Deminer

Demining or mine clearance is the process of removing land mines from an area. In military operations, the object is to rapidly clear a path through a minefield, and this is often done with devices such as mine plows and blast waves. By contrast, the goal of ''humanitarian demining'' is to remove all of the landmines to a given depth and make the land safe for human use. Specially trained dogs are also used to narrow down the search and verify that an area is cleared. Mechanical devices such as flails and excavators are sometimes used to clear mines.

A great variety of methods for detecting landmines have been studied. These include electromagnetic methods, one of which (ground penetrating radar) has been employed in tandem with metal detectors. Acoustic methods can sense the cavity created by mine casings. Sensors have been developed to detect vapor leaking from landmines. Animals such as rats and mongooses can safely move over a minefield and detect mines, and animals can also be used to screen air samples over potential minefields. Bees, plants, and bacteria are also potentially useful. Explosives in landmines can also be detected directly using nuclear quadrupole resonance and neutron probes.

Detection and removal of landmines is a dangerous activity, and personal protective equipment does not protect against all types of landmine. Once found, mines are generally defused or blown up with more explosives, but it is possible to destroy them with certain chemicals or extreme heat without making them explode.

Land mines

Land mines overlap with other categories of explosive devices, including unexploded ordnance (UXOs), booby traps and improvised explosive devices (IEDs). In particular, most mines are factory-built, but the definition of landmine can include "artisanal" (improvised) mines. Thus, the United Nations Mine Action Service includes mitigation of IEDs in its mission. Injuries from IEDs are much more serious, but factory-built landmines are longer lasting and often more plentiful. Over 1999–2016, yearly casualties from landmines and unexploded ordnance have varied between 9,228 and 3,450. In 2016, 78% of the casualties were suffered by civilians (42% by children), 20% by military and security personnel and 2% by deminers.

There are two main categories of land mine: anti-tank and anti-personnel. Anti-tank mines are designed to damage tanks or other vehicles; they are usually larger and require at least of force to trigger, so infantry will not set them off.

Anti-personnel mines are designed to maim or kill soldiers. There are over 350 types, but they come in two main groups: ''blast'' and ''fragmentation''. Blast mines are buried close to the surface and triggered by pressure. A weight between , the weight of a small child, is usually enough to set one off. They are usually cylindrical with a diameter of and a height of . Fragmentation mines are designed to explode outwards resulting in casualties as much as 100 metres away. A subtype of fragmentation mines called "bounding" mines are specifically designed to launch upward off the ground before detonating. Their size varies and they are mostly metal, so they are easily detected by metal detectors. However, they are normally activated by tripwires that can be up to 20 metres away from the mine, so tripwire detection is essential.

The casing of blast mines may be made of metal, wood, or plastic. Some mines, referred to as minimum metal mines, are constructed with as little metal as possible – as little as – to make them difficult to detect. Common explosives used in land mines include TNT (), RDX (), pentaerythritol tetranitrate (PETN, ), HMX () and ammonium nitrate ().

Land mines are found in about 60 countries. Deminers must cope with environments that include deserts, jungles, and urban environments. Antitank mines are buried deeply while antipersonnel mines are usually within 6 inches of the surface. Mines may be placed by hand or scattered from airplanes, in regular or irregular patterns. In urban environments, fragments of destroyed buildings may hide them; in rural environments, soil erosion may cover them or displace them. Detectors can be confused by high-metal soils and junk. Thus, demining presents a considerable engineering challenge.

Goals

Military

In military demining, the goal is to create a safe path for troops and equipment. The soldiers who carry out this task are known as combat engineers, sappers, or pioneers. Sometimes soldiers may bypass a minefield, but some bypasses are designed to concentrate advancing troops into a killing zone. If engineers need to clear a path (an operation known as ''breaching''), they may be under heavy fire and need supporting fire to suppress the enemy or obscure the site with smoke. Some risk of casualties is accepted, but engineers under heavy fire may need to clear an obstacle in 7–10 minutes to avoid excessive casualties, so manual breaching may be too slow. They may need to operate in bad weather or at night. Good intelligence is needed on factors like the locations of minefields, types of mines and how they were laid, their density and pattern, ground conditions and the size and location of enemy defenses.

Humanitarian

Humanitarian demining is a component of mine action, a broad effort to reduce the social, economic and environmental damage of mines. The other "pillars" of mine action are risk education, victim assistance, stockpile destruction, and advocacy against the use of anti-personnel mines and cluster munitions. Humanitarian demining differs from military demining in several ways. Military demining operations require speed and reliability under combat conditions to safely bypass a mine field so it is more acceptable if some mines are missed in the process. Humanitarian demining aims to reduce risk for deminers and civilians as much as possible by removing (ideally) all landmines and demining work can usually be temporarily halted if unfavorable circumstances arise. In some situations, it is a necessary precondition for other humanitarian programs. Normally, a national mine action authority (NMAA) is given the primary responsibility for mine action, which it manages through a mine action center (MAC). This coordinates the efforts of other players including government agencies, non-governmental organizations (NGOs), commercial companies, and militaries.

The International Mine Action Standards (IMAS) provide a framework for mine action. While not legally binding in themselves, they are intended as guidelines for countries to develop their own standards. The IMAS also draw on international treaties including the Mine Ban Treaty, which has provisions for destroying stockpiles and clearing minefields.

In the 1990s, before the IMAS, the United Nations required that deminers had to clear 99.6% of all mines and explosive ordnance. However, professional deminers found that unacceptably lax because they would be responsible if any mines later harmed civilians. In contrast, the IMAS call for the clearance of ''all'' mines and UXOs from a given area to a specified depth.

Contamination and clearance

As of 2017, antipersonnel mines are known to contaminate 61 states and suspected in another 10. The most heavily contaminated (with more than 100 square kilometres of minefield each) are Afghanistan, Angola, Azerbaijan, Bosnia and Herzegovina, Cambodia, Chad, Iraq, Thailand and Turkey. Parties to the Mine Ban Treaty are required to clear all mines within 10 years of joining the treaty, and as of 2017, 28 countries had succeeded. However, several countries were not on track to meet their deadline or had requested extensions.

A 2003 RAND Corporation report estimated that there are 45–50 million mines and 100,000 are cleared each year, so at present rates it would take about 500 years to clear them all. Another 1.9 million (19 more years of clearance) are added each year. However, there is a large uncertainty in the total number and the area affected. Records by armed forces are often incomplete or nonexistent, and many mines were dropped by airplane. Various natural events such as floods can move mines around and new mines continue to be laid. When minefields are cleared, the actual number of mines tends to be far smaller than the initial estimate; for example, early estimates for Mozambique were several million, but after most of the clearing had been done only 140,000 mines had been found. Thus, it may be more accurate to say that there are millions of landmines, not tens of millions.

Before minefields can be cleared, they need to be located. This begins with ''non-technical survey'', gathering records of mine placement and accidents from mines, interviewing former combatants and locals, noting locations of warning signs and unused agricultural land, and going to look at possible sites. This is supplemented by ''technical survey'', where potentially hazardous areas are physically explored to improve knowledge of their boundaries. A good survey can greatly reduce the time required to clear an area; in one study of 15 countries, less than 3 percent of the area cleared actually contained mines.

Economics

By one United Nations estimate, the cost to produce a landmine is between $3 and $75 while the cost of removing it is between $300 and $1000. However, such estimates may be misleading. The cost of clearance can vary considerably since it depends on the terrain, the ground cover (dense foliage makes it more difficult) and the method; and some areas that are checked for mines turn out to have none.

Although the Mine Ban Treaty gives each state the primary responsibility to clear its own mines, other states that can help are required to do so.
In 2016, 31 donors (led by the United States with $152.1 million and the European Union with $73.8 million) contributed a total of $479.5 million to mine action, of which $343.2 million went to clearance and risk education. The top 5 recipient states (Iraq, Afghanistan, Croatia, Cambodia and Laos) received 54% of this support.

Conventional detection methods

The conventional method of mine detection was developed in World War II and has changed little since then. It involves a metal detector, prodding instrument and tripwire feeler. Deminers clear an area of vegetation and then divide it into lanes. A deminer advances along a lane, swinging a metal detector close to the ground. When metal is detected, the deminer prods the object with a stick or stainless steel probe to determine whether it is a mine. If a mine is found, it must be deactivated.

Although conventional demining is slow (5–150 square metres cleared per day), it is reliable, so it is still the most commonly used method. Integration with other methods such as explosive sniffing dogs can increase its reliability.

Demining is a dangerous occupation. If a mine is prodded too hard or it is not detected, the deminer can suffer injury or death. The large number of false positives from metal detectors can make deminers tired and careless. According to one report, there is one such incident for every 1000–2000 mines cleared. 35 percent of the accidents occur during mine excavation and 24 percent result from missed mines.

Prodders

In World War II, the primary method of locating mines was by prodding the ground with a pointed stick or bayonet. Modern tools for prodding range from a military prodder to a screwdriver or makeshift object.. In They are inserted at shallow angles (30 degrees or less) to probe the sides of potential mines, avoiding the triggering mechanism that is usually on top. This method requires the deminer's head and hands to be near the mine. Rakes may also be used when the terrain is soft (e.g., sandy beaches); the deminer is further away from the mine and the rake can be used to either prod or scoop up mines from beneath.

Metal detectors

Metal detectors used by deminers work on the same principles as detectors used in World War I and refined during World War II. A practical design by Polish officer Józef Kosacki, known as the Polish mine detector, was used to clear German mine fields during the Second Battle of El Alamein.

Although metal detectors have become much lighter, more sensitive and easy to operate than the early models, the basic principle is still electromagnetic induction. Current through a wire coil produces a time-varying magnetic field that in turn induces currents in conductive objects in the ground. In turn, these currents generate a magnetic field that induces currents in a receiver coil, and the resulting changes in electric potential can be used to detect metal objects. Similar devices are used by hobbyists.

Nearly all mines contain enough metal to be detectable. No detector finds all mines, and the performance depends on factors such as the soil, type of mine and depth of burial. An international study in 2001 found that the most effective detector found 91 percent of the test mines in clay soil but only 71 percent in iron-rich soil. The worst detector found only 11 percent even in clay soils. The results can be improved by multiple passes.

An even greater problem is the number of false positives. Minefields contain many other fragments of metal, including shrapnel, bullet casings, and metallic minerals. 100–1000 such objects are found for every real mine. The greater the sensitivity, the more false positives. The Cambodian Mine Action Centre found that, over a six-year period, 99.6 percent of the time (a total of 23 million hours) was spent digging up scrap.

Dogs

Dogs have been used in demining since World War II.* They are up to a million times more sensitive to chemicals than humans, but their true capability is unknown because they can sense explosives at lower concentrations than the best chemical detectors. Well-trained mine-detection dogs (MDDs) can sniff out explosive chemicals like TNT, monofilament lines used in tripwires, and metallic wire used in booby traps and mines. The area they can clear ranges from a few hundred to a thousand meters per day, depending on several factors. In particular, an unfavorable climate or thick vegetation can impede them, and they can get confused if there is too high a density of mines. The detection rate is also variable, so the International Mine Action Standards require an area to be covered by two dogs before it can be declared safe.

Preferred breeds for MDDs are the German Shepherd and Belgian Malinois, although some Labrador Retrievers and Beagles are used. They cost about $10,000 each to train. This cost includes 8–10 weeks of initial training. Another 8–10 weeks is needed in the country where the dog is deployed to accustom the dog to its handler, the soil and climate, and the type of explosives.

MDDs were first deployed in WWII. They have been extensively used in Afghanistan, which still has one of the largest programs. Over 900 are used in 24 countries. Their preferred role is for verifying that an area is cleared and narrowing down the region to be searched. They are also used in Remote Explosive Scent Tracing (REST). This involves collecting air samples from stretches of land about 100 meters long and having dogs or rats sniff them to determine whether the area needs clearing.

Mechanical

Mine clearing machines

Mechanical demining makes use of vehicles with devices such as tillers, flails, rollers, and excavation. Used for military operations as far back as World War I, they were initially "cumbersome, unreliable and under-powered", but have been improved with additional armor, safer cabin designs, reliable power trains, Global Positioning System logging systems and remote control. They are now primarily used in humanitarian demining for technical surveys, to prepare the ground (removing vegetation and tripwires), and to detonate explosives.

Tiller systems consist of a heavy drum fitted with teeth or bits that are intended to destroy or detonate mines to a given depth. However, mines can be forced downwards or collected in a "bow wave" in front of the roller. They have trouble with steep slopes, wet conditions and large stones; light vegetation improves the performance, but thicker vegetation inhibits it. Flails, first used on Sherman tanks, have an extended arm with a rotating drum to which are attached chains with weights on the end. The chains act like swinging hammers. The strike force is enough to set off mines, smash them to pieces, damage the firing mechanism or throw the mine up. A blast shield protects the driver and the cabin is designed to deflect projectiles. Mine flail effectiveness can approach 100% in ideal conditions, but clearance rates as low as 50–60% have been reported.

First used in World War I with tanks, rollers are designed to detonate mines; blast-resistant vehicles with steel wheels, such as the Casspir, serve a similar purpose. However, those used in humanitarian demining cannot withstand the blast from an anti-tank mine, so their use must be preceded by careful surveying. Unlike flails and tillers, they only destroy functioning mines, and even those do not always explode.

Excavation, the removal of soil to a given depth, is done using modified construction vehicles such as bulldozers, excavators, front-end loaders, tractors and soil sifters. Armor plates and reinforced glass are added. Removed soil is sifted and inspected. It can also be fed through an industrial rock crusher, which is robust enough to withstand blasts from antipersonnel mines. Excavation is a reliable way of clearing an area to a depth that other mechanical systems cannot reach, and it has been used in several countries. In particular, the HALO Trust estimates that their excavation program destroys mines about 7 times faster than manual deminers.

A 2004 study by the Geneva International Centre for Humanitarian Demining concluded that the data on the performance of mechanical demining systems was poor, and perhaps as a result, they were not being used as the primary clearance system (with the exception of excavators). However, by 2014, confidence in these systems had increased to the point where some deminers were using them as primary clearance systems.

Mechanical demining techniques have some challenges. In steep, undulating terrain they may skip over some of the ground. Operators can be endangered by defective mines or mines with delay charges that detonate after the blast shield has passed over; shaped charge mines that are capable of piercing most armor; and intelligent mines that are off to the side and use a variety of sensors to decide when to fire a rocket at an armored vehicle. One answer is to use remote controlled vehicles such as the Caterpillar D7 MCAP (United States) and the Caterpillar D9 (Israel).

File:M4a4 flail cfb borden 1.JPG, World War II M4 Sherman tank fitted with a flail
File:Hydrema mine cleaning vehicle.jpg, Hydrema mine clearing vehicles use flails.
File:Casspir vehicle Ai101503g1.jpg, The Casspir, a steel, armor-bodied V-hulled vehicle de-mining Bagram Air Base
File:D9-IDF-1460a.jpg, IDF Caterpillar D9 uses a standard blade or a special mine plow.

Smart prodders

Despite advances in mine detection technology, "mine detection boils down to rows of nervous people wearing blast-resistant clothing and creeping laboriously across a field, prodding the ground ahead to check for buried objects." Often, especially when the soil is hard, they unwittingly apply too much force and risk detonating a mine. Prodders have been developed that provide feedback on the amount of force.

Detection methods under development

Universities, corporations and government bodies have been developing a great variety of methods for detecting mines. However, it is difficult to compare their performance. One quantitative measure is a receiver operating characteristic (ROC) curve, which measures the tradeoff between false positives and false negatives. Ideally, there should be a high probability of detection with few false positives, but such curves have not been obtained for most of the technologies. Also, even if field tests were available for all technologies, they may not be comparable because performance depends on a myriad of factors, including the size, shape and composition of the mines; their depth and orientation; the type of explosive; environmental conditions; and performance of human operators. Most field tests have taken place in conditions that favor the performance of the technology, leading to overestimates of their performance.

Electromagnetic

Ground-penetrating radar

Ground-penetrating radar (GPR) probes the ground using radar. A GPR device emits radio waves; these waves are reflected at discontinuities in permittivity and one or more antennae pick up the return signal. The signal is analyzed to determine the shapes and locations of the reflectors. Discontinuities occur between materials with different dielectric constants such as a landmine, a rock and soil. Unlike metal detectors, GPR devices can detect nonmetallic mine casings. However, radio waves have wavelengths that are comparable to the dimensions of landmines, so the images have low resolution. The wavelength can be varied; smaller wavelengths give better image quality but cannot penetrate as far into the soil. This tradeoff in performance depends on soil properties and other environmental factors as well as the properties of the mines. In particular, attenuation in wet soils can make it difficult to spot mines deeper than , while low-frequency radar will "bounce" off small plastic mines near the surface. Although GPR is a mature technology for other applications such as searching for archaeological artifacts, the effect of those factors on mine detection is still not adequately understood, and GPR is not widely used for demining.

GPR can be used with a metal detector and data-fusion algorithms to greatly reduce the false alarms generated by metallic clutter. One such dual-sensor device, the Handheld Standoff Mine Detection System (HSTAMIDS) became the standard mine detector of the U.S. Army in 2006. For humanitarian demining, it was tested in Cambodia for a variety of soil conditions and mine types, detecting 5,610 mines and correctly identifying 96.5% of the clutter. Another dual detector developed by ERA Technology, the Cobham VMR3 Minehound, had similar success in Bosnia, Cambodia and Angola. These dual-sensor devices are relatively light and cheap, and the HALO Trust has begun to deploy more of them around the world.

Infrared and hyperspectral

Soil absorbs radiation from the Sun and is heated, with a resulting change in the infrared radiation that it emits. Landmines are better insulators than soil. As a result, the soil overhead tends to heat faster during the day and cool faster at night. Thermography uses infrared sensors to detect anomalies in the heating and cooling cycle. In The effect can be enhanced using a heat source. The act of burying a mine also affects the soil properties, with small particles tending to collect near the surface. This tends to suppress the frequency-dependent characteristics that are evident in the larger particles. Hyperspectral imaging, which senses dozens of frequency bands ranging from visible light to long-wave infrared, can detect this effect. Finally, polarized light reflecting off man-made materials tend to remain polarized while natural materials depolarize it; the difference can be seen using a polarimeter