In GPR Concrete Scanning context and experience is very important. Knowing what peaks are the steel you are looking for and what peaks to ignore. GPR reads the contrast of materials ie (the difference in relative dielectric constant) It is not just looking for metal objects. The reason GPR is used to locate metal in so many applications is that metal is 100 on the dielectric scale where most concrete falls between 4 to 12 with even very green concrete no going to much past that point. This means the contrast is always going to be massive. Air is 1 on the dielectric scale and water is an 80 this is important because there is about the same change in the dielectric constant going from concrete to metal as there is in air to water. In the picture above there are two rebar ties(green) and an expansion joint(red). This data was collected on a rainy day and the join had collected some runoff. This made each joint we passed leave a strong hyperbola. There are lots of other causes for "false peaks" but with experience they become easy to spot.

This GPR Concrete Scanning job was for two cores in close proximity. The spots were marked out in orange. After scanning the hole was relocated a few inches to the left and the conduit was avoided. Always call before you dig and scan before you core.

This was the original saw cut trench to link up with the plumbing drain pipe (in green). The saw cut would of buzzed right through two main conduits running through the slab. We were able to locate these runs and they were able to saw cut most the way and just chip out around the conduits. This saved our client lots of time and money. The final construction often varies from the asbuilts. This is not the first time we have found conduit in a conduit free zone. This seems the be a regular occurrence. Call before you dig and scan before you cut or drill.