ITEP



Evaluation of mine surrogates in infrared

(MIMEVA PROJECT)

 

By Brian Hosgood and Giovanni Andreoli

Institute for the Protection and Security of the Citizen (IPSC)

Joint Research Centre of the European Commission

I-21020 Ispra (Italy)

Tel: +39 0332 789195

E-mail:


 

Introduction

 

As part of the MIMEVA project, thermal infrared responses of antipersonnel landmine surrogates were compared with those of the originals.  The experiments were carried out in the Gauss Laboratory of the Joint Research Centre, which has a large internal sandpit.

This document describes some of the experiments made on pairs of mines (VAR-40,  MAUS/1, AUPS and MK2) in December 2000 and January 2001.

 

Experiment set-up

 

Part 1: Pairs of mines, consisting of the surrogate and an inert original, were buried at the same depth in dry sand, and the area heated using a 2 kW tungsten halogen lamp. The lamp was mounted at 20° off-nadir at a height of 120 cm. At this height and setting the lamp provided an illumination of 43000 Lux (lx) on the sand surface which is similar to the amount of energy which could be provided by solar energy alone at mid-latitudes at certain times of the year. The responses of the test objects were observed during the heating and cooling phases using an Agema 570  camera, operating in the longwave infrared range (7.5 to 13 micron).  The camera was mounted vertically over the area of interest at a height of 180 cm. The experiment was also carried out with the same pairs of mines on the sand surface.

 

Part 2: As above, but based on the results of part 1, the 2kW lamp was adjusted to provide a more uniform heat pattern on the sand surface with a corresponding decrease in intensity. The illumination was measured to be 22000 lx ± 4%. The IR camera was lowered to a height of 150 cm above the surface to increase the spatial resolution of the images.

 

Results of first experiment

 

The results of the experiment are mainly in the form of several series of time sequence images. This document provides just an overview and a few examples of the images.

Image 1a shows the response of the first pair of mines (VAR-40) when surface-laid and after 25 minutes heating.  It can be seen that the surrogate apparently behaves in a very similar manner to the original. Image 1b shows the response of the same mines when buried under 2mm of dry sand and after 8 minutes of heating. Image 2a similarly shows the response of the second pair of mines (MAUS/1) when surface-laid and after 10 minutes heating while Image 2b shows the response of the same mines when buried under 2mm of dry sand and after 60 minutes of heating.  Again the response seems to be almost identical in the thermal IR images.  Small differences which can be observed appear to be due to the position of the lamp with respect to the targets: this observation was verified by reversing the positions of the mines and repeating the test.

 

IR Image 1a            

IR Image 1b

IR Image 1a                                                     IR Image 1b

 

IR Image 2a                                                     IR Image 2b

 

 

First conclusions

 

The first tests have shown that it is possible to perform this type of test under various conditions (eg. different soil types, object depth, orientation, illumination conditions) and that one test alone is not conclusive. It would also be possible to carry out further tests including a comparison of the thermal transmission properties of the mines, for example.  The tests conducted to date, however, show that the thermal properties of the surrogates appear to be very close to those of the originals whereas the simulants exhibit significant differences in thermal response both between themselves and in relation to the real object. The question remains if the comparison between the surrogates, simulants and the real objects should be made in free space in laboratory conditions or in conditions more similar to those in which the objects are found in the field.

 

Some observations can be made at this point which can help to improve the set-up for further experiments of this type.

 

Positioning of test objects: The objects were very carefully positioned for these tests. The sand surface was very carefully smoothed and levelled after positioning of the test objects in order to minimize eventual differences in the thermal images which are due to surface variations and roughness. The sand itself was previously sieved to remove any foreign objects which cause imperfections in the top surface or which could obstruct or deviate the heat flow. Furthermore, the air temperature and relative humidity inside the laboratory were continuously monitored and recorded, before during and after the tests.

From this point of view, the environmental conditions can be said to be satisfactory and adequate for further tests of this type. However, the initial temperature of the sand bed was not identical during all the experiments, being influenced by weather conditions at the test site.

 

Illumination and heating of test objects: Although the lamp used to heat the surface and objects was carefully selected, the heating pattern produced by such a lamp is still not homogeneous enough to be able to ignore eventual variations in the heat distribution.

This distribution is well documented by the thermal images themselves. This problem is currently under investigation, however there are no immediate solutions on the horizon.

The use of solar energy is to be avoided too since it does not allow for further testing under identical conditions. The energy provided by the source was sufficient, however relatively long periods of heating and observation (30 minutes to one hour) were required in order to obtain best results. Inverting the position of the objects at least shows what is due to the object itself and what is due to the imperfect illumination pattern. During the tests, the surface temperature was regularly monitored with a second non-contact IR thermometer (Omega OS 86). When a surface temperature of 60 to 65 ºC was reached, the heating was interrupted and the cool down phase was then monitored. This temperature was considered to be similar to that found in real conditions under strong sunlight and not enough to induce deformations or damage in the test objects or to cause any reaction in the explosive itself. The surface temperature of the buried test objects was also monitored with a separate temperature probe (Hanna instruments HI 9065).

The images show too how the objects are strongly influenced by the angle of illumination or heating. This indicates that this phenomenon could be of use too in order to compare the response of different objects (shallow buried and surface laid) in the thermal IR range and merits further investigation.

 

Image acquisition: The images were acquired using various time intervals for the first tests. The results show that each object or object set has an opportune moment at which best results can be obtained. This has been verified on previous occasions during other tests in the laboratory. Until these time factors are better understood, it is prudent to continue to make relatively long image acquisition series in order to cover the whole period of temperature variations between the objects and their surroundings. These times can be optimized however before further experiments. The spatial resolution of the images is satisfactory and the thermal resolution seems to be quite sufficient for these purposes. The field of view of the IR imager was verified by means of copper corner markers which were then removed for the duration of measurements.

 

The experiment set up for Test 1   

The experiment set up for Test 1                                   Levelling the test objects (VAR 40)

 

The test objects on the surface (Test 3)             Yellow spot indicates explosive

 

Thermal images

Thermal images showing response of AUPS mine and surrogate, buried under 2mm dry sand, during heat-up and cool-down phases

(MIMEVA - IR test 5)

 

Total measurement time = 70 minutes

 

 

Thermal images showing response of MK2 mine and surrogate, buried under 2mm dry sand, during heat-up and cool-down phases (MIMEVA - IR test 6)

 

Total measurement time = 70 minutes

 

 

Thermal images

 

 

Thermal images

Thermal images showing response of four APL simulants, buried under 2mm dry sand, during heat-up and cool-down phases (MIMEVA - IR test 7).

 

Total measurement time = 105 minutes

 

 

 

Thermal images showing response of 3 APL simulants, buried under 2mm dry sand, and 1 surrogate during heat-up and cool-down phases (MIMEVA - IR test 8)

Thermal images

Thermal images