Can microwaves get through the earth's atmosphere?

Answer 1

No

Yes (see image link below) but water (even as vapor in the air) reduces transmission a lot.

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Microwaves can and do penetrate the atmosphere. Infact they are often used as a primary form of communication with spacecraft because of this.

On rare occasions and due to weather conditions in the upper atmosphere, microwave radiation can be reflected back to earth.

On the other hand less energetic radio waves that are lower in the spectrum are easily reflected back to earth by the troposphere.

As a rule of thumb;

VLF - HF (Very low frequencies to high frequencies 200 kc to 32 MHz) are reflected easily. (Follow the curvature of the earth and have a ground wave and are reflected by the ionosphere (D and E layers of gases which are charged by solar activity).

HF - VHF (32mHz - 400mHz) penetrate moderately to penetrate easily (Starting to be LOS and can be reflected by the tropospheric conditions)

UHF - uF (400 MHz - 40,000 MHz) penetrate almost exclusively and are nearly LOS (line of sight)

Examples of microwave transmissions are ;

Satellite broadcasting which occurs around 10 gHz

Satellite to satellite and ground to satellite communications

RADAR

Speed traps

Wireless lans (5 gHz and 1.2 gHz)

Radio Astonomy

SETI

et.c

Answer 2

Yes, they can. Microwaves are used in ground radars. However, they don't penetrate all that well.