|Typical test results picked up by the seven channel sensor array. Object signals in two-colour tangential circles. Object size and circle diameter are corresponding.|
Lien Ta had just started to repair the irrigation ditch in his field when an explosion shattered the tranquility of the early morning. One small step on the wrong spot wiped out the life of this farmer. A family lost a member of its community and children lost their father and the security of their existence.
Regardless of whether a farmer tills his field in Vietnam, a woman in Angola fetches drinking water from a well or children in Bosnia go to school, they should all be able to do this on safe ground and on safe footpaths. But this is far from the case. Even years after conflicts and wars have almost disappeared into oblivion, the menace from landmines and UXO in these areas is extreme.
The United Nations is aware of over 60 affected countries in which the civilian population is still constantly threatened by hidden mines. Estimates extend from 60 to over 100 million mines laid during times of war and conflict. In many areas, the number of items of UXO still substantially exceeds the number of mines.
Besides the resultant personal threat to the individual, this also blocks
traffic routes on land and water. Urban areas are considered risky and
unsafe, and valuable agricultural land necessarily lies fallow.
Reconstruction of any kind and the creation of vital structures are
delayed or prevented to an unacceptable extent. It is only an immediate
and targeted solution to the problem that can provide a quick remedy and
make a contribution to the urgently required restoration of a situation
in which the public can live their lives safely in former conflict areas.
We must first fundamentally differentiate between surface and near-surface threats and the threat posed by UXO, frequently at great depth. The criterion of clear and, thus, reliable signal indication has absolute priority. In addition, other essential deciding factors include how easy the method is to apply and its efficiency and economy in use.
In the majority of cases, metal detectors based on eddy-current technologies are used for near-surface detection today. Regardless of whether they are handheld, individual sensors or large-area systems, which are sometimes designed with several channels in the form of sensor arrays, the technological fundamentals are very largely the same and have been tried and tested for many years now.
Attempts have been made to solve the problem of the high alarm rate and the non-detectability of non-metallic ordnance associated with this technique by opting for a combination with complementary sensor systems. Essential aspects in this case are the incorporation of “metal-independent” methods, such as ground penetrating radar (GPR), and infrared (IR) sensors. Material-analytical methods such as the Nuclear Quadropole Resonance (NQR) method complement the range of methods that can be used.
On the one hand, all new methods must meet the extreme requirements of the task at hand; on the other, they must comply with the economy/efficiency aspects.
Practical use frequently fails owing to the as yet inadequate ease of
handling of these methods, the technical complexity and expenditure
involved, which are still too great and, in some cases, the extreme
requirements applicable to user qualification. Ongoing development
projects, such as the research activities launched within the framework
of the European Union’s European Strategic Programme for Research and
Development in Information Technology (ESPRIT), do indicate, however,
that it is possible to reduce the existing handicaps. In small steps, we
are approaching the target of practical suitability, a race against time
that we must win. This is certainly no easy undertaking if we consider
the stringent requirements placed on use in the field.
Where are the Problems?
Well, minefields may be laid anywhere; not only level and easily accessible areas may be mined, but also slopes, road embankments, wooded areas, desert areas or beach areas, even front yards. One other factor is extreme infestation with extraneous objects that must be clearly detected. In addition, many of the areas are covered by vegetation that grows back constantly or are subject to constant change as the result of erosion or floods.
The detection tasks required will largely be performed by metal detectors until the above-mentioned methods and method combinations are advanced enough to a stage at which they can be introduced on a large scale. Here as well, further advances have been made in recent years.
The existing Continuous Wave (CW) and Pulse metal detectors in use worldwide have undergone substantial development. They are thus still the method that most widely covers the listed requirements of practical use.
In regards to the metal detectors, we shall explicitly illustrate further development by way of example of the Minex 2fd. This two-frequency CW unit has been meeting the requirements for ground adaptation for years now (i.e., the electronic circuitry adapts the unit automatically to changed ground conditions). This means that optimum detectability is guaranteed even in areas with magnetic or conductive soils and in saltwater and brackish water areas.
Integrated, selectable soil-adaptive functions that learn allow additional adaptation to extreme situations. When, in the 1950s and 1960s, the plastic age gained ground, mine manufacturers also developed so-called “plastic mines” which, in extreme cases, incorporate only a minimum metal share (e.g., the firing pin). Allowance has been made even for this development, a dramatic one for mine detection, by adapting the sensor performance. An adequately high transmit power and software-aided, automatic evaluation of the in some cases minimal secondary signals of the metal object guarantee reliable detection capability. The appropriate arrangement of the receive elements, some of them as twin, identical modules, allows precise positioning (pinpointing) of the object.
One further step towards enhanced efficiency of detection is the design of large-area sensor systems, generally by maximising the above method. A maximum transmit power in conjunction with a large number of receive elements in a suitable array makes it possible to quickly scan large areas. Using a high-resolution position-finding system then makes it possible to plot the object on corresponding location maps or to precisely mark the position of the object with paint directly on site. However, the flood of so-called false alarms necessarily accompanying this method must be countered appropriately. One way of doing this is to use an appropriately adapted combination of sensors (e.g., by adding GPR technology).
The illustration shows the test track plot results achieved in a first
test step, initially exclusively with a metal detector that was later
complemented by GPR.
Detection at Depth
As mentioned above, detection and clearance of the surfaces must also be followed by detection and clearance of the deeper-lying UXO. In this field as well, essential advances that have enhanced performance have been made in recent years. These include creating large-area sensors incorporating pulse technology and operating on the basis of the eddy-current method and creating appropriate methods for editing and representing the measured signals.
The magnetometer technology, developed by Prof. Friedrich Förster, is available for high-resolution detection of ferromagnetic objects at great depths. Having been further developed constantly over the years, it supplies the clearest results available today. Safety and efficiency/economy are of prime importance in the case of UXO detection as well. Here as well, the method of choice is to add corresponding evaluation software and to set up large, full-coverage sensor arrays analogously to the procedure used for surface detection.
The related evaluation software supplies clear magnetic field charts and,
on the basis of this, makes it possible to compute suitable object lists
for informing the clearance team deployed subsequently. When using such
systems, the quantity of data produced is very large, so it is practical
to make a separation on the basis of data acquisition, data evaluation
and clearance. Data acquisition and simultaneous evaluation of this data
are already technically feasible today. This “division of labour” has
proven ever more successful in recent years: site sounding and
information editing by specialised teams, followed by clearance and
disposal by appropriately trained Explosive Ordnance Disposal (EOD)
personnel. Similarly, the detection and evaluation method can be used as
a subsequent method of quality inspection after clearance has been
Mined areas can be used safely by the civilian population only if definitive clearance of all munitions and ordnance is carried out and completed and only when the cleared area has been certified and the areas released. Achieving this humanitarian goal in a very short time after the end of conflicts or wars still necessitates a great deal of commitment on the part of all concerned. It is the challenge to the menace of landmines and UXO. All technologies already available today offer an extraordinarily good basis for developing more extensive and optimal methods for efficient/economic and safe detection of the heritage of numerous crises. It is the joint task of all those involved—be they users or manufacturers—to continue this development process in a targeted manner. Regardless of this, however, it is absolutely essential to ensure appropriate support for this process at a political level, which requires elaborating corresponding fundamentals and standards and ensuring that they are introduced and applied worldwide.
Institut Dr. Förster
GmbH & Co. KG
In Laisen 70
Tel: +49 / (0)7121 / 140-311
Fax: +49 / (0)7121 / 140-280
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