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Simulating the Influence of Wave Whitecaps on SAR Images

Eugenio Pugliese Carratelli(1), Chapron Bertrand(2), Ferdinando Reale(3) and Fabio Dentale(4)

(1) CUGRI and University of Salerno, Piazza V. Emanuele, 84080 Penta di Fisciano, Italy
(2) IFREMER, Plouzane 29280, Brest 29280, France
(3) University of Salerno, Via Ponte don Melillo, 84084 Fisciano, Italy
(4) University of Salerno, Via Ponte Don Melillo, 84084 Fisciano, Italy

Abstract

Recent results (Kudryavtsev et al, 2003 a and b), seem to defy the conventional view that SAR radar response only depends on capillary wave modulation, and highlight the importance of wave breaking and the consequent formation of whitecaps on the image formation mechanism. Such an effect was already taken into account as a possible element of SAR sea current visualization by Johannessen et al. (2002), but it is still relatively new within the context of wind and wave analysis. On the one hand, the understanding of offshore wave breaking and whitecap formation has reached a reasonable level (Melville, 2002, Piazzolla et al 2002); on the other hand, a recent revival (Pugliese Carratelli et al, 2005, 2006) of numerical Montecarlo-like image simulation (Bruning et al, 1990), now gives greater freedom to introduce more complex mechanisms than the traditional spectral analytical procedure. Parameters related to geometric, kinematic and dynamic breaking criteria can now be much more exactly computed on the basis of a numerical realization than with a purely spectral approach. On the same token, the all-important Doppler shift effect and its role in generating the final SAR image can be easily incorporated, in spite of the inherently non-linearity of the backscattering mechanism. It is also to be expected that such an approach will eventually help to identify extreme waves from high SAR imagery. However, even assuming that a confident estimate can now be reached of the fraction of the sea surface covered by breaking waves as a function of wind and wave state, according to the results of – among others - Sang-Ho et al (2004), Y. Sugihara et al (2004), Lafon et al (2005), the scattering characteristics of whitecaps and foam are still far form being fully known; numerical simulation of the wave surface in connection with SAR data may provide in the future a tool to a better understanding of their effect. The work will present the results of up to date numerical SAR image simulation techniques incorporating the effects mentioned above, on both the image and the image spectrum.

ACKNOWLEDGEMENTS Some of the data used for this work were provided through ESA-ESRIN Project CAT-1 No 1172: “Remote sensing of wave transformation”; the authors are grateful to Dr. Jerome Benveniste (Esa – Esrin) for help and support

REFERENCES

Bruening, C., Alpers W. and Hasselmann K. “Monte Carlo Simulation studies of the nonlinear imaging of a two dimensional surface wave field by a synthetic aperture radar” Int. Journal of remote Sensing 11, 1990 Melville W. K. & P.r Matusov “ Distribution of breaking waves at the ocean surface”, Letters to Nature, 2002 Johannessen, J. A., V. Kudryavtsev, D. Akimov, T. Eldevik, N. Winther, and B. Chapron (2005), On radar imaging of current features: 2. Mesoscale eddy and current front detection, J. Geophys. Res., Kudryavtsev, V.N, D . Hauser, G.Caudal, B. Chapron “ A semiempirical model of the normalized radar cross-section of the sea surface 1. Background model, J. Geophys. Res., , Vol. 108, 2003 a Kudryavtsev, V.N, D . Hauser, G. Caudal, B. Chapron “ A semiempirical model of the normalized radar cross-section of the sea surface 2. Radar modulation transfer function, J. Geophys. Res., , Vol.108, 2003 b Lafon C., J. Piazzola, P. Forget, S. Despiau Modelling of whitecap coverage in coastal environment 37th International Liège Colloquium on Ocean Dynamics, Gas Transfer at Water Surfaces, May 2 - 6 2005 Piazzola J., P. Forget, and S. Despiau A sea spray generation function for fetch-limited conditions Annales Geophysicae (2002) 20: 121–131 c European Geophysical Society 2002 Pugliese Carratelli E., F. Dentale C.C. Giarrusso, F. Reale G. Spulsi ” Application of Satellite SAR Images to Sea and Wind Monitoring in Coastal Seas” Arabian Coast 2005 - Coastal Zone Management And Engineering, Dubai, United Arab Emirates, 27-29 November 2005 Pugliese Carratelli E., F. Dentale, F. Reale "Numerical Pseudo-Random Simulation of SAR Sea and Wind Response", SEASAR 2006 Symposium Frascati, Italy 23-26 January 2006 Sang-Ho Oh, Natsuki Mizutani, Noriaki Hashimoto, Kyung-Duck Su “Laboratory Observation of Breaking Criteria of Wind-Generated Deepwater Waves”, Proceedings of the 29th International Conference , Lisbon, Portugal, 19 – 24 September 2004 Sugihara Y., H. Tsumori, H. Yoshioka, S. Serizawa, A. Masuda, “Imaging Measurement of Whitecaps at Sea Observation Tower “, Proceedings of the 29th International Conference , Lisbon, Portugal, 19 – 24 September 2004

 

Workshop poster

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry