Analysis of ERS-1/2 synthetic aperture radar wave mode imagettes

Type Publication
Date 1998-04
Language English
Copyright 1998 by the American Geophysical Union
Author(s) Kerbaol Vincent1, Chapron Bertrand1, Vachon Paris W2
Affiliation(s) 1 : IFREMER, Ctr Brest, Dept Oceanog Spatiale, F-29280 Plouzane, France.
2 : Canada Ctr Remote Sensing, Ottawa, ON K1A 0Y7, Canada.
Source Journal Of Geophysical Research-oceans (2169-9275) (Amer Geophysical Union), 1998-04 , Vol. 103 , N. C4 , P. 7833-7846
DOI 10.1029/97JC01579
WOS© Times Cited 99
Note This article also appears in: Advances in Oceanography and Sea Ice Research Using ERS Observations
Abstract

The European Space Agency (ESA) ERS-1 and ERS-2 C band VV polarization active microwave instrument (AMI) offers the unique ability to combine interlaced wind scatterometer and high-resolution synthetic aperture radar (SAR) wave mode imagettes. In this study, more than 2000 imagettes were considered. Each imagette has been statistically analyzed in comparison with normalized radar cross-section (NRCS) measurements from the scatterometer mode. During ti lt ERS-1 AMI wave mode mission the incidence angle of the imagette center was modified from roughly 19.9 degrees to 23.5 degrees. Using ERS-1 and ERS-2 NRCS, calibration has thus been completed for both configurations, which allows a better characterization of some signal data saturation effects. However, since a SAR relies on platform displacement to achieve fine resolution, surface motions reduce its nominal resolution. As the wind speed increases, scatterer motion occurring during the SAR integration time also increases, causing the characteristic large azimuth cutoff wavelength. Acknowledging the strong dependence between sea state conditions and azimuth smearing effects, our results are highlighted by the global comparison with wind estimates derived from the scatterometer. The results demonstrate the ability to define a SAR wind algorithm from a kinematic point of view. Finally, a higher-order statistical analysis shows evidence of deviation from standard Rayleigh statistics, leading to a, balance between K law and lognormal distributions. This deviation is mainly due to the SAR's high-resolution properties.

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