Teledyne HydroPACT 350, User Manual

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5 – Operational Considerations
5-2 © Teledyne Limited DPN 402197 Issue 7.1
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The position of the altimeter
5.2.1.1 ROV position over the target
Figure 5-2 illustrates how errors in the measurement of depth of cover might occur when you survey a
target that is partially buried beneath an uneven seabed.
NOTE
Note that errors such as these arise from inaccuracies in measurements made by
the altimeter and
not to any errors in measuring the vertical range to target.
Figure 5-2: ROV positioning errors
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Flying with no lateral offset
Figure 5-2 (a) shows the best condition achievable when you use a single altimeter: The ROV
is level and is flying with the altimeter located directly over the target.
Under these conditions the depth of cover measurements are accurate.
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Flying with lateral offset
In Figure 5-2 (b), the lateral offset of the ROV has placed the altimeter to one side of the target
so that it measures its altitude above one of the trench walls. Consequently, the altimeter deliv-
ers information that will not allow accurate assessment of the depth of target cover.
It is therefore important to ensure that:
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You install the altimeter correctly according to the instructions in section 2.3.5 .
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You locate the altimeter near the centre of the coil array.
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You operate the ROV so that, as far as possible, the target remains positioned centrally
beneath the coil array.
It is important also to recognise that, under the above conditions, these errors affect only the depth of
cover measurements.
Summary:
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Install the altimeter correctly at the centre of the coil array.
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Pay careful attention to the relative position of the ROV over the target.