Every day across the globe, dual-wavelength or multi-wavelength lidar instruments assess Backscattering Angstrom Exponents (BAEp), which delineate the wavelength-dependent behavior of particles backscattering coefficients. Traditionally regarded as a proxy for particle size in literature, we challenge this interpretation and propose a reevaluation leveraging light polarization. Specifically, by utilizing light polarization, we can independently extract the Backscattering Ångström Exponents of spherical (s) and non-spherical (ns) particles within a particle mixture (p) = s, ns, denoted as BAES and BAEns respectively. We establish and experimentally verify the relationship between BAEp, BAES and BAEns, employing a case study involving mineral dust particles. Remarkably, BAES and BAEns can be simulated numerically using Mie theory for spherical particles and T-matrix numerical code for non-spherical particles, elucidating the influence of particle size and complex refractive index on these parameters. As a result, the range of involved (s) and (ns) -particles size or / and complex refractive index to be considered in lidar inversion algorithms, can be reduced, thus improving the accuracy of such retrievals. We believe this new methodology, published in 1, may then interest the lidar community: to be applied, it indeed only requires a 2/3 + 28 or multi-wavelength polarization lidar instruments, which are operated every day, worldwide.
Miffre et al. (Thu,) studied this question.
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