78 
  
  
0.35 
e 
Ww 
0.25 
0.15 
standard error [pixels] 
o 
No 
eo 
— 
  
0.05 
  
  
  
2 4 6 8 19 12 
  
  
  
displacement [pixels] 
Figure 5: Trajectories of particles attached to disc at 33 rpm (left).Standard error for the calculation of displacement 
vectors (right). j 
V; being the mean displacement, ||v;|| the i-th displacement in the trajectory and N the number of displace- 
ment vectors in the trajectory. Fig. 5 shows the standard error for displacement vectors up to 12 pixels per 
frame, calculated from more than 100000 vectors. The error always stays well below 3%. 
5 PARTICLE TRACKING BENEATH WATER WAVES 
  
+r 
HIP» 
  
[7 y 
fh 
ANS 
a AA 
È 
2, 
= 
el 
© 
o 
0.0 
RN 
40 YEAR WN 
  
  
  
-12.0 
  
+ + 4- » 
0.0 4.0 8.0 12.0 16.0 20.0 
  
  
depth [cm] 
depth [cm] 
o 
o 
: 
m 
o 
6i S X Y Aa 
Up OY b» 
; X SRY PRD 
-40 1 EL.) SP Ms XJ Po . 
  
  
-6.0 1 
  
-6.0 i$ 
  
  
  
  
  
: > - > 
0.0 2.5 5.0 75 10.0 125 0.0 2.5 5.0 7.5 10.0 128 
position [cm] position [cm] 
Figure 6: Trajectories of seeding particles beneath mechanically generated waves (top) and wind induced water 
waves (bottom). 
Fig. 6 shows three typical trajectories measured at circular wind/wave facility in Heidelberg and at the 
linear flumes in Delft and Scripps. Particle concentration in Heidelberg is about 800 particles/image, about 
250 particles/image in Delft and 600 particles/image in Scripps. The concentration in Delft is lower due 
to the more difficult visualization involved. In both cases 100 images were processed. For presentation 
only a fraction of the trajectories were plotted. Only trajectories tracked over 90 image frames(3s) were 
considered. Many particles can be tracked from the moment entering into the light sheet until leaving the