Mie scattering¶

By default, PLATON uses a parametric model to account for scattering, with an amplitude and a slope. However, PLATON also has the ability to compute Mie scattering in place of the parametric model.

To use Mie scattering, follow Quick start to see how to do forward models and retrievals using the default parametric model. To use Mie scattering instead:

calculator.compute_depths(Rs, Mp, Rp, T,
    ri = 1.33-0.1j, frac_scale_height = 0.5, number_density = 1e9,
    part_size = 1e-6, cloudtop_pressure=1e5)

This computes Mie scattering for particles with complex refractive index 1.33-0.1j. The particles follow a lognormal size distribution with a mean radius of 1 micron and standard deviation of 0.5. They have a density of \(10^9/m^3\) at the cloud-top pressure of \(10^5\) Pa, declining with altitude with a scale height of 0.5 times the gas scale height.

We also allow the computation of Mie scattering for three condensates using their actual, wavelength-dependent refractive indices, assuming a standard deviation in the lognormal size distribution of 0.5:

calculator.compute_depths(Rs, Mp, Rp, T,
    ri = "TiO2", frac_scale_height = 0.5, number_density = 1e9,
    part_size = 1e-6, cloudtop_pressure=1e5)

The supported species are MgSiO3_sol, SiO2_amorph, and TiO2, using the refractive index data of Kitzmann et al 2017.

To retrieve Mie scattering parameters, make sure to set log_scatt_factor to 0, and log_number_density to a finite value. n and log_k specify the real component and log10 of the imaginary component of the complex refractive index. We recommend fixing at least n. Example:

fit_info = retriever.get_default_fit_info(Rs, Mp, Rp, T,
    log_scatt_factor = 0, log_number_density = 9, n = 1.33, log_k=-1)

fit_info.add_uniform_fit_param('log_number_density', 5, 15)
fit_info.add_uniform_fit_param('log_part_size', -7, -4)