This graph shows the atmospheric transmission, the scattering from the atmosphere, and the total received signal from a smooth target with reflection coefficient 0.2. Transmission and scattering are the two components of the atmospheric effects on the signal received by a remote sensing instrument. The graph was made with the LOWTRAN7 atmospheric simulation program using subarctic midsummer conditions.
The atmospheric transmission attenuates the light illuminating the target and the light reflected by the target. The spectrum of the light is altered. Especially important are the strong absorptions of water vapour and oxygen (see the peak at 760 nm). The water vapour content of the atmosphere varies a lot even within small geographic distances.
The scattering is light reflected from the gas molecules instead of the target. This creates an additional component to the signal. The scattering is strongest in the small wavelengths. (This effects creates the blue colour of the sky.)
The result shown in the graph is averaged to the 1.6 nm basic channel width of the AISA instrument. The graph shows that the fine structure of the atmosphere has to be taken into account with hyperspectral data whereas it can be largely ignored with conventional multispectral data where the spectral channels are much wider.