Short-scale Variations Research Articles

Monitoring Plant Height and Spatial Distribution of Biometrics with a Low-Cost Proximal Platform.

Measuring canopy height is important for phenotyping as it has been identified as the most relevant parameter for the fast determination of plant mass and carbon stock, as well as crop responses and their spatial variability. In this work, we develop a low-cost tool for measuring plant height proximally based on an ultrasound sensor for flexible use in static or on-the-go mode. The tool was lab-tested and field-tested on crop systems of different geometry and spacings: in a static setting on faba bean (Vicia faba L.) and in an on-the-go setting on chia (Salvia hispanica L.), alfalfa (Medicago sativa L.), and wheat (Triticum durum Desf.). Cross-correlation (CC) or a dynamic time-warping algorithm (DTW) was used to analyze and correct shifts between manual and sensor data in chia. Sensor data were able to reproduce with minor shifts in canopy profile and plant status indicators in the field when plant heights varied gradually in narrow-spaced chia (R2 = 0.98), faba bean (R2 = 0.96), and wheat (R2 = up to 0.99). Abrupt height changes resulted in systematic errors in height estimation, and short-scale variations were not well reproduced (e.g., R2 in widely spaced chia was 0.57 to 0.66 after shifting based on CC or DTW, respectively)). In alfalfa, ultrasound data were a better predictor than NDVI (Normalized Difference Vegetation Index) for Leaf Area Index and biomass (R2 from 0.81 to 0.84). Maps of ultrasound-determined height showed that clusters were useful for spatial management. The good performance of the tool both in a static setting and in the on-the-go setting provides flexibility for the determination of plant height and spatial variation of plant responses in different conditions from natural to managed systems.

Daily and monthly ichthyoplankton assemblages of La Azufrada coral reef, Gorgona Island, Eastern Tropical Pacific

The description of the daily and seasonal variation of the species composition and abundance on the early stages of fishes in coral reefs can lead to a better understanding of fish population dynamics in these ecosystems, because settlement and recruitment processes depend on larval fish supply. Daytime and nighttime samples of ichthyoplankton were collected through circular surface tows using a bongo net between October 2010 and November 2011 at La Azufrada, the largest coral reef on the Colombian Pacific coast, located in Gorgona Island. A total of 2,171 fish larvae representing 87 species in 42 families were identified. The most important species by their frequency of occurrence and density were Anisotremus sp., Cetengraulis mysticetus, Bregmaceros bathymaster, and Gobiidae sp.4. Daytime and nighttime samples showed variations in the composition of the assemblage, with a greater number of species at night, evidencing short-scale variations over a diel cycle. On the other hand, environmental parameters such as oxygen, salinity, pH, temperature, and zooplankton biomass were also measured; however, none of them had a strong relationship with the larvae assemblage structure throughout the year. In conclusion, this study suggests that night conditions had a higher effect over the ichthyoplanktonic species found in La Azufrada coral reef than the observed changes in the environmental parameters.

Scope to map available water content using proximal sensed electromagnetic induction and gamma-ray spectrometry data

Dryland cotton farmers need to carefully manage the available water content (AWC) in the root-zone. To reduce cost of mapping, a digital soil mapping (DSM) approach might be useful. The purpose of this study was seeing if we could create DSM of the AWC at the field scale. In the first instance, digital data in the form of proximal sensed electromagnetic (i.e EM) and gamma-ray (γ-ray) spectrometry data were collected along with elevation. Using a grid-based sampling design, 52 soil sample locations were selected and sampled; topsoil (0–0.3 m), subsurface (0.3–0.6 m) and subsoil (0.6–0.9 m). In the laboratory, the field capacity (FC) and permanent wilting point (PWP) were determined using a pressure plate apparatus. The digital and soil (i.e. FC and PWP) data were then calibrated with multiple linear regression (MLR) and stepwise-MLR models compared for each depth (e.g. adjusted coefficient of determination [adj-R2]). The stepwise-MLR were shown to be superior. Subsequently, the DSM of FC and PWP were examined in terms of prediction agreement (Lin’s concordance). Leave-one-out cross validation results showed substantial 1:1 agreement between measured and predicted FC (0.80) and PWP (0.79) at all depths. The final DSMs of FC and PWP, and by difference AWC, were indicative of the two main geomorphological/geological units, with large AWC (> 0.3 m3 m−3) associated with the clay rich Vertosols and small AWC (< 0.15 m3 m−3) the loamy soil of the Pilliga Sandstone. Owing to the short scale variation and the fact that the local alluvium and Pilliga Sandstone were close together and the fact that the digital data varied in different ways, larger confidence interval (CI) values were evident where these areas were juxtaposed. Nevertheless, the final DSM allows the farmer to better manage AWC.

The legacy of industrial pollution in estuarine sediments: spatial and temporal variability implications for ecosystem stress

The direct impacts of anthropogenic pollution are widely known public and environmental health concerns, and details on the indirect impact of these are starting to emerge, for example affecting the environmental microbiome. Anthropogenic activities throughout history with associated pollution burdens are notable contributors. Focusing on the historically heavily industrialised River Clyde, Scotland, we investigate spatial and temporal contributions to stressful/hostile environments using a geochemical framework, e.g. pH, EC, total organic carbon and potentially toxic elements: As, Co, Cr, Cu, Ni, Pb and Zn and enrichment indicators. With regular breaches of the sediment quality standards in the estuarine system we focused on PTE correlations instead. Multivariate statistical analysis (principle component analysis) identifies two dominant components, PC1: As, Cr, Cu, Pb and Zn, as well as PC2: Ni, Co and total organic carbon. Our assessment confirms hot spots in the Clyde Estuary indicative of localised inputs. In addition, there are sites with high variability indicative of excessive mixing. We demonstrate that industrialised areas are dynamic environmental sites dependant on historical anthropogenic activity with short-scale variation. This work supports the development of ‘contamination’ mapping to enable an assessment of the impact of historical anthropogenic pollution, identifying specific ‘stressors’ that can impact the microbiome, neglecting in estuarine recovery dynamics and potentially supporting the emergence of antimicrobial resistance in the environment.

Digital regolith mapping of clay across the Ashley irrigation area using electromagnetic induction data and inversion modelling

In the cotton growing areas of NSW issues associated with water use efficiency and storage reservoirs are problematic, because leakage has led to point source salinization in some areas. Information about the areal distribution of clay is therefore necessary to assist farmers to understand where existing water storages may be better relocated. To map clay efficiently, we show how electromagnetic (EM) induction data from a reconnaissance survey of EM38 and EM34 instruments can be used in association with an EM inversion software package called EM4Soil. This is because the collected apparent electrical conductivity (ECa – mS m−1) data can be inverted to estimate the true electrical conductivity (σ – mS m−1) and correlated with clay. The first aim was to develop a quasi-two-dimensional (Q-2D) model, which could be used to establish a linear regression (LR) relationship between σ and clay collected from 10 soil sample locations to a depth of 12 m, along a single transect of EM38 and EM34 ECa data. This was achieved with an LR equation of the form Clay = 22.12 + 0.20σ with a good correlation coefficient (R2 = 0.74). The second aim was to use the LR to predict clay using a quasi-3D three-dimensional (Q-3D) model developed from EM38 and EM34 electrical conductivity (ECa) data collected on an approximate 0.5–1 km grid across 50,000 ha. A validation set of clay, collected from 34 soil sample locations, indicated a good concordance was achieved (Lin's = 0.80). We conclude the approach provides useful information on a reconnaissance scale and indicates where more detailed information may be collected to confirm problematic areas. In this regard, suitable structural work for improvements can be suggested. In addition, locations can be identified and where more suitable locations for storages can be investigated. To better resolve the areal short scale variation and where the present and prior streams are juxtaposed against the clay alluvial plain, more ECa data should be collected on a finer grid. To improve resolving the depth of clay and the underlying migrational channels, ECa data from an EM31 or a DUALEM-421 instrument could also be collected and used in inversion modelling.

Organic petrography and geochemical characterization of the Upper Cretaceous Second White Specks and Upper Belle Fourche alloformations, west-central Alberta: Analysis of local maturity anomalies

The Second White Specks is an enigmatic unconventional shale play in the Western Canada Foreland Basin (WCFB). This play has an inconsistent production performance that has impacted exploration and production risk, preventing extensive development. In this contribution, geochemical properties are studied with the purpose to identify possible geochemical factors that could contribute to the production variability of this unconventional petroleum system. The studied succession consists of the Second White Specks (SWS) and Upper Belle Fourche (UBF) alloformations, which are part of the SWS shale play. Organic petrology and Rock-Eval pyrolysis were combined to characterize the organic matter (OM), and assess OM richness, thermal maturity and hydrocarbon generation potential in the foredeep section of the basin. The results show that the OM richness and hydrocarbon generation potential in this area is good, and comparison with other studies show that they do not exhibit major lateral variations. The kerogen is marine Type II and is dominated by liptinite, vitrinite, inertinite macerals, and solid bitumen. Alginite and bituminite are the most abundant macerals. Altered bituminite provides evidence of anaerobic bacteria degradation. There is a modest contribution of inertinite that may be responsible for a dilution effect of the pyrolyzable carbon. The thermal maturity indicators in this study such as vitrinite reflectance, Tmax, and alginite UV fluorescence color indicate that the controls on thermal maturity and hydrocarbon generation are not well understood. There are lateral short scale variations or maturity anomalies that require further investigation, to reduce the exploration risk.

PSR B0943+10: low-frequency study of subpulse periodicity in the Bright mode with LOFAR

We use broadband sensitive LOFAR observations in the 25–80 MHz frequency range to study the single-pulse emission properties of the mode-switching pulsar B0943+10. We review the derivation of magnetospheric geometry, originally based on low-frequency radio data, and show that the geometry is less strongly constrained than previously thought. This may be used to help explain the large fractional amplitudes of the observed thermal X-ray pulsations from the polar cap, which contradicted the almost aligned rotator model of PSR B0943+10. We analyse the properties of drifting subpulses in the Bright mode and report on the short-scale (minutes) variations of the drift period. We searched for the periodic amplitude modulation of drifting subpulses, which is a vital argument for constraining several important system parameters: the degree of aliasing, the orientation of the line-of-sight vector with respect to magnetic and spin axes, the angular velocity of the carousel, and thus, the gradient of the accelerating potential in the polar gap. The periodic amplitude modulation was not detected, indicating that it may be a rare or narrow-band phenomenon. Based on our non-detection and review of the available literature, we chose to leave the aliasing order unconstrained and derived the number of sparks under different assumptions about the aliasing order and geometry angles. Contrary to the previous findings, we did not find a large (of the order of 10%) gradual variation of the separation between subpulses throughout Bright mode. We speculate that this large variation of subpulse separation may be due to the incorrect accounting for the curvature of the line of sight within the on-pulse window. Finally, we report on the frequency-dependent drift phase delay, which is similar to the delay reported previously for PSR B0809+74. We provide a quantitative explanation of the observed frequency-dependent drift phase delay within the carousel model.

Large-scale trench-normal mantle flow beneath central South America

We investigate the anisotropic properties of the fore-arc region of the central Andean margin between 17–25°S by analyzing shear-wave splitting from teleseismic and local earthquakes from the Nazca slab. With partly over ten years of recording time, the data set is uniquely suited to address the long-standing debate about the mantle flow field at the South American margin and in particular whether the flow field beneath the slab is parallel or perpendicular to the trench. Our measurements suggest two anisotropic layers located within the crust and mantle beneath the stations, respectively. The teleseismic measurements show a moderate change of fast polarizations from North to South along the trench ranging from parallel to subparallel to the absolute plate motion and, are oriented mostly perpendicular to the trench. Shear-wave splitting measurements from local earthquakes show fast polarizations roughly aligned trench-parallel but exhibit short-scale variations which are indicative of a relatively shallow origin. Comparisons between fast polarization directions from local earthquakes and the strike of the local fault systems yield a good agreement. To infer the parameters of the lower anisotropic layer we employ an inversion of the teleseismic waveforms based on two-layer models, where the anisotropy of the upper (crustal) layer is constrained by the results from the local splitting. The waveform inversion yields a mantle layer that is best characterized by a fast axis parallel to the absolute plate motion which is more-or-less perpendicular to the trench. This orientation is likely caused by a combination of the fossil crystallographic preferred orientation of olivine within the slab and entrained mantle flow beneath the slab. The anisotropy within the crust of the overriding continental plate is explained by the shape-preferred orientation of micro-cracks in relation to local fault zones which are oriented parallel to the overall strike of the Andean range. Our results do not provide any evidence for a significant contribution of trench-parallel mantle flow beneath the subducting slab.

Sensitivity of clay content prediction to spectral configuration of VNIR/SWIR imaging data, from multispectral to hyperspectral scenarios

The use of digital soil mapping, with the help of spectroscopic data, provides a non-destructive and cost-efficient alternative to soil property laboratory measurements. Visible, near-infrared and short wave infrared (VNIR/SWIR, 400–2500nm) hyperspectral imaging is one of the most promising tools for topsoil property mapping. The aim of this study was to test the sensitivity of soil property prediction results to coarsening image spectral resolution. This may offer an analysis of the potential of forthcoming hyperspectral satellite sensors, e.g., HYPerspectral X IMagery (HYPXIM) or Environmental Mapping and Analysis Program (EnMAP), and existing multispectral sensors, e.g., SENTINEL-2 Multispectral Sensor Instrument (MSI) or LANDSAT-8 Operational Land Imager (OLI), for soil properties mapping. This study used VNIR/SWIR hyperspectral airborne data acquired by the AISA-DUAL sensor (initial spectral and spatial resolutions of approximately 5nm and 5m, respectively) over a 300km2 Mediterranean rural region. Ten spectral configurations were built and divided in the following two groups: i) six spectral configurations corresponding to simulated sensors with regular spectral resolution from 5nm to 200nm (i.e., the Full Width at Half Maximum (FWHM) remains constant throughout the considered spectral domain; this includes the simulation of the forthcoming HYPXIM and EnMAP hyperspectral satellites) and ii) four spectral configurations corresponding to existing multispectral sensors with irregular spectral resolution (i.e., the FWHM differs from spectral sampling interval; Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), SENTINEL-2 MSI, LANDSAT-7 Enhanced Thematic Mapper (ETM+) and LANDSAT-8 OLI). The soil property studied in this paper is the clay content, defined as the percentage of granulometric fraction finer than 2μm by weight of the soil, which will be estimated using the partial least squares regression method. Our results showed that i) spectral configurations with regular spectral resolutions from 5 to 100nm provided similar and good clay content prediction performances (R2val>0.7 and RPIQ>3) and allowed clay mapping with correct short-scale variations, ii) the spectral configuration with a regular spectral resolution of 200nm provided unsatisfactory clay content prediction performance (R2val≃0.01 and RPIQ≃1.65) and iii) the ASTER sensor was the only existing multispectral sensor that provided both correct performance of clay content estimation (R2val≃0.8 and RPIQ≃3.72) and correct clay mapping. Therefore, clay mapping by the ASTER multispectral data should be pursued while awaiting the launch of forthcoming hyperspectral satellite sensors (e.g., HYPXIM and EnMAP), which will be good candidates for future large clay mapping campaigns over bare soils.

Geostatistical Simulation with a Trend Using Gaussian Mixture Models

Geostatistics applies statistics to quantitatively describe geological sites and assess the uncertainty due to incomplete sampling. Strong assumptions are required regarding the location independence of statistical parameters to construct numerical models with geostatistical tools. Most geological data exhibit large-scale deterministic trends together with short-scale variations. Such location dependence violates the common geostatistical assumption of stationarity. The trend-like deterministic features should be modeled prior to conventional geostatistical prediction and accounted for in subsequent geostatistical calculations. The challenge of using a trend in geostatistical simulation algorithms for the continuous variable is the subject of this paper. A stepwise conditional transformation with a Gaussian mixture model is considered to provide a stable and artifact-free numerical model. The complex features of the regionalized variable in the presence of a trend are removed in the forward transformation and restored in the back transformation. The Gaussian mixture model provides a seamless bin-free approach to transformation. Data from a copper deposit were used as an example. These data show an apparent trend unsuitable for conventional geostatistical algorithms. The result shows that the proposed algorithm leads to improved geostatistical models.

Half-tapering strategy for conditional simulation with large datasets

Gaussian conditional realizations are routinely used for risk assessment and planning in a variety of Earth sciences applications. Assuming a Gaussian random field, conditional realizations can be obtained by first creating unconditional realizations that are then post-conditioned by kriging. Many efficient algorithms are available for the first step, so the bottleneck resides in the second step. Instead of doing the conditional simulations with the desired covariance (F approach) or with a tapered covariance (T approach), we propose to use the taper covariance only in the conditioning step (half-taper or HT approach). This enables to speed up the computations and to reduce memory requirements for the conditioning step but also to keep the right short scale variations in the realizations. A criterion based on mean square error of the simulation is derived to help anticipate the similarity of HT to F. Moreover, an index is used to predict the sparsity of the kriging matrix for the conditioning step. Some guides for the choice of the taper function are discussed. The distributions of a series of 1D, 2D and 3D scalar response functions are compared for F, T and HT approaches. The distributions obtained indicate a much better similarity to F with HT than with T.

Structure, transport, and vertical coherence of the Gulf Stream from the Straits of Florida to the Southeast Newfoundland Ridge

Data from three independent and extensive field programs in the Straits of Florida, the Mid-Atlantic Bight, and near the Southeast Newfoundland Ridge are reanalyzed and compared with results from other historical studies to highlight the downstream evolution of several characteristics of the Gulf Stream's mean flow and variability. The three locations represent distinct dynamical regimes: a tightly confined jet in a channel; a freely meandering jet; and a topographically controlled jet on a boundary. Despite these differing dynamical regimes, the Gulf Stream in these areas exhibits many similarities. There are also anticipated and important differences, such as the loss of the warm core of the current by 42°N and the decrease in the cross-frontal gradient of potential vorticity as the current flows northward. As the Gulf Stream evolves it undergoes major changes in transport, both in magnitude and structure. The rate of inflow up to 60°W and outflow thereafter are generally uniform, but do exhibit some remarkable short-scale variations. As the Gulf Stream flows northward the vertical coherence of the flow changes, with the Florida Current and North Atlantic Current segments of the Gulf Stream exhibiting distinct upper and deep flows that are incoherent, while in the Mid-Atlantic Bight the Gulf Stream exhibits flows in three layers each of which tends to be incoherent with the other layers at most periods. These coherence characteristics are exhibited in both Eulerian and stream coordinates. The observed lack of vertical coherence indicates that great caution must be exercised in interpreting proxies for Gulf Stream structure and flow from vertically-limited or remote observations.

Monitoring scale-specific and temporal variation in electromagnetic conductivity images

In semiarid and arid landscapes, irrigation sustains agricultural activity but because of increasing demands on water resources there is a need to make gains in efficiency. As such spatial variation of soil properties such as clay and salinity needs to be understood because they strongly influence soil moisture availability. One way is to use electromagnetic induction because apparent soil electrical conductivity (ECa) is related to volumetric soil moisture (θ), clay and salinity (ECe). However, depth-specific variation has not been explored. Our aim is to generate electromagnetic conductivity images (EMCIs) by inverting DUALEM-421 ECa and show how true electrical conductivity (σ) can be correlated with θ, clay, ECe and bulk density (ρ) on different days post-irrigation (i.e., 1, 4 and 12 days). Two-dimensional multi-resolution analysis (MRA) is used to show how spatio-temporal variation in σ is scale-specific and how soil properties influence σ at different scales. We study this beneath a pivot irrigated alfalfa crop. We found that σ on days 1 and 4 was correlated with θ (Pearson’s r = 0.79 and 0.61) and clay (0.86 and 0.80) and the dominant scale of variation occurred at 9.3–18.7 m (50.21 % of total variation), >74.7 m (23.18 %) and 4.7–9.3 m (16.29 %). Between 9.3–18.7 and 4.7–9.3 m the variation may be a function of the cutter width (8 m), while >74.7 m may be change in clay and ECe and gantry spacing (~48 m). The sprinkler spacing (1.2 and 1.6 m) explains short-scale variation at 1.2–2.3 m.

Validation of AltiKa Matching Pursuit Rain Flag

The major drawback of Ka band, operating frequency of the AltiKa altimeter on board SARAL, is its sensitivity to atmospheric liquid water. Even light rain or heavy clouds can strongly attenuate the signal and distort the signal leading to erroneous geophysical parameters estimates. A good detection of the samples affected by atmospheric liquid water is crucial. As AltiKa operates at a single frequency, a new technique based on the detection by a Matching Pursuit algorithm of short scale variations of the slope of the echo waveform plateau has been developed and implemented prelaunch in the ground segment. As the parameterization of the detection algorithm was defined using Jason-1 data, the parameters were re-estimated during the cal-val phase, during which the algorithm was also updated. The measured sensor signal-to-noise ratio is significantly better than planned, the data loss due to attenuation by rain is significantly smaller than expected (<0.1%). For cycles 2 to 9, the flag detects about 9% of 1Hz data, 5.5% as rainy and 3.5 % as backscatter bloom (or sigma0 bloom). The results of the flagging process are compared to independent rain data from microwave radiometers to evaluate its performances in term of detection and false alarms.

USING LEGACY SOIL DATA FOR STANDARDIZING PREDICTIONS OF TOPSOIL CLAY CONTENT OBTAINED FROM VNIR/SWIR HYPERSPECTRAL AIRBORNE IMAGES

Abstract. Mapping of topsoil properties using Visible, Near-Infrared and Short Wave Infrared (VNIR/SWIR) hyperspectral imagery requires large sets of ground measurements for calibrating the models that estimate soil properties. To avoid collecting such expensive data, we proposed a procedure including two steps that involves only legacy soil data that were collected over and?or around the study site: 1) estimation of a soil property using a spectral index of the literature and 2) standardisation of the estimated soil property using legacy soil data. This approach was tested for mapping clay contents in a Mediterranean region in which VNIR/SWIR AISA-DUAL hyperspectral airborne data were acquired. The spectral index was the one proposed by Levin et al (2007) using the spectral bands at 2209, 2133 and 2225 nm. Two legacy soil databases were tested as inputs of the procedure: the Focused-Legacy database composed of 67 soil samples collected in 2000 over the study area, and the No-Focused-Legacy database composed of 64 soil samples collected between 1973 and 1979 around but outside of the study area. The results were compared with those obtained from 120 soil samples collected over the study area during the hyperspectral airborne data acquisition, which were considered as a reference. Our results showed that: 1) the spectral index with no further standardisation offered predictions with high accuracy in term of coefficient of correlation r (0.71), but also high bias (−414 g/kg) and SEP (439 g/kg), 2) the standardisation using both legacy soil databases allowed an increase of accuracy (r = 0.76) and a reduction of bias and SEP and 3) a better standardisation was obtained by using the Focused-Legacy database rather than the No-Focused-Legacy database. Finally, the clay predicted map obtained with standardisation using the Focused-Legacy database showed pedologically-significant soil spatial structures with clear short-scale variations of topsoil clay contents in specific areas. This study, associated with the coming availability of a next generation of hyperspectral VNIR/SWIR satellite data for the entire globe, paves the way for inexpensive methods for delivering high resolution soil properties maps.

Evaluating Digital Soil Mapping approaches for mapping GlobalSoilMap soil properties from legacy data in Languedoc-Roussillon (France)

Digital Soil Mapping is becoming increasingly operational because of shared approaches, clear specifications (e.g., GlobalSoilMap) and more “practical” applications across the planet. In a 27,236km2 French region located in the Northern Mediterranean area, this study evaluated four well-known Digital Soil Mapping approaches that were possibly applicable in the French context for inferring the GlobalSoilMap (GSM) grid using freely available data from the French spatial data infrastructure. These approaches used for soil input either a legacy 1:250,000 scale soil map—an area-weighted mean of soil mapping units and spatial disaggregation of soil mapping units (simulated)—or a set of 2024 legacy-measured soil profiles (1 profile/13.5km2) associated with a set of soil covariates using random forest and random forest plus kriging. These methods provided estimates of 29 soil properties over a 100m by 100m grid, i.e., clay, sand, silt, coarse fragment, organic carbon contents, pH and CEC, at the four upper GSM-specified depth intervals, plus soil depth.This experiment showed that the performances in mapping soil properties were highly variable (from R2=0 to R2=0.79). They were strongly correlated with the amount of spatially-structured variance of the soil properties captured by the available soil data. For example better performances were observed for organic carbon that is driven by large-scale climate variations than for texture and soil depth that are driven by short scale variations of parent materials and erosion–deposition ratio along a slope. Furthermore, the profile-based DSM models generally outperformed the soil map-based DSM models, and kriging did not improve the results of random forest. Finally improving the quality of soil data input was considered as the best way to improve the current mapping performances.In addition to providing a GlobalSoilMap proof-of-concept for Northern Mediterranean areas, this paper illustrates how a prior analysis of the available soil data may help in the anticipated estimation of the mapping performances and in the prior selection of the most promising DSM models to reach these performances.

Crustal origin of trench-parallel shear-wave fast polarizations in the Central Andes

In this study, SKS and local S phases are analyzed to investigate variations of shear-wave splitting parameters along two dense seismic profiles across the central Andean Altiplano and Puna plateaus. In contrast to previous observations, the vast majority of the measurements reveal fast polarizations sub-parallel to the subduction direction of the Nazca plate with delay times between 0.3 and 1.2 s. Local phases show larger variations of fast polarizations and exhibit delay times ranging between 0.1 and 1.1 s. Two 70 km and 100 km wide sections along the Altiplano profile exhibit larger delay times and are characterized by fast polarizations oriented sub-parallel to major fault zones. Based on finite-difference wavefield calculations for anisotropic subduction zone models we demonstrate that the observations are best explained by fossil slab anisotropy with fast symmetry axes oriented sub-parallel to the slab movement in combination with a significant component of crustal anisotropy of nearly trench-parallel fast-axis orientation. From the modeling we exclude a sub-lithospheric origin of the observed strong anomalies due to the short-scale variations of the fast polarizations. Instead, our results indicate that anisotropy in the Central Andes generally reflects the direction of plate motion while the observed trench-parallel fast polarizations likely originate in the continental crust above the subducting slab.

Potential mechanisms for anisotropy in ice-penetrating radar data

AbstractRadar data (center frequency 150 MHz) collected on the Antarctic plateau near the EPICA deep-drilling site in Dronning Maud Land vary systematically in backscattered power, depending on the azimuth antenna orientation. Backscatter extrema are aligned with the principal directions of surface strain rates and change with depth. In the upper 900m, backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression, while below 900 m the maxima shift by 90° pointing towards the lateral flow dilatation. We investigate the backscatter from elongated air bubbles and a vertically varying crystal-orientation fabric (COF) using different scattering models in combination with ice-core data. We hypothesize that short-scale variations in COF are the primary mechanism for the observed anisotropy, and the 900 m boundary between the two regimes is caused by ice with varying impurity content. Observations of this kind allow the deduction of COF variations with depth and are potentially also suited to map the transition between Holocene and glacial ice.

Processes underlying tidal variability of carbon dioxide in the Tagus Estuary (Portugal)

Tidal variation of CO2 system parameters was evaluated in the Tagus Estuary (SW Portugal) based on field observations performed in 2007 in the lower estuary under low river discharge conditions, during spring and autumn. Differences were found in the distribution patterns of environmental variables along a tidal cycle and at neap and spring tides essentially due to tide amplitude effects and tidal asymmetric behavior. A dominant east-westbound current was detected transporting CO2 enriched estuarine water offshore mainly during the ebb, and the reverse tidal current transporting more oxygenated marine water and with high chlorophyll a concentration during the flood. Distinct seasonal features were observed in terms of CO2 water properties and productivity. Regarding the tidal variability of the CO2 system parameters, besides the key processes controlling the variability, such as tidal advection and horizontal mixing of the two water masses present (estuarine and oceanic), specific biogeochemical processes emerged as playing an important role. Data obtained indicate that photosynthesis (in spring), aerobic respiration, and CaCO3 precipitation/dissolution (mainly in autumn) processes co-occur and control short-scale variations of CO2, reflecting the complexity of CO2 chemistry in the Tagus Estuary.

Short-scale variations of shear-wave splitting across the Dead Sea basin: Evidence for the effects of sedimentary fill

[1] We examine shear-wave splitting of SKS waveforms collected by a temporary array of 68 stations in the region of the Dead Sea basin. The observed splitting parameters exhibit systematic variations along a dense, EW-trending 60 km profile across the basin. The delay times vary significantly between 1.0 and 2.8 seconds with smaller values in the very center of the profile. The fast polarizations are oriented more-or-less parallel to the strike of the Dead Sea transform fault and vary between −10 and 20 degrees with respect to North. Finite-frequency waveform modeling reveals that the source-region of the small-scale lateral variations is likely located within the crust. The modeling further shows that purely isotropic velocity variations affect shear-wave splitting: To a large degree, the observed variations of splitting parameters can be explained by the sedimentary fill of the basin and its low isotropic seismic velocities, whereas the mantle is uniformly anisotropic. Our study indicates that precaution must be taken when interpreting short-scale lateral variations of shear wave splitting in terms of anisotropic structures in the crust or upper mantle.