Internal Gravity Wave Observing the relationship between group velocity and phase velocity

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Water tank Material: Acrylic board Height: 59cm Width: 58cm Depth: 10cm   Working fluid Stratified salt water.   Visualization Moiré technique. The vertical striped patterns with 1mm and 1.1mm intervals were used. The two patterns were placed 30cm apart.   Experimental process The wave source was a row of four 2cm diameter rods attached together in a raft-like fashion dipped halfway into the fluid and oscillated horizontally.