Surfaces

For: users selecting a lower-boundary BRDF and developers adding new surface models.

Next: Add a Surface BRDF, Surfaces tutorial, Library.

Surface models live in CoreRT because they are part of the lower-boundary interaction in the adding-doubling solver. Scene files refer to them through safe parser entries such as LambertianSurfaceScalar(0.15).

Scene File Surface Tags

Tag	Arguments	Use case	Notes
LambertianSurfaceScalar(albedo)	scalar albedo	Band-wide isotropic surface	Analytical surface Jacobian
LambertianSurfaceSpectrum([a1, a2, ...])	spectral albedo vector	Per-grid-point isotropic surface	Vector length must match the spectral grid
LambertianSurfaceLegendre([c0, c1, ...])	Legendre coefficients	Smooth spectral albedo parameterization	Evaluated over the spectral grid
rpvSurfaceScalar(rho0, rho_c, k, Theta)	RPV empirical BRDF parameters	Scalar land BRDF with hotspot/angular shape	Scalar only
RossLiSurfaceScalar(fvol, fgeo, fiso)	Ross-Li kernel weights	MODIS/RAMI-style land BRDF	Scalar only
CoxMunkSurface(wind_speed)	10 m wind speed in m/s	Ocean glint and polarization	Uses built-in water refractive-index lookup unless overridden
CoxMunkSurface(wind_speed=U)	keyword form	Ocean glint with optional keyword extensions	Supports n_water, whitecap_albedo, include_whitecaps, shadowing

Example:

radiative_transfer:
  surface:
    - LambertianSurfaceScalar(0.15)

Canopy Wrapper

Vegetation canopies are configured through an optional top-level canopy: section. The parser wraps each band surface in CanopySurface, so the existing surface becomes the soil BRDF unless a separate canopy soil tag is supplied.

canopy:
  LAI: 3.0
  n_layers: 2
  leaf_reflectance: 0.4
  leaf_transmittance: 0.05
  soil: from_surface

Internally the canopy is treated as scattering sub-layers above the soil boundary and is combined with the same adding-doubling interaction machinery used by the atmospheric column. The current canopy BRDF path is elastic-only.

Implementation Map

• Surface types are defined in src/CoreRT/types.jl.

• Surface layer construction lives under src/CoreRT/Surfaces/.

• Scene-file parsing is registered in BRDF_MAP in src/IO/Parameters.jl.

• New surface types should add a concrete AbstractSurfaceType, a create_surface_layer!/reflectance implementation as appropriate, and a parser registration.

Useful APIs

• AbstractSurfaceType

• LambertianSurfaceScalar, LambertianSurfaceSpectrum, LambertianSurfaceLegendre, LambertianSurfaceSpline

• rpvSurfaceScalar, RossLiSurfaceScalar, CoxMunkSurface

• CanopySurface, CanopySurface_from_prospect, create_surface_layer!