Library — GPR images
GPR Radargram Library: Real Pipe, Cable and Void Examples
A growing set of real radargrams from our field work, with names and places removed, showing what buried pipes, cables and voids look like on screen.
Quick AnswerA radargram is the image a ground penetrating radar builds as it moves along a scan line: distance runs across, depth runs down, and buried objects appear as curves, bands or bright patches. This library will show real examples from our surveys, labelled and anonymised, so you can compare them with your own. For the reading method, see: How to Read a GPR Radargram.
What is a radargram?
A radargram is a cross-section image of the ground beneath one scan line, built from thousands of radar echoes recorded side by side as the antenna moves. Each vertical strip is one trace: the record of a single pulse going down and its echoes coming back. Stack the traces in order and you get a picture in which the horizontal axis is distance along the line and the vertical axis is the time the echoes took to return, which the software converts to depth.
People search for them as GPR images or ground penetrating radar images, and the term covers several views. The most common is the single-line profile, sometimes called a B-scan. When many parallel lines are scanned over an area, the software can also cut horizontal depth slices, which show buried lines as stripes on a plan. If the method itself is new to you, start with our explainer and read GPR Full Form and how the system works.
How do you read hyperbolas, layers and voids?
Look for three shapes: upside-down U curves for pipes and cables, flat or gently sloping bands for layers, and bright, repeating patches for voids or air gaps. Almost everything on a utility radargram is a version of one of these.
Hyperbolas: pipes, cables and ducts
When the antenna crosses a buried pipe, the radar starts receiving its echo before it is directly overhead, and the echo takes slightly longer from the sides than from the top. The result is a curve shaped like an upside-down U. Its apex marks the pipe's position and the top of the pipe. A metal pipe gives a strong, sharp curve; a plastic pipe gives a fainter one, often clearer when the pipe is full of water. Several small hyperbolas side by side at the same depth usually mean a bank of cables or ducts.
Layers: road crust, fill and natural soil
Changes in material give horizontal bands. Under a road you will usually see the bituminous surface, then the base course, then fill, then natural ground. A band that suddenly dips and returns is often an old trench that was dug and backfilled, which is itself a clue that a service runs there. The water table can also show as a flat, strong band.
Voids and air gaps
An air-filled gap under a slab or road reflects strongly, because air and concrete or soil have very different electrical properties. It shows as a bright patch at the slab base, often with repeating echoes underneath it. A water-filled cavity reflects with the opposite polarity, which helps an interpreter tell the two apart. For the survey service behind this, see our void detection page.
What makes a radargram hard to read?
Signal loss in wet clay, clutter from rubble and rebar, ringing near the surface, and uncertainty in converting time to depth. These are the reasons two people can look at the same image and reach different conclusions.
- Attenuation: wet clay and salty ground absorb the signal quickly, so deeper objects fade or vanish.
- Clutter: brick bats, stones and old foundations each produce small hyperbolas that look like services.
- Reinforcement: rebar in a slab gives a row of closely spaced curves that can hide what lies beneath.
- Ringing: repeating horizontal bands near the top, often from the antenna's coupling with the surface.
- Depth conversion: depth depends on the speed of the radar wave in that ground, which changes with moisture.
The last point is the one most often misunderstood. A depth on a radargram is an estimate based on an assumed or measured wave speed, and its accuracy depends on how well that speed was calibrated on site. To understand the limits in numbers, see: GPR Depth Accuracy.
Why the same pipe can look different on two scans
The angle between the scan line and the pipe changes the picture completely. Crossed at right angles, a pipe gives a tight, clear hyperbola. Crossed at a shallow angle, the curve stretches out and its arms flatten. Scanned along its length, a pipe may not look like a curve at all: it becomes a flat band at one depth, easily mistaken for a layer. This is why good surveys scan in two directions, and why the library will show some features from more than one angle. Antenna frequency matters too. A higher frequency antenna shows shallow detail sharply but fades sooner; a lower frequency antenna sees deeper but blurs small objects.
What will the library show?
Real radargrams from our own field work, grouped by what they show, each with a short note on the ground, the setting and how the interpretation was checked. We are adding examples as we clear them for publication. Until there are enough real examples to be useful, this page explains the method and invites you to send your own.
| Category | What it typically looks like | Planned examples |
|---|---|---|
| Metal water and gas pipes | Strong, clean hyperbola | City road and industrial yard |
| Plastic pipes and HDPE ducts | Faint hyperbola, clearer when water-filled | Fibre duct routes |
| Power cables and cable banks | Small hyperbolas, often in a row | HT and LT cable corridors |
| Backfilled trenches | Dipping layers with disturbed texture | Old service trenches under roads |
| Voids under slabs and roads | Bright band with repeating echoes | Factory floors, culvert approaches |
| Reinforcement in slabs | Regular row of tight curves | Concrete scanning before coring |
| False alarms | Hyperbolas from stones and rubble | Fill in older city areas |
Many of these examples will come from wide, multi-service corridors where lines from several owners run side by side; for that kind of survey, read more about utility corridor mapping.
How is each example prepared?
Every radargram is anonymised, labelled with the processing applied, and published only where the interpretation has been checked. We follow the same steps for each one:
- Remove identifying details: client name, project name, exact location and coordinates are taken out. The city or region may stay where it helps explain the ground.
- State the setting: road, yard, slab or open ground, and the general soil type.
- State the processing: which filters were applied, so you can see what is raw and what is enhanced.
- Mark the interpretation: each feature is labelled on a copy, with the raw image shown beside it.
- Record the check: where a trial pit, chamber or record confirmed the feature, we say so; where it did not, we say that too.
We do not name the equipment model used. The patterns that matter for reading are common to all utility GPR systems.
Send us your radargram
If you have a radargram you are unsure about, send it to us; an engineer will look at it and reply with a second opinion. This is useful when a survey report and a site result disagree, when you are checking another contractor's work, or when you are learning to read GPR data yourself.
Fill in the form on this page and choose "Send my radargram for a second opinion". Then email the file to support@mezux.in, or send it on WhatsApp to +91 99100 10209, with the form name in the message. Screenshots are fine; raw data files are better, along with:
- the setting (road, yard, slab, open ground) and the general soil type;
- the direction of the scan line and any known services nearby;
- what you think the feature is, and why you are unsure.
With your permission, and after removing all names and locations, we may add it to the library. If you would rather not, we will keep it private.
When should you scan rather than interpret?
When the radargram you have is old, partial or from a different line than the one you plan to dig, a fresh survey is quicker and safer than any second opinion. Our standard GPR rate is ₹24 per metre, or ₹32 per metre with an L-section, GST extra, with a minimum order of ₹50,000 in Delhi NCR and ₹1,00,000 elsewhere in India. Every survey we deliver includes radargram snapshots for doubtful points, so you can see the evidence behind each mark; to learn more about the service, see GPR scanning. Send the route and get a quick estimate.
Frequently asked questions
Why does a pipe look like a curve on a radargram?
Because the radar picks up the pipe's echo before and after passing over it, and the echo takes longer from the sides. The apex of the curve marks the top of the pipe.
Can you tell a pipe from a cable on a radargram?
Sometimes, from the size and strength of the curve and from patterns along the line. An electromagnetic locator or a trial pit usually settles it.
Are the depths on a radargram exact?
No. They depend on the wave speed used for the conversion, which changes with soil moisture. Site calibration improves them.
Will you publish my radargram?
Only with your permission, and only after removing names, places and coordinates.
Do you charge for a second opinion?
Send the file through the form and we will tell you whether a quick review is enough or whether a fresh survey makes more sense.
When will real examples be added?
We are adding them as we clear them for publication. The page will grow over the coming months.
Send us your radargram
Written by Saniya Parveen · Technically reviewed by Rahul Rai · Updated 8 November 2026