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Which parts of the electromagnetic spectrum cannot be used for remote sensing of the Earth system and why? Is that different on the moon and if yes, why?

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3 Answers 3

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Long radio wavelengths >~1 km, can't penetrate the ionosphere. The situation at infrared wavelengths is complicated, where there are bands where the atmosphere is opaque, but "windows" where it isn't. Only a small part of the ultraviolet spectrum, just short of visible, is usable. At shorter wavelengths (x-ray, gamma ray) the atmosphere is opaque.

None of this is a problem for the moon if your sensors are based in space. One area of active interest is lunar x-ray fluorescence spectroscopy.

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  • $\begingroup$ So helpful:) thanks for answer $\endgroup$ Commented Mar 5, 2023 at 21:03
  • $\begingroup$ I would place the ionosphere within "The Earth's System", so perhaps long radio can be used via reflection / absorption. $\endgroup$
    – JEB
    Commented Mar 6, 2023 at 0:35
  • $\begingroup$ "Opaque" just means you're seeing a different part of the Earth's atmosphere. $\endgroup$
    – gerrit
    Commented Mar 6, 2023 at 8:08
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Absorption is an important part of sensing the Earth System, the atmosphere to be more precise. The microwave absorption spectrum looks like:

enter image description here

It is common to have multiple channels near 19, 61, 183, etc.. GHz with varying bandwidth. For a given peak, the relative signal strength at fixed center frequency vs bandwidth is sensitive to the total content of the absorber (e.g, water vapor, O2).

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To sense the earth requires wavelengths of the spectrum that are not absorbed by the gases present in the atmosphere. The moon has no atmosphere (or almost none) so this limitation on remote sensing does not apply to the moon.

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  • $\begingroup$ So helpful:), thanks for answer $\endgroup$ Commented Mar 5, 2023 at 21:02
  • $\begingroup$ To sense the earth requires wavelengths of the spectrum that are not absorbed by the gases present in the atmosphere — unless you want to sense the atmosphere, of course. OP referred to the "Earth System", which I would interpret to include the atmosphere. $\endgroup$
    – gerrit
    Commented Mar 6, 2023 at 8:10

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