Abstract
Lidar and polarimeter aerosol microphysical retrievals require calculating single-scattering properties that are computationally expensive. One of the easiest ways to speed up these calculations is to use a look-up table. Two important currently available look-up tables were created about 15 years ago. Advancements in modern computational hardware allows us to create a new look-up table with improved precision over a larger range of aerosol properties. In this new and improved Lorenz-Mie look-up table we tabulate the light scattering by an ensemble of homogeneous isotropic spheres at arbitrary wavelengths starting from 0.355 μm. The improved look-up table covers spherical atmospheric aerosols with radii in the range of 0.001–100 μm, with real parts of the complex refractive index in the range of 1.29–1.65, and with imaginary parts of the complex refractive index in the range of 0–0.05. We test twelve wavelengths from 0.355 to 2.264 μm and find that the elements of the normalized scattering matrix as well as the asymmetry parameter, the aerosol absorption, backscatter, extinction, and scattering coefficients are precise to within 1% for 99.99% of cases. The look-up table together with C++, Fortran, Matlab, and Python codes are freely available online.
Highlights
There is a growing interest in combining simultaneous lidar and polarimeter measurements to perform retrievals of vertically-resolved aerosol properties
4.3 Structure of Look-Up Table File In Section 3 we described the theoretical background of the scale invariance rule (SIR) look-up table (LUT) and in Section 4.2 provided a justification for the selection of quadratures that formed the actual LUT
We expect that the Q12(Θ, m, λ 0.355μm, r) directional scattering efficiency for small imaginary parts oscillates even more vigorously than the absorption efficiency. If we find it necessary to improve the precision of P12(Θ), in the version of the SIR LUT we will need to have more radius quadrature points M, denser coverage of imaginary parts of complex refractive index (CRI) around zero, and possibly use additional integration points to compute the values of Number of radius quadrature points
Summary
There is a growing interest in combining simultaneous lidar and polarimeter measurements to perform retrievals of vertically-resolved aerosol properties. There are many different types of lidars, but our Lorenz-Mie look-up table (LUT) unit tests focus on the NASA LaRC airborne secondgeneration high spectral resolution lidar (HSRL-2), which makes three-wavelength lidar measurements of the atmosphere (Burton et al, 2018). Retrievals of aerosol microphysical properties using lidar and polarimeter data separately or combined require significant light single-scattering calculations that can consume a majority of the computational time. We describe the improved LUT (which we call: SIR LUT) that uses scale invariance rule (SIR) built on Mishchenko (Mishchenko, 2006) to speed up these calculations with a precision target of 1% for all the optical properties. Our LUT targets spherical aerosols, i.e., Lorenz-Mie scattering theory is applied (Van de Hulst, 1981; Bohren and Huffman, 1983; Mishchenko et al, 2002), but this theoretical approach can be extended to nonspherical aerosols (Dubovik and King, 2000; Dubovik et al, 2002a; Dubovik et al, 2006; Dubovik et al, 2011; Dubovik et al, 2014)
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