Ground penetrating radar (GPR) is in regular use as a method of mapping defects in track ballast and sub-grade. The efficiency of GPR has recently increased dramatically because new equipment makes it possible to mount it on survey trains that travel up to 100mph.

Advances in software that allow automatic processing of data have accompanied this. The productivity of surveys has been further enhanced by the use of-multiple antennae arranged across the full width of track and beyond. This means that continuous profiles are obtained at several depths of penetration along the length of the track at several positions simultaneously. A graphical illustration of the range of applications for GPR and other geophysical methods in the rail environment is shown below.
GPR technology has also been adapted to road/rail vehicles for surveys at speeds up to 25mph, and manual instruments for use at walking pace. This makes it suitable for short or long lengths of track.
Variations in ballast thickness and excessive soil water seepage in the sub-grade is the root cause of many problems causing wear and tear. This ultimately can lead to failure of the sleepers and track. Ground penetrating radar is excellent at detecting changes in ballast thickness and variations in water content and that is what makes it such a useful tool.
GPR and other geophysical methods are also used for locating hidden structures and voids beneath masonry; and utilities.

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Zetica is based in Pangbourne, Berkshire, UK. www.zetica.com