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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
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