Guidance on RADius Relative Positioning System

IMCA M 224 February 2013

International MarineContractors Association

www.imca-int.com

AB

AB

The International Marine Contractors Association (IMCA) is the international trade association representing offshore, marine and underwater engineering companies. IMCA promotes improvements in quality, health, safety, environmental and technical standards through the publication of information notes, codes of practice and by other appropriate means. Members are self-regulating through the adoption of IMCA guidelines as appropriate. They commit to act as responsible members by following relevant guidelines and being willing to be audited against compliance with them by their clients. There are two core activities that relate to all members: Competence & Training Safety, Environment & Legislation The Association is organised through four distinct divisions, each covering a specific area of members’ interests: Diving, Marine, Offshore Survey, Remote Systems & ROV. There are also five regional sections which facilitate work on issues affecting members in their local geographic area – Asia-Pacific, Central & North America, Europe & Africa, Middle East & India and South America.

IMCA M 224

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The information contained herein is given for guidance only and endeavours to reflect best industry practice. For the avoidance of doubt no legal liability shall

attach to any guidance and/or recommendation and/or statement herein contained.

© 2013 IMCA – International Marine Contractors Association

Guidance on RADius Relative Positioning System IMCA M 224 – February 2013

1 Introduction ........................................................................................................... 1

2 Preface .................................................................................................................... 2 2.1 Definitions, Abbreviations and Acronyms ....................................................................................................... 2

3 Overview ................................................................................................................. 4

4 System Components ............................................................................................. 5 4.1 Interrogator Unit .................................................................................................................................................... 5 4.2 Processing Unit ....................................................................................................................................................... 5 4.3 Transponders .......................................................................................................................................................... 6 4.4 Transponder Line ................................................................................................................................................... 7

5 Sensor Design ......................................................................................................... 8 5.1 Introduction ............................................................................................................................................................. 8 5.2 Design Principles..................................................................................................................................................... 9

6 Operation ............................................................................................................. 12 6.1 Applications........................................................................................................................................................... 12 6.2 Multiple Sensor Heads ....................................................................................................................................... 12 6.3 Multiple Transponders ....................................................................................................................................... 13 6.4 Operation Display ............................................................................................................................................... 13

7 Servicing and Maintenance ................................................................................. 15 7.1 General .................................................................................................................................................................. 15 7.2 Periodic Maintenance ......................................................................................................................................... 15 7.3 Repairs and Modifications ................................................................................................................................. 16

8 Applications .......................................................................................................... 17 8.1 Platform Supply .................................................................................................................................................... 17 8.2 Tandem Loading .................................................................................................................................................. 17 8.3 Pipe Laying and Cable Laying ............................................................................................................................ 18 8.4 Wind Farms Servicing......................................................................................................................................... 18 8.5 Accommodation Vessel Operations ............................................................................................................... 19 8.6 Multi-Purpose Vessel Operations ................................................................................................................... 19 8.7 Heavy Lift ............................................................................................................................................................... 20 8.8 Seismic Survey ...................................................................................................................................................... 20

9 Technical Specification ....................................................................................... 21

10 Operational Experience ...................................................................................... 23 10.1 System Advantages and Disadvantages .......................................................................................................... 23 10.2 Statoil Infrastructure ........................................................................................................................................... 23 10.3 Offshore Loading ................................................................................................................................................. 24 10.4 Test Sites ............................................................................................................................................................... 24 10.5 RADius Multipath Mitigation ............................................................................................................................ 24 10.6 Co-location with Other Equipment ............................................................................................................... 25 10.7 Other Operational Experience ........................................................................................................................ 26

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1 Introduction

This document is produced by IMCA as an aid to members and others using position reference systems and forms part of a series of documents on those systems. Similarly to some previous documents on position reference systems, it has been prepared in the major part by the manufacturer of the system, in this case Kongsberg Seatex, to whom the reader should refer for further information.

Reliable and robust methods of positioning are required for safe vessel operations at offshore installations, as has been stated in other guidance. The development of dynamic positioning (DP) systems has grown over the past 35 years and today various manufacturers’ systems are available.

The growth in the use of DP has been accompanied by the development of internationally recognised rules and standards against which DP vessels are designed, constructed and operated. These include International Maritime Organization Maritime Safety Committee (IMO MSC) Circular 645 – Guidelines for vessels with dynamic positioning systems – DP rules of the main classification societies and IMCA M 103 – Guidelines for the design and operation of dynamically positioned vessels – and guidelines for DP capable offshore supply vessels (OSVs) IMCA M 182 – International guidelines for the safe operation of dynamically positioned offshore supply vessels.

The growth and development of DP systems has stimulated the development of DP position measurement sensors which have become more sophisticated as technology has allowed. This document describes the RADius microwave radar system offered by Kongsberg Seatex, see www.km.kongsberg.com

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2 Preface

RADius, which utilises radar principles, has been developed for applications in need of a robust and reliable relative positioning system. Many applications can benefit from RADius in operations, as there are different types of retro reflective transponders and different types of installation of the sensor heads (interrogators). Furthermore the RADius system is a solid state system – there are no motors, stabilised platforms or other moving parts – so the maintenance cost is low.

RADius features:

♦ multiple sensor heads;

♦ measuring and output of range and bearing;

♦ wide opening angles secure close-by operations;

♦ no moving parts;

♦ multi-user feasibility;

♦ multiple transponder capability;

♦ operates in all weather conditions, also extreme cold;

♦ complementary to existing global navigation satellite systems (GNSS);

♦ designed to meet all International Maritime Organization (IMO) DP class requirements;

♦ both battery and fixed power operated transponders;

♦ operates in license free radio band;

♦ ATEX (Appareils destinés à être utilisés en Atmosphères Explosives) certified transponders;

♦ easy to deploy and adapt.

2.1 Definitions, Abbreviations and Acronyms

2.1.1 Definitions

Host system In this manual defined as navigation computers, dynamic positioning systems, etc., receiving data from RADius.

Interrogator The interrogator transmits signals and receives the reflected signals from the transponder(s). Based on this, it calculates the distance and bearing to one or more transponders. Mounted on the DP vessel.

Transponder The transponder reflects the signals transmitted from the interrogator. Mounted on the remote object/vessel.

Latency The time it takes from the actual measurement is made until the telegram is transmitted on the serial port.

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2.1.2 Abbreviations and Acronyms

Item Description

ARTEMIS FM/CW system. Operates at 9.2 GHz

ATEX Appareils destinés à être utilisés en Atmosphères Explosives

DARPS Differential and Absolute Reference Positioning System

DGNSS Differential Global Navigation Satellite System

DGPS Differential Global Positioning System

DP Dynamic Positioning

DPO Dynamic Positioning Operator

EIRP Equivalent Isotropically Radiated Power

FBEAM Fanbeam Telegram Format

FCC Federal Communications Commission

FM-CW Frequency Modulated Continuous Wave

FPGA Field Programmable Gate Array

FPSO Floating Production, Storage and Offloading vessel

GNSS Global Navigation Satellite System

GPS Global Positioning System

GUI Graphical User Interface

IEC International Electrotechnical Commission

IMO International Maritime Organization

IMO MSC International Maritime Organization Maritime Safety Committee

IU Interrogator Unit

LAN Local Area Network

OSV Offshore Supply Vessel

PSXRAD Kongsberg Seatex RADius proprietary format

PU Processing Unit

RF Radio Frequency

ROV Remotely Operated Vehicle

SIMOP Simultaneous Operation

TID Transponder Identity

VSAT Very Small Aperture Terminal

VDU Video Display Unit

WEEE Waste Electrical and Electronic Equipment

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3 Overview

RADius utilises radar principles in short range and direction monitoring and is mainly intended to be used in operations where increased safety is crucial. The system could typically be used to control or assist automatic dynamic positioning (DP) of a vessel. The RADius system is designed to operate in close proximity to structures and other vessels. The use of identifiable transponders minimises the risk of tracking false echoes.

The RADius system performance is complementary to DGNSS. RADius performs well as a relative positioning system on a vessel which is close to a large structure, and does not suffer from the shadowy effects which can reduce the positioning performance of DGNSS.

Figure 1 – System performance

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4 System Components

RADius consists of one or several interrogators – typically located on a moving vessel – and one or several transponders deployed on the target vessel/installation being approached. The RADius system measures the distance and bearing between the interrogators on the moving vessel and the transponders on the target vessel/installation. All deployed transponders at the target have unique identities, thus multiple transponders can be utilised for integrity and high availability.

Figure 2 – System components

4.1 Interrogator Unit

Several interrogators can be easily deployed at suitable locations on the outside of the vessel. Each contains antenna elements with horizontal and vertical opening angles of 90°, a receiver, a transmitter and a signal processing front end. The interrogator unit is interfaced to the processing unit via an ethernet connection. There are no moving parts within the interrogator.

Figure 3 – Interrogator unit

4.2 Processing Unit

The RADius workstation is a module rack containing a processing unit with RADius software, a graphical user interface (GUI) and serial interface lines to the DP or other users, for example. The processing unit is interfaced to the interrogator(s) via an ethernet connection.

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4.3 Transponders

Transponders are deployed on a target vessel/installation that is to be approached by a vessel fitted with interrogator(s). The opening angle from the transponders is 90° vertically and horizontally. Transponders are either battery operated (with a battery life of over one year of operation) or connected to a power source. ATEX certified transponders (intrinsically safe) are also available.

Several transponder types are available.

Figure 4 – Transponder models

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4.4 Transponder Line

Figure 5 – RADius transponder line

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5 Sensor Design

5.1 Introduction

RADius represents a completely new way of utilising radar principles in short range and direction monitoring and is mainly meant to be used in operations where increased safety is crucial. The system could typically be used to control or assist automatic dynamic positioning (DP) of a vessel.

The RADius system is designed to operate close to structures and other vessels as the use of identifiable transponders minimises the risk of tracking false echoes.

Figure 6 – Illustration of position accuracy as a function of distance

As shown in Figure 6, DGPS and RADius have complementary characteristics when closing in on large structures. As a vessel approaches a large structure, a DGPS system can suffer from a limited view of the sky, resulting in degraded GPS availability. This can be crucial when the GPS constellation is at its minimum and the most important satellite disappears behind the structure. The RADius system performance increases as it moves closer to the transponders located on the structure.

Figure 7 – Typical scenario where a vessel operates close to a high structure

DGPS

RADius

Distance

Accuracy

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Innovative Technology

The RADius system is fully solid state and based on measuring reflected signals from a number of transponders that represent targets in the nearby area. Each reflected signal is mixed with a unique ID in order to separate different transponders, with advanced signal processing allowing simultaneous and continuous measurements from up to five transponders. RADius is designed to enable multiple vessels filled with interrogators to use the same transponders simultaneously.

Advanced Principles

One or more interrogator units are located on the manoeuvring vessel and one or more transponders are attached to different points of the target object. Signal processing removes possible interference with other transmitting devices in the same frequency band and application software makes configuration and monitoring of the RADius operation easy and effective. Interfaces to remote systems are provided through serial or ethernet lines.

RADius is designed to be a position reference system that contributes to meeting the position reference system requirements for all DP classes as specified in IMO MSC Circular 645.

Operational Features

RADius is capable of detecting and measuring the distance to transponders at a range of up to 1000 metres. Typical DP range with stable range and bearing will be up to 550 metres. The angle between the interrogator and each transponder is determined by the use of interferometric methods. RADius is delivered with an easy-to-use graphical user interface.

5.2 Design Principles

RADius is a high precision position reference and tracking system based on radar principles and the system may include a number of interrogators and transponders. Interrogators read the individual distance and direction to a number of transponders by using microwaves.

The interrogator includes a transmitter unit, a receiver unit and a pre-processor unit, and communicates with the processing unit through an ethernet link.

Each transponder includes antennas, a side band oscillator and a voltage source. The transponder generates sub-carriers at individual frequencies for identification. The RADius 550 and RADius 700 transponders are battery powered, with the RADius 600 transponder permanently connected to 6VDC through an AC/DC converter.

5.2.1 Distance and Bearing Determination

Figure 8 – Relative distance and bearing

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The RADius interrogator measures distance and bearing to the transponder – operating on one or any number up to five simultaneously. The ability to track several transponders simultaneously increases the integrity capability and the robustness of the system.

Figure 9 – RADius principle range determination

RADius measures range based on the FM-CW principle, sweeping the frequency transmitted and mixing the transmitted signal with the received signal. The transmitted signal changes frequency during the flight time of the received signal and the difference between the transmitted and received frequency is measured. The frequency difference is proportional to twice the distance to the transponder.

𝐷 = Doppler frequency shift or fd 𝐿 = wavelength at operating frequency or lamda

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =12∙ 𝐷 ∙ 𝐿 =

12∙ 𝑓𝑑 𝑥 𝜆

𝑓𝑏 = frequency difference between transmitted and received signal-beat frequency 𝑓𝑠 = sweep frequency deviation 𝑇𝑠 = sweep time (up or down) 𝑐 = speed of light

𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =12∙𝑓𝑏𝑓𝑠∙ 𝑇𝑠 ∙ 𝑐

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Figure 10 – RADius principle bearing determination

The RADius characteristics are determined from the measuring principles, leading to different performance at different ranges, with accuracy being best at close range. For the RADius 600 and 700 transponders, optimal accuracy is acquired at 10-200 metres. At 200-500 metres, the distance and bearing accuracy are degraded due to the nature of angle measurements. Beyond 500 metres, the system acquires the transponders but often only with range measurements.

𝜙𝑑 = 𝑠 ∗ (2𝜋/𝜆) = 𝑑 ∗ sin(𝑎) ∗ (2𝜋/𝜆)

𝑎 = arcsin 𝜙𝑑𝜆2𝑑𝜋

𝜙𝑑 = phase difference between signal at antenna 1 and antenna 2 𝑑 = distance between antennas

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6 Operation

The implementation is fully solid state and based on measuring reflected radar signals from a number of passive transponders nearby. Each reflected signal is mixed with a unique ID to separate different targets, with signal processing allowing simultaneous and continuous measurements to any practical number of transponders. RADius is designed for multiple users simultaneously leveraging the same transponders and is capable of detecting and measuring accurate range and bearing within a range of up to 500 metres (depending on the target transponder). The direction from the interrogator to each transponder is accurately determined by the use of interferometric methods, and – due to use of open standards – deployment of the operator interface is very flexible.

6.1 Applications

Many different applications can benefit from the robust and easily deployable RADius system. DP-capable vessels are often required to have redundancy in their positioning reference systems when performing different types of operations. Due to its wide opening angles, RADius contributes to secure close proximity operations in all weather conditions.

Typical applications:

♦ platform supply;

♦ tandem loading;

♦ wind farm servicing;

♦ accommodation vessel operation;

♦ multi-purpose vessel operations;

♦ heavy lift activities;

♦ pipe laying and cable laying;

♦ seismic survey.

6.2 Multiple Sensor Heads

RADius can be deployed as an omnidirectional system utilising four sensor heads, which can be placed at suitable locations on the vessel, depending on the construction and operation. This provides full 360° signal acquisition and avoids blind angles as there will be a sensor head at a receiving angle to the transponders at all times, regardless of the vessel’s relative position to the RADius transponder. Due to the light weight of both the transponders and the interrogator, deployment of the system is easy. The robustness of the system allows the interrogators to be mounted independently of each other, avoiding dead angles and to obtaining up to 360° coverage.

Figure 11 – Multiple sensor heads

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Signal processing effectively removes possible interference with other transmitting devices in the same frequency band. Accurate Doppler measurements allow for rapid and reliable determination of relative velocities between the manoeuvring vessel and transponders.

Application software makes configuration and monitoring of the RADius operation easy, and interfaces to remote systems such as dynamic position can be serial line or ethernet-based.

6.3 Multiple Transponders

The RADius system can acquire data from up to five transponders with each interrogator. These transponders can also be used simultaneously by other vessels or interrogators.

Figure 12 – Multiple transponders

6.4 Operation Display

6.4.1 Overview

Figure 13 – RADius single interrogator GUI

The RADius main window consists of three different parts:

polar plot – located on the left-hand side of the screen and shows the location of transponders and the operating sector of the interrogator;

buttons and drop-down menus – located in the upper part of the screen;

list of targets – located on the right-hand side of the screen.

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6.4.2 Multi-interrogator GUI

Figure 14 – RADius multi-interrogator GUI

When more than one interrogator is connected to the system, the multi-interrogator GUI is useful as it shows a polar plot for up to four interrogators. The single interrogator GUI is default at start-up, but clicking the Min button or double-clicking in the polar plot enters the multi-interrogator GUI. Clicking the Max button or double-clicking in the polar plot returns to the single-interrogator GUI.

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7 Servicing and Maintenance

7.1 General

RADius consists of both software and hardware parts. The software can be reinstalled or upgraded to the latest version in the field by loading it onto the processing unit. Service of the RADius hardware in the field can consist of:

♦ replacing damaged cables;

♦ replacing interrogator unit;

♦ replacing transponders;

♦ replacing processing unit;

♦ checking the fuse within the power connector on the processing unit;

♦ checking the fuse within the power connector on the power/connection shelf;

♦ checking the fuse on the output of the 48VDC power supply located beside output terminals.

The processing unit, interrogator unit or the transponders are not designed for service in the field and opening the housing results in damage or degradation of the units and voids the warranty. Failed units have to be shipped back to Kongsberg Seatex for service.

During the time a failed unit is in for service, a spare component can be rented from Kongsberg Seatex AS if needed.

7.2 Periodic Maintenance

The periodic maintenance of the RADius 1000 can be divided into five categories:

♦ software upgrade;

♦ cleaning of air inlet;

♦ inspection of cables and connectors (for possible damage);

♦ cleaning of IU cover;

♦ replacement of the RADius transponder battery.

Caution! Units with damaged plastic covers must be replaced immediately.

7.2.1 Software Upgrades

Kongsberg Seatex AS will regularly offer software upgrades with improvements and new functionalities for the RADius interrogator unit. The user should decide whether to upgrade the unit to the latest version.

7.2.2 Cleaning of Air Inlet

The air inlet at the rear of the processing unit needs to be cleaned or replaced regularly (at least twice a year) to avoid overheating of the unit. Remove the plastic cover (circled below) and clean or replace the filter.

Figure 15 – Air inlet filter

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7.2.3 Inspection of Cables and Connectors

The cables and connectors must be periodically inspected for possible damage. If the connectors are damaged, the connectors and cables must be replaced and the IU should be sent to Kongsberg Seatex AS for inspection and servicing. Alternatively, service personnel can be sent to inspect the RADius system on-site.

7.2.4 Cleaning of IU and Transponder Covers

Keeping the IU and transponder plastic cover clean is important to maintain a fully operational and accurate system. Use a moist cloth to clean the covers.

7.2.5 Replacing the RADius Transponder Battery

The battery on the RADius transponder should be replaced according to specification. Instructions for replacing the battery are found in the RADius 1000 Installation Manual.

7.3 Repairs and Modifications

Repair of the RADius consists of the replacement of damaged cables and the replacement of the processing unit, the interrogator unit or the transponders.

7.3.1 Repair of the RADius Processing Unit

The processing unit is not designed for service in the field. All repairs and modifications of the unit – except for installation of new software versions and setup of the system – have to be carried out by Kongsberg Seatex AS. A failed processing unit should be shipped back to Kongsberg Seatex AS for repair.

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8 Applications

8.1 Platform Supply

Platform supply is the most common application for a RADius system – an operation close to large structures where the GNSS performance may become degraded.

Figure 16 – Platform supply

8.2 Tandem Loading

Tandem loading, where a shuttle tanker approaches and connects to a floating production storage and offloading vessel (FPSO), is an operation carried out in the North Sea and outside Canada in close integration with the differential absolute and relative positioning sensor (DARPS) system. If the transponders are separated sideways and the offsets are known in the DP, the data received from the RADius system can be used as heading input for the relative orientation between the two vessels.

Figure 17 – Tandem loading

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8.3 Pipe Laying and Cable Laying

Pipe laying operations can often be a challenging task when DP operations are carried out in a follow-target scenario. Due to the relatively small separation between the pipe layer and the PSV supplying the pipe, the tuning of the DP relies heavily upon the system providing the relative position between the vessels.

Figure 18 – PSV alongside cable layer

8.4 Wind Farm Servicing

Wind farms need periodic maintenance and the need for an infrastructure of relative positioning systems, such as RADius, is currently being discussed. Preliminary testing shows that the challenge of multiple targets in a small area is feasible.

Figure 19 – Wind farms servicing

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8.5 Accommodation Vessel Operations

Accommodation vessel operations are typically connected with heavy maintenance operations on installations for a shorter period of time. The vessel will typically approach an installation to allow workers to embark/disembark by use of a gangway.

Figure 20 – Accommodation vessel

8.6 Multi-Purpose Vessel Operations

Multi-purpose vessel operation is a wide-ranging description. It could be well intervention combined with a remotely operated vehicle (ROV) operation or simultaneous operations (SIMOPs) with several vessels operating within close vicinity in a field.

Figure 21 – Multi-purpose vessel

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8.7 Heavy Lift

Heavy lift is operations close to a platform with low dynamics. Typical challenges can be shadowing from cranes or structures.

Figure 22 – Heavy lift

8.8 Seismic Survey

The RADius 610 S was developed for the positioning of seismic source arrays. RADius 610 S uses housing and connectors equal to the Seatrack 320 RGPS pod. Some seismic clients have required a secondary source for positioning of the survey equipment.

Figure 23 – Seismic survey

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9 Technical Specification

♦ Measurements

DP range up to 550 m (dependent on transponder type)

Range accuracy * 0.25 m (1 σ)

Angle accuracy * 0.25° (1 σ)

Update frequency rate 5 Hz

Latency < 0.5 sec

♦ Opening Angle

Vertical ± 45°

Horizontal ± 45°

♦ Operational

Frequency band 5.51to 5.61 Ghz

♦ Environmental

RADius 1000 Processing Unit

Enclosure material

Enclosure protection IP-30

Operating temperature range -15 to +55ºC/5 to 131 F

Operating humidity 20 to 80% relative

Storage temperature range -20 to +60ºC/-4 to 140 F

Storage humidity Less than 55%

Vibration test according to IEC/EN 60945

RADius 1000 Interrogator Unit

Enclosure material Anodised aluminium – rear

Enclosure material Plastic – front cover

Enclosure protection IP-66

Operating temperature range -30 to +55ºC/-22 to 131 F

Operating humidity (maximum) 100%

Storage temperature range -25 to +70ºC/-13 to 158 F

Storage humidity (maximum) 60%

Vibration testing according to EN 60945

♦ Physical Dimensions

Interrogator

Height x Width x Depth 412 x 562 x 184 mm

Weight 7.0 kg

Protection IP 66

RADius Workstation

Height x Width x Depth 300 x 500 x 150 mm

Weight 15 kg

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♦ Power

Interrogator

Input voltage 110/220 V AC

Power consumption 160 W

RADius Transponders See dedicated datasheets

ATEX certified Transponders See dedicated datasheets

♦ Interfaces

6 x RS422/232 (isolated) Proprietary NMEA 0183

Ethernet TCP/IP

Output formats: PSXRAD (multiple targets)

Fanbeam MDL

Artemis

* All accuracy specifications are based on real-life tests conducted in the North Sea under various conditions. Operation on other locations under different conditions may produce different results.

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10 Operational Experience

10.1 System Advantages and Disadvantages

Some advantages of this system identified by vessel owners and operators are:

♦ no false returns due to reflective tape attached to clothing, survival craft and other places;

♦ unlike DGNSS signals are not masked by the installation when working close in;

♦ minimal effect of weather and visibility on the system;

♦ simple installation on installation, battery powered thus requiring no external power;

♦ simple for DP operators (DPOs) and others to use.

Some disadvantages are:

♦ not useful at greater ranges;

♦ similar to other radar based systems it requires line of sight operation;

♦ limited working sector of 90°for interrogator unit antenna;

♦ battery operation of transponder.

10.2 Infrastructure

Kongsberg has been working to establish an infrastructure of RADius transponders that will enhance the safety of DP operations. This work is ongoing with installations either instrumented or in the engineering phase.

A typical installation will have a crane location in north/south or east/west configuration. Each crane location will typically be covered with three 600X transponders to ensure redundant coverage of two transponders, independent of the vessel’s orientation. A typical PS configuration will either be a single or dual interrogator configuration.

Figure 24 – Typical transponder configuration north/south

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10.3 Offshore Loading

Testing of tandem loading started late in 2004 at a testing site at Aasgaard C. The standard configuration has been one Artemis system combined with two DARPS systems. In conjunction with changes in the DP2 class specifications, which demand three independent systems based on separate technologies, the test programme was started.

Initial challenges were shadowing from funnels, establishment of transponder offset for use in the DP SW and range performance. The range performance was revealed to be a classic phenomenon, often known as blanking in the navigation community. In operations that require longer operational ranges, the transponders/interrogators should be installed high above sea level, typically 20 metres. The height requirement is not as important in operations that require shorter range capability.

Figure 25 – ESD boundary testing at Aasgaard C

10.4 Test Sites

In order to give vessels with RADius systems the possibility of training and field tests, Kongsberg can provide test transponders for deployment in regularly visited areas, such as ports and yards. Those interested in transponder installation, or finding locations with existing transponders, should contact Kongsberg Customer Support.

10.5 RADius Multipath Mitigation

Multipath – reflection of the signal on the sea – is a challenge for both radio and laser-based systems. In this context, multipath is normally worse on a calm surface. Blanking, as it often is referred to in navigational literature, occurs when the directed signal is cancelled out by the reflected signal, causing the remaining signal to be too weak to be registered by the sensor.

Operational experience has shown that the normal heave on a vessel eliminates this effect, as the blanking effect is strongly correlated with the height difference between the interrogator and transponder.

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Blanking effects follow physical laws and therefore can be avoided or reduced. In RADius operations the blanking effect is normally connected to the signal transmitted from the transponder to the interrogator, as the energy reflected from the transponder is much weaker than the transmitted signal from the interrogator.

10.5.1 Grouping of Transponders

The effect of grouping transponders can be seen in the illustrations below. The RADius can group up to three transponders.

Figure 26 – Simulated response with or without grouping

The black thick curve is the resulting SNR from the combined transponders. The red curve is the lowermost transponder.

The effect of blanking is a result of the height of the transponder and interrogator. If both the interrogator and the transponder are more than 20 metres above the sea level, the effects are significantly reduced.

10.6 Co-location with Other Equipment

10.6.1 Harmonic Emission

The second harmonic emitted from RADius is sweeping the frequency band 11.02-11.22 GHz at 5 Hz rate.

In some situations (depending on the heading of the ship, satellite antenna elevation, obstacles in front of RADius causing reflections) the second harmonic emission might have sufficient energy to cause problems for very small aperture terminal (VSAT) systems on the same vessel operating in the 11.02-11.22 GHz area. This has been observed on a few occasions on previous RADius versions and was solved by either changing the VSAT frequency or changing the location of the RADius/VSAT antennas.

10.6.2 Regulations

The United States Federal Communications Commission (FCC) sets maritime radio bands (47CFR 80.211): Requirements for users in the maritime radio navigation/determination band (5.47– 5.65 GHz): Spurious emission attenuation >43 + 10 log10 (Pmean-in-Watt) = 43 dBc. This corresponds to a maximum permissible RADius harmonic emission of -13 dBm.

Both current and previous versions of the RADius system comply with this requirement and we have an FCC Grant of Equipment Authorization. The RADius FCC identifier is: Q8IKSXRADIUS.

28 30 32 34 36 38 40 42 -

-

-

-

-

-

-

-

- Received power vs. distance

Distance between Interrogator/Transponder [m]

Rec

eive

d po

wer

at t

rans

pond

er [d

B]

280 300 320 340 360 380 400 420-80

-75

-70

-65

-60

-55

-50

-45

-40Received power vs. distance

Rece

ived

pow

er a

t tra

nspo

nder

[dB]

Distance between Interrogator/Transponder [m]

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10.6.3 Possible Solutions

Known interference issues have been solved by either changing the VSAT frequency or the location of the RADius/VSAT antennas.

10.6.4 High Power Transponder

An alternative to grouping is to use a transponder with a higher gain – a brute force approach where, after the blanking effect, the signal is still strong enough to be used by the sensor. Use of a high power transponder can be an advantage for applications where the number of transponders is relatively few and a longer operational range is required.

There will always be a trade off in how much energy should be allowed for each transponder and the number of transponders installed in the operational area.

10.6.5 Height Diversity

When installing several transponders close to each other height diversity should be used. Using a height separation of 750mm-1000mm will often improve the operational availability of the transponders.

10.7 Other Operational Experience

Since its introduction, the system seems to have been well received by vessel owners, operators and charterers as a useful reference system complementing the widespread use of DGNSS. The growth in variety of transponders and increased operational range has also improved user experience with this system.