4 ms·

How are they able to see the signature water gives off through all the noise that other types of molecules must be sending back? Isn't there even more noise to

• whimsicalism 6y ago
  Yes, we are really good at denoising. There can sometimes be a couple of possible different "solutions" to the spectroscopy curve, ie. different combination of elements that would lead to the same curve.
• jcranmer 6y ago
  To answer your second question first: Stuff being in the way will of course diminish the signal (by direct absorption or by scattering it). But space is pretty empty. The regular air on Earth contains ~10^19 particles per cm³, and it can take several km of air to start seriously interfering with light. A dense portion of space contains something like 10^4 particles per cm³, and a less dense region maybe 10^-4 particles per cm³. So, once you leave the atmosphere, the noise that's destroying the signal is simply far, far, far weaker than the signal. Now for your first question. As I mentioned in my first comment, the spectral lines arise from different orbitals. What this means is that there isn't a single line associated with a molecule, but actually several lines. So if you think you see a line from one molecule, you should be able to find the other associated lines, and the more of the lines you can find, the stronger the evidence. As a couple of people have noted, this isn't a perfect process, so you can get into arguments if your identification is actually correct or not.