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2 – System Overview

DPN 402197 © TSS (International) Ltd Page 13 of 14

2.4.3 Altimeter

The main function of the 350 System is to locate and survey a target laying on or bur-

ied beneath the seabed.

If the 350 System measures the altitude of its coil array above the seabed, then it can

also deliver a good estimation of the depth of target cover. A sub-sea altimeter can

supply such altitude measurements to the 350 System.

You should remember that an altimeter measures to a point on the seabed directly

beneath its transducer face. This single-point measurement may not be the same as

the local mean seabed level.

This means that uneven seabed topography might degrade the quality and accuracy of

depth of cover measurements derived using a single altimeter.

For surveys where you must measure an accurate and certifiable target burial depth,

you should use an independent seabed profiling system. Log the measurements from

such a system separately and then use the post-processing operation to merge them

with data acquired by the 350 System.

On some types of tracked ROV, you may arrange to keep the coil array of the 350

System at a fixed height above the seabed. In these circumstances, you could avoid

the need for an altimeter by configuring the SDC to use a fixed coil height.

The standard 350 System includes a sub-sea altimeter. You will need to install this

unit on the ROV frame close to the centre of the coil array. Refer to sub-section 3.2.3

for instructions to install the altimeter on the ROV, and sub-section 4.1.5 for instruc-

tions to connect it directly to the SEP.

Refer to Section 6.2.2.1 for instructions to configure the altimeter after installation.

2.4.3.1 Alternative Altimeter Types.

If you cannot connect the TSS or the Datasonics altimeter directly to the SEP for any

reason, the SDC can accept serial data from the alternative units listed in sub-section

4.1.5.

If you use an alternative type of altimeter, you must provide a separate power supply

to operate it. You must also connect its RS232 signals to an available SDC serial

communication port.

Because the RS232 signals from the altimeter are for use over distances of only

15 metres, you must use an existing multiplexed link between the ROV and the sur-

face vessel to carry your altimeter signals to the SDC.

Refer to sub-section 4.1.5.2 for instructions to connect an altimeter to the SDC.

Refer to Section 5 for instructions to configure the altimeter after installation.

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