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WaMoS II
RESEARCH
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Waves and Ice
Sea Ice Detection Using the WaMoS wave radar system Polarstern study Sea ice data was collected from a WaMoS II system on board the German polar research vessel Polarstern, belonging to the Alfred Wegener Institute (AWI). The data was collected in the late summer of 2001, from August 4th to September 30th in latitudes ranging from 82šN. to almost 90šN.
Image of the German polar research vessel Polarstern. The Figure below shows an example of a sampled WaMoS II image in near range mode on August 11th at 12:42 UTC. The surface backscatter signals were sampled in 256 level of gray-scaled values. Due to WaMoS II's use a direct gray level table the higher return from sea ice corresponds to higher gray values. In a similar way, the lower return from sea water corresponds to lower gray level values on the sampled image. In the very near vicinity of the radar antenna the backscatter signal is always high, independent of the target (i.e. sea ice or sea water). That is due to the fact that the angle of incidence of the incident electromagnetic fields is higher and, consequently, the received power of the backscatterd fields is as well much higher.
Ordinary marine X-band radar is a
suitable tool to detect sea ice in a local scale (ranges up to 10 km). The
sea ice radar video signal is sampled and stored in real time by the WaMoS
II system, which permits the image analysis of
the sampled sea surfaces. Some examples corresponding to
different sea ice conditions and range measurement
modes have been shown. In addition, the first
four statistical moments of each image have been calculated showing a
dependence of them with
the spatial ice structure features in the sea surface.
Due to the fact that the WaMoS II system
can work without any disturbance of the marine radar functions, the system
can be installed moving ships in order to systematically archive sea ice
data.
To download the entire article in PDF format click here.
Jan Mayen Study The WaMoS II wave monitoring system was installed onboard the Norwegian research vessel Jan Mayen during the cruise from March 12th until March 26th 2001 in the Greenland Sea. The aim of this installation was to examine the possibility of doing wave measurements under sea ice conditions, and to further investigate the imaging of ice in radar images.
The following figure shows a polar radar image of a sea surface covered with pancake ice.
Though the pancake ice prevented the existence of ripple waves, the rough edges of the ice plates are responsible for the ability to measure radar backscatter from the longer waves. Under these conditions it was possible to measure the sea state parameters with WaMoS II, The next figure shows a derived 2-dimensional wave number spectrum from these measurements.
The 2- dimensional wave number spectrum shows a clearly shaped wave system coming from North-East, with a spread of approximately 45°. The peak wave length was about 150m, and the significant wave height was 1.7 m. Conclusions: The results of this study shows, that the WaMoS II is able to measure the sea state parameters from a free surface as well as under ice covered conditions, as long as the ice thickness does not prevent the movement of the waves. Pancake ice complies with these conditions. In firm pack ice where no waves can be observed, WaMoS II is imaging ice structures according to their surface roughness. This work could be continued with the aim to interpret the ice structures, in the same sense as satellite measurements are doing. To download the entire article in PDF format click here
Download a Wave Radar FAQ document (in PDF Format)
Sea-Image Corporation is a distributor of OceanWaves GmbH products in North America.
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