The overlying strata of the coal bed roof are dominated by sedimentary rocks such as shale, sand stone and limestone, whose physical and mechanic properties differ greatly.

煤层顶板覆岩一般以页岩、砂岩、灰岩等沉积岩为主，其物理力学性质差异很大。

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The major pay bed is low permeable ultra dense sandstone. Its permeability and pore throat texture are very sensitive to the net pressure of overlying strata.

主要产层为低渗透超致密砂岩，其渗透率和孔喉结构对上覆地层净压力很敏感。

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The preconditioned fastest descent means in inversion achieves simultaneous in - versions of overlying-bed velocity and refractor depth.

反演过程中利用具先决的最速下降法，可解决覆盖层速度和折射界面深度同时反演问题。

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So by firing radio pulses through the overlying sheet and recording the return echoes, scientists can plot both the depth of the rock bed and - by definition - the thickness of the ice covering.

BBC: Antarctic ice volume measured