If the human did this task, it is likely that location values representing these priority areas would be passed to the system before robots have even entered the search area. If the robots/centralized manager determined the priority areas, it is obvious that they would have to be done after an initial mine detection phase had been carried out. Factors that might determine priority areas might include the distance an area is from humans or to a lesser extent, rare species of wildlife or animals. If humans traverse frequently across a particular area, this should be considered.
If any historical knowledge of a search area where military conflict occurred is known, this information could possibly be used to determine where a high concentration of landmines were most likely to have been planted. An example would be if a particular army in battle were retreating over a bridge, landmines are likely to have been planted in the vicinity of the bridge to hinder the attacking army’s movement. If a historian had some proof that something like this could have actually occurred within our search domain, this evidence could be taken into account, when priority areas were being determined.
Obviously if the determination of priority areas was automated, the previously mentioned factor would not apply. In terms of mapping our domain, a ‘square’ or regular search area is also preferable, because it is generally much easier for an automated robot fleet to traverse a regular shaped area rather than one that would have an ‘irregular’ appearance on a map. A regular-shaped search area also endorses thoroughness, as if the search area was irregularly shaped, there might be indecision amongst the robots about what areas have and have not been searched, although one might argue that this is always a problem.
Also, it would make the representation of locations and distances that bit easier to apply to the system, although it is very possible that some experts may disagree with this assumption. How locations and distances relating to our domain are represented on our system is an important issue. Principles used in navigation circles also apply here, except accuracy is of more importance in this domain. A system invented in the 1950’s, known as electromagnetic distance measurement (EDM), is based on a principle known as triangulation, and provides the basis for today’s Global Positioning Systems (GPS).
An earth-based GPS receiver can determine its geographic location from information it receives from several dedicated GPS satellites in earth orbit. There are presently 24 NAVSTAR satellites that broadcast GPS signals globally. The use of regular GPS will not provide us with the required accuracy for this domain, as it is only accurate to about 10 – 40 metres. A system known as Differential GPS improves this to around 1-3 metres, however this still isn’t sufficient .
However, the emerging development of Carrier Phase GPS, allows us to obtain sub-centimetre accuracy , which would be required when locating and clearing landmines. As expected, this is a very expensive technology, but like anything else, as the demand for it emerges, the cost should drop considerably. GPS can represent specific locations using (x,y,z) coordinates, where x and y determine its geographic position, and z determines its altitude relative to average sea level values. These coordinate values can then be represented to our robots/centralized system.
Expert systems must be knowledge-rich even if their methods are poor. 1 A good knowledge base is the key to a good expert system. In the landmine problem we would require many varying knowledge bases. Examples of these might include terrain types, mine types and weather conditions. When detecting or destroying a mine, the system will need to use its array of knowledge in order to make various important decisions. Being made immobile by either falling a great distance, sinking or getting stuck in unstable terrain is a major problem for a search and detection system.
In any search space it is likely that the terrain will be of a diverse nature. The topology of all countries varies enormously and because landmines have been used in up to 69 countries,7 this means the knowledge base of terrains will differ for each country and climate. Terrain is also one of the main factors in the planting of landmines. Terrain can be rocky, rolling or flat, and landmines cannot be planted in concrete, rock or deep water. It is essential that the search and detection devices will be able to distinguish between different types of terrain.
Another consideration would be water. Landmines have previously been planted in water that is shallow enough to wade through. There are up to fifteen various water mines in existence today. An example of such a landmine would be the ALCM-82 shallow water mine, used in North Korea2. A detection device must be able to distinguish between water that is shallow enough to wade through and deeper water. Another consideration for the knowledge base of detection systems would be forest and areas of high vegetation. Any system must know how to navigate these areas successfully.
Vegetation in some areas may have to be cleared before any detection can be carried out. The knowledge base must be able to distinguish between areas of not so dense vegetation that can easily be searched, and vegetation that must be cleared. Then the system, with the help of its knowledge base should be able to determine the best way to clear it. A machine produced by Mine Tech, known as the Agribush Flail, 3 can be used to clear vegetation in mine fields. A knowledge base of soil would also be needed, and again it must be able to distinguish between these types.
Probably one of the most important aspects of the knowledge base of any detection and detonation system would be its database of mine types. Mine types come in three main types – antipersonnel landmines, anti-tank landmines and blast antipersonnel mines. Anti-personnel mines with fragmentation are only partially dug inside the ground. In some cases, they bounce up before exploding, or they might explode in a certain direction. Fragmentation mines are frequently triggered by wire and are lethal within a radius of about 30m. Anti-tank mines are packed with explosives to disable any tanks unfortunate enough to come across them.
They react on ground pressures of 150-300 kg or by induction. Blast antipersonnel mines include less than 100 grammes of explosive. As they are small and easy to manufacture, they are currently the most plentiful type of mine. When surrounded by grass, they can be difficult to see. Blast mines can be detonated by a ground pressure of about 10kg/dm2, usually using trip wire. These mines are not designed to kill, but to badly maim4. A detection system must be able to tell the difference between these three main types of mine.
Once it has identified the main type of landmine then there are up to 700 different mine types within each category. This adds up to over 2000 different types of landmines with each mine producing country making up to 100 different mines each. The former Soviet Union has produced up to 115 different mines alone5. All these land mines vary in case material, shape, length, height, diameter and the material they are made of. Each mine has also has a different effect such as blast, fragmentation, side attack, direct fragmentation, shaped and dual shaped charge.
A good knowledge base of landmine types is especially important for the detonation of landmines. The detonation of an antipersonnel mine that can spread up to fifteen meters of shrapnel can have a detrimental effect for the surrounding environment, making the land useless until all the remaining pieces of metal have been cleared. A good system must be able to identify each landmine type and associate an appropriate way of detonation with each mine type. The options here include moving the mine to a safe place and detonating it there, or to detonate it on the spot.
One major problem posed in landmine detonation and clearance is the high false alarm rate which most of today’s systems encounter. The US army’s false alarm rate is one false alarm per 1. 25 square meters6. This is a huge problem, as any humanitarian de-mining technique’s main goal is to be as accurate as possible. When accuracy is taken into account, every piece of material that could be a landmine must be treated as such. One way to reduce the false alarm rate of a system would be to include a good knowledge base of materials that could possibly be landmines.
This knowledge base would have to contain all known materials that any existing landmine consists of. These include metal, plastic, wood, concrete, glass and ceramic. However, it would be important that the system would be able to determine whether a detected piece of metal was actually a mine or not. One thing that all mines have in common is that they are all packed with TNT or other types of explosive. If an explosive material is detected then a detection system can almost guarantee that it has discovered a landmine.
If no explosive is detected, then the piece of metal may simply be a piece of shrapnel from a mine that was previously detonated. Of course, the piece of metal could also be there for other reasons. Design of Robots In this section we must consider possible design principles for our robot fleet. These include issues such as: – how the robots will be organized in order to work as a unit – how the robots will communicate with each other – detection and destruction mechanisms – protection of robots from unintentional mine blasts Robot Configuration Obviously, how the robots communicate with each other is very important.
We could adopt a policy whereby the robots communicate directly with each other, constantly notifying each other of developments in their particular area of the search space. Alternatively, we could also have a centralized system, where there would be one automated robot manager in the vicinity of the search area, which would designate tasks for each robot, while monitoring the status of all robots working in the search domain . With this system, the robots may not need to communicate with each other, and they would only do what they are told to do by the central manager.
So for example, if two of the robots were in danger of colliding with other, the centralized manager would send a warning to each of the robots, rather than the two robots warning each other. Aerial search and destroy technologies If we were to adopt an aerial ‘search and destroy’ strategy, we would have a couple of options. After our research on balloon technology, we realized that this is currently not a feasible solution, although technological advances are being made in this area. Virgin’s multi-millionaire owner Richard Branson is currently campaigning for corporate support to finance research in this area.
 Branson believes that balloon technology, used in conjunction with the latest radar technology that is capable of detecting and mapping mines at 100m/s, could possibly result in a major breakthrough in fighting the landmine problem. Currently, the main problem with balloon technology is its inability to cope with windy conditions, although Floatograph Technologies in Napa, California are making major strides in this area. They claim that they are currently developing a balloon that can handle hurricane force winds .
It wouldn’t be surprising if more significant breakthroughs were made in this area over the next few years. However, there presently is a better solution – known as the ‘Camcopter'. This is a remote controlled helicopter that has been specially designed for identification and detection of landmines. It contains an on-board GCD camera and infrared sensor, which is used in conjunction with a Ground Control System. During testing, the ‘Camcopter’ performed at impressive cruising speeds of 90km/h, and reached altitudes of up to 1700 metres, albeit in favourable weather conditions.
It has a maximum fuel capacity of 5 to 30 litres, and an average burn-off rate of 4 litres per hour. Like most anti-mine systems being developed, it performs best in flat, uninhabited areas where vegetation is minimal, although it is capable of working well in less favourable conditions. Although balloon technology could possibly be a more cost-effective solution, the ‘Camcopter’ appears to be the best aerial mine location system present at the moment. Physical Communication of System How each of the robots will physically communicate with each other, or with a centralized coordinator is another issue.
Infrared is currently being used to allow robots to communicate and identify each other’s position, but this is not applicable here, because it’s range wouldn’t be sufficient for this domain. A system based on broadband cables or fibre-optics is immediately dismissed because of the simple reason that we can’t allow the presence of long cables all over our domain, risking the detonation of landmines, which could possibly result in the destruction of one or more robots. So therefore, we need a wireless solution. In tandem with this wireless solution, we could use a socket-based technology for robots, known as RoboComm.
It is basically aimed at simplifying asynchronous computer-robot/robot-robot communication, using standard socket principles in conjunction with Java based objects . Using this system, robots can broadcast to the centralized server, or to each other, depending on how the system is configured. To compliment this we need some sort of wireless medium, probably radio of satellite. Examples of radio-based modems would include the YDI series, most notably the YDI Model 192MM, and the Paradise Datacomm P400-480 series provide more than adequate satellite coverage.
A radio modem installed in each robot would ensure adequate coverage, but the much superior data transfer rate of the satellite modem may be required, depending on the complexity of the design. A brief example would be if human analysts located a long distance away from the search wished to view the robots in the search area, a camera could be installed on some or all of the robots. Using our satellite link, we could transmit the pictures to probably anywhere in the world. Radio waves would not provide us with this facility.
However, radio technology is currently much more accessible than satellite in the world’s poorer areas, where coincidentally the vast majority of the world’s landmines are situated. Neutralization and destruction of landmines During our research we have discovered three main methods to deal with this area of our study. The first, ‘Mine Marking and Neutralization Foam’, provides a method to safely mark and remove exposed landmines if neutralization is not possible of preferable at a particular point. Polyurethane foam is applied to the landmines.
With its bright colour easily marking the mine, the foam then hardens, impregnates the exposed parts of the mine, rendering the fuse inoperable. This hardened foam then prevents detonation of the mine even if it is accidentally landed on, or stepped on. The foam acts as an adhesive to stick a rope to the mine so that it can be safely removed to be later detonated in a controlled explosion. Although this method may be successful in humanitarian efforts involving human de-miners, it is obviously unsuitable for our requirements as it only deals with mines that are exposed on the surface of the earth.
The second method is a device known as an ‘Explosive De-mining Device’ (EDD). This device is a tripod mounted shaped charge integrated into a fixed-time delay fuse assembly. After rigourous international testing, these devices proved themselves to be very effective, mainly because their ability to destroy plastic, metal and wooden mines at a ground depth of up to 22 inches. Advantages of the device include the fact that it is simple to operate, and is sufficiently stable to be moved and stored as a class 1. 1D explosive .
The main disadvantage of these devices is that even though they are simple to use, the operation of the device is still hazardous as it involves the use of shaped charge explosives. Currently there is no way of electronically detonating the device, and the time delay fuse could prove dangerous should our robot get into difficulty. Detonating metallic mines also creates more metallic fragments to further confuse later de-mining operations, and may also hinder the use of such land for agriculture in the future.
A third option, which is in our opinion the most suitable one, is a de-mining system that consists of a Chemical Neutralization Device. This involves the remote control firing of a bullet through a “gun” into the mine. These bullets contain a capsule of chemicals such as diethyl amine, diethylenetriamine and diethylzinc. These bullets penetrate the mine casing and initiate a reaction within the mine that will burn the explosive charge. They work even if the mines are buried and air is not required to sustain the combustion within the mine as the explosive itself has oxidizing power in NO2 groups.
This then disables the mine allowing it to be extracted form the earth and moved to a safe location for a controlled explosion to ensure that the explosives are completely one hundred percent destroyed. The advantage of these chemicals is that they don’t detonate the explosive. We would recommend the use of such devices because there are no harmful environmental side effects associated with this system. The amount of chemicals used is very small and they are consumed during the neutralization process . The benefit of a system that destroys mines without leaving fragments behind is hugely significant for us.
However, problems do exist, because at the moment the chemicals must be tailor mixed depending on mine case thickness. The de-miner must therefore know the exact type of mine that they are dealing with, and what mix formula to use on it. The special handling and storage requirements of the chemicals further increase the complexity of the system. The aim for future developments , is to have one chemical and one delivery system to neutralize all mines, elimination of the need for specialized storage and handling requirements, and to make the system simpler, less expensive and disposable.
Detection methods for Landmines Infrared Detection As mines release heat at a different rate than their surroundings, we can measure the thermal contrast between the soil close to a mine and the rest of the soil using Infrared detection. This can be done during natural temperature variations in the environment. The main problem with this however is that infrared can depend heavily on the environment, and is known to work poorly in hot conditions. The presence of thick foliage can also cause problems.
Image from Infrared during the day Image from Infrared during night Ground penetrating Radar (GPR) This is also a very expensive method of mine detection. This system works by emitting an electromagnetic wave into the ground, through a wide-band antenna. Reflections in the soil caused by dielectric variations such as the presence of an object are measured. By moving the antenna, it is possible to reconstruct an image representing a vertical slice of the soil.
A problem here is that resolutions needed to cope with very small objects enforces the use of frequencies of some GHz, limiting the penetration depth and increasing the image clutter. Seismic Wave Analyser This works by simultaneously using sound waves to create tiny soil disturbances, and precision radar to measure the resulting movement. It uses a transducer to create seismic waves that travel through the soil. The tiny movements in the soil can be detected by electromagnetic waves from a small radar system attached to an airborne robot.