Some Basic Remote Sensing Terms and Concepts

 AOD (t) - Aerosol Optical Depth  
 AOT -Aerosol Optical Thickness
 These terms are often used interchangeably although they are technically different.

An optical measurement of light extinction which is used to represent aerosol amount in the entire column of the atmosphere. This is a unitless measurement. Values are wavelength dependent. AOD is the main parameter of interest to those using remote sensing aerosol products.  It is typically reported at 0.55 um.  

Typical AOD values:                                                    
0.02 - very clean isolated areas. 
0.2 – fairly clean urban area
0.4 – somewhat polluted urban area
0.6 – fairly polluted area
1.5 – heavy biomass burning or dust event

An example of what a moderate to high AOD value would look like from the ground.

 Particle Size Distribution – aerosols in the optically active size ranges are best represented as a bimodal distribution.  The aerosol size distribution can  be represented as a volume or number distribution. In the example below it is shown as a volume distribution.