One of the largest threats to the human race today is the existence of over 100 million land mines in over 70 countries, and some sources say an additional 5 million new ones are buried annually. Undiscovered mines pose problems for countries who need to reclaim as much land as possible for agricultural purposes, as well as innocent civilians who continue to suffer long after the conflicts have ended. An estimated 26,000 people are killed each year by land mines, many of whom are children playing in fields. There are a number of ways to detect these devices, from simple metal detectors to advanced sonic generators, but so far none of these methods have proven to be 100% effective, and the cost of some methods are prohibitive.
One of the oldest methods for detecting land mines is a simple loop metal detector. Trained soldiers would sweep over a suspected minefield and use long prods to investigate any positive signs of buried metal. Any mines found by this method would either be defused on the spot or marked for future action. In conjunction with the mine sweeping efforts, heavy bulldozers would often be equipped with forward-mounted flails or weights designed to detonate the mines. This method was generally used to provide safe passage for troops, not to clear out an entire field. The level of false positive readings was also very high, since other metal shrapnel would set off the detectors and disguise the signature of a real mine. Anti-personnel devices were also primarily made of ceramics or plastics not easily detected by traditional electronic sweepers.
Another way to detect land mines is through the use of trained animals. Dogs can be trained to sniff out the chemical signatures of buried land mines and signal their human controllers, but such work can be exhausting for the animals and dangerous for the human disposal teams. Other animals have also been used in a similar fashion, including several species of rats. These rats can be trained to walk through a field and signal any positive hits. These animals are especially useful since they are too light to detonate most devices. The search process can still be very labor-intensive, with cost estimates running from $300 to $3,000 US Dollars (USD) per detected mine.
Small robots are also used to detect land mines, although refinements still need to be made before they can be used on a large scale. These remote controlled robots are attached to compact metal detectors or ground-penetrating radar units and sent out into suspected mine fields. A human operator can look for distinctive electronic signatures which could mean that a mine is present. The robot releases a marking spray and returns to its staging area. Creating such a robot is very expensive, however, and the identification technology is still not perfected.
To eliminate the problem of false positive readings and metal pollution, scientists are also working on a sonic detection system designed to penetrate the ground and actually cause the casings of land mines to vibrate. Conventional sound wave generators are not practical for detection purposes, since the amount of sound energy required would deafen anyone in the area. Much like a laser beam concentrates light energy, a new form of sonic generator would focus the sound waves on a specific area and detect the vibrations of any devices buried there. The sound would not be audible even a few feet away from the device, making it safe for human use. The safe removal of detected mines would still remain problematic, but at least the number of false positives would be reduced.
One interesting new method for detecting mines is still in the experimental stage, but shows great promise. A form of the leafy plant called watercress has been genetically engineered to turn red in the presence of chemicals associated with these devices. The plan to use this modified watercress would first involve spraying a suspected minefield with a special fertilizer. Watercress seeds would then be dropped into the field and allowed to grow. Within a few weeks, any exposure to the chemicals contained in land mines will cause the watercress leaves to turn red, thus marking the mines' lcoation The modified watercress only grows in the special fertilizer, which would reduce the chances of an invasive overgrowth similar to kudzu. This method would be organic, accurate and economical, since a large area of arable land could be cleared of explosives in far less time than the methods currently in use.