Title :
A wavelet-based algorithm to estimate ocean wave group parameters from radar images
Author :
Niedermeier, Andreas ; Borge, José Carlos Nieto ; Lehner, Susanne ; Schultz-Stellenfleth, Johannes
Author_Institution :
German Aerosp. Center, Remote Sensing Technol. Inst., Oberpfaffenhofen, Germany
Abstract :
In recent years, new remote sensing techniques have been developed to measure two-dimensional (2-D) sea surface elevation fields. The availability of these data has led to the necessity to extend the classical analysis methods for one-dimensional (1-D) buoy time series to two dimensions. This paper is concerned with the derivation of group parameters from 2-D sea surface elevation fields using a wavelet-based technique. Wave grouping is known to be an important factor in ship and offshore safety, as it plays a role in dangerous resonance phenomenons and the generation of extreme waves. Synthetic aperture radar (SAR) data are used for the analysis. The wavelet technique is introduced using synthetic ocean surfaces and simulated SAR data. It is shown that the group structure of the ocean wave field can be recovered from the SAR image if the nonlinear imaging effects are moderate. The method is applied to a global dataset of European Remote Sensing satellite (ERS-2) wave mode data. Different group parameters including the area covered by the largest group and the number of groups in a given area are calculated for over 33 000 SAR images. Global maps of the parameters are presented. For comparison, classical 1-D grouping parameters are calculated from colocated wave model data showing good overall agreement with the wavelet-derived parameters. ERS-2 image mode data are used to study wave fields in coastal areas. Waves approaching the island of Sylt in the North Sea are investigated, showing the potential of the wavelet technique to analyze the spatial wave dynamics associated with the bottom topography. Observations concerning changes of wavelength and group parameters are compared to linear wave theory.
Keywords :
bathymetry; edge detection; geophysical signal processing; ocean waves; oceanographic techniques; radar imaging; remote sensing by radar; spaceborne radar; synthetic aperture radar; terrain mapping; wavelet transforms; 1D buoy time series; 2D sea surface elevation fields; ERS-2; European Remote Sensing satellite; North Sea; Sylt; bottom topography; edge detection; group parameters; nonlinear imaging effects; ocean waves; radar imaging; remote sensing; spatial wave dynamics; synthetic aperture radar; wavelet-based algorithm; Ocean waves; Radar imaging; Radar remote sensing; Remote sensing; Sea measurements; Sea surface; Spaceborne radar; Surface topography; Surface waves; Two dimensional displays;
Journal_Title :
Geoscience and Remote Sensing, IEEE Transactions on
DOI :
10.1109/TGRS.2004.836873