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