The following are three real-life examples that demonstrate the success of the various methods employed and services offered by Radar Solutions International.
The search for the ancient Greek city of Helike
Determining the lateral footing of a bridge in Massachusetts
An evaluation of the deterioration of a concrete tank
The Search for the Ancient Greek City of Helike
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ABOVE: Ancient Greek structure detected using GPR during our 1996 and 1998 surveys, at 2.4m depth near the Ancient Helike site. Photo courtesy the Helike Project. |
ABSTRACT
In 373 BC, the Classical city of Helike, on the southern shore of the Gulf of Corinth in Greece, was destroyed by a catastrophic earthquake, mass-movement of the deltaic sediments upon which it was built, and a large tidal wave (tsunami) which immediately ensued. Due to subsequent burial by sedimentation, and tectonic uplift of the northern Peloponnesos, the ruined site is now believed to be on land, possibly a few kilometers southeast of Aigion, in the area of the coalesced deltas of the Selinous, Kerynites, and Vouraikos Rivers. Since 1988, the search for Helike has been conducted by the Directors of the Helike Project, Dr. Steven Soter and Dr. Dora Katsonopoulou.
In the Summer of 1996 Doria Kutrubes, Geophysicist and President of Radar Solutions, directed a ground penetrating radar (GPR) survey in seven areas near the presumed site of Helike. She was assisted by Dr. Steven Soter, currently with the American Museum of Natural History in New York, New York, Dr. Dora Katsonopoulou, of the American School of Classical Greek Studies, Athens, Greece, and other Friends of the Helike Project, Joan Friedman, Maria Argyropoulou, and Maria Stefanopoulou.
Data collected using GSSI's SIR-2 and monostatic 400 MHz antenna achieved a maximum penetration of 3 m, observing several hyperbolic targets. One of these was a tile floor dating from the Roman Era (pictured below), located at a 1.4 meter depth. In another area, many of these hyperbolic reflectors were aligned over a 40 meter distance, suggesting the presence of an ancient wall. GSSI's multi-low-frequency bistatic antenna, used in the 80 MHz configuration, achieved depths of approximately 5 to 6 meters in some areas. Data from these surveys are still being evaluated for purposes of 2D and 3D imaging.
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ABOVE: 3D depth slices revealing a Roman era tile floor over a meter below the surface. |
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ABOVE LEFT: One dimensional GPR record of the same Roman era tile floor, collected using a GSSI 400 MHz antenna. This and other GPR data were gathered by geophysicist Doria Kutrubes, of Radar Solutions International. ABOVE RIGHT: Roman era basin, showing the type of tiled floor discovered in the Helike Project using GPR. |
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During the summer of 1997, numerous boreholes were conducted to ground-truth observed GPR anomalies and to determine the depth to the Classical Helike horizons. The 40 meter long linear feature was confirmed to be an ancient wall, likely from Classical Greek times. The wall, shown below, was composed of small boulders and cobbles cemented together with mortar. The wall appears to be over 1.5 meters high and 80 cm wide. The top of the wall is less than 90 cm below grade in some locations where local farming and soil removal had occurred.
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GPR records recorded from data acquired transverse to the wall's long axis (LEFT) produced high-amplitude hyperbolic reflectors, similar to that observed on the GPR record (RIGHT). This particular GPR record was obtained during the Summer of 1998 from another area were high-amplitude hyperbolic reflectors were observed along a 150 meter long alignment. Speculation suggests the presence of yet another, larger wall, possibly the wall surrounding the ancient City of Helike, itself. |
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Ms. Kutrubes and Dr. Soter returned to Greece during the Summer of 1998 to continue with GPR, and magnetic surveys. Data from these surveys have partially been interpreted. Some information has been presented at various conferences attended by Dr. Soter and Dr. Dora Katsonopoulou. Please visit there website at: http://www.geoprobe.com/helike/
Other Acknowledgments: We also wish to thank Geophysical Survey System, Inc. for the use of their multi-low frequency antenna.
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Use of GPR in 2D and 3D Imaging of Bridge Footings
GPR was used at an eastern Massachusetts bridge to help determine the lateral extent of a bridge footing. Data were collected continuously along a 2-foot survey grid using a GSSI SIR System-2 and monostatic 900, 400, and 200 MHz antennas. Common mid-point (CMP) gather measurements were made using bistatic 400 MHz antennas to determine the interval velocity of the soil. Because of its unexpected shallow depth, the 900 MHz antenna provided the best 2D resolution of the bridge footing’s transverse and longitudinal sections.
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| This figure shows the 3D image of the bridge footing, as displayed as depth below ground surface. | Edward Dobson, seen here towing the 400 MHz antenna, lends a hand with the GPR survey. |
For more details of this survey and a copy of this paper in Adobe Acrobat Reader Format, please click on the link below:
Kutrubes, D.L., Maser, K., 1998, Use of GPR in 2D and 3D imaging of bridge footings and scour studies: Symposium for the Applications of Geophysics to Environmental and Engineering Problems (SAGEEP98), March 1998, Chicago, IL., pp. 893-902.
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Use of GPR for Determining Concrete Deterioration
A 1.5 GHz ground-coupled antenna was used with a digital ground penetrating radar system to evaluate the amount of deterioration within an aboveground concrete holding tank at an active paper mill. Because of the corrosiveness of the slurry held within a the 72 year-old tank, deterioration could manifest itself by delamination and/or by surface cracking. Delamination is most likely to occur at the inner wall where the concrete may be in direct contact with the corrosive slurry. concrete meet, but can also occur at either the bottom or top rebar schedules within the concrete. Surface cracking can indicate both a surficial stress problems, caused by the elliptical shape of the structure, as well as more severe voiding/delamination problem.
Attenuation was mapped and contoured for the tile/concrete boundary and the upper rebar schedule. Deterioration at the concrete surface was achieved by calculating the real concrete dielectric permittivity (i.e. dielectric "constant") from the reflection coefficient of the surface reflector. Attenuation and dielectric information were then compared with visual observations of the data to determine the overall deterioration of the structure. Overall, the curved walls revealed more deterioration, over 25%, while the straight sections of wall had about 10 to 14% deterioration.
For more details on this survey see:
Kutrubes, D.L., 2000, Use of a ground-coupled monostatic antenna for determining deterioration of concrete structures: Symposium for the Applications of Geophysics to Environmental and Engineering Problems, 21-24 February 2000, Washington, D.C., pp. 851-5.
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