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Echolocation

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Echolocation

Have you ever heard that bats use echolocation to understand their surroundings? Since they are generally nocturnal with poor vision, they use sound in order to probe their environment, making them a deadly night-time predator. But how is this possible? In this article, we will discuss the meaning of echolocation, how it works, where it is used, and we will cover some examples.

Meaning of echolocation

The meaning of echolocation is already in the word itself.

Echolocation is the use of echoes, i.e. reflected sound, to locate objects.

How echolocation works

The basic principles behind echolocation are the constant nature of the speed of sound through a given medium (another word for material) and the fact that sound waves partially get reflected off of interfaces (another word for boundary surfaces) between different mediums. The idea is to produce a sound travelling in a particular direction, wait until you hear its echo, and then calculate the distance the sound has travelled. This can be done using the equation of constant motion:

,

or, in symbolic form,

,

whereis the distance the sound has travelled in metres,is the speed of sound through the medium that the sound is travelling through in metres per second, andis the time between producing the sound and hearing its echo in seconds. The distanceto the object that the sound reflected off is given by, because the sound will have travelled twice that distance once you hear the echo:

.

See the figure below for a schematic representation of echolocation.

Echolocation Diagram showing how bats use echolocation StudySmarterA bat is producing the sound indicated with blue, and the echo through reflection off of the prey is indicated with red, Wikimedia Commons Public Domain

You are in an empty and quiet space, and there is a big wall facing you. You want to know how far away it is, so you clap your hands and record the time that passes until you hear an echo. You see that it took. You conveniently know the speed of sound in air to be, so you calculate the distanceto the wall as follows:

.

You conclude that the wall isaway from you.

Extra information from echolocation

This is not the only information that can be gathered from an echo. In addition, by employing knowledge of the Doppler effect, the frequency of the echo compared to the frequency of the original sound gives information about the velocity of the object. Furthermore, the loudness of the echo (the amplitude of the sound wave) can be used to gather information about the reflection of the sound wave, which is influenced heavily by the density of the object. Therefore, the density of the detected object can also be determined. Lastly, if you can determine the direction of objects (see below for how animals do this), then you can also determine the size of objects by seeing in which directions the object is present (bear in mind that you already know how far away the object is, so some simple trigonometry will give you a size).

Uses of echolocation

Echolocation is used by animals and ships, but it is also used in medicine. One part of a ship's use of sonar is the use of echolocation. A ship can send an ultrasonic sound wave (i.e. of a frequency higher than, outside the range of human hearing) through the water, and detect its echo. This way, it can map objects that are around the ship as well as the seabed, and it uses this information to navigate.

In medicine, an ultrasound scan can be used to look at an unborn baby. For this, we use equipment that emits ultrasound waves and can also detect them. The soundwaves will reflect off of tissue boundaries, so the equipment can form a 3-dimensional image of where all the tissue boundaries are. This way, it can construct a complete image of the baby inside the womb. This is also a form of echolocation. See the article on applications of ultrasound for more information on the use of echolocation by ships and in the medical field.

Uses of echolocation by animals

Echolocation common shrews StudySmarterThese Eurasian (or common) shrews use echolocation to detect their insect prey at night in dense undergrowth. The shrew's eyesight is very poor, so it relies heavily on echolocation to understand its surroundings, Wikimedia Commons CC BY-SA 3.0

Some animals that use echolocation are bats, some birds, whales, some shrews, and even some blind people. Using echolocation means that you don't have to rely on your eyesight to navigate. For all animals, this is useful during the night-time. For animals that live underwater, this is also useful during the daytime, because light does not travel very far through water, while sound does. Thus, whales are able to "see" a lot further using echolocation than using their eyes, which is highly beneficial in the vast oceans.

Echolocation sound

In general, the sounds produced by animals for echolocation are very loud so that they can perceive objects that are far away, and very high-frequency (mostly ultrasonic) because high pitches give information with better resolution (this can be compared to lightwave resolution and the use of scanning electron microscopes).

Echolocation types

All echolocation is based on the same principle. One could choose to differentiate between biological and technological echolocation and call them different types. One could also choose to differentiate between what medium is used for the sound to travel through, which would categorise bats (air) and whales (water) into using different echolocation types. There is also a big difference in how animals determine the position of objects.

Dolphins have a special organ that concentrates their sound into a beam travelling in a particular direction. If an echo is heard, this must come from an object in that direction. Dolphins can 'scan' a whole animal by producing sound beams in multiple directions, and are able to tell different animal species apart via this method.

Echolocation dolphin sound beam StudySmarterEcholocation used by a dolphin, where the organ above its jaws produces the concentrated beam of sound, Wikimedia Commons CC BY-SA 3.0

Alternatively, bats emit sound in all directions (they effectively just scream), but they use the fact that they have two ears to determine the direction that an echo is coming from, and the difference in timing and loudness that both ears perceive gives the bats the information they need. For example, if the right ear hears the echo before the left ear, then the echo must come from the right, so the object must be to the right. This is also how humans can interpret the direction of a sound.

Examples of echolocation

For these examples, assume that the speed of sound is aboutthrough water and aboutthrough air.

A dolphin produces a short sound burst of, and aftershe hears an echo. How far away is the object that the dolphin just perceived?

Answer: The dolphin lives underwater, so sound will travel at the speed of sound in water,. We calculate the distancefrom the dolphin to the object by using the formula relating the travel distanceof the sound, the echo time, and the speed of sound in the medium:

.

We conclude that the perceived object isaway from the dolphin.

A bat produces a screech and afterhe hears an echo. His left ear picks up the sound earlier than his right ear. How far away is the perceived object from the bat and what direction is it in?

Answer: The sound from the echo is coming from the left, so the object is to the left of the bat. The bat is on land or flying in the air, so the sound will travel through the air. We calculate:

.

We conclude that the perceived object isaway from the bat.

Echolocation - Key takeaways

  • Echolocation is the use of echoes, i.e. reflected sound, to locate objects.
  • Ifis the speed of sound in the correct medium andis the time between producing the sound and hearing the echo, then the distanceto the perceived object is given by .
  • Echolocation can also provide information about the velocity, density, and size of an object.
  • Animals and ships use echolocation to map their surroundings. It is an alternative to eyesight.
  • The sounds produced for echolocation are generally loud and ultrasonic.
  • There is no standard differentiation of echolocation into types, but there are differences in how animals use echolocation.
  • Make sure to use the correct speed of sound in your calculations.

Frequently Asked Questions about Echolocation

Echolocation is the use of echoes, i.e. reflected sound, to locate objects.

Echolocation works by producing a sound and measuring how much time passes before you hear an echo. This tells you how far away the object is.

Examples of echolocation are bats, whales and other animals using it to detect prey and predators, but also boats using it as part of their sonar to map the underwater world.

Some blind people have managed to develop a basic version of echolocation, so yes, this is possible with practice.

Echolocation cannot be divided into a standard list of types, but some difference between uses of echolocation are the sound medium, the production of the sound, the perception of the echo, and the pitch and intervals of the original sound.

Final Echolocation Quiz

Question

Which things are essential for echolocation?

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Answer

A wave

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Question

Describe the process of echolocation.

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Answer

1. Make a sound
2. Wait until you hear its echo
3. Calculate the distance to the object (based on the speed of sound in the right medium and the time between making the sound and hearing the echo)

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Question

If the speed of sound is constant, why don't we always use the same value in the formulas for echolocation?

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Answer

Because - although it is constant within a specific medium - the speed of sound is different for every medium. We need to know through which medium the sound is travelling before we can fill in a value.

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Question

A bat screeched, and it hears an echo first in its left ear and then another in the right. On which side is the object that is closest to the bat?

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Answer

On its left.

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Question

Why do you need at least two ears to get information about the direction of an object using echolocation if (like bats)  you can't produce directed sound beams?

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Answer

You will need to know the direction of the echo, and this is only possible by measuring the timing difference of the echo's arrival between multiple ears.

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Question

What information other than position can you gather about an object using echolocation?

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Answer

Velocity, size, and density.

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Question

Why is echolocation useful underwater during the day?

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Answer

Light does not get transmitted well through water, so your sight is limited to a couple of meters. Sound waves travel much further, so you can map a much bigger chunk of your surroundings using echolocation.

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Question

Echolocation ALWAYS uses sound.

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Answer

True

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Question

Define echolocation.

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Answer

Echolocation is the use of echoes, i.e. reflected sound, to locate objects.

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Question

Name one biological and one physical reason why echolocation sounds are mostly ultrasonic.

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Answer

1. Other animals (predators and prey) cannot hear where you are.
2. Higher frequency waves provide a higher resolution mapping.

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Question

Do you think a ship has only 1 or many microphones for the purpose of detecting echoes?

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Answer

Ships always have multiple microphones, so they can know the direction of the objects they detect. If you spot a dangerous underwater rock, you want to know where it is!

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Question

Why can't all animals echolocate?

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Answer

You need to produce your own (loud) sound in order to echolocate. This costs valuable energy compared to standard vision, which simply uses light waves that were reflected by objects and created by the Sun.

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