Multifrequency Microwave Tomography Between Boreholes

International audienc

Microwave tomography imaging for geophysical applications

International audienc

GPR performances for thickness calibration on road test sites

International audienc

<title>GPR performances on a road test site</title>

International audienc

Automated data extraction from synthetic and real radargrams of complex structures

This paper presents a comparative study of two algorithms for detecting and analyzing the characteristic shapes of reflection obtained as a result of Ground-Penetrating Radar (GPR) scanning technology. The first algorithm is a sub-array processing method that uses direction-of arrival algorithms and the matched filter technique; this approach is implemented in SPOT-GPR (release 1.0), a new freeware tool for the detection and localization of targets in radargrams. The second algorithm, APEX, is based on machine learning and pattern recognition techniques and it allows finding the coordinates of apexes and further characteristic points of hyperbolas in radargrams. Both software solutions are implemented in MATLAB environment. As a first step, we compare the accuracy of our algorithms when applied to synthetic data, calculated by using the open-source finite-difference time-domain simulator gprMax; the scenarios are two concrete cells hosting different metallic and dielectric targets. Then, we compare the accuracy of our algorithms when applied to experimental data, recorded over district heating pipes in a trench, with known geometry and depth of the pipes. For the latter scenario, we have also generated a gprMax radargram, matching the geometry and scanning settings of the real one; both algorithms are tested on this synthetic radargram, as well. Overall, both algorithms perform well and rather uniformly in localizing the targets. The accuracy of the algorithms is at centimeter level, which is sufficient in most applications

Step-frequency radar applied on thin road layers

International audienceIn the field of road construction and maintenance, the need for information on the thickness of very thin road layers is not satisfied by means of commercial pulse GPR, due to the inability of such devices to operate over ranges of several gigahertz. As a result, research has focused on the design of a step-frequency radar technique, able to work with very high-frequency synthetic pulses.An ultrawide band antenna, belonging to the family of Vivaldi antennas, has been developed for road applications. It has been created using stripline technology and yields a band width greater than one decade. During an initial step, this antenna was tested on various bituminous concrete samples with a network analyzer. Different parameters were studied, including band width, offset between antennas, and height and shape of the frequency-dependent pulse.A second step involved GPR dynamic measurements. A customized software program enabled recording data from the network analyzer. Several radar profiles were developed from selected road construction and maintenance test sites (e.g. the Circular Pavement Fatigue Test Track, composed of a number of known structures). Results show improved resolution when compared to a commercial impulse GPR system

Applications of Ground Penetrating Radar in Civil Engineering – COST Action TU1208

This paper focuses on the use of Ground Penetrating Radar (GPR) in civil engineering. Open issues in this field are identified and desirable advances in GPR technology, application procedures, data processing algorithms and analysis tools, are addressed. European associations, institutes and consortia interested in this topic are mentioned, together with the main relevant international events. The new COST (European COoperation in Science and Technology) Action TU1208 'Civil Engineering Applications of Ground Penetrating Radar' is presented, started in April 2013: this interdisciplinary project offers important research opportunities and will strengthen European excellence in all the fields concerning the success of GPR technique, with a main focus on its applications in civil engineering. Four Working Groups (WGs) carry out the research activities: WGI focuses on the design of innovative GPR equipment, on the building of prototypes, as well as on the testing and optimization of new systems; WG2 focuses on the GPR surveying of pavement, bridges, tunnels and buildings, as well as on the sensing of underground utilities and voids; WG3 deals with the development of electromagnetic forward and inverse scattering methods and of advanced data processing algorithms; WG4 explores the use of GPR in fields different from civil engineering and the integration of GPR with other nondestructive testing techniques. The COST Action TU1208 is still open to the participation of new parties: in this paper, information is provided for scientists and scientific institutions willing to join the Action and participate to its activities

Design of UWB Printed Antennas for Telecommunications and GPR applications. Frequency and Time Domain Characterizations

International audienc

Step-frequency radar applied on bituminous concrete

International audienceIn the road field, the need to get information on the thickness of very thin road layers is not solved by GPR. The reason is that the devices are not able to work over several gigahertz. That is why, a research has focused on the conception of a step frequency radar technique, enable to work with very high central frequency synthetic pulses. In collaboration with the LCPC (Central Laboratory of Bridges and Roads), an ultra wide band antenna has been developed at the LEAT (Electronic, Antennas and Telecommunication Laboratory). The ultra wide band antenna, developed for roads application, forms parts of the family of the Vivaldi antennas. It has been realized in stripline technology and one obtains a bandwidth greater than one decade. In a first step, this antenna has been tested on various bituminous concrete samples, with a network analyzer. Different parameters were studied like the bandwidth, the off-set between antennas, the height, and the shape of the pulse depending to the frequencies. A second step concerns GPR dynamic measurements. An homemade software enables to record data from the network analyzer. As LCPC has large testing facilities in the road field, such as a circular Pavement Fatigue Test Track, composed of different known structures, several radar profiles have been done. Results are compared with classical GPR profiles