The Challenge is to locate a potentially injured Coal Miner, in a Coal Mine that has just collapsed, using some kind of technology (You don't want to send in even more people in to a dangerous location, if you don't have to do so). Sounds easy doesn't it? The first answers is always "Use GPS". GPS is 100% completely useless underground in a Coal Mine. Next problem is that Coal absorbs most radio frequencies. The physical environment also has several challenges. Dust so thick that you can not see through it. Work shifts last twelve hours, which makes powering anything a challenge, and you are not allowed to replace the batteries in most areas of the Coal Mine. Also there are extremely stringent regulations on the use of Lithium Batteries. There are few to none, power outlets where you could plug anything in to power it. There also issues of Intrinsic Safety, where available energy is extremely limited. Your total energy budge must not be capable of igniting a Methane Gas atmosphere. Finally it must be small physically, would you want to carry your design around for twelve hours?
Keep in mind that idea is to location someone after the mine has suffered some type of catastrophic damage. This means that placing 'way points', or anything like that is not the way to go for reference points, as there is no way to know how they might be damaged. This doesn't rule reference points out, but you can not rely on them. Running wires (Leaky Feeders for example), or fiber, of any type is also not going to work, as they are prone to being damaged.
Do you have an idea that no one has yet thought of?
