Breaking the Ice
Navigation in the Arctic
Arctic navigation is becoming increasingly important, because oil exploration and normal shipping in the region are both on the rise. Navigation integrity is particularly important, because an accident could be very damaging to the sensitive Arctic environment. Thus, this article investigates the Arctic extension of space-based augmentation systems (SBAS) such as WAAS, EGNOS, and MSAS. More specifically, it analyzes the potential benefit of adding new SBAS reference stations for the far North, use of Iridium satellites to broadcast integrity information to the users, and multi-constellation GNSS to improve vertical performance.
The Arctic houses an estimated 90 billion barrels of undiscovered, technically recoverable oil and 44 billion barrels of natural gas liquids according to the U.S. Geological Survey. These potential energy reserves represent 13 percent of the untapped oil in the world.
Russia, Canada, and the United States plan to explore the Arctic for extensive drilling soon. At the same time, the Arctic is becoming more accessible to normal shipping because of global climate change. New summer sea lanes have already opened up, and projections of sea ice loss suggest that the Arctic Ocean will likely be free of summer sea ice sometime between 2060 and 2080.
The combination of undiscovered oil and climate change are driving a dramatic increase in the demand for navigation in the Arctic. In this article, we examine different approaches to improve accuracy and enable integrity in the Arctic, including the addition of more satellite-based augmentation system (SBAS) reference stations in or near the Arctic, integration of Iridium satellites with GNSS, and use of multi-constellation GNSS.
More SBAS Reference Stations
At present, none of the three operational SBAS provide meaningful service in the far North. In fact, Figure 1 (see inset photo, above right) shows the current SBAS availability coverage with vertical alert limit (VAL) equal to 35 meters, and horizontal alert limit (HAL) equal to 40 meters.
Figure 1 is based on two of the currently operating SBASes: the U.S. Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS).
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For the purposes of our analysis, we assume that all these references stations provide the same measurement quality as current WAAS reference stations. We also assume the availability of continuous user connectivity, that is, the user is always able to receive the SBAS corrections.
Although SBAS GEO coverage is limited in the Arctic, other ways exist with which to maintain the connectivity, such as using low earth orbit (LEO) satellites. We will address this topic in more detail in the next section.
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Iridium for SBAS Messages
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The over-the-pole design of Iridium orbits ensures very good high-elevation satellite visibility in the Arctic. Because Iridium satellites already provide voice and data services to satellite phones and integrated transceivers around the globe, Iridium is a strong candidate for enabling SBAS linkage to Arctic users.
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As a bonus, Iridium satellites could improve the vertical dilution of precision (VDOP) if the Iridium satellites also broadcast ranging signals. VDOP is a measure of how well the positions of the satellites are arranged to generate the vertical component of the positioning solution. Higher VDOP values mean less certainty in the solutions and can be caused if the satellites have low elevation angles in relation to users.
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With added Iridium satellites, the VDOP values increase to 1.6 from 2.1 for 24 GPS satellites, and to 1.3 from 1.8 for 31 GPS satellites. Moreover, the VDOP values are more even over the Earth’s surface. For both scenarios of 24 and 31 GPS satellites, adding Iridium satellites improves VDOPs in the Arctic.
Multiple Constellations for High Availability of Integrity
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If using only two constellations, adding GLONASS to GPS is the most beneficial combination. GLONASS satellites orbit at 19,100 kilometers (11,842 miles) altitude with a 64.8-degree inclination. Compared to the 55-degree inclination of the GPS orbital planes, the GLONASS constellation produces better coverage in high latitudes. The VDOP improvement in the Arctic is more dramatic using three or even all four constellations.
For the complete story, including figures, graphs, and images, please download the PDF of the article, above.
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