The surface of a liquid such as a glass of water looks quite flat to the naked eye. Yet it can reflect a very disturbed environment that causes minute ripples to form on the surface. A pecial optical system is used to detect these vibrations that cause light rays impinging on the undulating surface to be reflected at a different angle depending on the slope of the tilted surface contours. In this case essentially flat surfaces are reproduced as blue, surfaces tilted one way are red and those in the opposite direction are green. This information can then later be used to determine the topography of surfaces that appear very flat to the eye.