Geophysical techniques

There are various techniques for mapping the subsurface or constructions. Based on our knowledge and practical experience we determine which technique will be most succesful for each investigation. Important factors to take into consideration are for example depth, specific circumstances, precision, measurement speed and costs.

Performing the measurements
Objects or geological transitions in the subsurface have a direct or indirect effect on the signals sent by the measuring equipment or the natural magnetic fields. Geophysical measuring equipment registers these effects. With the collected data a 3D image of the subsurface or construction can be created.

The measurements are performed by moving the equipment over the research location by foot or by car. Sometimes electrical wires are placed on the surface. Deep-seated, small objects or thin soil layers with similar characteristics are very difficult or sometimes impossible to detect from the surface. In these cases the equipment is brought closer to the objective, for example by using a borehole.

All applied geophysical techniques are non-destructive, making the location accessible immediately aftet the survey. Sometimes a location has to be partly fenced off or mobile fences are used.

Results
In most cases the results are not immediately available in the field. The collected data need to be analyzed in the office and a report is made. The results are presented, depending on the objective of the survey, in an index map, a cross direction profile or a contour chart of the subsurface.

UXO
The geophysical surveying techniques applied by T&A for the detection of explosives all respond to substance changes in the subsurface caused by metal objects. All of these detection techniques have been tested worldwide and have been found suitable for the detection of explosives.

Techniques used by T&A:

  • TISA 2D Borehole Radar
  • TISA 3D Borehole Radar 
  • 3D Radar
  • Borehole magnetometer (CPT) 
  • Borehole metaldetector 
  • EM-61 Metal Detector 
  • Ground Penetrating Radar 
  • Manual metal detector  
  • Magnetometer and Gradiometer 
  • Multisonde gradiometer 
  • NanoTEM 
  • Sidescan sonar 
  • Sub-Bottom Profiler 


3D-Radar makes is possible to quickly and efficiently create a 3D image of the subsurface. T&A Survey officially represents the 3D Radar in the Netherlands, Belgium and Luxembourg.

Ground penetrating radar is an electromagnetic reflection technique which quickly and with great accuracy maps the top meters of the sub-surface in a non-destructive way. This geophysical technique is mainly used for locating  objects and layers in the ground. The ground penetrating radar is extremely accurate.

Principles of measurement
Ground penetrating radar uses electromagnetic waves transmitted into the subsurface by an antenna. When the characteristics of a material change, these waves are being reflected in the ground or in a construction. The reflected waves are registered by a receiving antenna. Both metal and plastic objects reflect the waves, making the detection of both kinds of material possible.

Execution of measurements
In many occasions the equipment is attached to a vehicle, but it can also be moved by hand. The technology is most suitable for surveys of a large areas without obstacles on the surface, for example the detection of objects under a railway, mapping the ballast bed on a railway or mapping the thickness of asphalt or the base and sub-base of tramways, roads and dikes.

Advantages of the 3D Radar
  • More measurements in both horizontal and vertical direction compared to other measuring technologies.
  • Because the 3D-Radar works with several frequencies at the same time, it is possible to zoom in on various depths.
  • Because of the width of the equipment  (1.5 to 2.5 meters) a much bigger area can be measured in one survey line.

The result is a detailed 3D image of the subsurface.