The radiative transfer is at the heart of HYGEOS research and development activities. We have an in-depth understanding of the physical processes governing the interactions of solar radiation with atmospheric components, water, vegetation and soil. Associated with high programming skills and up-to-date technologies, we develop innovative methodologies to process ground-based and satellite sensors data and retrieve Earth surface physical properties that can be exploited in a wide range of applications.

Thus, HYGEOS has built a Monte Carlo radiative transfer code that simulates the radiation received by a satellite sensor after the exact and precise propagation of sun light in the atmosphere and ocean. In particular, it accounts for the reflection and transmission by a wind-roughened sea surface, including wave shadowing effects. Developed on graphics card (GPU), this tool called SMART-G is continuously upgraded and is considered like a reference. As such, it is used for feasibility studies of future spatial missions and to verify common assumptions in operational processing chains. HYGEOS also contributed to the creation of a data simulator of METimage and 3MI sensors onboard the future EUMETSAT EPS-SG mission. This tool can mimic with a high accuracy the measured radiances, including multi-angular viewing and polarisation. It is therefore used to generate synthetic dataset exploited in various projects to prototype the retrieval algorithms of, for instance, the cloud properties (3MI Cloud) or the cloud top altitude (METimCTP).

Over water targets, the atmospheric components highly contribute to the radiation received by the satellite sensors in the visible spectrum. Consequently, the accuracy of water properties retrieval depends strongly on the accuracy of the atmospheric correction algorithm. That’s why HYGEOS has developed POLYMER, a precise atmospheric correction algorithm to assess the colour of oceanic, coastal and inland waters. POLYMER’s strength is its ability to recover the water properties of areas affected by the sun glint phenomenon, the very bright reflection in the specular direction, what significantly improves the spatial coverage of resulting products compared to those obtained using other methods. POLYMER can handle data from high (MSI/Sentinel-2), medium (OLCI/Sentinel-3, VIIRS/NPP, MODIS/Aqua, MERIS/ENVISAT) and coarse (SeaWiFS, GOCI) resolution imagers. Then, POLYMER is used in the Copernicus Global Land Service to produce operationally the Lake Water Quality characteristics. Furthermore, POLYMER is used in various ocean colour and water quality projects and is being exploited for 15 years for operational applications by private companies. POLYMER is available for download.

HYGEOS’s expertise in radiative transfer is expanded to solar energy applications. Indeed, the production of solar power plants is significantly impacted by the atmosphere composition. This impact is increased in the giant concentrating solar power plants where the mirror-receiver distance is longer than 1km. In particular, the aerosols generate production losses by diffusing and absorbing the sun radiation along the atmospheric column but also in the slant path between the mirror and the tower receptor. HYGEOS performs accurate simulations of the plant productivity considering the atmospheric conditions, as done in ASoRA project in collaboration with EDF. A doctoral research work, defended in March 2021, studied all the interactions between the solar radiation on one hand, and the atmosphere, the ground surface and any objects on the other hand, to provide the best estimate of the solar resource in a solar tower power plant.

HYGEOS developments benefit from our close links with academic world and research institutes. Such strong collaborations guarantee state-of-the-art scientific methodologies that we regularly present in peer-reviewed publications. HYGEOS is also investing in the training of PhD students.