Book 24, Question 126
How can a machine see underground without digging?
Ground-penetrating radar sends tiny pulses of radio waves into the ground and listens for echoes. When the waves hit something different, like a pipe, a buried wall, or a layer of rock, some bounce back. A computer turns the echoes into a picture. The machine looks like a small cart that is pushed along the ground, a bit like a lawn mower.
More fun facts
- Ground penetrating radar, or GPR, sends pulses of high frequency radio waves down into the ground.
- When a pulse hits a boundary between different materials, some of its energy bounces back up to a receiver.
- The rest of the pulse keeps traveling down and may bounce off deeper layers.
- By timing how long the echo takes to go down and back, scientists can estimate how deep each layer is.
- Higher frequency waves show finer detail but cannot reach as deep.
- A top layer of soaked clay or salty water can limit how deep the radar sees to just centimeters.
- Lava and volcanic cinders are excellent for GPR, so USGS scientists used it to see the layers inside a Hawaiian volcanic cone.
Sources: U.S. EPA, U.S. Geological Survey
Questions kids ask
Is GPR fast to use?
Yes. It collects data quickly, and experts can often start reading the results while they are still collecting them.