Remote-sensing technologies are a pillar of many Earth observation applications, e.g., climate monitoring, weather forecasting, biodiversity tracking, land-use change monitoring, natural disaster monitoring, natural resources management, etc. The increasing sophistication of satellite remote-sensing gives nowadays access to highly accurate radiometric data meeting requirements for Earth observation applications, e.g., around 2 to 3 % relative radiometric accuracy for radiometers on-board Sentinel satellites.
For climate monitoring purposes, precision and trueness of these radiometric data must be routinely monitored over long periods of time. This is critical to proper assessment of possible sources of uncertainty in the collected data, i.e., to propagate uncertainty from the observations up to the delivered geophysical products and associated data. These activities heavily rely on ground-based observations often acquired at different temporal, spatial and spectral resolutions. Thus, ground observations cannot be straightforwardly compared with similar space-based derived products. Therefore, complex radiative transfer simulation tools are necessary to understand to what extent these two types of measurements can be compared, accounting for their respective uncertainties.
The compartmentalisation of the Earth observation community into specialised subcommunities led to the simultaneous development of radiative transfer models and simulation software packages, each addressing their specific problem and therefore shipping specific physical and programming features and data sets. No tool currently allows to merge all the resulting scientific advances into a single software package to tackle heavily coupled radiative problems. This is the problem Eradiate aims at tackling.
Eradiate is a 3D radiative transfer model based on the Monte Carlo ray tracing technique. It is being designed and developed by Brussels-based company Rayference, with funding from the MetEOC-3 project.
A flexible 3D radiative transfer model
Eradiate aims at providing a flexible framework for activities related with calibration and validation in the Earth observation community, where flexibility is to be understood in a variety of ways.
Flexibility in physical complexity. Increasing the level of realism by accounting for more complex physics should be a burden for the computer, not for the physicist. Running the polarised version of a simulation should not be more complicated than attaching polarised optical properties to the objects in your scene and selecting a vector Monte Carlo algorithm. Eradiate therefore has the ambition of supporting multiple radiative models in a unified framework.
Flexibility in scene complexity. Radiative transfer model users have different needs when it comes to defining a scene on which to perform radiative transfer simulation. Some may need simple one-dimensional atmospheric model to quickly evaluate a radiative flux; others may need to represent each tree leaf of a forest; and some may need both at the same time! Eradiate will provide a unified scene construction interface which will allow to naturally populate a scene with simple or complex objects, and to combine both.
Flexibility in usage. Radiative transfer model users may need fluxes and radiances; but sometimes, these quantities are just an element in a longer data flow. Eradiate will ship a standalone, full-featured solver, as well as specialised solvers for selected canonical problems and library components allowing to embed the model in other applications.
A bridge between communities
One goal is to 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.
Eradiate is to be maintained on the long term. This means that it will be carefully designed and coded with rigorous style and processes. It will also be throroughly tested and validated through documented tests and benchmarks. It will be shipped with comprehensive and thorough documentation.
Since Eradiate is meant to be a simulation tool for the scientific community, it will be released under an open-source license. More than that, the contribution of the scientific community to the project will be encouraged through a community-based development process.
Eradiate will consist of a core module which will define common interfaces, documentation frameworks, core RTE solvers and evaluation protocols. Specialised modules oriented towards user communities will provide specific scenes, optical property models, databases and interfaces, as well as test cases. Community developers will be welcome to provide bug reports, fixes, new feature suggestions and implementation.
Funding and development
The general design of Eradiate is funded by the MetEOC-3 project (EMPIR grant 16ENV03).
Design and development is currently performed by Brussels-based company Rayference.
‘Eradiate’ is an uncommon English word for ‘radiate’. This name was chosen among a dozen of candidates using the majority judgment voting method proposed by mathematicians Michel Balinski and Rida Laraki.