Theory of Operation10.1 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 InformationWorkhorse ADCP Multi-Directional Wave Gauge
The ADCP is used in the following applications:
Coastal Protection and Engineering
Port Design and Operation
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:
High definition of wave direction resolves waves arriving from several sources
Simple logistics of a single bottom-mounted deployment
Less risk of loss or damage
High quality surface measurements made from more secure seabed site
[Information taken from the RD Instruments world wide web site:
RD Instruments Home Page
Manufacturer of ADCP and other marine instruments that provide profiles of water currents.
The findings in this world wide web site are not to be construed as an official
Department of the Army position unless so designated by other authorized documents.
The contents of this world wide web site are not to be used for advertising
or promotional purposes. Citation of trade names does not constitute an official
endorsement or approval of the use of such commercial products.