On board wave monitoring – WaMoS II – Wave Monitoring System

For surveying the ocean wave field WaMoS II, an operational wave monitoring system based on a com- mon marine X-Band can be used。 Mounted on a ship, oil rig or onshore it is a proven instrument that measures the wave energy its directions and heights as well as the surface currents。 The  system con- sists of conventional navigational X-band radar, a high speed video digitizing and storage device  and a standard PC。 The analogue radar video signal is read out and transferred to the PC for storage   and

further real time processing。 The data can be ac- cessed either directly, via removable media, or on-line via modem/telephone or Internet。 The measurement is based on the backscatter of microwaves from the ocean surface that is visible as ’sea clutter’ on the nautical radar。 One measurement consists of a 32 consecutive radar images。 This allows to describe the sea surface in space and time。 From that observable sea clutter an analysis is carried through to deduce the unambiguous directional wave spectrum and the surface currents in real time。 Sea state parameters such as wave heights, periods, wave lengths, wave directions and the surface currents are estimated by a straight forward analysis。 Based on a standard marine X-Band radar the wave monitoring system WaMoS II has been  proven  to  be  a  powerful tool to monitor spectral sea state parameters from fixed platforms as well as from moving vessels [5]。

Figure 5: Systematic drawing of WaMoS II system components

From spectral wave parameters to single wave events

The ongoing project SinSee is dealing with the re- lation between ship movements and particular wave events。 It is the inpidual wave that influences the ship movements, which is difficult to measure from board a ship。 In order to close this gap, new methods are developed within SinSee to retrieve the sea sur- face elevation in space and time。 I。e。 in addition to the spectral parameters, the inpidual wave height, the wave group behaviour and the inpidual shape of the waves encountered will be extracted from the X-band radar data。

Here an algorithm to determine inpidual wave heights from sea surface elevation maps is presented。 The proposed algorithm allows for the first time to investigate properties of single waves in space and time simultaneously。 It enables further to estimate the maximum wave height from spatial wave data and hence to study extreme wave events。来;自]优Y尔E论L文W网www.youerw.com +QQ752018766-

A case study was carried out with the aim to investi- gate the correlation between inpidual wave param- eters derived from radar images and inpidual waves

measured by a buoy。 The data used in the following is measured on board a test platform (FINO) in the Southern North Sea。 Since August 2003 a  WaMoS II system is installed to measure waves and currents, with the aim to derive statistics on the general wave climate as well as on the probability of occurring extremes。 In close vicinity of the platform, a wave buoy is moored。 It is set up to store the data with a frequency of 2Hz, which means it is possible to determine the sea surface elevation from the buoy。 Figure 6 shows a radar raw image captured at that platform。 The antenna is located in the center of the image。 The range of the radar is about 2 km, the rings are plotted every 500m。

One radar image consists of about 700 000 pixels。 The spatial distance of each pixel is 7。5m。 One radar revolution corresponds to 2 seconds。 A complete measurement consists of 32 images, containing the spatial and temporal information of the inpidual waves。 The position of the buoy is marked in the up- per part of the radar image。 The position of the buoy is covering 1 pixel in the radar image that is shown in figure 6。 As the radar measurement consists of a time series of radar images, each pixel theoretically can be looked at as an independent buoy。