Let’s say you were playing with a metal bucket in the sand. Your parents call you back home for dinner, and it starts raining. By the time you come back outside, oh no! The metal bucket has been buried in the mud. How would you find it?

You could dig holes randomly around your backyard. You could ask your parents if they saw where it fell. You could try getting a dog to sniff for the metal bucket. But all of these things are based on chances: the holes you dig could miss the bucket, your parents might not remember where the bucket was, and the dog might not be able to smell the bucket at its depth.

What if there was a way you could see through the dirt? With eyes like that, you wouldn’t even have to worry about digging the wrong hole: just look around and dig where the bucket is!

It turns out that such a thing exists. No, it’s not possible to make dirt invisible (yet). But thanks to a technology called RADAR, you can see through it!

RADAR stands for RAdio Detection And Ranging. Let’s break each of those words up one by one.

Radio:

You probably know that energy comes in waves. You might have heard about sound waves traveling to your ears, or microwaves heating your food. Radio waves are just another kind of energy, so they move in waves. These waves are too long to be picked up by your senses (unlike sound waves and visible waves), but specially made instruments called antennae can hear them. These antennas capture the waves. Then, a computer turns them into graphs that humans can understand.

Detection:

Remember the metal bucket? Since you can’t see it on your own, the radar detects it for you. When radio waves are sent out from the radar, they bounce off of objects and come back, to be captured by the antenna. Just as sunlight reflects more off some colors (like white) and less off others (like black), radio waves bounce back harder when they hit things made out of metal. This is how your antenna can tell where the metal bucket is: its signal is WAY stronger than all the dirt around it.

But how do you know how deep to dig? That’s where the last part of RADAR comes in: ranging.

Think about it this way: if you threw a ball at a wall that was one foot away from you, it would bounce back in less than a second. If you threw it at a wall 10 feet away, the ball might take three or four seconds to return. If you threw the ball at a really far away wall, the ball would never bounce back, and if it did, it would be too slow to get back to you.

Even if you can’t see the walls, you would be able to tell how far away they are because of how long it takes the ball to return. Now, just replace “ball” with “radio wave” and you’ve got the concept of ranging!

Now you can put it all together: The Radio waves are sent out of the antenna in all directions. The ones that bounce back take different amounts of time, and by doing some complicated math, you can figure out exactly how far they traveled. The ones that bounce back with the most energy hit things made of metal or something highly reflective, and by feeding all this information into a computer, you can make a model of your backyard with your lost metal bucket standing out from the less reflective dirt.

Great job! You just learned how scientists see through clouds, satellites take pictures, and metal detectors find gold. It all comes back to radar. Come back for the next article on the history of radar!