Does infrared vision work underwater?

If an aquatic creature could sense body heat like some snakes would that ability be of any use when below water?

It technically works underwater but the effective range would be rather short. Something would have to be giving off a good bit of heat for it to leave a thermal signature detectable at any meaningful range.

Isn't it something like 1/10th the original detection range? I know in IR cameras and sensors we can detect a volcano erupting from space as long as it's above ground. We cannot yet detect volcanic eruptions underwater via IR. (Unless it's in really shallow water.) We can detect it easily via sonar and seismograph but IR is difficult.

Short version: technically yes. Long version is technically yes but not very well. Basically water is a really great thermal sink and it's also really good at absorbing red and infrared light. So stuff that is in the thermal range to emit infrared light has to fight to stay at that temperature and even stuff that can do that, the light's not going to travel very far.

Edited by KnightofLsama on Jan 15th 2019 at 10:00:52 PM

Note that the figure about water having 1/10 the transmission of infrared compared to air applies exponentially over increasing distance. One of the things that makes water so special as a substance is its strong absorption of most wavelengths of light.

Edited by Fighteer on Jan 21st 2019 at 9:19:44 AM

It explains how submarines can hide from satellites.

Water does make pretty good camouflage in a variety of situations. Most IR/Thermal detection depends on heat saturation vs cooling rate of the surrounding waters. For example subs near the surface can be detected by thermal wakes. However by going a mere dozen meters down the thermal wake pretty much vanishes. If something is seeing a thermal footprint from long range would mean the surrounding waters are positively saturated by heat. It would look like a big ass blob of heat.

Ohhh, nice setup to a monster story.

Considering the thermal conductivity of water, ocean currents, and thermoclines you'd need a truly massive heat source to create a trackable heat wake in the ocean.

So any oceanographer or intelligence analyst seeing a wake like that is calling for his Brown Pants.

Either that or calling for a technician to diagnose a potential problem because obviously nothing that large exists by natural or known standards.

When the tech says the thing is working fine and that massive heat blob is real, THEN it's Brown Pants time.

This question reminds me of the old favorite of science educators: "What would happen if you detonated the world's largest nuclear bomb at the bottom of the Marianas Trench?" The answer is: not much. You'd kill some marine life, but the shock wave would barely result in ripples at the ocean surface, and the heat would dissipate long before it was detectable.

Seismologists would certainly know something had happened, but that's because of the shock wave transmitted through the planet's crust. Oh, and sonar detectors would probably go off around the world, but that's it.

Edited by Fighteer on Jan 23rd 2019 at 12:36:28 PM

Sometimes those questions are kind of fun to ponder. XKCD does its share of oddball and interesting what-if scenarios.

The US series of experiments on the effects of underwater nukes was an interesting read on what it might do on the surface. Basically, a shallow water detonation is more likely to be nasty as long as it is not too deep. I am thinking something more along the lines of the Bikini Atoll tests which flipped large warships around like bath toys.

Alternatives to short range IR/Thermal would be sonar or detecting electrical currents. Materials like this substance which can reportedly mimic a sharks ability to track prey. You could still use some sort of thermal IR for short range stuff in various conditions and have it backed up by other sensing methods.

Edited by TuefelHundenIV on Jan 23rd 2019 at 6:32:41 AM

Magnetometers are used to detect submarines IRL as well.

So infrared detection would be useless for a underwater creature, what about electroreception for a land animal?

Would actually be really useful for a modern civilization. Knowing what circuits are hot and which ones are safe would be neigh indispensible.

For a non-tool using creature? Hit and miss. A magneto-sense would certainly work but it wouldn't have many advantages over sight and sound.

Some migratory critters (birds in particular) can sense and detect Earth's magnetic north for purposes of instinctual navigation.

If you are talking realism, there's usually a reason evolution ended up the way it has.

Electroreception doesn't work all that well above water because air conducts electricity a lot worse than saltwater. Electric field strength is an inverse square function of its distance from the source, so without a ion-filled body of saltwater to carry the current, you're going to have a difficult time sensing the field from far away. Plus electromagnetic waves (including both visible light and IR) travel far better in air, so being able to sense electric fields on top of that would be kind of redundant.