CUSTOMER :

Survey Operations

LBL Acoustic Work Instruction

GR-SRV-409Prepared by:N.R. ShillingSenior Surveyor

Approved by:PJ JansenChief Surveyor

1.0Issue for UseJan.16.02

Ver.Reason for IssueIssue DatePrepared byApproved by

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TABLE OF CONTENTS

31.Scope

2.Objective33.References34.Definitions35.Responsibilities36.Procedures56.1System Objectives56.2System Description56.3System Installation66.4Array Calibration76.5System Operation9

1. Scope

This Work Instruction covers the basic operation of Long Baseline Acoustic systems.

2. Objective

The objective of this work instruction is to enable suitably qualified personnel to calibrate and operate Long Baseline Acoustic systems.

3. References

GR-SRV-032

Sub-Surface Navigation Practice

GR-SRV-062

LBL Operations

GR-SRV-301

Surface Navigation Practice

GR-SRV-311

Single Beam Echosounder Practice

GR-SRV-322

Gyro Calibration and Verification Practice

Transponder Check Procedure Form

4. Definitions

CIF

Common Interrogation Frequency

COMPATT

Computing and Telemetering Transponder

CRF

Common Reply Frequency

CTD

Conductivity, Temperature and Depth

EHF

Extra High Frequency

GPS

Global Positioning System

HF

High Frequency

ICF

Individual Channel Frequency

IRF

Individual Reply Frequency

LBL

Long Baseline

LF

Low Frequency

LOP

Lines of Position

MF

Medium Frequency

PAN

Programmable Acoustic Navigator

RMS

Root Mean Squared

ROV

Remotely Operated Vehicle

SSBL

Super Short Baseline

UTM

Universal Transverse Mercator

5. Responsibilities

The Project Surveyor has the overall responsibility for the successful completion of the Survey Project including direct liaison with the Client.

The Party Chief/Senior Surveyor has the responsibility for the survey operations on board the ship, including communications with the Offshore Clients Representative and acting as an interface between Client and Office. He will report to the Project Surveyor on the status and progress of the offshore operation.

All survey and personnel are responsible for complying with this procedure.

6. Procedures

6.1 System Objectives

The LBL system is a high accuracy sub-surface positioning system using a network of calibrated intelligent transponders. The LBL system would typically be used for the following operations:

Positioning pipelines during initiation and laydown.

Positioning seabed structures during installation.

Spoolpiece acoustic metrology.

ROV positioning during as-built surveys of the initiation and laydown areas.

6.2 System Description

Long Baseline or Range-Range acoustic navigation provides accurate position fixing over a wide area by ranging from the survey vessel or ROV to transponders deployed at known positions on the seabed. This type of sub-sea positioning system provides accurate local control and high repeatability, and with the redundancy available from 3 or more LOPs it is possible to compute estimated error for a position fix.

The Sonardyne LBL System comprises: a surface interrogation and control unit, known as a Programmable Acoustic Navigator (PAN), a surface vessel or ROV mounted transducer and a series of Computing and Telemetering Transponders (Compatt). Sonardyne have adopted four standard frequency bands for acoustic positioning systems supplied to the offshore industry and are as follows:

BandBand WidthMax. RangeTypical Accuracy

Low Frequency (LF)7.5-15 kHz10-12 km2.5-5 m

Medium Frequency (MF)18-36 kHz2-3 km0.25-1 m

High Frequency (HF)30-64 kHz>1 km