原子钟的地球物理适用性：直接大陆大地水准面制图
Geophysical applicability of atomic clocks: direct continental geoid mapping
摘要：
大地水准面是地球的真实物理图形，是地球重力场的一个特殊的等势面，它能解释所有地下密度变化的影响。它的形状最接近（在最小二乘意义上）海洋的平均水平，但大地水准面在大陆上更难以确定。卫星飞行任务进行距离测量并得出重力场，以提供全球大地水准面图。然而，它们需要校准和大量的计算，包括积分，这是一个非唯一的操作。在这里，我们提出了一个直接的方法和一个新的工具，直接测量地球位势差异的大陆使用原子钟。广义相对论预测，在海平面上的时钟频率是恒定的，而且更快（分别是）。更慢）时钟速率高于（相应地，低于海平面。原子钟技术即将达到钟速精度水平，即在确定等势面（包括大地水准面）高度时相当于1厘米。我们讨论了这种测量的价值和未来的适用性，包括直接大地水准面映射大陆，联合重力和地球位测量反演地下密度异常。我们的综合计算表明，一个半径为1.5公里，密度异常为20%的球体埋在地壳中2公里深处，引起的大地水准面扰动已经可以检测到的原子钟的可实现的精度。因此，原子钟地球势测量与相对重力数据一起使用，利用其不同的深度灵敏度，可以成为测绘地球内部密度异常的有用工具。
英文摘要：
The geoid is the true physical figure of the Earth, a particular equipotential surface of the gravity field of the Earth that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General Relativity Theory predicts constant clock rate at sea level, and faster (resp. slower) clock rate above (resp. below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate that is equivalent to 1 cm in determining equipotential surface (including geoid) height. We discuss the value and future applicability of such measurements including direct geoid mapping on continents, and joint gravity and geopotential surveying to invert for subsurface density anomalies. Our synthetic calculations show that the geoid perturbation caused by a 1.5 km radius sphere with 20% density anomaly buried at 2 km depth in the crust of the Earth is already detectable by atomic clocks of achievable accuracy. Therefore atomic clock geopotential surveys, used together with relative gravity data to benefit from their different depth sensitivities, can become a useful tool in mapping density anomalies within the Earth.
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