Interferometry and the Very Large Array

Congratulations! You’ve just been hired to record the crowd at the Super Bowl!

The producer wants you to figure out how loud each section, and ideally how loud each fan, is cheering so that they can better choose where to station the T-shirt cannons. They don’t want to know the actual dialogue – they’re not the NSA – only each fan’s loudness, or amplitude*. You don’t even have to record the fans’ cheering over time, but just how loud each one is, on average, over the full game.

*technically, loudness is a psychoacoustic property of the amplitude, the average intensity, and the frequency spectrum of the signal, but in this article we’re assuming (for the purposes of keeping it relatively short) that they’re essentially the same.

The only problem?

You’re on the other side of the field, 160 feet away from the nearest spectator. And you have one microphone with which to record all twenty thousand fans.

Source: Getty Images

Hi! This is an introduction to astronomical interferometry and radio telescopy! This article might assume that you have some familiarity with Fourier transforms, but that’s about it. This article is currently in beta; if you find any issues, errors, or omissions, please let me know through the comments below. Thanks!