7 Q 

 ships at sea. 1 ' 7 However, the wave directionality of the model has only heen 



indirectly validated. The question has risen whether the adequate verification of 

 the point spectra can imply that the wave energy has been distributed and propa- 

 gated in the proper directions. A more direct method of validating the directional 

 aspects of the model is necessary. The measurement of the directions, heights and 

 frequencies of the waves provides an important step in the verification of the 

 model. This can be accomplished in a variety of ways, as will be discussed 

 shortly. 



COMPLEXITY OF WAVE ENVIRONMENT 



Waves in the ocean and coastal environment reveal three dimensional charac- 

 teristics. They can be found to be long-crested or short-crested. The complexity 

 of these waves stems from the fact that they reflect, diffract, refract, become 

 standing or trapped partially or totally, and interact with other physical parame- 

 ters such as wind , other waves , and currents . Therefore , data measured from the 

 field must be properly interpreted to represent the given sea conditions (Figure l). 



Long-crested seas are not common, and may be locally wind generated or 

 decaying swell in an otherwise benign sea. Short-crested seas occur for most of 

 the time. Waves of varying height, frequency and direction interact continually in 

 the ocean. The processes and results of these interactions produce confused seas 

 and make the observation of these conditions difficult. 



Another seaway condition difficult to represent is wave-current interaction. 

 Currents can refract, reflect, attenuate and amplify waves, depending on their 

 relative magnitudes and directions, see Figure 2. Further discussions are pre- 

 sented by Forristall 10 and Lai. 11 ' 12 



TECHNIQUE OF WAVE MEASUREMENT 



Because of the nature and complexity of ocean waves , many techniques for 

 measuring waves and their directions have been developed to take advantage of dif- 

 ferent wave characteristics. The instruments used to obtain these measurements 

 operate on principles based on either pressure, orbital wave velocity, wave slope, 

 any combination of these, or the reflection of radar. 



Some systems that lend themselves to measurement of nearshore directional 

 waves include: pressure sensor biaxial current meter combinations, triaxial 

 current meters, arrays of pressure sensors and shore-based radars, such as X-band 



r 



