Geoscience Reference
In-Depth Information
Fig. 7 Scheme of LSPIV system
concept is similar to conventional PIV, seeding and illumination are considerably
different.
Sometime particles naturally present on free surface can be used as a tracer, but
often they are not well distributed, so additional seeding particles need to be added
to increase the efficiency of resolving velocity on the entire image. Given the large
scale of flow and the necessity of measuring surface velocities, the tracer character-
istics are quite different in respect to standard PIV and its choice is a very important
aspect. First of all, seeding particles have to be lighter than water density; they have
to be big enough, comparing with the pixel size, that in large-scale investigation is
much larger than in standard PIV, considering the distance from the camera and the
image plane; finally, they have to travel on the free surface with the flow velocity.
Foams and straw (or other plant residues) are the two kinds of seedings usually
