Target Detection by Marine Radar (IEE Radar, Sonar Navigation and Avionics)

739 Pages·2004·35.99 MB·English

by  John N. Briggs

Target Detection by
Marine Radar
John N. Briggs
The Institution of Electrical Engineers
Published by: The Institution of Electrical Engineers, London,
United Kingdom
© 2004: The Institution of Electrical Engineers
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British Library Cataloguing in Publication Data
Briggs, John
Target detection by marine radar. - (IEE radar series ; 16)
1 .Tracking radar 2.Radar in navigation
!.Title !!.Institution of Electrical Engineers
623.8#933
ISBN 0 86341 359 5
Typeset in India by Newgen Imaging Systems (P) Ltd., Chennai, India
Printed in the UK by MPG Books Limited, Bodmin, Cornwall
Foreword
The opportunity arose, with the end of hostilities in 1945, to make available to
Merchant Shipping the new technology of radar, which had developed so rapidly
in the secrecy of war. In the United Kingdom, the Government made a design avail-
able to manufacturers and this was followed by Performance Specifications for Radar
for Merchant Ships in 1946. This specification and its later revisions were prepared
by the Ministry of Transport in consultation with representatives of shipowners, light-
house and harbour authorities, marine manufacturers, the General Post Office and the
Admiralty. The GPO at the time were responsible for the use of radio frequencies and
the Admiralty contributed the technical expertise with a new Transport Experimen-
tal group at ASE (Admiralty Signals Establishment) in Eastney which subsequently
developed into the Civil Marine Division of ASWE (Admiralty Surface Weapons
Establishment). Together with these Performance Specifications a system of type
testing of designs was put in place to certify their compliance.
Radar on Merchant Ships was initially installed for commercial purposes. The
early customers were ferries, which could then maintain better schedules in fog, and
large fishing vessels. Radar was treated with great suspicion by the mariners of the
day and was usually the preserve of the master, who locked it so that it could only
be used when he was on the bridge. Ports also started using radar for the commercial
purposes of berthing ships in fog; one example is the Port of Liverpool, in 1948.
With improving technology and ease of use, the Merchant Ship radar became
more accepted but it was some time before the use of radar for safety purposes was
recognised. In fact the melancholy situation in the 1950s was that the introduction of
radar had not resulted in any reduction of the number of serious collisions at sea. The
collision between the passenger ships Andrea Doria and Stockholm off Nantucket in
1956 is a well recorded example of the misinterpretation of radar information in a
passing situation in fog. Accordingly the International Conference on The Safety of
Life at Sea in 1960 revised the International Regulations for Preventing Collisions at
Sea by adding rules to take account of the use of radar and recommendations on the
use of radar information as an aid to avoiding collisions at sea.
Today radar with plotting is accepted by mariners as the primary tool to assist in
collision avoidance. The International Conference on Safety of Life at Sea in 1974
adopted provisions making radar a mandatory carriage requirement for Merchant
Ships in a phased programme starting in 1980 and finally completed in 2002. All
Merchant Ships over 300 gross tonnage now carry a radar and many carry two. Many
small craft also carry radar voluntarily as manufacturers have produced cost effective
designs for their needs.
The Maritime and Coastguard Agency is the direct successor of the Marine Safety
Division of the 1946 Ministry of Transport and the consultation processes used then
in agreeing radar specifications are still used today through its Safety of Navigation
Committee. The task is somewhat more complicated today as specifications are sel-
dom written for national needs but are designed to be internationally agreed so that
standards can be maintained all over the world. The ensuing type approval process
has also led to international agreement with one approval often being acceptable to
Administrations world-wide.
No standard setting of the regulatory bodies of the world would be successful,
however, if the basic physics of the radar and the resulting technology constraints
were not fully understood by those responsible for the drafting. The author of this
book is to be congratulated in his descriptions of the physical processes at work and
the methods by which the technology can be used in the specialised world of civil
marine radar.
Kim Fisher FRIN FIEE
MCA
Chairman UKSON
Preface
Radar is a legal necessity for the safe navigation of merchant ships, is voluntarily
carried by many leisure craft, within vessel traffic services (VTS) is indispensable to
the operation of major ports and harbours, and has several important other maritime
applications. This book tells how these civil surveillance radars detect their targets.
Brief historical outlines help explain the way modern practice developed from the
first faltering steps of the 1930s. We describe and illustrate today's radars, as well as
passive and active beacon targets. But natural features such as coastlines and - vital
for collision avoidance - vessels of all shapes and sizes are not specifically designed
to reflect radar transmissions. Radar operation however relies on their ability to return
echoes. This ability is therefore examined in detail from both practical and theoretical
standpoints.
Our reason for adding to the many existing radar treatises is, for the first time,
to concentrate solely on the civil marine scene, unadulterated by consideration of
aircraft flying at 40000 ft, stand-off jammers, Doppler effects and the host of other
factors, civil and military, which do not concern civil marine operations.
Radar design is constrained by the laws of man and of physics, so we explain
the framework lying behind the numerous international regulations governing marine
radar and highlight the fundamental technical constraints. Detection is an engineering
problem founded on scientific and statistical principles, so we have to include more
mathematics than we might wish, but which can be skipped on first reading. Without
excluding anything of practical significance, we have simplified our account as much
as possible, helping the many users, managers and regulators whose backgrounds lie
elsewhere, even perhaps outside the marine industry.
We include full technical analysis of the many factors in play within the radars and
within targets, the great and sometimes under-estimated parts taken by the weather
and the environment, and not least, the ability of operators to set the controls to
influence performance for good or ill. Our analysis shows why, when and whether
radar will pick up targets as diverse as yachts, low-lying coasts or super-tankers.
Numerous graphical and other diagrams and worked examples help the reader to grasp
the principles underlying radar operation and to quantify the practical importance of
the many factors in play. The analysis culminates in full instructions for use of a set
of spreadsheets, available on the IEE website (www.iee.org), which give detection
ranges, probability of detection and many other performance parameters for the user's
own equipment, illustrated by a set of case studies.
The accuracy with which targets are positioned on the radar screen and with which
their progress is tracked and predicted depends upon how definitely they have been
detected, so we devote a chapter to the general question of accuracy, which underlies
the ability of plotting aids such as ARPA to predict closest point of approach and
give other warnings vital to the navigator. Not being master mariners, we leave
interpretation of the displayed traces to the specialist navigation textbooks. In the
final chapter, Chris Baker looks at some of the ways in which marine radar may
develop to meet the challenges of the next two decades.
We have striven to be comprehensive, minimising the need to hunt up references
elsewhere. Copious cross-references, a logical layout, the glossary and the index
should quickly guide the busy reader to specific items.
Although we authors take full responsibility for the errors and omissions that
surely remain, this book would have been impossible without the help, advice and
encouragement of many experts.
J.N.B. would like to thank several old GEC-Marconi colleagues whose friendship
often goes back too many years to admit. They include John Ashley, Niall Davies,
Steve Holland, George Hurd who made extensive comments on an early draft, Bob
James, David Ogleby who identified the need for such a book when scheming VTS
systems, Richard Parsons, Janet and Peter Sykes, and Dudley Taylor whose computer
expertise was vital at times. Several friends with senior engineering management
experience elsewhere in the marine radar industry freely gave valuable help, including
among others David Hannah, Richard Trim and Professor Phil Williams. J.N.B. is
particularly in debt to Phil for valuable comments on the whole draft text and for
permission to quote freely from his privately published CD work 'Civil Marine Radar'
with its wealth of technical detail and historical aspects describing the evolution of
Decca radars. In the early days Professor John Kemp, then Editor of the Journal of
Navigation and Julian Parker, then Secretary of the Nautical Institute gave valuable
encouragement to persevere with what seemed a daunting endeavour. The Royal
Institute of Navigation generously supplied a scarce copy of The Uses of Radar at
Sea. Jonathan Ansell of Easat Antennas freely gave much background information on
modern VTS and scanner developments, while Peter Munro of Munro Engineering
kindly read and commented on Chapter 8.
Officials have been equally helpful. Martin Hart and his colleagues at the Maritime
and Coastguard Agency checked and corrected the regulatory sections of Chapter 1
and looked up a number of technical points. J.N.B. also benefited from extensive
discussions with Roy Lee on regulatory aspects. Dr J. M. Williams took much trouble
to explain the fundamentals of ships' radar reflectivity, which Chapter 10 attempts to
summarise. Bill Paterson, then Director of Engineering, Northern Lighthouse Board,
facilitated the atmospheric refraction experiments described in Chapter 5. Dr Nick
Ward, Principal Development Engineer, Trinity House Lighthouse Service, kindly
dug out a number of IALA papers and supplied illustrations.
A number of leading manufacturers and other organisations also kindly contributed
illustrations, as acknowledged in the text. We do not however endorse particular
suppliers' products - all the leading manufacturers offer highly developed equipment
capable of excellent performance. Other illustrations are from the authors' collections.
J.N.B. would like to thank Sarah Kramer, Commissioning Editor at the IEE, and
the IEE team for their forbearance, also Professor Hugh Griffiths, Radar Series Editor.
His predecessor, Professor Ramsay Shearman, gave much guidance and prevailed on
Professor Baker to contribute to the book.
Finally, and most important of all, J.N.B. must record his thanks to his long-
suffering wife Betty for putting up with the disruption of the supposed leisure of
retirement with 'yet more work'.
Chris Baker is especially indebted to Professor Hugh Griffiths (University College
London), Dr Andy Stove (THALES Sensors), Dr Steve Harmari and Mr Graham Binns
(QinetiQ) and Professor Ramsay Shearman for their invaluable advice and numerous
corrections to Chapter 16. In particular C. J.B. wishes to thank J.N.B. for the invitation
to write the chapter and for having the patience to integrate it with the earlier chapters.
Contents
Foreword ............................................................................. xxv
Preface ................................................................................ xxvii
1. Introduction ................................................................. 1
1.1 Purpose and Scope ....................................................... 1
1.1.1 Purpose ....................................................... 1
1.1.2 Scope .......................................................... 3
1.2 Radar Users and Uses .................................................. 4
1.2.1 Merchant Ships ............................................ 4
1.2.2 Leisure Craft ................................................ 5
1.2.3 Fishing Vessels and Small Commercial
Vessels ........................................................ 5
1.2.4 High Speed Craft ......................................... 5
1.2.5 Vessel Traffic Services ................................ 5
1.2.6 Military Applications ..................................... 6
1.3 The Past and Future ...................................................... 7
1.3.1 The History of Marine Radar ........................ 7
1.3.2 Secondary Radars ....................................... 10
1.3.3 VTS ............................................................. 12
1.3.4 The Current Generation of Radars ............... 13
1.3.5 Future Possibilities ....................................... 14
1.4 The Regulators .............................................................. 15
1.4.1 Overview ...................................................... 15

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vi Contents
1.4.2 UNCLOS ...................................................... 15
1.4.3 IMO .............................................................. 15
1.4.4 National Consultations ................................. 16
1.4.5 SOLAS and the Colregs ............................... 17
1.4.6 IALA ............................................................. 17
1.4.7 Enforcement ................................................ 18
1.4.8 ISO .............................................................. 18
1.4.9 IEC .............................................................. 18
1.4.10 ITU ............................................................... 19
1.4.11 National Regulations .................................... 19
1.4.12 National and Supra-national Groups;
the European Community ............................ 19
1.4.13 The Courts ................................................... 20
1.5 The Regulations ............................................................. 21
1.5.1 Radar for Ships within SOLAS ..................... 21
1.5.2 Radar for Craft Outside SOLAS ................... 23
1.6 Theory and Calculations ................................................ 23
1.6.1 Sources ....................................................... 23
1.6.2 Mathematics and Units ................................ 24
1.6.3 Basis of Performance Calculations .............. 26
1.6.4 Spreadsheet Calculation .............................. 26
1.6.5 Approximate Methods .................................. 26
1.7 The Layout of This Book ............................................... 27
1.8 References .................................................................... 28
2. The System and the Transmitter ............................... 31
2.1 The Operator and the System ....................................... 31
2.1.1 Scope of Chapter ......................................... 31
2.1.2 Operators Afloat ........................................... 31
2.1.3 Integrated Bridge Systems ........................... 35
2.1.4 Operators Ashore ........................................ 35

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Contents vii
2.1.5 Basic Radar Operation ................................. 37
2.1.6 Target Detectability ...................................... 39
2.1.7 Radar Construction ...................................... 41
2.1.8 Decibels ....................................................... 42
2.2 Components of the Radar ............................................. 44
2.2.1 Transmission ............................................... 44
2.2.2 Reception .................................................... 47
2.2.3 Non-coherent System .................................. 48
2.2.4 Coherent-on-receive System ....................... 48
2.2.5 Fully Coherent System ................................. 50
2.2.6 Ambiguity; Image Frequency, prf
Constraints .................................................. 50
2.2.7 Typical Station Configuration ....................... 51
2.3 Transmitter ..................................................................... 52
2.3.1 Overview ...................................................... 52
2.3.2 Magnetron Power Source ............................ 53
2.3.3 Modulator ..................................................... 54
2.3.4 Influence of Transmitter on System .............. 55
2.3.5 Spectrum Problems ..................................... 55
2.4 Transmitted Frequency ................................................. 57
2.4.1 Frequency and Wavelength ......................... 57
2.4.2 Choice of Band ............................................ 59
2.5 Choice of Other Parameters .......................................... 59
2.6 Feeder ............................................................................ 60
2.6.1 Waveguide ................................................... 60
2.6.2 Mismatch ..................................................... 64
2.6.3 Feeder Losses ............................................. 66
2.6.4 Ringing ........................................................ 67
2.7 Scanner, Qualitative Description ................................... 67
2.7.1 Plane and Circularly Polarised Rays ............ 67
2.7.2 Directional Radiation .................................... 69

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