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Tracking of fresh-water plumes in Dutch coastal waters by means of HF radar


Presented at the IGARSS'99 Session: Eddies, Fronts and Currents


Klaus-Werner Gurgel , H.-H. ESSEN and T. SCHLICK

University of Hamburg, Institute of Oceanography, Tropolwitzstrasse 7, D-22529 Hamburg, Germany.
Tel: +49-40-42838-5742, Fax: +49-40-42838-5713,
email: klaus-werner.gurgel@uni-hamburg.de
WWW: http://wera.cen.uni-hamburg.de/index.shtml


A full paper has been published in the conference proceedings


Abstract

Since more than 20 years high-frequency (HF)-radars have been used for measuring surface current fields and ocean-wave spectra. The physics behind is backscattering from a moving rough sea surface. Radar systems, working at frequencies between 25 and 30 MHz, are deployed along the coast and cover an area of up to 50 km * 50 km, which can be observed continuously at 10 minute intervals.

Recent developments at the University of Hamburg led to a new HF radar system called WERA (Wellen Radar). WERA is a frequency-modulated continuous-wave (FMCW) radar which, when linked to a linear array of receice antennas, simultanously measures surface currents and ocean waves. The highest spatial resolution is 300 m. The area covered in this mode is about 35 km * 35 km.

Results from an experiment at the Dutch coast in fall 1997 are presented. Fresh water plumes, travelling along the Dutch coast, could be observed. The plumes are originated from the Rhine and Ijssel outflow into the North Sea. The measurements were conducted at Petten, 25 km south of the island Texel. The WERA high resolution mode showed much more details of the plume structure than was possible with the resolution of 1.2 km of the pulsed Coastal Radar (CODAR) of the University of Hamburg. Horizontal shear of the surface current of up to 50 cm/s within 300 m has been observed.

In addition to the surface currents, the spatial distribution of backscatter strength will be investigated. In accordance with theory, some evidence has been found that backscatter strength is related to sea-water conductivity.


This work has partly been funded by the European Commision DG XII within the MAST-2 programme, project SCAWVEX, ct94-0103.
klaus-werner.gurgel@uni-hamburg.de
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