bluuebunny/crossref_metadata_2025 huggingface dataset:
The finite element method for solving the oblique derivative boundary value problems in geodesy
Authors: Macák Marek , Minarechová Zuzana , Čunderlík Róbert , Mikula Karol
Published: March 2020

We present a novel approach to the solution of the geodetic boundary value problem with an oblique derivative boundary condition by the finite element method. Namely, we propose and analyse a finite element approximation of a Laplace equation holding on a domain with an oblique derivative boundary condition given on a part of its boundary. The oblique vector in the boundary condition is split into one normal and two tangential components and derivatives in tangential directions are approximated as in the finite difference method. Then we apply the proposed numerical scheme to local gravity field modelling. For our two-dimensional testing numerical experiments, we use four nodes bilinear quadrilateral elements and for a three-dimensional problem, we use hexahedral elements with eight nodes. Practical numerical experiments are located in area of Slovakia that is given by grid points located on the Earth's surface with uniform spacing in horizontal directions. Heights of grid points are interpolated from the SRTM30PLUS topography model. An upper boundary is in the height of 240 km above a reference ellipsoid WGS84 corresponding to an average altitude of the GOCE satellite orbits. Obtained solutions are compared to DVRM05.
Differential geometry and curvatures of equipotential surfaces in the realization of the World Height System
Authors: Holota Petr , Nesvadba Otakar
Published: March 2020

The notion of an equipotential surface of the Earth’s gravity potential is of key importance for vertical datum definition. The aim of this contribution is to focus on differential geometry properties of equipotential surfaces and their relation to parameters of Earth’s gravity field models. The discussion mainly rests on the use of Weingarten’s theorem that has an important role in the theory of surfaces and in parallel an essential tie to Brun’s equation (for gravity gradient) well known in physical geodesy. Also Christoffel’s theorem and its use will be mentioned. These considerations are of constructive nature and their content will be demonstrated for high degree and order gravity field models. The results will be interpreted globally and also in merging segments expressing regional and local features of the gravity field of the Earth. They may contribute to the knowledge important for the realization of the World Height System.
Statistical Emulators for Regional Climate Models: Preliminary results
Authors: Doury Antoine , Somot Samuel , Gadat Sébastien , Ribes Aurélien , Corre Lola
Published: March 2020

Statistical Emulators for Regional Climate Models: Preliminary results

Predicting some robust information on climate at some local geographical scale is of primary importance to assess the impact of the future climate change. But even more important is to quantify the whole range of uncertainties around the evolution of the climate that translates (i) the imperfections of the climate models, (ii) the natural variability variability and (iii) the uncertainties about the future human emissions of greenhouse gases. One of the nowadays tools used to produce future simulations at the local scale is the Regional Climate Models (RCM): they correspond to high resolution climate models used to downscale over a specific region the information simulated by a Global Climate Model (GCM) scenario simulation.

To cover the full range of uncertainties one should ideally force each RCM with every GCM under different emission scenarios and make several members. It comes down to filling up a huge 4D-matrix [Scenario, GCM, RCM, members]. However regarding the increasing number of climate models (regional and global) and the increasing cost of the RCMs due to their increased complexity and resolution, filling up such matrix becomes unrealistic.

To address this issue we propose a novel approach to merge statistical and dynamical downscaling techniques. The principle relies on three phases. Firstly, some RCM simulations are performed using the classical dynamical downscaling approach. Then, following the statistical downscaling principle, a statistical model is trained to learn the relationship between the large scale information given by the GCM and the local one produced by the RCM, using the runs previously performed. We call this statistical model an emulator. Finally this emulator allows to downscale more GCMs simulation, at a very reasonable cost in order to get a robust ensemble.

In this preliminary work we focus on emulating the surface temperature at the daily scale by testing different machine learning methods (RandomForest, Boosting, Neural Network) sometimes coupled with an a-priori signal decomposition. We train and test the emulator with simulations from the ALADIN RCM forced by the CNRM-CM5 GCM over the period 1950-2100. The different methods are discriminated over hidden simulations using skill scores measuring the match between the emulated series and the pseudo-reality RCM series. Day-to-day scores such as correlation or RMSE are used as well as statistical scores to control on the distribution of the predicted series.
Development of a novel method for Nitrogen Dioxide vertical profile retrieval
Authors: Hong Hyunkee , Park Junsung , Lee Hanlim
Published: March 2020

Abstract Text
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We developed an algorithm, for the first time, to retrieve nitrogen dioxide (NO2) vertical profile (surface NO2 volume mixing ratio) using multi NO2 slant column densities (SCDs) at ultra-violet (UV) and visible (VIS) channels since the sensitivity of nadir measurements decreases due to absorption of the gas near the surface and with decreasing wavelength. Firstly, to create a look-up table, synthetic radiances were calculated from the vector discrete ordinate radiative transfer (VLIDORT) model in the UV and VIS range using various parameters such as aerosol properties (e.g., aerosol optical depth, single scattering albedo, and aerosol loading height), geometry information (e.g., solar zenith angle, viewing zenith angle, and relative azimuth angle), NO2 vertical profile, and surface reflectance. Secondly, spectral fitting was performed at an interval of 1 nm from the center wavelength of 350 nm to 380 nm with a fitting window of about 30 nm to calculate the ratio of average NO2 SCDs in the VIS range to those in UV range. To validate the NO2 vertical profile retrieval algorithm, synthetic radiances were calculated based on NO2 vertical profiles with random values. NO2 vertical profiles are assumed to have exponential distribution and are generated with random NO2 upper limits with a range of 0 to 3 km, random total NO2 VCDs with a range of 1 to 5 × 1016 molecules cm-2, and a random relaxation parameter of exponential distribution with a range of 0.5 to 1.5. The results showed that the NO2 upper limit was 0.3 km or lower and the surface NO2 volume mixing ratio was estimated within 15% error. In addition, we also retrieved tropospheric NO2 vertical profiles using OMI LV1B radiance data.

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Degree of size reduction of selected crushed-stone source rocks and its relationship to technological-mechanical performance parameters
Authors: Krutilová Kateřina , Přikryl Richard
Published: March 2020

Degree of size reduction of selected crushed-stone source rocks and its relationship to technological-mechanical performance parameters

 

Kateřina Krutilová (1), Richard Přikryl (2)

 

(1) Stone testing laboratory Ltd., Hořice v Podkrkonoší, Czech Republic

(2) Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University in Prague, Albertov 6, 128 43, Prague 2, Czech Republic

 

Particle size reduction (PSR) is one of the principal processing methods employed in extractive industry including production of crushed stone aggregates. The purpose of particle size reduction is production of certain size fractions which are directly applicable for final uses or necessary for further industrial activities. On industrial scale, crushing of rocks for crushed stone production is commonly performed in 2-3 successive steps (stages). The conditions of crushing in these individual steps is selected in order to reach lower reduction ratio, thus facilitating production of particles with favourable geometry. Conditions of crushing are influenced by numerous factors, of which only part was thoroughly investigated. In the recent study, we attempt to correlate knowledge on PSR behaviour of various petrographic types with other technological-mechanical performance parameters (e.g. Los Angeles attrition value, Nordic abrasion test, aggregate crushing value) and/or physical / mechanical properties of aggregate source rocks (specifically volcanic rocks of variable composition, ages, and properties). PSR behaviour obtained by experimental laboratory crushing (one-step process) is reported as degree of size reduction and reduction ratio. 
Geophysical and geomorphological observations of the glacier-covered, subantarctic Mount Michael volcano (Saunders Island), South Sandwich Islands
Authors: Richter Nicole , Leat Philip , Derrien Allan , Wintersteller Paul , Meschede Martin , Walter Thomas R.
Published: March 2020

The nine active volcanoes of the sub-Antarctic South Sandwich Islands are a particularly remote region of active volcanism. Remote sensing methods, including satellite monitoring and aerial surveys, besides rare ship visits during austral summers, are the only means of investigating the uninhabited and largely ice-covered volcanoes. Mount Michael volcano on Saunders Island hosts a permanent active lava lake within its summit crater, a sure indicator of the existence of a shallow magmatic storage and transport system of unknown architecture and depth. Also, more than 75 % of the island’s area is glacier covered, which makes the island an important study site for investigating volcano-glacier interactions in the sub-Antarctic climate zone.

We describe new data for the active Mount Michael volcano on Saunders Island, including marine bathymetric and satellite-derived observational data, UAV-derived topographic data, and infra-red camera observations. This data together provide a much higher resolution understanding of the topography, geomorphology, glacial state and dynamics, as well as status of volcanic activity than has been previously achieved. We present a geomorphological and structural analysis of the outer subaerial and shallower submarine flanks of Saunders Island, estimate glacier volumes, morphologies and motion rates, and relate this to the underlying volcano morphology, structural architecture, and edifice stability. All of this is pioneer work at a remote volcano that can be largely regarded as terra incognita. With this study we highlight the unprecedented detail and the valuable information that can be retrieved from modern generation satellites, such as TerraSAR-X and Sentinel-2, as well as UAV-based photogrammetry in particularly remote and inaccessible locations on Earth.
Tidal bedforms dynamics, Weser River, Germany
Authors: Lefebvre Alice , Herrling Gerald , Zorndt Anna , Krämer Knut , Becker Marius , Winter Christian
Published: March 2020

The distribution, morphology and dynamics of tidal bedforms in the Weser estuary, Germany, between the tidal limit (river-km 0 at the tidal weir in Bremen) and the open North Sea (river-km 111 in the Outer Weser) has been analysed for a five-year period based on monthly bathymetric surveys carried out along the main waterway. For the years 2009 to 2014, bedforms were detected from gridded bathymetry data (2x2 m) and their geometric properties described. In particular, the presence and position of a slip face, here defined as the portion of the lee side steeper than 15°, was traced. This was shown to be a practical criterion for the presence of permanent flow separation and turbulent wake in the lee of bedforms. Here it is used as a simplified indicator of bedform roughness: if a bedform does feature a slip face, it is assumed to be an active roughness element. The results were related to river discharge, water levels, and flow velocities.

Bedforms were present along most of the river channel, apart from a large section between river-km 55 and 75. There, muddy cohesive sediment in the estuarine turbidity maximum zone hindered the formation of bedforms. Along the channel and throughout the years, bedform lengths varied between 20 and 60 m and heights between 0.3 and 1.6 m.

During times of high fluvial discharge, in winter and spring, ebb velocities were stronger than flood velocities. The bedforms then were small, long and ebb-oriented (i.e. the ebb lee side was shorter than the flood lee side) and many bedforms featured an ebb slip face but no flood slip face. This suggests that throughout the survey area, bedforms were active roughness elements during the ebb phase only.

In summer and autumn, when the discharge was low, bedforms in the upper reach (ca. river-km 15 to 30) gradually became flood-oriented and many bedforms there developed a flood slip face, implying that these bedforms were active roughness elements during the flood. Between km 30 and 55, bedforms were predominantly ebb-oriented, and many bedforms had an ebb slip face but only few had a flood slip face, so most bedforms were only active during the ebb phase.

The annual variations of bedform dimensions and shapes reveal an intricate feedback between river and tidal flows, channel morphology, sediment dynamics and bedforms. The results have implications for bedform research, river management and numerical modelling.
The effect of weathering on rock wall erosion and rockfall generation at La Cornalle, Switzerland
Authors: Fei Li , Derron Marc-Henri , Choanji Tiggi , Jaboyedoff Michel , Sun Chunwei
Published: March 2020

The weathering posing a significant influence on the rock wall retreat has been widely recognized. In this paper, multi-methods monitoring is designed to detect the erosion and rockfall activity on a rockslide cliff composed of marl-sandstone (maybe mixed with limestone) in Western Switzerland. The monitoring program includes weekly SfM and monthly LiDAR scanning measurements of rock cliff surface, hourly time-lapse imaging of the rock cliff, manual measurement of rock surface moisture, automated recordings of rock temperature and influencing meteorological factors (air temperature, humidity, wind, and precipitation) collected by a weather station. Sequential 3D Points Clouds acquired by LiDAR and SfM from December 2019 are used to visually identify the location of erosion and rockfall at monthly resolution. According to the rock wall structural analysis, the rock mass consists of a network of discontinuities mainly oriented nearly parallel and perpendicular to the direction of the layers. Some fractures are filled with calcite which might lead to a zone of weakness in the rock mass. During the field survey, we saw some calcite crystals covering on the rock block surface in the deposit area and exposed on rock cliff outcrop. We suppose that some rockfalls are generated along those discontinuities filled with calcite where the chemical reaction is active when there is constant water infiltrating during rainfall season. According to the preliminary panoramic thermal image of the cliff surface shot by DJI Mavic 2 Enterprise on 19 December 2019, some weathered and fresh surface areas show different temperatures in the same rock layers which suggest the thermal imaging monitoring may help us to identify the weathering spatial characteristics. In this study, we try first to reveal the effect of temperature variations (thermal stress) on crack deformation from rock temperature values extracted from thermal images and the deformation measured by the crack meter during 24h in winter and summer. Secondly, we explore the role of freeze-thaw cycle playing in the rock fall initiation and rock face erosion. Thirdly, we make clear the link between surface weathering spatial distribution and location of erosion, rockfalls. This provides a model of weathering and rockfall estimation.
Hylite: a hyperspectral toolbox for open pit mapping
Authors: Thiele Sam , Lorenz Sandra , Kirsch Moritz , Gloaguen Richard
Published: March 2020

Hyperspectral imaging is a powerful tool for mapping mineralogy and lithology in core and outcrops, as many minerals show distinct spectral features in the commonly analysed visible, near, short-wave and long-wave infrared regions of the electromagnetic spectrum. High resolution ground and UAS (unmanned aerial system)-based sensors thus have significant potential as a tool for rapid and non-invasive geological mapping in mining operations, exploration campaigns and scientific research. However, the geometrical complexity of many outcrops (e.g. cliffs, open-pit mines) can result in significant technical challenges when acquiring and processing hyperspectral data. In this contribution we present updates to the previously published MEPHySTo python toolbox for correcting, georeferencing, projecting and analysing geometrically complex hyperspectral scenes. We showcase these methods using datasets covering volcanogenic massive sulphide (VMS) mineralisation exposed within open pit mines in Rio Tinto (Spain), and interpret possible structural and lithological controls on mineralization. Potential applications of hyperspectral mapping for grade control, outcrop mapping and the characterisation of different mineral deposit styles are also discussed.
Understanding the complex east-west relationships in the European geoscience research landscape
Authors: Matenco Liviu
Published: March 2020

We know that national research priorities across the European continent are markedly different in many situations. However, there is little understanding at the level of defining major collaborative research programme and professional associations, where, for instance, EGU has showed for several years an increase in disequilibrium for homogenizing priorities and leadership interest. The variable rate of success in west to east European funding leads to polarization rather than integration of science and research approach in an European landscape that becomes less homogeneous. Such unfortunate trends lead at the extreme to major collaborative disagreement, where the recent delay in setting the EU research budget by objections of Central European countries is a prime example. I examine here the state of the Western European often unconscious bias in research priorities across the continental and what can be done more effectively to avoid scientific nationalism and polarization of interest. A beneficial combination can be achieved only by knowing and understanding the national specificity of each other in both directions, east- and west-wards.
High-resolution numerical modelling of the altimetry-derived gravity disturbances and disturbing gradients
Authors: Čunderlík Róbert , Macák Marek , Kollár Michal , Mikula Karol
Published: March 2020

Recent high-resolution mean sea surface models obtained from satellite altimetry in a combination with the GRACE/GOCE-based global geopotential models provide valuable information for detailed modelling of the altimetry-derived gravity data. Our approach is based on a numerical solution of the altimetry-gravimetry boundary-value problem using the finite volume method (FVM). FVM discretizes the 3D computational domain between an ellipsoidal approximation of the Earth's surface and an upper boundary chosen at a mean altitude of the GOCE satellite orbits. A parallel implementation of the finite volume numerical scheme and large-scale parallel computations on clusters with distributed memory allow to get a high-resolution numerical solution in the whole 3D computational domain. Our numerical experiment presents the altimetry-derived gravity disturbances and disturbing gradients determined with the high-resolution 1 x 1 arc min at two altitude levels; on the reference ellipsoid and at the altitude of 10 km above the ellipsoid. As input data, the Dirichlet boundary conditions over oceans/seas are considered in the form of the disturbing potential. It is obtained from the geopotential evaluated on the DTU18 mean sea surface model from the GO_CONS_GCF_2_TIM_R5 geopotential model and then filtered using the nonlinear diffusion filtering. On the upper boundary, the FVM solution is fixed to the disturbing potential generated from the GO_CONS_GCF_2_DIR_R5 model while exploiting information from the GRACE and GOCE satellite missions.
The Great Thermal Divergence and the slope break of the 660 phase transitions
Authors: Nagel Thorsten , Petersen Kenni Dinesen , Vesterholt Anders
Published: March 2020

About 2.5 Ga ago, two distinct mantle sources for basalts developed: one with a lower mantle potential temperature (MPT) being today relatively depleted and feeding the mid-ocean ridges, and one with a higher MPT being relatively enriched and pluming today's ocean-island-basalt (OIB) volcanism (Condie et al., 2016). Previous to that, basalts record rather uniform MPTs corresponding to today's higher-temperature OIB reservoir. The cooler mantle domain started forming, when the slowly cooling thermally uniform mantle reached a MPT of 1550-1500 °C (Condie, 2018). We attribute this “Great Thermal Divergence” (Condie et al., 2016) to a transition from non-layered to layered mantle convection. For primitive mantle compositions, a 1530-adiabat propagates precisely to the high-temperature slope break of the 660 phase transition at about 1800 °C/23 GPa. Mantle with MPT higher than that does not experience the suppression of convective passage through the lower-upper mantle boundary, which results from the negative slope of the ringwoodite-to-perovskite-plus-periclase transition. We propose that mantle convection prior to 2.5 Ga was capable of stirring the whole mantle. A 660 phase transition with a negative slope formed only 2.5 Ga ago and thus established a thermomechanical boundary layer that allowed the formation of two thermally distinct mantle reservoirs.

Condie, K. et al. (2016): A great thermal divergence in the mantle beginning 2.5 Ga: Geochemical constraints from greenstone basalts and komatiites. Geoscience Frontiers, 7, 543-553.
Statistics on the Performance of Instrument Types and the Significance of HVSR data for Shallow Vs HVSR/DC Joint Inversions - A Result from the Large-N Maupasacq Experiment (Southern France)
Authors: Neukirch Maik , García-Jerez Antonio , Villaseñor Antonio , Stehly Laurent , Boué Pierre , Chevrot Sébastien , Sylvander Matthieu , Díaz Jordi , Ruiz Mario , Luzón Francisco , Collin Magali , Calassou Sylvain , Polychronopoulou Katerina , Martakis Nikos , Bitri Adnand
Published: March 2020

Horizontal-to-Vertical Spectral Ratios (HVSR) and Rayleigh group velocity dispersion curves (DC) can be used to estimate the shallow S-wave velocity (Vs) structure. Knowing the shallow Vs structure is important for geophysical data interpretation either in order to better constrain data inversions for P-wave velocity (Vp) structures such as travel time tomography or full waveform inversions, or to directly study the Vs structure for geo-engineering purposes (e.g. ground motion prediction). The purpose of this study is to appraise in particular how much information HVSR can add in a large N experiment and how different instrumentation types affect this. 

During the Maupasacq large-scale experiment, 197 three-component short-period stations, 190 geophone nodes and 54 broadband seismometers were continuously operated in Southern France for 6 months (April to October 2017) covering an area of approximately 1500 km2 with a site spacing of approximately 1 to 3 km. On the obtained HVSR and DC data, a statistical Joint inversion is performed for the shallow Vs structure. The results indicate that the addition of HVSR data to the DC inversion reduces the variance of the recovered shallow Vs model and improves the convergence to a smaller data misfit. While broadband and short period instruments delivered similar results, geophone nodes performed significantly worse due to their much higher cut off frequency. 
Understanding settlement-landscape interaction with literary records and geoinformatics: The case of Homer’s Late Bronze Age Southeast Aegean
Authors: Votsis Athanasios , Babushkina Dina
Published: March 2020

Advances in Digital Humanities are providing increasingly rich research material for understanding (1) the environmental and locational attributes of ancient settlements and (2) the regional structure of systems of settlements. Non-material records, in particular, provide information about the social and cultural drivers of human-landscape interaction in settlements that, when combined with material records, aid in refining existing models of settlement-landscape evolution and sustainability. We present a case study from Late Bronze Age Southeast Aegean that utilizes literary records, biogeophysical data and geoinformatics methods to offer insights into the abovementioned topics in that region. Specifically, we utilize a georeferenced version of the record of cities and their sociocultural and environmental descriptions, provided in the Catalog of Ships in Homer’s Iliad. We combine this information with datasets from the spatial (physiography, climatology) and temporal (continuities/discontinuities, population) context of those settlements. Ultimately, we are interested in deriving identifiable patterns in our dataset – more specifically, whether there exist patterns of settlement-environment interaction that are inherently more sustainable than others, as well as getting a glimpse into the hierarchy of values underlying this interaction.
Constraining the Eruption History of the Rangitoto Volcano using Palaeomagnetic Data
Authors: Allington Megan , Nilsson Andreas , Hill Mimi , Suttie Neil , Hjorth Ingeborg , Aulin Linda , Augustinus Paul
Published: March 2020

Rangitoto is an island volcano situated outside the city of Auckland, New Zealand. The volcano is the youngest and largest volcano in the monogenetic Auckland Volcanic Field (AVF), with the last eruption occurring about 550-500 calibrated years BP, a date determined from studying historical records. The eruption history of Rangitoto is unknown, however all other volcanoes in the AVF have a brief eruption history. In February 2014 a core spanning 127 metres in length was recovered, consisting of 53 lava flows varying in thickness from 1 to 15 metres. Radiocarbon dates taken from marine sediments found at the bottom of the core, underneath the Rangitoto’s lava flows, suggest that there was early activity as far back as 6000BP, after which Rangitoto may have been dormant until the main shield building phase at around 600BP. Magnetic mineralogy analysis has also shown that much of the core is a reliable recorder of the past geomagnetic field. 156 samples have been analysed for palaeodirectional data and 21 acceptable palaeointensity estimates have been accrued from a range of depths throughout the core length. The collected palaeomagnetic data are used to reconstruct variations in the geomagnetic field, which in turn are used to constrain the eruption rate. Preliminary results suggest that the palaeomagnetic data are incompatible with a short eruption duration of the shield building phase implied by the radiocarbon data (under 100 years) and more compatible with a longer duration of shield building for Rangitoto Island. We discuss alternative explanations for this discrepancy and potential implications of our results in regard to improving hazard planning in Auckland.
Predictability of large scale drivers leading intense Mediterranean cyclones
Authors: Alvarez-Castro M. Carmen , Gualdi Silvio , Yiou Pascal , Vrac Mathieu , Vautard Robert , Cavicchia Leone , Gallego David , Ribera Pedro , Pena-Ortiz Cristina , Faranda Davide
Published: March 2020

Windstorms, extreme precipitations and instant floods seems to strike the Mediterranean area with increasing frequency. These events occur simultaneously during intense tropical-like Mediterranean cyclones. These intense Mediterranean cyclones are frequently associated with wind, heavy precipitation and changes in temperature, generating high risk situations such as flash floods and large-scale floods with significant impacts on human life and built environment. Although the dynamics of these phenomena is well understood, little is know about their climatology. It is therefore very difficult to make statements about the frequency of occurrence and its response to climate change. Thus, intense Mediterranean cyclones have many different physical aspects that can not be captured by a simple standard approach. 

The first challenge of this work is to provide an extended catalogue and climatology of these phenomena by reconstructing a database of intense Mediterranean cyclones dating back up to 1969 using the satellite, the literature and reanalyses. Applying a method based on dynamical systems theory we analyse and attribute their future changes under different anthropogenic forcings by using future simulations within CMIP framework. Preliminary results show a decrease of the large-scale circulation patterns favoring intense Mediterranean cyclones in all the seasons except summer.
Large-scale controls of soil organic carbon in (sub)tropical soils
Authors: von Fromm Sophie F. , Hoyt Alison M. , Asefaw Berhe Asmeret , Shepherd Keith D. , Vågen Tor-Gunnar , Winowiecki Leigh A. , Desta Lulseged T. , Tondoh Jerome E. , Sila Andrew M. , Towett Erick K. , Weullow Elvis , Aynekulu Ermias , Six Johan , Trumbore Susan E. , Doetterl Sebastian
Published: March 2020

Soil organic carbon (SOC) is a key component of terrestrial ecosystems. Experimental studies have shown that soil texture and geochemistry have a strong effect on carbon stocks. However, those findings primarily rely on data from temperate regions or use model approaches that are often based on limited data from tropical and sub-tropical regions.

Here, we evaluate the controls on soil carbon stocks in Africa, using a dataset of 1,580 samples. These were collected across Sub-Saharan Africa (SSA) within the framework of the Africa Soil Information Service (AfSIS) project, which was built on the well-established Land Degradation Surveillance Framework (LDSF). Samples were taken from two depths (0–20 cm and 20–50 cm) at 46 LDSF sites that were stratified according to Koeppen-Geiger climate zones. The different pH-values, clay content, exchangeable cations and extractable elements across various soils of the different climatic zones (i.e. from arid to humid (sub)tropical) allow us to identify different soil and climate parameters that best explain SOC variance across SSA.

We tested if these SOC predictors differed across climatological conditions, using the ratio of potential evapotranspiration (PET) to mean annual precipitation (MAP) as indicator. For water-limited regions (PET/MAP > 1), the best predictors were climatic variables, likely because of their effect on the quantity of carbon inputs. Geochemistry dominated SOC storage in energy-limited systems (PET/MAP < 1), reflecting its effect on carbon protection. On a continental scale, climate (e.g. PET) is key to predicting SOC content in topsoil, whereas geochemistry, particularly iron-oxyhydroxides and aluminum-oxides, is more important in subsoil. Clay content had little influence on SOC at both depths. These findings contribute to an improved understanding of the controls on SOC stocks in tropical and sub-tropical regions.
Carbon sequestration in tropical meandering rivers
Authors: Salerno Luca , Bassani Francesca , Camporeale Carlo
Published: March 2020

Lateral activity and morphological evolutions of fluvial corridors play an active role in the river carbon cycle that is not completely understood so far. Organic carbon (OC) is produced and conveyed by river dynamics, but a quantification of OC sequestration from river systems is still lacking.
By combining stochastic processes and deterministic modeling for the meandering evolution, we develop a minimalistic model to evaluate the amount of carbon moved by tropical meandering rivers through the reworking of riverbed and riparian vegetation. The model assess the eroded area (by river sinuosity) and couples it with satellite-based data of vegetation carbon density. We assess the carbon sequestration in riparian zone of six fluvial reaches of the Amazon basin, and test the results with satellite-based data of vegetated area lost in the same regions. The process of continuous rejuvenation of the riparian community, due to uprooting of trees by the stream followed by recolonization, allows the riparian zone to produce more OC compared to an equivalent riparian vegetated area not subjected to flood disturbances and lateral erosion. This study shows that river carbon sequestration is closely connected to the river activity and is negatively affected by the anthropogenic activities, such as damming and mining.
The rotation and interior of Ganymede
Authors: Van Hoolst Tim , Baland Rose-Marie , Coyette Alexis , Yseboodt Marie
Published: March 2020

The rotation rate of Ganymede, the largest satellite of Jupiter, is on average equal to its orbital mean motion but cannot be constant on orbital time scale as a result of the gravitational torque exerted by Jupiter on the moon. Here we discuss small deviations from the average rotation rate, evaluate polar motion, and discuss Ganymede's obliquity. We examine different time scales, from diurnal to long-period, and assess the potential of using rotation as probes of the interior structure.

The ESA JUICE (JUpiter ICy moons Explorer) mission will accurately measure the rotation of Ganymede during its orbital phase around the satellite starting in 2032. We report on different theoretical aspects of the rotation for realistic models of the interior of Ganymede, include tidal deformations and take into account the low-degree gravity field and topography of Ganymede. We assess the advantages of a joint use of rotation and tides to constrain the satellite's interior structure, in particular its ice shell and ocean.
Deciphering the brittle failure of eclogites at high-pressures: hydrofractures as fluid-escape pathways
Authors: Bukała Michał , Hidas Károly , Garrido Carlos J. , Barnes Christopher , Klonowska Iwona , Majka Jarosław
Published: March 2020

The Tsäkkok lens (northern Scandinavian Caledonides) represents the outermost part of the rifted Baltica passive margin and consists of sediments and pillow basalts of MORB affinity that were metamorphosed in eclogite facies. The Tsäkkok eclogites underwent metamorphism in a cold subduction regime (~8 °C/km) at the onset of the Iapetus Ocean closure. These rocks record pervasive high-pressure, fracturing during prograde dehydration at eclogite-facies conditions reaching up to 2.2 GPa and 590 ºC. Locally, the omphacite-dominated groundmass is transected by fractures sealed either by omphacitite or garnetite veins. Garnetite veins form a dense network that disrupt intact eclogite blocks, whereas omphacitite is found in rare, single veins. The garnetite veins are dominated by dense, poikiloblastic garnet clusters and display two chemically different zones, i.e., a high-Mn inner zone and a low-Mn outer zone. Detailed microstructural and geochemical mapping by EDS-EBSD SEM revealed that the high-Mn inner zone is disrupted and sealed by the low-Mn garnet zone. Garnets in the vein usually show little elongation and moderate intracrystalline substructure that is dominated by slightly changing misorientations without clear subgrain boundaries. By contrast, garnets of the sealed domain display an abrupt grain size reduction and anomalously high density of sharp intracrystalline misorientations in equant grains. The interstitial space between garnet grains in both of the inner and outer zones of the vein is infilled by omphacite + rutile + quartz + phengite + glaucophane.

The textural relationship between the inner- and outer zones of the garnetite vein implies syn-deformation growth of the outer zone, while the mineral assemblage attests for high-pressure conditions of the vein formation. Considering the lack of significant offset along the vein, we interpret the observed microstructures as formed during the sudden opening and closing of a brittle fracture, typical of hydrofracturing, and fast crystal growth assisted by high-pressure fluids. Presumably, these fractures constitute a fluid escape pathway during dehydration at prograde/peak conditions.

Research funded by NCN project no. 2019/33/N/ST10/01479 (M.Bukała) and no. 2014/14/E/ST10/00321 (J.Majka), as well as the The Polish National Agency for the Academic Exchange scholarship no. PPN/IWA/2018/1/00046/U/0001 given to M.Bukała.

 
Earth Surface Monitoring with Spire’s New GNSS Reflectometry (GNSS-R) CubeSats
Authors: Freeman Vahid , Masters Dallas , Jales Philp , Esterhuizen Stephan , Ebrahimi Ellie , Irisov Vladimir , Ben Khadhra Kais
Published: March 2020

Spire Global operates the world’s largest and rapidly growing constellation of CubeSats performing GNSS based science and Earth observation. The Spire constellation, performs a variety of GNSS science, including radio occultation (GNSS-RO), ionosphere and space weather measurements, and precise orbit determination. In December 2019, Spire launched two new satellites to perform GNSS reflectometry (GNSS-R). GNSS-R is a relatively new technique based on a passive bistatic radar system. The potential of space-borne GNSS-R observations for ocean and land applications has been demonstrated by other GNSS-R missions, including the NASA Cyclone Global Navigation Satellite System (CYGNSS) and the UK’s Technology Demonstration Satellite, TechDemoSat (TDS-1). 

We present initial results from these new Spire GNSS-R satellites that are primarily focused on retrieving soil moisture but also estimate other Earth surface properties such as ocean wind speeds and flood inundation/wetland mapping. Prior to the launch of Spire’s GNSS-R satellites and in preparation for Level-2 data production, we developed algorithms and processing chains for land applications. We will present Spire's Soil Moisture (SM) retrieval method using CYGNSS observations. We evaluated the implemented SM change detection algorithm by comparing the Spire’s daily SM product with NASA’s Soil Moisture Active Passive (SMAP) observations and in-situ SM measurements. The results of study indicate remarkable retrieval skills of the GNSS-R technique for soil moisture monitoring at a medium spatial resolution. Spire’s GNSS-R satellites are tuned for land applications with a series of hardware and software optimizations for better signal calibration and acquiring many more data per satellite compared to CYGNSS. A more robust GNSS-R SM retrieval at finer spatial resolution will be possible in the near future after having more Spire satellites in orbit.

Spire’s current and future GNSS-R satellites will provide unprecedented sub-daily global coverage with sub-kilometer spatial resolution. Such intensive data acquisition is of great importance for many land and ocean applications. 
Image improvement of Late Miocene (Messinian) to Plio-Quaternary units in the Algero-Balearic basin
Authors: Blondel Simon , Raad Fadl , Camerlenghi Angelo , Lofi Johanna , Del Ben Anna
Published: March 2020

This study intends to contribute to the understanding of the Mediterranean Salt Giant in the Western Mediterranean, formed about 6 Ma ago during the Messinian Salinity Crisis. It provides reprocessed multichannel seismic reflection data that aim at improving our knowledge of the stratigraphy in the Algero-Balearic deepwater basin and its continental margins, in the absence of lithological information from wells.

We investigate the seismic expression of the Messinian salinity crisis from the south-east of the Balearic promontory to the central Algero-Balearic abyssal basin and the salt tectonic processes associated to these facies. Here the segmentation of salt structures has been previously described using shallow chirp sonar data, low-resolution vintage multichannel seismic data and high-resolution multi-channel seismic data post-stack migrated with a constant velocity field. The structure of the northern Algero-Balearic basin is controlled by two abrupt fault scarps oriented SW–NE (mainly the Emile Baudot Escarpment transform fault) and WSW-ENE (mainly the Mazarron Escarpment transform fault) emplaced during the basin extension, and later intruded by steep and narrow volcanic ridges of Pleistocene age. It is a good analogue to early stage salt tectonic for older and more complex salt giants in the North Sea or the Gulf of Mexico.

We reprocessed 2D Kirchhoff PSTM multichannel seismic data acquired by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (SBALDEEP Cruise of 2005 and SALTFLU cruise of 2012; the latter within a Eurofleet cruise) spanning the South-East continental margin of the Balearic islands and the Algero-Balearic basin. The reprocessing was designed for improving the continuity of the reflectors by applying Kirchhoff PSTM using a detailed velocity model, while preserving amplitude information. The objectives are to better apprehend the structural complexity of the area and to retrieve the amplitude variation within the Messinian units, in an attempt to derive the composition of the salt and the pressure regime.

We present preliminary results where we delineate four different domains based on i) the seismic facies, ii) the amount of salt deformation, iii) the thickness of the overburden and iv) the pre-salt configuration. We try to assess the presence of the Messinian trilogy in the south-eastern continental slope. We attempt to reconstitute the paleo-depositionnal environment of the various depositional units, and the effect of crustal structures and salt tectonic gravity spreading and gliding on their syn to post-depositional evolution. Finally, we search for evidence of fluid circulation within the Messinian and the Plio-Quaternary deposits over the study area.
From red to white: the time-varying nature of ocean heat flux to Arctic sea ice
Authors: Toppaladoddi Srikanth , Wells Andrew
Published: March 2020

Arctic sea ice is one of the most sensitive components of the Earth’s climate system. The underlying ocean plays an important role in the evolution of the ice cover through its heat flux at the ice-ocean interface which moderates ice growth and melt. Despite its importance, the spatio-temporal variations of this heat flux are not well understood. In this work, we combine direct numerical simulations of turbulent convection over fractal surfaces and analysis of time-series data from the Surface Heat Budget of the Arctic Ocean (SHEBA) program using Multifractal Detrended Fluctuation Analysis (MFDFA) to understand the nature of fluctuations in this heat flux. We identify key physical processes associated with the observed Hurst exponents calculated by the MFDFA, and how these evolve over time. We also discuss ongoing work on constructing simple stochastic models of the ocean heat flux to the ice, and potential use as a parameterisation.
Assimilating satellite soil moisture and flood extent maps into a flood prediction model.
Authors: Hostache Renaud , Matgen Patrick , van Leuuwen Peter-Jan , Nichols Nancy , Chini Marco , Pelich Ramona , Delenne Carole
Published: March 2020

The main objective of this study is to investigate how innovative satellite earth observation techniques that allow for the estimation of soil moisture and the mapping of flood extents can help in reducing errors and uncertainties in conceptual hydro-meteorological modelling especially in ungauged areas where potentially no or limited runoff records are available. A spatially distributed conceptual hydrological model is first developed allowing for the simulation of soil moisture and flood extent. Using as forcing of this model rainfall and air temperature time series provided in the globally and freely available ERA5 database it is then possible to carry out long-term simulations of soil moisture, discharge and flood extent. Next, time series of soil moisture and flood extent observations derived from freely available satellite image databases are jointly assimilated into the hydrological model in order to retrieve optimal parameter sets. For this assimilation experiment, we take benefit of recently introduced Particle Filters with tempering that circumvent some of the usual particle filter limitations such as degeneracy and sample impoverishment. As a proof of concept, we set up an identical twin experiment based on synthetically generated observations and we evaluate the performance of the calibrated model.
Operational satellite validation with data from the Pandonia Global Network (PGN)
Authors: Cede Alexander , Tiefengraber Martin , Dehn Angelika , Lefer Barry , von Bismarck Jonas , Casadio Stefano , Abuhassan Nader , Swap Robert , Valin Luke
Published: March 2020

The Pandonia Global Network (PGN) is a worldwide operating network of passive remote sensing spectrometer systems named “Pandora”. PGN is measuring atmospheric trace gases at high temporal resolution with the purpose of air quality monitoring and satellite validation. PGN is an activity carried out jointly by NASA, through the Pandora project at Goddard Space Flight Center, and ESA, through the Austrian contractor LuftBlick, as part of their Joint Program Planning Group Subgroup on calibration and validation and field activities. Many of the more than 50 actual PGN instruments are directly owned by NASA or ESA, another part belongs to other collaborating governmental and academic institutions. A major objective of the PGN is to support the validation and verification of more than a dozen low-earth orbit and geostationary orbit based UV-visible sensors, most notably Sentinel 5P, TEMPO, GEMS and Sentinel 4. PGN instruments are homogeneously calibrated and their data are centrally processed in real-time. Starting in June 2019, the PGN team has made more and more network locations “official PGN sites”, which means all required technical and logistical steps for this purpose have been performed. At the end of 2019 there are 18 such official network sites, where quality assured data are uploaded daily to EVDC (ESA Atmospheric Validation Data Centre), where they are used for operational validation of Sentinel 5P retrievals (see e.g. http://mpc-vdaf-server.tropomi.eu/no2/no2-offl-pandora). The current official PGN data products are total vertical column amounts of NO2 and O3 from direct sun observations. Research data products include total vertical columns amounts of SO2 and HCHO from direct sun observations as well as surface concentrations, tropospheric columns amounts, and vertical profiles for NO2 and HCHO from sky observations. These named research products are planned to become official over the course of the year 2020.