Limitations of Ground Penetrating Radar (GPR)

GPR limitations are sometimes a common occurrence depending on the jobs you use GPR on, when GPRs work, they are great for collecting accurate (NDD) Non-destructive data for utility services and other underground targets or obstructions.

GPR is a great piece of equipment for any professional locator that understands its limitations and has been trained correctly in the specifics of its abilities. Any good locator will use GPR in conjuction with other utility locating equipment and techniques that can help you determine what services were located and the quality of the data collected. If used correctly by an experience operator, you will usually get good results for Non Destructive utility locating services.

However, below are some ideas to take into account when using a GPR or when hiring a utility locator that uses GPR on your projects.

1. Contrast

Knowing the target and the material in which it is buried can be crucial in GPR locating.

PVC in dry sand will be hard to see. Both have low dialectic constants, which means it will be hard to see any difference in contrast of any unknown targets and the material that surrounds it. There are options and features on most GPR units that provide better contrast in these conditions. Another tip is testing the quality of the signal and contrast by scanning over any known utilities and adjust any settings to make it easier to see.

Some other material dielectric constants. (These can vary significantly and is only a guide)

Material	Diametric Constant
Air (dry)	1.0
Polypropylene	2.2
Dry Sand	2.5-3.5
Polystyrene	2.6
organic materials	2-5
PVC	3
Ice (at -5 degree c)	3
Mylar (used for electrical insulation)	3.2
Nylon	3.4
Paper	3.7
Asphalt	3-5
Soil mineral	3-7
Dry Masonry	3-5
dry clay	4-8
Pyrex Glass	5.6
Porcelain	6.0
Dry Concrete	5-8
Moist Concrete	8-16
Moist Masonry	5-26
Granite	7-9
Aluminum Oxide	8.5
Sandstone	9-11
Silicon	12
silts	5-30
Clays	5-40
Water	80.0

Material and Dielectric Constants for GPR

2. Composition

It cant tell you exactly what the utility composition is, you will have to learn from available information and experience.

GPRs only give contrast to targets, however some materials are displayed differently because of there dialectic constants. An experienced operator can usually make good assumptions on what is displayed to them on screen, and use other ways of using that data to make accurate predictions of the material or utility that has been located. This is why data retrieved from GPRs are always classified as Quality Level D under AS5488, subsurface data collecting standards.

3. Poor Medium Conditions

Highly conductive materials such as wet clay or salt water areas, can distort/spread eat up your signal. This is most obvious with metal layers over a scanned area, such as metal mesh or the metal mesh in tiles.

4. Surface Obstructions.

If you are unable to get the transmitter and receiver over an area for scanning, this can limit your gpr scanning ability. Surface obstructions can limit ability to find a clear path to scan for good transmitted and received signal, kerb/gutter/storm water drain, buildings, poles.

Here is a short video, thanks to Danial Bigman on the Limitations of GPR. This video gave me the inspiration for this blog post and to share these ideas with you.

Some other limitations that can impact your GPR results are:

Training with specific models of GPRs
Experience of the operator

Hope this has help you understand abit of what runs through the mind of a Professional Utility Locator when scanning with a Ground Penetrating Radar. Please feel free to comment or ask any questions, Thank You 🙂 Dave.