Measuring floodwater in ND

The USGS uses an Acoustic Doppler Current Profiler (ADCP) to measure flooding in Fargo, North Dakota. The ADCP measures water currents with sound, using a principle of sound waves called the Doppler effect. The ADCP works by transmitting "pings" of sound at a constant frequency into the water. As the sound waves travel, they ricochet off particles suspended in the moving water, and reflect back to the instrument.