How to study Antarctic ice without blowing it up
不用炸药，怎样看清南极冰层？
一辆承担运输任务的极地履带车，还能成为研究冰层的工具。文章先解释需要看清什么，再介绍传统方法的代价、替代声源的试验与比较。精读重点是沿着“问题—机制—限制—验证”读懂方法改进，同时保留研究结论的适用范围。
原文来源：The Economist
学习目标
- 解释声音信号为何能够帮助重建冰雪内部结构
- 拆解倒装、长主语和多层宾语从句
- 辨认比较对象与替代词those的指代
- 用证据和限定语概括实验结果
中英对照阅读
THE PISTENBULLY 300 Polar Antarctic vehicle is a 8.5-tonne heavy-duty specialised monster built to withstand extreme polar conditions. It features wide tracks, massive pulling strength, powerful cranes and multi-purpose tools designed for the toughest ice and snow operations. No Antarctic base should be without one. Research led by Liu Guofeng at China University of Geosciences in Beijing, however, suggests the PistenBully may be capable of more than just fetching and carrying. As Dr Liu writes in the Journal of Glaciology, it is also able to do actual science.
PistenBully 300 Polar南极作业车是一台重8.5吨的重型专用“巨兽”，为承受极端极地条件而造。 它配有宽阔的履带、强大的牵引力、有力的起重装置，以及为最艰苦冰雪作业设计的多用途工具。 任何南极科考站都不应缺少这样一辆车。 不过，北京的中国地质大学由Liu Guofeng带领开展的研究表明，PistenBully的本领可能不只限于取东西和搬运。 正如Liu博士在《冰川学杂志》中所写，它还能真正参与科学研究。
Antarctica’s ice sheet is the largest reservoir of freshwater on Earth, but it is shrinking. Just above the ice proper, but below the surface snow, is a transition zone 50-100 metres thick called the firn layer. This is where snow is compressed into ice. It is also where meltwater from above is captured in pores and refrozen. Knowing the firn layer’s exact thickness and understanding how it behaves is crucial to predicting what will happen, over the long term, to the ice sheet and thus to the world’s sea levels. Visualising this subsurface melange is difficult, though.
南极冰盖是地球上最大的淡水储库，但它正在缩小。 在真正的冰体上方、表层积雪下方，有一个厚50至100米的过渡带，称为粒雪层。 积雪在这里被压实成冰。 上方流下的融水也会在这里被困在孔隙中，重新冻结。 要预测从长远看冰盖、进而全球海平面将如何变化，了解粒雪层的确切厚度及其行为至关重要。 不过，要让这层表层以下混合物的结构显现出来并不容易。
Current practice, borrowed from oil- and gas-prospecting, is to use an “active source”. This is geologist-speak for dropping a stick of dynamite down a drill hole and listening to the explosion’s sound, propagated through the rock—or, in this case, ice. The listening is done by sensors called geophones. Since sound travels at different speeds through water, ice and snow, a computer analysis of when and how powerfully the echoes arrive at different geophones permits construction of a high-resolution image of the firn layer.
目前采用的方法借鉴自油气勘探，是使用一种“主动声源”。 地质学家的这套说法，指的是把一根条状炸药放入钻孔，监听爆炸产生的声音在岩石——在这里则是冰——中传播的情况。 承担监听任务的是称为地震检波器的传感器。 由于声音在水、冰和雪中的传播速度不同，计算机分析回声何时、以多大强度到达不同检波器，便能据此构建粒雪层的高分辨率图像。
This works, but is not ideal. First, someone has to drill the hole down which to drop the dynamite. That is not always possible in polar conditions. Then, the explosive must be purchased, brought to Antarctica and the actual dropping carried out. Moreover, detonating dynamite in sensitive environments is not to be done lightly. An alternative source of sound would thus be good. And, after hearing the din created by a convoy of PistenBullys, Dr Liu thought they might be the very thing.
这个办法有效，却并不理想。 首先，得有人钻出一个可向下放入炸药的孔。 极地条件下，这并不总能做到。 接着，必须采购炸药、将其运到南极，并实际完成投放。 此外，在脆弱环境中引爆炸药，也不能轻率为之。 因此，如果能有另一种声源就好了。 听到一队PistenBully车辆发出的喧闹声后，Liu博士觉得它们或许正是所需的东西。
To this end, he and his colleagues experimented with geophones already in place in the Larsemann Hills of East Antarctica. They commandeered some PistenBullys and arranged for them to be driven around the hills. They found that if the vehicles were sent along both sides of a line of geophones, parallel with the sensors, they got the effect they were after.
为此，他和同事利用已经布设在东南极拉斯曼丘陵的检波器展开试验。 他们调来了一些PistenBully车辆，并安排车辆绕着丘陵行驶。 他们发现，让车辆沿一列检波器的两侧、平行于传感器排列方向行驶，就能得到他们想要的效果。
Since the Larsemann Hills’ firn had already been mapped the old-fashioned way, Dr Liu was able to compare his machine-created images with those obtained using dynamite. They were pretty much identical. He thus seems to have devised a way of mapping the firn’s structure that is simpler than blowing it up, but equally good.
由于拉斯曼丘陵的粒雪层此前已用传统方法绘制成图，Liu博士能够把车辆声源生成的图像与用炸药取得的图像作比较。 两者几乎完全一样。 因此，他似乎设计出了一种描绘粒雪层结构的方法，比用炸药更简单，却同样有效。