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Eingeladener Vortrag
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Proposals for Performance Demonstration and Modular Reliability Assessment for Humanitarian Demining
(2003)
For safe and reliable demining it is necessary to determine the actual true performance of mine searching equipment in detecting mines. The subject to detect a hidden subject by penetrating physical interaction with the target is similar to that of non-destructive testing where it is looked for hidden cracks etc. in material via waves and rays. The non destructive testing profession is now about 100 years old and developed some procedures to check reliability of testing. Those principles like the performance demonstration where the successful detections are statistically evaluated against false calls rates and their implementation in an industrial standard (ASME section XI appendix VIII) are analysed. A first adoption to demining was accomplished in the prescription for blind trials in the CEN workshop agreement CEN BT 126
CWA07 for test and evaluation of metal detectors. A number of blind trials were accomplished within an ITEP project to learn about the necessary statistical layout of those trials to achieve true, reproducible and repeatable results to give guidance to selection and improvement of metal detectors. The special focus in these investigations was on the influence of the human factor due to the degree of experience of the operators and the infulence of uncooperative soil. The correlation of the results of the physical parameter measurement and the statistical results is analysed in a first attempt.
Because the demining process is always connected with a danger for human beings, it is necessary to make sure the proper functioning of mine searching equipment in detecting mines. Detecting a hidden target by penetrating physical interaction of rays or waves is similar to non-destructive testing. The non-destructive testing profession developed procedures to check the reliability of testing. These procedures, like the performance demonstration where the successful detections are statistically evaluated against false call rates and their implementation in an industrial standard (ASME section XI appendix VIII) are used as a template. A first adoption to demining was accomplished in the prescription for blind trials in the CEN workshop agreement CWA 14747: 2003 for test and evaluation of metal detectors. Within an ITEP project a number of blind trials were carried out to learn about the necessary statistical basis of those trials to achieve true, reproducible and repeatable results to give guidance for the selection and improvement of metal detectors. The special focus in this first investigation was on the influence of the human factor due to the different degree of experience of the operators and the influence of the soil.
The detection of defects in aircraft components or parts of a power plant or mines in the ground is connected with the task to distinguish between signals caused be the item searched for and noisy signals from other sources. The reliability of the system is the better the better the system is in detecting the wanted signal and avoiding false alarms caused by noise. It is usual to measure the reliability of diagnostic systems in terms of ROC-curves (Re-ceiver Operating Characteristics) and POD-curves (Probability of Detec-tion). The ROC curves describe the POD versus Probability of False Alarm with growing system sensitivity along the curve. POD curves describe the Probability of Detection for a fixed sensitivity for a variation of item sizes or depths. Reliability of the whole system is always a composition of the physics
and technique, application influences and the human factors. For the scien-tific understanding and possibilities of improvement, decomposition accord-ing to a modular model is helpful. The authors present their experiences with the reliability evaluation of metal detectors for humanitarian demining and an NDT system of mechanized ultrasonic phased array testing of copper welds. The special concern in demining is the influence of soil types, detec-tors and the experiences of human beings.
ITEP project 2.1.1.2 - Final report - Reliability model for test and evaluation of metal detectors
(2004)
Metal detectors used in demining have been tested within the frame of the International Test and
Evaluation Programme project ITEP 2.1.1.2. Detection reliability tests were performed in accordance
with the CEN workshop agreement describing specifications for test and evaluation (CWA 14747:2003). Results of these tests are aimed to verify and should help to optimise the proposed testing
procedures.
The total reliability of a mine searching system is driven by the triple of intrinsic
capability, which describes the physical-technical basis capability, the application and
environmental factors and the human factors. Some of them can be determined in
laboratory measurements but the human factor and a part of environment conditions
and their interaction with the device need to be treated statistically. That is why the
test & evaluation procedure described in CEN CWA 14747:2003, includes in addition
to parameter tests of metal detectors also the reliability or blind field tests under local
conditions with local personnel. A series of three big field trials had been
accomplished in the ITEP-project 2.1.1.2 Reliability Model for Test & Evaluation of
Metal Detectors to specify the optimum conditions for reliable trial results with
affordable effort. For each set of specific working conditions, characterized in terms
of a combination of one mine type in one soil with one detector handled by local
personnel, the searching system will show up a working performance in mine
detection rates as a function of mine depth and show up a certain overall false call
rate. During the ITEP-trials in Benkovac and Oberjettenberg the authors learnt to
determine this function separately for each mine type in each soil, which is especially
important for low metal mines in uncooperative soil which will be illustrated for the
mine PMA2 in different types of soil. The question of representativeness for field
conditions on the one hand and necessary statistical set up for the possibility to
distinguish between individual detector performances is still under discussion.
Trial design for testing and evaluation of metal detectors used in humanitarian landmine clearance
(2006)
Statistical design of experiments applied to tests of metal detectors used for mine detection
(2006)
Trial Design for Testing and Evaluation of Metal Detectors Used in Humanitarian Landmine Clearance
(2006)
Statistical design of experiments applied to tests of metal detectors used for mine detection
(2006)
This thesis proposes a design of experiment for testing and evaluation of the equipment and the methods used in manual mine clearance. The thesis is based on several metal detector trials and a trial of manual demining methods. The core of this dissertation comprises four metal detector trials performed in Germany and Croatian in 2003 and 2005. The purpose of these trials was to investigate the feasibility of the tests described in the CWA (Comité Européende Normalisation/CEN/Workshop Agreement) 14747:2003, the standard for testing metal detectors for humanitarian demining. The goals of the trials were: to find an appropriate design of experiment for testing metal detectors; to establish the use of ROC diagrams (Receiver Operating Characteristics) and POD curves (Probability of Detection) in the analysis of the experimental results; and to gain practical experience in organising and conducting metal detector trials. Apart of this thesis is devoted to a trial of manual demining methods performed in Mozambique in 2004. The main goal of that trial was to compare the speed of various manual demining methods, including the most common excavation methods. The outcome of this work is the proposals and recommendations for an update of the standard for testing metal detectors CWA 14747:2003. Maximum detection height measurements were performed as a part of the metal detector trial carried out in Croatiain2005. The results reveal a high variability of the maximum detection height. This high variability needs to be taken into account in all experiments. Apart of the variability is caused by the differences between the operators and by the setup of the metal detector. It is therefore recommended that two kinds of experiments with the maximum detection height as a response variable are defined in the next update of CWA 14747:2003. The first kind should include the setup, the soil and the operator as factors in the design of experiment. The in-soil measurements with the same detector should be performed with repeated setups and with several operators. The second kind of experiments should be experiments evaluating the influence of other predictor variables. In those experiments, it is recommended to perform one-factor or multiple-factor in-air measurements with the operators and the setup as a block. The main part of the metal detector trials described in this thesis was the detection reliability tests. Detection reliability tests as described in CWA14747:2003 come closest to representing the real field conditions in demining. They include many environmental influences and, most importantly, many of the human factor influences. However, each test design is a compromise between fully representative conditions and cost effectiveness. In this thesis, a fractional factorial design based on the Graeco-Latin square is proposed as a solution to the experimental problem. The results are reported in the form of ROC diagrams and POD curves. The crossover design enables each operator to work with fewer detector models with in a certain time. The variations of the design enabled an unbiased comparison of detectors in each soil and with each target model separately. It is recommended that the solutions proposed in this thesis be incorporated in the standard CWA14747:2003. It has been shown that maximum detection heights measurements provide the information about the best possible performance of a metal detector in are liability test.