Which aerosol model should be used for what location and weather condition?

[rese_support]

The composition of the aerosol particles is primarily controlled by natural and man-made sources at the earth's surface. The aerosol content of the atmosphere at a given location will therefore depend on the trajectory of the local air mass during the preceding several days. However, some general easy-to-use guidelines for the selection are :1. rural aerosol If in doubt, select the "rural" aerosol type. It represents conditions one finds in continental areas not directly influenced by urban/industrial sources. This aerosol consists of dust-like and organic particles.2. urban aerosol In urban areas, the rural aerosol background is often modified by the addition of particles from combustion products and industrial sources (carbonaceous soot-like particles). However, depending on wind direction and shortly after raining, the rural aerosol might also be applicable in urban areas.3. maritime aerosol In areas close to the sea or close to large lakes, the aerosol largely consists of sea-salt particles, mixed with continental particles. In these areas, the aerosol choice would depend on wind direction: for an off-shore wind, the rural aerosol (or urban) type is still the best choice, otherwise the maritime. Again, since the wind conditions are often not known, select the rural type if in doubt.4. desert aerosol As the name implies, this type is intended for desert-like conditions, with dust-like particles of larger size.In forested, agricultural areas and scrub land the rural aerosol is usually the adequate choice. This also holds for polar, arctic, and snow covered land. Notice : (i) The SPECTRA module can be used to assess the influence of the selected aerosol type. The target spectrum for a certain target (e.g. vegetation, water) can be displayed for the different aerosol types and compared to library spectra. The aerosol with the closest match would be the logical choice. (ii) If the sensor has a blue spectral band and a 1.6 or 2.2 um band (e.g. Landsat TM), ATCOR starts with the user-selected aerosol/atmosphere, but is able to adapt the path radiance, i.e. aerosol properties, in cases where reference areas (coniferous forest, dark soils) are found in the scene. Thus, ATCOR will cope with non-standard aerosol conditions, e.g. a mixture of rural and urban aerosols.