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Acoustic Doppler Current Profiler

Theory of Operation
10.1 Principles of ADCP Wave Measurement

The basic principle behind wave measurement is that the wave orbital velocities below the surface can be measured by the highly accurate ADCP. The ADCP is bottom mounted, upward facing and has a pressure sensor for measuring tide and mean water depth. Time series of velocities are accumulated and from these time series, velocity power spectra are calculated. To get a surface height spectrum the velocity spectrum is translated to surface displacement using linear wave kinematics. The depth of each bin measured and the total water depth are used to calculate this translation. To calculate directional spectra, phase information must be preserved. Each bin in each beam is considered an independent sensor in an array. The cross-spectrum is then calculated between each sensor and every other sensor in the array. The result is a cross-spectral matrix that contains phase information in the path between each sensor and every other sensor at each frequency band. The cross-spectrum at a particular frequency is linearly related to the directional spectrum at a particular frequency. By inverting this forward relation, we solve for the directional spectrum.

[ Taken from the Waves User's Guide, RD Instruments April 2001, page 65 ]

ADCP Additional Information
Workhorse ADCP Multi-Directional Wave Gauge

The ADCP is used in the following applications:

  1. Coastal Protection and Engineering
  2. Port Design and Operation
  3. Environmental Monitoring
  4. Shipping Safety
The ADCP is capable of measuring a complete frequency-direction wave spectrum and can operate in shallow and deep water. One advantage of the ADCP is that, unlike a directional wave buoy, the ADCP can operate with less risk of loss or damage. In addition to wave frequency-direction spectra, the ADCP is also capable of measuring velocity profiles and water level as well.

Benefits of the ADCP:

  1. High definition of wave direction resolves waves arriving from several sources
  2. Simple logistics of a single bottom-mounted deployment
  3. Less risk of loss or damage
  4. High quality surface measurements made from more secure seabed site

[Information taken from the RD Instruments world wide web site:]

Additional Links

• RD Instruments Home Page
  Manufacturer of ADCP and other marine instruments that provide profiles of water currents.

• Waves User's Guide

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