The Kufrah paleodrainage system in Libya: A past connection to the Mediterranean Sea?

International audiencePaillou et al. (2009) mapped a 900 km-long paleodrainage system in eastern Libya, the Kufrah River, that could have linked the southern Kufrah Basin to the Mediterranean coast through the Sirt Basin, possibly as long ago as the Middle Miocene. We study here the potential connection between the terminal part of the Kufrah River and the Mediterranean Sea through the Wadi Sahabi paleochannel, which may have constituted the northern extension of the lower Kufrah River paleodrainage system. New analysis of SRTM-derived topography combined with Synthetic Aperture Radar images from the Japanese PALSAR orbital sensor allowed the mapping of seven main paleochannels located west of the Kufrah River, each of which is likely to have formed a tributary that supplied water and sediment to the main paleodrainage system. The northernmost four paleochannels probably originated from the Al Haruj relief, a Pliocene alkaline basaltic intracontinental volcanic field, and potentially connected to the Wadi Sahabi paleochannel. The remaining three paleochannels are in the more southerly location of the Sarir Calanscio, North-East of the Tibesti mountains, and barely present a topographic signature in SRTM data. They end in the dunes of the Calanscio Sand Sea, forming alluvial fans. The most southern paleochannel, known as Wadi Behar Belama, was previously mapped by Pachur (1996) using LANDSAT-TM images, and was interpreted by Osborne et al. (2008) as representing part of an uninterrupted sediment pathway from the Tibesti mountains to the Mediterranean Sea. Processing of SRTM topographic data revealed local depressions which allow to connect the seven paleochannels and possibly the terminal alluvial fan of the Kufrah River to the Wadi Sahabi paleochannel, through a 400 km-long, south-north oriented, paleocorridor. These new findings support our previous hypothesis that proposed a connection between the lower Kufrah River in the region of the Sarir Dalmah and the Wadi Sahabi paleochannel, which connected to the Mediterranean Sea. Including the newly mapped paleochannels, the Kufrah River paleowatershed, at its maximum extent, would have covered more than 400,000 km2, representing close to a quarter of the surface area of Libya

Etude Des Signaux Recueillis Par Un Radar Embarque Sur Un Vehicule En Deplacement. Application a L'Interpretation Des Signaux Recoltes Par Le Radar Wisdom De la Mission Spatiale Exomars

The ExoMars mission of the program Aurora (ESA) aims to send a vehicle (Rover) on Mars in 2013. Beyond the technological aspects of the mission, the Rover will also carry scientific instruments for the analysis of Mars subsurface to search traces of past or present life in the Martian soil. The Rover will embark a drilling machine which will give access to samples of sub-surface of Mars to 2 meters depth. This constitutes the great originality of ExoMars, because the Mars sub-surface remains still unknown and seems to be the best place to shelter good conditions to create life. This drilling machine will be guided by a radar system sounder UHF, the WISDOM instrument, which will also make possible to probe the Mars sub-surface to a few meters of depth to detect water and to study the geological structures. We have analytical and numerical electromagnetic models to simulate the behavior of an electromagnetic wave in the Mars sub-surface, but also to simulate the interactions between the wave and the structure of the Rover. The objective of the work which we present consists in the study of the factors able to create disturbances of measurements in order to correct the effects on the measured signal. Initially we present the solution which we retained in order to be able during the same calculation to simulate the displacement of the Rover on several tens of meters. We also present the results relating to the effect of the orientation of the antenna during displacement due to topography of the observation site

An Extended Field of Crater Structures in Egypt: Observations and Hypotheses

We detected more than 1000 crater structures in the Western Egyptian Desert, distributed over 40000 km2, among which 62 were studied on the field. Two hypotheses are proposed for their origin: hydrothermal vent complexes or impact craters generated by a rubble-pile asteroid

EFFECT OF SALINITY ON THE DIELECTRIC PROPERTIES OF GEOLOGICAL MATERIALS : IMPLICATION FOR SOIL MOISTURE DETECTION BY MEANS OF REMOTE SENSING

International audienceThis paper deals with the exploitation of dielectric properties of saline deposits for the detection and mapping of moisture in arid regions on both Earth and Mars. We then present a simulation and experimental study in order to assess the effect of salinity on the permittivity of geological materials and therefore on the radar backscattering coefficient in the [1-7GHz] frequency range. Dielectric mixing models were first calibrated by means of experimental measurements before being used as input parameters of analytical scattering models (IEM, SPM). Simulation results will finally be compared to field measurements (Pyla dune, Death Valley, Mojave Desert) and will be used for the interpretation of SAR data (AIRSAR, PALSAR)

Cassini VIMS and Altimeter Joint Study of Titan Surface

The joint NASA-ESA-ASI Cassini- Huygens mission reached the saturnian system on July 1st 2004. It started the observations of Saturn's environment including its atmosphere, rings, and satellites (Phoebe, Iapetus and Titan). Titan, one of the primary scientific interests of the mission, is veiled by an ubiquitous thick haze [1]. Its surface is unreachable to ultraviolet and visible wavelengths, but can be seen in some infrared atmospheric windows and for greater wavelengths, in the case of an unclouded low atmosphere [2,3]. Onboard the Cassini spacecraft, the VIMS (Visual and Infrared Mapping Spectrometer) instrument has already proved to be able to successfully pierce the veil of the hazy moon and image its surface in the infrared wavelengths, taking hyperspectral images in the range 0.4 to 5.2 ?m. Since July 2004, VIMS acquired image cubes with spatial resolution ranging from a few tens of kilometers down to less than one kilometer per pixel, demonstrating its capability for mapping more than 70% of Titan's surface and studying its composition and geology [4,5,6,7,8,9,10,11]. Also in the Cassini orbiter payload is the Ku-band RADAR experiment that can operate in altimeter mode. Exclusively dedicated to Titan's observations, this second active mode has been designed primarily to retrieve Titan's surface elevation and study its topography. We present here the comparative analysis of the altimeter track recorded during the first Titan flyby (26 October 2004, tagged TA) and VIMS images over the same regions acquired during the 13th flyby (30 April 2006). In particular, we present here the first nontopographic analysis of Cassini altimeter data along with a tentative correlation with VIMS observations

Cassini VIMS and Altimeter Joint Study of Titan Surface

The joint NASA-ESA-ASI Cassini- Huygens mission reached the saturnian system on July 1st 2004. It started the observations of Saturn's environment including its atmosphere, rings, and satellites (Phoebe, Iapetus and Titan). Titan, one of the primary scientific interests of the mission, is veiled by an ubiquitous thick haze [1]. Its surface is unreachable to ultraviolet and visible wavelengths, but can be seen in some infrared atmospheric windows and for greater wavelengths, in the case of an unclouded low atmosphere [2,3]. Onboard the Cassini spacecraft, the VIMS (Visual and Infrared Mapping Spectrometer) instrument has already proved to be able to successfully pierce the veil of the hazy moon and image its surface in the infrared wavelengths, taking hyperspectral images in the range 0.4 to 5.2 ?m. Since July 2004, VIMS acquired image cubes with spatial resolution ranging from a few tens of kilometers down to less than one kilometer per pixel, demonstrating its capability for mapping more than 70% of Titan's surface and studying its composition and geology [4,5,6,7,8,9,10,11]. Also in the Cassini orbiter payload is the Ku-band RADAR experiment that can operate in altimeter mode. Exclusively dedicated to Titan's observations, this second active mode has been designed primarily to retrieve Titan's surface elevation and study its topography. We present here the comparative analysis of the altimeter track recorded during the first Titan flyby (26 October 2004, tagged TA) and VIMS images over the same regions acquired during the 13th flyby (30 April 2006). In particular, we present here the first nontopographic analysis of Cassini altimeter data along with a tentative correlation with VIMS observations

The Earthlike Shoreline Morphology of Titan's Ontario Lacus

Ontario Lacus' shoreline features include Earth-like rivers, deltas and flooded topography. Ontario is a dynamic lake, similar in many ways to terrestrial lakes, with active shoreline processes

The European Space Agency BIOMASS mission: Measuring forest above-ground biomass from space

The primary objective of the European Space Agency's 7th Earth Explorer mission, BIOMASS, is to determine the worldwide distribution of forest above-ground biomass (AGB) in order to reduce the major uncertainties in calculations of carbon stocks and fluxes associated with the terrestrial biosphere, including carbon fluxes associated with Land Use Change, forest degradation and forest regrowth. To meet this objective it will carry, for the first time in space, a fully polarimetric P-band synthetic aperture radar (SAR). Three main products will be provided: global maps of both AGB and forest height, with a spatial resolution of 200 m, and maps of severe forest disturbance at 50 m resolution (where “global” is to be understood as subject to Space Object tracking radar restrictions). After launch in 2022, there will be a 3-month commissioning phase, followed by a 14-month phase during which there will be global coverage by SAR tomography. In the succeeding interferometric phase, global polarimetric interferometry Pol-InSAR coverage will be achieved every 7 months up to the end of the 5-year mission. Both Pol-InSAR and TomoSAR will be used to eliminate scattering from the ground (both direct and double bounce backscatter) in forests. In dense tropical forests AGB can then be estimated from the remaining volume scattering using non-linear inversion of a backscattering model. Airborne campaigns in the tropics also indicate that AGB is highly correlated with the backscatter from around 30 m above the ground, as measured by tomography. In contrast, double bounce scattering appears to carry important information about the AGB of boreal forests, so ground cancellation may not be appropriate and the best approach for such forests remains to be finalized. Several methods to exploit these new data in carbon cycle calculations have already been demonstrated. In addition, major mutual gains will be made by combining BIOMASS data with data from other missions that will measure forest biomass, structure, height and change, including the NASA Global Ecosystem Dynamics Investigation lidar deployed on the International Space Station after its launch in December 2018, and the NASA-ISRO NISAR L- and S-band SAR, due for launch in 2022. More generally, space-based measurements of biomass are a core component of a carbon cycle observation and modelling strategy developed by the Group on Earth Observations. Secondary objectives of the mission include imaging of sub-surface geological structures in arid environments, generation of a true Digital Terrain Model without biases caused by forest cover, and measurement of glacier and icesheet velocities. In addition, the operations needed for ionospheric correction of the data will allow very sensitive estimates of ionospheric Total Electron Content and its changes along the dawn-dusk orbit of the mission

Titan's diverse landscapes as evidenced by Cassini RADAR's third and fourth looks at Titan

International audienceCassini's third and fourth radar flybys, T7 and T8, covered diverse terrains in the high southern and equatorial latitudes, respectively. The T7 synthetic aperture radar (SAR) swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high, dissected, and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids. The T8 swath is dominated by dunes likely made of organic solids, but also contain somewhat enigmatic, probably tectonic, features that may be partly buried or degraded by erosion or relaxation in a thin crust. The dark areas in T7 show no dune morphology, unlike the dark areas in T8, but are radiometrically warm like the dunes. The Huygens landing site lies on the edge of the T8 swath; correlation of the radar and Huygens DISR images allows accurate determination of its coordinates, and indicates that to the north of the landing site sit two large longitudinal dunes. Indeed, had the Huygens probe trajectory been just 10 km north of where it actually was, images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen?illustrating the strong diversity of Titan's landscapes even at local scales