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Returning echoes
(by Danny Zurc & Alejandro Valencia-Tobon)

Most bats emit and detect ultrasound signals while flying, in a process known as ‘echolocation’ (they have an active sonar system). The principle behind echolocation is to emit high-frequency signals (in bats, mainly ultrasonic signals above 20 kHz) and then analyse those returning echoes. By detecting such returning echoes, bats can recognise, classify and localise those objects that reflected back sound signals.

The problem is that bats confront multitude of issues and masking effects while flying; for example: dealing with external noise, clutter echoes, sound signals emitted by other bats, and the physical effects (temperature, humidity and distance) that generate an atmospheric attenuation of sound. Such ecological constraints have meant a selection pressure which seem to have led to an adaptation process in which ultrasound signals appear to be unique to each species. Biologists came to this conclusion by comparing narrowband and broadband components of echolocation signals.

Note: similar echolocation principle is used by humans. For example, blind people can make mouth click sounds and use the returning echoes to locate possible obstacles. Other applications include submarine sonar systems and the detection of underwater mining, and the ultrasound scan that physicians use to obtained medical images of different organs.

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