# Does water/ice obstruct microwaves and radiowaves?

I read an article (http://www.brighthub.com/science/aviation/articles/70016.aspx) that stated that airplanes use radio waves for communication because they aren't obstructed by weather.

I was hoping to conduct an experiment on how 2.8 cm microwaves are affected by hail, and in a preliminary test I found that a relatively small amount of water (maybe 1 cm in depth) was enough to block these waves.

So I hoped to get some help here to resolve this cognitive dissonance. In the article are they talking about longer waves that maybe aren't affected by water as much as the smaller waves I'm using?

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 More specifically, I was planning to investigate scattering. – DarkLightA Feb 7 at 21:48

I've read through that article, and there are several mistakes in it. I'll answer your question first, and then point out the errors in the article at the end of my answer. :)

Depending on the frequency, microwaves are strongly absorbed by water and can also be absorbed by oxygen. This is because microwaves can induce several rotational modes of vibration in a water molecule. This is why microwaves are used for cooking as well. But the consequence is that if you point your microwave emitter at hail/ice/water, a large fraction of the emission will be absorbed.

Radio waves are made of lower energy photons than microwaves (since the energy is related to frequency by $E = h \nu$) and aren't easily absorbed or scattered by anything in the lower atmosphere, which makes them a good candidate to send and receive signals over large distances. They are scattered by the charged particles in the ionosphere, and this effect is used in radio communications. But there are no planes in the ionosphere, so this effect doesn't have to be accounted for in radars. :)

Now for my nitpicks.

Firstly - they mention a magnetron which emits microwave radiation travelling with

a speed almost equivalent to light waves but with longer wavelengths and higher frequencies

which is rubbish. It's moving at exactly the frequency of light, since it is made up of photons.

They also say

As radio waves travel at light speed, they are faster than most of the objects.

Which is also rubbish. They travel faster than all of the objects. Nothing can travel at the speed of light. These may seem like nitpicks, but for a "scientific" article, I think it's important to get these details light.

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