On the use of light polarization to investigate the size, shape and refractive index dependence of backscattering Angstroem exponents

In this letter, we exploit the polarization property of light to investigate the Angstroem exponent describing the wavelength dependence of optical backscatter between two wavelengths. Where previous interpretation of Angstroem exponent was that of a particles size indicator, the use of light polarization makes it possible to investigate the Angstroem exponent dependence on the particles shape by separately retrieving the backscattering Angstroem exponent of the spherical and nonspherical particles contained in an atmospheric particle mixture. As an output, analytical solutions of the Maxwell equations, Lorenz Mie theory, spheroidal model,can then be applied to investigate the Angstroem exponent dependence on the particles size and complex refractive index for each assigned shape. Interestingly, lidar retrieved vertical profiles of backscattering Angstroem exponents specific to s and ns particles can be used by the optical community to evaluate a range of involved particles sizes and complex refractive indices for both particles shapes, spherical and nonspherical, as we remotely demonstrate on a case study dedicated to a dust nucleation event.