View source for Measuring current fields in the German Bight by radar techniques


===The background===
[[Image:CurrentFields_1.jpg|thumb|right|'''Figure 1''' Radial component of the ocean surface current measured from Büsum.]]In 2006 and 2007, partly funded by the Ministry of Science, Economic Affairs and Transportation of the state of Schleswig-Holstein and coordinated by Rathyeon Anschütz GmbH, a consortium of ten marine technology companies and the three research institutes, FTZ Westcoast, IfM Geomar and GKSS developed an environ- mental monitoring and warning system for oceans and, especially, for coastal waters. "Classical" sensors for environmental monitoring are combined with components for maritime safety techniques and traffic surveillance, remote sensing, model simulations and operational fore- casts as well as information, alarm and warning functions. At present the OMS (Ocean Monitoring System) comprises remote sensing components like two X-band radars with wave detection software and two over the horizon radars for surface current measurement. It also includes oceanographic data acquisition units (three multi-sensor buoys and one measuring pile) as well as a data base, web-based visualisation and information structures, real time numerical modelling capacities (high resolution regional forecast models with data assimilation) and broadcast solutions for public warning.
[[Image:CurrentFields_2.jpg|thumb|left|'''Figure 2''' Map of the installed systems within the OMS project. Crown Copyright and/or database rights. Reproduced by the permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office.]]
The data centre of the OMS is located at the FTZ Westcoast in Büsum. This institute of Kiel University also operates the three buoys and the pile for ocean data acquisition. Each of the buoys is equipped with an Acoustic Doppler Current Profiler (ADCP). Among other purposes, ADCP data are used to validate measurements from the over the horizon radars (Fig. 1). Antenna arrays of these systems are deployed on the island of Sylt as well as on the jetty of Büsum harbour (Fig. 2 and 3, HF radar on Helgoland is intended).
===Over the horizon radar for surface current fields measurements===
A ground wave HF radar for coastal applications called WEllen RAdar (WERA) was developed at the University of Hamburg (Gurgel et al., 1999<ref name="G">Gurgel, K.-W., Antonischki, G., Essen, H.-H. & Schlick, T. (1999). Wellen Radar (WERA): a new ground-wave HF radar for ocean remote sensing. Coastal Engeneering, 37 (2-4), 219-234.</ref>). 
The system is obtainable from Helzel GmbH. HF radars are operated in the 3-30 MHz frequency range (50 m to 10 m wavelength), where the electromagnetic waves can travel far beyond the horizon by ground wave propagation along a good conducting layer (salty ocean water). The signals are scattered back from ocean waves of half the electromagnetic wavelength (Bragg scattering). 
[[Image:CurrentFields_3.jpg|thumb|right|'''Figure 3''' Over the horizon radar installation at the west jetty of Büsum harbour. The system measures current maps in the range between Cuxhaven and St. Peter Ording (see Fig. 1).]]
The system measures the Doppler spectrum caused by moving ocean waves, which can be processed to give the speed of the ocean surface current. The second-order modulation of the sea echoes can be used to detect the ocean wave height and the wave directional spectrum. Ground wave radar systems can be installed at the coast close to the water to ensure a good coupling to the ocean and achieve working ranges up to 200 nautical miles. Because one HF radar measures the radial component of the current, a second HF radar some 10 km away is required to calculate the 2-dimensional surface current from the two radial components. 
The system is running successfully. The next step is to validate the results between the different systems shown in Fig. 2 for the observed area.

==References==
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{{author 
 |AuthorID=16917
 |AuthorFullName= Vanselow, Klaus Heinrich
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{{author 
 |AuthorID=16919
 |AuthorFullName= Ricklefs, Klaus
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{{author 
 |AuthorID=5381
 |AuthorFullName= Gurgel, Klaus-Werner
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[[Category:Coastal and marine observation and monitoring]]
[[Category:Observation of physical parameters]]
[[Category:North Sea]]