2021年经济学人 海神的召唤(1)

Oceanic cartography

绘制海洋地图

Full fathom¹ five

海神的召唤

How to map the seabed from the sky

如何从空中绘制海底地图

An alien seeking a name for the third planet from the sun might reasonably plump for "Sea" or "Ocean", rather than "Earth". Two-thirds of its surface is covered by salt water, and its predominant colour, viewed from far away in space, is blue. What underlies² all this brine, though, remains³ surprisingly mysterious to the planet's ape-descended inhabitants. As recently as 2019, for example, researchers found several thousand new underwater mountains, known as seamounts, by measuring the effects of their gravity on the ocean's surface. More such discoveries almost certainly await.

外星人在为太阳外的第三颗行星命名时可能会选择“Sea”或“Ocean”，而不是“Earth”。因为它的表面有三分之二被海水覆盖，从太空远处望过去它的主色是蓝色。然而，对于生活在这个星球上由猿类进化而来的居民来说，这些海水的背后仍然是个谜。例如，就在2019年，研究人员通过测量海洋表面重力的影响发现了数千座新的水下山脉，即所谓的海山。几乎可以肯定的是，有更多这样的发现在向我们招手。

One important reason for ignorance about the seabed is the lack of a tool that can easily map its topography from an aircraft flying above the water. That, though, is about to change. Researchers at Stanford University, led by Amin Arbabian, an electrical engineer, have developed what they call the Photoacoustic Airborne Sonar System, PASS. This makes it possible to scan the ocean floor rapidly, from a helicopter, rather than relying on a slow-moving ship or submarine.

海床被忽视的一个重要原因是：人们缺乏一种可以在水上飞行的飞机上绘制出海床地形的工具。不过，这种情况即将改变。在电子工程师阿敏·阿巴比亚的带领下，斯坦福大学的研究人员已经开发出了他们所谓的光声机载声纳系统PASS，使得从直升机上快速扫描海底而非依靠缓慢移动的船只或潜艇成为可能。

The problem to be solved is that sound waves, in the form of sonar, are the only reasonable way to accomplish such mapping. Both light beams and the radio waves of radar⁴ are rapidly absorbed by water. Sound, by contrast, propagates well. What it does not do well is cross the boundary between water and air. When this happens its amplitude⁵ is diminished a millionfold. That diminution⁶ applies in both directions, so a pulse of sonar broadcast from an aircraft and reflected back to it from the sea floor would have a trillionth of its original amplitude. Expecting to detect such a reflection would be a fool's errand.

需要解决的问题是，声纳形式的声波是完成这种测绘的唯一合理方式，光束和雷达的无线电波都会被水迅速吸收，相比之下声音传播的效果会更好，它的缺点是无法很好地跨越水和空气之间的边界，这种情况下它的振幅会减小一百万倍，这种减小会发生在来往两个过程中，所以从飞机发出的声纳脉冲再从海底反射回飞机时其振幅只有原来的万亿分之一，因此期望探测到这样的反射是徒劳的。

PASS partly overcomes the air-sea boundary problem by circumventing⁷ the first of those crossings. It does so by generating the sonar pulses not on board the aircraft but rather in the water itself, using intense bursts of laser light fired at the water's surface. These heat the water, causing rapid expansion. That generates a sound wave which propagates to the sea floor, whence it is reflected back to the surface. Only then does it cross the energysapping interface⁸ between water and air. Though that still weakens the signal a lot, the other part of PASS, a device called a CMUT, is sensitive enough to detect it.

PASS通过绕过第一个交叉点克服了海空的边界问题。它并不是在飞机上产生声纳脉冲，而是用强烈的激光射向水面从而在水里产生声纳脉冲，使得海水变热，迅速膨胀。之后产生声波，声波传播到海底，然后又反射回海面，只有这样声波才能穿过水和空气之间的能量消耗边界。尽管信号仍会被大大削弱，但PASS的另外一部分(一种叫做CMUT的设备)已经足够灵敏，完全可以检测到信号。

1 fathom   

v.领悟，彻底了解

参考例句：

• I really couldn't fathom what he was talking about.我真搞不懂他在说些什么。
• What these people hoped to achieve is hard to fathom.这些人希望实现些什么目标难以揣测。

2 underlies   

v.位于或存在于（某物）之下( underlie的第三人称单数 )；构成…的基础（或起因），引起

参考例句：

• I think a lack of confidence underlies his manner. 我认为他表现出的态度是因为他缺乏信心。 来自《简明英汉词典》
• Try to figure out what feeling underlies your anger. 努力找出你的愤怒之下潜藏的情感。 来自辞典例句

3 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

4 radar   

n.雷达，无线电探测器

参考例句：

• They are following the flight of an aircraft by radar.他们正在用雷达追踪一架飞机的飞行。
• Enemy ships were detected on the radar.敌舰的影像已显现在雷达上。

5 amplitude   

n.广大；充足；振幅

参考例句：

• The amplitude of the vibration determines the loudness of the sound.振动幅度的大小决定声音的大小。
• The amplitude at the driven end is fixed by the driving mechanism.由于驱动机构的作用,使驱动端的振幅保持不变。

6 diminution   

n.减少；变小

参考例句：

• They hope for a small diminution in taxes.他们希望捐税能稍有减少。
• He experienced no diminution of his physical strength.他并未感觉体力衰落。

7 circumventing   

v.设法克服或避免（某事物），回避( circumvent的现在分词 )；绕过，绕行，绕道旅行

参考例句：

• They found a way of circumventing the law. 他们找到了规避法律的途径。
• This viewpoint sees the Multinational Corporation as capable of circumventing or subverting national objectives and policies. 这种观点认为，跨国公司能够遏制和破坏国家的目标和政策。 来自辞典例句

8 interface   

n.接合部位，分界面；v.(使)互相联系

参考例句：

• My computer has a network interface,which allows me to get to other computers.我的计算机有网络接口可以与其它计算机连在一起。
• This program has perspicuous interface and extensive application. 该程序界面明了，适用范围广。