View_factors

Urban albedos and radiative fluxes for the Community Land Model Urban (CLMU) parameterization, following Chapter 2 of Oleson et al. (2010). Computes view factors, incident direct beam and diffuse solar radiation, absorbed and reflected solar radiation (with closed-form multi-reflection solution for the urban canyon), incident longwave radiation, and absorbed/reflected/emitted longwave radiation for urban surfaces: roof, sunlit wall, shaded wall, and road. The urban canyon is represented as an infinitely long canyon of width W bordered by buildings of height H. The iterative multi-reflection scheme (Eqs. 2.63-2.85, 2.138-2.170) is solved in closed form using the matrix geometric series S_absorbed = (I - A) * (I - T*A)^{-1} * S_0, where A is the albedo matrix, T is the view-factor transport matrix, and S_0 is the initial incident radiation vector. Migrated from UrbanCanopy.jl@9200edd4 src/albedos_radiative_fluxes.jl:27 (`UrbanRadiation` @component). Parameterized as observed-only: H_W, W_roof, S_atm_*, L_atm_down, μ_zen, surface albedos α_*, emissivities ε_*, and surface temperatures T_* are inputs (parameters); 62 view factor, intermediate, absorbed-flux, and reflected-flux quantities are algebraic state outputs.