Fig. 6

Tip-tilt effect in underwater channel. a. Core A variation from an on-axis position measured over 20 s. b. Core B variation from an on-axis position measured over 20 s. c. Core C variation from an on-axis position measured over 20 s. 1-50 red circles represent the data collected before, and 51-100 blue circles represent the data collected later. Although the changes in each step are random, the whole looks like an ellipse and each vortex core always wanders within the ellipse, no matter the collected data is earlier or later