About the seeker spr & GPR
Can it see through everything?
Simply put, the Seeker SPR shows you what is on the other side. Slowly move the unit over the medium you want to investigate, like a wall, concrete floor, road or any other non-conductive surface. The Seeker SPR’s antenna sends safe ultra wide spectrum RF energy pulses through that medium and back to the antenna to create an image of the subsurface on the operator interface. For you, it is that simple.
The Seeker SPR has the same basic principles as a metal detector. A metal detector sends energy into the earth in up to 17 frequencies. When that energy meets a metallic object, it is translated into a recognizable tone. The Seeker SPR sends out thousands of frequencies that return to the antenna and translate material composition definition in the subsurface.
Radar is sensitive to changes in material composition. Detecting these changes requires movement. In the case of air traffic control radar, the targets are moving, so a stationary transmitter works. In the case of GPR, we are looking for stationary targets, so it is necessary to move the radar to detect the target.
Can it see through everything?
Almost. Radar is the only remote sensing technology that can detect both conductive and non-conductive materials. Although radar can easily see conductive materials such as metal and salt water, it cannot see through them. Also, concrete is conductive when it is fresh, but becomes non- conductive as it cures.
What can I find with the Seeker SPR?
The Seeker SPR is designed to display differences in material composition. It can be used to locate any object that has a different composition than it's surrounding materials. For example, a pvc pipe will have a different composition than the surrounding soil. Voids and excavations that have been filled in will also have different compositions than the surrounding soil. However, it does not know what the actual materials are that it is imaging. For this reason, it is not suited to locating gold, precious gems, and treasure.
Yes, GPR is extremely safe. It emits less power than a cell phone.
The depth of your findings will be determined by three factors:
- Soil type
- Antenna frequency
- Size of Target
The radar signal is attenuated or absorbed differently in various soil conditions. Dense wet clays are the most difficult material to penetrate whereas clean dry sand is the easiest. Lower frequency antennas will yield greater depth penetration, however, the minimum size of object which is visible to the radar increases as the antenna frequncy decreases.
| Antenna | Approximate Penetration in Dense Wet Clay | Approximate Penetration in Clean Dry Sand | Example of smallest visible object |
|---|---|---|---|
| 100 MHz | 20ft (6m) | 60ft+ (18m+) | Tunnel @ 60ft (18m) depth 2ft (60cm) Pipe @ 20ft (6m) depth |
| 250 MHz | 13ft (4m) | 40ft (12m) | 3ft. (90cm) Pipe @ 12m 6in. (15cm) Pipe @ 13ft (4m) |
| 500 MHz | 6ft. (1.8m) | 14.5ft. (4.4m) | 4in. (10cm) pipe @ 4m 3/16 in. (0.5 cm) hose 1.8m and less |
| 1000 MHz | 3ft (90cm) | 6ft (1.8m) | 3/16 in. (0.5 cm) hose @ 3ft. (90cm) Wire mesh, shallow |
| 2000 MHz | .5 ft. (15cm) | 2ft. (60cm) | Monofilament fishing line |
The 500 MHz antenna is the antenna which is most widely used for locating utilities.
The 1000 MHz antenna is the most widely used for locating rebar and utilities in walls and floors.
Note that in many cases if it is not possible to penetrate to the depth of a buried utility due to soil conditions, it is still often possible to detect the disturbed soil from the original excavation.
Generally, GPR will reveal the horizontal positioning of targets in their exact locations, however, there are a number of factors which can affect the accuracy of the depth measurements. The speed of the radar signal is dependent upon the composition of the material being penetrated. The depth to a target is calculated based on the amount of time it takes for the radar signal to be reflected back to the antenna. Radar signals travel at different velocities through different types of materials. The moisture content of the material also affects the velocity of the signal. It is usually not possible to know the exact velocity that the radar signal travels through a material, however it is usually possible to estimate this to within +/- 10%. It is possible to use a depth to a known object to determine a precise velocity and thus calibrate the depth calculations. This technique only works well however, when the material being investigated has a consistent composition such as concrete. When investigating underground, the inescapable limitation is that due to natural differences in the composition of the geological layers, the exact velocity will vary from one point to the next. There are some techniques for modeling the variations in velocity along the path of a survey, however, ultimately these are all estimations and none are completely precise.
Typical training time for a new operator is one day. This consists of a presentation on the principles and theory of gpr, reading data, and system settings. Following this, the operator spends a few hours practicing and learning hands on in the field on actual equipment and they are ready to go!
There are three main approaches to surveying with GPR the selection of which depends on the desired results and whether real-time results are required or if post processing is desired.
If the goal is to identify one or more specific targets, the easiest way to achieve this is to examine the site to be surveyed for any clues such as manholes, catch basins, valves, etc. If there are any, they can serve as an excellent starting location for the investigation. Typically, in this approach, one would move the radar across the medium being investigated until they detect the object on screen, they would then determine the precise center of the object and either mark this on the ground or log the GPS coordinates of the point. At this point, one would move over and repeat this process essentially tracing the target. This works best when real time results are required.
A mark out is generally accomplished by scanning a site on a grid pattern. When a target is observed, a mark is placed on the ground by the operator. This is usually in the form of a flag or spray paint mark. Since the radar data will reveal only that a target is in the earth which has a different composition than the surrounding material, it is not possible on only one pass to determine if the target is a rock or a utility or other type of target. The easiest way to differentiate them is to make another pass and see if the target continues or not. One can choose to either place marks at every target and connect the dots later or to immediately move over and make another pass on the target to determine if the target is linear or not.
3D data can be useful for more complex sites with many targets. The generation of 3D data requires that data be collected on a regular grid in perpendicular directions and also usually requires some degree of post-processing. The amount of post processing required increases as the uniformity of the medium being investigated decreases. Also, there is a practical correlation between the uniformity of the medium being investigated and the clarity of the images which can be expected to be produced through post-processing. Furthermore, usable 3D presntations usually require that data be collected on a much denser grid than is necessary with 2D data presentation. In many cases, the number of survey lines is doubled or quadrupled. For these reasons, 3D data tends to be used more often on smaller scale surveys of concrete floors and walls than it is on large scale ground surveys.
A common misconception is that the size of the antenna affects the amount of area covered. Tthis is not the case. The size of the antenna relates to the frequency of the antenna and subsequently, the depth that it can penetrate (for more information see: How deep does it go?). While the signal from a GPR antenna does spread in the direction of travel, the lateral width which it scans per pass is razor thin regardless of the antenna used. Furthermore, targets are most easily identified with GPR when the survey path is perpendicular to the orientation of the target. For this reason, surveys are usually conducted on a grid in two perpendicular directions:
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A typical GPR survey pattern for walls and floors |
A typical GPR survey pattern for ground surveys | A typical GPR survey pattern along a proposed trenchline |
The spacing of the grid is determined based on the size of the targets that need to be identified and what sort of results are going to be produced from the survey. Typical grid spacings can be 1m, 3ft, 5ft, 10ft, 20ft for ground surveys and 1in-1ft. for walls and floors.
The speed at which data can be collected along a survey line is limited by two factors: 1) any time spend interpreting real-time data and/or spent doing on the spot markout 2) The Seeker SPR is capable of capturing data at highway speed, so the main practical limitation is keeping the antenna in smooth contact with the ground.
There are two basic configurations of the Seeker SPR: Cart and handheld. Handheld units are all in one units which contain either 1000 MHz or 2000 MHz antennas. Due to the characteristics of these antennas, they are ideal for scanning floors and walls, but generally do not offer sufficient depth to locate exterior buried utilities. Cart systems are modular and expandable. They can be used with a variety of antennas ranging from 100 MHz to 2000 MHz. They be configured to be handheld for walls and floors or cart-based. They can even be configured to interface to almost any available GPS unit.
Above: is an example of the same Cart system w/ a 1 GHz antenna configured three different ways.
Below: A 1 GHz SPOT handheld system.
The Seeker SPR can be integrated with almost any type of GPS from handheld to RTK. For most applications, GPS positions are logged constantly while surveying. In the field, or at the office, as points of interest are identified, they are logged for future reference and can have numbers and descriptions assigned to them. These points can then be exported for use in spreadsheets, databases, GIS and CAD software. For certain specialized applications such as lakes and terrain with very irregular topography, GPS positioning can be used to trigger each scan made by the system. High accuracy RTK GPS systems are usually the type of GPS system which yields the best results for these applications.
