Unique High Frequency Systems
How accurately can you measure an asphalt or concrete wearing course 40mm to 60mm thick?
At Utsi Electronics we manufacture two very high frequency GPR systems GroundVue 5 (4GHz) and GroundVue 5C (6GHz). A series of tests using GroundVue 5C to simulate measuring a thin wearing course resulted in better than 1mm accuracy of depth.
How Were the Tests Done?
The main problem in measuring a wearing course is the difficulty of measuring any variations which is, of course, the problem our client faced. To prove the accuracy of depth measurement, very accurately measured depths are needed. UtEl therefore used a series of glass panes, measured using a micrometer, as steps. Figure 1 above shows the depth measurements of the radar, compared with those using the micrometer.
The conclusion of the tests is that GroundVue 5C’s measurement capability is better than 1mm in air.
What about other materials?
As is well known, GPR systems measure accurately in nanoseconds time. Absolute depths depend on the conversion from time to distance for which the transmission velocity is needed. These depth measurements were carried out in air for which the transmission velocity is already known (c. 0.3m/ns).
Air is, however, a more difficult medium in which to measure accurately than either tarmac or concrete because the transmission velocity is much greater (roughly three times faster). Based on these measurements GroundVue 5C can measure thin layers of concrete or asphalt to an accuracy of at least one third of 1mm, provided that the layer thickness is greater than 6mm.
To ensure that this accuracy is achieved, the transmission velocity should always be calibrated, as with any GPR application.