Absolute Positioning by Radar

Dr Nick Ward, Research Director

General Lighthouse Authorities of UK & Ireland

14th IAIN Congress 2012, 01 - 03 October, 2012 - Cairo, Egypt

Seamless Navigation (Challenges & Opportunities)

Introduction

The IMO Maritime Safety Committee has stated that “e-navigation systems

should be resilient and take into account issues of data validity, plausibility

and integrity for the systems to be robust, reliable and dependable.

Requirements for redundancy, particularly in relation to position fixing

systems should be considered” (MSC 85/26, Annex 20).

Global Navigation Satellite Systems will provide the primary means of

positioning for e-Navigation, but a backup is needed

GLA study on resilient positioning:

Enhanced radar AtoN infrastructure, in conjunction with NT Radar

Hardened GNSS – improved receivers, supporting infrastructure

Alternative terrestrial radio-navigation system (eLoran)

Absolute positioning by radar

Computation of position

possible from radar targets

using:

known positions of targets

range and bearing to vessel

Alternatively map-matching

can be used if:

coastline presents distinctive

outline on display

map can be fixed to known

reference points

Image: Kongsberg

Feasibility & cost

Changes to onboard equipment

Calculation not difficult

Need to standardise

Must demonstrate benefits

Trials to prove accuracy

Position calculation

Calculation not difficult, but….

Effect of error in ship’s heading

needs to be considered

Sum of the ship’s heading and

radar azimuth measurement

Errors in ship’s heading from

gyrocompass

Significant as errors on the radar’s

azimuth measurement

New Technology (NT) Radar

Image: Kongsberg

NT Radar

Radar technology changing to

improve target detection

Coherent, Doppler signal

processing for clutter

discrimination

Modulated low power pulses for

long periods

Advances in processing

technology, solid state

Better performance & reliability

IMO MSC Resolution 192(79)

IMO Maritime Safety Committee

approved new radar performance

standards in 2004

Removed the requirement for S-

Band Radars to trigger racons from

2008

Allowing changes in radar

technology

Image: Tideland

Effect on Racons

Lower peak-power (100s of W

instead of 10s of kW)

Solid-state (non-magnetron)

S-Band radars

Effect on racon performance

Compatibility not relaxed for

X-band radar systems Image: USCG NAVCEN

Racon return on NT radar

Racon on Kish LH and AIS targets

Radar AtoN options

Racon - long range, power required, identity by Morse

character, highest cost

Active reflector - moderate range, power required, vertical

separation to reduce nulls, identification possible, medium

cost

Passive reflector - limited range, no identity – need to know

deployment pattern, no power required, lowest cost

Modified racons

Trials carried out with NT radar indicated reduced range

Specification improvement restored lost performance

Racons could be provided with added functionality:

for example by modulating the return pulses

replace Morse coded paint with a point target

identity, position, name and status

avoid obscuring other targets.

Opens way for absolute positioning

Accuracy considerations

Beamwidth of radar: typically 1° for X-band, 2° for S-band

Accuracy of radar target location:

Racons – point target, but delay needs to be compensated

Active reflectors – point target, may be a delay

Passive reflectors – point target, no delay, but may be lost in

clutter

Radar chart – survey/registration/referencing

Accuracy limitation

1° means 10 m accuracy at < 1 n.m.

(IMO Res. A.915(22))

Doppler Beam Sharpening (DBS) techniques may improve

cross-range resolution

Solid state coherent radar should give better than 10 metres

(95%) accuracy at up to about 12 NM from at least two active

radar reflectors - low power may limit range of racons

Conventional radar should give better than 100 m

Enhanced Radar AtoN infrastructure

Number, type and

distribution of radar AtoNs

Costs of deploying

additional radar AtoNs

Determine effective ranges

Determine optimum mix

Images: Echomax

Map matching

Accuracies of 100 m possible in a harbour approach situation

Higher levels of accuracy may be achievable

Extensive coverage would require costly surveys

Liability and copyright considerations

Mandatory carriage unlikely

Increasing use of chart radars

ECDIS may correlate radar returns with charted objects

Conclusions

Absolute positioning possible using modern radars with

enhanced radar AtoNs and/or radar map matching

Initial analysis indicates that accuracies comparable with

GNSS may only be achieved at limited ranges

Cost/regulatory implications with map matching option

Not yet proven as an alternative to GNSS for position input to

e-Navigation – need for further investigation

Further work

Apparent limitations on performance need to be investigated

Investigate cost of charts & processing capabilities on radar

Simulate numbers and distribution of radar AtoNs required

Validate simulations by trials at sea

Prove general principle, accuracies and ranges achievable

More information

nick.ward@gla-rrnav.org