Internal Gravity Wave

The size of the water tank

In order to observe the transmission of a group of waves, you need a water tank at least a few times larger than the wave group, and the wave group must also be a few waves in length. The final condition that defined the size of the tank was that it must not be so large that the waves die out before making it across the tank.

 

Camera aperture

When using the Moiré technique, which utilizes two grids, if the camera aperture is set too wide, you can't see Moiré stripes. On the other hand, if you close the aperture and get under exposure, you can place a panel with a slit parallel to the stripes of the grids in front of the camera to fix the situation. However, you will then have to open the aperture considerably to avoid a narrow view.

 

A non-reflective wall

In the narrow environment of a water tank, waves reflecting off the walls can get in the way. You can effectively prevent reflection of the waves by bending a plastic sheet in a snake-like wave and fitting it to the inside walls of the tank.