GNGTS 2015 - Atti del 34° Convegno Nazionale

according to the low: (4) where is the factor of enlargement for the k th tone and Ceil stands for the minimum integer not smaller than the argument. In other words, initially an enlargement factor equal to Ceil ( M ) will be calculated for the most disturbed tone, while the other ones will be about proportionally less enlarged with the care that the reconfiguration will never shorten the integration time of any harmonic tone (which is guaranteed by the Ceil function). However, the hardware of the system does not allows an enlargement of the default integration time beyond a factor equal to 10, and therefore in Eq. 4 includes a saturation to 10 if the set prolongation factor of the integration time is longer than 10 times the default integration time at some frequency. Experimental results. The results exposed in the following are relative to two measurement campaigns performed in the framework of the scientific short term mission “Use of GPR and standard geophysical methods to explore the subsurface”, supported by the European Cost Action TU1208 “ Civil Engineering Applications of Ground Penetrating Radar” and performed between July 14 and 24, 2015. Here we will show some results achieved in the site of Laferla Cross. The site is located outside an historical church, where we have checked the presence of cavities and buried subsidences. In particular, there is a project of moving the church from its current position in order to preserve it from some sliding phenomena of the soil, that indeed have already meaningfully damaged it. In this paper, we will show data gathered with the “long” antennas of the system, according to the explanation provided with regard to Fig. 1. The central frequency is about 130 MHz. More details about the purposes of these campaigns are available in Persico et al. (2015). Here it is sufficient to say that six Bscans have been gathered, and the Bscan n. 1, has been repeated twice in order to calibrate the integration times. The variance vs. the frequency is shown in Fig. 3 (upper panel). As can be seen, the most disturbed frequencies are around 100 MHz, because there is the range reserved to the broadcast FM radio transmissions. Moreover, also the shielding of the antennas is in general less efficient at low frequencies. As can be seen from the upper panel of Fig. 3, the higher levels of the variance is recorded at two frequencies between 100 and 200 MHz. The order of magnitude reached by the variance is about 1.8 times 10 10 , this means that some effect from these interferences can be perceived. We have reconfigured the integration times with a factor M =10 both for the long and medium antennas, whereas a factor 1 has been left for the high frequency antennas because we do not see any meaningful disturbance for it. In the medium panel of Fig. 3, the graph of the produced elongations is shown. When the value of the function is equal to 10, it means that the integration times has been prolonged up to 10 times the default integration time, when the value is 9, the extension has been equal to 9 times the default integration time and so on. As can be seen, the extension factor is never smaller than 1, so that no harmonic has been integrated for a time shorter than the default value. Finally, in the lower panel of Fig. 3, the two radargrams with the default integration time and the reconfigured integration times are shown. Seeing at the two figures, we can appreciate that some reflections appear as interrupted of two-piece-like in the left hand panel and continuous in the right hand panel. Conclusions. In this paper, some effects of electromagnetic interferences on GPR data have been shown, and above all a possible counteraction based on the reconfiguration of the integration times of the harmonic tones of a stepped frequency (reconfigurable) GPR system has been described. Preliminary experimental tests is a site of cultural interest have been shown. Indeed, the effect of the disturbance in the presented example was visible but not much strong. Indeed, this happens because the default integration times of the prototypal system are intrinsically quite high, of the order of 100 μs as said. However, this has a meaningful price in terms of practicality of the measure. In particular, at the moment the system does not allows to 164 GNGTS 2015 S essione 3.3