Wet Components Research Articles

New Approaches and Algorithms for the Analysis of Vertical Refractivity Profile Below 1 km in a Subtropical Region

In this communication, 17 years of high resolution surface and radiosonde meteorological data from 1997-2013 for the subtropical Gulf region are analysed. Relationships between the upper air refractivity, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> , and vertical refractivity gradient, ΔN, in the low troposphere and the commonly available data of surface refractivity, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> are investigated. A new approach is discussed to estimate N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> and ΔN from the analysis of the dry and wet components of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , which gives better results for certain cases. Results are compared with those obtained from existing linear and exponential models in the literature. The investigation focusses on three layer heights at 65 m, 100 m and 1 km above ground level. Correlation between the components of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> with both N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> and ΔN are studied for each atmospheric layer. Where high correlations were found, empirical models are derived from best-fitting curves.

Wet multi-disc friction components heat dissipation capability and optimal oil supply under continuous braking condition

Purpose – The purpose of this study is to investigate wet multi-disc brake temperature field and optimal oil supply under continuous braking condition. The oil supply of wet multi-disc brake has a direct impact on the drivability and fuel economy for tracked vehicles. Too small flow will result in the higher temperature and failure of brake while excessive one will lead to slow engagement increasing disengaged torque and the transmission efficiency could decline notably. The optimal oil supply and brake temperature field were obtained in this research. Design/methodology/approach – This article investigated on the heat dissipation capability and optimal oil supply of the brake by the means of CFX model. The working condition was continuous braking and the lubricating and cooling factors were included in the model. Findings – That the complex trends with increased oil flow is inconsistent with the traditional formula in which the effects of grooves were neglected. The fitting curve of optimal oil supply can predict various needed oil flow in various rotating speed and it provides a theoretical guidance for oil supply design. Originality/value – Traditional empirical formula of heat transfer coefficient and Reynolds equation solved by different methods could be difficult to deal with the complex boundary conditions of wet multi-disc brake. CFX model can solve the problem of complex boundary condition. The optimal oil supply curve can provide a theoretical guidance for oil supply design.

Implications for melt transport and source heterogeneity in upwelling mantle from the magnitude of Sp converted phases generated at the onset of melting

AbstractRecently detected converted phases in upwelling mantle have been attributed to seismic velocity gradients at the onset of melting. In this study, we investigate conditions required to generate a melting onset phase by combining melt migration models with synthetic receiver functions. We find that increasing upwelling velocity, increasing mantle viscosity, and decreasing water content in the mantle source increases the predicted strength of a melting onset phase. Differences in these parameters between study regions may explain observed variations in converted phase magnitude. For a wet mantle source, the amplitude of synthetic receiver functions, calculated using a standard relationship for dependence of seismic velocity on melt fraction, is lower than observed amplitudes. One possibility is that the observed receiver functions indicate a heterogeneous mantle source in which wet and dry components melt independently. Alternatively, the dependence of seismic velocity on melt fraction at very low melt fractions may be much stronger than that used here, as suggested in recent studies.

Shale Gas Drives Vertical Integration

Guest editorial The November issue of JPT quotes the views of Mary Van Domelen, senior engineering advisor at Performance Technologies, given in her presentation “The Pros and Cons of Vertical Integration” in shale gas-related operations. All her examples of current activity are in the realm of the vertical with the operator and a service company offering fracturing and other drilling or completion services. Her presentation was part of the SPE Liquids-Rich Basins Conference, held in September 2013 in Midland, Texas. Interestingly, both dry and wet gas can benefit immensely from a different form of vertical integration provided certain new technologies take hold. This is a vertical involving the producer and a service that monetizes low-value portions of fluids in unique ways. Wet Gas Today, almost all the profit is in the wet gas component. But a subplot is that ethane usually makes up nearly half the volume of natural gas liquids (NGLs). Unlike the bigger molecules, such as propane and butane, ethane has no direct use until cracked to make ethylene. Thirty-three of the 36 crackers in the United States are located on the Gulf Coast, about 1,200 miles from the Marcellus shale in Pennsylvania. Consequently, there is an ethane glut, resulting in low prices. Dow Chemical’s David Bem reported in December that ethane dropped to natural gas price levels in 2013 and had begun to track with it (Fig. 1). This would be a windfall for ethylene producers except that the crackers are located at a distance. Local cracking seemed to be where matters were headed. However, early in November 2013, Shell announced that it had shelved plans to build a cracker in Pennsylvania. This leaves the ethane stranded absent a pipeline to transport it down to the Gulf of Mexico. A better solution would be small crackers, 50 to 100 times smaller than conventional plants, distributed close to the production. Development is in progress to realize this “GTL Lite” concept. The definition of liquid in this context is broad: It could be any high-value liquid, not just diesel that traditionally comes from larger GTL plants. Security of supply is much simpler with small units, particularly because a lot of the producers themselves are small. And it is immensely simpler if the producer and cracking process owner are vertically integrated. Even long-term pricing would not be a contractual hurdle. But true vertical integration is hampered by the fact that the producer has no domain understanding of the other area, which is essentially downstream in character. For unconventional hydrocarbons, including heavy oil, a blurring of the upstream, midstream, and downstream sectors is occurring. Small footprint processing, when commonly available, will only serve to hasten this blurring.

Secondary microbial gas formation associated with biodegraded oils from the Liaohe Basin, NE China

A suite of oils and associated gases from the Liaohe Basin NE China, which have similar maturity and source rock origin but with varying degrees of biodegradation, have been analyzed for the molecular compositions of oil and gas as well as for the isotopic values. Isotopic compositions of the gas samples show wide variation (δ13C1 from −55.4‰ to −36.8‰, δ13C2 from −39.4‰ to −28.5‰, δ13C3 from −31.9‰ to −16.4‰ and δ13n-C4 from −26.6‰ to −20.4‰). Most gas samples display clear geochemical evidence of alteration by biodegradation, with relatively high dryness (C1/C1–4>0.97), high ratios of isobutane/n-butane (0.4–1.8) and C2/C3 (0.3–42.3). The carbon isotopic compositions of wet gas components (C3 and C4) in the biodegraded gases are heavier than these in non-biodegraded gases with Δδ13C (C3−C2) of up to 13.4‰, but methane and ethane isotope signatures are variably heavier or lighter than those in non-biodegraded gases. Carbon dioxide contents and isotopic values provide evidence for gas origins. Gases with isotopically heavy carbon dioxide (δ13C>+2‰), and isotopically light methane (δ13C<−50‰) indicate that secondary microbial methane was generated from CO2 reduction under anaerobic conditions. Gases with isotopically heavy methane (>−45‰), together with heavy carbon dioxide (>+8‰), probably indicate a high degree of CO2 conversion to methane under later stages of secondary microbial methane generation. We speculate that the presence of isotopically heavy methane (>−45‰) and isotopically light carbon dioxide (<−8‰) may be indicative of anaerobic methane oxidation but much additional work is needed to evaluate that.It seems likely that most of the variations in isotopic signatures of gases related to biodegraded oil can be described by various sequential biodegradation, carbon dioxide reduction and gas mixing processes. Methanogenesis through carbon dioxide reduction does not necessarily produce isotopically depleted methane. The methane becomes richer in 13C when a large fraction of carbon dioxide is reduced to methane, resulting in newly generated methane that is sometimes heavier than the original thermogenic methane. Anaerobic methane oxidation may exist in the present case study. Mixing of newly generated methane with thermogenic methane already in place in the reservoir, coupled with anaerobic methane oxidation, can result in very complicated isotopic signatures. Care should be taken when gas isotopic values were applied for source and maturity assessment.

The relationship between wet component of atmospheric refractivity and movement and landfall of tropical cyclone in the Bay of Bengal region

In this paper, a simple relationship is employed to investigate the relative impacts on the movement and landfall of tropical cyclone in the Bay of Bengal region when wet component of atmospheric refractivity of different tropospheric levels is used as an input. Four tropical cyclones during pre-monsoon and post-monsoon season over the Bay of Bengal region were selected for the study. The radiosonde/radiowind data of coastal stations, namely Kolkata (Dumdum), Agartala, Bhubaneswar, Visakhapatnam, Machlipatnam, Chennai and Karaikal, were collected for the period of the cyclones under study. The wet component of atmospheric refractivity of different standard levels was plotted against time for the stations for every cyclone. The study suggests that the cyclone moves towards and crosses near the station having a relatively steeper increase in the wet component of atmospheric refractivity up to mid-tropical level. A possible explanation is also presented.

An investigation into the correlations among GNSS observations and their impact on height and zenith wet delay estimation for medium and long baselines

Most stochastic modelling techniques neglect the correlations among the raw un-differenced observations when forming the variance–covariance matrix of the Global Navigation Satellite System (GNSS) observations. Some methods were developed to model these correlations. One such method is the Minimum Norm Quadratic Unbiased Estimator (MINQUE). Studies have shown that MINQUE improves ambiguity resolution, and ultimately, the positioning solution in short baselines. However, its effect in cases of processing with longer baselines and on the estimation of zenith wet delay (ZWD) is somewhat unknown. In this paper, a comparison between the impact of neglecting the correlations among the observations using an elevation-angle-dependent model (EADM) and modelling the correlations using MINQUE on height determination and ZWD for medium and long baselines is carried out. The initial testing was carried out across two Australian GNSS stations with a medium-length baseline throughout a three-week campaign. The results showed that using MINQUE did not resolve the coordinate, height and wet delay components as accurately as the EADM. The results were further verified with two long-baseline campaigns whereby EADM was also able to provide better wet delay estimates. The coordinate results were, however, mixed. Overall, the study concluded that the inclusion of the correlations among the observations, in general, do not improve the resolution of the coordinate and wet delay estimates.

Absolute radiometric calibration of the KOMPSAT-2 multispectral camera using a reflectance-based method and empirical comparison with IKONOS and QuickBird images

This paper presents absolute radiometric calibration coefficients (gains) that explain the relationship between the digital number (DN) and at-sensor radiance for the multispectral camera (MSC) on Korea's first high-resolution satellite (KOMPSAT-2). Absolute radiometric calibration was performed using a reflectance-based method. In addition, the suitability of vicarious results from radiance- and reflectance-based validations was analyzed with reference to IKONOS and QuickBird images. The latter are spectrally similar to KOMPSAT-2 images and have been validated in a large number of studies. For all bands, the R 2 values of fitted lines for the gain ranged from 0.82 to 0.94, representing an improvement compared to previous findings for the KOMPSAT-2 MSC. To analyze the suitability of the vicarious results, same-pixel at-sensor radiances across different spectral bands were compared. In all bands, except the red band of QuickBird, the at-sensor radiances of KOMPSAT-2 MSC were highly correlated with those of IKONOS and QuickBird. In addition, same-pixel comparisons of reflectance across different spectral bands showed that the slopes of the least-squares lines for each band were similar to the results of the radiance comparison. The standard deviation among top of atmosphere (TOA) reflectances was within 0.019 for all bands. To calculate the tasseled cap transformation (TCT) coefficients for the KOMPSAT-2 MSC, an empirical method was applied using radiometric normalization. The results were similar to those obtained using the TCT coefficients for IKONOS and QuickBird in the brightness, greenness, and wetness components. The TCT images showed similar patterns. The absolute radiometric calibration coefficients presented here appear to be a good standard for maintaining the optical quality of the KOMPSAT-2 MSC, for which prelaunch, on-board, and vicarious calibration data are lacking.

Tropospheric delays from GNSS for application in coastal altimetry

In the scope of the development of an improved methodology for the computation of the wet tropospheric correction for coastal altimetry, based on the use of tropospheric delays derived from GNSS (Global Navigation Satellite Systems), various studies have been conducted aiming to improve the estimation, at global scale, of GNSS-derived tropospheric delays.Amongst these studies, two are presented in this paper: (1) a global assessment of zenith total delays (ZTD) determined at international data centres such as EPN (EUREF Permanent Network) and IGS (International GNSS Service) by comparison with ZTD solutions computed at the University of Porto (U.Porto) using state-of-the-art methodologies and ZTD estimated from ERA Interim, the latest reanalysis dataset from ECMWF (European Centre for Medium-Range Weather Forecasts), (2) evaluation of the accuracy of the hydrostatic component of the tropospheric delay (zenith hydrostatic delay, ZHD) estimation from different sources of surface pressure.When compared with ERA Interim, both IGS and U.Porto ZTD are homogeneous with a mean standard deviation of the differences, for all analysed sites, of 12mm. The U.Porto and IGS ZTD agree within 4mm (1σ), while for EPN the same result is only valid for the period after November 2006. Before that date, the EPN solutions are slightly degraded and require an adequate correction.Aiming to evaluate the accuracy of ZHD determination from various sources of atmospheric pressure, a study is presented that compares ZHD values determined with in situ measurements of surface pressure at a global set of 63 coastal barometric sites (GNSS stations), the corresponding values obtained from ECMWF operational model, ERA Interim sea level pressure (SLP) and ZHD from the Vienna Mapping Functions 1 (VMF1).Results show that the global grids of sea level pressure provided by ECMWF operational model, either at 0.25° or 0.125° spacing, or the ERA Interim reanalysis product at 1.5°, allow the estimation of the hydrostatic component of the tropospheric delay with an accuracy of 1 to 3mm at global scale, provided an adequate model for the height dependence of atmospheric pressure is adopted. In comparison, for VMF1 grids provided at 2.5° spacing, although the overall accuracy of ZHD estimation is 2–4mm in most sites, in regions with high variability and strong seasonal signal in the surface pressure, VMF1 can reveal errors with a clear annual pattern and epochs for which the error exceeds the centimetre level. When used to estimate the wet component of the tropospheric delay (zenith wet delay, ZWD) for coastal altimetry, these errors can translate into errors of similar magnitude in sea level studies.

A method of mapping forest fuel types in peat swamp forest

In response to growing concerns over the burning of peat swamp forests, researchers have begun developing methods of mapping forest fire. Forest fire is one of the major causes of deforestation of tropical peat swamps in Malaysia. A way of identifying which peat swamp forest is vulnerable to forest fire is to develop a fuel type map to classify forest fire into different risk levels. In this study, remote sensing and geographical information system (GIS) techniques were integrated. Landsat Thematic Mapper (TM) image dated April 3rd, 1999, which corresponded to fire incident in this study area was used. The objective of this paper is to map fuel types in peat swamp forests. Results show that greenness and wetness components of Tasselled cap, used in classification, accurately captured greener and wetter area by combining supervised image and Tasselled cap image. The overall kappa statistics was 0.94 for combined supervised and Tasselled Cap classification. High values of kappa statistics for certain vegetation classes were due to the availability of representative pixels in the classes.

The effects of pyrobitumen on oil cracking in confined pyrolysis experiments

Three sets of pyrolysis experiments were performed for oil alone, pyrobitumen alone and oil plus pyrobitumen at two heating rates of 2°C/h and 20°C/h in confined systems (gold capsules). The results of these experiments demonstrated that pyrobitumen significantly promoted the generation of methane while not only inhibiting the generation, but also accelerating the cracking of wet gases during oil cracking experiments in confined systems. Furthermore, the cracking rate of wet gases increases with pyrobitumen/oil ratios. As a result, C1/ΣC1–5 ratio is significantly higher in the experiment of oil plus pyrobitumen than oil alone at the same temperature conditions. Although the amount of methane increased, the weight of the total gaseous hydrocarbons decreased and the volume of the total gaseous hydrocarbons remained unchanged with the addition of pyrobitumen. This result can be ascribed to some oil and wet gas components being combined with the pyrobitumen phase and released later mainly as methane at higher temperatures and maturities. The activation energies for the generation and cracking of wet gases decrease with the carbon number and are relatively lower in the experiments of oil plus pyrobitumen than oil alone. The distribution ranges of the activation energies for the generation of wet gases also decrease with the carbon number.

Microbial Processes and Natural Gas Accumulations

Microbial processes are responsible for the formation, alteration, and destruction of some natural gas accumulations. Individual microbial gas accumulations may be significant (> 1 Tcf; trillion cubic feet or 28.3 billion cubic meters) and collectively account for more than 20% of the global gas resource-base, dominating in some individual basins. Often cited resource estimates do not effectively account for the contribution of microbial gas to mixed biogenic- thermogenic gases nor do these estimates fully account for secondary microbial gas. Microbial gas accumulations form through multiple stages, initiating with the breakdown of large macromolecules into smaller components that the methanogens can effectively utilize as an energy source. There are two primary methanogenic pathways, acetate fermentation and CO2 reduction, both of which may utilize sedimentary organic matter or preexisting oil accumulations as a source. Microbial gas is typically considered dry (i.e., depleted in C2+ components), but there is clear evidence that ethane and possibly propane may also form through microbial processes. Numerous authors have provided guidance on the conditions that favor primary microbial gas formation and accumulation including: an anoxic setting, high rates of sedimentation, formation of early traps, low temperatures, favorable migration history, and limited availability of sulfate. Scenarios conducive with secondary microbial gas accumulations have also been discussed. These include the presence of a significant oil pool that can be biodegraded or a coal or organic-rich shale that has achieved thermal maturity levels approaching or beyond the top of the oil-window, which have been uplifted, fractured, and invaded by meteoric water to reintroduce a microbial population. Gas accumulations may also be biodegraded. Biodegradation results in the preferential removal of C3-5 n-alkanes, leaving isotopically heavier residuals. Ethane is relatively resistant to biodegradation compared to the C3+ homologues. At more advanced levels of biodegradation, the wet gas components are removed yielding a dry gas. As with the biodegradation of oil, the biodegradation of a gas accumulation results in a reduction of the resource-base. The molecular and isotopic compositional changes induced by bacterial alteration of gas accumulations can often complicate their interpretation suggesting more advanced levels of thermal maturity.

Neural Networks for Arctic Atmosphere Sounding From Radio Occultation Data

This paper illustrates a procedure for the retrieval of tropospheric profiles (temperature, pressure, and humidity) using only refractivity profiles coming from Global Positioning System (GPS)-low-Earth-orbit radio occultation, without the constraint of independent knowledge of atmospheric parameters at each GPS occultation. In order to achieve this goal, we have used an approach based on neural networks (NNs), exploiting a data set of 1106 occultations collected over the Arctic region during the winter season of 2007 and 2008. Total refractivity (N) profiles from Formosa Satellite 3 (FORMOSAT-3)/Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) satellites have been used as input for training the NNs, whereas the target profiles of dry and wet components (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> ) were derived using prior information on dry and wet fractions of the total refractivity provided by the analysis of the European Centre for Medium-Range Weather Forecast (ECMWF). Once we have retrieved N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> by the trained networks, the other atmospheric parameters (pressure, temperature, and vapor) can be computed, and we have done so relative to colocated ECMWF data, which we have assumed as atmospheric truth. Finally, some comparisons with radiosonde observations (RAOBs) are shown, and performances and potential of the proposed approach are discussed. Profiles computed using 1-D variational retrieval by the COSMIC Data Analysis and Archive Center have also been considered as a benchmark in the RAOB comparison.

3-D IMAGING, ANALYSIS AND MODELLING OF POROUS CEREAL PRODUCTS USING X-RAY MICROTOMOGRAPHY

Efficient design of multi-component food products containing dry and wet components such as biscuits with a moist fruit filling, is of growing interests for food industry. Technology is needed to prevent or reduce water migration from the moist filling to the dry porous cereal material. This can be done by using moisture barrier systems. Knowledge of the microstructure and its relation to water mobility is necessary to develop stable products. This paper describes a study that uses X-ray microtomography (μCT) for the characterisation and visualisation of the 3-D structure of crackers with different porosity, coated biscuit shells and soup inclusions. μCT was used for imaging the inner cellular structure of the cereal matrix or to analyse the integrity of moisture barriers applied on the cereal product. 3-D image analysis methods were developed to obtain quantitative information about the cellular matrix which can be used as input for simulation models for moisture migration. The developed 3-D image analysis method maps the open cellular structure onto a network (graph) representation in which the nodes correspond to the pores and the vertices to the pore-topore interconnection. The pores (nodes) have properties such as volume, surface area and location whereas the vertices have properties such as direct (open connection) and indirect (separated by a single lamella) area. To check the segmentation and network description a model for pore to pore resistance was used. The obtained results demonstrate the potential of μCT and 3-D image analysis for extracting structural information which can be used in models for the moisture penetration in a cellular bakery product.

Gas genetic type and origin of hydrogen sulfide in the Zhongba gas field of the western Sichuan Basin, China

Abstract Natural gases and associated condensate oils from the Zhongba gas field in the western Sichuan Basin, China were investigated for gas genetic types and origin of H 2 S by integrating gaseous and light hydrocarbon geochemistry, formation water compositions, S isotopes (δ 34 S) and geological data. There are two types of natural gas accumulations in the studied area. Gases from the third member of the Middle Triassic Leikoupo Formation (T 2 l 3 ) are reservoired in a marine carbonate sequence and are characterized by high gas dryness, high H 2 S and CO 2 contents, slightly heavy C isotopic values of CH 4 and widely variable C isotopic values of wet gases. They are highly mature thermogenic gases mainly derived from the Permian type II kerogens mixed with a small proportion of the Triassic coal-type gases. Gases from the second member of the Upper Triassic Xujiahe Formation (T 3 x 2 ) are reservoired in continental sandstones and characterized by low gas dryness, free of H 2 S, slightly light C isotopic values of CH 4 , and heavy and less variable C isotopic values of wet gases. They are coal-type gases derived from coal in the Triassic Xujiahe Formation. The H 2 S from the Leikoupo Formation is most likely formed by thermochemical SO 4 reduction (TSR) even though other possibilities cannot be fully ruled out. The proposed TSR origin of H 2 S is supported by geochemical compositions and geological interpretations. The reservoir in the Leikoupo Formation is dolomite dominated carbonate that contains gypsum and anhydrite. Petroleum compounds dissolved in water react with aqueous SO 4 species, which are derived from the dissolution of anhydrite. Burial history analysis reveals that from the temperature at which TSR occurred it was in the Late Jurassic to Early Cretaceous and TSR ceased due to uplift and cooling thereafter. TSR alteration is incomplete and mainly occurs in wet gas components as indicated by near constant CH 4 δ 13 C values, wide range variations of ethane, propane and butane δ 13 C values, and moderately high gas dryness. The δ 34 S values in SO 4 , elemental S and H 2 S fall within the fractionation scope of TSR-derived H 2 S. High organo-S compound concentrations together with the occurrence of 2-thiaadamantanes in the T 2 l reservoir provide supplementary evidence for TSR related alteration.

Atmospheric turbulence in phase-referenced and wide-field interferometric images

Phase referencing is a standard calibration procedure in radio interferometry. It allows to detect weak sources by using quasi-simultaneous observations of closeby sources acting as calibrators. Therefore, it is assumed that, for each antenna, the optical paths of the signals from both sources are similar. However, atmospheric turbulence may introduce strong differences in the optical paths of the signals and affect, or even waste, phase referencing for cases of relatively large calibrator-to-target separations and/or bad weather. The situation is similar in wide-field observations, since the random deformations of the images, mostly caused by atmospheric turbulence, have essentially the same origin as the random astrometric variations of phase-referenced sources with respect to the phase center of their calibrators. In this paper, we present the results of a Monte Carlo study of the astrometric precision and sensitivity of an interferometric array (a realization of the Square Kilometre Array, SKA) in phase-referenced and wide-field observations. These simulations can be extrapolated to other arrays by applying the corresponding corrections. We consider several effects from the turbulent atmosphere (i.e., ionosphere and wet component of the troposphere) and also from the antenna receivers. We study the changes in dynamic range and astrometric precision as a function of observing frequency, source separation, and strength of the turbulence. We find that, for frequencies between 1 and 10 GHz, it is possible to obtain images with high fidelity, although the atmosphere strongly limits the sensitivity of the instrument compared to the case with no atmosphere. Outside this frequency window, the dynamic range of the images and the accuracy of the source positions decrease. [...] (Incomplete abstract. Please read manuscript.)

Measurement Analysis of Amplitude Scintillation for Terrestrial Line-of-Sight Links at 42 GHz

Tropospheric scintillation is a rapid fluctuation of the signal amplitude and phase due to irregularities in the refractive index caused by atmospheric turbulence. If not considered properly, amplitude scintillation may affect the performance of a low-power margin communication system. In this paper we study the amplitude scintillation observed on three converging terrestrial 42 GHz links. Probability density functions of amplitude scintillation for different seasons of a year are presented. In addition, the cumulative distributions of the dry and wet amplitude scintillation are shown. The measured long-term probability density functions of the three links are compared with the Moulsley-Vilar model. The results show that for small values of amplitude scintillation the Moulsley-Vilar model fits well the measured statistics, but overestimates the statistics for large values of amplitude scintillation. Good agreements are found between the Gaussian model and the measured short-term amplitude scintillation distributions. In addition, the link diversity of amplitude scintillation over combinations of two and three links are presented. Furthermore, the monthly average wet component of refractivity has been calculated using meteorological measurements, and as expected it shows a peak during the summer time.

Effects of wildfires on environmental variability: a comparative analysis using different spectral indices, patch metrics and thematic resolutions

Knowledge on environmental variability and how it is affected by disturbances is crucial for understanding patterns of biodiversity and determining adequate conservation strategies. The aim of this study is to assess environmental variability in patches undergoing post-fire vegetation recovery, identifying trends of change and their relevant drivers. We particularly evaluate: the value of three spectral indices derived from Landsat satellite data [Normalized Burn Ratio (NBR), Normalized Difference Vegetation Index (NDVI) and Wetness Component of the Tasseled Cap Transformation (TCW)] for describing secondary succession; the effectiveness of three metrics (diversity, evenness and richness) as indicators of patch variability; and how thematic resolution can affect the perception of environmental variability patterns. While the system was previously characterised as highly resilient from estimations of vegetation cover, here we noted that more time is required to fully recover pre-fire environmental variability. Using mean diversity as indicator of patch variability, we found similar patterns of temporal change for the three spectral indices (NBR, NDVI and TCW). Analogous conclusions could be drawn for richness and evenness. Patch variability, measured as diversity, showed consistent patterns across thematic resolutions, although values increased with the number of spectral classes. However, when the variance of diversity was plotted against thematic resolution, different scale dependencies were detected for those three spectral indices, yielding a dissimilar perception of patch variability. In general terms, NDVI was the best performing spectral index to assess patterns of vegetation recovery, while TCW was the worst. Finally, burned patches were classified into three classes with similar trends of change in environmental variability, which were strongly related to fire severity, elevation and vegetation type.

Remote sensing derived edge location, magnitude, and class transitions for ecological studies

Regionally intensive human activities related to resource extraction (i.e., harvesting, oil and gas extraction) are increasing the occurrence of edges found in some forested landscapes. Edges between different land cover types represent important transition zones for abiotic and biotic processes. However, boundary detection methods often identify edges solely in areas of high contrast, such as transitions between forest and non-forest areas, and are insensitive to the relative contrast and orientation of different transitions. Edge contrast and orientation can determine the magnitude and even the occurrence of ecological edge effects and should be measured to provide information on landscape condition and habitat potential. Wombling was applied to the wetness component of a tasselled cap transformation (TCT) of a Landsat scene acquired over a portion of the eastern slopes of the Rocky Mountains in Alberta, Canada. By incorporating wombled edge contrast and orientation, and edge class transition type obtained from a land cover dataset, the nature of all transitions between land cover classes within the image was characterized and quantified. The consistency between edges identified by wombling and other common methods of edge delineation (such as spatial clustering) and methods of edge quantification (such as landscape pattern indices, or LPIs) was also assessed. Land cover transitions showed a broad range of edge contrast. Comparisons of edge contrast and the LPI edge density showed a positive correlation (r2 = 0.33); however, the strength of this relationship varied with the dominant land cover type (e.g., r2 = 0.016 for broadleaf open forest to r2 = 0.48 for dense coniferous forest). Stratifying edge contrast to higher values (i.e., >1 standard deviation) increased agreement with edge density, indicating that the LPI is preferentially relating high contrast edges. This study demonstrates how unique edge characteristics may be generated from a remotely sensed continuous variable (TCT wetness). This knowledge of the location, magnitude, and class transitions found at edges provides insights into the nature of the edge effects and enables the development and testing of hypotheses informing wildlife habitat use and selection.

Origins of chemical diversity of back‐arc basin basalts: A segment‐scale study of the Eastern Lau Spreading Center

We report major, trace, and volatile element data on basaltic glasses from the northernmost segment of the Eastern Lau Spreading Center (ELSC1) in the Lau back‐arc basin to further test and constrain models of back‐arc volcanism. The zero‐age samples come from 47 precisely collected stations from an 85 km length spreading center. The chemical data covary similarly to other back‐arc systems but with tighter correlations and well‐developed spatial systematics. We confirm a correlation between volatile content and apparent extent of melting of the mantle source but also show that the data cannot be reproduced by the model of isobaric addition of water that has been broadly applied to back‐arc basins. The new data also confirm that there is no relationship between mantle temperature and the wet melting productivity. Two distinct magmatic provinces can be identified along the ELSC1 axis, a southern province influenced by a “wet component” with strong affinities to arc volcanism and a northern province influenced by a “damp component” intermediate between enriched mid‐ocean ridge basalts (E‐MORB) and arc basalts. High–field strength elements and rare earth elements are all mobilized to some extent by the wet component, and the detailed composition of this component is determined. It differs in significant ways from the Mariana component reported by E. Stolper and S. Newman (1994), particularly by having lower abundances of most elements relative to H2O. The differences can be explained if the slab temperature is higher for the Mariana and the source from which the fluid is derived is more enriched. The ELSC1 damp component is best explained by mixing between the wet component and an E‐MORB‐like component. We propose that mixing between water‐rich fluids and low‐degree silicate melts occurs at depth in the subduction zone to generate the chemical diversity of the ELSC1 subduction components. These modified sources then rise independently to the surface and melt, and these melts mix with melts of the background mantle from the ridge melting regime to generate the linear data arrays characteristic of back‐arc basalts. The major and trace element framework for ELSC1, combined with different slab temperatures and compositions for difference convergent margins, may be able to be applied to other back‐arc basins around the globe.