In the framework of the Dutch humanitarian demining research programme, sponsored by the Ministry of Defence and the Minister of Development Co-operation, a test facility has been realised to test, improve and develop detection equipment for land mines. With this facility the performance of individual and/or a combination of different sensors (i.e. sensor fusion) against a variety of mine threats can be assessed and compared. The test facility is situated on the proving ground - Waalsdorp - near TNO Physics and Electronics Laboratory (TNO-FEL). It entails six test lanes filled with different soil types, mines and mine-like objects. Furthermore, the groundwater table can be regulated for each test lane individually. All of the separate test
lanes are covered by a moveable sensor platform.
Description of the test lanes
The facility consists of six test lanes of 30 square meters each (l´ w´ d =10´ 3´ 1.5m). (See Figure 1). Four lanes are filled with a native soil with original structure and texture. These soils include sand, clay, peat and a ferromagnetic soil. A fifth lane is filled with a sandy soil with forest remnants like roots and twigs. A sixth lane is filled with a sandy soil but also has a vegetation cover. The soils of the other lanes are bare.
Each type of soil has been characterised. A chemical and physical description is available which gives insight in the texture and structure of the different soil types. The test lanes are completely constructed without the use of electrically conducting material. A zone of 5 meters around the test lanes is cleared from all metal. The distance between the different test lanes (1m) has proven to be sufficient to prevent the disturbance of tests by objects situated in adjacent lanes. An important parameter for the performance of the sensors is the soil moisture content, since it affects electromagnetic and thermal properties. Therefore, this test facility has the opportunity to regulate soil moisture by controlling the groundwater level for each test lane separately. This opens to the possibility of testing and interpreting the performance of detection systems under different soil moisture conditions. Two systems have been installed to measure temperature and soil moisture profiles of the different soils. In addition the temperature is recorded of several diagnostic mines. These measurements are carried out in order to gain insight into the temperature and moisture distribution within the soils, which is especially useful in the case of modelling the thermal or electromagnetic detection of the mines.
Description of the sensor platform
Like the test lanes, the measuring platform is made out of materials that are not electrically conducting (Figure 2). The sensor platform, on which several different sensors can be installed simultaneously, meets the criteria for testing individual detection sensors. It can be adjusted in the X- as well as the Y- and Z- direction with a reproducibility better than 1 cm in every direction. The platform can be moved at a controlled variable or steady speed along the measuring bridge, which is built along the length of the test lanes. Trigger signals that control sensor data acquisition can be made available at any position along the test lanes. Alternatively continuous position measurements are available for continuous data acquisition.
The height of the installed sensors can be altered from 0 to 200 cm. The angle of the sensors can be changed to view the surface from a different perspective. The measuring bridge can support up to 600 kg.
Figure 3 shows the test platform during a test. Figure 4 shows a TIR image taken of one of the test lanes.
Description of the test mines
A set of test objects, representing anti-personnel mines, anti-tank mines, and false targets (stones, cans etc.) have been placed at various depths (0-30 cm) in the test lanes. The mines are made of various materials and have different shapes and sizes. Non-metal mines, mines with a casing made out of plastic, metal or another material are included. The test mines have signatures close to those of real mines. To simulate the explosives, the devices have been filled with a silicone rubber. Experiments have proven that this is an excellent surrogate of TNT since both substances have the same electromagnetic and thermal characteristics.
The test lane with sand, clay, peat and the ferromagnetic soil mainly have anti-personnel mines, which have been laid at various depths in a similar structured pattern. The forest soil and the soil with the vegetation cover have a different pattern, including more anti-tank mines. These patterns are kept constant in order to allow the soil to consolidate.
Besides the permanent part of a test lane, there is a part that is been reserved for placing mines (or e.g. calibration objects) ad-hoc without disrupting the permanently laid mines. The position and other data of all objects are registered and updated in a, for this purpose developed, database.
An example of some test-mines is given in figure 5. A complete overview of possible test targets is given in table 1.
For the benefit of interpreting the measured data, additional supporting equipment was necessary. The weather conditions around the test lanes are measured and recorded by a professional weather station. This station measures parameters such as ambient temperature, global solar and sky radiation, relative humidity, wind speed, wind direction, air pressure and precipitation.
Possibilities for research
In order to test in an efficient and univocal way, universal test- and evaluation protocols have been developed whereby all the data from extensive system collection can be combined.
Special attention has been given to the reproducibility of the tests being performed at the test facility. Since the delivery the test facility has supported several national and international projects such as HOM2000, IPPTC and projects for the European Union.
By means of a continuous maintenance and upgrading programme, the facility will be in an excellent condition to support future national and international projects on mine detection systems.