. "5 Climate-Change-Related Technical Issues Impacting U.S. Naval Operations." National Security Implications of Climate Change for U.S. Naval Forces. Washington, DC: The National Academies Press, 2011.
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National Security Implications of Climate Change for U.S. Naval Forces
CURRENT STATE OF NAVIGATION SYSTEMS INFRASTRUCTUREWITH RESPECT TO ARCTIC NAVIGATION
Navigation in the polar regions is challenging not only due to sea-ice and adverse weather conditions but also due to limitations of current navigation systems and infrastructure at high latitudes, which are degraded relative to performance in other regions of the world. This performance degradation affects surface, subsurface, and aircraft operations to varying degrees. Its significance to mission execution depends upon each mission’s requirements for safe navigation in restricted water/airspace, precision localization and mapping, and the underlying accuracy of reference navigation charts.
Specifically, Global Positioning System (GPS) performance is degraded due to poor satellite geometry, larger ionospheric effects, and multipath interference. Similarly, the radio-navigation infrastructure that provides GPS corrections and/or position reference does not routinely extend to the polar regions. Magnetic heading becomes unstable and inertial navigation systems (INSs) suffer poor alignment above 70º north latitude due to the reduced effect of Earth’s rotation. To prepare for expanded operations in the Arctic, the Navy should assess current military navigation system performance in polar regions and how it might inhibit operations. In addition, the Navy should seek to enhance the navigation infrastructure as necessary to prevent such limitations. Precision navigation is particularly crucial for combat military operations (precise tracking and targeting) and certain search and rescue operations.
GPS Performance Issues
Global Positioning System satellite orbit inclinations are at 55º to optimize performance in temperate and tropical regions of high activity. This results in low satellite elevation angles in polar areas, with approximately 45º being the highest satellite elevation angle possible at the poles. Data for satellites at low-elevation angles are more susceptible to ionospheric refraction and provide especially poor geometry for determination of a vertical position. The overall effect is minor for surface platform navigation, but it may be problematic for precision surveying and certain aircraft operations.
GPS coverage for surface navigation is only slightly degraded in the high latitudes (50 ft. horizontal precision has been demonstrated at the North Pole), but this accuracy is adequate for the navigational purposes of surface ships, aircraft, and submarines rising to the surface to obtain a navigation fix for undersea navigation systems. On the other hand, the degradation in vertical dilution of precision (VDOP) is much more significant and can result in altitude errors of up to 150 to 250 feet, which in turn could affect some Navy operations or system performance. Due to low-elevation angles, some attention to ensure clear lines of sight for the GPS antenna orientation is warranted for optimum performance.