The surfaces of terrestrial planet and small bodies of the Solar System are interfaces between endogenous (e.g., internal heat flux) and exogenous (e.g., space weathering) processes. Understanding how they form and evolve over time is essential for a better assessment of planetary body formation and evolution. Interestingly, they are mostly composed of granular materials (e.g., regolith, sand, dust) that are subject to different kinds of transport processes, triggered by interior dynamics or fluid envelops. Mass wasting is therefore a main process modeling the surface. Granular on the surface material may organize in bedforms (e.g., dunes, yardangs, deltas) revealing interactions with liquids and air, when an atmosphere is present. The roughness of planetary surfaces from microscopic to topographic scales is a key parameter in meteorology, hydrology, volcanology and geomorphology. Studying these processes in different environmental contexts, both on Earth, terrestrial planets and their moons, is fundamental to better understand the mechanisms of physical and chemical erosion, or sediment transport. Experiments and observations performed on Earth can be used to validate observations made on planets, most often only remotely sensed.
The next missions of solar system exploration in which we are particularly involved (Bepi-Colombo, JUICE) will show up in 2024 at the earliest. We are also involved in the proposed Earth Hyperspectral Explorer-Hypex2 mission project. Meanwhile, we aim at continuing interpretation of VIMS, RADAR and CIRS-Cassini data on rings and satellites, as well as public data of imagery and spectro-imagery (for which we developed expertise these four last years) on Mars, developing new skills in multimodal data analysis and concurring multi-physics modelling on wealthy public database of terrestrial and planetary surfaces, insuring continuous survey of our targets with alternative telescope facilities, in particular the JWST, in order to pursue the science objectives listed below:
Soil surface water content and roughness are essential parameters of soil surface. In a context of climate change, surface state is a relevant criterion of soil classification based on their water regime and their evolution to drought, desertification, and water and wind erosion. In hydrology, surface water content and roughness control the runoff process of infiltration and water storage in general. They are also key parameters of energy balance: surface temperature and thus evapotranspiration depend on surface soil moisture; roughness limits wind erosion by reducing the wind speed on the ground; it influences the distribution of incident radiation, and therefore, the temperature and humidity of soils. In defense or homeland security, trafficability that partly results from the identification of wetlands and/or soil roughness can be critical to the success of a military or humanitarian operation. Last, but not least, the estimation of these two variables on planetary surfaces allows us to better understand space weathering, erosion and mass transport.
This research project aims to model soil spectral and directional reflectance as a function of water content and surface roughness. This is a long process that will require setting up field and lab experiments to validate it. It began in October 2014 with the PhD thesis of Sébastien Labarre (co-funded by CEA and DGA) on "Characterization and modeling of multi-scale roughness of natural surfaces in the optical domain" and with the CAROLInA (Characterization of multi-scAle Roughness using OpticaL ImAgery) research project funded by CNES. It continues with the PhD thesis of Aurélien Bablet (co-funded by IPGP and ONERA) which started in October 2015 on "Modeling the spectral and directional reflectance of bare soils as a function of their water content and surface roughness" and with the SOILSPECT research project funded by the Programme National de Télédétection Spatiale (PNTS).
Solar System exploration unveiled the ubiquity of mass wasting. The project aims at combining data analysis with model simulation at various scales and wavelengths, thereby allowing a quantitative assessment of the geomorphology across a wide range of planetary environments. It will help to inform geomechanical models applied to mass wasting in surface and sub-surface properties, as well as various triggering and feedback mechanisms operating throughout the Solar System. Ultimately, this project will provide new understanding on how planetary surfaces form and evolve over time, from small bodies to icy moons and planets.
period. Indeed, weathering processes regulate the chemical composition of the upper continental crust, and at geological time scale weathering also regulates the CO2 concentration in the atmosphere via weathering‐climate feedback. Particularly, the research conducted during this task focus on processes such as the relationships between climatic events, large scale landslides and torrential transport of sediment by the river in Tropical Islands. Additionally, understanding such processes could also help to prevent related natural hazards. Assessing sediment transport requires the quantification of the sediment volumes involved. This can be done by analysing the evolution of the topography at different periods.
To do so, we develop an automatic photogrammetric workflow allowing to derive digiral topography models (DTM) out of historical aerial photographs. Thereby we can observe the evolution of the river bed and get information about the dynamics of the sediment transfer from the production areas (steep slopes) to the ocean. The tool has been tested with aerial images over the Rempart river (Reunion Island) ranging between 1978 and 2003.