# Presentation: 202517

## Improvements in AERONET Algorithm Increases Accuracy of Absorption Retrievals

- Fig. 1

- Fig. 2

- Aerosol absorption as parameterized by the single scattering albedo (SSA) is very important in accounting for the influence of particulates on radiative forcing of the Earth’s climate system. However, the magnitude of this absorption is very difficult to measure.  Surface reflectance measured from MODIS combined with ecosystem based BRDF models are inputs to the new Version 2 AERONET algorithm that allow for more accurate absorption retrievals compared to Version 1.
- The AERONET Version 2 retrievals provide greater confidence in the analysis of seasonal, regional and particle mixture variations in aerosol absorption.

## Name: Tom Eck, Brent Holben, and Alexander Sinyuk  NASA/GSFC 

**E-mail:**Thomas.F.Eck@nasa.gov
**Phone: **301-614-6625
**References:**
- Eck, T.F., B. N. Holben, J. S. Reid, A. Sinyuk, O. Dubovik, A. Smirnov, D. Giles, O’Neill, N.T., S.-C. Tsay, Q. Ji, A. Al Mandoos, M. Ramzan Khan,  E. A. Reid, J. S. Schafer,  M. Sorokine, W. Newcomb, and I. Slutsker. Spatial and Temporal Variability of Column Integrated Aerosol Optical Properties in the Southern Arabian Gulf and United Arab Emirates in Summer, In Press, Journal of Geophysical Research-Atmospheres.
- Holben, B.N. et al., AERONET - A federated instrument network and data archive for aerosol characterization, Remote Sensing of Environment, 66, 1-16,  1998.
- Sinyuk, A., O. Dubovik, B. Holben, T.F. Eck, F-M Breon, J. Martonchik, R. Kahn, D. J. Diner, E. F. Vermote, J-C Roger, T. Lapyonok, and I. Slutsker, 2007, Simultaneous retrieval of aerosol and surface properties from a combination of AERONET and satellite, Remote Sensing of Environment, 107, doi:10.1016/j.rse.2006.07.022.
**Data Sources:  **The measurements we have analyzed were made by sun-sky radiometers that are a part of NASA’s AErosol RObotic NETwork (AERONET), which is a federated global network of standardized radiometers calibrated to consistent reference sources and processed with state of the art algorithms. Over 200 sites located in diverse environments on all continents and oceanic islands are currently a part of AERONET.
- During the United Arab Emirates Unified Aerosol Experiment (UAE2 ) field campaign in summer of 2004 NASA established 14 sun-sky radiometer sites in various environments including Arabian Gulf islands, coastal locations, and inland deserts. This measurement campaign provided the highest density mesoscale network of sites ever established by AERONET, and allowed for regional study of the temporal and spatial variation of aerosol properties in addition to rigorous characterization of both satellite and ground based remote sensing retrievals.
**Technical Description of Figures:**
***Figure 1: ***Comparison of Version 1 versus Version 2 AERONET almucantar retrievals of single scattering albedo (SSA) for a desert dust case in the UAE [Eck et al., 2007]. In the Version 2 retrievals the dust SSA is nearly the same for sites with vastly different surface reflectances (Hamim is bright sandy desert and Sir Bu Nuair is relatively dark sea water), as expected since dust is not affected by relative humidity (which differs significantly between these sites). The low SSA at 440 nm in Version 2 is also expected since iron oxides in mineral dust are absorbing in the shorter wavelengths.
***Figure 2: ***Average single scattering albedos as a function of Angstrom exponent (440-870 nm) for Hamim for August 1- October 4, 2004 [Eck et al., 2007]. These Version 2 SSA retrievals show a strong dynamic in aerosol absorption at longer wavelengths since the desert dust (low Angstrom exponent- large particles) is weakly absorbing in the near infrared (high SSA) while the fine mode pollution aerosol (large Angstrom exponent- small particle size) has much stronger near infrared absorption (lower SSA) due to the black carbon content of the aerosol.
**Scientific significance: **Accurate knowledge of** **aerosol absorption and it’s spectral variation is critical for reducing the current large uncertainties in aerosol radiative forcing on climate,** **however it is** **poorly known over many areas of the globe.  This work is the first to publish the new AERONET Version 2 retrievals of almucantar scans to more accurately infer the single scattering albedo.
**Relevance for future science and relationship to Decadal Survey: **Aerosol absorption is the most important atmospheric aerosol parameter after aerosol optical depth in characterizing the radiative forcing of aerosols at the earth’s surface and the top of the atmosphere. AERONET retrievals of SSA have and will continue to be utilized in climate forcing studies and in the validation of current and future satellite missions, such as GLORY that will attempt to measure aerosol absorption from space.