- Email: [email protected]
Aerosol size distribution derived from combined ground-based measurements of scattering and extinction
AerosolSci, Vol. 30, Suppl. 1, pp. $885--S886, 1999 © 1999 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021-8502/99/$ - see front matter
Pergamon
AEROSOL SIZE DISTRIBUTION DERIVED FROM COMBINED GROUND-BASED MEASUREMENTS OF SCATTERING AND EXTINCTION C. Sanchez-Oliveros, F.J. Olmo and L. Alados-Arboledas. Grupo de Fisica de la Atm6sfera. Departamento de Fisica Aplicada. Facultad de Cieneias. Universidad de Granada. 18071 Granada. Spain. Phone 34 58 244024. Fax. 34 58 243214. Email: alados@ ugr.es
KEYWORDS Aerosol Size Distribution, Inversion, Scattering, Extinction.
METHODS Satellite remote sensing of aerosols has to be validated by means of ground based measurements. Aerosol optical features can be obtained through measurements of direct and diffuse solar radiation by using inversion and radiative transfer techniques. The Reception and Treatment Centre of Satellite Imagery of the Granada University has carried out a serie of observational campaigns to get experimental information concerning the aerosol optical properties, such as the aerosol panicles size distribution and the scattering phase function, specially at large scattering angles. Ground-based measurements are performed with a combined sunphotometer/sky radiometer that can measure both the sky radiance and the attenuated direct sunlight, using the same detectors and optics by a neutral filter. Measurements are performed from 300 to 1100 nm in 10 nm steps; the half power bandwidth of the measurements is 6 nm. The experimental sequence includes measurements of transmission of the direct sunlight in order to retrieve the aerosol optical thickness in selected spectral bands out of the strong gaseous absorption bands. After that almucantar sky radiance at both sides of the sun is measured in the same spectral bands. Each sequence takes about 20-25 minutes. This paper describes the initial analysis performed over the data obtained in the experimental campaigns.
RESUME The inversion of combined scattering and extinction measurements gives great information about the size distribution of aerosol particles v(r). Until some years ago, most of the authors had centred their studies on the extinction measurements. However, this permits only to obtain reliable information of the particles with radios around 21am. The inclusion of scattering measurements increases this range to values up to 10~m, which allows to analyse multimodal aerosols size distributions. In this way the contribution of the greater particles can be evidenced. The data analysed include extinction and radiance measurements. The radiance measurements have been carried out both at the solar almucantar and at the principal plane. In the first case, the acimut angle relative to the sun varies between - 180° and 180°. At the principal plane the observations cover cenital angle from -90 ° to 90°. All the measurements have been accomplished in the city centre of Granada (37.18N 3.6W) during the years 1996 to 1998.The measurements have been performed under cloudless sky conditions. The analysis has been carried out for six wavelengths outside of the strong absorption bands. Such wavelengths are 440 520 560 620 670 and 780 nm.
$885
$886
Abstracts of the 1999 EuropeanAerosolConference
The accuracy of the measurements is of great importance so we have carried out the periodic calibration of the spectroradiometer. Two different calibrations have been accomplished in order to calibrate both the extinction and the scattering measurements. For the extinction ones, we have used a modified Langley plot method and for the radiance measurements, we have carried out an absolute laboratory calibration under controlled temperature conditions. The radiative transfer code and inversion scheme considered for the retrieval of the aerosol optical properties is the SKYRAD.pack developed by Nakajima. This code can retrieve aerosol features, such us the aerosol optical thickness, the aerosol scattering phase function, the aerosol size distributions and the aerosol refractive index, for different experimental conditions from proper given input parameters. For the cases presented in this study we can see that the aerosol size distributions show the presence of two different particles modes, one closed to 0. l l.tm and another around 2~tm. We analyse the changes in the aerosol size spectrum along some days. The influence of observation geometry and relative humidity on these changes is studied. The evolution of the aerosol size distributions is in accordance with that of the aerosol optical thickness XA(~,), and the Angstrom turbidity parameter- ~ and 13 throughout the series of measurements. Though in the calculation of ot and 13 is supposed that the size distribution of the particles is unimodal (Junge's distribution), however the value of the parameter et is related to the particles size, so we have analysed the changes of the aerosol size spectrum when this parameter changes. We have found greater values in the aerosol size distributions for greater particles when ct takes a great value, on the other hand we can appreciate as the 0. llam mode increase when decreases. On the other hand we have appreciated the increases in XA(~,) values are related to the increases in the aerosol size distributions.
Pergamon
AEROSOL SIZE DISTRIBUTION DERIVED FROM COMBINED GROUND-BASED MEASUREMENTS OF SCATTERING AND EXTINCTION C. Sanchez-Oliveros, F.J. Olmo and L. Alados-Arboledas. Grupo de Fisica de la Atm6sfera. Departamento de Fisica Aplicada. Facultad de Cieneias. Universidad de Granada. 18071 Granada. Spain. Phone 34 58 244024. Fax. 34 58 243214. Email: alados@ ugr.es
KEYWORDS Aerosol Size Distribution, Inversion, Scattering, Extinction.
METHODS Satellite remote sensing of aerosols has to be validated by means of ground based measurements. Aerosol optical features can be obtained through measurements of direct and diffuse solar radiation by using inversion and radiative transfer techniques. The Reception and Treatment Centre of Satellite Imagery of the Granada University has carried out a serie of observational campaigns to get experimental information concerning the aerosol optical properties, such as the aerosol panicles size distribution and the scattering phase function, specially at large scattering angles. Ground-based measurements are performed with a combined sunphotometer/sky radiometer that can measure both the sky radiance and the attenuated direct sunlight, using the same detectors and optics by a neutral filter. Measurements are performed from 300 to 1100 nm in 10 nm steps; the half power bandwidth of the measurements is 6 nm. The experimental sequence includes measurements of transmission of the direct sunlight in order to retrieve the aerosol optical thickness in selected spectral bands out of the strong gaseous absorption bands. After that almucantar sky radiance at both sides of the sun is measured in the same spectral bands. Each sequence takes about 20-25 minutes. This paper describes the initial analysis performed over the data obtained in the experimental campaigns.
RESUME The inversion of combined scattering and extinction measurements gives great information about the size distribution of aerosol particles v(r). Until some years ago, most of the authors had centred their studies on the extinction measurements. However, this permits only to obtain reliable information of the particles with radios around 21am. The inclusion of scattering measurements increases this range to values up to 10~m, which allows to analyse multimodal aerosols size distributions. In this way the contribution of the greater particles can be evidenced. The data analysed include extinction and radiance measurements. The radiance measurements have been carried out both at the solar almucantar and at the principal plane. In the first case, the acimut angle relative to the sun varies between - 180° and 180°. At the principal plane the observations cover cenital angle from -90 ° to 90°. All the measurements have been accomplished in the city centre of Granada (37.18N 3.6W) during the years 1996 to 1998.The measurements have been performed under cloudless sky conditions. The analysis has been carried out for six wavelengths outside of the strong absorption bands. Such wavelengths are 440 520 560 620 670 and 780 nm.
$885
$886
Abstracts of the 1999 EuropeanAerosolConference
The accuracy of the measurements is of great importance so we have carried out the periodic calibration of the spectroradiometer. Two different calibrations have been accomplished in order to calibrate both the extinction and the scattering measurements. For the extinction ones, we have used a modified Langley plot method and for the radiance measurements, we have carried out an absolute laboratory calibration under controlled temperature conditions. The radiative transfer code and inversion scheme considered for the retrieval of the aerosol optical properties is the SKYRAD.pack developed by Nakajima. This code can retrieve aerosol features, such us the aerosol optical thickness, the aerosol scattering phase function, the aerosol size distributions and the aerosol refractive index, for different experimental conditions from proper given input parameters. For the cases presented in this study we can see that the aerosol size distributions show the presence of two different particles modes, one closed to 0. l l.tm and another around 2~tm. We analyse the changes in the aerosol size spectrum along some days. The influence of observation geometry and relative humidity on these changes is studied. The evolution of the aerosol size distributions is in accordance with that of the aerosol optical thickness XA(~,), and the Angstrom turbidity parameter- ~ and 13 throughout the series of measurements. Though in the calculation of ot and 13 is supposed that the size distribution of the particles is unimodal (Junge's distribution), however the value of the parameter et is related to the particles size, so we have analysed the changes of the aerosol size spectrum when this parameter changes. We have found greater values in the aerosol size distributions for greater particles when ct takes a great value, on the other hand we can appreciate as the 0. llam mode increase when decreases. On the other hand we have appreciated the increases in XA(~,) values are related to the increases in the aerosol size distributions.