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Summary of Proposal OCE1271

TitleWave field retrieval from TSX data to estimate/forecast sea state and wave induced sea level rise.
Investigator Uiboupin, Rivo - Tallin University of Technology, Marine Systems Institute
Team Member
Dr. Raudsepp, Urmas - Tallinn University of Technology, Marine Systems Institute
Mr Alari, Victor - Tallinn University of Technology, Marine Systems Institute
SummaryThe first objective of the project is to develop and implement methods for retrieval of two dimensional (2D) ocean/marine wave spectra from satellite imagery (Synthetic Aperture Radar- SAR). SAR enables to study spatial variation of surface waves in near shore regions (main advantage compared to altimetry) where local bathymetry, surface wind and surface currents have active interaction with gravity waves. The high resolution data from X-band (TerraSAR-X) and C-band (Radarsat-2, ASAR/Sentinel-1?) radars will be used. Two algorithms,one for each band (C and X), will be used to retrieve 2D marine wave spectra which enable to find parameters relevant for navigation in the coastal areas: significant wave height, peak wavelength and wave direction. Algorithms will be tuned using hindcast results of wave model prior to the validation against buoy measurements to improve the accuracy.
Secondary objective is to assimilate/integrate the SAR wave fields into SWAN wave model to carry out operational validation and improve model forecast.
The study area is Baltic Sea which has low wave heights and wavelengths compared to the open ocean, therefore high resolution SAR imagery is needed to resolve the small scale wave field features. Consequently, high resolution SAR data from TSX SpotLight and StripMap modes are suitable for this purpose.
The wave field parameters (significant wave height and wave direction ) will be retrieved from image wave number spectrum.The relation between significant wave height and wave number spectrum is relatively well known. However, the the algorithm includes empirically derived constants which can be tuned for different SAR imaging modes. Considering that during the project 11 in situ wave buoys will be installed in Gulf of Finland and Gulf of Riga over a long period it would provide good basis for retrieval of the constants applied in the equations that are used for converting SAR image spectrum to wave field parameters (e.g. SWH). A brief overview for retrieval of wave field parameters from SAR data is given in the following papers:
(1) Li X.M., Lehner S., Rosenthal W. 2010. Investigation of Ocean Surface Waves Refraction Using TerraSAR-X Data. IEEE Transaction on geoscience and Remote Sensing, 48(2),830-840.
(2) CollardF., Ardhuin F, Chapron B. 2005. Extraction of Coastal Ocean Wave Fields from SAR Images. IEEE Journal of Oceanic Engineering. 30(3), 526-533 The wave fields retrieved from TSX data will be compared with the results of Radarsat-2 data.
DELIVERABLES: The outcome of the project are scientifically based and validated wave field retrieval algorithms for Spotlight and Stripmap mode TSX images. Second deliverable is the list of quality parameters of the algorithm performance. Third output is a protocol/report on the assimilation of SAR based wave products into operational wave forecast model.

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