Navigating without GPS

摘要

The military has become increasingly dependent on Global Positioning Systems (GPS) for accurate and precise positioning, navigation and timing (PNT) in a wide variety of operational environments -- from tactical vehicles to GPS-guided missiles. However, as military operations are increasingly carried out in areas where GPS is denied, unreliable or not accessible, military use of GPS has evolved from being a strategic advantage to a vulnerability. Many environments in which the military operates -- such as buildings, urban canyons, under dense foliage, underwater and underground -- have limited or no GPS access. Moreover, adversaries can easily block GPS access by jamming, spoofing and other GPS-denial threats.