With the increase of the necessity to know about the directionality within the ocean wave 
field, GKSS decided to develop WaMoS as an operational system [4]. It is usefull for a broad 
variety of operations at the open sea and in coastal areas. The WaMoS is already in 
operational use on-board the oilrig 2/4K in the Norwegian field "EKOFISK" [5] and on top 
of a light house on the Spanish Coast at "Cabo Matxitxako" [6]. 
2. The map of wave energy 
The physical description of the energy within a wavefield is most commonly given by its 
spectral presentation. This gives the decomposition of the total wave energy into its 
components with different lengths, periods or travel directions. Among the different 
presentation methods the two dimensional spectrum is the only complete method to describe 
wave directionality (see.: fig. l.a and 2.a). These figures have the structure of a polar plot, 
which is commonly used for the presentation of two dimensional wave energy. In a polar plot 
the two coordinates are the azimuthal angle and the radial distance from the centre. The 
position of the wave component within this plane provides information on its length, period 
and its travel direction. 
You should look at a two dimensional spectrum as you would look at a "map of wave 
energy". For its interpretation the following rules may help: 
1. The level of the isolines give the amount of energy of the corresponding wave component. 
2. From the radial distance of the isolines to the centre the length or the period of the 
corresponding wave component may be deduced. In fig.l.a) the circles give the length of 
the wave component (In an other way of presentation the circles may give the wave 
periods, e.g.: the length of X= 40m corresponds to a period of t = 5sec; or X = 100m 
to t = 8sec). 
3. The azimuthal angle gives the propagation direction of the wave component in 
geographical orientation. 
4. As in a spectral presentation the radial coordinat is either frequency (f=l/x, where t is the 
wave period) or wavenumber (k=l/A,, where X is the wavelength), the greatest lengths or 
periods are close to the centre and the smallest have the longest radial distance from the 
origin. 
The example (figures l.a), a two dimensional wave energy spectrum shows four independent 
wave systems. The swell with 320m wave length, which is propagating towards 160deg has 
the highest energy. There are two more swell systems detected during this situation. The one 
propagates with 120m wave length towards 350deg. and the other with 110m towards 70deg. 
Their common contribution to the total energy is the same as from the first system. The local 
wind sea travelling towards 130 is quite weak. Fig. 2.a shows the situation 9 hours later. The 
swell is shorter now with 250m length with a higher wave height. The local wind sea going 
to 130deg is still quite weak. 
The integrated spectra E(j) and 0(f) which are plotted in figures l.b), l.c), 2.b) and 2.c) 
have been deduced from the radar measurements under the use of the integrations and 
transformations presented in the scheme of figure 3. As on 15.01.94 at 9:00 UTC a unimodal 
situation within each frequency bandwidth was measured (see: fig. 2.a), the frequency 
presentation (fig. 2.b and 2.c) is good enough to fully describe the wave situation. But the 
multimodal situation (see: fig l.a) measured 9 hours before (15.01.94 00:00 UTC) is rather