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7 – Operating Procedure

DPN 402197 © TSS (International) Ltd Page 23 of 30

It is therefore important to ensure that:

❐ You install the altimeter correctly according to the instructions in sub-section 3.2.3.

❐ You locate the altimeter near the centre of the coil array.

❐ 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:

Install the altimeter correctly at the centre of the coil array.

Pay careful attention to the relative position of the ROV over the target.

Be aware of any errors that may arise from the local seabed topography.

For surveys where the depth-of-cover information is critical, consider using a scan-

ning profiler to survey the seabed on either side of the target. You may then merge

information from the profiler with measurements from the 350 System during the sur-

vey analysis operation.

The effects of roll, pitch and skew

In severe cases of roll such as shown in Figure 7–3, errors might appear in the verti-

cal range and lateral offset measurements on the target.

Figure 7–3: ROV roll errors

Figure 7–3(a) shows the ideal condition where the ROV is level over the target. In

these conditions, the measurements for VRT and LAT will be accurate and valid.

Figure 7–3(b) shows the same situation, but with 15° roll applied to the ROV. If left

uncorrected, under these conditions errors will exist in the measurements of both the

vertical range and the lateral offset.

For a target located centrally beneath the coil array as shown, the displayed value for

lateral offset will contain an error as follows:

Error = Z.sin (Roll angle)

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Banner DF-G1-PR-Q7 Instrucciones de operaciones Pagina 134