An Adaptive Base Point Algorithm for the Retrieval of Aerosol Microphysical Properties

Abstract

Abstract:We propose a new iterative algorithm for the retrieval of the microphysical properties of stratospheric and tropospheric aerosols from multiwavelength lidar data. We consider the basic equation as an ill-posed problem and solve the system derived from spline collocation via a Padé iteration. The algorithm takes special care of the fact that the reconstruction of the distribution via spline collocation is very sensitive to the choice of base points of the chosen spline basis. The algorithm makes use of this fact by changing the base points used for the spline collocation at certain iteration steps. In addition, the effects of projection to ensure a nonnegative solution are examined. We tested how well this and other algorithms are suitable for retrieving the complex refractive index of the particles as well. We also examine whether the algorithm is capable of distinguishing between different, very small imaginary parts of the refractive index, which is often a main problem in practice. Finally, the algorithm is applied to real multiwavelength Raman lidar data and our results are partially validated by the thermodynamic chemical model Isorropia II.

Optical-microphysical properties of Saharan dust aerosols and composition relationship using a multi-wavelength Raman lidar, in situ sensors and modelling: a case study analysis

“…The measured vertical profiles of the aerosol backscatter and extinction coefficients at multiple wavelengths can be inverted to derive particle microphysical parameter profiles (Müller et al, 1999;Veselovskii et al, 2002Veselovskii et al, , 2009Osterloch et al, 2011). However, this kind of inversion is an illposed problem requiring regularization (Engl et al, 2000), therefore, "unique" (unambiguous) solutions will never be available.…”

Multi-wavelength Raman lidar, sun photometric and aircraft measurements in combination with inversion models for the estimation of the aerosol optical and physico-chemical properties over Athens, Greece

“…It is well known that, when multi-wavelength lidar data are used, the main microphysical aerosol properties can be obtained using inversion techniques (Müller et al, 1999a, b;Veselovskii et al, 2001;Osterloh et al, 2011). Our work goes a step further, which is the main goal of this paper: using a novel procedure, we combine 6-wavelength Raman lidar data, inversion models and an aerosol thermodynamic model to retrieve simultaneously the vertical profiles of optical, microphysical and (propose) chemical properties of aerosol particles, consistent with the retrieved refractive index and single scattering albedo values.…”

Microphysical particle properties derived from inversion algorithms developed in the framework of EARLINET

“…Since the distribution of the B-spline nodes also plays a critical role, we modified the first algorithm TSVD such that non-equidistant node grids can be used too (Böck-mann, 2001). The iterative method was equipped with an adaptive non-equidistant node grid by Osterloh et al (2011).…”

“…for moderate absorption. To account for the non-negative restriction of the PSD we use a projected iteration (Osterloh et al, 2011).…”

“…In order to account for this behaviour, the nodes automatically slide towards radius intervals that have larger weight in the PSD during the iteration process, in contrast to fixed non-equidistant Chebyshev nodes. For more details we refer to Osterloh et al (2011). If we use either TSVD or Páde regularization, we obtain a logarithmically coloured refractive index grid that indicates the error magnitude, as explained above (Figs.…”