The collection of water current data is very important as this information plays a key role in various fields such as scientific research, natural resource management, and navigation safety. Current data provides critical insights into the dynamics of water movement, which helps in predicting climate change, understanding fish migration patterns, and managing marine and river ecosystems. In addition, current data is also vital for planning and building maritime infrastructure such as harbours and bridges, as well as for offshore drilling operations and renewable energy development such as wave power generation. In the context of navigation, accurate current information ensures vessel safety, prevents maritime accidents and improves the efficiency of shipping routes. With the increasing threat of climate change and intensified human activities in water areas, accurate and detailed current data collection is becoming increasingly essential to support sustainable decision-making and environmental risk mitigation.
An Acoustic Doppler Current Profiler (ADCP), or Acoustic Doppler Profiler, often referred to as ADCP, is an instrument that scientists use to measure the speed of water moving across the entire water column. An ADCP moored to the seafloor can measure the speed of currents from the seafloor to the surface at equal intervals. They can also be mounted horizontally on seawalls or bridge piers in rivers and canals to measure current profiles from shore to shore, as well as on the bottom of ships to take constant measurements of currents as the ship moves. In very deep areas, the ADCP can be lowered by cable from the surface. ADCPs are used to measure water velocity and direction throughout the water column, with frequency determining maximum range in Current Profiling and Bottom Tracking. All ADCPs have Current Profiling functions to measure water speed and direction, as well as Bottom Track to measure vessel speed and direction, provide water depth, and are used for underwater navigation, which is necessary to accurately measure water speed.
How ADCP Work
ADCPs measure water currents using sound according to the principle of sound waves, called the Doppler effect. Sound waves have a higher frequency or pitch when propagating towards you than when propagating away from you. You can hear the Doppler effect when a car is traveling at high speed, with the distinctive sound disappearing when the car passes.
ADCPs work by sending a “ping” sound into the water at a constant frequency (pings are so high that humans and even dolphins cannot hear them). As the sound waves propagate, they bounce off particles in the moving water and return to the device. Due to the Doppler effect, sound waves that bounce off particles moving away from the profiler have a slightly lower frequency when they return. Particles moving towards the device will reflect back waves with a higher frequency. The frequency difference between the wave sent by the profiler and the received wave is called the Doppler shift. The instrument uses this shift to calculate the velocity of the particles and the surrounding water.
Sound waves that hit particles far from the profiler will return farther than waves that hit nearby particles. By measuring the time it takes for the wave to bounce back and the Doppler shift, the profiler can measure the speed of the wave.
ADCP Advantages and Disadvantages
Advantages:
- In the past, measuring current depth profiles required the use of long current measuring cables. This is no longer necessary.
- Small-scale current measurement
- Unlike previous technologies, the ADCP measures the absolute velocity of water, not just how fast one body of water moves relative to another.
- It measures water column lengths up to 1000 m.
Disadvantages:
- High-frequency soundings provide more accurate data, while low-frequency soundings reach deeper into the water. Scientists therefore have to make a trade-off between the distance that can be measured with a profiler and the accuracy of the measurement.
- Also, ADCPs tuned for fast pings drain the battery quickly.
- If the water is very clear, for example in the tropics, pings may be inactive.
- Hit enough particles to get reliable data
Bubbles in stormy water or flocks of floating sea creatures can lead to incorrect current calculations. - Users should take precautions to avoid getting shells and algae on the transducers.
