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A Shipborne HF Radar

In contrast to a microwave radar, which is well known in navigation and remote sensing applications, a decametric waves radar ( HF radar ) has been used to measure surface currents by using the process of backscattering of electromagnetic waves from the rough sea surface. The University of Hamburg HF radar, based on CODAR , uses electromagnetic waves of about 10 m length, which interact with ocean waves of 5 m length.

From 1985 to 1992, the University of Hamburg CODAR has been extended for shipborne operation. The first experiment has been carried out on board the German icebreaker Polarstern, which most of the time has been sailing within the ice, far away from open water. The main result of this experiment was, that the attenuation of icecovered sea reduces the performance and working range extremely. Good mesurements have only been possible with the ship sailing at the ice edge or in open water. However, this application did not need an icebreaker, so the following experiments have been carried out using the University of Hamburg R/V Valdivia.

Figure of Valdivia

The intention for operating the CODAR onboard a ship was to enable the measurement of surface current fields in front of the rough Norwegian coast, where the combination of a land based and a shipborne CODAR has been used during the NORCSEX'88 experiment, and on the open sea at the ice edge and at the Arctic Front. There are several difficulties to be solved for successful measurements of surface current fields from a slowly sailing ship. A discussion of the shipborne CODAR can be found here.

An example of surface currents measured by the shipborne CODAR can be found here. The background colours indicate the temperature measured in 4 m depth. The surface current field calculated from density gradients given by CTD and XBT cruises can be seen here. Note the eddie near the bottom of the figures.

This work has been supported by the German Research Foundation (DFG) within the Sonderforschungsbereich 318, Klimarelevante Prozesse im System Ozean-Athmosphäre-Kryosphäre.
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