
350 Cable Survey System
DPN 402197 © TSS (International) Ltd Page 8 of 10
The System then uses this information, together with the measured altitude of the
ROV, to estimate the forward range:
It is important to note that this range is an estimate only. Factors that affect the accu-
racy of this estimate are:
❐ The flatness of the seabed topography.
The calculation assumes that the height of the coils relative to the target cable is
the same as the altitude measured by the altimeter. Errors caused by uneven sea-
bed topography are likely to be larger at greater forward ranges. The accuracy of
the estimate will degrade further with a target buried beneath the seabed.
❐ Operating the ROV with pitch.
Any angle of pitch will affect the forward search angle
φ
directly. The magnitude of
errors caused by angles of pitch increases rapidly with forward range.
A.4.3 Skew Measurement
The Run Display screen includes a graphical element that shows the angle of skew
between the ROV and the target cable (see sub-section 6.2.1.2 for further details of
this display feature). The System uses the lateral and the fore-aft coils on one side of
the array to measure skew.
Figure A–9 shows a survey ROV above the target cable. A small angle of skew exists
between the target and the ROV.
The 350 System measures the target co-ordinates as explained in sub-section A.4.1
above. These measurements retain the specified accuracy for that part of the target
directly between the two coil triads.
Figure A–9: Vehicle following target with skew angle
The example of Fig A–10 shows the target with a skew
angle
θ
and the output voltages from the lateral coil (v
x
)
and the fore-aft coil (v
y
) in the port coil triad.
Signal voltages supplied by the coil will be at a maximum
with the major axis of the coil perpendicular to the target.
A coil lying parallel to the course of the target will give a
very weak output. The peak amplitude of output voltage
will vary with the sine of the relative angle between the
major axis of the coil and the target cable.
Forward range
Altitude
φtan
-------------------≅
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