Impulse Radar or GPR is a radio echo sounding system and the principal technique for mapping the arrangement of elements within a structure: radio waves are used in sounding as these can cross air gaps which stop acoustic waves. Radar thus provides a method for the internal assessment of a wide variety of materials and is particularly appropriate for identifying the general arrangement of shallow buried objects and the internal elements of concrete, asphalt and masonry structures. The key advantage of this technique lies in the rapidity with which data can be gathered without the need for extensive opening up, and the small spaces within which it can be operated.
Surveys are carried out by profiling the structure over a grid of survey lines which give data to provide a three dimensional reconstruction of the arrangement, form and condition of the materials.
One of the most frequent applications is in mapping the position of steel in concrete: not only is it more rapid than a covermeter, but can also map multiple layers of steel, through the full depth of a slab or beam.
Analysis of the changes of velocity, absorption and diffraction of the sounding waves allows more detailed estimates of material condition to be made.
The most detailed results come from a range of about 500mm into solid constructed materials, but useful information can be collected from much deeper and more complex structures.
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