An acoustic Doppler current profiler uses acoustics (sound waves) to measure the velocity of the water around it.
Why we collect this data
The ADCP gives us insight into how the water moves. It can also provide some information on the amount of particles in the water.
How it works
An ADCP works like a radar gun that law enforcement use to measure the speed of moving vehicles. This piece of equipment uses sound waves and the Doppler effect to calculate how fast particles in the water are moving.
More specifically, the ADCP sends out sound waves at a constant frequency. These sound waves bounce off the particles in the water and reflect back to the ADCP at different frequencies than was sent out. If the particles are moving away from the source of the sound (the ADCP), the sound wave that they send back is at a lower frequency. Conversely, if it is moving towards the source, it bounces back at a higher frequency. The ADCP uses the changes in frequency to calculate the velocity.
Image credit: http://www.teledynemarine.com/workhorse-monitor-adcp?ProductLineID=12