Remote Sensing C

[syo_astro]

Differences in energy levels of electrons most often fall around the "middle" of the spectrum meaning that those wavelengths are the ones most often absorbed...

I am unsure what "middle of the spectrum" means, and I think it's a bit of an unclear description. You might know the gist, but I think this will gnaw at me even if you explained that part better. It also might take quite a bit of explaining, and I know you're trying to keep it brief. But solids and liquids interact with light differently from gases, and I don't know if that's really been explicitly mentioned.

knottingpurple kind of mentioned this with those X-ray or ocean examples. I...should read all posts and rules, but I like glass. Glass allows visible light to pass through, but it does NOT allow IR light to pass through (aka Greenhouse Effect). Solids and liquids are not gases, and if you look at the spectrum for glass, you wouldn't see solely the "differences in energy level" thing for gases. Don't get me wrong, it's related, but...it's complicated / better for another post.

Can anyone briefly explain why longer waves generally penetrate objects more and shorter waves don't penetrate objects as well as longer waves?

If you wanted to know about spectra for solids / liquids, then please phrase specifically / use an example. It sounds like you're asking about longer wavelengths passing through better, in which case your answer would rely on scattering (e.g. When you look at atmospheres). But I won't give extra paragraphs on that in case I'm wrong.

Edit:
Standing by most of what I say, but I just want to clarify that I'm not saying that differences in energy levels is wrong / not present. Just that when we observe light emitted by or passing through solids that things get complicated. How light interacts with diffuse gases vs. solids (among other things, even high-density gases or dust) does not only have to be described by electrons transitions (the glass example was not great...maybe should've just stuck with X-rays or dust). Got a PM and figured clarification would help. Again, still going to wait on a more direct question before going through all the processes by which light can be observed or not.

[biz11]

I am unsure what "middle of the spectrum" means, and I think it's a bit of an unclear description.

I was considering ultraviolet, visible, and infrared the "middle" of the spectrum, I know that it is not really accurate, sorry for the confusion. However, after looking into this more your completely right syo_astro, scattering and conductivity appear to be more important in determining penetration then I had realized.
That being said there is no general statement like having x property gives it more penetration power, to get a good answer you would need to specify what the material you are referring to geniusjohn5.

For example, our atmosphere is very seemingly random in what it absorbs.

[whythelongface]

After trawling the Physics Stack Exchange and the Lillesand Remote Sensing and Image Interpretation, 5th ed., my take on this is that light interacts with matter in several different ways. Light can be transmitted, it can be reflected, it can be scattered, or it can be absorbed (attenuated). The question being asked here is why objects are more transparent to longer-wavelength light.

Knottingpurple makes a good point in that the oceans aren't transparent to practically any wavelength. Not only does it absorb well, but it also can absorb a lot of energy. Put water under the sun, man's not hot; the sun will be hotter than the water. Different things interact with light in different ways - that's why we have a multitude of atmospheric windows where the greenhouse gases present are transparent to a certain spectral range of radiation. As a general rule of thumb, though, I think biz11 is correct. His point was that if quanta of specific energies are absorbed by atoms and molecules, more often than not those energies fall into the visible/UV range, as predicted by the Rydberg Equation. Light in the IR, microwave, radio, and terahertz ends of the spectrum would not be energetic enough; light in the x-ray/gamma ray end would be too energetic, much more so than UV or visible light[citation needed].

I've seen many contradictory statements of gamma rays interacting with the atmosphere, though. Some people say that the atmosphere is opaque to them; other people say that the sun just doesn't produce enough of them1. Same with x-rays, I guess.

1 The sun produces gamma rays, but it takes ages for a gamma ray to escape the sun from the core and as a result most of the gamma rays have lost so much energy that they emerge as IR and visible light.

[ashucha]

Does the wiki contain most of the information necessary to do well on a test or should most of the information come from outside sources? Thanks! (BTW I was just placed in this event and didn't even want to do it and the tournament is in a week so if anyone could tell me in the next few days or so, that would be helpful!)

Also, does anyone know a test bank from which I can get practice tests other than the Test Exchange as that only has one test from 2017, which shares the same topic? Thank you in advance!

[knottingpurple]

Does the wiki contain most of the information necessary to do well on a test or should most of the information come from outside sources? Thanks! (BTW I was just placed in this event and didn't even want to do it and the tournament is in a week so if anyone could tell me in the next few days or so, that would be helpful!)

Also, does anyone know a test bank from which I can get practice tests other than the Test Exchange as that only has one test from 2017, which shares the same topic? Thank you in advance!

I'm confused why you're saying the test exchange only had 1 test, Princeton is on there which is a great test, all old MIT tests are at scioly.mit.edu/archive I think, and even all the other less high profile tests on there are perfectly good practice.

There's definitely more vocabulary and more satellite details and so on than is on the wiki, but it is a decent starting point, and there are also plenty of other posts in this thread about how to start learning the event.

(Whythelongface was thrown into this event with like a week's notice too, and it's now his favorite, so I'm sure he'll give you more advice if he hasn't already gotten here.)

[whythelongface]

Does the wiki contain most of the information necessary to do well on a test or should most of the information come from outside sources? Thanks! (BTW I was just placed in this event and didn't even want to do it and the tournament is in a week so if anyone could tell me in the next few days or so, that would be helpful!)

Also, does anyone know a test bank from which I can get practice tests other than the Test Exchange as that only has one test from 2017, which shares the same topic? Thank you in advance!

Yes, I was thrown into the event headfirst. I had always assumed it was some sort of event about telecommunications or something, but it turned out to be quite interesting (it helped that I placed first at the competition so it would look awful if I backed out). It is now by far my favorite event.

Concerning the test exchange, I think you might be looking at the wrong one. The test bank on the Wiki is very outdated, there is only one test (which I wrote) on the most recent topic. However, the test exchange featured at the top right corner of this page has a multitude of Remote Sensing tests from last year, and the topic hasn't changed...

Sounds like you're in the same boat I was in last year. Hope you enjoy it!

[biz11]

Can someone explain the Tyndall effect? Specifically, what exactly is happening in the Tyndall effect to cause the scattering. Does it work the same way as Rayleigh scattering, but is just given a different name because the particles are larger?

[whythelongface]

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[Unome]

Can someone explain the Tyndall effect? Specifically, what exactly is happening in the Tyndall effect to cause the scattering. Does it work the same way as Rayleigh scattering, but is just given a different name because the particles are larger?

I'm pretty sure that because of the size of the particles involved, the Tyndall effect would be an example of non-selective scattering? The Tyndall effect exists in colloids, where fairly large molecules remain suspended and scatter light. I think the molecules involved are much, much bigger than the wavelength, so it would not selectively scatter short wavelengths. Rayleigh scattering, on the other hand, selectively scatters the blue end of the visible range because the particles are so much smaller than the wavelength.

Tyndall is definitely selective, and per Wikipedia, in the same way as Rayleigh.

[knottingpurple]

Can someone explain the Tyndall effect? Specifically, what exactly is happening in the Tyndall effect to cause the scattering. Does it work the same way as Rayleigh scattering, but is just given a different name because the particles are larger?

I'm pretty sure that because of the size of the particles involved, the Tyndall effect would be an example of non-selective scattering? The Tyndall effect exists in colloids, where fairly large molecules remain suspended and scatter light. I think the molecules involved are much, much bigger than the wavelength, so it would not selectively scatter short wavelengths. Rayleigh scattering, on the other hand, selectively scatters the blue end of the visible range because the particles are so much smaller than the wavelength.

It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth power of the frequency, so blue light is scattered much more strongly than red light.

So according to Wikipedia, the Tyndall effect also selectively scatters blue, and is the reason blue irises appear blue, etc, so although you're right about the wavelength not being much bigger than the particle size in the Tyndall effect, it's not true that this makes it entirely non-selective. If you just wanted which more common term for a type of scattering this resembles, you wold probably say Mie scattering, not non-selective scattering.