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Proceedings Paper

Radar image sequence analysis of inhomogeneous water surfaces
Author(s): Joerg Seemann; Christian M. Senet; Heiko Dankert; Helge Hatten; Friedwart Ziemer
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Paper Abstract

The radar backscatter from the ocean surface, called sea clutter, is modulated by the surface wave field. A method was developed to estimate the near-surface current, the water depth and calibrated surface wave spectra from nautical radar image sequences. The algorithm is based on the three- dimensional Fast Fourier Transformation (FFT) of the spatio- temporal sea clutter pattern in the wavenumber-frequency domain. The dispersion relation is used to define a filter to separate the spectral signal of the imaged waves from the background noise component caused by speckle noise. The signal-to-noise ratio (SNR) contains information about the significant wave height. The method has been proved to be reliable for the analysis of homogeneous water surfaces in offshore installations. Radar images are inhomogeneous because of the dependency of the image transfer function (ITF) on the azimuth angle between the wave propagation and the antenna viewing direction. The inhomogeneity of radar imaging is analyzed using image sequences of a homogeneous deep-water surface sampled by a ship-borne radar. Changing water depths in shallow-water regions induce horizontal gradients of the tidal current. Wave refraction occurs due to the spatial variability of the current and water depth. These areas cannot be investigated with the standard method. A new method, based on local wavenumber estimation with the multiple-signal classification (MUSIC) algorithm, is outlined. The MUSIC algorithm provides superior wavenumber resolution on local spatial scales. First results, retrieved from a radar image sequence taken from an installation at a coastal site, are presented.

Paper Details

Date Published: 18 October 1999
PDF: 11 pages
Proc. SPIE 3808, Applications of Digital Image Processing XXII, (18 October 1999); doi: 10.1117/12.365865
Show Author Affiliations
Joerg Seemann, GKSS Research Ctr. (Germany)
Christian M. Senet, GKSS Research Ctr. (Germany)
Heiko Dankert, GKSS Research Ctr. (Germany)
Helge Hatten, GKSS Research Ctr. (Germany)
Friedwart Ziemer, GKSS Research Ctr. (Germany)

Published in SPIE Proceedings Vol. 3808:
Applications of Digital Image Processing XXII
Andrew G. Tescher, Editor(s)

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