📚 Echo Sounding: Principles, Calculations and Applications | 回声测深：原理、计算与应用
Echo sounding is a method of using reflected sound waves to determine the depth of water or the distance to an object. A pulse of sound is emitted, travels through a medium, reflects from a boundary, and returns to a detector. By measuring the time interval between emission and reception and knowing the speed of sound, the distance can be calculated. This technique underpins SONAR, medical ultrasound and industrial testing, and is a standard application of wave reflection in the CIE A-Level Physics syllabus.
回声测深是一种利用反射声波来测定水深或物体距离的方法。发射一个声脉冲，声波在介质中传播，遇到边界反射后被探测器接收。通过测量发射与接收之间的时间间隔，并已知声速，就可以计算距离。该技术是声呐、医学超声和工业检测的基础，也是 CIE A-Level 物理大纲中波的反射的标准应用。
1. What Is Echo Sounding? | 什么是回声测深？
Echo sounding is a distance-measuring technique that uses the reflection of sound. A transmitter sends a short pulse of sound towards a boundary, such as the seabed. The pulse travels through the medium, reflects at the boundary, and returns to a receiver. The total time between transmission and reception is measured, and the distance to the boundary is calculated from the known speed of sound.
回声测深是一种利用声音反射来测量距离的技术。发射器向边界（例如海底）发送一个短声脉冲。脉冲在介质中传播，在边界处反射，然后返回接收器。测量发射和接收之间的总时间，并根据已知声速计算到边界的距离。
In CIE A-Level Physics, echo sounding appears under wave properties and applications of sound. It is a direct application of the wave equation and reflection. The method is sometimes called echo ranging or echo location because it locates a boundary by timing the return of an echo.
在 CIE A-Level 物理中，回声测深出现在波的性质和声音应用部分。它是波动方程和反射的直接应用。该方法有时被称为回声测距或回声定位，因为它通过测量回声返回的时间来确定边界的位置。
2. The Wave Physics Behind an Echo | 回声背后的波动物理学
Sound is a longitudinal mechanical wave, so it requires a medium and travels as a series of compressions and rarefactions. When a sound wave meets a boundary between two materials with different acoustic properties, part of the wave energy is reflected and part is transmitted. The reflected part forms the echo.
声音是一种纵波，属于机械波，因此需要介质，并以一系列疏密波的形式传播。当声波遇到声学性质不同的两种材料之间的边界时，部分波能会被反射，部分会透射。反射的部分形成回声。
The strength of the echo depends on the acoustic impedance mismatch between the two media. A large difference, such as water-to-rock or water-to-air, produces a strong reflection. A small difference produces a weak reflection. Echo sounding relies on detecting this reflected pulse.
回声的强度取决于两种介质的声阻抗差异。差异越大（例如水与岩石或水与空气），反射越强。差异越小
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