LESS

3D Radiative Transfer Model

Version 3.0.9rc1 · Release candidate

LESS is a GPU- and CPU-accelerated 3D radiative transfer model for quantitative remote sensing. It combines a Python interface with NVIDIA OptiX, Vulkan Ray Query, and Intel Embree native backends for optical, thermal, solar-induced fluorescence (SIF), vegetation photosynthesis, energy-balance, and LiDAR simulations.

LESS 3.x is a completely new native implementation of the original LESS model. The original LESS 2.x implementation remains available at lessrt.org.

Highlights

• Remote-sensing-oriented Python API — describe a scene using terrain, objects, optical properties, illumination, sensors, and products.
• Three native backends — OptiX for NVIDIA GPUs, Vulkan Ray Query for supported GPUs, and Embree for CPU execution for simulation across supported platforms.
• Persistent scenes — geometry is prepared automatically on the first simulation and reused when only illumination, spectra, or properties change.
• Mesh and turbid vegetation — simulate explicit geometry, volume canopies, or mixed scenes.
• Imaging and biophysical products — optical and thermal imagery, BRF, radiation fields, irradiance maps, SIF, photosynthesis, energy balance, and LiDAR.
• Sensor effects — pushbroom geometry, spectral response, PSF/MTF, detector noise, ADC quantisation, and geolocation.
• Interactive inspection — use scene.show() to explore scenes and products in a browser-based viewer.

Installation

python -m pip install "less3d==3.0.9rc1"

Prebuilt wheels are provided for Windows and Linux with Python 3.10–3.13. A compiler and CUDA toolkit are not required. Compatible graphics drivers are still required for GPU backends.

Check whether a feature can run with a particular backend on the current computer:

import less

less.can_use("optical_imaging", backend="optix")
less.can_use("irradiance_map", backend="embree")

After creating a scene, scene.can_use("feature") performs the same check using that scene's selected backend.

Available in 3.0.9rc1

The following workflows are available with OptiX, Vulkan, and Embree when the selected backend meets its hardware and driver requirements:

Repetitive scenes require flat, statistically homogeneous terrain and cannot be combined with terrain_following=True. Moving a TurbidBoundary instance requires scene.rebuild(); ordinary property and illumination changes do not.

Quick start

import less

# Create a 10 m × 10 m bare-soil scene.
scene = less.Scene()
scene.size = 10.0
scene.terrain = less.Terrain(
    property=less.Lambertian(reflectance=0.3)
)
scene.illumination = less.Illumination(
    source=less.Sun(zenith=30, azimuth=150),
    atmosphere=less.NoAtmosphere(),
)

# Simulate a nadir RGB image.
sensor = less.OpticalImager(
    less.Orthographic(image_size=256),
    bands=[650, 550, 450],
    quality=128,
)
image = scene.simulate(sensor)
image.save("output.png")

Change the illumination and simulate again; the prepared geometry is reused automatically:

scene.illumination = less.Illumination(
    source=less.Sun(zenith=60, azimuth=90),
    atmosphere=less.NoAtmosphere(),
)
image2 = scene.simulate(sensor)

Forest example

import less
import numpy as np

scene = less.Scene()
scene.size = 30.0
scene.terrain = less.Terrain(
    property=less.Lambertian(reflectance=0.12)
)
scene.illumination = less.Illumination(
    source=less.Sun(zenith=35, azimuth=225),
    atmosphere=less.NoAtmosphere(),
)

birch = less.Object("birch", mesh=less.asset_path("FREX.obj"))
birch.set_property(
    "leaves",
    less.Prospect(cab=40, car=8, cw=0.012, cm=0.009, N=1.5),
)
birch.set_property("stem_branch", less.Lambertian(reflectance=0.1))

xy = np.random.default_rng(42).random((50, 2)) * 30
scene.add(birch, positions=np.c_[xy, np.zeros(50)])

image = scene.simulate(less.OpticalImager(
    less.Orthographic(image_size=512),
    bands=[550, 670, 800],
    quality=256,
))
image.save("forest.tif")

GeoTIFF output preserves the physical values of the simulated product.

Examples and viewer

import less

less.examples.list()
less.examples.run("autumn_forest")
less.examples.run("maize_field")

scene.show()

Numerical results

Simulation products use the same physical quantities and units on all three backends. Monte Carlo estimates can differ because their random samples differ. For quantitative work, increase the sampling quality until your scene averages and spatial patterns are stable.

Documentation

Start with the public tutorials:

• 中文：安装
• 中文：核心概念与场景生命周期
• 中文：API 参考
• English: Installation
• English: Concepts and scene lifecycle
• English: API reference

Building LESS from source, running the test suites, or extending it with new sensors, products or backends is covered in DEVELOPMENT.md. None of it is needed to use the published wheel.

Citation

If you use LESS in your research, please cite:

Qi, J., Xie, D., Yin, T., Yan, G., Gastellu-Etchegorry, J.-P., Li, L., Zhang, W., Mu, X., and Norford, L. K. (2019). LESS: LargE-Scale remote sensing data and image Simulation framework over heterogeneous 3D scenes. Remote Sensing of Environment, 221, 695–706.

License

LESS is free for academic teaching and qualifying non-commercial research. Use is governed by the current LICENSE. Commercial use requires a separate written license.

Commercial use includes company use, commercial consulting or services, commissioned research, commercial synthetic-data generation, and integration into commercial products, platforms, or services. University or non-profit projects performed for a company, or projects that give a company confidential deliverables, preferential access, publication control, or intellectual- property rights, are commercial use. An unrestricted donation or public research grant does not by itself make qualifying academic research commercial; use by a company remains commercial regardless of its funding source.

Third-party components remain subject to their respective license terms. See the LICENSE file for details. Earlier LESS releases remain governed by the license terms that accompanied those releases; those earlier grants are not revoked.

For commercial licensing or clarification, contact the LESS Development Team through the project homepage.