When we speak about “observing waves”, we usually mean looking at the water’s surface as an opaque surface that reflects the sky and where we see waves mainly due to being lit differently on different sides. But there are other ways to observe waves!
For example by how they focus light on the ground below. In the picture below you clearly see several groups of waves formed of smaller ripples.
Of course what we see when we look at the lighter and darker spots on the sea floor is not only an image of the waves above, but it is also influenced by the structure of the seafloor itself. You see that below: The ripples in the sand distort the image of the waves a little. Nevertheless, it isn’t too difficult to see which general shapes are due to the waves and which due to irregularities in the surface below.
Sometimes the lighting is such that you can see both into the water in some places and then see the sky reflected in others. The places that reflect the sky are showing waves the way we would usually observe them. In the picture below, we see wind ripples in the background, and in the foreground two main wave fields: one coming towards the viewer with crests parallel to the shore line on which I am standing, and a second field, whose crests are perpendicular to those of the first field.
But in the region where we can look into the water, only the second wave field shows up clearly in the lighter and darker regions on the sea floor!
Still, those regions give us a lot of information about the wave field that we don’t usually observe. For example all the small structures below don’t show up as clearly when we look at the sky-reflecting regions, do they?
I find it quite fascinating how all those structures that show up on the ground are a lot more difficult to observe when just looking at the sea surface.
Would you have guessed that there are so many tiny ripples on the surface?
And also here, the wave crests perpendicular to the shore I am standing on show up a lot more clearly in the light and dark on the sea floor than on the surface, don’t they?
Even easier to spot in a movie:
Beautiful day to be watching the water! :-)