Orientation of the sea and swell in the directional spectrum 



The heading of the airplanes taking the stereo data for Data Set 2 was 

 330°„ Since the planes flew one behind the other, correctly directed arrows 

 with shafts parallel to the short sides of figure 6.2 will point toward 330°. 

 Since the buoy shown in figure 6.2 drifted generally downwind and since the 

 wind was from. 330 , or so, as reported in Part 7, an arrow parallel to the 

 short sides of figure 6<,2 and pointing to the left will point toward 330°. 



Due to the 180° indeterminancy in direction in the directional spec- 

 trujTLs this is equivalent to letting the positive r axis in the directional 

 spectrum point toward 150°. The peak in the directional spectrum indi- 

 cates waves traveling toward 180° approximately. 



With the direction fixed, the secondary peak in the spectrum indicates 

 that the swell is traveling either toward 90° or toward 270 . It is im- 

 probable that the swell is traveling toward 90° because there is no area where 

 it could have been generated between the point of observation and the east 

 coast of the United States. 



The assumption that the spectral components are traveling within +90° 

 of the direction toward which the wind is blowing is not correct for the swell 

 and thus tke final directional spectrum may have to have a range of more 

 than 180° in direction. 



The secondary maximum shown in figure 11,18 should be considered 



to be composed ot two parts. One part is the continuation of the local sea 



by means of the dasJied lines of the energy as a function of direction as shown 



220 



