The catch is that because low-frequency waves can travel great distances, when they do bounce off cavities or objects underground, they often end up far from the detection equipment at the surface.

捕捉过程是这样的，因为低频波可以传输到更远的距离，当它们遇到地下的空穴或其他物体反射回来的时候，已经距地面的接收装置很远了。

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What is needed is a system that USES low-frequency radio waves.

这需要的是一种利用低频无线电波的系统。

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The other problem is that submarines receive messages using low-frequency radio waves that can penetrate water, but only a few characters per second can be transmitted at these frequencies.

另一个问题时潜艇在水下时用低频进行通信，因为低频可以穿透海水传播，但用低频通信时，通信速度只能每秒几个字符。

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Because of the distance that low-frequency sound waves can travel under water, a set of four ships emitting sound at 235 decibels could monitor 80% of the world's oceans for submarines.

ECONOMIST: The American navy may soon have a whale of a problem

Although they have not been found to cause any harm, the cables on conventional pylons, which transmit a three-phase alternating current, generate a strong electric field and a continuous buzz of low-frequency radio waves.

ECONOMIST: Monitor

The nuclear test monitors pick up "infrasound", or low frequency, waves from about 20 meteors a year -- "if conditions are right, perhaps as small as a pea, " she said.

CNN: Planet of sound: Meteor blast resonated around Earth