Combined Migration of GPR data for layered media

<p>In this contribution we will propose the combination of migration results achieved from the same GPR dataset, aimed to mitigate the effects of the nonuniformity of the propagation velocity of the waves throughout the investigated domain. The nonuniformity of the propagation velocity can be appreciated from the diffraction hyperbolas [1] possibly present in the data, or directly from the results of the focusing [2] achieved from different trial values of the propagation velocity. In ref. [3] an algebraic combination of two (but theoretically even more) migration results achieved from different migration parameters applied to the same data has been shown. In that paper, the case of a horizontal variation and the case of a vertical variation of the propagation velocity of the electromagnetic waves in the soil were considered. Here, we will consider the case of a layered medium with non-flat interface between two adjacent layers, which is a case of interest in several practical application, and is a case where we have both a vertical and a horizontal variation of the parameters. Analogously to ref. [3], we will consider both the aspect of the focusing and that of the combined time-depth conversion.</p><p> </p><p><strong>References</strong></p><p><strong> </strong></p><p>[1] R. Persico G. Leucci, L. Matera, L. De Giorgi, F. Soldovieri, A. Cataldo, G. Cannazza, E. De Benedetto, Effect of the height of the observation line on the diffraction curve in GPR prospecting, Near Surface Geophysics, Vol. 13, n. 3, pp. 243-252, 2015.</p><p>[2]G. Gennarelli, I. Catapano, F. Soldovieri, R. Persico, On the Achievable Imaging Performance in Full 3-D Linear Inverse Scattering, IEEE Trans. on Antennas and Propagation,  vol. 63, n. 3, pp. 1150-1155, March 2015.</p><p>[3] R. Persico, G. Morelli, Combined Migrations and Time-Depth Conversions in GPR Prospecting: Application to Reinforced Concrete, Remote Sens. 2020, Volume 12, Issue 17, 2778, open access, DOI 10.3390/rs12172778</p><p> </p><div><br><div> <p> </p> </div> </div>

Point markers in replacement of odometer driven positioning: effects and possible problems

<p>It is widely known that, in GPR prospecting [1-2], sometime it is not possible to make use of the customary odometer for the recording of the position of the measurement points along the observation line. Consequently, in these cases the human operator is compelled to make use of point markers placed at known positions (measured with a tape) along the observation line. In particular, this can happen on the sand of a desert and on the polar ice [3], but it might happen also just due to some ill-functioning of the odometer. Notwithstanding, quite rarely the effects of the use of the point markers have been examined on the basis of some experimental test. At the conference, we will show an experiment where the same observation line has been gone through several times, first making use of the odometer included in the exploited GPR system and then making use of marker points. A third time, the same path was still travelled without odometers and taking the marker points without making use of any laptop command. These were replaced just by stopping for some seconds the GPR in any marker point (but keeping it switched on). This option can be useful in cases where e.g. the command has to be given through a touchscreen. The observation line was 15 m long, and was placed on a flat smooth and tough floor. This means that the line offered favourable conditions for the use of the odometer, and so the positions of the anomalies identified making use of the odometer are considered as the correct positions of the buried targets. This has allowed a quantification of the displacements from the correct position of the buried anomalies when making use of marker points taken with a step of one meter from each other. A  larger and deeper dealing is available in [4].</p><p><strong>References</strong></p><p>[1] R. Pierri, G. Leone, F. Soldovieri, R. Persico, "Electromagnetic inversion for subsurface applications under the distorted Born approximation" Nuovo Cimento, vol. 24C, N. 2, pp 245-261, March-April 2001.</p><p>[2] R. Persico, M. Ciminale, L. Matera, A new reconfigurable stepped frequency GPR system, possibilities and issues; applications to two different Cultural Heritage Resources, Near Surface Geophysics, vol. 12, n. 6, pp. 793-801 (doi: 10.3997/1873-0604.2014035), December 2014.</p><p>[3] H. Jol, Ground Penetrating Radar: Theory and applications, Elsevier, 2009.</p><p>[4] R. Persico, <strong>Ground Penetrating Radar: Physics and Practical Aspects, </strong>Springer Handbook of Cultural Heritage Analysis, edited by Sebastiano D’Amico and Valentina Venuti, Springer, 2020.</p>

Horizontal strains over the length of single section of observation line – problem analysis

The problem of studying values of horizontal strains occurring over the length of single sides of observation line has been raised in the article. A particular attention has been paid to relevance of this issue in the aspect of assessments made with respect to hazards of mining areas. Lack of knowledge of factually occurring values of horizontal strains in the aspect of commonly determined mean index values (assigned for the entire side length) in case of substantial mutual differences may result in low credibility of prepared assessments. It may also explain arising damages to facilities on lands of thus defined category of a mining area.

Observation of 1- to 5-second microtremors and their application to earthquake engineering. Part I: Comparison with long-period accelerations at the Tokachi-oki earthquake of 1968

abstract A study on elucidation of possible amplification characteristic of strong motions due to deep situated deposit was made by means of 1 to 5 sec microtremors observation. At the Tokachi-oki earthquake of 1968 (M=7.9) several accelerograms were obtained, among which some are dominant but others are not significant in longer periods than 1 sec. To understand whether these differences are from source and path effects or site conditions is important for estimating seismic input motions to high-rise buildings. A long-period microtremors observation was introduced to pursue this problem. Observations were carried out in three cities where the typical acceleration records had been obtained, employing a specially designed instrument good for the microtremors with periods ranging from 0.5 to 6 sec. Each observation line was chosen so as to traverse the accelerograph site along which a remarkable geological change of the underground structure is expected, for example, from the outcrop of bedrock to the alluvial deposit. Through comparison of the obtained spectra and their peaks with those derived from the strong-motion records, it was derived that their predominancy and predominant period in the long-period range are clearly responsible to the presence of deep situated deposit. A formulation of observation and analysing procedures of the long-period microtremors was also proposed, paying attention to overcome the defects in the well-known technique for the short-period microtremors.