你知道，如果你想测量重力场，中某种东西的势能，你需要，在某处定义一个零点，对吧？

You know, if you want to measure the potential energy of something in a gravitational field, you have to define the zero somewhere, right, because it's arbitrary.

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这使得当这颗卫星在大约255公里的海拔高度上围绕地球盘旋时，能以高的精度测量重力。

This allows gravity to be measured with great precision as the satellite circles Earth at an altitude of approximately 255 kilometres.

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讨论了应用GPS测量重力点的大地高，从而获得地面点的扰动重力（或称纯重力异常）值这样新的重力边值条件，如何从理论与实际上确定重力场的问题。

This paper discusses the problem of gravity field determination by application of such a new gravity boundary condition as the disturbing gravity by use of GPS.

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You know, if you want to measure the potential energy of something in a gravitational field, you have to define the zero somewhere, right, because it's arbitrary. You can set it anywhere you want. It's the same with enthalpy.

你知道，如果你想测量重力场,中某种东西的势能，你需要，在某处定义一个零点，对吧？,因为势能的值是任意的,你可以把它设定在。

麻省理工公开课 - 热力学与动力学课程节选