Mtecroscopte Structures of Wind Waves 
The skewness of the slope distribution is shown to be related 
to an excess of wavelets riding on the down-wind face of the basic wa- 
ve profile. Because the down-wind face is sloped, the skewness results. 
On the other hand, wave breaking introduces a local excess of wave- 
lets near the crests of the basic waves, and consequently, peakedness 
results at high wind velocities. 
Ve SURDACE CURVA LURE 
V.1 Distribution of surface curvature observed from vertical 
The surface-curvature distribution for each wind velocity 
was determined by setting the optical instrument in the vertical plane 
and sorting the light pulses according to their intensities. During a 
portion of the experiment, only two channels were available; the to- 
tal number of pulses was counted in one channel and the pulses with 
intensities within the preset intensity range were counted in the other 
channel. The frequency of occurrence of light pulses within a particu- 
lar range can thus be determined. This process is repeated by chan- 
ging the band settings to obtain the surface-curvature distribution, as 
shown in figure 11. The short vertical line is once again used to indi- 
cate the standard deviation of the data from the average, which is 
generally less than 5 percent. 
The lower cutoff radius of curvature of the present optical 
instrument is 0.067 cm. This cutoff, marked by a long vertical line 
shown on the left in each block of figure 11, is set just above the ma- 
ximum instrument noise, which is about 5 percent of the maximum 
signal intensity and about 1.7 percent of the maximum detectable 
radius of curvature. The upper cutoff (the maximum detectable radius 
of curvature) is 4 cm. Below the lower cutoff, no signal can be picked 
up by the instrument. Any wave that has a radius of curvature greater 
than the upper cutoff is registered as having a 4-cm radius of curvatu- 
re. Except at very low wind velocities, less than 2 m/sec, the radius 
of curvature of the water surface seldom reaches the upper cutoff 
value. 
V.2 Angular distributions of surface curvatures 
This portion of the experiment was conducted with the pulse 
analyzer described in previous sections. For each wind velocity, the 
optical instrument is set at various angles of inclination. The signals 
are directed, according to their intensity, to proper channels of the 
analyzer and are counted there. Each channel is assigned a certain 
range of signal intensity, between zero and the saturation voltage. 
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