Remote Sensing from the Ground

Compared to remote sensing from space, remote sensing from the ground has well-defined backgrounds (sun or dark space), and for AOD data, no assumptions on particulate absorption are required. Ground remote sensing can, in fact, provide data for all three particle characteristics: AOD, co0, and

DJF 0.116

JJA 0.140

MAM 0.138

DJF 0.116

JJA 0.140

MAM 0.138

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(550nm)

Figure 3.2 Seasonal AOD patterns at 550 nm wavelength of a satellite remote-sensing composite tied to AERONET data.

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Figure 3.2 Seasonal AOD patterns at 550 nm wavelength of a satellite remote-sensing composite tied to AERONET data.

AnP. Direct solar attenuation measurements with sun photometers provide highly accurate data for AOD and AnP. Additional sky radiance data can provide (via inversions) consistent columnar data on all aerosol properties, including ro0. However, accurate ro0 estimates can only be expected if the associated (mid-visible) AOD exceeds 0.3. A higher (compared to satellite retrievals) temporal resolution allows for much better statistics, but the requirement for a cloud-free scene remains. There are major drawbacks in trying to derive global AOD fields from sun/sky photometer sites: (a) site distribution is sparse and uneven; (b) there is potential for local bias, which makes statistics at a site unfit to represent the site's surrounding region. However, if statistics from sky/sun photometer sites are available and if a good regional representation applies (e.g., demonstrated by invariant satellite retrievals for different spatial domains around that site), then sky/sun photometer data are preferable for that region over spaceborne remote-sensing data.

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