The year 2018 has been a landmark year for Vadose Zone Journal for several reasons.First of all, from 1 Jan. 2018, VZJ flipped from a subscription journal to a golden open access (OA) journal.This now makes the research published in VZJ accessible to a global readership, and it expands our visibility and impact beyond the vadose and critical zone research community.This flip went smoothly, and it was prepared and implemented in an excellent manner by our editorial office and the Tri-Societies.It could not have succeeded without the relentless support and engagement of Pamm Kasper, VZJ managing editor, and our publication system managers Lauren Coleman and Abby Morrison.We are also grateful for the support that we received from the board of the Tri-Societies and the Soil Science Society of America in making this change.Secondly, the international visibility and attractiveness of VZJ has continued to improve.The impact factor (IF) of VZJ for 2017 reached an all-time high of 2.7 since its beginning, and it increased by 0.7 compared with 2016.We are now again a Q1 journal in water research, and we are confident that we will become Q1 again in soil and environmental research in the next years.The reasons for the increased IF are several-fold, but key to this success is the high quality of papers that we have received in the last years, the establishment of update papers, as well as the publication of reviews that were very well received.Several review and update papers showed very high download rates for several months.
Due to the recent developments of multi-configuration EMI systems consisting of transmitter and multiple receivers in a portable rigid boom, detailed large-scale characterization of the top-and subsoil is nowadays possible.Using Transmitter-Receiver separations ranging from 0.3 m up to 4 m, multiple apparent electrical conductivity (ECa) values are measured for different but overlapping investigation volumes.The measured data can be used in a qualitative way to investigate the spatial ECa patterns∕clusters to determine the best locations for soil sampling.Since changes in ECa can be caused by many factors including soil water content, texture, and salinity changes, soil samples need to be used to determine the different topand subsoil properties that are responsible for the ECa contrasts.In this way, the obtained soil properties can be extrapolated into the obtained clusters resulting in a large-scale top-and subsoil characterisation over several hectares for every square meter.In order to enable a more quantitative use of the data and to obtain a reliable model of the electrical conductivity changes with depth, a calibration of the EMI measurements is required, which can be achieved using soil sampling, independent electrical resistivity tomography (ERT), or vertical electrical sounding (VES) measurements.Here, we give an overview of several agricultural applications, calibration approaches to obtain quantitative ECa values, and inversion results to obtain a quasi-3D image of the top-and subsoil.Especially the subsoil patterns were often responsible for the observed patterns in leaf area index (LAI) and airborne hyperspectral plant performance data.
Reliable high-resolution 3-D characterization of aquifers helps to improve our understanding of flow and transport processes when small-scale structures have a strong influence. Crosshole ground penetrating radar (GPR) is a powerful tool for characterizing aquifers due to the method's high-resolution and sensitivity to porosity and soil water content. Recently, a novel GPR full-waveform inversion algorithm was introduced, which is here applied and used for 3-D characterization by inverting six crosshole GPR cross-sections collected between four wells arranged in a square configuration close to the Thur River in Switzerland. The inversion results in the saturated part of this gravel aquifer reveals a significant improvement in resolution for the dielectric permittivity and electrical conductivity images compared to ray-based methods. Consistent structures where acquisition planes intersect indicate the robustness of the inversion process. A decimetre-scale layer with high dielectric permittivity was revealed at a depth of 5–6 m in all six cross-sections analysed here, and a less prominent zone with high dielectric permittivity was found at a depth of 7.5–9 m. These high-permittivity layers act as low-velocity waveguides and they are interpreted as high-porosity layers and possible zones of preferential flow. Porosity estimates from the permittivity models agree well with estimates from Neutron–Neutron logging data at the intersecting diagonal planes. Moreover, estimates of hydraulic permeability based on flowmeter logs confirm the presence of zones of preferential flow in these depth intervals. A detailed analysis of the measured data for transmitters located within the waveguides, revealed increased trace energy due to late-arrival elongated wave trains, which were observed for receiver positions straddling this zone. For the same receiver positions within the waveguide, a distinct minimum in the trace energy was visible when the transmitter was located outside the waveguide. A novel amplitude analysis was proposed to explore these maxima and minima of the trace energy. Laterally continuous low-velocity waveguides and their boundaries were identified in the measured data alone. In contrast to the full-waveform inversion, this method follows a simple workflow and needs no detailed and time consuming processing or inversion of the data. Comparison with the full-waveform inversion results confirmed the presence of the waveguides illustrating that full-waveform inversion return reliable results at the highest resolution currently possible at these scales. We envision that full-waveform inversion of GPR data will play an important role in a wide range of geological, hydrological, glacial and periglacial studies in the critical zone.
ABSTRACT To investigate transient dynamics of soil water redistribution during infiltration, we conducted horizontal borehole and surface ground penetrating radar measurements during a 4‐day infiltration experiment at the rhizontron facility in Selhausen, Germany. Zero‐offset ground penetrating radar profiling in horizontal boreholes was used to obtain soil water content information at specific depths (0.2, 0.4, 0.6, 0.8 and 1.2 m). However, horizontal borehole ground penetrating radar measurements do not provide accurate soil water content estimates of the top soil (0–0.1 m depth) because of interference between direct and critically refracted waves. Therefore, surface ground penetrating radar data were additionally acquired to estimate soil water content of the top soil. Due to the generation of electromagnetic waveguides in the top soil caused by infiltration, a strong dispersion in the ground penetrating radar data was observed in 500 MHz surface ground penetrating radar data. A dispersion inversion was thus performed with these surface ground penetrating radar data to obtain soil water content information for the top 0.1 m of the soil. By combining the complementary borehole and surface ground penetrating radar data, vertical soil water content profiles were obtained, which were used to investigate vertical soil water redistribution. Reasonable consistency was found between the ground penetrating radar results and independent soil water content data derived from time domain reflectometry measurements. Because of the improved spatial representativeness of the ground penetrating radar measurements, the soil water content profiles obtained by ground penetrating radar better matched the known water storage changes during the infiltration experiment. It was concluded that the combined use of borehole and surface ground penetrating radar data convincingly revealed spatiotemporal soil water content variation during infiltration. In addition, this setup allowed a better quantification of water storage, which is a prerequisite for future applications, where, for example, the soil hydraulic properties will be estimated from ground penetrating radar data.
Ground-penetrating radar (GPR) full-waveform inversion (FWI) can determine high-resolution electromagnetic properties of the subsurface and has gained increasing attention in near-surface geophysics. However, the application of GPR-FWI to field surface data is limited due to the high computational costs. Here we apply for one of the first times a 2D time-domain gradient-based FWI to synthetic and field multi-offset surface GPR data set. We use subset FWI (SFWI) to reduce computational costs by implementing the simulation on a model subset rather than the whole model. Thus we obtain theoretical speedup and memory saving factor equal to the size ratio of the model to its subset. The properties of the model subset depend on the illumination of the chosen acquisition geometry, based on which we provide rules of thumb for selecting the model subset. Our study reveals that, SFWI can be further improved by parallelizations, where source parallelization allows for higher efficiency than model domain parallelization. Both 2D synthetic and field data validate that SFWI provides results comparable to FWI but without the redundant computations present in FWI. In a field example with surface geometry, SFWI provides a speedup of more than six times for a 45 m survey line. In another field example with crosshole geometry, SFWI achieves more than a three-times acceleration for a 21 m multi-borehole plane. Our study proves that SFWI has the potential for high-performance computation to solve large-scale GPR survey problems.
Core Ideas Horizontal straight holes for rhizotube installation were bored by a homemade system. Dynamics of root growth and soil moisture could be described by rhizotron facilities. Soil moisture could be monitored by TDR and GPR approaches in rhizotron facilities. Minimally invasive monitoring of root development and soil states (soil moisture, temperature) in undisturbed soils during a crop growing cycle is a challenging task. Minirhizotron (MR) tubes offer the possibility to view root development in situ with time. Two MR facilities were constructed in two different soils, stony vs. silty, to monitor root growth, root zone processes, and their dependence on soil water availability. To obtain a representative image of the root distribution, 7‐m‐long tubes were installed horizontally at 10‐, 20‐, 40‐, 60‐, 80‐, and 120‐cm depths. A homemade system was developed to install MR tubes in the silty soil in horizontally drilled straight holes. For the stony soil, the soil rhizotubes were installed in an excavated and subsequently backfilled pit. In both facilities, three subplots were established with different water treatments: rain sheltered, rainfed, and irrigated. To monitor soil moisture, water potential, and soil temperature, time domain reflectometer probes, tensiometers, and matrix water potential sensors were installed. Soil water content profiles in space and time were obtained between two MR tubes using cross‐hole ground‐penetrating radar along the tubes at different depths. Results from the first growing season of winter wheat ( Triticum aestivum L.) after installation demonstrate that differences in root development, soil water, and temperature dynamics can be observed among the different soil types and water treatments. When combined with additional measurements of crop development and transpiration, these data provide key information that is essential to validate and parameterize root development and water uptake models in soil–vegetation–atmosphere transfer models.
Abstract Improved understanding of crops’ response to soil water stress is important to advance soil-plant system models and to support crop breeding, crop and varietal selection, and management decisions to minimize negative impacts. Studies on eco-physiological crop characteristics from leaf to canopy for different soil water conditions and crops are often carried out at controlled conditions. In-field measurements under realistic field conditions and data of plant water potential, its links with CO 2 and H 2 O gas fluxes, and crop growth processes are rare. Here, we presented a comprehensive data set collected from leaf to canopy using sophisticated and comprehensive sensing techniques (leaf chlorophyll, stomatal conductance and photosynthesis, canopy CO 2 exchange, sap flow, and canopy temperature) including detailed crop growth characteristics based on destructive methods (crop height, leaf area index, aboveground biomass, and yield). Data were acquired under field conditions with contrasting soil types, water treatments, and different cultivars of wheat and maize. The data from 2016 up to now will be made available for studying soil/water-plant relations and improving soil-plant-atmospheric continuum models.
High-contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer. These layers can act as low-velocity waveguides for GPR waves. We used a field example from a hydrological test site in Switzerland to show that full-waveform inversion of crosshole GPR signals could image a subwavelength thickness low-velocity waveguiding layer. We exploited the full information content of the data, whereas ray-based inversion techniques are not able to image such thin waveguide layers because they only exploit the first-arrival times and first-cycle amplitudes. This low-velocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer. The waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within the waveguide and receivers straddling the waveguide depth range. The excellent fit of amplitudes and phase between the measured and modeled data confirms its presence. This new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic, hydrological, and engineering investigations.
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