Why are ground penetrating radar hyperbola different sizes? This is something that many users I meet and those that attend our classes are never taught. Most folks I come across only know 1 or 2 reasons why hyperbolic GPR responses vary in size. But in this video I go over four things that influence response size.
1) Targets are different sizes. Smaller targets will produce a smaller hyperbola while larger targets will produce larger hyperbola. This is the reason most frequently cited by students in our training programs until they complete our course.
2) Orientation of data acquisition. The angle that you cross your target (especially long cylindrical targets like pipes) at will dictate how broad or narrow your GPR response is. If you cross at 90 degrees you will get a narrow hyperbola, but if you cross at an angle smaller than 90 degrees you will get a broader hyperbola.
3) Target depth. The same target, buried in the same materials, at different depths will yield different reflection geometries. The more shallow the target is the narrower the hyperbola will be. This is because the GPR signal spreads with depth so the signal’s footprint (sometimes called the cone) will not be so large at shallower depths. For targets that are deeper, the footprint is larger and the antenna signal may hit the target from further away creating a broader response from the target.
4) Different materials. The same target, buried at the same depth, but in different materials will produce different response sizes. The GPR wave moves at different speeds in different materials so when it is moving at slower speeds (such as in wet clay), the response from the target will be more narrow. In situations with faster wave velocities (such as in dry sand), a target will produce a broader hyperbola.
These are the various reasons why hyperbola differ in size. If I missed one, please put it in the comments below.
If you use GPR and didn’t know all of these reasons immediately, then you should get further training. Check out our upcoming webinars, classes, and live workshops at LearnGPR.com.
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