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"I see you, a thief on the roof. My new satellite link has both infrared and the x-ray spectrum. I see your heart beating. I see you are afraid."—Gunther Hermann, Deus Ex
Whenever someone calls for the infrared camera on TV shows and film these days, either the handheld version or one mounted on Spy Satellites, the device will have amazing qualities, chief among them being able to see through walls. It's incredibly convenient for the good guys being able to make out what's happening inside the building. Sadly, real thermal imaging infrared cameras don't work like that at all. Heat simply doesn't go through walls in such a way to form a picture. Walls are generally supposed to stop heat from getting through them, which is why they are insulated. In fact an infrared camera meant for thermal imaging (as opposed to near-infrared), the kind most often seen on TV and movies, cannot even see through a sheet of regular glass that's perfectly clear to anyone using the Mark One Eyeball. Anyone looking at a sheet of glass with a thermal imager is more likely to see their own reflection. Steam is not good for IR either, but any light fog (which is usually cool) could be penetrable to an extent.
The truth is plainly obvious from all those televised high-speed chases in Los Angeles where, to pump up the ratings during sweeps, the chase takes place at night so the Forward Looking Infrared camera on the police helicopter gets to show the Cool High Tech imagery. You can see the heat of the car engine, the tires, the ground where something hot has been, even the reflection of heat off the ground, yet you can't see the driver and his passengers although the few millimeters of metal making up the car body is a lot thinner than the several inches of material making up the average house wall. Not to mention, it conducts heat better. One can therefore conclude that either writers and directors don't watch Fox, or that it's yet another case of technology gone awry in the service of the plot.
The infrared spectrum is over three thousand times wider than the visible spectrum (visible = 400nm to 700nm; infrared = 700nm to 1,000,000nm) and has substantially different properties depending on which part of the infrared spectrum you are at. The infrared spectrum is typically divided into four groups:
- Near-infrared (wavelengths of 700 nm to 1400 nm): Produced by objects that are glowing hot (light bulbs, the sun, fires). Most "night vision" cameras use this because the sensors are cheap (just stick a visible-light-blocking filter over a digital camera sensor) and because you can illuminate an area with IR-emitting LEDs without anyone noticing. Most greyscale night images are using this part of the infrared spectrum. Glass is quite transparent to this, as are many lightweight fabrics (most notably, those used in swimsuits). Metal reflects it, and most opaque objects block it. If you assume it behaves like visible light, you usually won't be wrong.
- Mid-infrared (wavelengths of 1400 nm to 8000 nm): Produced by objects that aren't quite glowing hot (jet engines and the like). Used mostly by heat-seeking missiles.
- Long-wave or thermal infrared (8000 nm to 15,000 nm): Produced by objects that are at "reasonable" temperatures. This is the band that is used by heat-detecting cameras. These cameras are quite expensive, and need to be cooled down below the temperature of the environment (otherwise, they'd see themselves rather than the world around them). Most solid objects will block or smear the IR from objects behind them, while adding their own heat to the mix.
- Far infrared (15,000 nm to 1,000,000 nm): Produced by cold objects (think "liquid nitrogen" cold) and by specialized scientific equipment. Not much practical use.
Terahertz radiation (T-rays) sit uncomfortably on the border between infrared and microwaves. They're hard to produce and hard to detect, but most non-conductive objects (walls, clothing, etc) are transparent to them while most conductive objects (metal, the water in your body) reflect them. They're
mostly a scientific curiosity right now already being used for airport security in a number of countries, and known as "nude scanners".
- Mobile Suit Gundam Wing is quite guilty of a variation of this, with heat sensors able to tell whether a mobile suit is manned. In space. Through several feet of armor. In a cockpit that is insulated enough to allow remain at a comfortable temperature even in space. Mobile suits have fusion reactors as well. And rockets all over. As well as using high-powered beam weaponry. But no, apparently the only source of heat on a mobile suit comes from the pilot.
- A mobile suit in deep space would not have to be well insulated--with vacuum being the ideal insulator, they'd be far more concerned with radiating away the heat the vessel would accumulate in space combat. Either way, the pilot's body heat isn't going to be visible.
- Used by RoboCop to surreptitiously pinpoint the location of a hostage-taker; after that it's just a matter of reaching through the wall and grabbing.
- Not a camera, but the monsters of Tremors 2: Aftershocks see in infrared. And subvert the usual X-Ray properties assumed to go with it; at one point the heroes hide themselves by holding doors in front of their bodies while moving, making themselves nigh-invisible to the beasties. A character also hides in the bucket of a backhoe which, as the monsters are short, they can't look over the sides to see into while milling around.
- Generally subverted in Predator when Dutch realized the creature sees in infrared when it couldn't spot him covered in (cooler) mud which temporarily disguised his body heat. When the film shows scenes from the Predator's point of view, the body heat of the humans is blocked by cooler objects in the foreground such as vegetation, just like it really would be. However, in real life, the mud would warm up due to the body heat pretty quickly, as demonstrated by the Myth Busters.
- In the second film, the Predator sees through walls, sadly.
- Interestingly, while the Predator Vision shots are clearly false-colored normal shots, the production did get hold of an infrared camera, initially hoping to shoot with that. Unfortunately, what came out was barely intelligible: turns out IR cameras don't work so good in steaming tropical heat.
- Made even more bizarre by the fact that in both of the original movies the Predators are implied to thrive in hot, humid environments - one only appeared in Los Angeles when a massive heatwave struck the Western Coast.
- Averted in Aliens, where the titular creatures don't show up on infrared at all, also done as a bit of a gag at this trope's expense, as the Marines realize this while the Aliens are right in front of their faces, and completely invisible. True to this, the Alien Vs. Predator games force the Predator to switch between four vision modes (one of them being normal human sight, probably for gameplay purposes) to highlight enemies; the IR scan won't highlight Aliens. Later adopted in the Alien Vs. Predator movie, where the Predator is distinctly shown switching vision modes to track Aliens instead of humans.
- The Predator switches through different modes of vision in Predator 2 as well, amusing after they were convinced it could only see in the infrared spectrum.
- The new Alien Vs Predator game also has three vision modes (normal visible light, infrared, green vision thingy) in order to see humans and aliens when they try to hide, but neither can be seen when they are behind walls.
- In Predators, it's stated that the Predators are learning to adapt; when Adrian Brody tries to use the same tricks as Dutch, the lead Predator switches vision modes to a heartbeat sensor.
- This was definitely popularized by, and may have come from, both the movie and television versions of Blue Thunder, where the helicopter mounts IR sensors that do precisely this.
- A real Infrared Xray Camera appears in Licence to Kill, which Pam Bouvier nearly shoots James Bond and Q with. It prints out an infrared xray picture of the two.
- Navy Seals (1990). The SEAL Team sniper uses a .50 caliber rifle with a thermal scope with these miraculous capabilities. His call sign is (appropriately) "God".
- Occurs in Lilo and Stitch, when Dr. Jumba Jookiba tracks Stitch inside a dog pound via a pair of infrared binoculars. Possibly justified due to alien technology.
- A dual-scope setup is installed on a WA2000 sniper rifle (that uses a tripod, no less) by the Cold Sniper Emiya Kiritsugu in the light novel Fate/Zero; one is night-vision, the other thermal. Done somewhat correctly, as it's used to track magi, who when using magecraft will have an increased body temperature from the Circuits. The target in question was about 300 meters away, and the sniper switched over to night-vision to confirm his target before lining up a shot.
- CSI: Miami where it was used to look into a boat.
- NCIS to look through the walls of a house.
- This was subverted in the NCIS: Los Angeles episode, The Watchers when we find out that Hetty installed heaters in the roof of the boatshed to prevent this.
- An episode of Myth Busters showed the inability of infrared to look through glass when an infrared sensor was spoofed by placing a small pane of glass in front of it, allowing access to a monitored hallway.
- A fourth season episode of Buffy the Vampire Slayer had the Initiative using an infrared scanner to spot the vampire Spike through the walls of a dorm. Doubly implausible in that his "room temperature" signature actually showed up as a blue spot, against the background heat of the room.
- On 24, CTU (Usually Chloe) regularly sends Jack a rundown of the occupants of a particular building and what their current location is, all by using infrared satellites.
- The old TV series Probe featured a piece of Applied Phlebotinum which could, among other things, see a lock mechanism inside its metal casing.
- The first episode of the second season of Knight Rider falls right into this trope; because the actual x-ray camera doesn't work through leaded plates, Michael needs to use a modified version of the infrared camera to see what's going on inside.
- Numb3rs used a variant when body-heat signatures pinpointed survivors trapped in the wreckage of a train crash. Arguably might've been justified, in that Charlie sent small camera-armed robots into the wreck to observe the trapped victims directly, rather than through intervening walls. Unfortunately, the signatures of two unlucky victims vanished within seconds of their demise, whereas a real body's heat would take many minutes to disperse.
- The short-lived series Blue Thunder had this as one of the abilities of the eponymous super-copter. The infrared scanner could see through walls and showed the results on the usual color-coded display screen in the cockpit. One notable example had the camera looking through the wooden walls of an old barn to detect an aircraft with a suspiciously warm engine.
- On an episode of Burn Notice where Team Westen deals with a Mafiya human-trafficking ring, Fiona uses one of these to scope out the interior of a Russian restaurant. Sam asks where she got it; apparently her neighbor is a peeping Tom.
- A Law and Order episode used infrared scanner imaging to secure a search warrant on a mosque. The defendant's lawyer successfully argued that the technology violated the Fourth Amendment without a warrant specifying its use and got the evidence seized there thrown out.
- An actual "X-ray camera" does in fact exist. Although it uses terrahertz microwaves rather than infrared or X-ray to function, and has more in common with radar than anything else, it can still see through walls and clothing, but not metal.
- The KGB developed an X-Ray that could show the lock of a safe while it was being cracked; its drawback was the high levels of radiation produced. It was joked in the KGB that you could tell a veteran safecracker by their lack of teeth.
- Astronomers have of course used cameras of various wavelengths for some time. Generally more useful for looking at stellar objects rather than through walls, mind you.
- Also an example of some of the problems with infrared: astronomy at infrared frequencies languished for decades until satellites could carry telescopes and new observatories were built on high mountaintops because the infrared light could not penetrate far through air.
- That's why there're X-ray telescopes mounted in satellites orbiting the Earth (like Chandra); X-rays coming from celestial bodies cannot penetrate Earth's atmosphere.
- Many species in 1st and 2nd Edition D&D had "infravision"; the fifteen years of arguments and debates about how exactly this power worked and what you could and could not do with it led to the "darkvision" power in 3rd edition.
- Darkvision it itself unrealistic, as it apparently shows shapes just fine but lacks color information... which actually acts more like sonar than anything else! This does, however, provide an interesting explanation for Dwarves' predilection for carved runes -- writing on paper is a color difference that is not visible to darkvision, while chiseled runes (which have a depth difference) are.
- Alas, many Tabletop Games took their inspiration and many of their buzzwords directly from 1st edition, so it's exceedingly common to find "infravision" in any non-realistic game. The arguments continue, of course.
- Creatures with infravision usually are also described as having glowing eyes when it's active. Granted, some illumination wouldn't hurt if they want to see walls, but how it can work in eyes...
- And that's nothing compared to the races who instead got "ultravision", the ability to see via ultraviolet wavelengths. Ah yes, the ability to see by direct starlight...
- Which became simply "Low-light vision" in 3rd edition, and is simply an improved ability to see in dark conditions (like what cats and other nocturnal animals actually have).
- Mutants and Masterminds averts this trope, noting that it works largely like regular sight and is blocked by walls (although they fail to note that glass blocks it), only allowing Infravision as an alternative to regular sight. Of course, it is possible to get Penetrates Concealment Infravision by paying a few more points but this is also a game where it's possible to get Heat Vision, so physics has little to do with it.
- Averted in the Splinter Cell series, where you can't see through walls or objects with infrared - even enough air provides an opaque obstacle as its lower temperature masks the heat from the target.
- However, in one mission in Chaos Theory you can see through thin paper walls (thin as in "reach through and grab somebody" thin). The thermal signature is really faint, so it may very well be plausible.
- Partially subverted in the Metroid series, where the thermal visor can't see mechanical targets (turrets, drones, etc) or things you've shot with the ice cannon, can be overloaded by enemies that generate large quantities of heat, and is completely useless in lava areas. You can see electrical conduits in the walls, though - evidently the Space Pirates bought really cheap wire and/or put too many appliances on the circuits.
- Although this can actually be Truth in Television. Even if the conduits weren't overheating, if they were of a material with a different heat capacity than the wall they could heat up or cool down the area of the wall they were in contact with. Using a thermal imager it's possible to identify the studs in a wall because of the slight difference in temperature between the wooden or metal studs and the air spaces/insulation between them which creates a slight difference in the temperature of the wall. Of course you'd never see that (one of the cool things infrared can do) on TV or in the movies...
- Metroid is apparently in The Future after all. But the cheap wiring fits with evidence the Scan Visor gives in Metroid Prime 3 that the Space Pirates seem to cheap out on maintenance quite a bit.
- Used in Soldier of Fortune: Double Helix. The infrared goggles allow you to see people and dogs (and nothing else) in range as bright red silhouettes, even through walls.
- Most of the Rainbow Six games, however, avoid this. Infrared goggles don't see through anything solid, and the vision gets less distinct as distance increases. Enemies further away will be only slightly brighter colors than the background haze, and if sufficiently far will blend in entirely. They are mostly useful for seeing enemies in smoke-filled areas.
- Same with Splinter Cell. Oddly, compared to the realism of most of the series, glass is thermically transparent. Unless, of course, there's a light shining through it.
- Averted in Metal Gear Solid 3 Snake Eater. The thermal imaging scope cannot see through obstructions.
- In Ghost Squad, you can actually use the infrared goggles to snipe through the walls of a straw hut. Why they had infrared goggles on a daylight mission is left unanswered.
- Possibly for the same reason actual military forces keep night vision goggles on them, even on day missions. On the other hand, one soldier in Black Hawk Down decided to forgo night vision in favor of grabbing extra ammo, along with many others. They paid dearly for this when they ended up stuck on the battlefield all the way into the night, without one of their greatest tactical advantages. Obviously, while this explains why the above soldier had infrared, but not why it worked. It really depends on ambient temperature.
- F.E.A.R. 2's elite power armor has a fairly realistic false color thermal imaging mode; it doesn't exclusively show people, as fire and other power armor (which are incredibly heat inefficient) also shows up.
- Perfect Dark has the X-ray Scanner (which can see through walls) and the IR scanner (which can show cloaked enemies). Both are useful, but limit the player's field of vision.
- In The Simpsons episode "Homer Bad Man", Kent Brockman uses an infrared camera and mistakes a turkey roasting in the oven for Homer.
- Thundercats villain Red Eye uses one of these.