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Reliability of Antipersonnel Landmines Detection Vjera Krstelj, Faculty of Mech. Engineering & Naval Architecture, University of Zagreb, Croatia Contact

Abstract

Tens of millions of Antipersonnel Landmines have been laid in more than 60 countries around the world. While politicians in some countries are making every effort to prevent new millions of mines to be laid, the one thing that can help life where mines already exist is technology.

One technology that has repeatedly proved to be successful in detecting mines and promises even greater success in the future is Non-destructive Testing (NDT).

Having recognized NDT as a powerful resource of methods and techniques for Antipersonnel Landmines Detection (APLD), scientific and other involved communities have developed numerous methods and procedures of applying this technology.

The growing number of NDT methods and procedures call for standardization and proper quality assurance system to enable safe implementation and reliable results of detection.

This paper investigates problems associated with reporting on the reliability results and UN requested reliability threshold (99.6%).

Keywords: landmines, detection, reliability, confidence, standards

1. INTRODUCTION

World's attention has often been captured during the last years by the landmine problems and its devastating effects on the civilian population directly as well as indirectly denying access to land, houses and infrastructure.

These weapons of terror, and that is what Antipersonnel Landmines (APL) and Unexploded Objects (UXO) really are, easy to manufacture and very expensive to clear, promise long-term implementation of R&D involved and of all the developed technologies and methodologies of detection and clearance.

According to UN statistics, mankind will need approx. 1000 years to clear the estimated worldwide number of mines, if today's techniques continue to be applied.

Conferences are being held to foster and strengthen collaborations and provide a forum for reporting progress among NDT scientists and experts in synergistic interaction with others in science and technology. The goal is to develop technology and methodology capable enough in surveys to locate underground and underwater features such as APL and UXO.

Secondly, it is important to improve the capability of inspection methods in reliable detection and to lower the cost with minimum impact on the reliability.

NDT is now a relatively mature field, even though contribution in capability and reliability of many methods and procedures is still in the process of testing, validation and improvement.

As an interdisciplinary field NDT benefited from capabilities that were developed in many other fields of science and technology leading to methods, techniques and instruments with greater sensitivity, user-friendliness and high operational speed as well. At the same time, the applicability to complex materials, structures and problems related to nondestructive determining of quality and integrity of the materials or structures is being greatly increased.

Accepting the reality that no single method can provide all the necessary information, efforts are being made to integrate several methods to form multi-sensor system that would take advantage of the complementary capabilities. It offers better probability of detection and increases the functionality as well. The selected methods and inspection requirements depend on the inspected conditions, site-scan accessibility and characteristics of the part under examination.

The field of implementation is still open and transfer of technology and methodology to locate APL or UXO should be done with due concern about the consequences in capability and efficiency as well as reliability and accuracy of NDT methods and techniques used.

In mine detection the advantage has to be given to the methods which can accelerate the procedure because of extremely dangerous working conditions and very high concentration needed in this work. The processing speed and real-time imaging allowing reduce the time spent in site-scan and interpreting readings are solved using computer hardware and software, as well as progress in microelectronics. The equipment is developed down to portable instruments and sometimes, if possible, even to pocketsize measures, at the same time including additional hazard regarding sensitivity.

There is obviously a number of approaches to establish suitable detection procedures regarding methods and to address requirements and standards relevant to NDT application in the field of sub-surface surveys. There are experiences from trials, when even though equipment, techniques and personnel were believed to be quite efficient, the actual results of certain NDT methods were unreliable. Working outside the laboratory and under stress of danger at work makes the task more difficult and special care should be paid to assure competitive procedures and personnel to perform correctly all necessary tasks to obtain reliable results.

One would expect the overall quality of detection to improve significantly if performance demonstration and all related certification procedures were applied, because methods and procedures have not yet been fully developed, and those that are in place still have to be further evaluated.

However, highly motivated field teams under pressure to tackle the mine detection problem as soon as possible, often use unproven methods which may cause great material damage and in the worst case loss of life.

It must not be forgotten that implementation of NDT methods in any field needs general compliance of all system requirements i.e. systematic approach in transfer regarding NDT operations and necessary system reliability assurance.

2. THE RELEVANCE OF STANDARDS FOR HUMANITARIAN MINE CLEARANCE OPERATION

Needless to say, for humanitarian de-mining detection the goal must be a rate of reliability approaching perfection, i.e. 100%. Time is of less importance than accuracy. In such case, standardization of procedure is of great help.

NDT is generally considered 'special' in the sense that characteristics inspected are measured indirectly by methods which have inherent limitations, often under difficult inspection conditions in the field. As was explained, reliability of examinations is influenced by various factors so

...what is the task?
The task can be described as finding out underground or underwater APL or UXO of prescribed characteristics, usually the nature, location, size and orientation of the object to be detected.


...what is the result?
The results are decided upon by day-to-day performance and it is very important to understand the difference between theoretical requirements and practical achievement.


...what do we have at this moment?
We have International Standard for Humanitarian Mine Clearance Operation that speaks about methods and directions that all of us are obliged to follow. It is issued under the auspices of UN and is effective upon receipt. Other standards such as those issued by the host nation are to be complied with, provided they match or exceed those set out in this document, otherwise, these international standards will apply.

The following subjects are covered: Safety, Training and Qualifications, Survey, Minefield Marking, Mine Clearance Operations, Explosive Ordinance Disposal, Medical, Communications and Minefield Information Management.

According to the listed subjects, we can see that detection is not listed as the subject of this standard. However, the first sentence in Introduction regarding safety says: "The safety standards outlined in this document deal with mine detection, marking, clearance,................, all of which demand safety consideration."

The standard considered is a single and valuable attempt at setting rules in the work related to mine detection and de-mining so it is a sound foundation of standardization development within this field. However, it has to rely upon recognized ISO and EN procedures in drafting and adopting any international standards.

In the standard considered, it is noted that

"Standard will be regularly reviewed and updated by the United Nations and comments and suggestions for improvement are welcome....,"
so that in this paper some comments will be given that are strategically important since their origin is in the field practice.

In spite of the fact that this standard addresses minimum requirements for humanitarian APL and UXO detection and clearance, deviation from this standard is unavoidable.

Let us consider the statement about regulations of qualification and competitiveness:

"All personnel involved in clearance operations must receive the proper training, must be qualified, experienced and medically fit".
From this statement one cannot find out whether mine detection is involved as a part of clearance activities. Let us consider the requirement of proper training specified as needed in the same statement. Knowing field practices i.e. various methods and procedures of mine detection, which could be manual or mechanical, the question is asked: What is meant by "proper training"?

There is great difference in qualification for manual mine clearance versus mechanical, adding to this the possibilities of various methods which could be applied in both manners.

There is also the need for clear definition regarding protective equipment because the statement:

"All personnel involved in mine clearance activities must wear adequate protective equipment when appropriate",
does not explain who should stipulate appropriate situation.

One more example of that kind is related to the conditions in mine detection processes for which the standard prescribes that:

" ... working periods as an operation should be undertaken in daylight and dry condition,"

so the question is what happens with underwater mines, mines in houses, mills and storage, mostly under the ground level, where daylight can hardly be expected and dry conditions are practically out of question.

Working in compliance with that particular requirement of UN standard would mean that all the mines in the water and mentioned situations would remain as they are.

Of uppermost importance and of significant influence are points 5.9 and 5.10 related to "Clearance standards", which state:

5.9 An area is cleared when all mines and munitions have been removed and/or destroyed. All debris, from mines and munitions, such as fusing systems, percussion caps and other items that constitute an explosive hazard, is to be removed.
5.10 The area should be cleared of mines and UXOs to a standard and depth which is agreed to be appropriate to the residual/planned use of the land, and which is achievable in terms of the resources and time available. The contractor must achieve at least 99.6% of the agreed standard of clearance. The target for all UN sponsored clearance programs is the removal of all mines and UXO to a depth of 200mm.

It is very hard to believe that all mines could be cleared off. We have to define and agree upon that level of mine detection or clearance reliability and confidence which could be achieved regarding methods and procedures used and the conditions in the field. This agreed level should be linked to the result of methodology and technology achievement, and shall follow the methodology and technology advancement.

Also, it is not clear what is meant by 99.6%. In order to be properly used, it should be precisely defined.

We could think that 99.6% value describes the percentage of reliability, nevertheless it could also be the confidence level. But in both cases we do not know whether it is to be applied to the reliability of the results in mine clearing or mine detection.

To introduce effective NDT quality system in APLD, it is necessary first of all to clarify appropriate terminology and definition symbols, signs and designation, for mutual understanding and communication.

3. THE PROPOSITION FOR MINIMUM KEY DEFINITIONS TO BE INCORPORATED

The "Capability" of a method depends on the inherent limitations of the method, technique and procedure used. Also, the general term "effectiveness" describes usually the overall probability of detection without taking into account factors related to inspection system or human errors. Sometimes it is about cost-and time-effectiveness.

Key words backed with their definitions are the first point in understandable and effective standard and transfer of methodology. It is the base for any further procedure and one should start by considering the detection methods and results validation.


The consistency with other standards has to be fulfilled. Thus, here are some basic definitions given as they could be as well as the quantified relations;

REPEATABILITY - of results of measurements*1


Closeness of the agreement between the results of successive measurements of the same measure carried out under the same conditions of measurement.

REPEATABILITY - of a measuring instrument*1


Ability of a measuring instrument to provide closely similar indications for repeated applications of the same measure under the same conditions of measurement.

REPRODUCIBILITY *1


Closeness of the agreement between the results of successive measurements of the same measure carried out under changed conditions of measurement.
The repeatability and the reproducibility will depend on many factors but the very influenced one from the method aspect is sensitivity. There are many definitions of the sensitivity of a method. One should distinguish sensitivity of equipment, instrument or system and the sensitivity which includes the method as well, which rely on the physical principle and material characteristics.


SENSITIVITY of the equipment, instrument, system *1


Change in the response of the measuring equipment, instrument or system divided by the corresponding change in the stimulus.

SENSITIVITY of the method*3


The ability to obtain the smallest measurable and discrete response of the presence of a specific target in a specific environment at a given range. Parameters and/or units of measure are expressed in terms of size of target, the lowest signal reproducible by a device or a signal level that has equal probability of being signal vs. noise.
Certainly, the sensitivity of a system affects greatly the sensitivity of a method, and therefore it is useful to introduce the term "conditional sensitivity" for sensitivity of equipment, instrument or system. Conditional sensitivity needs to be determined within performance demonstration on samples and standards which insure traceability which could be defined as:


TRACEABILITY *1


Property of the results of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.
Taking into account all influencing factors related to the methodology, inspection system including equipment and human errors the terms generally used regarding the results of detection or clearance should be Probability of detection, Probability of recognition, Reliability and Confidence of results.

Some authors and experts use the term "performance" for the day-to-day reliability of detection, interpretation, location and accurate sizing of prescribed characteristics

PROBABILITY OF DETECTION *3


A numerical representation between 0 and 100 percent of the likelihood that an operator or sensor will correctly declare the existence of APL or UXO from system responses.
Probability of Detection", POD, is the measure of revealed objects/flaws divided by the number of existing ones.

PROBABILITY OF RECOGNITION


A numerical representation between 0 and 100 percent of the likelihood that an operator or sensor will correctly distinguish characteristics of APL or UXO.
Similarly to POD, the "Probability of False Call", POF, is the measure of "revealed" objects/flaws divided from existing ones.

It is possible to determine the probability of detection at a given confidence level using a carefully controlled statistical performance demonstration program. The true reliability depends on how much confidence is desired.

The smallest sample size that can be used to confirm Antipersonnel Landmines Detection Probability over 90% at confidence level of 99.6% is app. 30 mines included in demonstration program. The higher the reliability requirements, the larger the sample sizes needed.

4. Instead of Conclusion

The search for smarter methods that can rapidly and inexpensively detect APLD in complex field and structures at very high probability and repeatability will continue to present a challenge for NDT.

Within EFNDT, a special working group for development of APLD methods (EFNDT/ WG5/ APLD) was organized at the initiative of the Croatian Society for NDT, which is promoting and coordinating the R&D of advanced APLD and UXO detection methods. In raising the humanitarian demining detection equipment performances, the possible breakthrough is supposed to result from R&D process conducted by intensively collaborating experts.

One of the most important initiatives in WG5 is to move forward to meet the global demand for safety and to acknowledge the importance of ICNDT in supporting the relationships among the NDT Community, enhancing the role of NDT in the big task of service to the humanity, and healthy and productive environment both for the present and the future generations.

References

1. Krstelj V., Stepanic J.,: Non Destructive Testing in antipersonnel landmine detection, Proceedings, International Conference; MATEST ´99, Cavtat 1999, 109-114.
2. Krstelj V., Stepanic J.,: Humanitarian de-mining detection equipment and working group for antipersonnel landmines detection, INSIHGT, European Issue, Vol.42. No. 3. March 2000., 187-190.
3. International Vocabulary of Basic and General Terms in Metrology, 1996
4. EN ISO 8402:1995, Quality management and quality assurance standards - Vocabulary
5. EN ISO 9000-1:1994, Quality management and quality assurance standards, Part 1: Guidelines for selection and use
6. EN 45000:1989, General criteria for the operation of testing laboratories
7. 128.174.5.51/denix/Public/News/UXOCOE/Requirements/glossary.html

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