Observations of Hurricane Bonnie in spaceborne synthetic aperture radar (SAR) and next generation Doppler weather radar (NEXRAD)

Atmospheric circulation systems have being shown to produce observable signatures on spaceborne synthetic aperture radar (SAR) imagery of the ocean surface. Capillary and small gravity ocean waves of roughly the scale of the SAR electromagnetic wavelength, the so-called Bragg waves, provide the surface roughness that allows for SAR mapping of both ocean and atmospheric mesoscale features. Two RADARSAT SAR images were acquired over Hurricane Bonnie on 25 and 27 August 1998. Simultaneous Doppler weather radar observations were also acquired at next generation radar (NEXRAD) stations on the U.S. East coast. These coincident datasets were coregistered and analyzed The observed ocean patterns in the C-band HH SAR images correlate well with the cyclonic circulation pattern of the hurricane winds and the presence of convective cells within the system. Significant signal attenuation in regions of heavier rainfall is observed in the SAR images. Understanding rain effects in SAR imagery is of increasing importance as we develop new scatterometer-like algorithms to produce high-resolution winds from spaceborne SAR imagery. Increased knowledge of hurricane SAR signatures will also help us derive reliable information on offshore storms that cannot be easily obtained from other sources.