Radiation transfer for
satellite data homogenisation

Rayference is a R&D company providing technical and scientific expertise in 1D and 3D radiative transfer modelling supporting Earth Observation applications. This expertise is applied in areas such as inverse modelling for the retrieval of atmospheric and surface properties from space observations, vicarious calibration (metrology), fundamental and thematic climate data record generation or sensitivity analyses for the preparation of new space missions and associated services.

Product Portfolio

Radiation transfer modelling

Rayference develops and operates a suite of atmospheric and surface 1D and 3D radiative transfer models to perform sensitivity analyses, vicarious calibration, retrieval algorithm design and benchmarking or look-up table generation.

FASTRE is a very fast 1D radiative transfer model including Jacobian estimation designed for the retrieval of surface and atmospheric single scattering properties from satellite observations. Our CISAR algorithm relies on the FASTRE model which has been used in a large variety of projects for the retrieval of surface properties such as surface reflectance free from any atmospheric effects, downward surface flux, surface albedo, cloud and aerosol single scattering properties.

Eradiate is a flexible, modern, open-source 3D radiative transfer model based on the Monte Carlo ray tracing technique designed to represent complex earth scenes. This model aims at providing a flexible framework for activities related with calibration and validation in the Earth observation community. Thanks to its capacity to represent a wide range of different scenes, Eradiate will break boundaries between the Earth observation subcommunities and help them share their scientific advances. We want to make it easy for scientists to improve the accuracy of their numerical simulations by accounting for radiative coupling. For that purpose, Eradiate will ship solvers and optical properties originating from the subcommunities with a common interface. Adding a standard atmosphere profile on top of a detailed forest canopy should not be a painful endeavour, nor should be adding a standard desert surface underneath a complex cloud.

Rayference provides advance radiative transfer modelling expertise to a series of research projects.

Polar plot of Raytran surface BRF simulations over Libya-4 for an area of 20 × 20km and a sun zenith angle of 50°. Sand reflectance is equal to 0.3. Circles represent zenith angles, and polar angles represent azimuth angles with a zero degree azimuth pointing to the north. The * symbol indicates the Sun position (after Govaerts (2015)).

Inverse modelling

Rayference is specialized in the development of advanced algorithms based on the inversion of radiative transfer models. We have developed the Combined Inversion of Surface and AeRosol (CISAR) algorithm which provides among others the surface reflectance and fluxes, the single scattering albedo, phase function, fine/coarse mode ratio and the total column aerosol optical thickness based on the inversion of the FASTRE model.

The figure shows an example of aerosol optical thickness retrieval with the CISAR algorithm from PROBA-V data at 1km resolution during a dust storm occuring on the first of February 2015 over the Mediterranean basin. The processing has been performed in the context of the ESA SPAR@MEP project.

Satellite data radiometric calibration

Radiometric calibration is the process of comparing raw observations with a trusted reference, applying an unbroken chain of comparison and uncertainty propagation following metrological principles. Rayference has developed a suite of vicarious calibration methods to support post-launch calibration verification or correction. These methods rely on simulated data with different radiative transfer models over Pseudo Invariant Calibration Sites (PICS) such as deep convective clouds, bright desert and sea surfaces . The current mean accuracy of this method when applied on several tenth of observations acquired in the visible to SWIR spectral regions over the CEOS Libya-4 is about 2.5%.

Rayference provides advance radiometric calibration expertise to a series of research projects.

Top-of-atmosphere bidirectional reflectance factor mean relative bias between observations and simulations over Libya-4. The spectral range of each simulated band is represented by the shape of its sensor response function and the magnitude of the bias by the × symbol. The maximum of the sensor response function shape is scaled to this value. The following color code is used: Landsat-8/OLI (blue), Sentinel-2A/MSI (green), Aqua/MODIS (red), Envisat/MERIS (magenta). Wavelength is expressed in μm (after Govaerts et al. 2018)

Comparison of observations against simulated top-of-atmosphere reflectance over Libya4 (Govaerts et al, 2018)

About us

Our mission

We provide high quality service on the use of radiation transfer theory applied to the field of environment and climate monitoring as well as solar energy assessment.