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MULTI-BAND AUTOMATIC SUN AND SKY SCANNING RADIOMETER 
SYSTEM FOR MEASUREMENT OF AEROSOLS 
B.N. HOLBEN 
Code923, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 
T.F. ECK 
Huges STX Corporation, Code 923, NASA/GSFC, Greenbelt, MD 20771 
I. SLUTSKER 
Science Systems and Applications Inc., Code 923, NASA/GSFC, Greenbelt, MD 
D. TANRÉ 
Lab. d'Optique Atmosphérique, U.S.T. de Lille, 59655-Villeneuve d'Ascq,France 
J.P. BUIS 
CIMEL Electronique, 5 cité de Phalsbourg, Paris, France 
A. SETZER 
Instituto de Pesquisas Espaciáis, Sao José dos Campos, SP,Brazil 
E. VERMOTE 
Univ. of MD, Code 923, NASA/GSFC,College Parle, MD 
J. A. REAGAN 
Univ. of Arizona, Tucson, AZ 
Y.A. KAUFMAN 
Code 913, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 
ABSTRACT: 
A weather resistant automatic scanning sun photometer system is assessed and demonstrated as practical for 
measurements of aerosol concentrations and properties at remote sites. Interfaced with a transmitter using 
the Geostationary Data Collection System, the data are processed in near real-time. The processing allows a 
time dependence of the aerosols and water vapor and an ongoing assessment of the health and calibration of 
the instruments. The systems automatic data acquisition, transmission and processing offer immediate 
application to atmospheric monitoring and modeling on a regional to global scale and validation of Satellite 
retrievals. We estimate that under normal circumstances the retrieved aerosol optical thickness has a 
network wide accuracy of ±0.02 from 340 nm to 1020 nm, water vapor ±0.2 cm and size distribution from 
0.1 to 3. |i.m. 
KEY WORDS: Sun Photometry, Aerosols, Optical Thickness, Radiometer 
1 - INTRODUCTION 
Ground based atmospheric aerosol measurements using sun photometry has changed little since 
Voltz (1959) introduced the first handheld more than three decades ago. Modem units can collect data more 
accurately and quickly but the method remains largely the same, that is a filtered detector measures the 
extinction of direct beam radiation according to Beers Law: 
V = V 0 exp-(Tm) (1) 
where: V=Digital voltage 
Vo=extratrestrial voltage 
m=optical airmass 
T=total optical thickness 
Other strategies have been developed and are commercially available. The shadow band radiometer 
measures spectral total and diffuse radiation to obtain the direct component from which aerosol optical 
thickness is computed. The instrument has been shown to be reliable over long periods of time and is