Title

Measurements of aerosol optical properties over the ocean using sunphotometry and lidar

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physics

First Committee Member

Kenneth J. Voss, Committee Chair

Abstract

Aerosols suspended in the atmosphere scatter and absorb downwelling and upwelling radiation and also serve as cloud-condensation nuclei. This interaction perturbs the radiation balance in the atmosphere and causes changes in regional and global climates. Aerosols also effect the remote sensing of the earth's surface and atmosphere as the signals measured by the satellite sensors must pass through the aerosol layers. It is necessary to determine the optical properties of the aerosols in order to better understand the atmospheric system, provide accurate input to climate models, and to correct remotely sensed data. The primary aerosol optical properties are the aerosol optical depth (AOD) and its spectral dependence characterized by the Angstrom exponent, the aerosol phase function, the aerosol single scattering albedo, the vertical structure of the aerosol backscatter and extinction coefficients, and the aerosol backscatter-extinction ratio. There is little information on the optical properties of marine aerosols because measurements over the ocean are difficult to perform. In order to determine the optical properties of the marine aerosols, a series of measurements were performed using sunphotometers, automated shadowband radiometers, and a micro-pulse lidar system.The AOD and the Angstrom exponent in the visible and near-infared were determined using data taken in support of the Atmosphere/Ocean Chemistry Experiment (AEROCE) in Miami, Bermuda, and Barbados from August 1993 to December 1995. The AOD measurements were made using hand-held sunphotometers and automated shadowband radiometers. The resulting AOD data were correlated with surface measurements of aerosol concentrations to analyze seasonal trends in the AOD and to determine characteristic AOD and Angstrom exponent patterns for key marine aerosol species. Measurements of the vertical structure of the aerosol optical properties were performed using a micro-pulse lidar system. Measurements were made on Tenerife, Canary Islands during the Aerosol Characterization Experiment 2 (ACE-2) in June and July of 1997 and on a SeaWiFS initialization cruise (MOCE-4) around Hawaii in January and February of 1998. The data were used to develop vertical profiles of the optical properties of the key marine aerosols.Introductory and background theoretical information, descriptions of each type of instrument along with corresponding calibration and error correction procedures, and the conclusions drawn from each experiment are presented. The results show that the spectral dependence of the AOD over the oceans can be accurately described by the Angstrom exponent. Also, seasonal variations in the AOD are caused by seasonal changes in the concentrations of key marine aerosol species and each species was found to have unique AOD and Angstrom exponent characteristics. Results from work with the lidar have shown that the micro-pulse lidar system can operate successfully in the field and that accurate optical profiles can be calculated. Also, specific characteristics of the aerosol layers present during ACE-2 and MOCE-4 are presented. Finally, future applications of the result obtained in this study are discussed in the concluding chapter.

Keywords

Physics, Atmospheric Science; Remote Sensing

Link to Full Text

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