A satellite altimeter model for ocean slick detection - art. no. C04004

Type Article
Date 2006-04
Language English
Author(s) Tournadre Jean1, Chapron Bertrand1, Reul NicolasORCID1, Vandemark D2
Affiliation(s) 1 : Inst Francais Rech Exploitat Mer, Oceanog Lab, F-29280 Plouzane, France.
2 : NASA, Goddard Space Flight Ctr, Wallops Isl, VA 23337 USA.
Source JGR - Oceans (0148-0227) (American Geophysical Union), 2006-04 , Vol. 111 , N. C4 , P. NIL_1-NIL_13
DOI 10.1029/2005JC003109
WOS© Times Cited 28
Keyword(s) Slick, Sigma blooms, Altimeter waveforms
Abstract [1] About 5% of Ku-band altimeter ocean data are degraded by the occurrence of high radar return cross sections (sigma(0)), usually called sigma(0) blooms. During blooms, which occur during no or low wind conditions, the mean altimeter waveform can significantly depart from the expected shape. In about 60% of the cases the waveforms are distorted to such an extent that either the range tracker loses lock or the off-nadir angle estimate becomes unrealistic. The analysis of high data rate altimeter waveforms during bloom events reveals the presence of V-shaped patterns similar to the ones observed during rain events. These patterns trace small-scale (i.e., smaller than the altimeter footprint) changes in surface backscatter. Such variations of surface roughness are commonly observed in SAR images under low wind conditions. On the basis of the experience gained through the analysis of high-resolution altimeter waveforms in the presence of rain cell, a model is developed to analyze the altimeter response to phenomena whose length scale is smaller than the altimeter footprint. The model is applied to simple patterns ( linear slicks and circular patches) as well as to realistic surface sigma(0) estimated by SAR. It is also used to analyze bloom events in terms of surface slicks. The model results shows that the small-scale sigma(0) variations explain the behavior of altimeter waveforms in bloom events. The results also show that a good proportion of data during bloom events are still valid for estimating geophysical parameters as the Brown model remains valid. Use of high-resolution altimeter waveforms may also offer an interesting mean to study marine slick occurrence rates and type.
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