GNSS availability during solar maximum: a threat to maritime - - PowerPoint PPT Presentation

GNSS availability during solar maximum: a threat to maritime navigation?

• George Shaw & Nick Ward
• General Lighthouse Authorities of the United Kingdom and

Ireland

Presented at ENC GNSS 2010 19 – 21 October 2010 ‘Maritime Transport & Mobility Applications’ session

Contents

Reliance of shipping on GPS Impact of ionospheric effects on GNSS Impact of reduced GPS constellation Multi-constellation benefits of Galileo A threat to maritime navigation? Conclusion

Source: Trinity House

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Ships rely heavily on GPS

GNSS is essential for efficiency and safety of shipping GPS is at the heart of today’s integrated bridges

• Drives chart displays
• Controls the autopilot
• Stabilises radar display and gyro-compass

GPS provides ship position for AIS and VTS GPS provides coordinates for emergency rescue

GLA DGPS Reference Stations

DGPS is a primary Aid to Navigation

Ionosphere effects GNSS propagation

Ionospheric scintillation and delay, courtesy University of Bath

Temporal and spatial gradients in the Total Electron Content (TEC)

GNSS is at risk during Solar Maximum

Polar scintillation, courtesy University of Bath

GNSS signal refraction & diffraction Phase scintillation

• significant delay in pseudorange

measurement

Amplitude scintillation

• strong fades may lead GNSS receiver

losing signal tracking

Standalone range errors up to 60m Loss of navigation solution

Solar Maximum is predicted in 2013 SWPC predicts 11 year cycle solar maximum in May 2013 Increase in solar storms & flares ‘Superstorms’ possible

• ‘Carrington Event’ of 1859

Highest levels of scintillation

• ccur in bands of latitude:
• equatorial (±10º),
• auroral regions (65º - 75º)
• polar cap (>75º)

Coincides with possible reduced GPS US GAO prediction

• Probability of maintaining full

GPS constellation falls to typically 85% over 2011-13 GLA / GRACE study

• simulation of 21 GPS satellites
• 2 representative marine GPS

receivers (hardware-in-the-loop)

• analysis of impact on DGPS

AtoN & ships’ navigation aids

Results in GPS outages and errors

GPS coverage ‘windows’ found

• only 3 satellites in view

horizontal position errors typically increased by 50%

• ccasional error spikes of the order of

many tens of metres GPS outages last up to 10 minutes up to 10km error build up for a fast vessel travelling at 35 knots

Very limited help from Galileo in 2013

Multi-constellation (and GPS modernisation)

• measures to improve GNSS resilience
• increased number of satellites
• greater frequency diversity

Galileo

• only 4 initial satellites (IOV phase) by 2011
• IOC (18 SVs) and FOC (30 SVs) help eventually (2018)

GLONASS

• only the newest (GLONASS K) satellites are expected to

provide a CDMA signal compatible with GPS and Galileo

• full complement not available in the timescale

Credit: Tim Stevens

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A threat to maritime navigation?

Beacon DGPS should be resilient and continue to provide integrity

• invalidates GPS satellites not in view (by not transmitting corrections)
• monitors integrity and provides corrections for visible satellites

Increased position errors of standalone GPS

• may go unnoticed by the mariner
• impairs the mariner’s situational awareness

Ships’ navigation systems may alarm when GPS indicates ‘no position solution’

• impairs the mariner’s situational awareness
• forces reversion to fallback navigation techniques

visual references, chart and compass

• limited training and familiarity with fallbacks

Reduced availability of GNSS during solar maximum with possible reduced GPS poses a distinct threat to maritime navigation

• Mitigation of future solar maxima
• Galileo fully operational
• Internal mitigation of ionosphere effects within the GNSS receiver
• using space weather models to issue timely Notices to Mariners

Conclusion