Application of randomly oriented spheroids for retrieval of dust particle parameters from multiwavelength lidar measurements

Abstract

[1] Multiwavelength (MW) Raman lidars have demonstrated their potential to profile particle parameters; however, until now, the physical models used in retrieval algorithms for processing MW lidar data have been predominantly based on the Mie theory. This approach is applicable to the modeling of light scattering by spherically symmetric particles only and does not adequately reproduce the scattering by generally nonspherical desert dust particles. Here we present an algorithm based on a model of randomly oriented spheroids for the inversion of multiwavelength lidar data. The aerosols are modeled as a mixture of two aerosol components: one composed only of spherical and the second composed of nonspherical particles. The nonspherical component is an ensemble of randomly oriented spheroids with size-independent shape distribution. This approach has been integrated into an algorithm retrieving aerosol properties from the observations with a Raman lidar based on a tripled Nd:YAG laser. Such a lidar provides three backscattering coefficients, two extinction coefficients, and the particle depolarization ratio at a single or multiple wavelengths. Simulations were performed for a bimodal particle size distribution typical of desert dust particles. The uncertainty of the retrieved particle surface, volume concentration, and effective radius for 10% measurement errors is estimated to be below 30%. We show that if the effect of particle nonsphericity is not accounted for, the errors in the retrieved aerosol parameters increase notably. The algorithm was tested with experimental data from a Saharan dust outbreak episode, measured with the BASIL multiwavelength Raman lidar in August 2007. The vertical profiles of particle parameters as well as the particle size distributions at different heights were retrieved. It was shown that the algorithm developed provided substantially reasonable results consistent with the available independent information about the observed aerosol event.Citation: Veselovskii, I., O. Dubovik, A. Kolgotin, T. Lapyonok, P. Di Girolamo, D. Summa, D. N. Whiteman, M. Mishchenko, and D. Tanré (2010), Application of randomly oriented spheroids for retrieval of dust particle parameters from multiwavelength lidar measurements,

Triple-wavelength depolarization-ratio profiling of Saharan dust over Barbados during SALTRACE in 2013 and 2014

“…Besides a precise description of dust in atmospheric models, there is also a strong need for a better knowledge of the link between the microphysical and optical dust properties to improve dust profiling and retrieval techniques (Veselovskii et al, 2010Müller et al, 2013;Lopatin et al, 2013;Chaikovsky et al, 2016;Bovchaliuk et al, 2016). Recently, a new aerosol retrieval technique was proposed, which makes use of depolarization-ratio profiling and permits the separation of fine dust, coarse dust, and residual (marine or anthropogenic) aerosol profiles in terms of light backscatter, extinction, and mass concentration (Mamouri and Ansmann, 2014).…”

Study of African Dust with Multi-Wavelength Raman Lidar During “Shadow” Campaign in Senegal

“…The ground based measurements performed during the SAMUM campaign demonstrated that the imaginary part of the dust RI could vary from m I =0.005 at 532 nm to m I =0.02 at 355 nm [3]. Such a strong enhancement of m I may lead to a decrease of the backscattering coefficient [5].…”

“…Extinction and backscattering Ångström exponents were calculated using the model of randomly oriented spheroids as described in [5] for a bimodal particle size distribution: …”

Using paraxial approximation to describe the optical setup of a typical EARLINET lidar system

“…More precisely, the lidar techniques that are widely used for aerosol research are capable of providing range-resolved information for (a) the aerosol backscatter coefficient (β αer ) using the backscatter lidar technique (e.g., Fernald et al, 1972;Klett, 1981), (b) the aerosol extinction coefficient (α αer ) using the Raman lidar technique (Ansmann et al, 1990(Ansmann et al, , 1992 and (c) the volume and particle linear depolarization ratios using the depolarization lidar technique (e.g., Sassen, 2005;Freudenthaler et al, 2009). Many studies have demonstrated that the provision of the aforementioned aerosol optical properties for multiple wavelengths facilitates the retrieval of aerosol microphysical properties through inversion techniques (Müller et al, 1999;Veselovskii et al, 2002Veselovskii et al, , 2010. The accuracy of the optical properties used as inputs for the inversions is critical.…”