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Measuring aerosol optical depths from satellite : aerosol measurements and models

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Title:Measuring aerosol optical depths from satellite : aerosol measurements and models
Authors:Porter, John Nolan
Date Issued:1993
Abstract:One of the primary uncertainties in measuring aerosol optical depths from satellite is in the choice of the aerosol phase function. Various investigators have suggested the ratio of AVHRR channels 1 and 2 could be used to derive a variable phase function suitable for many different aerosol cases. In order to investigate this possibility, a new aerosol model was developed from a large data set of in-situ aerosol size distribution measurements and used to model the satellite response. The model results suggest the ratio of AVHRR channels 1 to 2 can be used to roughly derive the aerosol phase function value. In order to test the modeling results, aerosol optical depths were obtained from satellite images and were compared with ground based sun photometer measurements. Both methods were in reasonable agreement for this study although clouds made exact comparisons difficult. Error analysis of the aerosol optical depth derived from AVHRR satellites was also performed. The error was found to be dependent on the scattering angle with largest errors occurring near 120 degrees corresponding to the minimum in the aerosol phase function. Sources of error studied here include sun glint, sensor noise, sensor calibration, water vapor absorption for channel 2 and ozone absorption for channel 1. For the scattering angles with the largest errors, near 120 degrees, the one standard deviation errors in the aerosol optical depth were approximately ±0.03. Either spatial or temporal averaging can reduce the sensor noise resulting in one standard deviation errors of ±0.02. Similar errors exist for channel 2. Errors in the AVHRR ch1/ch2 ratio range from 75%, 35%, 18% and 12% for respective aerosol optical depths of 0.05, 0.1, 0.2, 0.3. Spatial or temporal averaging can reduce this error to 13%, 6%, 4% and 3% for similar optical depths. In addition, the systematic error caused by the AVHRR's coarse digitization was studied and an example of its effect is given as well as a possible way to minimize this problem.
Description:Thesis (Ph. D.)--University of Hawaii at Manoa, 1993.
xv, 127 leaves, bound 29 cm
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Meteorology

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