Bands of the Spectrum Usable and Partially Used in Earth Sciences

Bands of the Spectrum Usable and Partially Used in Earth Sciences 

Microwaves should more properly be called centi-millimetric waves. With micro-waves we approach the domain of remote detection however, this does not mean that lower frequencies will not be exploited in the future despite growing galactic noise. The scientific literature does not agree on the limits of the spectrum bands, so we should not be surprised to see some overlaps. Centi-millimetric waves are the best known, since radar operates in this region of the spectrum. 

Many scientists consider microwaves to extend from 10 to 10 Hz (30 cm-3 mm). Others push these upper and lower limits to 300 MHz (1 m) and 300 GHz (1 mm) the latter limits are those most commonly observed in remote detection. As we shall see later, microwaves are extremely promising, since they are not blocked by cloud. 

For some, infrared begins at 3 mm, for most at 1 mm. Everyone is agreed on 0.7-0.75 fj.m as the upper limit of the visible part of the spectrum. 

This is the part most familiar to us, extending from 700 to 400 nanometers (7000-4000 A 0.7-0.4 jum). The visible band is presently being favored by renewed interest, since in multispectral photography we can go down as far as 300 mju (ultraviolet) and go up as far as 900 m (near infrared). 

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