Scientific and technical objectives

1. Utility location and mapping from the surface

The detection of utilities’ underground plant imposes a particular set of constraints on the design of an effective sub-surface radar system. The majority of buried plant is within 1.5m of the ground surface, but it may have a wide variation in its size, may be metallic or non-metallic, may be in close proximity to other plant and may be buried in a wide range of soil types with implications for large differences in both the absorption and the velocity of propagation of electro-magnetic waves.
The ground conditions may also vary rapidly within the area of a radar survey where, for
example, variations in water content can be crucial and, particularly in urban areas, where
there could be imported backfill of inconsistent quality. Consequently, it can be extremely
problematic to achieve both adequate penetration of the radar pulse and good resolution of neighbouring plant, and some design compromises may have to be made.
A careful technical analysis of such limitations, carried out in an earlier European
Commission co-funded project (GIGA) by some of the partners of the current proposal concluded that, for state of the art impulse radars:

penetration depth is limited to about 1 metre when the soil is highly conductive (e.g. clay with a 50 dB/m two-way attenuation);
within such penetration depths, a detection rate of about 80% could be expected with a confidence of 90%2; however, it has also been demonstrated that detecting any small (less than 20mm), non-metallic objects beyond a depth of 0.5 metres, especially when buried in highly conductive terrains, is extremely difficult.

Thus, the main scientific and technical objective set for the development of an enhanced GPR for utilities mapping from the surface is:

to develop a GPR radar system capable of enhancing typical state-of-the art performance as stated above by a factor of 1.5;
to develop a microwave trans-receiver with high sensitivity to low signal levels (i.e. small targets at depths beyond 0.5 m);
to develop an innovative “hardware active background canceller” able to adaptively cancel the effects of the soil from the micro-wave trans-receiver;
to develop an adaptive Ultra Wide Band (UWB) antenna with radiation characteristics that can be adjusted in real-time to the type of soil;
to adapt an existing artificial test site to the specific purposes and objectives of the ORFEUS project.

2. Utility location and avoidance from the underground

Horizontal Directional Drilling (HDD) is a “trenchless” method used for installing pipes and cables of various sizes, minimizing disturbances to the traffic and people living nearby. This technique is very powerful but its uncontrolled use can cause great damage to existing buried infrastructures. Clearly, before this type of system can be used the operator must have an accurate knowledge of utilities and other potential obstructions in its path. Hazards include energised power cables, telecommunications lines (wire and fibre-optic), steel and plastic gas piping, potable water and sewer lines made from various materials, including clay and concrete. Striking one of these assets can be extremely dangerous for the safety of the operators, but can also cause huge economic losses due to the interruption of public services.
HDD employs a slant shaped bore-head for steering underground. Small diameter jets, mechanised cutting tools or displacement heads attached to a flexible drill string are
positioned to form a bore as the head is thrust forward. The steering head is launched from the surface at an inclined angle. Controlling the orientation of a slant face of the head affects steering in both vertical and horizontal planes.
The performance of conventional, downward-looking GPR is not adequate to provide the whole picture and the proposed new generation of stepped-frequency GPRs operated from the ground surface will provide a significant improvement. The additional information from a borehole GPR, which should be able to detect exactly what is near to the bore-head, will help to provide a complete map of the local underground situation that hitherto has not been available.
The design of such system is very difficult and several mechanical and electromagnetic problems must be resolved. To date, no Horizontal Directional Drilling machine worldwide has a system incorporated in its bore-head that is able to detect underground infrastructure while drilling.
Thus, to design and develop a side and forward looking borehead mounted radar, will include:

designing an impulsive GPR to be accommodated in the bore-head of a horizontal directional drilling machine, capable of searching in front of the bore-head but also laterally;
designing a GPR antenna capable of installation on a bore-head or a drill rod and an associated dielectric ’window’;
designing and building a miniaturised and ruggedised electronic sub-system capable of surviving the harsh mechanical environment of the bore-head;
designing an appropriate data transmission system, whether wireless or via the drill rods.

3. Characterisation of underground environment

To increase the detection range in (highly) conducting soils it is mandatory to use ground-coupled antennas. The characteristics of ground-coupled antennas depend strongly on the ground conditions; this phenomenon has a direct effect on GPR penetration depth and has not been extensively studied nor have practical solutions been implemented to improve performance.
GPR is mostly sensitive to the pore fluid properties with soil water content the main factor. It’s crucial that these relationships are well understood and this forms the main scientific objective in this part of the project. On this basis a predictive model will be developed to provide the optimisation routine for real-time adaptation of ground-coupled antenna performance, necessary for increasing penetration depth and high resolution at greater depths.
Combining electromagnetic characterisation, at GPR frequencies, with geotechnical investigations and supplementing them with regional geological settings history information will yield a much more reliable final characterisation of the ground.
The necessary tasks involve:

providing predictive models to be used in the real time optimization of adaptive ground coupled antennas;
conducting geotechnical characterisation of the natural test sites;
developing reliable methodologies for the in-situ measurement of soil characteristics relevant to GPR;
to link the microwave characterisation to the geo-technical data and the more widely available morphogeological characteristics to generate knowledge for building a “map of GPR applicability in Europe”.