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spec_bands field (in radiative_transfer) ​

The spectral grid(s) the RT solve runs on, in wavenumber (cm⁻¹) internally. spec_bands is a Vector{String} — one string per band — and each string is parsed without eval by _safe_parse_spec_band in src/IO/Parameters.jl. Multiple entries run as a band-batched solve: the whole pipeline (absorption, Mie, RT) loops over bands, one 3-D (NquadN, NquadN, nSpec) array set per band.

Field signature ​

yaml
radiative_transfer:
  spec_bands:
    - "<band_expression>"   # one entry per band

surface: needs one entry per band (fewer is an error at model construction, surplus entries are ignored with a warning; see Schema/surface.md), and the per-band absorption settings (fixed_molecules / variable_molecules, LUTfiles, h2o_absorption) line up with spec_bands in the same way.

Supported expression forms ​

1. Explicit list ​

yaml
spec_bands:
  - "[19417.0 19418.0]"             # space-separated
  - "[19417.0, 19417.5, 19418.0]"   # comma-separated

A bracketed list of numbers, each a full-precision spectral point in cm⁻¹. Used for tiny single-point or hand-picked-point scenes (config/quickstart.yaml, config/canopy_forest.yaml).

2. Range: start:step:stop ​

yaml
spec_bands:
  - "(1e7/780):0.1:(1e7/750)"    # wavenumber range from wavelength math
  - "12950.0:0.02:13050.0"       # plain wavenumber range

start, step, and stop are each evaluated by a small safe recursive-descent arithmetic parser (_safe_parse_number) supporting + - * /, unary sign, and parentheses — e.g. "(1e7/775):0.05:(1e7/755)" is a common way to express a wavelength window in wavenumber terms, since  . No eval is used, so only numeric literals and these four operators are accepted — arbitrary Julia expressions are rejected. A 2-part start:stop (unit step) form is also accepted.

3. Wavelength input via collect(...)u"nm" ​

yaml
spec_bands:
  - "collect(400.0:1.0:700.0)u\"nm\""     # range, given in nm
  - "collect([400.0, 700.0])u\"nm\""      # explicit list, given in nm

Wrapping either the range or the bracketed-list form in collect(...)u"nm" interprets the enclosed values as wavelengths in nanometers; they are converted to wavenumber via   and the result is sorted ascending (wavelength-ascending inputs invert to wavenumber-descending, so the sort keeps the internal grid monotonically increasing). collect(...)u"cm_inv" is also accepted as a no-op tag (values already in the internal unit); a bare collect(...) with no unit suffix is equivalent to omitting collect entirely.

Units and ordering ​

  • Internal unit is always cm⁻¹; wavelength-tagged (u"nm") input is converted at parse time, before the value ever reaches the solver.

  • A raw wavenumber start:step:stop range should already be ascending — collect follows the sign of step and the parser does not re-sort a plain (non-u"nm") range or list.

Examples ​

Single band, single point (quickstart) ​

yaml
radiative_transfer:
  spec_bands:
    - "[12987.0]"

O₂ A-band, wavelength-derived wavenumber range ​

yaml
radiative_transfer:
  spec_bands:
    - "(1e7/780):0.1:(1e7/750)"

Multiple bands (one BRDF and one absorption VMR list per band) ​

yaml
radiative_transfer:
  spec_bands:
    - "[20000 20003]"
    - "[12500 12503]"
  surface:
    - "LambertianSurfaceScalar(0.05)"
    - "LambertianSurfaceScalar(0.40)"

See Schema/absorption.md for how fixed_molecules / variable_molecules line up per band, and Schema/surface.md for the per-band surface: vocabulary.

See also ​