Observation of Hurricane Winds using Synthetic Aperture Radar Data
Jochen Horstmann(1) , Hans Graber(2) , and Donald Thompson(3)
GKSS Research Center,
Max-Planck Str. 1,
(2) Center for Southeastern Tropical Advanced Remote , 4600 Rickenbacker Causeway, Miami, Florida 33149, United States
(3) Johns Hopkins University, Johns Hopkins Road, Laurel MD 20723, United States
In the last five years several synthetic aperture radar (SAR) images of hurricanes have been acquired by the Canadian satellite RADARSAT-1 as well as the European satellite ENVISAT. Several of these SAR images have captured hurricanes of category 4 and 5. These SAR data give the unique opportunity to investigate the possibilities of SAR data for observation and forecast of hurricanes.
In this study wind fields under hurricane conditions are retrieved from the SAR utilizing an algorithm, which has shown to give good results under low and moderate wind conditions. The algorithm extracts wind directions from wind induced streaks imaged by the SAR at scale above 200m. Wind speeds are extracted from the SAR measured normalized radar cross section (NRCS) utilizing the C-band model CMOD5, which describes the dependency of the NRCS on wind. It will be shown that the algorithm enables to measure wind directions as well as wind speeds of over 50 m/s. The SAR-retrieved wind fields are compared to results of a high resolution numerical hurricane model, which resolves the limitations of SAR wind retrieval. Furthermore, the SAR retrieved wind fields will be used to retrieve the pressure fields, which in turn will be compared to the pressure fields resulting from the numerical model. Finally, the possibilities of SAR for estimating wind fields, pressure fields as well as shape and dimension of the hurricane eye will be discussed with respect to hurricane forecast.