ATMOSPHERIC BOUNDARY-LAYER ROLLS OBSERVED BY THE SYNTHETIC-APERTURE RADAR ABOARD THE ERS-1 SATELLITE

Two synthetic aperture radar (SAR) images acquired by the European Remote Sensing Satellite ERS-1 over the Jade-Weser estuary in the German Bight of the North Sea on January 2 and 20, 1992, are analyzed. The images show sea surface manifestations of atmospheric boundary layer rolls. This is inferred from the orientation of the quasi-periodic sea surface patterns which are aligned approximately with the wind direction, from the ratio of the wavelength of the patterns to the height of the boundary layer, and from the conditions encountered in the atmospheric boundary layer as measured quasi-simultaneously by radiosondes. The atmospheric boundary layer rolls were generated by a dynamic instability on January 2 and by a thermal instability on January 20. For the first time, quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar SAR image. It is shown that wind velocities derived from SAR image intensity variations are in agreement with theoretical estimates.