300
Mid-plane interface Mid-plane interface
350- 200u)400 u),- -400-
450 >-600
500- ~Side-walledge - 80
5501 10000 200 400 600 800 1000 200 400 600 800 1000
X pixels X pixels
Figure 4-3 A sample edge image and the corresponding interface image as a result of pruning.
The interface images of a whole sequence of 200 are then averaged, thereby obtaining an average interface for a particular tunnel condition. Also, the standard deviation value of the fluctuations of the interface location is calculated as
1001000 ,2
0~j(K0K) Z~j&K
1000l000 (4.1)
jl )
where I is the a column vector of Y pixel values at]*' X pixel, K =[1, 2,.,1016], & denotes element by element multiplication and L ] denotes rounding off to the nearest integer value. The advantage of computing the standard deviation value is two fold. First, it gives a measure of the fluctuations of the air-water interface. Second, it is essential to identify outlier points. An average interface image and the corresponding standard deviations (from mean at an average interface image pixel coordinate) are shown in Figure 4-4.