iala reccomendation

8/12/2019 IALA Reccomendation

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AISMAssociationof

InternationaledeSignalisation

Maritime

IALA

InternationalAssociationofM

arineAidsto

NavigationandLighthouseAu

thorities

IALA Recommendation V-128

On

Operational and TechnicalPerformance Requirements for

VTS Equipment

Edition 2.0

June 2005

Edition 1.0 June 2004

Edition 1.1 June 2005

20ter, rue Schnapper, 78100Saint Germain en Laye, France

Telephone +33 1 34 51 70 01 Fax +33 1 34 51 82 05E-mail - [email protected] Internet - www.iala-aism.org


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IALA Recommendation V-128 Operational and Technical Performance Requirements forVTS Equipment Ed. 2.0 Dec 2005 (Ed 1 June 2004)

Page 2 of 84

Document RevisionsRevisions to the IALA Document are to be noted in the table prior to the issue of a

revised document.

Date Page / Section Revised Requirement for Revision

May 2005 Addition of Annex 6

Hydrological and

Meteorological equipment

Annexes added as they are completed to

ensure all aspects of VTS equipment are

covered.

Restructured to include

operational performance

requirements. Annex 2 amended

to reflect new annex on

operational performance

requirements.

Annex ---- added

Annexes added as they are completed to

ensure all aspects of VTS operations and

equipment are covered.


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Recommendation on Operational and TechnicalPerformance Requirements for VTS Equipment

(Recommendation V-128)

THE COUNCIL:RECALLINGthe function of IALA with respect to Safety of Navigation, the

efficiency of maritime transport and the protection of the environment;

NOTING that Chapter V (12) of the International Convention for the Safety of Life at

Sea (SOLAS) 1974 (as amended) requires Contracting Governments planning or

implementing VTS wherever possible to follow the guidelines adopted by the

Organization by Resolution A. 857(20);

NOTING ALSO that IMO Resolution A.857(20), Annex section 2.2.2recommends

that in planning and establishing a VTS, the Contracting Government or Governments

or the competent authority should inter-aliaestablish appropriate standards for shoreand offshore-based equipment;

NOTING FURTHERthatNational Members provide shore infrastructure to support

the aim of IMO to improve the safety of navigation and the protection of the

environment;

RECONGNISING that IALA fosters the safe, economic and efficient movement of

vessels through improvement and harmonisation of aids to navigation, including

vessel traffic services, worldwide;

RECOGNISING ALSOthat harmonisation of vessel traffic services would be

enhanced by the introduction of international Technical Performance Requirements

for VTS equipment;

HAVING CONSIDEREDthe proposals by the IALA VTS Committee on

Operational and Technical Performance Requirements for VTS Equipment;

ADOPTSthe Operational and Technical Performance Requirements for VTS

equipment as set out in the annexes to this recommendation as follows:

Annex 1 Operational Performance requirements for core VTS equipment

Annex 2 Technical Performance Requirements - Radar

Annex 3 Technical Performance Requirements - Automatic Identification System

(AIS) equipment

Annex 4 Technical Performance Requirements - Radiocommunications Service

Annex 5 Technical Performance Requirements - Hydrological and Meteorological

equipment

Annex 6 - Technical Performance Requirements - Closed Circuit Television

Annex 7 Direction Finding (DF) equipment. (To be developed)

Annex 8 DGNSS and additional position related services equipment. (To be

developed)

Annex 9 Equipment for transfer of near real-time data between VTS centres. (To be

developed)


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RECOMMENDS that Competent Authorities providing Vessel Traffic Servicestake into consideration the appropriate Technical Performance Requirementscontained in the Annexes to this recommendation when establishing appropriatestandards for shore and offshore-based VTS equipment.

* * *


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Annex 1

RECOMMENDATION ON THE OPERATIONAL PERFORMANCE

REQUIREMENTS FOR CORE VTS EQUIPMENT

DOCUMENT REVISIONS ...................................................................................................................2

RECOMMENDATION ON OPERATIONAL AND TECHNICAL PERFORMANCE

REQUIREMENTS FOR VTS EQUIPMENT......................................................................................3

(RECOMMENDATION V-128).................................................................................................................3

ANNEX 1.................................................................................................................................................5

1. INTRODUCTION ......................................................................................................................10

1.1 ABBREVIATIONS ....................................................................................................................10 1.2 SUPPORTING DOCUMENTS .....................................................................................................11

2. VTS RADAR SYSTEM..............................................................................................................11

2.1 GENERAL ...............................................................................................................................11 2.2 CHARACTERISTICS OF THE RADAR TARGET...........................................................................12 2.3 RADAR DETECTION PERFORMANCE AND DISTURBANCES......................................................13 2.4 RADAR ACCURACY AND DISCRIMINATION ............................................................................14 2.5 AVAILABILITY .......................................................................................................................15 2.6 CALCULATION .......................................................................................................................15

3. CLOSED CIRCUIT TV CAMERAS AS A VTS SENSOR (CCTV)......................................16

3.1

GENERAL ...............................................................................................................................163.2 DETECTION PERFORMANCE OF CCTVCAMERAS ..................................................................16

3.3 CHARACTERISTICS OF THE CCTV..........................................................................................17 3.4 AVAILABILITY .......................................................................................................................17

4. COMMUNICATIONS ...............................................................................................................17

4.1 VERY HIGH FREQUENCY (VHF) ....................................................... ..................................... 174.2 LONG DISTANCE COMMUNICATION .......................................................................................17 4.3 RADIO DIRECTION FINDER (RDF) .................................................... ..................................... 174.4 COMMUNICATION WITH ALLIED SERVICES ............................................................................18 4.5 AVAILABILITY .......................................................................................................................18

5. AUTOMATIC IDENTIFICATION SYSTEM (AIS)...............................................................18

5.1 AVAILABILITY .......................................................................................................................18 6. LONG RANGE SENSOR DATA ......................................................... .....................................18

6.1 AVAILABILITY .......................................................................................................................19

7. HYDROMETEO EQUIPMENT .......................................................... .....................................19

8. VTS DATA SYSTEM ........................................................ .........................................................20

8.1 GENERAL ...............................................................................................................................20 8.2 EMERGENCY SITUATIONS ......................................................................................................20 8.3 CONTROL OF DISPLAYED INFORMATION................................................................................20

9. LIST OF PARTICIPATING VESSELS ........................................................ ...........................21

10. GATHERING AND RECORDING OF INFORMATION .....................................................22


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ANNEX 2...............................................................................................................................................24

TECHNICAL PERFORMANCE REQUIREMENTS FOR VTS RADAR SERVICES................24

11. INTRODUCTION ......................................................................................................................26

11.1 SCOPE ....................................................................................................................................26

11.2 DEFINITIONS AND CLARIFICATIONS .......................................................................................26 11.2.1 Software tools...............................................................................................................2711.2.2 Abbreviations .................................................................................... ........................... 27

11.3 REFERENCES ..........................................................................................................................29

12. GENERAL PROVISIONS.........................................................................................................30

12.1 IMPLEMENTATION OF RADAR SERVICES .................................................................................30 12.2 RADAR PARAMETERS ............................................................................................................30

12.2.1 Radar frequency ............................................................ ............................................... 3112.2.2 Antenna parameters ............................................................................................. ........3212.2.3 Transmitter characteristics ..........................................................................................3212.2.4 Receiver characteristics .......................................................... ..................................... 3312.2.5 System losses ....................................................... ......................................................... 33

12.2.6 Signal processing, extraction and tracking......... ......................................................... 3412.3 RADAR TARGET CHARACTERISTICS.......................................................................................35

12.3.1 Target properties..........................................................................................................3512.3.2 Radar cross-section....................................................... ............................................... 3512.3.3 Characteristics of wind farms .....................................................................................36

12.4 RADAR RANGE PERFORMANCE ..............................................................................................38 12.4.1 Antenna height ........................................................................ ..................................... 3812.4.2 Propagation conditions ........................................................... ..................................... 3812.4.3 Lobing ..................................................................................... ..................................... 4012.4.4 Shadow effect ...............................................................................................................4012.4.5 Tide...............................................................................................................................40

12.5 NOISE AND CLUTTER AFFECTING RADAR PERFORMANCE .......................................................40 12.5.1 Thermal noise...............................................................................................................41

12.5.2 Surface and volume clutter...........................................................................................4112.5.3 Ice............. ........................................................... ......................................................... 4212.5.4 Precipitation.................................................................................................................42 12.5.5 Man-made noise ............................................................ ............................................... 4312.5.6 Multiple reflections (ghost images) ................................................... ........................... 43

12.6 TARGET DISCRIMINATION AND POSITION ACCURACY.............................................................43 12.6.1 Range resolution ............................................................................... ........................... 4312.6.2 Azimuth resolution............................................... ......................................................... 4412.6.3 Range accuracy................................................... ......................................................... 4412.6.4 Azimuth accuracy .......................................................... ............................................... 44

12.7 SECURITY IMPLICATIONS .......................................................................................................44

13. PERFORMANCE REQUIREMENTS FOR VTS RADAR SERVICES ...............................45

13.1 GENERAL REQUIREMENTS......................................................................................................45 13.2 OBJECTS TO BE DETECTED .....................................................................................................45 13.3 GENERAL FEATURES AND CHARACTERISTICS.........................................................................45

13.3.1 Clutter and noise reduction facilities ......................................................... ..................4513.3.2 Side lobe suppression .................................................... ............................................... 4613.3.3 Dynamic characteristics............................ ........................................................... ........4613.3.4 Built-in test features ...................................................... ............................................... 46

13.4 RADAR COVERAGE AND DETECTION PERFORMANCE ..............................................................46 13.4.1 Detection range and conditions ................................................................................... 46

13.5 TARGET DISCRIMINATION......................................................................................................51 13.6 PLOT EXTRACTION AND TRACKING .......................................................................................51

13.6.1 Plot Extraction .................................................... ......................................................... 5113.6.2 Track Initiation.............................................................................................................5113.6.3 Maintaining Track................. ............................................................ ........................... 5113.6.4 Track Termination........................................................................................................52


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13.6.5 Track Data Output .......................................................................................................5213.6.6 Plot extraction and tracking performance ...................................................................52

13.7 RELIABILITY AND AVAILABILITY ...........................................................................................54 13.8 REDUNDANCY........................................................................................................................55 13.9 EQUIPMENT STANDARDS AND SPECIFICATION LEVELS ...........................................................55

14. PERFORMANCE VERIFICATION METHODS...................................................................56

ANNEX 3...............................................................................................................................................59

15. INTRODUCTION ......................................................................................................................60

15.1 ABBREVIATIONS ....................................................................................................................60 15.2 REFERENCES ..........................................................................................................................60


16.1 OBJECTIVES OF AIS ...................................................... ......................................................... 6116.2 APPLICATION .........................................................................................................................62

17. DESCRIPTION OF AIS AS A VTS SENSOR....................................................... ..................63

17.1

GENERAL ...............................................................................................................................6317.2 COVERAGE ASPECTS ..............................................................................................................63

18. AIS SERVICE .......................................................... ........................................................... ........64

18.1 EQUIPMENT............................................................................................................................64 18.2 AISINTERFACES....................................................................................................................64

19. OPERATIONAL ASPECTS OF AIS IN RELATION TO THE VTS ...................................64

19.1 GENERAL REQUIREMENTS......................................................................................................64 19.2 USE OF VIRTUAL MMSIFOR VTSCOMMUNICATION .............................................................65 19.3 SHORT SAFETY-RELATED MESSAGES......................................................................................65 19.4 USE OF BINARY MESSAGES FOR DATA EXCHANGE ..................................................................65 19.5 USE OF THE VTSTARGETS MESSAGE ....................................................................................65

19.6 ASSIGNED MODE ...................................................................................................................66 19.7 GRAPHICAL PRESENTATION ...................................................................................................66 Symbol usage .................................................... ........................................................... ..................66

Interaction with radar tracks.......................................................... ............................................... 6619.8 DATA VALIDITY ....................................................................................................................66

20. TRANSMISSION LAYER.........................................................................................................67

ANNEX 4...............................................................................................................................................68

PERFORMANCE REQUIREMENTS FOR RADIO COMMUNICATIONS SERVICE IN VTS

68

21. INTRODUCTION ......................................................................................................................69

21.1 BACKGROUND ......................................................... ......................................................... 6921.2 OBJECTIVESOF RADIOCOMMUNICATIONSEQUIPMENT ....................................... 69

22. REFERENCES............................................................................................................................69

23. DEFINITIONS ......................................................... ........................................................... ........69

24. FUNCTIONAL REQUIREMENTS..........................................................................................70

24.1 CHARACTERISTICS OF RADIOCOMMUNICATIONS EQUIPMENT ................................................70 24.2 MALFUNCTIONS,WARNINGS,ALARMS AND INDICATIONS ......................................................70

25. OPERATIONAL REQUIREMENTS ............................................................ ...........................70

25.1 RADIOCOMMUNICATIONS COVERAGE....................................................................................70 25.2 RECORDING AND PLAYBACK OF DATA ..................................................................................71


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25.3 AVAILABILITY .......................................................................................................................71

26. DESIGN AND INSTALLATION ......................................................... .....................................71

26.1 DURABILITY AND RESISTANCE TO ENVIRONMENTAL CONDITIONS .........................................71 26.2 INTERFERENCE.......................................................................................................................71 26.3 POWER SUPPLY ......................................................................................................................71 26.4 SITE SELECTION AND INSTALLATION .....................................................................................71 26.5 MAINTENANCE ......................................................................................................................71

27. INTERFACING....................................................... ........................................................... ........71

28. BACK-UP AND FALL-BACK ARRANGEMENTS ....................................................... ........72

29. SAFETY PRECAUTIONS.........................................................................................................72

30. DOCUMENTATION..................................................................................................................72

ANNEX 5...............................................................................................................................................73

PERFORMANCE REQUIREMENTS FOR HYDROLOGICAL AND METEOROLOGICAL

EQUIPMENT IN VTS ...................................................... ........................................................... ........73

31. INTRODUCTION ......................................................................................................................74

31.1 BACKGROUND .......................................................................................................................74 31.2 SCOPE ....................................................................................................................................74 31.3 OBJECTIVES OF HYDROLOGICAL/METEOROLOGICAL EQUIPMENT .......................................74 31.4 DEFINITIONS AND CLARIFICATIONS .......................................................................................74

31.4.1 Abbreviations .................................................................................... ........................... 7431.5 REFERENCES ..........................................................................................................................75


32.1 SENSORS ................................................................................................................................76

32.2 RELIABILITY ..........................................................................................................................76 32.3 MALFUNCTIONS AND INDICATORS.........................................................................................76


33.1 INFORMATION PRESENTATION ...............................................................................................76


34.1 DURABILITY AND RESISTANCE TO ENVIRONMENTAL CONDITIONS ........................................77 34.2 INTERFERENCE.......................................................................................................................77 34.3 POWER SUPPLY REQUIREMENTS/OPTIONS ...........................................................................77 34.4 INSTALLATION .......................................................................................................................77 34.5 MAINTENANCE ......................................................................................................................78

35. INTERFACING....................................................... ........................................................... ........78

36. BACK-UP ARRANGEMENTS ............................................................ .....................................78


38. MARKING AND IDENTIFICATION......................................................................................78

39. DOCUMENTATION..................................................................................................................79

GENERAL:...........................................................................................................................................79 INSTALLATION:...................................................................................................................................79 OPERATION:........................................................................................................................................79 FAILURE ELIMINATION,MAINTENANCE AND SERVICE: .................................................... ..................79

ANNEX 6...............................................................................................................................................80


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PERFORMANCE REQUIREMENTS FOR CLOSED CIRCUIT TELEVISION SERVICE IN

VTS 80

40. INTRODUCTION ......................................................................................................................81

40.1 BACKGROUND ......................................................... ......................................................... 8140.2 OBJECTIVESOF CCTVEQUIPMENT..............................................................................81

41. REFERENCES............................................................................................................................81

42. DEFINITIONS ......................................................... ........................................................... ........81


43.1 CHARACTERISTICS OF THE CCTV..........................................................................................82 43.2 RELIABILITY,ACCURACY,RANGE,AND RESOLUTION.............................................................82 43.3 MALFUNCTIONS,WARNINGS,ALARMS AND INDICATIONS ......................................................82


44.1 ERGONOMY............................................................................................................................82 44.2 OPERATIONAL CONTROLS ......................................................................................................82

44.3 DETECTION PERFORMANCE ...................................................................................................82 44.4 RECORDING AND REPLAYING OF DATA .................................................................................83 44.5 SOFTWARE REQUIREMENTS ...................................................................................................83 44.6 AVAILABILITY .......................................................................................................................83


45.1 DURABILITY AND RESISTANCE TO ENVIRONMENTAL CONDITIONS .........................................83 45.2 INTERFERENCE.......................................................................................................................83 45.3 POWER SUPPLY ......................................................................................................................83 45.4 SITE SELECTION AND INSTALLATION .....................................................................................83 45.5 MAINTENANCE ......................................................................................................................84

46. INTERFACING....................................................... ........................................................... ........84

47. BACK-UP AND FALL-BACK ARRANGEMENTS ....................................................... ........84


49. MARKING AND IDENTIFICATION......................................................................................84

50. DOCUMENTATION..................................................................................................................84


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RECOMMENDATION ON THE OPERATIONAL PERFORMANCEREQUIREMENTS FOR VTS EQUIPMENT

1. INTRODUCTIONThe purpose of this document is to give an overview of the operational performance

standards and requirements for VTS equipment including:

VTS Radar System

Closed Circuit TV Cameras as a VTS sensor (CCTV)

Communications

Automatic Identification System (AIS)

Hydrometeo Equipment

VTS Data SystemRequirements of the VTS equipment may have a high impact on acquisition and life-

cycle costs of a VTS and therefore the performance recommendations are divided intothree different capabilities:

Basic - applicable to VTS information service and, whereapplicable, navigational assistance service.

Standard - applicable to all types of VTS as identified by IMO information service, navigational assistance service and trafficorganizational service for areas with medium traffic density and/orwithout major navigational hazards.

Advanced- applicable to VTS areas with high traffic density and/orspecific major navigational hazards.

These capabilities may be used as applicable within a VTS, e.g. part of a VTS area

may call for a Basic and another part may call for a Standard capability.

1.1 Abbreviations

AIS Automatic Identification System

ASL Above Sea Level

CCTV Closed Circuit Television

CPA Closest Point of Approach

EIA Electronics Industry Association

ETA Estimated Time of Arrival

ETD Estimated Time of Departure

IALA International Association of Marine Aids to Navigation andLighthouse Authorities

IEEE The Institute of Electrical and Electronic Engineers

IMO International Maritime Organization

ITU International Telecommunication Union

MMSI Maritime Mobile Service Identity


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MRCC Maritime Rescue Co-ordination Centre

nm Nautical Mile/

RDF Radio Direction Finder

RMP Recognized Maritime Picture

S-band 2.0 4.0 GHz

TCPA Time to Closest Point of Approach

VHF Very High Frequency

VTS Vessel Traffic Services

VTSO Vessel Traffic Services Operator

X-band 8.0 12.0 GHz

Degree

Less than or equal to

Plus or minus

1.2 Supporting Documents

IEEE Std 686-1997 IEEE Standard Radar Definitions

IMO Performance Standards for radarreflectors (latest

edition)

IMO Resolution A.857(20)

EIA Standard RS-170 Electronics Industry AssociationRecommended Standard RS-170

2. VTS RADAR SYSTEM

2.1 General

The performance requirements placed on the VTS radar service vary a great deal

depending on traffic density, type of VTS, regional features and the VTS coverage

area. Basic functions will be provided by the VTS Radar, enhanced functions may be

provided by the VTS processing system. The purpose of this document is to describe

the general performance requirements of the radar service. By meeting these general

requirements, it is possible to provide the service required of the VTS radar

equipment in the VTS coverage area.

The VTS Radar System should be capable of performing the functions shown in

Table 1:


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Parameters / Capability Basic Standard Advanced

Path, time and track prediction, X

CPA, X X X

TCPA, X X X

Anchor watch, XVessels vector, X X X

Course, speed and label/identity, X X X

Collision alerts. X X X

Table 1: Performance Functions

These parameters will assist in the development of the traffic image.

2.2 Characteristics of the Radar TargetThe radar systems detection and measurement capacity depends on the characteristics

of the radar and the target. These include the targets average reflective area and itsoscillation in relation to the time and the measuring frequency used. The distribution

of the targets reflective parts, the incidence angle and turning speed have a major

impact on the power reflected back from the target.

The detection capacity required of the system is determined according to the type of

service, traffic density and potential navigational hazards. Table 2 below describes the

typical reflection features and type of capability requirements of VTS targets. The

table illustrates typical target parameters, including reflection characteristics, andidentifies the detection capabilities required for differing types of targets.

Following assessment of the type of targets required to be detected, which may differ

within the VTS area, the table identifies the type of capability required and defines

typical characteristics for use in setting performance standards.

Note: When selecting a radar system the system should be designed in such a way that

the defined target types can be detected and tracked reliably in the required area

covered by the VTS service in visibility conditions, at precipitation rates at sea states

and in propagation conditions relevant for the individual radar site.


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Type of Capability Design Requirements

Radar crosssection

TARGETBasic

Standard

Advanced

S-band X-band

Heightof

Target

1

Aids to Navigation etc. without radar reflector.Small open boats,fibreglass, wood orrubber with outboardmotor and at least 4meters long, smallspeedboats, smallfishing vessels, smallsailing boats and the

like.

X 1 m21 mASL

2Inshore fishing vessels,sailing boats,speedboats and the like.

X 3 m22 mASL

3Aids to Navigation withradar reflector.

X X 4 m2 10 m23 mASL

4Small metal ships,fishing vessels, patrolvessels and the like.

X X X 40 m2 100 m25 mASL

5 Coasters and the like. X X X 400 m2 1,000 m2 8 mASL

6Large coasters, bulkcarriers, cargo ships andthe like.

X X X4,000

m210,000

m212 mASL

7Container carriers,tankers etc.

X X X40,000

m2100,000

m218 mASL

Note: The figures in the above table are typical examples and as an averageonly.

Table 2. Typical Reflection Features and Type of Capability2.3 Radar Detection Performance and Disturbances

Factors disturbing and restricting the performance of radar systems include noise as

well as interference and clutter signals from various sources. Each radar site should bedesigned and equipped with devices to reduce the adverse effects of rain and sea

clutter and enhance the probability of target detection per scan. The radar should also

be designed and installed so as to eliminate to the maximum extent possible, false

echoes caused by side lobes or reflections from nearby structures.When selecting a

radar system and the measuring frequency, regional special conditions such as heavy

rainfall should be taken into account.

There are several technological solutions available to raise the performance of theradar system to the required level. Most typical solutions include higher average


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transmission power, larger antennas, circular polarization, reducing the receiver noise,

sector blanking and more effective processing and filtering of the transmitted and

received signal.

2.4 Radar Accuracy and Discrimination

The measurement of accuracy and discrimination of the system is determined by the

VTS authority based on Type of Capability. The recommendations for targetseparation for different types of capability are listed in Table 3.

Type of Capability

Basic Standard Advanced

Radar accuracy and physical

separation between small point

targets for discrimination in

display and tracking Display Tracking Display Tracking Display Tracking

Short range applications

(20 nm

coverage)

N/A 100 m 125 m 80 m 100 m

Angle between targets

as seen from the radar

1.2o 1.3o 0.7o 0.8o 0.55o 0.6o

Or distance in meters,

whichever is the greater

25 m 40 m 20 m 30 m 15 m 25 m

X-band

Corresponding 3 dB

antenna horizontal

beam width

0.6 - 0.7o 0.4 - 0.45o 0.35 - 0.4o

Angle between targets

as seen from the radar

N/A 3.5o 4o 1.8o 2o

Or distance in meters,

whichever is the greater

N/A 20 m 30 m 15 m 25 m

In

azimuth

S-band

Corresponding 3 dB

antenna horizontal

beam width

N/A 1.8 - 2o 1 - 1.25o

Table 3. Target Separation and Accuracy


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The system should be designed in such a way that the defined radar accuracy and

discrimination can be achieved in the entire area(s) covered by the VTS service. In

long measuring distances, the impact of the height and type of antenna on the

measuring accuracy and resolution should be taken into account. The system should

also be capable of displaying and tracking all targets of interest simultaneously in

normal conditions without the need for manual adjustments by the operator.

2.5 Availability

The VTS authority should define the requirements for the availability of the radar

service. The recommendations for availability are listed in Table 4 below.1

Availability for radar service

Type of Capability


Recommended availability

for the radar service99 % 99.6 % 99.9 %

Table 4. Availability

Availabilityis defined in IMO Resolution A.915 (220 Ref.40) as:

The percentage of time that an aid, or system of aids, is performing arequired function under stated conditions. The non-availability can be causedby scheduled and/or unscheduled interruptions.

Where the coverage from two or more radar sites provides overlapping coverage, as

long as one of the radars is available and provides similar capabilities in the area of

waterway normally covered, the requirements for radar service are met. Thus from aservice perspective, unusable time for a waterway can be calculated as the time when

any portion of the waterway is without a usable radar.

The radar coverage provided by adjacent countries, may, if agreed, be taken into

account when calculating the performance of the VTS radar. In addition, in areas of

high traffic where two waterways meet with converging traffic the location of radar

sites should be determined in a manner that minimises shadowing.

Single coverage: Unless dual coverage is provided throughout the whole coverage

area, some VTS sites provide a mix of overlapping and single radar coverage. VTS

sites that provide single coverage to at least some portion of a waterway are

considered to be single coverage sites,

2.6 CalculationAdministrations may choose to calculate service availability using one of two

methods:

1) by waterway model, or

2) by radar site/ radar site combination model

1Reference ALA Guideline 1035 on Availability and Reliability of Aids to Navigation,December 2004


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Waterway availability model: In this model administrations need to define which

waterways are high risk and which waterways are low risk. Separate calculations for

high and low risk are required, providing both exist within the coverage area.

Individual waterway availability calculations are then averaged to produce one figure

for each waterway risk category. If desired, a figure for each waterway may be

reported.

Radar site availability model: In this model, administrations must define which

radar sites serve low risk waterways and which serve high risk waterways. The overall

availability is calculated by averaging the availability of the associated individual

radar sites as illustrated in the examples below.

Example 1: An Advanced site receives complete radar coverage. For example, a VTS

area having two radar sites where at Radar site A the availability was 99% and Radar

site Bs availability was 99,7%, but both radar sites suffered coincidental outages

during 0,1% of the period. Although neither radar site individually met the availability

target the combined availability was 99.9% and met the performance goal achieved.

Example 2: A Basic site receives coverage from radar site A (as above) covering alow risk waterway. Radar site C, adjacent to radar site A, provides completely

overlapping coverage to the low risk waterway portion served by radar site A. Radar

site Cs performance was 99%, but neither unusable period (of radar sites A and C)

coincided. The low risk waterway covered by radar site A received usable signals for

100% of the time.

While these two distinctly different situations have different availability requirementsbased upon the level of risk, the concept of availability remains consistent the

minimum requirement is met for the coverage area.

Note: Higher availability percentage targets may be applicable to more critical parts

of the VTS area. Risk assessment may support lower availability percentage targetsin less critical areas.

3. CLOSED CIRCUIT TV CAMERAS AS A VTS SENSOR(CCTV)

3.1 General

The performance requirements of a CCTV service vary depending on traffic density,

type of VTS service, special regional features, coverage of the VTS area and the

intended use.

VTS Authorities should consider the need for low-light level, colour, intensified andlaser-gated low-light level, as well as digital image processing and video compression

of CCTV installations.

3.2 Detection Performance of CCTV CamerasDepending upon the circumstances, cameras should be capable of identifying the type

and possibly the name of the vessels concerned.

The CCTV should enable identification of the type of vessel at a minimum range of 3

nm from the camera location, but this will depend on the individual circumstances,

including local topography. The identity of a vessel by shape, colour and other

features should be capable of being determined normally at a minimum range of 1nm, but again this will depend on the individual circumstances. These ranges are


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based on where the nominal visibility is in excess of 10 nm. Image quality and

update/refresh rates should meet these requirements.

3.3 Characteristics of the CCTV

Cameras may be used either in low traffic density areas where this is a more cost

effective solution to radar or in conjunction with radar as an additional sensor,

depending on the level of risk.

The camera should be capable of automatically tracking a vessel manually selected by

the VTS Operator via the VTS Screen, if required by the VTS Authority. In addition,

there should be the possibility for the VTS Operator to manually de-select the

automatically acquired target and manually select another target and/ or area of the

acquired target, in order for the VTS Operator to perform specified monitoring tasks,

such as pilot embarkation/disembarkation.

Where more than one camera is installed to cover a VTS area it is desirable for the

output from both to be fused together to provide one composite picture.

3.4 AvailabilityThe requirements for the availability of CCTV is a matter for the VTS Authority to

determine.

4. COMMUNICATIONS

Reliable communications are essential to deliver VTS services and coverage should

be available throughout the VTS Area from one or communication technologies as

listed below.

4.1 Very High Frequency (VHF)

The VTS Authority should utilise dedicated working VHF Channels designated by theNational Radio Authority for specific types of operations. In addition, one or more

VHF Channels may be utilised in different sectors of the VTS Area.

It is common for the VTS to have its own independent VHF network, for the use

within specifically designated VHF Channels.

The VHF equipment must comply with national and international regulations.

4.2 Long Distance Communication

In the case where a VTS Authority requires long distance communication such as pre-

arrival information, any available communication systems should be used and

therefore an independent network is not required.

4.3 Radio Direction Finder (RDF)A number of VTS Authorities require RDF receivers to identify the target of a

transmitting vessel on VTS display. This may be used to correlate with the radar

target.

In order to ensure accurate identification on the VTS display the use of two or more

separate RDF bearing stations are required. Bearing angles on the target should be as

close to 90 as possible. The recommended bearing accuracy for the types of

capability are provided in Table 5


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Type of Capability


Recommended BearingAccuracy

2.5 1.5 1.0

Table 5. Bearing Accuracy

All bearings should be automatically displayed on the VTS display when the signal

has been received after a delay of no more than 3 seconds. The bearings should

remain visible on the VTS display as long as the vessel is transmitting a signal. The

VTS operator should have the ability to suppress RDF information on the VTS

display.

It is foreseen that this requirement may decrease as AIS usage by VTS Authorities

increases, but will not become obsolete as, depending on the circumstances, AIS

information may not always be available.

RDF is not suitable of being used for continuous tracking.

4.4 Communication with Allied Services

VTS Centres should be equipped with the ability to communicate with relevant allied

services by the use of reliable communication networks. It is recommended that VTS

Centres should be equipped with a digital switched network, with caller identification.

4.5 Availability

The requirements for the availability of Communications is a matter for the VTSAuthority to determine.

5. AUTOMATIC IDENTIFICATION SYSTEM (AIS)

Where both AIS and radar data are available they should be fused and presented to theVTSO as one unambiguous target using best available target data. However, the VTS

Operator should have the ability to choose whether to display the information on a

sensor basis. That is, whether individual targets are to be displayed using the AIS

derived data only or the radar derived data only or from both subject to track fusion in

accordance with the requirements of the VTS Authority.

If AIS information shows differences when compared to other sources, VTSOs should

use appropriate procedures and evaluate the obtained information and where

applicable advise the vessel immediately.

5.1 Availability

The requirements for AIS availability is a matter for the VTS Authority to determine.

6. LONG RANGE SENSOR DATA

Where AIS, radar and Long Range Sensor Data (e.g. LRIT positional data) are

utilised they should be fused and presented to the VTSO as one unambiguous target as

shown in Figure 1. However, the VTS Operator should have the ability to choose

whether to display the information on a sensor basis. That is, whether individual

targets are to be displayed using the AIS derived data, the radar derived data, or the


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LRIT derived data only, or from all three subject to track fusion in accordance with

the requirements of the VTS Authority.

If Long Range Sensor Data information shows differences when compared to other

sources, VTSOs should use appropriate procedures and evaluate the obtained

information and where applicable advise the vessel immediately.

Figure 1.Example integrated AIS, radar and Long Range Sensor Data (e.g. LRITpositional data) Source: REEFVTS, AMSA and MSQ

6.1 Availability

The requirements for Long Range Sensor data availability is a matter for the VTS

Authority to determine.

7. HYDROMETEO EQUIPMENT

It is essential that a VTS Centre has access to local Hydrometeo information relevant

to the VTS Area(s) and can, if required by the VTS Authority, disseminate this to

their users and allied services.

Where a VTS Authority determines a need to establish their own monitoring stations,

it should be noted that the individual VTS Authorities should determine the accuracy

and availability requirements for each VTS Centre, as these will be based on

individual circumstances. The following Table 5 gives an indication of typical

minimum accuracy requirements.

Note: The target availability should be as prescribed by IMO A.915(22).


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Parameter Minimum

Accuracy

Height of Tide 0.10 m

Rate of Tidal Stream/ Current 0.5 knots

Direction of Tidal Stream/Current 10 Degrees

Wave height 10% of the height

Wave Direction 20 Degrees

Wind speed 1m per sec

Wind Direction 10 Degrees

Visibility 10% of the distance

Air Temperature 10C

Air Humidity 5 %

Air Pressure 2 hPa

Sea Surface Temperature 10C

Table 6: Indication of typical minimum accuracy

The VTS Authority should specify the time periods over which the various dataparameters should be updated and may be averaged, if required, as these factors will

depend upon the local circumstances pertaining to the VTS Centre.

8. VTS DATA SYSTEM

8.1 General

A VTS Data System should have the capability to be flexible and easily upgraded and

maintained alongside the routine operations of the VTS Centre without the need for

interrupting the service.

VTS Centres should operate within a dual server environment to minimise disruptionto normal operations.

8.2 Emergency Situations

To optimize the operations of the VTS Centre the data information should be easily

transferred to another location capable of maintaining the VTS service in the event of

an emergency situation resulting in temporary closure of the VTS Centre.

8.3 Control of Displayed Information

To ensure the best possible traffic image is maintained the duty VTSO should have

the capability to select the primary target source being displayed for individual vessels

or all vessels. For example, selecting the radar target for a vessel with a faulty AISunit or the AIS network is unreliable.


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9. List of Participating Vessels

The list of participating vessels should include static information and dynamic

information concerning the vessel, for example Vessels Name, Call Sign, IMO

Number, MMSI, ETA, ETD, Draft, Course, Speed and Position, if required.

An example of a typical list is shown below. This example is taken from the Baltic

AIS Network which is integrated to the VTS system.

Figure 2. Example of List of Participating Vessels Source: ArchepelagoVTS, FMA.


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10. GATHERING AND RECORDING OF INFORMATION

Provision should be made for the storage, security, retrieval and presentation of this

information.

The data type, resolution and period of time for which information gathered by a VTS

is required to be stored should be identified in internal procedures. This time period

should be such that it allows for the full retrieval of data post-incident/accident, in

compliance with national requirements and those of the incident/accident

investigation procedures of the VTS authority and other authorised parties. This type

of information should include:

Communications, internal and external as defined in IALARecommendation V-127

Sensor data, i.e. data used to generate the traffic image

such as radar, CCTV, AIS and long-range sensor data. Shipping information data, i.e. vessel and cargo data,including vessel movement information.

Meteorological and hydrological data; and

Data from other sources if relevant.

Synchronization of voice / track dataThe IMO recommends a minimum of 30 days for the time-period to allow for the full

retrieval of data post-incident/accident. The VTS authority should define the period

of time and temporal resolution of sensor data and other tracking performance

parameters depending on traffic density and types of tracks.

If required by the VTS Authority, the data should be recorded automatically and

capable of being replayed onto a separate replay system.

Gathering and Recording of information

The period of time for which information gathered by a VTS is required to be

stored should be identified in internal procedures. This time period should be such

that it allows for the full retrieval of data post-incident/accident, in compliance

with national requirements and those of the incident/accident investigation

procedures of the VTS authority and other interested parties. This type of

information may include:

Communications (internal and/or external); Sensor data (i.e. data used to generate the traffic image such as

radar, CCTV, AIS);

Shipping information data ( e.g. vessel and cargo data, includingvessel movement information);

Meteorological and hydrological data; and

Data from other sources.Provision should be made for the storage, security, retrieval and presentation of

this information.

IALA Recommendation V-127 On Operational Procedures for Vessel Traffic

Services Edition 1 June 2004


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Annex 2

Technical performance requirements for VTS radarservices

Table of Contents

1. INTRODUCTION ......................................................................................................................26

1.1 SCOPE 261.2 DEFINITIONS AND CLARIFICATIONS 26

1.2.1 Software tools 271.2.2 Abbreviations 27

1.3 REFERENCES 29


2.1 IMPLEMENTATION OF RADAR SERVICES 30

2.2 RADAR PARAMETERS 302.2.1 Radar frequency 312.2.2 Antenna parameters 322.2.3 Transmitter characteristics 322.2.4 Receiver characteristics 332.2.5 System losses 332.2.6 Signal processing, extraction and tracking 34

2.3 RADAR TARGET CHARACTERISTICS352.3.1 Target properties 352.3.2 Radar cross-section 352.3.3 Characteristics of wind farms 36

2.4 RADAR RANGE PERFORMANCE 382.4.1 Antenna height 38

2.4.2 Propagation conditions 382.4.3 Lobing 402.4.4 Shadow effect 402.4.5 Tide 40

2.5 NOISE AND CLUTTER AFFECTING RADAR PERFORMANCE 402.5.1 Thermal noise 412.5.2 Surface and volume clutter 412.5.3 Ice 422.5.4 Precipitation 422.5.5 Man-made noise 432.5.6 Multiple reflections (ghost images) 43

2.6 TARGET DISCRIMINATION AND POSITION ACCURACY 432.6.1 Range resolution 432.6.2 Azimuth resolution 442.6.3 Range accuracy 442.6.4 Azimuth accuracy 44

2.7 SECURITY IMPLICATIONS 44

3. PERFORMANCE REQUIREMENTS FOR VTS RADAR SERVICES ...............................45

3.1 GENERAL REQUIREMENTS 453.2 OBJECTS TO BE DETECTED 453.3 GENERAL FEATURES AND CHARACTERISTICS 45

3.3.1 Clutter and noise reduction facilities 453.3.2 Side lobe suppression 463.3.3 Dynamic characteristics 463.3.4 Built-in test features 46

3.4 RADAR COVERAGE AND DETECTION PERFORMANCE 463.4.1 Detection range and conditions 46


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3.5 TARGET DISCRIMINATION 513.6 PLOT EXTRACTION AND TRACKING 51

3.6.1 Plot Extraction 513.6.2 Track Initiation 513.6.3 Maintaining Track 513.6.4 Track Termination 523.6.5 Track Data Output 523.6.6 Plot extraction and tracking performance 52

3.7 RELIABILITY AND AVAILABILITY 543.8 REDUNDANCY 553.9 EQUIPMENT STANDARDS AND SPECIFICATION LEVELS 55

4. PERFORMANCE VERIFICATION METHODS...................................................................56

LIST OF FIGURES..............................................................................................................................58

LIST OF TABLES................................................................................................................................58


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11. Introduction

Performance requirements for VTS radars are generally different to the requirements

for marine navigational radars. VTS radars normally need to operate simultaneously

on short and long range and this leads to dynamic requirements that far exceed those

required onboard a ship.

Furthermore, weather related phenomena such as ducting will influence VTS radars

more than ships radars. This can have a significant influence on the performance

either positive or negative.

Good clutter suppression is needed for sea clutter and, in most parts of the world, for

rain clutter as well. In addition, the need to see small targets in rough weather

conditions is essential, especially if objectives include detection of targets for security

purposes.

The introduction of AIS further develops VTS into a modern information system, and

the presentation of radar information needs to follow the trend, putting new demands

on the radar performance. Antenna side lobes and ghost targets (multiple reflections)

may lead to false and dangerous results when radar returns and AIS plots are

associated. High precision is therefore required to allow for unambiguous correlation

of position obtained from two information sources.

11.1 Scope

No other comprehensive standard, guideline or textbook exist for the use of radars in

VTS. The aim of this recommendation is therefore to:

- provide comprehensive guidance on the subjects relevant for the VTSapplication based on the VTS functional model,

- set generic performance requirements for Radar Services in VTS systems,and

- provide guidelines for their implementation.

11.2 Definitions and Clarifications

For general terms used throughout this annex refer to:

- IEEE Std 686-1997 IEEE Standard Radar Definitions.

Specific terms are defined as follows:

- Availability is the probability that a system will perform its specified

function when required.

- Normal weather and propagation conditionsare the conditions persisting99% - 99.9 % of the time as defined by the individual VTS authority. The

rest of the time is considered having adverse weather and propagation

conditions.

- Polarisation of a radar signal is determined by the orientation of theelectrical field. In the case of circular polarisationthe field rotates left or

right.

- Radar PD is the probability of detection at the output of a radar, subsequent

to signal processing and plot extraction, but prior to tracking, andpresentation.


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- Reliabilityis the probability that a system, when it is available performs aspecified function without failure under given conditions for a given period

of time.

- Sea characteristics include wave/swell height, direction and speed ofwaves/swell and distance between waves/swell.

- Squintare the angular difference between the axis of antenna rotation and aselected geometrical axis.

- Track swapis the transfer of a track identity (track label) to another track.

11.2.1 Software tools

CARPET Computer Aided Radar Performance Tool

TNO Physics and Electronics Laboratory, P.O.Box 96864, 2509JG The Hague, Netherlands, http://www.tno.nl

AREPS Advanced Refractive Effects Prediction System

Space and Naval Wafare Systems Center, San Diego,http://sunspot.spawar.navy.mil.

11.2.2 Abbreviations

AIS Automatic Identification System

AREPS Advanced Refractive Effects Prediction System

ASL Above Sea Level

CARPET Computer Aided Radar Performance Evaluation Tool

CW Continuous Wave

dB Decibel

dBi Decibel isotrope

dBm Decibel milliwatt

DF Direction Finder

FTC Fast Time Constant

GHz GigaHertz

GIT Georgia Institute of Technology

GPS Global Positioning System

IALA International Association of Marine Aids to Navigation and Lighthouse

Authorities

ICAO International Civil Aviation Organization

IEC International Electro-Technical Commission

IEEE The Institute of Electrical and Electronic Engineers

IMO International Maritime Organisation

ITU International Telecommunication Union

kHz kiloHertz

Ku-band 12.0 18.0 GHzkW kiloWatt


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LNFE Low Noise Front End

m metre

m2 square metre

MDS Minimum Detectable Signal

MHz MegaHertzmm/h millimetre per hour

m/s metre/second

MSC Maritime Safety Committee

MTBF Mean Time Between Failure

MTTR Mean Time to Repair

N/A Not applicable

NM Nautical Mile (also nmi)

PD Probability of Detection

PFA Probability of False Alarm

PRF Pulse Repetition Frequency

PW Pulse Width

R Range

RCS Radar Cross Section

RF Radio Frequency

S-band 2.0 4.0 GHz

TNO Toegepast Natuurkundig Onderzoek

UTC Universal Time Co-ordinatedUTM Universal Transverse Mercator

VTS Vessel Traffic Services

X-band 8.0 12.0 GHz

s microsecond

Degree

> Greater than

Greater than or equal to

Less than or equal to


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11.3 References[1] IEEE Std 686-1997 IEEE Standard Radar Definitions

[2] Merrill I Skolnik Introduction to Radar Systems, McGraw-HILL HigherEducation, ISBN 0-07-290980-3

[3] P.D.L. Williams,H.D, Cramp and KayCurtis,

Experimental study of the radar cross section ofmaritime targets, ELECTRONICCIRCUITS ANDSYSTEMS, July 1978. Vol 2. No 4.

[4] Ingo Harre RCS in Radar Range Calculations for Maritime Targets.http://www.mar-it.de/Radar/RCS/RCS_18.pdf

[5] IMO Performance Standards for radar reflectors (latestedition)

[6] InternationalTelecommunicationsUnion (ITU)

ITU-R SM.1541 Unwanted emissions in the out-of-banddomain

ITU-R SM.329-9 Spurious emissions


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12. General Provisions

The provision of guidance on aspects such as implementation of radar services,

general radar parameters, radar target characteristics, radar range performance, the

effects of noise and clutter on radar performance and target discrimination and

position accuracy are key to the provision of effective VTS radars.

12.1 Implementation of radar services

Implementation of radar services for VTS requires a sound knowledge of:

- VTS operational requirements;

- Target characteristics and detection range;

- Accuracy and resolution;

- Coverage analysis;

- General physical capabilities and constraints applicable to radar services;

- Interference risks (assessment of);

- Weather influences, including propagation;

- System design, including external interface and program planning.

Requirements of the VTS radar may have a high impact on acquisition and life-cycle

costs of a VTS and therefore the performance recommendations are divided into three

different capabilities:

- Basic - applicable to VTS information service and, where applicable,navigational assistance service.

- Standard - applicable to all types of VTS as identified by IMO informationservice, navigational assistance service and traffic organizational service

for areas with medium traffic density and/or without major navigational

hazards.

- Advanced - applicable to VTS areas with high traffic density and/or specificmajor navigational hazards.

These capabilities may be used as applicable within a VTS, e.g. part of a VTS area

may call for a Basic and another part may call for a Standard capability

The individual VTS authority should decide on the level of specification and define

requirements related to climate and topography as identified in this document.

Consideration of other local conditions may dictate individual performance

requirements that are independent of the level of recommendation.

Requirements to detect very small vessels for safety or security reasons may further

extend requirements, beyond those identified in this document for Advanced

recommendations.

12.2 Radar ParametersRadar Parameters refer to the limiting factors with respect to radar coverage and

include:

- radar frequency band;

- radar location;


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- antenna height;

- local weather;

- transmitted power;

- antenna characteristics;

- receiver sensitivity;

- receiver dynamic characteristics;

- processing capabilities;

- system losses.

These aspects combine to determine the minimum magnitude of radar returns that can

be detected.

The parameters are often dependent on each other, and different vendors may choose

different methods to solve the same issue. Therefore, it is recommended that overall

radar performance requirements are specified, taking the local weather intoconsideration, rather than specifying radar parameters.

However, in order to understand how the parameters affect radar performance, the

influence from some of the parameters are described as follows.

12.2.1 Radar frequency

Radar frequencies selected for VTS lie typically within the S-band and X-band

frequencies, however, higher frequencies such as Ku band may also be utilised.

The major operational effects of different frequencies are:

- For a given physical antenna size, azimuth resolution will increase withhigher frequency;

- Antenna gain and, thereby, overall system sensitivity, increases with higherfrequency for a given physical antenna size. However, system losses also

increase with frequency and may be severe at very high frequency, such as

Ku band;

- Radar cross section of targets in general will increase with frequency,however, specific types of targets may give particularly strong returns in agiven frequency band;

- Disturbance by precipitation increases with frequency.

The majority of VTS services use X-band radars as a best compromise, especially

since technologies for rain clutter suppression have matured. Also, as a result of

production volume, X-band radars are the least expensive.

The second most used frequency is S-band, due to better weather penetration in heavy

rainfall.

Frequency band allocation is granted by the ITU, whereas permissions to transmit on

given frequencies are granted on a national basis.

Modern transmitter and processing technologies allow several radars in close vicinity

to transmit on the same frequency without running the risk of disturbing each other.

The same techniques provide protection against interference from other radars, e.g.radars onboard ships.


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12.2.2 Antenna parameters

The antenna gain is one of the most important factors determining the radar range.

The gain is mainly determined by the operating frequency and the horizontal and

vertical beam widths of the antenna array.

Narrowing the horizontalas well as verticalbeam widths will result in reduction of

the volume clutter and thereby improved performance in precipitation. Thehorizontalbeam width is also the governing parameter in respect to azimuth

resolution and it has significant influence on the amount of surface clutter received.

The verticalbeam characteristics are the governing factor in respect to coverage at

short range.

Use of circular polarizationwill reduce unwanted returns from precipitation while

maintaining good returns from targets of interest to the VTS operator. However,

some radar reflectors are specifically designed for linear polarisationand theirvisibility may therefore be reduced by the use of circular polarisation.

If small targets, such as rubber or rigid hull inflatable boats, are identified by the VTS

as a target of concern, then the selection of antenna polarization is even more complex

and should be studied carefully.

Use of high antennarotation speedincreases the scan data rate, but the hits per scan

(echo returns per scan from a particular target) is decreased correspondingly. In some

cases this may mask a weak target that would otherwise be detected by using a lower

antenna speed.

12.2.2.1 Side lobes

A small part of the radio frequency energy from each transmitted pulse is radiated

outside the main antenna beam, producing side lobe patterns whose axis in thehorizontal plane have various angles with respect to the main beam.

Side lobes have no effect in case of distant or small surface targets, but the echo from

a large target at short range may produce an arc similar to a section of a range ring, or

they may appear as a series of echoes forming a dotted arc.

Side lobes may also occur far from the main beam, producing targets that are very

difficult to discriminate from real targets.

The side lobe levels are entirely dependent on the antenna design. Far side lobe

characteristicsare very important, as side lobes far from the main beam may result in

false targets, appearing to the operator with the same characteristics as a valid target.

12.2.3 Transmitter characteristics

For traditional pulsed radars the average power and peak pulse power has an influence

on the detection range. However, its importance is often overestimated. High peak

power often results in higher losses in the transmission lines of the radar and it will

always result in a larger amount of unwanted information (e.g. sea clutter).

Shorter pulse lengths provide better range resolution, a reduction of returns from rain

and sea clutter and better overall performance. The use of relatively short pulses (50

to 300 nanoseconds) is often beneficial for VTS applications.


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12.2.4 Receiver characteristics

The receiver sensitivity (often expressed by the receiver noise factor) is one of the

main factors with respect to detection of small distant targets in clear weather. The

noise figure may be expressed in different terms such as Low Noise Front End

(LNFE) noise figure and overall noise figure, making it difficult to compare radars

from different vendors.A better expression for receiver sensitivity is the Minimum Detectable Signal (MDS);

however, this is not ideal either as it may be difficult to measure this figure in a

reliable manner.

The dynamic characteristics are very important, especially if operational conditions

require:

- Simultaneous detection of targets on short and long range;

- Supply of signals for more than one display with different range settings;

- Simultaneous supply of signals for different operational roles;

- Supply of signals for automatic video processing and automatic tracking.

Minimum detectable signals at the receiver input and processed onwards lie typically

at -90 to -105 dBm in VTS applications, or may be as low as -115 dBm for security

applications.

Very large targets at close range are, however, not fully within the beam at short

range, limiting the input at the receiver to about + 10 dBm for the typical case.

Consequently, the overall dynamic range needed for the individual radar for a VTS

application is typically between 100 and 125 dB.

12.2.4.1 Pulse compression

For pulse compression radars the pulse compression circuit in the receiver will

generate so called time side lobes which may appear as weaker, false signals in front

of and behind large targets.

Special attention should be paid to this effect.

12.2.4.2 Continuous wave

For continuous wave radars similar effects as for pulse compression radars can be

observed due to the receiver processing.

In addition, spill-over of energy between transmitting and receiving antennas maylimit the useful dynamic range.

The use of small antennas allowed by the technology may lead to reduction of

azimuth resolution and result in higher susceptibility to rain and sea clutter.

12.2.5 System losses

System losses reduce performance, especially the ability to detect small distant

targets. Common reasons for system loss are:

- Long waveguide runs;

- Moisture in the waveguide runs;


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- Flexible and especially flexible/twistable waveguide parts. (Not to beconfused with elliptical waveguides which, in general, have small losses);

- Teflon or plastic gaskets used instead of proper pressure windows,especially if mounted between plain and choke flanges;

- Excessive number of joints in the waveguide system;

- Poor rotary joints;

- Poor workmanship in the manufacture of waveguide parts;

- Matching losses in receivers and distribution of signals, both withinadequate bandwidth / speed;

- Digitalisation of signals using too few bits;

- Losses in detection and tracking.

Furthermore, discontinuities in waveguide installations can result in reflections

causing the centre of the radar picture to be totally saturated. In extreme cases this

can even disturb the transmitted pulse, giving reduced angular resolution as well asreduced performance with respect to discrimination of targets from clutter.

12.2.6 Signal processing, extraction and tracking

As mentioned, the radar return signal down-converted to video level contains wanted

signals from objects of interest, unwanted signals (clutter for example sea clutter)

and some basic system noise (for example, thermal noise) all mixed together. The

purpose of the signal processing is to enhance the signals from the objects of interest

relative to the clutter and noise. Different techniques are used. Effective methods

include:

1. Sweep-to-sweep correlation:Normally, the pulse repetition rate of a radar is sohigh that a target is hit several times while the antenna beam turns past it. Incontrast, noise will pop up randomly. Therefore, by correlation of radar returnsignals from consecutive transmissions, noise can be suppressed efficiently,relative to targets (and clutter).

2. Signal differentiation:Extended areas of clutter (e.g. from rain showers) can bereduced by signal differentiation (in radars this is called Fast Time Constant(FTC)).

3. Signal integration:The multiple hits on a target as described above can be addedtogether. This will enhance the returns from the objects of interest relative to

noise and, to a lesser extent, relative to clutter. Further, it will reduce thefluctuations of target echoes.

4. Frequency Diversity:Frequency diversity radars employ two transmissionfrequencies. The radar returns on the two frequencies from a target will normallybe similar, while radar returns from clutter will be different. If an antenna withfrequency dependent squint such as a slotted waveguide antenna is used, therewill also be a temporal difference between the returns on the two frequencies.This means that the target will be present in both radar returns, while it is verylikely that the clutter will be present in only one of the returns. The total effect ofusing frequency diversity will be an enhancement of target radar returns, relativeto clutter radar returns.

5. Scan-to-scan correlation:By comparing radar returns from consecutive rotationsof the antenna, fast disappearing echoes (e.g. sea waves) can be filtered away


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while persisting echoes (e.g. ships) can be retained for further processing.Again, the overall effect is to enhance target radar returns, relative to clutter radarreturns.

The output of the signal processing is the processed radar data in a polar grid, i.e. a

circular area divided into radar cells, with each cell being characterized by a range

value, a range depth, an azimuth value, an azimuth width and a radar return intensityvalue. Plot extractionis the process of identifying groups of neighbouring radar cells

containing radar return intensity values above a defined threshold value. Such a

group of radar cells is called a plot,and is intended to correspond to a physical target.

Plots are updated on each rotation of the radar. Plots which persist from rotation to

rotation, and which move within reasonable physical limits of speed and acceleration,

are intended to correspond to physical targets. A series of plots associated in this way

is called a track. Erratically appearing plots are rejected as representatives for

physical objects and, therefore, as candidates for tracks.

Tracking is the process of associating plots from consecutive rotations of the radar to

existing tracks and to initiate new, tentative tracks on plots not associated to existingtracks.

12.3 Radar Target CharacteristicsTo understand the behaviour of radar targets it is essential to determine expected

performance from radar services.

The strength of the echo returned from a target is largely governed by the size of the

target, its aspect and its height above the radar horizon. However, these are not the

only factors and a small target of good reflecting properties may well give a stronger

echo than a much larger target of poor reflecting properties.

12.3.1 Target properties

Aspect angle (i.e. the angle at which the radar pulse hits the target) is an important

factor affecting echo strength. Certain types of objects that might be expected to give

a good echo prove to be very poor radar targets because they reflect most of the

energy that strikes them in a direction other than straight back to the radar. The worst

of these are gently curved smooth surfaces, such as sandy beaches, sandbanks, mud

banks, and gently sloping hills that are regular in shape and not covered with trees or

thick undergrowth. For the same reason lighthouses that are conical in shape do not

give as good a response as might be expected.

Vertical, comparatively smooth surfaces, such as cliffs and isolated buildings, give

strong reflection provided they face the radar.

Complex structures such as metal ships with several corners also give strong

reflections, whereas ships made of other materials typically give weaker re