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One such satellite, NASA's ICESat, carries a laser altimeter to measure the height of the ice surface.

其中的一颗卫星，美国宇航局的icesat就携带着一个激光高度探测仪来探测冰面的高度。

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Ice crystals form on the leaf surface.

VOA: special.2010.01.12

The men could not climb out, because the ice surface was nearly vertical, and they huddled together for warmth.

NEWYORKER: Neptune��s Navy

Satellites have long been used to track ice extent (area), but calculating the thickness of the marine floes requires the overflying spacecraft to gauge the difference between the top of the ice surface and the top of the water - a relatively simple calculation then gives the overall volume.

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The torpedo-shaped instrument gathers data about the difference between the level of the seawater beneath the ice and the surface of the ice itself.

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