The DVL is a device that measure the speed of water. It is largely used in underwater navigation. In the case of our AUV, the DVL is a device with a half-sphere-shaped placed at the bottom of the frame.
The DVL is using the Doppler effect in order to calculate the speed of the water around itself.
From Wikipedia: “The Doppler effect (or Doppler shift) is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague.”
The DVL sends an accoustic wave at a specific frequency. This wave is going to be reflected by the bodies that it will meet. In our case, this is generally a wall or the floor of the pool. The DVL will then receive the reflected wave and it will be able to observe a delta between the sent wave and the received one.
From this observation, we can have sort out the following statements:
- If F_r < f_o, the submarine is moving away from the body that reflected the wave.
- If F_r > F_o, the submarine is moving toward the body that reflected the wave.