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scattering block (optional) ​

Mie aerosol configuration: per-aerosol size distribution, refractive index, vertical distribution, and the Fourier decomposition method. Skip this block entirely for clear-sky / Rayleigh-only / canopy-only runs.

Required when present ​

  • aerosols — Vector{Dict}. One dictionary per aerosol species (see Per-aerosol fields below).

  • r_max — Real [µm]. Maximum particle radius for the size distribution quadrature. 30 µm covers most tropospheric Mie cases.

  • nquad_radius — Integer. Number of radius quadrature points. Typical: 250–500.

  • λ_ref — Real [µm]. Reference wavelength for the aerosol optical depth normalization.

  • decomp_type — String. Fourier decomposition algorithm:

    • "NAI2()" — Siewert NAI-2 (default for most cases; cheaper).

    • "PCW()" — Domke PCW (precomputed Wigner symbols; uses more memory but cheaper for very large nquad_radius).

Optional fields ​

  • n_ref — Complex. Reference refractive index for the AOD normalization. Defaults to the first aerosol's (nᵣ, nᵢ) if omitted.

Per-aerosol fields ​

Each entry in aerosols: is a dict. Two forms are supported.

Mie/lognormal aerosol (full Mie computation) ​

FieldTypeDescription
τ_refRealAerosol optical depth at λ_ref.
μRealGeometric mean radius [µm].
σRealGeometric standard deviation.
nᵣRealReal part of refractive index.
nᵢRealNegative imaginary part (vSmartMOM uses n = nᵣ - i·nᵢ; see commit b8227c2).

Analytic phase-function aerosol (skip Mie computation) ​

FieldTypeDescription
τ_refRealAerosol optical depth at λ_ref.
phase_functionString or DictAnalytic phase function constructor. Allowed: HenyeyGreensteinPhaseFunction(g=0.7), SyntheticPolarizedHenyeyGreensteinPhaseFunction(g=0.45, polarization_fraction=0.6).
ssa (optional)RealSingle-scattering albedo. Default 1.0. Alias: ϖ.
μ, σ, nᵣ, nᵢ (optional, all-or-none)RealMie microphysical metadata; retained but the analytic phase_function overrides the optics.

The analytic path is intended for fast prototyping and synthetic test scenes; linearized Jacobians are currently defined only for Mie/lognormal aerosols (analytic phase functions throw in LinMode).

Vertical distribution (required, exactly one form) ​

FormFieldsUse case
Altitude-form (Sanghavi convention, preferred)z₀, σ₀Log-normal in altitude. Generalizes cleanly across atmospheric profiles.
Pressure-form (legacy unified convention)p₀, σpNormal in pressure. The historical default before the sanghavi-unified merge.

Both forms with both pairs is rejected.

Examples ​

Single Mie aerosol with altitude-form profile ​

yaml
scattering:
  aerosols:
    - τ_ref: 0.05
      μ:    0.20      # geometric mean radius (µm)
      σ:    1.6
      nᵣ:   1.45
      nᵢ:   0.001
      z₀:   3.0       # altitude-form: log-normal centered at 3 km
      σ₀:   1.5
  r_max: 30.0
  nquad_radius: 300
  λ_ref: 0.55
  decomp_type: "NAI2()"

Two-aerosol setup (fine + coarse mode) ​

yaml
scattering:
  aerosols:
    - τ_ref: 0.10
      μ: 0.15
      σ: 1.5
      nᵣ: 1.45
      nᵢ: 0.001
      z₀: 2.0
      σ₀: 1.2
    - τ_ref: 0.02
      μ: 1.5
      σ: 2.0
      nᵣ: 1.50
      nᵢ: 0.005
      z₀: 5.0
      σ₀: 2.0
  r_max: 50.0
  nquad_radius: 500
  λ_ref: 0.55
  decomp_type: "PCW()"

Henyey-Greenstein analytic phase function (no Mie) ​

yaml
scattering:
  aerosols:
    - τ_ref: 0.5
      phase_function: "HenyeyGreensteinPhaseFunction(g=0.8)"
      ssa: 0.95
      p₀: 800.0     # pressure-form profile
      σp: 100.0
  r_max: 30.0
  nquad_radius: 300
  λ_ref: 0.55
  decomp_type: "NAI2()"

Phase D interaction with truncation: auto ​

When radiative_transfer.truncation = auto (the v0.7 default):

  • No scattering block ⇒ NoTruncation() (Rayleigh only fits any stream_l_cap).

  • scattering block present ⇒ δBGE(stream_l_cap, Δ_angle) (Mie phase functions typically have hundreds of Greek moments).

The choice is logged at @info level so you always see what was applied. To force NoTruncation() even with aerosols (e.g. for a benchmark that requires no transform), set truncation: "NoTruncation()" explicitly.

See also ​