Jin Wu 
shaped pulses, varying from 0 to 10 V in amplitude and having dura- 
tions of a few milliseconds. However, the pulse height analyzer 
(ND-110 128- channel analyzer manufactured by Nuclear Data, Inc. ) 
requires pulses of much shorter periods and places very stringent 
requirements on the risetime. The pulse conditioning circuit shown 
in figure 4a is thus required. 
The pulse conditioner is capable of analyzing both pulse height 
and pulse width (pulse period). In both modes, the signal activates 
the Schmitt trigger. This in turn sets the binary and opens electronic 
switch N° 1, In the height mode, the track hold amplifier output is 
compared with the incoming signal. When the input drops, the ampli - 
fier is put in hold. In other words, the amplifier tracks the signal to 
its maximum value and holds this value until it is reset. On the other 
hand, when the signal drops below the threshold of the Schmitt trigger 
monostablet, is started. This closes electronic switch N° 2 foma 
sec. During this time the amplitude of the track hold amplifier is ga- 
ted to the pulse height analyzer as a pulse with a suitable width and 
risetime. At the end of this time, T> is started again to reset the bi- 
nary and to close electronic switch N° 1. By doing so the track hold 
amplifier is reset until a new pulse is received. 
In the time mode, the operation is identical except that the 
Schmitt trigger controls a ramp generator, which is tracked to con- 
vert time to amplitude. Consequently, the amplitude gated to the pul- 
se height analyzer is proportional to the signal pulse duration. The 
pulse described above, from the signal to the pulse height analyzer, 
are shown in figure 4b, The widths of 17, and T, are exaggerated for 
clarity. 
Ill EXPERIMENTAL CONDITIONS 
IiI. 1 Wind conditions 
The wind-velocity profiles were found to follow essentially 
the logarithmic law near but not too close to the water surface (Wu 
1968). The shear velocities, obtained at different wind velocities, 
are presented in figure 5. Lines shown in the same figure are the 
shear velocity for a laminar boundary layer. 
1 
1s O64.) 
uy= (F ey Ue (5) 
and for a turbulent boundary layer in the aerodynamically smooth 
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