AERONET and PHOTONS/AERONET

 

 

The Aerosol Robotic Network (AERONET) program is a federation of ground-based remote sensing aerosol networks established by NASA and LOA-PHOTONS (CNRS) and is greatly expanded by collaborators from national agencies, institutes, universities, individual scientists, and partners. The standardized network procedures of instrument maintenance, calibration, cloud screening, and data processing allow for quantitative comparison of the aerosol data obtained in different times and locations.

 

 

AERONET sites world map distribution.

 

 

In all stations, spectral observations of sun and radiance are made at several nominal wavelengths. Aerosol Optical Depth (AOD) is derived from solar extinction measurements (Holben et al., 1998). In addition, the Ångström Exponent (AE) is derived from a multispectral log–linear fit to the classical equation of Ångström (AOD( l)~l^-AE) which provides the spectral dependence of the AOD.

 

 

The relationship between fine and coarse aerosols in the atmospheric column can be followed by AE. Since coarse-mode aerosols is a feature that differentiates dust from fine-mode anthropogenic and biomass burning aerosols, an increase (decrease) in AE involves an increase (decrease) of the ratio fine/coarse particles which denotes the low (high) influence of the dust plume during an event. In this context, the qualitative anticorrelation of the observed AE and the modelled AOD is a useful indicator for operational dust model evaluation with sunphotometers. In Basart et al. (2009), an aerosol characterization for North Africa, North-eastern Atlantic, Mediterranean and Middle East based on AOD, AE and its spectral curvature is presented.

 

 

Modelled dust optical depth (DOD) at 550 nm is evaluated in the present daily comparison. Since AERONET sun photometers don't yield AOD at that wavelength, it is calculated from AOD values at 440, 675 and 870 nm and the AE 440-870 using the Ångström law. We will assume that cases dominated by desert dust are those AE ≤ 0.75, cases dominated by biomass burning-urban/industrial particles are those with and AE ≥ 1.5 and classify the remaining cases as mixed aerosol. Additionally, the comparison is complemented with AOD_coarse and AOD_fine obtained from the Spectral Deconvolution Algorithm (SDA) which yields fine (sub-micron) and coarse (super-micron) AOD at a standard wavelength of 500 nm.

 

 

For the daily NRT evaluation, Version 2 Level 1.5 of AERONET products are used. Level 1.5 data is automatically cloud screened but may not have final calibration applied. Thus, these data are not quality assured.

 

 

Most of the AERONET-Cimel stations used in this NRT evaluation have been calibrated within AERONET-EUROPE TNA supported by the European Community–Research Infrastructure Action under the FP7 “Capacities” specific programme for Integrating Activities, ACTRIS Grant Agreement no. 262254.