This graph shows the "absorption spectrum" of principle constituent gases comprising earth's atmosphere. Absorption ranges from zero (transparent - colored white in the figure) to 1 (opaque- colored dark in the figure). Notice that gases do not absorb uniformely over the electromagnetic spectrum. Rather, there are some wavelengths where a gas may absorb a great deal of radiation, while the same gas is highly transparent at other wavelengths. Such absorption spectra provide rather unique radiative "fingerprints" of each gas, which is very useful for remote sensors. For example, if you had a million dollars to build a radiometer to remotely sense the presence of ozone, at what wavelength(s) would you set the device?