Quick Start

This page demonstrates the basic workflow for both the C++ and Python interfaces.

C++ quick start

The following example computes fluxes for a 4-layer atmosphere with a Henyey-Greenstein phase function and a Lambertian surface.

#include "DisortConfig.hpp"
#include "DisortSolver.hpp"

using namespace disortpp;

int main() {
    int nlyr = 4;
    int nstr = 16;

    // Create and configure
    DisortConfig cfg(nlyr, nstr);
    cfg.flags.use_lambertian_surface = true;
    cfg.flags.comp_only_fluxes = true;
    cfg.allocate();

    // Layer optical properties
    cfg.delta_tau = {0.1, 0.5, 1.0, 2.0};
    cfg.single_scat_albedo = {0.9, 0.9, 0.9, 0.9};
    cfg.setHenyeyGreenstein(0.8);  // all layers

    // Boundary conditions
    cfg.bc.direct_beam_flux = 3.14159;
    cfg.bc.direct_beam_mu = 0.5;
    cfg.bc.surface_albedo = 0.1;

    // Solve
    DisortSolver solver;
    DisortResult result = solver.solve(cfg);

    // Access results
    double flux_up_toa = result.flux_up[0];
    double flux_down_boa = result.totalFluxDown(nlyr);
}

Python quick start

The Python interface mirrors the C++ API closely:

import disortpp
import numpy as np

nlyr = 4
nstr = 16

# Create and configure
cfg = disortpp.DisortConfig(nlyr, nstr)
cfg.flags.use_lambertian_surface = True
cfg.flags.comp_only_fluxes = True
cfg.allocate()

# Layer optical properties
cfg.delta_tau = [0.1, 0.5, 1.0, 2.0]
cfg.single_scat_albedo = [0.9, 0.9, 0.9, 0.9]
cfg.set_henyey_greenstein(g=0.8)

# Boundary conditions
cfg.bc.direct_beam_flux = np.pi
cfg.bc.direct_beam_mu = 0.5
cfg.bc.surface_albedo = 0.1

# Solve
solver = disortpp.DisortSolver()
result = solver.solve(cfg)

# Access results
flux_up = np.array(result.flux_up)
flux_down = np.array(result.flux_down)
print(f"Upward flux at TOA: {flux_up[0]:.6f}")

Workflow overview

Every DisORT++ calculation follows the same three steps:

  1. Configure – create a configuration object (DisortConfig or DisortFluxConfig), set dimensions, flags, optical properties, boundary conditions, and call allocate().

  2. Solve – pass the configuration to a solver (DisortSolver or DisortFluxSolver).

  3. Extract results – read fluxes, mean intensities, and (if requested) angular intensities from the result object.

Choosing a solver

Criterion

DisortSolver

DisortFluxSolver

Output

Fluxes + intensities

Fluxes only

Surface model

Lambertian + BRDF

Lambertian only

Stream count

Any even number >= 4

4, 6, 8, 10, 12, 14, 16, 32, 64

Performance

Baseline

30–50 % faster

Config class

DisortConfig

DisortFluxConfig

Level and layer indexing

DisORT++ uses a layered atmosphere model. Levels are the boundaries between layers, numbered from 0 (top of atmosphere, TOA) to N (bottom of atmosphere, BOA), where N is the number of layers:

Level 0  ──────────────  TOA
         │  Layer 0   │
Level 1  ──────────────
         │  Layer 1   │
Level 2  ──────────────
         │    ...     │
Level N  ──────────────  BOA

  • delta_tau[i] and single_scat_albedo[i] describe layer i (between levels i and i + 1).

  • temperature[i] describes level i.

  • Flux arrays (flux_up, flux_down, etc.) are indexed by level.