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7 – Operating Procedure

DPN 402197 © TSS (International) Ltd Page 3 of 30

7.1.2 Tone Frequency

Your choice of tone frequency that you inject onto the target cable should take

account of several factors, including:

❐ Specific requirements of the survey planning team.

❐ The length of the target cable.

The distributed capacitance between the cable and sea water attenuates high

tone frequencies more rapidly than low tone frequencies. For this reason, surveys

on long cables might be easier to conduct if you select a frequency near the lower

end of the acceptable range. However, the 350 System is more sensitive to high

frequencies than low, and the System can therefore detect the cable at a greater

range when you select a high frequency tone.

❐ Noise in the survey area.

High levels of background noise will reduce the ability of the 350 System to calcu-

late the target co-ordinates accurately, particularly when the tone exists at a low

amplitude. Use the Scope and Spectrum Analyser window of DeepView to find a

relatively quiet part of the band and try to set a tone frequency within that region of

the band.

Refer to Appendix C.1 for further relevant details.

7.1.3 Survey Requirements

During the early stages, the survey planning team will need to define the type of data

required from the survey:

❐ The 350 System can complete a quick and simple check on the track and depth of

cover of a target by making a series of widely spaced measurements.

❐ Alternatively, to work to the highest achievable accuracy, you might need to stop

the ROV at carefully specified intervals to perform accurate measurements on the

target and to measure the mean seabed level with a separate profiling system.

The 350 System always delivers measurements of the highest achievable accuracy

under the given conditions. The compromise that you need to make between survey

accuracy and operating speed arises from the need to manoeuvre and measure the

position of the ROV with greater precision when you demand a sharper survey resolu-

tion.

7.1.4 Installation Requirements

Before starting a survey the survey planning team should define the installation

requirements of the 350 System. They should consider:

❐ The type of ROV to be used and where the SEP and the coils will be mounted.

The 350 System is suitable for use on most types of ROV, including towed sleds.

TSS can offer further advice if necessary.

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