Thermal Imaging and Object Detection at Sea

[fizzziks]

So my mind tends to wander, but I was thinking... since active/passive sonar is used to detect objects underwater, couldn't thermal imaging be used as well (in conjunction)? Isn't there any reason why we couldn't combine the two sensors into cooperatively working together to detect submarines, enemy swimmers, underwater mines, etc assuming the radiating heat is sufficient enough and to the required intensity of the thermal imager?

Does this make sense at all? I was hoping to spur some discussion on the topic.

 

[russ_watters]

What is there under water that radiates heat? Most of the animals are cold blooded and those that aren't are heavily insulated due to the water's ability to remove heat quickly.

 

[Mech_Engineer]

I don't know for sure, but my guess why it hasn't been done is because water is opaque to infrared, meaning you can't "image" underwater in the infrared spectrum.

Edit:

My suspicions are correct. The following picture shows that water absorbs infrared much more readily than visible. This means if you can't see it with visible light, you certinly won't see it in infrared.

[PLAIN]http://www1.lsbu.ac.uk/water/images/watopt.gif