I, like a lot of others, believe that Dark Knight is a cornerstone in modern cinema. Why? Reasons are easy to find. A casual watch of the movie will delight you with its story, character development, gadgets etc but you need to watch it very closely to fully appreciate the amount of time and effort devoted into each and every scene. Be it the scene where batman is gliding through a tall building by converting his cape into a glider, or the scene where “Bat Cycle” does an incredible job of toppling off an entire truck. But the sequence which held my imagination was where Batman maps the entire city to locate joker by turning every phone in Gotham City into a high frequency generator which works more or less on the principle of SONAR.

City-wide surveillance system in Bat Cave
Real time mapping & Visual Feed

Now think for a moment and try to find the source where Christopher Nolan might have had the inspiration to imagine something like this. The answer my friend are Bats! Doesn’t sound that surprising right? (Whine 1: It’s a Batman movie for God’s sake! what else you expect?) Yeah! but I just could not help but to appreciate Nolan’s idea and wonder whether such a thing could exist in reality. If yes! then in what form will it be? Who is supposed to use it? Who will care about the privacy issues? And many other irrelevant question as you might be thinking that this technology is a far-flung futuristic stuff. Hold on mate as tech is about to get real.

Bats have been using this technique (also known as echolocation) since their birth much similar to a human child opening his/her eyes to understand the world around. Microbats (this type of bats don’t have any eyes) use echolocation to navigate and forage, often in total darkness by emitting frequencies from 14,000 to well over 100,000 Hz, mostly beyond the range of the human ear (typical human hearing range is considered to be from 20 Hz to 20,000 Hz)

Wavelength employed has to be less than the size of prey

A bats brain computes the time it takes to receive the send signal taking into consideration the Doppler Effect (you know the change in shrillness of sound when a train is approaching you, in this case high frequency sound will be heard, or leaving you. See the infographic for better understanding) for sound and precisely calculates the spatial location of the prey.

An Inforgraphic on Doppler Effect in sound waves by Ryo Kuwabara (2013)

Whine 2: Why can’t humans have this echolocation embedded into our auditory system? This video shows how brains of young bats are hard-wired to recognize any flat surface as a surface of water. Hence echolocation certainely has its disadvanteges but so far has worked well enough for bats living in their niche considering that any light based mapping system will be redundant as bats live in dark caves where light is a distant phenomenon.


Researchers at the Swiss Federal Institute of Technology in Lausanne have successfully mapped the dimensions of a closed area by measuring “room impulse responses.” At the most basic level, they blast a noise out of a speaker and then use the microphones to record what happens when the sound waves bounce off of the room’s walls, ceiling, floor, and any other objects. In this way, it’s really similar to how a bat, dolphin, or superhuman uses echolocation.

The algorithm determines the correct combination of echoes and assign them to corresponding walls. So far, the team has tested the algorithm successfully in a small lecture room—an adjustable wall even allowed them to change the shape of the room to test various scenarios. This technology has immediate applications in virtual reality, architectural acoustics, audio forensics, teleconferencing, and indoor localization. This last one could be really cool, since the algorithm can be reversed if the building’s dimensions are already known. So don’t be surprised if someday soon there’s an orientation app that uses acoustic vibrations to guide you around a museum, office building, or airport.

Quick Review

SONAR is not a new thing, animals like bats have been using it since ages now humans have started to realise its applications augmenting the present spatial mapping plateforms. What Nolan potrayed in Dark Knight is already a theme for research and we have succesfully imaged rooms, pillars and even cathedrals. The future is probably not that far as you think.

Key Words:  Acoustical Mapping, High Frequency Generator, Animal Echolocation




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