Data Interpretation

Why you lose your GPR signal strength (Ground Penetrating Radar)

By August 24, 2017 No Comments

One of the biggest problems people have when using ground penetrating radar is difficulties in seeing deep enough. Most people are aware or one issue that contributes to this problem, but there are actually three reasons that you lose signal strength.

1) Conductivity – this is the most commonly cited of the three issues and for good reason. Soil conductivity can have a major impact on signal attenuation. As the electromagnetic GPR wave passes through a given material, lets say soil, it excites the free electric charges in that material. The excited charges begin to move and bump into other particles in the material. When this happens, friction creates heat, ultimately releasing some of the waves energy reducing the signal strength and limiting how deep you can “see”.

2) Scatter – This occurs when your wave is traveling through a material that has some small inconsistencies (heterogeneities). When the wave encounters the inconsistencies there will be minor reflections. The inconsistencies or irregularities will often be smaller than your GPR wavelength and will only scatter or reflect a small amount of energy. But, if there are many, than the accumulated effect will be a reduction in your overall signal strength and ultimately limit your ability to “see” deep.

3) Reflections – These are actual reflection events, possibly ones that you are interested in. These are reflections from targets or layers. If the two materials that the wave is reflecting off of are very different, then much of the energy can be lost. For example, if you want to find a buried pipe, but you are collecting data on a road and the pipe is buried in wet clay, then you will loose much of the energy when the wave reflects off of the asphalt/clay interface (could be close to 50%). This can dramatically reduce the likelihood of identifying your target of interest.

It’s important to recognize that all of these play a role in your possible success. If you are in “ideal” conditions with non-conductive soils, but the soil has irregularities and your target is buried below 2 or three interfaces, you must be aware of the limitations.

Good luck!

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