FAQ’s


  • What is 2D GPR scanning?
    GPR scanning is a linear process similar to using a stud finder.  It is the most commonly used method of scanning.  You roll an antenna which sends radio waves out and returns the results back to the antenna and displays the results to your screen.  The technician marks the surface when he detects an object.
  • What is 3D GPR scanning?
    Similar to the standard 2D scanning but depending on how big the area is the technician rolls several linear scans all parallel to each other, in equal distance with each other and rolls in a direction perpendicular to the first set of rolls.  In other words similar to a grid sheet of paper.  After all the linear rolls have been completed the GPR unit compiles the results and shows a “top” view of the surface similar to looking at an xRay film.  This method of scanning provides a nice view of the surface and allows the technican to see a detailed result which aids in determining object placement.  The 3D result is also a good result to use in reports for the client.  
  • What is a Grid Project?
    A grid project is another name for and a term used to describe a 3D scan. It is due to the result which looks like a grid pattern. 
  • What does “EM” mean?
    EM is the acronym for electric magnetic or electromagnetic.  Our GPR antennas contain an EM sensor which is used to detect electrical sources within the surfaces being scanned.  The depth of the EM sensor detection is usually much greater than the thickness of the surface being scanned.  So in these cases we will detect electricla conduits below or behind the surfaces being scanned.  For example a flexible conduit hanging below an 8” thick concrete floor slab.  
  • What is a “hyperbola”?
    A Hyperbola is the term used to describe an upside “V” shape that marks an object within the GPR scan results.  
  • What is the large plastic grid sheet taped on the floor/wall for?
    When we lay down a grid sheet is for providing a consistant linear path for our scanning antenna to follow. Without it the results would not be favorable.
  • What types of materials can be scanned using GPR?
    GPR radio waves are able to go through most non ferrous surfaces such as soil, concrete, brick, CMU, mortar, stone, marble, tile, carpet, wood and many other materials.  The antenna’s return results when they bounce off of ferrous items within these surfaces.  
  • Can you scan ground (soil, dirt etc.)?
    Yes, ground which is usually soil or dirt which may be covered with foliage is able to be scanned.  The antenna is similar to but configured differently than the antennas we use to scan concrete or similar items.  They are also more powerful and set to go much deeper. 
  • Can GPR tell how thick a floor slab is?
    Yes, but the technician has to set the bottom of the scan measurements.  Looking for a baseline like a previous hole or opening to go by initially is more accurete.
  • Does the surface of the floor or wall have to be smooth?
    The smoother the better. The antenna has to be squared to the surface being scanned to assure the radio waves are being sent straight out and returned the same.  If any imperfections make the antenna “buggy” bounces or hops around it will cause the signal to become out of square which will throw off the results.
  • What if the surface is wet?
    Any water or moisture within the surface being scanned, such as wet concrete, will slow down and interfere with the radio signal resulting in a weak and shallow result.
  • Can GPR scan concrete pan decks?
    Yes, but it is very difficult to get the results.  Some of these floors can not be read.  Especially when the floor is shallow and contains wire mesh.  The radio signals that are searching for ferrous objects hit the steel pan and bounce around causing a chaotic response.  Especially where there is a lot of metal reinforcement like where the wire mesh is overlapped showing several pieces of steel on top of a steel base.  There is too much metal for acceptable results.
  • What if the floor is not level or has dips or slopes?
    If the floor is not level the signal will be out of square causing the hyperbola (object found) to be slightly off of the location displayed.  The difference in placement can usually be guessed but is not 100%.  We would suggest giving the mark a buffer when cutting close to it.
  • How deep (how thick) can GPR scan?
    GPR scanning made for scanning concrete or similar surfaces can comfortably scan 10” to 12”. GPR is able to scan a few more inches sometimes up to 16” but the items past 12” will be very faint and difficult to read.  If there are a lot of objects in the floor such as reinforcement or conduits this will make it more difficult to read and in most cases unable to get decent results.  Wet or moist surfaces will decrease the depth of the scan.
  • What is the average size(dimensions) of a GPR scan?
    Our typical scan is 28”x28” or sometimes 32”x32”.  We are able to scan with any dimensions needed.  Keep in mind that the larger the area the longer the scan time.
  • How close can GPR get to walls or objects?
    The GPR antenna is able to get up to 4-1/2” up to or against an objects that will keep the antenna from rolling.  The actual antenna center which is the marking point is in the middle of the “buggy”.  This is due to the send and recieve modules in the antenna that make up the configuration necessary to obtain results.  So when the buggy’s wheels hit a wall or object the center is close to 5” from that object making this as close as you can get results.
  • Does scanning have any temperature constraints?
    We are able to scan in any of our local temperature constraints.  
  • What type of power is needed for the GPR equipment?
    We use a standard 120V outlet.  Our GPR equipment is able to run off of batteries but we typically do not use them and do not carry batteries in the vehicles.  The batteries are not reliable and do not last long so we try to avoid their use.
  • How long does it take to scan?
    An average scan usually takes approximately 15-20 minutes to mark the object locations.  It usually takes another 10-15 minutes to mark up the objects showing a view that demonstrates the contents of the surface.  Some surfaces which are usually the same throughout an entire building can be heavily congested with reinforcement and conduits which will add to the time.  Some scans can take over an hour to complete.  Ocasionally we will get a difficult scan taking up to 2 hours to complete and mark up.
  • What types of objects can GPR see?
    GPR will pick up mostly ferrous items but can see anything that will cause the radio waves to change speed will show up in a surface.  For example, when scanning concrete you will pick up cracks, voids, air pockets or anything that is “not” the concrete.
  • Are all objects found able to be identified?
    GPR mostly shows hyperbolas which will tell the operator there is an object at that position.  For example, rebar.  The operator rolls the antenna in the same direction several times moving over a few inches each time marking that object as it is found.  If the object is marked in a linear pattern each time the operator moves over it is marked as a linear object such as piece of rebar.  GPR detects ferrous items but can not show any detailed information about that object.  It could be anything metallic   By scanning a large enough area the operator will obtain a pattern which will help identify the object such as the identifiable layout of rebar.  Any objects that are a different depth or is diagonal to the other objects are usually a conduit.  So the operator has to explore the area and come up with a reasonable idea of the items found.  Such as rebar, tension cables, conduits and even wire mesh.  These will all look similar so it has to be investigated and a conclusion is made.  The results are an educated guess.  There is no way to obtain 100% positive  identify using a non-destructive method of investigation.  The only way to get an absolute result is to demo the material to uncover the object.
  • Can GPR differentiate between rebar and post tension cables?
    Not 100%. They both show the same results and look the same on the GPR screen.  By investigating their position, depth and placement to their surrounding items will assist in identifying the items.  But as with any non-destructive demo investigation it is impossible to identify items with certainty. 
  • Can GPR tell if an object is electric and hot?
    The EM sensor embeded within the GPR antenna is able to show electric signals.  By matching up the scan data with the electric signals any objects that line up with the signals are identified as “hot” or an electric source.
  • Does anything interfere with the scanning equipment?
    Fluorescent lighting tubes within the scan location will interfere with the GPR radio signal and produce faulty results.  Electric conduits can in some cases interfere with the scan results.
  • Is GPR scanning safe to people nearby while scanning?
    Yes. GPR uses simple radio waves that do not cause harm.
  • Can you scan ceilings?
    Yes.  Although it is hard to keep the “buggy” in a straight line it is possible to scan ceilings.  It is the same process as scanning a floor but upside down.  It also helps if you refrain from drinking while scanning (DWS);)
  • Can GPR pick up plastic items such as conduits in PVC?
    Technically the answer is yes.  Although items such as plastic absorb radio waves making the radio signal pass right through them and not returning a hyperbola back to the antenna.  You will see a faint barely visible response.  Oddly, the air within a hollow pipe such as a conduit will show up before and better than the plastic itself.
  • Can GPR pick up cracks and voids in concrete?
    Yes, any difference in the material such as a crack, air void or air pocket will show up on the GPR results.
  • Can GPR see items like metal vents below a concrete floor slab?
    In some cases where the material/surface is not too thick a metalic object such as a vent or duct work will produce a response as a ferrous item under the slab.
  • Is it possible to scan through materials on top of concrete?
    Yes, we can scan through almost any material that is not metalic or extremely wet or saturated.  The surface must be flat and smooth to allow the antenna to roll without interference. We prefer to leave commercial carpet on the floor so we do not have to deal with the carpet glue.  Often we will put down a thin carpet, cardboard or a thin piece of wood to level out a scan area that is rough and bumpy.  
  • Can I get images of the scanned locations?
    Yes, we can provide images.  The request for images must be prior to starting the scans.  To get a 3D image of the location (a top view, similar to an xRay) we must perform a grid project (3D scan) so the scanner software can compile a view appropriate for JPG images.  We are then able to send the file to the client.  If we are unable to perform a 3D scan of the area of we have already scanned then we can take a photo of the screen showing the 2D (side view) scan and a photo of the marked floor. 
  • Are reports of the scan findings available?
    Similar to the FAQ above we are able to provide a report of the scanning findings.  Images are important to the report and it is preferred to include photos.  If not it will be a written report of the findings but with no or limited photos.
  • Can you get images of the scans while on site?
    Yes, and again, similar to the prior FAQ on images the request must be made prior to the start of scanning.  if not all we will be able to provide are photos of the 2D results screen and photos of the marked floor.
  • How are the objects within the floor or wall marked?
    While we are scanning we will put small dashes on the floor using marker.  When the scanning is done we will go back and draw the objects we believe the scan marks represent.  On bare surfaces like concrete that will have a floor covering put down we will typically use permanant marker.  On a floor like a finished concrete or a tile floor we will use a wax pencil similar to a crayon.  This can be washed off easily.  For carpeted floors we will use painters tape and mark the tape using markers.
  • Do you provide after hours or nighttime services?
    We can provide services any time day or night.  Prices may vary depending on the start time and the amount of time spent on the job.  
  • Is GPR better than xRay?
    There are several benefits to using GPR over xRay.  But there are a couple of benefits to using xRay as well.  One of the main downfalls to xRay is that it is radioactive.  That has its own set of challenges.  As well you can not scan a surface where you can not put a part of the xRay equipment directly on the other side of the desired location.  With GPR you can scan any surface without needing to get to the other side of the surface.  There are many advantages.  Call for a more detailed  explanation. 
  • Does GPR equipment need to be calibrated?
    Yes.  The GPR antenna radio waves can be set to many speeds but the rate of the antenna movement has to synchronize with the radio waves.  This is done using an encoder. This encoder can be calibrated to match the speed of the antenna movement. We have been trained to perform this calibration ourselves.  Once set we test the system to assure it has been set properly.  
  • What is NDT (non destructive testing)?
    Non Destructive Testing is a way to examine a surface without harming or destroying it.  Depending on what you are looking for there are many ways to look at a materials composition and its contents.  In the case of determining what is in concrete or similar surfaces it would be nice to look right through the concrete like superman.  For us humans we need to use xRay, radar, magnetism, sound or even temperature.  We use these techniques to determine what objects are in the concrete before cutting or coring.  We want to find items such as electrical conduits, rebar, post tension cables, wires, plumbing, cracks, voids, aggregate composition or other possible items.  
  • Are GPR results 100% guaranteed? 
    No.  As with any NDT (non destructive testing) methods the results are not absolute. This means that we are not able to see the objects with our own eyes so we have to use one of the many methods of inspection to get an idea of what we are looking at.  Kind of similar to using a metal detector on the beach.  It will beep when you run over a metalic object but you will not know what it is until you dig it up.  Some methods will show you more than others.  In most cases GPR is the best tool for inspecting concrete.  But there are a few occasions where xRay would do a better job like the concrete being thicker than 12” or there are too many metalic objects in the concrete making the GPR results too congested to get a good view.  Otherwise GPR would be the best tool for the job.
  • What type of scanning equipment do you use?
    We use Mala Geosystems equipment.  We have tried many other systems and Mala offered the best results more accurately.  For more information on our systems you can visit our Downloads page or Information page.  
  • Where can I get more information about GPR?
    Here is a link to Mala Geoscience Page.  It contains a lot of valuable information about Ground Penetrating Radar. Mala

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