AERONET—A Federated Instrument Network and Data Archive for Aerosol Characterization

https://doi.org/10.1016/S0034-4257(98)00031-5Get rights and content

Abstract

The concept and description of a remote sensing aerosol monitoring network initiated by NASA, developed to support NASA, CNES, and NASDA’s Earth satellite systems under the name AERONET and expanded by national and international collaboration, is described. Recent development of weather-resistant automatic sun and sky scanning spectral radiometers enable frequent measurements of atmospheric aerosol optical properties and precipitable water at remote sites. Transmission of automatic measurements via the geostationary satellites GOES and METEOSATS’ Data Collection Systems allows reception and processing in near real-time from approximately 75% of the Earth’s surface and with the expected addition of GMS, the coverage will increase to 90% in 1998. NASA developed a UNIX-based near real-time processing, display and analysis system providing internet access to the emerging global database. Information on the system is available on the project homepage, http://spamer.gsfc.nasa.gov. The philosophy of an open access database, centralized processing and a user-friendly graphical interface has contributed to the growth of international cooperation for ground-based aerosol monitoring and imposes a standardization for these measurements. The system’s automatic data acquisition, transmission, and processing facilitates aerosol characterization on local, regional, and global scales with applications to transport and radiation budget studies, radiative transfer-modeling and validation of satellite aerosol retrievals. This article discusses the operation and philosophy of the monitoring system, the precision and accuracy of the measuring radiometers, a brief description of the processing system, and access to the database.

Introduction

Accurate knowledge of the spatial and temporal extent of aerosol concentrations and properties has been a limitation for assessing their influence on satellite remotely sensed data (Holben et al., 1992) and climate forcing (Hansen and Lacis, 1990). With the exception of the AVHRR weekly ocean aerosol retrieval product (Rao et al., 1989), the voluminous 20-year record of satellite data has produced only regional snapshots of aerosol loading, and none have yielded a database of the optical properties of those aerosols that are fundamental to our understanding of their influence on climate change. With the advent of the EOS era of laboratory quality orbiting spectral radiometers, new algorithms for global scale aerosol retrievals and their application for correction of remotely sensed data will be implemented (Kaufman and Tanré, 1996). However, the prospect of fully understanding aerosols influence on climate forcing is small without validation and augmentation by ancillary ground-based observations as can be provided by radiometers historically known as sun photometers. Following is a description of a new Sun–sky scanning radiometer system that standardizes ground-based aerosol measurements and processing, can provide much of the ground-based validation data required for future remote sensing programs and may provide basic information necessary for improved assessment of aerosols impact on climate forcing.

Section snippets

Background

The technology of ground-based atmospheric aerosol measurements using sun photometry has changed substantially since Volz (1959) introduced the first handheld analog instrument almost 4 decades ago. Modern digital units of laboratory quality and field hardiness can collect data more accurately and quickly and are often interfaced with onboard processing Schmid et al. 1997, Ehsani et al. 1998, Forgan 1994, Morys et al. 1998. The method used remains the same, that is a filtered detector measures

Automatic sun and sky scanning spectral radiometer

Most if not all sun photometer networks have had limited success when people are required to make routine observations. Therefore, an automatic instrument is a fundamental component for routine network observations. The measurement protocol must be reasonably robust such that unwanted data may be successfully screened from useful data, data quality, and instrument functionality may be evaluated and the instrument should be self-calibrating or at the least collects data for its calibration.

Data transmission

Data are transmitted from the memory of the sun photometer via the Data Collection Systems (DCS) to the geostationary satellites GOES-E, GOES-W, or METEOSAT (GMS is anticipated in 1998) and then retransmitted to the appropriate ground receiving station. The data can be retrieved for processing either by modem or Internet linkage, resulting in near real-time acquisition from almost any site on the globe excluding poleward of 80° latitude. The DCS is a governmental system operated for the purpose

Processing system

A fundamental component of the AERONET system is a package of user-friendly UNIX software that provides near real-time information on the status and calibration of the instruments, data processing with referenced and generally accepted processing algorithms, an orderly archive of the data, and convenient electronic access for all users to the raw and processed database. We shall discuss these aspects of the current operational state of the software and future enhancements.

Global perspective

Through 1997 approximately 100 instruments have been included in the network and 60 instruments were deployed world-wide on various islands, North America, South America, Europe, Africa, and the Middle East, fostered by collaboration between international, national, and local agencies, private foundations, and individuals (Fig. 5). As the database continues to expand, the processing system becomes more sophisticated, and more users have access to the database, the need to provide better access

Conclusion

We believe that a successful system for long-term monitoring and characterization of aerosols requires automatic low maintenance radiometers, real time data reception, and processing as well as an easily accessible database for the scientific community. We have combined commercially available hardware, international agency collaborations, a public domain software, and a collaborative philosophy among investigators to form a network that has yielded regionally based aerosol amounts and

Acknowledgements

The authors wish to thank Diane Wickland and Tony Janetos of NASA Headquarters for providing the initial support for this project, Michael King of NASA’s EOS Project Science Office for continued support, Chris Justice for contributing to the vision of the network, and John Vande Castle and Gunar Fedosejevs for actively participating in development of the network. Many thanks to Bruce Forgan for his detailed constructive recommendations to this manuscript and the other anonymous reviewers for

References (46)

  • Y.J. Kaufman et al.

    Strategy for direct and indirect methods for correcting the aerosol effect on remote sensingfrom AVHRR to EOS-MODIS

    Remote Sens. Environ.

    (1996)
  • J.J. Michalsky

    The astronomical almanac’s algorithm for approximate solar position (1950–2050)

    Solar Energy

    (1988)
  • A.M. Bass et al.

    The ultraviolet cross-section of ozone1. The measurements

  • R.E. Bird et al.

    Simple solar spectral model for direct and diffuse irradiance on horizontal and tilted planes at the Earth’s surface for cloudless atmospheres

    J. Clim. Appl. Meteorol.

    (1986)
  • C.T. Bruegge et al.

    Water vapor column abundance retrievals during FIFE

    J. Geophys. Res.

    (1992)
  • A. Burcholtz

    Rayleigh-scattering calculations for the terrestrial atmosphere

    Appl. Opt.

    (1995)
  • B. Edlen

    The refractive index of air

    Meteorology

    (1966)
  • A.R. Ehsani et al.

    Design and performance analysis of an automated 10-channel solar radiometer instrument

    J. Atmos. Ocean. Tech.

    (1998)
  • B.W. Forgan

    General method for calibrating Sun photometers

    Appl. Opt.

    (1994)
  • Halthore, R. N., and Fraser, R. S. (1987), Inversion of aerosol optical thickness measurements to obtain aerosol size...
  • R.N. Halthore et al.

    Sunphotometric measurements of atmospheric water vapor column abundance in the 940-nm band

    J. Geophys. Res.

    (1997)
  • J.E. Hansen et al.

    Sun and dust versus greenhouse gasesan assessment of their relative roles in global climate change

    Nature

    (1990)
  • L. Harrison et al.

    Automatic multifilter rotating shadow-band radiometeran instrument for optical depth and radiation measurements

    Appl. Opt.

    (1994)
  • B.N. Holben et al.

    Aerosol retrieval over land from AVHRR data—application for atmospheric correction

    IEEE Trans. Geosci. Remote Sens.

    (1992)
  • B.N. Holben et al.

    Effect of dry-season biomass burning on Amazon basin aerosol concentrations and optical properties, 1992–1994

    J. Geophys. Res.

    (1996)
  • M. Iqbal

    An Introduction to Solar Radiation

    (1983)
  • F. Kasten et al.

    Revised optical air mass tables an approximation formula

    Appl. Opt.

    (1989)
  • Y.J. Kaufman

    Measurements of the aerosol optical thickness and the path radiance—implications on aerosol remote sensing and atmospheric corrections

    J. Geophys. Res.

    (1993)
  • Y.J. Kaufman et al.

    Size distribution and phase function of aerosol particles retrieved from sky brightness measurements

    J. Geophys. Res.—Atmos.

    (1994)
  • M.D. King et al.

    Aerosol size distributions obtained by inversion of spectral optical depth measurements

    J. Atmos. Sci.

    (1978)
  • Kneizys, F. X., Shettle, E. P., Abreu, L. W., et al. (1988), Users guide to LOWTRAN 7, AFGL-TR-88-0177, NTIS AD...
  • W.D. Komhyr et al.

    Dobson Spectrophotometer 83a standard for total ozone measurements, 1962–1987

    J. Geophys. Res.

    (1989)
  • J. London et al.

    Atlas of the Global Distribution of Total Ozone July 1957–June 1967, NCAR Technical Note 133+STR

    (1976)
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