Ricerc@Sapienza

Ground Penetrating Radar (GPR) systems shall be periodically calibrated and
their performance verified, in accordance with the recommendations and
specifications of the manufacturer. Nevertheless, most GPR owners in Europe
employ their instrumentation for years without ever having it checked by the
manufacturer, unless major flaws or problems become evident, according to the
results of a survey carried out in the context of COST (European Cooperation in
Science and Technology) Action TU1208 “Civil engineering applications of
Ground Penetrating Radar.” The D6087–08 standard, emitted by the American
Society for Testing Materials (ASTM International), describes four procedures for
the calibration of GPR systems equipped with air-coupled antennas. After a
critical analysis of those procedures, four improved tests were proposed by a
team of Members of the COST Action TU1208, which can be carried out to
evaluate the signal-to-noise ratio, short-term stability, linearity in the time axis,
and long-term stability of the GPR signal. This paper includes a full description of
the proposed tests and presents the results obtained by scientists from Belgium,
Czech Republic, Portugal, and Serbia, who executed the tests on their GPR systems. Overall, five pulsed control units and nine antennas were tested (five
horn and four ground-coupled antennas, with central frequencies from 400 MHz
to 1.8 GHz). While the performed measurements are not representative enough to
establish absolute thresholds for the tests, they provide a valuable indication
about values that one could obtain when testing GPR equipment, if the equipment
is working reasonably well. Moreover, by periodically repeating the tests on the
same equipment, it is possible to detect any significant shift from previously
obtained values, which may imply that the GPR unit or antenna under test is not
working in a normal or satisfactory manner. We also believe that executing the
tests described in this paper is a useful exercise to gain awareness about the
behaviour of a GPR system, its accuracy and limits, and how to best utilize it.