See what a radar will record on your site — before anyone goes there.

This video walks through a ground penetrating radar survey from start to finish, using our simulator. The site and all the data you will see are simulated.

1. Know the site. Step one: know the site. Before going out, get the utility plans, which in Belgium means KLIP and KLIM-CICC, then visit the site. This is a fictitious street. Under the road there are base layers and soil, with a water main, a gas main, a utility trench, a chamber and tree roots. Making the layers transparent shows where these run. On a real site you cannot see this; that is the question the radar has to answer.

2. Choose the antenna. Step two: choose the antenna. Frequency is the key trade-off: the higher the frequency, the finer the detail, but the shallower the reach. 900 megahertz suits shallow detail. 200 megahertz reaches deeper, but small targets become hard to separate. Utility work commonly uses 400 megahertz, so we choose that here.

3. Plan the lines. Step three: plan the lines. Radar sees best what it crosses, so lines should run as square as possible to the pipes you are looking for. We start with one line, 12 metres long. The arrow on this plan shows the line and the walking direction.

4. Acquire. Step four: acquire. The radar moves along the line while the antenna sends short electromagnetic pulses into the ground. The wave reflects wherever the material changes, and the radar records when each echo returns and how strong it is. Every short step gives one trace. Trace by trace, they build up the radargram, also called a B-scan.

5. Read the radargram. Step five: read the radargram. Across is distance along the line. Down is two-way travel time: the later the echo, the deeper the reflector. Look at this hyperbola. As the antenna approaches a pipe the distance shrinks, then it grows again, which draws an arch. The top of the arch is directly above the pipe. So reading a radargram starts with finding these hyperbolas. Flat reflections are usually layer boundaries. Below is one single trace, the A-scan, and its spectrum. A radargram is hundreds of these side by side.

6. Process. Step six: process. In the raw record, the strong direct wave from the ground and antenna hides much of the detail. Removing the background, the part common to all traces, makes the hyperbolas stand out. Waves weaken with depth, so gain brings up the deep signals. Too much gain amplifies the noise as well.

7. Velocity and depth. Step seven: velocity and depth. Radar measures time, not depth. To convert, you need to know how fast the wave travels in this ground. Click the top of a hyperbola, then adjust the velocity until the theoretical curve fits the real one. That velocity is the wave speed in this soil. Depth equals velocity times time, divided by two.

8. Grids and time slices. Step eight: grids and time slices. One line gives one section, and it cannot show which way a pipe runs. So we survey many parallel lines over the same area, here sixteen lines, half a metre apart. Combining the energy at the same time on every line gives a plan view called a time slice, like looking down at one depth. Between about 0.5 and 0.8 metres, this wide band is the utility trench. Further down, at about one metre, the water main appears, including its bend, which a single section would never show.

9. Interpret. Step nine: interpret. List each target with its position, depth and how confident we are. The simulator knows the true answer, so we can check: the water main and the trench are clear, and the tree roots are just detectable. The polyethylene gas main and the small plastic connection were not seen: their contrast with the soil is too weak. That is a real limit of radar, and clients must be told.

10. Deliver. Step ten, the last one: deliver. On a real survey, findings are marked on the ground with spray or pegs, and the client receives radargrams with depths and confidence grades, a plan in Belgian Lambert 2008, and a report. This is the report the simulator produces: objects, verdicts and reasons together, ready to print as a PDF. Remember two things. Radar complements KLIP and KLIM-CICC plans; it does not replace them. And radar cannot tell whether a cable is live.