EARTH DYNAMICS | GPR

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<td width="904" height="330" valign="top"><font face="Arial"> <b><font FACE="Arial"> <p align="center"><font size="4">THE GROUND PENETRATING RADAR (GPR) METHOD</font></p> <div align="left"> </font><table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="98%" height="941"> <tr> <td width="100%" height="941"><font face="Arial"> <p><font face="Arial"><b>The GPR method provides information which can be used to help determine:</b></font></p> <blockquote> </font><table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr><td valign="top" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial">The location and depth of metallic and non-metallic buried objects such as voids, utilities, pipes, drums, tanks, cables and boulders</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial" size="3">The presence of rebar in concrete</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial" size="3">T</font><font face="Arial">he extent of contaminant plumes</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial">The location of archaeological sites</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial" size="3">T</font><font face="Arial">he condition of brick, masonry and concrete structures</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial" size="3">T</font><font face="Arial">he condition of sub-grades beneath roads, railroad tracks, and runways</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i><font face="Arial">The boundaries of buried landfills and trenches</font></i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i>Depth and thickness of soil strata on land and under fresh water</i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i>Bedrock topography</i></font></td></tr> <tr><td valign="baseline" width="42"><img src="_themes/earthdyn2/abstrbu2.gif" width="12" height="12" hspace="15" alt="bullet"></td><td valign="top" width="100%"><font face="Arial"><i>Depth to the water table</i></font></td></tr> </table><font face="Arial"> </blockquote> <p><font face="Arial">In a GPR survey, high frequency (10 MHz to 3,000 MHz) electromagnetic (EM) pulses are used to detect changes in EM properties (dielectric permittivity, conductivity and magnetic permeability) as a function of depth.<img border="2" src="gprtunnel.jpg" width="220" height="309" align="left" alt="GPR Survey in 90 year old tunnel"> Energy is propagated into the ground from a transmitting antenna and is reflected back to a receiving antenna from subsurface boundaries at which there are EM property contrasts. As the antennas are moved along the survey line, a series of scans are collected and positioned side by side to form a profile of the subsurface.</font></p> <p><font face="Arial">The lateral resolution of a GPR survey depends upon the spacing of the GPR profiles and the rate at which data is collected along the profile. The vertical resolution of the technique is a complex function of the amplitude and wavelength of the EM pulse, the propagation characteristics of the host material and the target, the complexity of the geology, noise from manmade and natural sources, and the depth shape and size of the target. Typically, vertical resolution of a few centimeters can be obtained with high frequency antennas (1 GHz) at depths of less than one meter, while lower frequency antennas (10 MHz) may have a resolution of a meter or so at depths to over fifty meters. Penetration depths of 5,000 meters have been achieved under certain conditions such as polar ice or salt deposits.</font></p> <p><font face="Arial">The GPR method is limited to areas which do not contain high conductivity soils, or sediments which are saturated with salt water or other highly conductive fluids.</font></p> <p align="center"><img border="0" src="GPR_UST.gif" width="469" height="355"></p> <p align="center"><b>Example of GPR Data</b></p> </font></td> </tr> </table><font face="Arial"> </div> <p align="center"> </p> </font></b> </font></td> </tr> </table><font face="Arial"></center> </div> <p align="center"><img src="_themes/earthdyn2/hline.gif" width="600" height="10"></p> <p align="center" style="margin-bottom: -17; "> <script language="JavaScript"></script><a href="index.htm" language="JavaScript" onmouseover="if(MSFPhover) document['MSFPnav6'].src=MSFPnav6h.src" onmouseout="if(MSFPhover) document['MSFPnav6'].src=MSFPnav6n.src" target="_top"><img src="_derived/home_cmp_ed-global-010_hbtn.gif" width="95" height="20" border="0" alt="Home" align="middle" name="MSFPnav6"></a> <script language="JavaScript"></script><a href="Key_Personnel.htm" language="JavaScript" onmouseover="if(MSFPhover) document['MSFPnav7'].src=MSFPnav7h.src" onmouseout="if(MSFPhover) document['MSFPnav7'].src=MSFPnav7n.src" target="_top"><img src="_derived/Key_Personnel.htm_cmp_ed-global-010_hbtn.gif" width="95" height="20" border="0" alt="Personnel" align="middle" name="MSFPnav7"></a> <script language="JavaScript"></script><a href="Client_List.htm" language="JavaScript" onmouseover="if(MSFPhover) document['MSFPnav8'].src=MSFPnav8h.src" onmouseout="if(MSFPhover) document['MSFPnav8'].src=MSFPnav8n.src" target="_top"><img src="_derived/Client_List.htm_cmp_ed-global-010_hbtn.gif" width="95" height="20" border="0" alt="Client List" align="middle" name="MSFPnav8"></a> <script language="JavaScript"></script><a href="News.htm" language="JavaScript" onmouseover="if(MSFPhover) document['MSFPnav9'].src=MSFPnav9h.src" onmouseout="if(MSFPhover) document['MSFPnav9'].src=MSFPnav9n.src" target="_top"><img src="_derived/News.htm_cmp_ed-global-010_hbtn.gif" width="95" height="20" border="0" alt="News" align="middle" name="MSFPnav9"></a> <script language="JavaScript"></script><a href="Site_Map.htm" language="JavaScript" onmouseover="if(MSFPhover) document['MSFPnav10'].src=MSFPnav10h.src" onmouseout="if(MSFPhover) document['MSFPnav10'].src=MSFPnav10n.src" target="_top"><img src="_derived/Site_Map.htm_cmp_ed-global-010_hbtn.gif" width="95" height="20" border="0" alt="Site Map" align="middle" name="MSFPnav10"></a></p> <p align="center" style="margin-bottom: -17; ">  </p> <p align="center" style="margin-bottom: -17; "> <u><b><i>Contact Information</i></b><i><b><font size="2"><br> </font></b></i></u><font size="2">2284 NW Thurman Street, Portland, Oregon  97210</font></p> <p align="center" style="margin-bottom: -17; margin-top:15"> <font size="2">voice: (503) 227-7659  fax: (503) 227-1074</font></p> <p align="center" style="margin-bottom: -17; margin-top:15">  </p> <p align="center" style="margin-top: 10"> <font size="1">Last modified: March 07, 2008</font></p> </font></body>