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How to know the shape of a specific location on Earth?

  1. May 5, 2015 #1
    How do you know the shape (land altitude, roughness, etc.) of a specific location on Earth through a satellite? For example, if a specific place is covered by clouds is there a way to know the shape of the ground at this specific point?

    I have read through the absorption spectra of the atmospheric gases, and microwave passes all through them. If that is the case, then the satellite should just have a filter for microwave and the shape can be known?
     
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  3. May 5, 2015 #2

    Drakkith

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    Maps are made. If the satellite can't see a particular location, it just waits until it can.

    Since the Earth does not naturally give off any significant amount of microwave radiation, I'm not sure how effective this would be unless you use microwave radar on the satellites. I don't know if this technique is used or not.
     
  4. May 5, 2015 #3

    RaulTheUCSCSlug

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    Some satellite are able to produce topographic maps, which means it will lay out a map that will tell you how "tall" the mountain is relative to other spots around it. If you have taking multi-variable calculus, it is kind of like a conic section.
     
  5. May 6, 2015 #4
    If the satellite were to provide the radiation, will it work? How accurate will it be?

    How do these satellites produce the maps?
     
  6. May 6, 2015 #5

    Drakkith

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    I'm almost certain it's regularly used, but I don't know the details.
    Try here and see if it helps: http://en.wikipedia.org/wiki/Remote_sensing
     
  7. May 6, 2015 #6
    Thanks. I did read on articles and it seems it is used, although they focus more on ocean and sea characteristics. I'm just not sure if their method is applicable on land topography.

    Anyway, is there a way to know the Earth's surface based upon the reflected radiation of the Earth from the Sun? I'm concerned that the outgoing radiation will be absorbed by the atmospheric gases and not reach the satellite.
     
  8. May 6, 2015 #7

    A.T.

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  9. May 6, 2015 #8

    RaulTheUCSCSlug

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    Depending on the time it takes for a wave to hit the surface of the earth then back at a satellite, one can tell the distance it is. If it takes longer then it means that the spot is steeper, but if it takes less time then it is higher at that point. Does that make sense?
     
  10. May 6, 2015 #9

    DaveC426913

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    If you're looking for geographic features, such as altitude and roughness (which is simply fine-resolutioned altitude), then any radiation that can penetrate cloud cover will be visible. Presumably, radar would work very well.

    But why the urgency to pierce a cloud that will be gone by tomorrow? Why not simply do multiple passes with the satellite on multiple days?

    What is the application here?
     
  11. May 6, 2015 #10

    CWatters

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    They use Radar on spacecraft orbiting Mars. Not just so they can see through cloud but so they can see what's below ground as well.
     
  12. May 7, 2015 #11
    There is an equation for this, right? Although, since the satellite will be orbiting hundreds of kilometers from the Earth surface, how much precision is needed?

    That is a simple solution. I'm just concerned what if a certain location has high density and frequency of clouds. And at what frequencies that these radars work from?
     
  13. May 7, 2015 #12

    davenn

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    doesn't affect the radar
    do some google searching on ground mapping radar

    you will find 100's of hits :smile:

    Dave
     
  14. May 7, 2015 #13

    RaulTheUCSCSlug

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    Well you would be surprised on how simple some of the calculations maybe, as with what someone said about the radiation mapping, since there is few things that interfere with the radiation, the calculations would just need the speed of the radiation, and would be fairly precise. At least that is what I would imagine, I have never worked on satellites, and have only done physics problems from my book that work with ideal situations! :oldbiggrin::oldbiggrin::oldbiggrin:
     
  15. May 8, 2015 #14

    DaveC426913

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    I am pretty sure ecastro was responding to this part of my question:
     
  16. May 8, 2015 #15

    davenn

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    maybe ? :smile:

    its irrelevant as the radar will map the ground regardless of cloud cover or not ...
    for satellites ( depending on their orbital elements), they don't pass over the same place each day it could be a while before their orbit takes them over the exact same area

    Dave
     
  17. May 12, 2015 #16
    I read an article regarding the precision of the radar measurements. It seems that the radar (at least in the C Band and L Band microwaves) can be affected by humidity.
     
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