Acoustic Doppler Current Profiler

The today most important instrument for runoff and flow measurement is the ultrasonic Doppler profile flowmeter (English: Acoustic Doppler Current Profiler ( ADCP ) ), an active sonar, which for the Doppler frequency shift of the reverberation of scattering bodies in the water ( mainly plankton) uses to determine the local flow velocity. The device is equipped with three or four independent oscillators ( ' transducer '), the opposing each form pairs. Are each a transducer pair measures the horizontal movement in one direction, the vertical movement is measured by both in parallel. Add the device at fixed time intervals from the sound pulses in the range of 500 kHz -10 MHz. Between pulses, the backscattered signals are received again. These allow over their lifetime an assignment to the relative distance to the signal transmitter (transducer). The devices can measure the three-dimensional water velocity at various depth horizons depending on the type and configuration. Using the relationship:

Wherein the measured Doppler frequency shift from the device and the frequency of the transmitted signal, the relative velocity u may be calculated of the body of water. In autonomously operating devices, the measured velocities of the different layers are stored and can be read later. The devices can also be mounted in solder Eight of a ship. Then the relative velocity between water bodies and ship is measured. About an on-board device, the measurement results can be analyzed at any time. The seabed is in the range of the ADCP as it is possible about the relative speed of the bottom of the ship ( bottom track) to calculate the absolute water velocity of the individual layers below the ship.

In principle, the resolution of the measurement method is by reverberation uncertainty relation

Limited, the resolution of the flow rate, the distance resolution, the speed of sound and the center frequency of the transmitted signal is. Thus, the higher the frequency, the better the resolution achievable, the shorter due to the frequency dependent attenuation, the length of the airfoil. The resolution can be increased with the aid of large transmission signal bandwidth compared to the reverberation uncertainty relation (broadband ADCP, BB- ADCP ).

The German Federal Institute of Hydrology ( BfG ) in Koblenz has a evaluation software AGILA (named after the software developer Matthias Adler ) developed for the uniform evaluation of ADCP measurement data. The software is now largely established in German-speaking countries as the standard. In addition, there are also software solutions, which further exploit the vendor- specific data and provide additional evaluation parameters, such as suspended solids, turbidity, etc. are available.

If, in addition to the transducers for flow measurement, a further transducer vertically upwards ( in a subject on the seabed system ) directed so it is possible to measure parameters such as wave height and wave period in addition to the flow profile directly.

See also: Underwater Sound

Note on the use of the term ADCP

As mentioned above, the ADCP can be read as an abbreviation for Acoustic Doppler Current Profiler, and is also often used colloquially for vendor-independent flow profiler, but is also a trademark of RD Instruments.