To determine directional wave parameters, information about the orbital velocities is required. These velocities are measured by the slanted beams, and the cell in which they are measured is referred to as the Wave Velocity Cell. The definition of this cell differs between instrument types.
Aquadopp (Generation 1 and 2)
The orbital velocities are collected in a fixed cell throughout the deployment. The cell size is set during configuration. The measurement volume begins 0.5 m above the transducer head. The upper boundary of the cell is located at 0.5 m plus two times the cell size.
AWAC (Generation 1)
For first-generation AWACs, both the location and size of the wave velocity cell are adaptively defined for each wave burst. The mean and minimum pressure readings from the preceding current profile measurements indicate the location of the wave trough and the mean water level (Figure 1). The extent and location of the wave velocity cell are calculated using Equations 1 and 2.
| \(Cell\ size = max(0.12\times P_{min},0.15)\) | (1) |
\(V_{end} = (0.9\times P_{min}-0.5)\times \cos 25 {}^\circ \) | (2) |
The position of the cell is optimized to be as close to the free surface as possible without making contact to allow for strong orbital velocities readings. An acoustic test is performed on the quality of the signal in preceding current measurement data. In clear water with little scatterers, the cell is drawn in closer to the instrument where the SNR is better.
AWAC (Generation 2) and Signature
The Generation 2 AWAC and the Signature both collect a short velocity profile in the upper part of the water column. During post-processing, the user defines the wave velocity cell depth by selecting a percentage of the total water depth.
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