Coastal engineers are investigating a regular train of surface waves produced by a test boat in a marina. Two marker posts can be positioned along the direction in which the wave crests travel. The engineers have a long measuring tape and a video camera that records both posts at a known frame rate.
At a rail maintenance depot, engineers are testing a straight section of steel rail before it is installed. The rail is securely supported. They have a vibration generator connected to a signal generator, a movable pickup connected to an oscilloscope, and a tape measure.
Explain how each investigation should be carried out so that the recorded quantities lead to a reliable value for wave speed. Your answer should justify the use of video at the marina and of electronic detection on the rail.