Sediment transport by boiling seeping water: exploring effects of grainsize and atmospheric conditions

International audienceMany active and recently active surface processes on Mars have been controversially linked to the action of liquid water, yet the sediment transport capacity of water under martian environmental conditions is poorly understood. An understanding of the sediment transport capacity allows the amount of water required for any given landform to be back-calculated from its observed size/volume at the martian surface. Here we present a series of experiments where we explore the effects of grainsize, atmospheric pressure, humidity and temperature on the sediment transport capacity of seeping liquid water under martian conditions

REVISITING APOLLO 17 STATION 6 BOULDERS WITH PHOTOGRAMMETRY, VIRTUAL REALITY AND STEREOSCOPY

International audienceDuring their third Extra-Vehicular Activity, Apollo 17 astronauts had the opportunity to photo-document with their Hasselblad cameras a collection of five large boulder fragments and regolith, lying at the base of a long trail descending from the North Massif [1] (Fig. 1). We recombined these original photographs using photogrammetry techniques to reproduce 3D digital models of the boulders [2]. These digital copies of the boulders can then be reinvestigated using either a web based platform (e.g., Sketchfab), or with a Virtual Reality headset on a dedicated SteamVR scene. Whereas the original images were not native stereo pairs, series of stereoscopic pairs can also easily be numerically recomputed from the 3D model in order to provide immersive views using a more conventional stereoscope system, for outreach purposes

REVISITING APOLLO 17 STATION 6 BOULDERS WITH PHOTOGRAMMETRY, VIRTUAL REALITY AND STEREOSCOPY

International audienceDuring their third Extra-Vehicular Activity, Apollo 17 astronauts had the opportunity to photo-document with their Hasselblad cameras a collection of five large boulder fragments and regolith, lying at the base of a long trail descending from the North Massif [1] (Fig. 1). We recombined these original photographs using photogrammetry techniques to reproduce 3D digital models of the boulders [2]. These digital copies of the boulders can then be reinvestigated using either a web based platform (e.g., Sketchfab), or with a Virtual Reality headset on a dedicated SteamVR scene. Whereas the original images were not native stereo pairs, series of stereoscopic pairs can also easily be numerically recomputed from the 3D model in order to provide immersive views using a more conventional stereoscope system, for outreach purposes

Contribution of automatically generated radar altimetry water levels from unsupervised classification to study hydrological connectivity within Amazon floodplains

Study region: The Curuaí floodplain in the low Amazon river in the Pará state of Brazil and Juruá basin, a major Solimões tributary. Study focus: Characterizing the hydrological dynamics of Amazon floodplains is essential to better understand and preserve these environments providing important resources to local populations. Radar altimetry is an effective remote sensing tool for monitoring water levels of continental hydrosystems, including floodplains. An unsupervised classification approach on radar echoes to determine hydrological regimes has recently been tested and showed a strong potential on the Congo River basin. This method is adapted to Envisat and Saral satellite radar altimetry data on two study areas in the Amazon Basin. The aim is to improve inland water detection along altimeter tracks to automatically generate water level time series (WLTS) over rivers, lakes, and poorly monitored floodplains and wetlands. New hydrological insights: Results show a good agreement with land cover maps obtained with optical imagery over selected Amazonian wetlands (70–80% accuracies with Envisat data and 50–60% with Saral data). Automatically generated WLTS are strongly correlated to the manually generated WLTS (R² ≈ 0.9; RMSE < 1 m). Compared to the manual method, the automatic method is faster, more efficient and replicable. Densifying the WL network in the floodplains bring crucial information on the connectivity dynamic between lakes and rivers

EVOLUTION OF THE LAKES NETWORK OF CURUAI FLOODPLAIN BY CLASSIFICATION OF RADAR ALTIMETRY ECHOES

International audienc

EVOLUTION OF THE LAKES NETWORK OF CURUAI FLOODPLAIN BY CLASSIFICATION OF RADAR ALTIMETRY ECHOES

International audienc

Investigating Lunar Boulders at the Apollo 17 Landing Site Using Photogrammetry and Virtual Reality

International audienceThe Taurus-Littrow valley on the Moon was the location of intensive geologic fieldwork during three days in December 1972. In situ activities at sampling stations were systematically documented by the astronauts using a series of overlapping images taken with their Hasselblad cameras. We investigated how this Apollo image archive can be used to perform 3-D reconstructions of several boulders of interest using close-range photogrammetry. We specifically focused on seven different boulders located at Stations 2, 6, and 7, at the foot of South and North Massifs, respectively. These boulders represent samples from highland materials, which rolled down the slopes of the surrounding hills. We used the Agisoft Metashape software to compute 3-D reconstructions of these boulders, using 173 scanned images as input. We then used either a web-based platform or a game engine to render the models in virtual reality. This allowed the users to walk around the boulders and to investigate in detail their morphology, fractures, vesicles, color variations, and sampling spots, as if standing directly in front of them with the astronauts. This work suggests that many features can be reconstructed in other sites of the Apollo missions, so as other robotic landing sites. Virtual reality techniques coupled to photogrammetry is thus opening a new era of exploration, both for past and future landing sites

Amazonian floodplains modeling sensitivity to grid size and diffuse runoff

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FLOOD EXTENT AND VOLUME CHANGES ANALYSIS IN CURUAI FLOODPLAIN USING REMOTE SENSING

International audienceThe Amazon is the world's largest watershed and affects the South American and global climate. This region has seen an increase in the recurrence of extreme hydrological events (droughts and floods) in the recent decades. Located near Santarém and Óbidos, where records of maximum level were recently recorded, the Curuai floodplain is about 4,000 km² and is the subject of several studies. Remote sensing is the most appropriate tool for the study of this area due to its complexity and the reduced number of in situ measurement stations. The aim of this study was to estimate the flooded extent and volume from Sentinel-1 radar images for two hydrological years (2020-2021 and 2021-2022). For this purpose, an approach based on the classification by the multi-thresholds Otsu method was implemented. The results show that the flood extent varies from 31.58% to 54.85% of the study area and the variation of flooded volume is 19.69 km³. They also show that a larger area is flooded 100% of the time in the hydrological year 2021-2022 than in 2020-2021. The comparison with the literature reinforces facts such as the permanent presence of channels in the southeast and questions the classification by the multi-thresholds Otsu method. The limitations of this methodology open up perspectives for further study with regard to the comparison of several classification methods and the use of altimetry data for the calculation of the depth and, consequently, the flooded volume

INUNDATION PROJECTED UNDER CLIMATE CHANGE WITHIN THE CURUAI FLOODPLAIN

International audienceAccess to water and aquatic ecosystems preservation are among the most important challenges of the 21 st century. Hydrodynamic and aquatic ecosystems are dependent on water fluxes in the river and in the floodplains. However, due to their difficult access, these fluxes are poorly understood and a limited amount of data is available to study them. Predictions of flows in rivers and floodplains help to develop sustainable management of water resources and aquatic ecosystems, especially in the Curuai floodplain, at local and global scales. Different climate change scenarios in the Amazon can be used to analyse the hydrodynamic flow response in the floodplain. The MGB software allows access to daily flow data in main rivers of Amazon. The initial simulations are made on 20-year runs from the year 2021 to get the general trend of the discharge evolution in rivers. Three of the twenty-eight possible climate models will be used for the discharge scenarios implementation to conduct a significant effect study of the best (95%), intermediate (50%) and worst (5%) climate model. From the general trend obtained with these three climate models, we will choose three years of interest to study the hydrodynamic effects. Three consecutive 2-year simulations for each of the three climate models will give access to river discharge scenarios. Then, the HEC-RAS software will be used to refine the hydrological inputs in the Curuai floodplain by distributing diffuse discharge in the catchments. With a fine resolution, a local prediction of the hydrodynamic movements can be made