Maritime navigation at great risk of disruption
During the last days, the sun emitted three massivesolar flares, asNASA’s Solar Dynamics Observatoryhas observed. The solar activity can affect the availability of Global Navigation Satellite Systems and therefore maritime navigation.
The sun unleashed a colossal solar flare on May 12, in what has become the most powerful solar eruption of the year, according to Huffington Post.
The giantsolar flare, which registered as one of the largest eruptions the sun can unleash, was captured on camera by NASA’s Solar Dynamics Observatory.Solar flare registered as an X1.7-class sun eruption – the strongest type of solar flare the sun can fire off, according to the SWPC Space Weather Prediction Center officials.
When aimed directly at Earth, X-class solar flares can pose a risk to astronauts and satellites in orbit, as well as interfere with communications and GPS signals on the ground.
The UK Maritime and Coastguard Agency (MCA) has issued a Marine Information Note relating to solar activity which advises the maritime community that availability of Global Navigation Satellite Systems (GNSSs) may be adversely affected during the current increase in sunspot activity and as a consequence maritime navigation could be effected.
The maximum of the solar cycle is predicted around May 2013, with increased frequency ofGNSS performance degradation likely during the period 2012 to 2015 due to increasedionospheric scintillation and signal propagation delays.
The use of Position, Navigation and Timing (PNT) information derived from GlobalNavigation Satellite Systems (GNSS) is widespread within many vessels’ navigationsystems and underpins situational awareness for many mariners. GNSS provides thepositions of the ship and surrounding vessels and of Aids to Navigation (AtoN) for theElectronic Chart Display and Information System (ECDIS) and hence is the basis ofrelative positions displayed to the mariner. GNSS is also used in applications such as thecorrection of gyro compass drift, precise manoeuvring of ships (such as during thenavigation of tight channels and docking), the position information within the AutomaticIdentification System (AIS), and vessel location reports in emergency situations.
The impact of the ionosphere on GNSS performance can be significant due to thepropagation effects on the GNSS signals-in-space as they pass through the ionizedionosphere at altitudes above 50km from the earth’s surface. GNSS signal propagation isaffected to a greater extent during periods of higher solar activity (e.g. sun spots and solar flares), when the effect of ionizing solar radiation creates more free electrons in theionosphere. Solar activity is cyclical, peaking at a maximum approximately every 11 years,during which periods GNSS performance can be severely degraded, especially atequatorial, auroral and polar latitudes. Solar maximum is predicted to occurduring 2013, and this might be expected to lead to a period of reduced GPS constellation.
Reliance of shipping on GNSS
Satellite navigation is now essential to the efficiency and safety of shipping. GPS is at theheart of today’s integrated bridges, with chart displays driven by GPS receivers that alsocontrol the auto-pilot. Separation from other vessels is ensured by radar used incombination with the Automatic Identification System (AIS), but on many vessels, these arenot independent of GPS and they specifically alarm when GPS is lost; GPS stabilises theradar display and the ship’s gyro-compass. It also provides the ship’s coordinatestransmitted by AIS to the displays on other vessels in the vicinity and to the Vessel TrafficServices (VTS) ashore. GPS even guides rescuers to the vessel in an emergency.
Ionospheric effects on GNSS
During quiescent periods of solar activity, ionospheric effects on GNSS can be managedsuch that the residual errors caused by the ionosphere do not generally pose a problem tomaritime navigation performance. The use of embedded models (such as the Klobucharmodel) within a standalone GPS receiver is effective at reducing the pseudorangemeasurement error induced by the ionosphere propagation delay. Where DGPScorrections are available, over baseline separations up to several hundred kilometres, theDGPS corrections significantly reduce the common mode errors, including the effects ofthe ionosphere. However, at the peak of the solar cycle with high levels of sunspot activity,solar storms and flares, the application of ionospheric models and differential correctionsmay be less effective and this could increase the integrity risk to maritime navigation.Studies have indicated that amplitude scintillation has been observed to cause substantialerrors in GPS pseudorange measurements. Standalone range errors of up to 60 metreshave been reported.
Impact on marine navigation
Maritime navigation systems and services that rely on GNSS are at greatest risk ofdisruption from the ionosphere during the period from 2012 to 2015. The intensity of theradio flux during the solar peak may be less than in previous peaks and the impact onGNSS may on average be less severe. However, even during a quieter solar maximum,the occurrence of individual sun spots could give rise to significant effects for discreteevents. The effects vary with latitude, season and time of day (the hours soon after sunsetbeing most affected). It is also worth noting that during the last solar maximum the level ofdependence on GNSS was quite low, whereas it is now very high.5.2 The most significant errors experienced by GNSS are due to the effect of solar activity onthe ionosphere. The magnitude of the effect of the ionosphere varies in both time andspatial extent. The effect is much greater during the day than during the night.
For more information, view the UK MCA Marine Information Notice regarding Global Navigation Satellite Systems (GNSS) – Availability During Increased Sunspot Activity
Source: UK MCA, Huffington Post, NASA
