La convection des fluides dans le sol de Mars et les échanges induits avec l'atmosphère et la paléo-hydrosphère de la planète

Mars est un objet privilégié pour comprendre l'évolution d'une planète. Des témoins géologiques de son activité interne et des échanges surface-atmosphère sont préservés sur 4 Ga. Cette thèse étudie ces échanges au travers de la circulation des fluides dans la croûte. Le climat froid et sec de l'Amazonien (< 3 Ga) implique la condensation, sublimation et diffusion des espèces volatiles dans le régolithe. Ce paradigme est modifié par la découverte de l'importance de la convection d'air dans les sols poreux (aérothermalisme). Ce processus a été mis en évidence par l'imagerie thermique (Mars Odyssey/THEMIS) et la morphologie (e.g., Mars Express/HRSC) pour Cerberus Fossae et le volcan Arsia Mons. La période Hespérienne est marquée par la libération massive d'eau aboutissant à la formation des terrains chaotiques et des chenaux de débâcle. Nous proposons que ces objets résultent de la convection d'argiles. Cette hypothèse originale est corroborée par les détections de phyllosilicates (données CRISM et OMEGA).Mars' geological record, with objects reflecting its internal activity and surface-atmosphere exchanges, extends for more than 4 Ga. It offers a unique situation for understanding planetary evolution. The topic of this thesis is the circulation of fluids in the crust, making part of these exchanges. First, the paradigm that condensation, sublimation and diffusion of volatiles within the regolith dominate the cold and dry Amazonian era (<3 Ga) is modified by the finding of the importance of air convection in porous soils (aerothermalism). This process was revealed from thermal imagery (Mars Odyssey/THEMIS) and morphology (e.g., Mars Express/HRSC) for Cerberus Fossae, and Arsia volcano. Second, the Hesperian era is characterised by the formation of chaotic terrains and outflow channels carved by massive release of water. In our views, the chaotic terrains may be formed by convection of clay deposits. This original hypothesis is supported by associated detections of phyllosilicates (CRISM and OMEGA data)

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)

International audienceOntario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and Radar in 2009 and 2010). In this study, we take advantage of each imaging dataset to establish a global survey of Ontario Lacus' environment from 2005 to 2010. We perform a geomorphological mapping and interpretation of Ontario Lacus, mainly based on a joint analysis of VIMS and Radar SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which closely resembles Titan's lakes: the pans of the Etosha Basin, located in Namibia. From this comparison, we infer that Ontario Lacus is an extremely flat depression where liquids, only located in the darkest areas in the Radar data, cover topographic lows where the "alkanofer" would raise above the depression floor. The rest of the depression appears rather as a muddy flat surface likely composed of a thick coating of photon-absorbing materials, explaining its still rather dark appearance in the infrared and radar data. We also determined whether surface changes occurred during the 5 years time interval between 2005 and 2010. We found that the depression contour is constant at the resolution of ISS and VIMS data, both being consistent with the depression contour derived from the Radar data. Our interpretation, in which the liquids are located only in some parts of Ontario Lacus, agrees with the lack of significant change of the depression contour between 2007 (and 2005 with more uncertainties) and 2010

Télédétection dans l'infrarouge thermique

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La convection des fluides dans le sol de Mars et les échanges induits avec l'atmosphère et la paléo-hydrosphère de la planète

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Thermal infrared observation of pre-seismic vertical permeabilitychanges. The Boumerdes-Zemmouri (M = 6.8) case

International audienceSince nearly 20 years, huge transient thermal warm anomalies have been observed in different regions worldwide. The main peculiarity of these thermal anomalies is their close relationship with the occurrence of earthquakes of magnitude > 5. Most of the thermal anomalies appear tens of days before the earthquake and reach a maximum positive value of 10 K few hours before the main shock. They are located at hundreds kilometres from the epicentres and can cover areas of 10,000 km2. Some hypotheses have already been proposed to explain these thermal anomalies, e.g., variation of the groundwater level, release of greenhouse gases creating a localised greenhouse effect or air ionisation. This study focuses on the Boumerdes-Zemmouri earthquake (M = 6.8) that hit Algeria in 2003. This earthquake was preceded by a thermal anomaly observed by AVHRR (Advanced Very High Resolution Radiometer; 1 km/pixel) thermal sensor on the NOAA-15 satellite. This region is very adapted to a preliminary study as 1) the tectonic is less complex than in other regions, 2) the semi-arid environment allows high temporal coverage as cloud cover is not significant, and 3) vegetation is excessively sparse. The objective of this study is to interpret this excess temperature and to improve our understanding of the processes behind their development. The thermal anomaly was located in a sedimentary basin 400 km south from the epicentre and covered a maximal surface of 41,000 km2. It appeared ten days before the earthquake and reached a maximum temperature anomaly of +7 °C a few hours before the main shock. The results obtained from a combination of MODIS thermal infrared data with climate reanalyses from ECMWF (European Center for Medium Range Weather Forecasts) demonstrated first that this thermal anomaly cannot be explained by meteorological variations, neither by changes in the physico-chemical properties of the surface. We suggest that this earthquake-related thermal anomaly in Algeria can be explained by subsurface alterations induced by the pre-seismic stresses (Lopez et al, in preparation). Publications have shown that pre-seismic stresses may change the groundwater circulation and/or its physico-chemical properties. Development of thermal anomalies prior to an earthquake suggests that pre-seismic stresses change the vertical permeability of the system and thus have an influence on the groundwater circulation. This leads to a short-term increase of the aquifers and the atmosphere connexion. Indeed, the southern limit of the thermal anomaly seems to be controlled by the extension of aquifer artesianism (Lopez et al, submitted). Moreover, the transfer of elastic stresses might explained the distance observed between the thermal anomaly and the epicentre. The original combination of thermal infrared images with other EO dataset and geophysical data may lead to a new vision of a subject so far very little studied. In that context, the thermal infrared sensor might play a future key role in understanding the development and transfer of pre-seismic loading or unloading stresses in (semi)-arid regions

Influence of the surface permeability on the GRACE water mass variations. Case of the Lake Chad basin.

International audienceSince its launch in 2002, the Gravity Recovery And Climate Experiment (GRACE) has been measured the tiny variations of the gravity field due to redistributions of water mass in the surface envelops of Earth. At a spatial resolution of 400 km, these satellite data offer a unique perspective to understand the evolution of continental water storage at regional and global scales, and therefore they enable the monitoring of the hydrological systems such as river basins. It is well known that seasonal cycle, droughts, vegetation and human extractions are the main contributors of the hydrology signals sensed by GRACE. However, the coupling between land surface and the atmosphere is important in semi-arid and arid regions, in particular in West Africa [1]. We propose to quantify the surface water fluxes in the Lake Chad region by using the 10-day water mass solutions of the GRACE mission in the context of the regular West African monsoon. Alternation of the evaporation/condensation cycles during the recent period are interpreted in terms of surface vertical permeability changes that control the thermal evolution in this region [2]. GRACE solutions reveal an interannual increase of surface water mass at the beginning of the dry seasons, especially between 2005 and 2008. We propose that this gain of surface water mass is caused by a seasonal cycle of clay fracturing that controls the evaporation/condensation cycle. [1] Koster et al. (2004). Science, 305, 1138-1140. [2] Lopez et al. (2016). Surv. Geophys., 37 (2), 471-502

Analysis of the space-based surface temperature distribution in Badain Jaran Desert

EGU&apos;20, European Geosciences Union, Vienne, AUTRICHE, 04-/05/2020 - 08/05/202

On the Use of Satellite Remote Sensing to Detect Floods and Droughts at Large Scales

International audienceHydrological extremes, in particular floods and droughts, impact all regions across planet Earth. They are mainly controlled by the temporal evolution of key hydrological variables like precipitation, evaporation, soil moisture, groundwater storage, surface water storage and discharge. Precise knowledge of the spatial and temporal evolution of these variables at the scale of river basins is essential to better understand and forecast floods and droughts. In this article, we present recent advances on the capability of Earth observation (EO) satellites to provide global monitoring of floods and droughts. The local scale monitoring of these events which is traditionally done using high-resolution optical or SAR (synthetic aperture radar) EO and in situ data will not be addressed. We discuss the applications of moderate- to low-spatial-resolution space-based observations, e.g., satellite gravimetry (GRACE and GRACE-FO), passive microwaves (i.e. SMOS) and satellite altimetry (i.e. the JASON series and the Copernicus Sentinel missions), with supporting examples. We examine the benefits and drawbacks of integrating these EO datasets to better monitor and understand the processes at work and eventually to help in early warning and management of flood and drought events. Their main advantage is their large monitoring scale that provides a "big picture" or synoptic view of the event that cannot be achieved with often sparse in situ measurements. Finally, we present upcoming and future EO missions related to this topic including the SWOT mission

Formation of Titan's Lakes by Episodic Dissolution and Precipitation of a Surface Layer Under Semi-Arid Conditions: Comparison with the Pans and Calcretes of Etosha (Namibia)

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Formation of Titan's lakes by episodic dissolution and precipiation of a surface layer under semi-arid conditions : comparison with the Pans and calcrete of Etosha (Namibia)

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