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7 – Operational Considerations
7-2 © Teledyne TSS DPN 402196 Issue 4.1
❐ Electrical interference
7.2.1 ROV Handling
The following paragraphs describe the potential sources of error that might arise as a result of unskilled
or inappropriate operation of the ROV.
7.2.1.1 ROV Position over the Target
Figure 7-1 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 7-1: Altimeter errors during trench surveys
Flying with no lateral offset
Figure 7-1 (a) shows the best condition achievable when you use a single altimeter: The ROV is level
and is flying with the altimeter directly over the target.
Under these conditions the depth of cover measurements are accurate.
Flying with Lateral Offset
In Figure 7-1 (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 delivers information
that will not allow accurate assessment of the depth of target cover.
It is therefore important to ensure that:
❐
You install the altimeter correctly according to the instructions in section 3.1.4 "Altimeter" on
page 3-13 .
❐
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.
ALTIMETER
SEARCH-COILS
Altitude
Measurement
PIPELINE
VRT Measurement
(a) Correct Reading
ALTIMETER
SEARCH-COILS
Altitude
Measurement
PIPELINE
VRT Measurement
(b) Incorrect Burial Depth
due to Lateral Offset