Measuring instruments and methods for water level 

Water level measuring instruments are acoustic. This means that the water level is measured by placing a sensor above the water surface, which sends an audio signal downwards. When the signal hits the water surface it is reflected and the sensor receives the return signal. The time difference between sending and receiving is calculated into a distance between the sensor and the sea level from the audio signal’s speed in the air.

The construction of water level measuring instruments
Water level measuring sensors are located inside a metal box, which is usually mounted on a harbour quay. The box also contains communication equipment, which ensures that the measured water levels are continuously transmitted to a central database.

Under the metal box, there is a plastic tube that stops below the water surface. The tube ensures that the audio signal from the sensor always has an unobstructed passage down to the water surface.