Detailed Spatial Measurements Research Articles

Examining Infrasound Propagation at High Spatial Resolution Using a Nodal Seismic Array

AbstractInfrasound—acoustic waves in the atmosphere below 20 Hz—is a useful monitoring tool. Topography and atmospheric structure strongly control infrasound propagation, and at common source–receiver distances neither of these effects can be ignored when quantitative source constraints are sought. Detailed spatial measurements of the infrasound wavefield would inform propagation models and improve source estimates. However, the “large‐N” deployment strategy now well‐known in seismology has not yet been realized for infrasound studies. Here, we use the 900‐node seismic array from the 2014 Imaging Magma Under St. Helens (iMUSH) experiment as a proxy for a large‐N infrasound network, by leveraging acoustic–seismic coupled arrivals. The active‐source component of iMUSH consisted of 23 shallowly buried explosions around Mount Saint Helens volcano; these explosions produced epicentral infrasound recorded on the nodes. We find that the bulk presence of ground‐coupled infrasound on the nodes is controlled by wind noise and source–receiver distance, with observed arrivals for eight explosions. Explosions with the most extensive coupling produce complex spatial waveform patterns across the array. These patterns are related to both topographic and atmospheric propagation effects, as well as spatially variable site (coupling) effects. We compare our observations to simple topographic diffraction and high‐resolution wind advection models, and full‐wave numerical simulations. We find strong spatial correlations between (a) coupled arrival strength and modeled topographic obstruction and (b) coupled arrival time and along‐path winds. Our seismoacoustic analyses and results are applicable to other existing and future nodal seismic data sets and can expand the utility of such deployments.

Groundwater discharge and streams drive spatial alkalinity and pCO2 dynamics in two contrasting tropical lagoons

Coral reef lagoons are areas of complex carbon cycling, however, regional (e.g. land use) and global (e.g. climate) factors, including land runoff and ocean acidification, are adversely affecting carbonate-building coral reef systems. Coupled with this, surplus nutrients entering coastal waters can prompt excess algae growth, which can stimulate further carbon dioxide (CO2) production in the water column, thus enhancing coral/sediment dissolution. However, new inputs of alkalinity into coastal systems can buffer against acidification. By combining the natural groundwater tracer radon (222Rn) with carbonate chemistry in two contrasting Cook Island lagoons (the fringing Muri Lagoon on Rarotonga and the comparatively larger Aitutaki near-atoll lagoon), we were able to identify multiple drivers of coral reef acidification and regulation. Despite the lagoons having similar rates of submarine groundwater discharge (3.1 to 3.3 cm d−1; although the rate in Aitutaki is a maximum rate based on an assumed 100 m seepage face), groundwater inputs of CO2 and alkalinity were primarily driven by different sources (discrete offshore seeps in Muri Lagoon and dredged channels in Aitutaki Lagoon). Streams delivered low alkalinity water to both lagoons, but high pCO2 waters to the Aitutaki Lagoon in contrast to Muri Lagoon. Aragonite saturation states (ΩAr) ranged between 2.2 and 5.2, with areas of low ΩAr corresponding to areas of high radon and excess algal growth in Muri Lagoon, and areas that receive low alkalinity surface water in Aitutaki. Time-series sampling indicated that tidal heights and the ability of seawater to overtop the fringing reef influenced groundwater dynamics, lagoon hydrodynamics and carbonate chemistry. Groundwater discharge and stream flows were a significant freshwater source of new geologic CO2 and alkalinity to each lagoon, while recirculated seawater is likely a significant source of biologic CO2 driven by microbial respiration in sediments. The study found that while groundwater inputs of alkalinity may reduce acidification, they do not fully counteract ongoing acidification and CO2 inputs. This study also highlighted the need for future studies to undertake detailed spatial measurements to accurately characterise tropical island carbon dynamics due to the heterogeneous nature of these environments.

Stem and root assessment in mangrove forests using a low-cost, rapid-scan terrestrial laser scanner

Accurate assessment of forest structure and biomass is hampered by extensive field measurements that are time-consuming, costly, and inefficient. This is especially true in mangrove forests that have developed complex above-ground root structures for stability and survival in the harsh, anaerobic, and reducing conditions of water-logged sediments. These diverse structures can differ even among similar species, providing complex three dimensional structures and making them difficult to accurately assess using traditional allometric methods. Terrestrial laser scanners (TLS) have been used widely in collecting forest inventory information in recent years, mainly due to their fine-scale, detailed spatial measurements and rapid sampling. In this work we detected stems and roots in TLS data from three mangrove forests on Pohnpei Island in Micronesia using 3D classification techniques. After removing noise from the point cloud, the training set was acquired by filtering the facets of the point cloud based on angular orientation. However, many mangrove trees contain above-ground roots, which can incorrectly be classified as stems. We consequently trained a supporting classifier on the roots to detect omitted root returns (i.e., those classified as stems). Consistency was assessed by comparing TLS results to concurrent field measurements made in the same plots. The accuracy and precision for TLS stem classification was 82% and 77%, respectively. The same values for TLS root detection were 76% and 68%. Finally, we simulated the stems using alpha shapes for volume estimation. The average consistency of the TLS volume assessment was 85%. This was obtained by comparing the plot-level mean stem volume (m3/ha) between field and TLS data. Additionally, field-measured diameter-at-breast-heights (DBH) were compared to the lidar-derived DBH using the reconstructed stems, resulting in 74% average accuracy and an RMSE of 7.52 cm. This approach can be used for automatic structural evaluation, and could contribute to more accurate biomass assessment of complex mangrove forest environments as part of forest inventories or carbon stock assessments.

Experimental Study and Numerical Modeling of Downward Flame Spread Along a Single Pine Needle: Part 1 (Experiments)

ABSTRACTThis work presents an experimental study of downward flame spread over a vertically positioned single pine needle of Pinus Sibirica. Detailed spatial measurements in the gas phase have been carried out to determine the chemical and thermal flame structure of the spreading flame. In addition, temperature distribution in pine needle is also measured. In the gas phase micro thermocouple measurements were used to determine temperature distribution; mass spectrometry with microprobe sampling was used to measure the concentration profiles of О2 and the main combustion products (СО2, СО, Н2О). The micro thermocouple method was also used to measure temperature distribution in a pine needle for flame spread along it. The data obtained from the experiments on single vertical pine needles reveals two stages in downward flame propagation: (1) a zone in the vicinity of the leading edge of the spreading flame where virgin pine needle decomposes to form char and volatile pyrolysis products formed. The pyrolysis products mix with air and ignited by flame behind causes flame to propagate; and (2) a zone where heterogeneous burning of char occurs. The downward flame spread velocity along a single pine needle was also measured for several counter-flow air velocities to obtain dependence of flame spread rate on counter-flow velocity. The data obtained in this work can also serve as a much needed base for testing and refining the numerical models describing flame spread along individual components of forest fuels (FF). Further, as the flame propagation along a bed of FF is similar to that along charring polymer materials, the data obtained and the applied methods of research may be also of interest to those studying the charring polymer combustion mechanism.

Computational Modeling of Multiphase Reactors.

Multiphase reactors are very common in chemical industry, and numerous review articles exist that are focused on types of reactors, such as bubble columns, trickle beds, fluid catalytic beds, etc. Currently, there is a high degree of empiricism in the design process of such reactors owing to the complexity of coupled flow and reaction mechanisms. Hence, we focus on synthesizing recent advances in computational and experimental techniques that will enable future designs of such reactors in a more rational manner by exploring a large design space with high-fidelity models (computational fluid dynamics and computational chemistry models) that are validated with high-fidelity measurements (tomography and other detailed spatial measurements) to provide a high degree of rigor. Understanding the spatial distributions of dispersed phases and their interaction during scale up are key challenges that were traditionally addressed through pilot scale experiments, but now can be addressed through advanced modeling.

Detailed spatial measurements and Monte Carlo analysis of the transportation phenomena of thermal and epithermal neutrons from the 12-GeV proton transport line to an access maze

In order to investigate the neutron transportation from a beam-line tunnel to an access maze at a 12-GeV proton accelerator, we measured the spatial distribution of thermal and epithermal neutrons by using the Au activation method in detail. Gold foils were placed at about 70 positions in the maze in the case of the insertion (or extraction) of a copper target of 1 mm thickness into (or from) the beam axis in front of the maze. After the end of accelerator operation, relative activities of the Au foils were simultaneously measured by using an imaging plate technique and the radioactivity of one reference foil was also measured with a HPGe detector to convert to the absolute activities of all foils. It was found that the neutrons reach to the depth of the maze in the case of the insertion of the copper target. This result reflects higher proportion of high-energy particles from the copper target to that from other beam loss points and high-energy particles become the successive source of low-energy neutrons. Furthermore, it was found that several circumstances such as door walls and electric wire cables obviously affect the absorption effect of thermal neutrons. The reaction rates obtained in this study were also used for the benchmark of the Monte Carlo simulation code, MARS15 (version of February 2008). The results of the MARS15 calculations precisely reproduced experimental results and significant effects of the electric wire cables and door walls.

Spatio‐temporal distribution of near‐surface and root zone soil moisture at the catchment scale

AbstractSoil moisture is highly variable both spatially and temporally. It is widely recognized that improving the knowledge and understanding of soil moisture and the processes underpinning its spatial and temporal distribution is critical. This paper addresses the relationship between near‐surface and root zone soil moisture, the way in which they vary spatially and temporally, and the effect of sampling design for determining catchment scale soil moisture dynamics. In this study, catchment scale near‐surface (0–50 mm) and root zone (0–300 mm) soil moisture were monitored over a four‐week period. Measurements of near‐surface soil moisture were recorded at various resolutions, and near‐surface and root zone soil moisture data were also monitored continuously within a network of recording sensors. Catchment average near‐surface soil moisture derived from detailed spatial measurements and continuous observations at fixed points were found to be significantly correlated (r2 = 0·96; P = 0·0063; n = 4). Root zone soil moisture was also found to be highly correlated with catchment average near‐surface, continuously monitored (r2 = 0·81; P < 0·0001; n = 26) and with detailed spatial measurements of near‐surface soil moisture (r2 = 0·84). The weaker relationship observed between near‐surface and root zone soil moisture is considered to be caused by the different responses to rainfall and the different factors controlling soil moisture for the soil depths of 0–50 mm and 0–300 mm. Aspect is considered to be the main factor influencing the spatial and temporal distribution of near‐surface soil moisture, while topography and soil type are considered important for root zone soil moisture. The ability of a limited number of monitoring stations to provide accurate estimates of catchment scale average soil moisture for both near‐surface and root zone is thus demonstrated, as opposed to high resolution spatial measurements. Similarly, the use of near‐surface soil moisture measurements to obtain a reliable estimate of deeper soil moisture levels at the small catchment scale was demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.

Lines of dense nanoparticle colloidal suspensions evaporating on a flat surface: Formation of non-uniform dried deposits

Line evaporation of dense nanoparticle suspensions is studied theoretically and experimentally. The 2-D lines are drawn by a pen-like nozzle continuously dispensing a commercially available concentrated organic suspension (50 wt%; 4.3 vol%) of 5 nm gold nanoparticles in toluene solvent. Such particle-containing lines show promise for industrial applications where circuits are inkjet-printed and heat-treated to dry off the organic solvent and sinter the nanoparticles, thus producing a continuous electrically conducting path. The employed nanosuspension displays spontaneous thickening upon contact with a solid surface in the ambient atmosphere, and thus does not dry according to the well-established coffee-stain forming mechanism applicable to dilute particle suspensions. In the present work, model lines (∼1 mm width) are studied to elucidate the drying peculiarities of such nanoparticle slurries. These scaled-up lines allow detailed spatial measurements of their topography throughout their prolonged evaporation period, and make possible direct comparisons between experiment and theory. The results show the particle deposits formed by evaporative drying of these lines to be of non-uniform thickness with a dent in the middle of the lateral cross-section. Formation of this practically undesirable landscape is attributed to the highly non-uniform evaporative character of sessile or pendent liquid lines, which results in a non-uniform consolidation of the porous phase formed upon contact with the solid surface. The formulated description of the shape changing process, as done in the framework of the consolidation theory, yields predicted deposit speck shapes that compare favorably with the temporally resolved experimental data.

TURBULENT CHARACTERISTICS OF SHALLOW FLOW OVER ROUGH SURFACE WITH REGULARLY ARRAYED SPHERES

Turbulent nature of near-bed flow field was investigated in an open channel over a rough-bed artificially arrayed with glass beads, where ratios of the glass diameter to flow depth are 03, 0.5 and 0.8. Detailed spatial measurements of streamwise and vertical velocity fluctuations were made using Particle Image Velocimetry (PIV) in a vertical plane along the completely rough bed surface. Results indicated significant degrees of spatially regular variation in the time-averaged velocities, in which the upflow generated over upper region of roughness top is about 8% of the cross sectional average velocity, much stronger than the downflow. In addition, Reynolds shear stress and turbulent intensity showed minimum values at the ridge of roughness elements and maximum ones at the trough. These organized flow structure were suggested to be due to the vortex shedding brought about by the roughness elements.

Spatial distribution of soil moisture over 6 and 30 cm depth, Mahurangi river catchment, New Zealand

Ground-based measurement of the spatial distribution of soil moisture can be difficult because sampling is essentially made at a point and the choice of both sample depth and sample spacing affects the interpretation of the measurements. Hydrological interest has generally been in soil moisture of the root zone. Microwave Remote Sensing methods are now available that allow the interpretation of spatial distributions of soil moisture, however, their signals respond to moisture in the upper few centimetres of soil. These instruments are still being developed, but one of the questions surrounding their application is how to interpret the surface moisture in a hydrological context. In this study we compare measurements of soil moisture in 0–30 cm of soil with those in 0–6 cm to examine how representative this surface measure is with regard to the root zone. Detailed spatial measurements of soil moisture were conducted at three pasture sites in the 50 km 2 Mahurangi River catchment of northern New Zealand as part of a comprehensive hydrology project; MARVEX (MAhurangi River Variability EXperiment). In three field sites, on each of three occasions, field measurements were made using both 30 and 6 cm dielectric-based instruments. Spatial grids of several hundred moisture measurements were collected over 0–30 cm and compared with those collected simultaneously over 0–6 cm. Results indicate that temporal and spatial issues interfere with correlation of the two sets of series. Rapid wetting of 0–6 cm compared with 0–30 cm is seen following storm activity. Some evidence of the decoupling of moisture content response is also evident when sites are measured on days following a storm. Rapid, but not unrealistic, response to intense rainfall was also observed. Implications are that detailed and accurate knowledge of local soil conditions and a sound model of soil water redistribution are required before surface soil moisture measurements can be used to infer root zone behaviour. Such knowledge was not available in this study, from either published data or field observation. In this study, without suitable a priori knowledge, soil property information was found via calibration.