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DATA - Version 2 AOD Descriptions
 

 

TIME FORMAT
  • All times are provided as Greenwich Mean Time (GMT) for the solar day.
  • All averages are calculated using the GMT solar day.
  • The GMT solar day may overlap two calendar days for some AERONET sites.
  • "Day" is defined as the GMT solar day.
DATA FORMAT
Data Format Description
All Points These data are available for each measurement or retrieval moment.
Daily Average These data are calculated from all points for each day when three (3) or more points are available.
Monthly Average of Daily Averages

These data are calculated using the daily average for each day to compute the monthly average.

Equation for the Monthly Average of Daily Averages

Monthly Average of Weighted Daily Averages

These data are calculated using the weighted daily average for each day to compute the monthly average.

Equation for the Monthly Average of Weighted Daily Averages


DATA TYPES

*See references below table for more detailed information.

Data Type Description
Aerosol Optical Depth (AOD) - includes the aerosol optical depth as well as derived products such as precipitable water and Angstrom parameter
Level 1.0 AOD (Unscreened) Unscreened and may not have final calibration applied
Level 1.5 AOD (Cloud Screened) Automatically cloud cleared but may not have final calibration applied. These data are NOT quality assured.
Level 2.0 AOD (Quality Assured) Pre- and post-field calibration applied, automatically cloud cleared and manually inspected
Precipitable Water The total water vapor in the column derived from the 935nm channel.
Percent Triplet Variability Each AOD measurement is comprised of a triplet measurement: These measurements are taken every 30 seconds for one minute. The variability of this measurement can provide insight on the quality of the data.
Angstrom Parameter The angstrom parameter is calculated for all available wavelengths within the Angstrom parameter range. For example, the Angstrom 870-440nm includes the 870, 670, 500 and 440 nm AOD data. A special case for a polarized instrument is Angstrom 870-440nm which only includes 870, 670 and 440 nm AOD data (polarized instruments do not have 500nm channel).
Instrument Information  
Exact Wavelength The exact filter wavelength is used to determine AOD and other parameters.
Raw Data - includes radiance data measured using the almucantar and principle plane scenarios
Almucantar Sky Radiance Calibration applied to almucantar scenario data (See Page 30 of the Cimel Sun Photometer User Manual for more information on almucantars)
Principal Plane Sky Radiance Calibration applied to principal planes scenario data (See Page (See Page 31 of the Cimel Sun Photometer User Manual for more information on almucantars)
Polar Principal Plane Sky Radiance Calibration applied to polarized principal planes scenario data (See Page 31 of the Cimel Sun Photometer User Manual for more information on almucantars)
Sky and Surface Radiance for Bidirectional Reflectance Distribution Function (BRDF) Calibration applied to BRDF scenario data

Total Optical Depth

- includes the total optical depth and other components such as ozone, NO2 and Rayleigh optical depths.
Level 1.0 (Unscreened) Unscreened and may not have final calibration applied
Level 1.5 (Cloud Screened) Automatically cloud cleared but may not have final calibration applied. These data are NOT quality assured.
Level 2.0 (Quality Assured) Pre- and post-field calibration applied, automatically cloud cleared and manually inspected
AERONET-SDA Retrievals - includes the fine and coarse mode aerosol optical depth as well as the fine mode fraction.
Level 1.0 SDA (Unscreened) Utilizes AERONET AOD, which is unscreened and may not have final calibration applied (Level 1.0 AOD)
Level 1.5 SDA (Cloud Screened)

Utilizes AERONET AOD, which is automatically cloud cleared but may not have final calibration applied. These data are NOT quality assured (Level 1.5 AOD).

In addition, the following criteria must be met for SDA retrievals:

1. At least three wavelength combinations must include 440 and 870nm with either 490, 500 or 675nm.

2. The AOD for each channel must be greater than or equal to 0.02/m, where m is the optical air mass.

3. Outliers are removed according to the following criterion:

Abs(AOD500nm-AODSDA500nm)>(0.02+AOD500nm*0.005)

AERONET-MAN (microtops instrument) implements the following additional criterion:

4. If within the series any tau_fine or tau_coarse is beyond tau_mean plus/minus 2*stdev for the series we eliminate this measurement.

Level 2.0 SDA (Quality Assured)

Utilizes AERONET AOD, which is pre- and post-field calibration applied, automatically cloud cleared and manually inspected (Level 2.0 AOD).

In addition, the following criteria must be met for SDA retrievals:

1. At least four wavelengths must be included for input. The spectral range must be bounded by 380 and 870nm with at least two additional wavelengths between the bounds (e.g., 440, 500, 675nm). The three channel combination of 380, 500, and 870nm will also be accepted.

2. The AOD for each channel must be greater than or equal to 0.02/m, where m is the optical air mass.

3. Outliers are removed according to the following criterion:

Abs(AOD500nm-AODSDA500nm)>(0.01+AOD500nm*0.005)

AERONET-MAN (microtops instrument) implements the following additional criterion:

4. If within the series any tau_fine or tau_coarse is beyond tau_mean plus/minus 2*stdev for the series we eliminate this measurement.

Total Mode AOD 500nm [tau_a] AOD at 500nm computed using a best-fit second order polynomial (SDA output)
Fine Mode AOD 500nm [tau_f] Fine mode AOD at 500nm (SDA output)
Coarse Mode AOD 500nm [tau_c] Coarse mode AOD at 500nm (SDA output)
Fine Mode Fraction 500nm [eta] Fine mode fraction at 500nm (SDA output)
2nd Order Reg Fit Error - Total AOD 500nm [regression_tau_a] Regression error in Total AOD 500nm (SDA output)
RMSE Fine Mode AOD 500nm [Dtau_f] Estimated error in Fine Mode AOD 500nm (SDA output derived from the estimated AOD accuracy)
RMSE Coarse Mode AOD 500nm [Dtau_c] Estimated error in Coarse Mode AOD 500nm (SDA output derived from the estimated AOD accuracy)
RMSE Fine Mode Fraction 500nm [Deta] Estimated error in Fine Mode Fraction 500nm (SDA output derived from the estimated AOD accuracy)
Angstrom Exponent - Total 500nm [alpha] Angstrom exponent at 500nm (SDA output of {-d ln (AOD) / d ln(wavelength)} at 500nm)
dAE/dln(wavelength)-Total 500nm[alphap] Spectral derivative of the Angstrom exponent at 500nm (SDA output)
AE-Fine Mode 500nm [alpha_f] Angstrom exponent of the fine mode AOD at 500nm (SDA output)
dAE/dln(wavlength)-Fine Mode 500nm[alphap_f] Spectral derivative of the fine mode Angstrom exponent at 500nm (SDA output)
870nm Input AOD, etc. Input AOD (to the SDA retrieval) at 870nm, etc.

Please read these papers for a thorough explanation of the data types:

  • Cimel Sun Photometer Manual (PDF)
  • Angstrom, A., On the atmospheric transmission of Sun radiation and on dust in the air, Geogr. Ann., 12, 130-159, 1929.
  • Dubovik, O. and M. D. King, 2000: A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements, J. Geophys. Res., 105, 20 673-20 696.
  • Holben B.N., T.F.Eck, I.Slutsker, D.Tanre, J.P.Buis, A.Setzer, E.Vermote, J.A.Reagan, Y.Kaufman, T.Nakajima, F.Lavenu, I.Jankowiak, and A.Smirnov, 1998: AERONET - A federated instrument network and data archive for aerosol characterization, Rem. Sens. Environ., 66, 1-16.
  • O'Neill, N.T., T.F.Eck, , A.Smirnov, B.N.Holben, and S.Thulasiraman, Spectral discrimination of coarse and fine mode optical deph, J. Geophys. Res., 108(D17), 4559, doi:10.1029/2002JD002975, 2003.
    • Recent changes to the coarse/fine mode optical depth deconvolution algorithm, June 2005. (PDF) | (TXT)
 
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Last Updated: February 19, 2014