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Comparison of modified Twomey method and an anomalous diffraction approximation technique for aerosol size distribution retrivial

dc.contributor.authorEsposito, F.
dc.contributor.authorFranssens, G.
dc.contributor.authorPavese, G.
dc.contributor.authorSerio, C.
dc.date2001
dc.date.accessioned2017-05-04T09:47:14Z
dc.date.available2017-05-04T09:47:14Z
dc.identifier.urihttps://orfeo.belnet.be/handle/internal/5277
dc.descriptionDirect solar radiation measurements were performed both in a moderately polluted location of Southern Italy. We use a spectro-photo-radiometer covering the range 400 nm- 1100 nm, with a resolution of 3 nm, to obtain the aerosol optical depth. We use this data to compare two inversion techniques to deduce the aerosol size distribution. The first one is a modified Twomey non-parametric technique, with a second-derivative regularisation. It is applied to the discretized integral equation, relating aerosol optical depth to particles size distribution by Mie theory, and is valid without any restriction on wavelength or particle radius. The second method uses a new algorithm based on the Anomalous Diffraction Approximation (ADA) to Mie theory, applicable to spherical particles with radius large compared to the wavelength and refractive index close to 1. A specially designed set of ortho-normal basis functions, each possessing the spectral behavior of an extinction function, describes the measured spectral extinction. The expansion coefficients of this representation are obtained from a constrained least squares extinction fit. The fit cost function is minimized by a Generalized Reduced Gradient Method (GRGM), which allows the specification of additional constrains on the sought coefficients (e.g. positiveness).
dc.languageeng
dc.titleComparison of modified Twomey method and an anomalous diffraction approximation technique for aerosol size distribution retrivial
dc.typeConference
dc.subject.frascatiPhysical sciences
dc.audienceScientific
dc.subject.freeAlgorithms
dc.subject.freeApproximation theory
dc.subject.freeDiffraction
dc.subject.freeIntegral equations
dc.subject.freeParticle size analysis
dc.subject.freeRadiometers
dc.subject.freeRefractive index
dc.subject.freeSolar radiation
dc.subject.freeSpectrophotometers
dc.subject.freeAnomalous diffraction approximation (ADA)
dc.subject.freeGeneralized reduced gradient methods (GRGM)
dc.subject.freeAtmospheric aerosols
dc.source.titleProceedings of SPIE 4168 - Remote Sensing of Clouds and the Atmosphere V
dc.source.volume4168
dc.source.page236-242
Orfeo.peerreviewedNo
dc.identifier.doi10.1117/12.413869
dc.identifier.scopus2-s2.0-0035051151


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