Multiple frequency
SPIDAR's unique capabilities enable users to concurrently collect both high frequency signals providing high resolution data for shallow depths and low frequency signals providing deep data at a lower resolution.
1000 / 500 MHz pulseEKKO PRO combination used for pavement forensics. The 1000 MHz provides detailed asphalt or concrete imaging and the 500 MHz is used for granular base and sub-base imaging. |
100/ 500 MHz pulseEKKO PRO combination. The 100 MHz is used for water depth measurement and the 500 MHz for ice thickness determination. |
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Multiple channels
Simultaneous acquisition of data by several GPRs operating at the same frequency enables quick mapping of large areas in one pass to obtain 3D visualization of the subsurface.
The DeckMap configuration shown above conceptually provides the same result as a Conquest. While Conquest standard grid surveys require collection of 7 consecutive lines of data at 10 cm line spacing, the DeckMap with 7 sensors provides the same result in one pass. DeckMap is much more than a faster Conquest. The area that can be scanned is huge and field work has shown scanning of 2000 m
2 areas at 10 cm line spacing is quite practical.
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Multiple polarizations
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Targets will respond and reflect EM signals depending on the direction of exciting field, their geometry and material properties. The field detected at the receiver will be a function of both the excitation orientation and the target characteristics.
A full description of a target response needs a GPR with the ability to change the excitation field direction and also to detect all of the components from the response of the target. Such GPR systems are called Multi-Polarization or Polarimetric GPRs.
Multiple polarization arrays enables extracting complex target geometry. Users can determine velocity in order to estimate material properties and water content.
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Multiple offsets
Multiple offset arrays are used to determine velocity to estimate material properties and water content.
The most common multiple offset surveys are:
Common Mid Point (CMP)
CMP measurements provide a means of estimating velocity and enhancing GPR responses. CMP data are acquired with the transmitter and receiver placed equidistant from a mid-point. GPR CMP data traces are then acquired varying the transmitter and receiver separation. This changes the signal travel path which in turns enables ground properties to be determined.
The response from a flat reflector or a localized target directly beneath the mid-point gives rise to a hyperbola in the antenna separation - travel time display. Analysis tools, such as semblance analysis, can be used to find the subsurface velocity which best explains the hyperbolic behavior.
Using Topp et al's empirical relationship, GPR velocity can be equated to water content.
Wide Angle Reflection and Refraction (WARR)
This survey acquires data while varying the separation between the transmitter and receiver with the prime purpose of estimating GPR velocity. It is similar to the CMP except that one antenna, typically the transmitter, remains fixed while the receiver is moved away in equal step intervals.
WARR surveys can be conducted rapidly if the moving antenna is connected to an odometer to measure offset. A much faster method is to use a multi-channel system with one fixed transmitter and multiple receivers at different offsets.
If multiple WARR surveys are done continuously with the proper spacing along a survey line, this creates a "multi-fold" survey line. Collecting "multi-fold" data and combining or “stacking" the CMP traces increases the quality of the GPR cross sectional image.
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