Railway Investigatons
High speed data collection and ruggedised antennas are essential for railway GPR investigations. Typically GPR is used to assess the condition and depth of the ballast and any underlying developing subsurface problems. In more recent developments of high speed rail travel, a concrete base is used instead of ballast.
GroundVue 3_8 is one of the fastest (if not the fastest) high speed GPRs in the world. It can be used with any frequency of antenna in any combination, on any number of channels up to a maximum of eight. The full frequency range is from 6GHz down to 250MHz.
Rail investigations normally require GPR antennas to be positioned above the railtrack. Traditional bowtie antennas, intended for ground coupled use, are not well suited to this type of investigation. It is more usual to use air coupled horn antennas which can be attached to a train, positioned so as not to collide with track furniture. We can offer the high frequency horn antennas used to assess the condition of the ballast (detection of ‘dirty’ ballast) but we can also offer lower frequency antennas for deeper penetration into the sub-ballast.
For high speed railtrack, we are the only GPR company to be able to offer the fine definition of a 4GHz horn antenna. This is a very different type of investigation from the ballast inspection and the principal target is delamination. A 4GHz horn antenna detects delamination at a much earlier stage than anything below 3GHz in frequency, for example. This has proved critical on road and bridge inspection (see Publications for relevant papers) and is proving equally critical on high speed railtrack.
In addition to the GroundVue 3_8 multi-channel, we have clients looking at the potential use of automatic depth detection using a lower frequency of GroundVue 8 (currently marketed as the e-Spott with either a 3GHz or 1.5GHz central frequency).
The other advantage that we can offer with GroundVue 3_8 is the ability to continuously calibrate average transmission velocity. GroundVue antennas are simultaneously triggered without cross channel interference (most radar antennas are sequentially triggered). Combining 1 transmitter with 2, 3 or 4 receivers allows the GPR to resolve the transmission velocity of the EM waves. This has two useful purposes: 1) it allows more accurate depth measurement than spot calibrations and 2) areas where there is a build up of unwanted materials are automatically highlighted as having an anomalous calibration factor. This is automatic velocity calibration (as used on the road network) and it is an extremely useful way of identifying problem areas which need further examination. It works particularly well for voids or where there is unwanted water because air and water have a dramatic effect on transmission velocity.