These transducers operate in pairs; the transducer transmits a pulse that reflects on the metal plate on the bottom of the wind tunnel which is then 'catch' by the wind and carried to the to receiver.
When there is no wind, the pulse will move with the speed of sound from the transmitter to the receiver.
When the wind blows in a certain direction, the pulse will travel faster than the speed of sound. If the wind is blowing in the opposite direction of the vessel's course, the pulse will be received later than if there is no wind.
The four transducers take turns to transmitting and receiving the pulses. A microprocessor in the WS-200 sensor is thereby combining measurements from all four transducers to calculate the resultant wind speed and direction.
The arrows indicate the direction from transmitter to receiver. During this process, the sensor concurrently monitors and compensates the temperature, since temperature affects the speed of sound.