CHIME radiance simulation

Scientific challenge

The Copernicus Hyperspectral Imaging Mission for the Environment (CHIME) will acquire hyperspectral observations in the visible to shortwave infrared spectral range. Preparing and evaluating its instrument and processing chain requires realistic radiance scenes that reproduce the spectral and spatial variability of the Earth as viewed from space.

A key challenge is to represent surface heterogeneity, atmospheric effects and three-dimensional radiative transfer processes at a resolution sufficiently fine to provide meaningful input to an instrument performance simulator. Such input must be distinguished from the simulated measurements and Level-1 products produced after modelling the instrument response.

S2GOS contribution

DTE-S2GOS generates high-spectral- and high-spatial-resolution front-of-telescope (FoT) radiance using detailed three-dimensional Earth scenes and the Eradiate radiative transfer model. These radiances describe the incoming signal before it is modified by the CHIME optical system, detectors and onboard acquisition chain.

The simulation accounts for the interaction of solar radiation with the surface and atmosphere, including spatially varying surface properties and three-dimensional effects such as adjacency. It draws on the scene generation and atmospheric simulation capabilities also used for the ACIX-IV use case.

S2GOS does not develop the CHIME instrument simulator. Instead, its intended contribution is to supply physically consistent FoT radiance scenes that can be used as input to the separately developed CHIME instrument performance simulation chain. Instrument-specific effects, including the detailed spectral and spatial response, detector behaviour and onboard processing, are outside the scope of this S2GOS use case.

Demonstration

The demonstration uses the Furioso region of interest in Patagonia National Park, Chile, with contrasting seasonal scene conditions. High-resolution radiance simulations illustrate the variability of the incoming signal that a hyperspectral instrument would observe.

The two figures below show RGB visualisations derived from Eradiate simulations for December and June. They illustrate seasonal differences in the simulated scene; they should not be interpreted as final CHIME Level-1 products or as outputs of the CHIME instrument simulator.

RGB visualisation of an Eradiate simulation over the Furioso region of interest in December.

RGB visualisation of an Eradiate simulation over the Furioso region of interest in June.

The exact radiance sampling, data format and interface to the external simulator must be agreed with its developers before end-to-end interoperability can be demonstrated.

Expected results

This use case aims to provide:

Physically consistent FoT radiance datasets with fine spatial and spectral sampling, suitable for subsequent instrument simulation.
Realistic variability arising from three-dimensional surface structure, atmospheric conditions, observation geometry and seasonal changes.
Reference input scenes for assessing the effects of instrument characteristics and processing on the observed signal.

By separating the simulation of the Earth–atmosphere radiance field from the simulation of the instrument response, this approach supports independent assessment of both components and facilitates reuse of S2GOS scenes for different observation scenarios.