THE FIRST casualty of war is truth. But a reliable GPS signal comes a close second(紧随其后). Jamming(干扰) signals from a global navigation satellite system (GNSS), such as America’s GPS, is so easy it has become common when the shooting starts. Stronger signals from newer kit can make jamming harder, but the potential scale of the threat now looks much greater than previously thought. A paper posted in June by a team led by Todd Humphreys of the University of Texas, Austin, traced scores of broad GPS disruptions across Europe and elsewhere since 2019 to a constellation of Russian satellites.(今年6月，德克萨斯大学奥斯汀分校的托德·汉弗莱斯领导团队发表的一篇论文，将2019年以来欧洲及其他地区数十起大范围GPS中断事件追溯到一个俄罗斯卫星星座。) Jamming or even inadvertent(无意的) interference from space, the research suggests, could affect an entire continent.
战争的第一牺牲品是真相，而可靠的GPS信号紧随其后。干扰全球导航卫星系统（GNSS）的信号——例如美国的GPS——如此容易，以至于一旦开火，干扰便成为常态。来自新装备的更强信号可以使干扰更难，但威胁的潜在规模现在看起来比之前想象的要大得多。今年6月，德克萨斯大学奥斯汀分校的托德·汉弗莱斯领导团队发表的一篇论文，将2019年以来欧洲及其他地区数十起大范围GPS中断事件追溯到一个俄罗斯卫星星座。研究表明，来自太空的干扰甚至无意干扰，可能影响整个大陆。
One alternative to GNSS is simply to mount cameras on a craft and use software to keep track of the terrain below. But that works only over land, and can be stymied(阻碍) by cloud cover, haze or darkness. So two other, quite different, methods are under investigation. One employs quantum phenomena—the angular momentum of photons and the spin of electrons—to follow magnetic maps of Earth’s surface.(一种利用量子现象——光子的角动量和电子的自旋——来跟随地球表面的磁场图。) The other establishes an observer’s position by tapping(利用) ambient(周围的) radio waves broadcast for other purposes. Neither method can yet match the precision of GNSS, but both are becoming credible backups.
GNSS的一种替代方案是在飞行器上安装摄像头，并使用软件跟踪下方的地形。但这只在陆地上有效，且可能被云层、雾霾或黑暗所阻碍。因此，另外两种截然不同的方法正在研究中。一种利用量子现象——光子的角动量和电子的自旋——来跟随地球表面的磁场图。另一种通过利用为其他目的广播的环境无线电波来确定观察者的位置。这两种方法目前都无法达到GNSS的精度，但都在成为可靠的备份。
Many rocks are weakly magnetic, and their distribution in Earth’s crust results in irregularities in the planet’s magnetic field. The resulting landscape of anomalies(异常) is detectable under almost any conditions, and equally well over land and sea. Fit a plane with a magnetometer capable of spotting these anomalies, and a magnetic navigation (MagNav) system that can match them to existing maps, and its position can be accurately plotted.(给飞机配备能够发现这些异常的磁力计，以及能够将它们与现有地图匹配的磁导航（MagNav）系统，其位置就能被精确标绘。) Last year Q-CTRL(澳大利亚量子技术公司), an Australian firm, demonstrated a MagNav system that was more accurate than a leading GPS alternative in a trial flight over New South Wales.
许多岩石具有弱磁性，它们在地壳中的分布导致地球磁场出现不规则性。由此产生的异常景观几乎在任何条件下都可探测到，在陆地和海洋上同样有效。给飞机配备能够发现这些异常的磁力计，以及能够将它们与现有地图匹配的磁导航（MagNav）系统，其位置就能被精确标绘。去年，澳大利亚公司Q-CTRL在新南威尔士州的一次试飞中展示了一套MagNav系统，其精度超过了领先的GPS替代方案。