Eugenio Pugliese Carratelli
Active (i.e. Radar) Satellite remote sensing data of the sea have been employed for many years for wind and sea state analysis; there is still a lot to be done, however, in order to improve the scope and the accuracy of their applications. The understanding of sea state and wind velocity from altimeter and SAR data - as well as, possibly from scatterometer - is indeed far from perfect, mostly because the effect of foam and spray on the scattering properties is not clear.
A simple description of the techniques involved is given (in Italian) on GuardiaPiemontese2012
Most of the work is based on the pseudo random numerical generation of the water surface to simulate active sensor response. Compared to analytical procedures, such an approach allows a much greater freedom in specifying and testing non linear hypotheses on the backscattering functions; the basic idea - i.e. to simulate a great number of sea surface realisations and to evaluate the scattering coefficient by ensemble averaging the statistics of surface tilt an other parameters -is not new in principle and it dates back to 1990 (Bruening et al.). It has however been improved and extended to wave lengths down of the order of one meter, well under SAR pixel size, thus allowing a better representation of sub pixel phenomena.
Some description of the work carried out on this field is described in papers presented - mostly - at specialised ESA-ESRIN seminars:
ENVISATFrascati2006 Montreux2007 Seasar2008
A similar approach was followed, as early as 2000, for the radar altimeter wave form reconstruction:
More recently whitecapping and floating foam has been taken into account; the radar cross section of a wave field under strong wind derives from the presence of foam as much as – if not more – from capillary wave roughness. Thus, before an effective local backscattering model can be successfully employed to reconstruct wave information from SAR, the behaviour of foam must be correctly modelled and its local backscattering properties have to be properly quantified
A peculiar aspects of the work concerns the application of hurricane data through the participation to the "RADARSAT Hurricane Applications Project Workshop", led by the Canadian Space Agency; the it is hoped that scattering data on a fully foam and spray covered sea – as it is mostly likely to be during an hurricane – may provide information on the scattering behaviour of the foam covered fraction of less strong sea states.
A FirstReport2010 produced in cooperation with Luis Cordoba (CUJAE , Havana - CUBA) and Francisco J. Ocampo Torres (CICESE-Ensenada – MEXICO) provides some information
A different -if closely related - line of work is aimed at direct applications to engineering problems, and results have been presented at International Seminars, congresses and published on papers:
On SAR applications: ArabianCoastDubai05 IAHRVenice2007
On Altimeter : Koweit2008 PIANCPalermo2008 BARCELONA2009 ChennaiCOPEDEC2012 GuardiaPiemontese2012 Journal of Coastal Research
The following presentations may provide a clearer idea of the work being carried out
ppt presentation at a Palermo PIANC
presented at the Italian Meteo Office (In Italian)
ChennaiCOPEDEC2012presentation
Giuseppe Spulsi, Maria Rosaria Della Rocca, Claudia Giarrusso and Ferdinando Reale have greatly contributed to this line of research.
Last revised 2013 EPC