Teledyne 440, Системное руководство, Страница: 147 / 256

7 – Operational Considerations
DPN 402196 Issue 4.1 © Teledyne TSS 7- 3
Summary:
1. Install the altimeter correctly near the centre of the coil array.
2. Pay careful attention to the relative position of the ROV over the target.
3. Be aware of any errors that may arise from the local seabed topography.
4. For surveys where the depth-of-cover information is critical, consider using a scanning profiler
to survey the seabed on either side of the target. You may then merge information from the
profiler with measurements from the 440 System during the survey analysis operation.
7.2.1.2 Trim
In severe cases of roll such as shown in Figure 7-2 , errors might appear in the vertical range and
lateral offset measurements on the target.
Figure 7-2: ROV roll errors
Figure 7-2 (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 7-2 (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:
Where Z is the vertical distance between the coils and the target.
For example, measurements on a target located 1.0 metre below the centre of the coil array will
include a lateral offset error of 0.17 metres with 10° of roll applied to the ROV.
Measurements of VRT performed by the 440 System will remain relatively unaffected by small angles
of roll. Under the conditions described in the above example, the vertical measurement will contain an
error of only 15mm caused by the ROV attitude.
Summary :
1. Inaccuracies in vertical range measurements made by the System increase by no more than
3.5% for roll angles up to ±15°.
2. Where possible operate the ROV with an even trim throughout a survey
VR
T
(a)
With a level
coil array
VR
T
Horizontal
Range
Error
(b)
With applied roll
Error Z Roll angle
 
sin =