23. Where a directional distribution is well behaved (one main peak 

 direction with lesser energy at nearby directions and very little energy at 

 directions well away from the peak) , these gages can do extremely well in 

 estimating peak direction, generally within a few degrees. However, if there 

 are two equal energy wave trains at the same frequency but well separated 

 directions (as in the example given in par. 11), these gages will tend to give 

 an angle somewhere midway between the two peak directions. While such a 

 result gives a kind of mean angle for the wave field as a whole, it does not 

 represent either wave train very well since it attributes the peak wave energy 

 to a direction in which there is no wave energy. Hence, gage output can be 

 quite misleading. 



24. With a more advanced analysis algorithm, data from any of the above 

 gages can be processed to detect two separate wave trains at the same frequen- 

 cy, but only if their propagation directions are separated by 70 deg or more 

 (Oltman-Shay and Guza 1984). This algorithm is an improvement, but it still 

 does not give enough information for a complete sea state description. 



25. This discussion does not mean that information from any of these 

 gages is of little use. A partial frequency- direction spectrum is immensely 

 preferred over a spectrum with no directional information. Furthermore, these 

 devices are compact and relatively simple to deploy. In complex bathymetry or 

 in highly variable wave fields near solid structures, they are among the most 

 reliable direction- sensing devices in existence. 



26. An improvement to these gages, developed by Cartwright and Smith 

 (1964), is an articulated (cloverleaf) buoy which is able to estimate three 

 components of sea surface curvature as well as heave, pitch, and roll. This 

 buoy's directional distribution resolving ability is improved because six 

 properties of the sea surface are measured instead of the three used in the 

 simpler gages. It is able to resolve peak energy directions quite well and 

 angular spreads of about 60 deg. If energy is spread over angles of less than 

 60 deg, the spread is not well resolved. For example, it could not distin- 

 guish very well the different cases in the experiments by Vincent and Briggs 

 (1989), and Kaihatu and Briggs (in preparation). However, resolution of the 

 cloverleaf buoy is better than that of the simpler gages, and it provides a 

 hint of the true spread of a natural sea. 



27. This property of the cloverleaf buoy led to a series of measure- 

 ments reported by Mitsuyasu et al . (1975) at various sites near Japan. From 



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