Comprehensive Manual30
© 2018 Nortek AS
the magnetometer (compass). By using XYZ coordinates, the data will not be transformed to ENU
coordinates, and are thus not in the risk of being incorrectly transformed.
The whole deployment system might move into a different measurement site if care is not taken.
The shifting tide combined with a slack mooring line might result in a shift in deployment location.
It is important to consider stretching of the mooring components under tension, especially the
mooring line, in order to know the exact horizontal and vertical position of the instrument.
The deployment depth should not exceed the depth limitations of the instrument’s pressure
sensor. The absolute maximum pressure the sensor can handle is a pressure twice its range. For
example, the standard 50 m pressure sensor can safely withstand 100 m depth, but it will not
record meaningful data beyond 50 m. It has only been calibrated to 50 m. Beyond 100 m it will be
damaged.
Special consideration must be taken when using a Vector with a cable probe (opposed to the fixed
stem type). For the cable probe, it is critical that during data collection in ENU coordinates, the “X”
receiver arm (marked with red) is aligned with the “X” mark on the Vector housing. This is because
the compass and tilt sensor is located in the Vector housing. The internal tilt sensor determines
up or down, and ultimately ensures that the correct coordinate system is used for the directional
estimates. If you collect data in beam or XYZ coordinates, you can mount the probe in whatever
direction you want.
Boundaries are not a concern in mid waters, but if you want to use the instrument near the bottom
or surface, you should consider the effects of boundaries as you design your experiment. Use the
Distance Check functionality for useful input.
If the batteries need to be replaced or re-changed or the data need to be downloaded on a regular
basis, the deployment should facilitate easy recovery and redeployment.
2.1.7 Orientation of Vector probes
The Vector XYZ coordinates are different depending on the orientation of the tilt sensor and if it is
cabled or fixed stem probe. The tilt sensor and compass are both located in the housing. The SNR,
amplitude and correlation data you have gathered are not dependent on attitude, they are always
collected with reference to beam coordinates. In the image below you can see the XYZ coordinates
relative to the probe head.
Figure: XYZ coordinates relative to probe head
The orientation of the tilt sensor is easy to find out by doing simply bench test and rotating the
instrument to see when pitch and roll approaches zero.
To Next Page
Loading...
