Requirements of a global near-surface soil moisture satellite mission: accuracy,repeat time,and spatial resolution

Soil moisture satellite mission accuracy, repeat time and spatial resolution requirements are addressed through a numerical twin data assimilation study. Simulated soil moisture profile retrievals were made by assimilating near-surface soil moisture observations with various accuracy (0, 1, 2, 3, 4, 5 and 10%v/v standard deviation) repeat time (1, 2, 3, 5, 10, 15, 20 and 30 days), and spatial resolution (0.5, 6, 12 18, 30, 60 and 120 arc-min). This study found that near-surface soil moisture observation error must be less than the model forecast error required for a specific application when used as data assimilation input, else slight model forecast degradation may result. It also found that near-surface soil moisture observations must have an accuracy better than 5%v/v to positively impact soil moisture forecasts, and that daily near-surface soil moisture observations achieved the best soil moisture and evapotranspiration forecasts for the repeat times assessed, with 1–5 day repeat times having the greatest impact. Near-surface soil moisture observations with a spatial resolution finer than the land surface model resolution (∼30 arc-min) produced the best results, with spatial resolutions coarser than the model resolution yielding only a slight degradation. Observations at half the land surface model spatial resolution were found to be appropriate for our application. Moreover, it was found that satisfying the spatial resolution and accuracy requirements was much more important than repeat time.     

Trace Elements in Sediments and Mussels – Spatial Distribution,Chemical Partitioning,and Risk Assessment

Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.     

Erratum: Trace Elements in Sediments and Mussels – Spatial Distribution,Chemical Partitioning,and Risk Assessment

Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.     

Effect of pricing policy on water conservation: a case study

The main source of water for Abu Dhabi City is desalinated seawater from the Arabian Gulf. The cost of water production through desalination is higher than other conventional methods of potable water production. In spite of all awareness campaigns to advise the consumers in Abu Dhabi of the importance of the water and its high cost, the average consumption rate is still one of the highest in the world (636 1/cap d). This means that, with respect to water, the worst combination of conditions are existing in Abu Dhabi (high consumption rate and high production cost).As a result, the Water and Electricity Department (WED) of Abu Dhabi (now it is a private company) which is the Department responsible for water production, transmission and distribution, has decided to change the pricing policy of water. The new policy is based on fixing meters in buildings and charging the consumers for the actual amount of water consumed, instead of a system which was based on a flat rate of 50 Dhs per month (1 US$=3.7 Dhs) irrespective of the amount of consumption.This paper attempts to evaluate the effect of introducing the new pricing mechanism in Abu Dhabi City, and compares it with the old flat rate tariff. The water consumption of randomly selected 90 households with different socio-economic levels were analyzed before and after introducing the new pricing system. As a result of the new pricing policy, 73% of the households in the sample reduced their consumption by an average of 29%. The calculated price elasticity of demand revealed an elasticity coefficient e=−0.1. The new price of water (2.2 Dhs/m³) accounts for only 29% of the total cost to produce and supply the water to consumer taps.     

Control of preexisting faults and near-surface diapirs on geometry and kinematics of fold-and-thrust belts (Internal Prebetic,Eastern Betic Cordillera)

We have determined, for the first time, the 3D geometry of a sector of the eastern Internal Prebetic comprised between Parcent and Altea diapirs, combining structural, borehole and multichannel seismic reflection data. The tectonic structure of the Jurassic-Cretaceous carbonate series is characterized by regional ENE-WSW fold-and-thrusts that interact with oblique N-S and WNW-ESE folds, detached over Triassic evaporites and clays. The structural style comprises box-shape anticlines, and N-vergent anticlines with vertical to overturned limbs frequently bordered by reverse and strike-slip faults. The anticlines surround a triangular broad synclinal structure, the Tárbena basin, filled by a late Oligocene to Tortonian sedimentary sequence that recorded folding and thrusting history. The location and geometrical characteristics of fold-and-thrusts may be controlled by the positive inversion of pre-existing Mesozoic normal faults, and by the position and shape of near-surface diapirs composed of Triassic rocks. Therefore, we propose an initial near-surface diapir emplacement of Triassic evaporitic rocks driven by late Jurassic to early Cretaceous rifting of the southern Iberian paleomargin. Thrusting and folding started during the latest Oligocene (∼28–23 Ma) roughly orthogonal to the NW-directed shortening. Deformation migrated to the south during Aquitanian (∼23–20 Ma), when tectonic inversion implied the left-lateral transpressive reactivation of N-S striking former normal faults and right-lateral/reverse reactivation of inherited WNW-ESE faults. We show two mechanisms driving the extrusion of the diapirs during contraction: lateral migration of a pre-existing near-surface diapir associated with dextral transpression; and squeezing of a previous near-surface diapir at the front of an anticline. Our study underlines the value of 3D geological modeling to characterize geometry and kinematics of complex fold-and-thrust belts influenced by preexisting faults and near-surface diapirs.     

近地表强衰减介质中的地震波传播模型

建立符合油气储层近地表复杂介质强衰减性质的数学-物理模型是油气勘探和开发的重要课题.本文针对D'Alembert黏弹性介质模型存在的量纲不统一和不能充分刻画孔隙介质结构的不足,通过引入孔隙度和渗透率等参数修改耗散项,改进了原D'Alembert模型,获得了能精细刻画具有强吸收衰减特征的近地表复杂介质模型,即改进的近地表黏弹性模型.基于这种改进的模型,推导了波频散和衰减的表达式,并研究了孔隙度、流体黏度等物理参数对波频散和衰减的影响,获得了相应的规律性认识.为了验证新模型预测近地表介质中波衰减的有效性,本文将新模型应用于胜利油田YX工区的近地表实测数据,同时与弹性Biot模型和BISQ模型以及黏弹性BISQ模型进行了比较.结果表明,与其它三个模型比较,改进的近地表黏弹性模型能够很好地刻画近地表介质的强衰减性,而且新模型所涉及到的物理参数明显少于其它几种模型,有利于新模型在油气储层近地表复杂介质地震勘探的实际应用.

     

地震干涉测量法近地表散射波分离技术

针对山地地震勘探数据低信噪比问题,近地表散射波分离意义显得尤为突出,地震干涉测量法为此提供了一种技术手段.本文将地震干涉测量理论和散射理论结合起来,导出了近地表散射波地震干涉测量表达式,分为互相关型和褶积型表达式,它们由实际波场和背景波场干涉测量构成.根据近地表散射波分离理论,结合陆上地震勘探实际观测系统,采用褶积和反褶积混合型地震干涉测量配置,用实际地震资料展示了近地表散射波分离技术的应用效果.经过理论分析和砾石区实际资料试验,表明地震干涉测量不仅能分离测线上散射源产生的散射波,而且能分离部分侧面散射波.该技术的优点在于它适应于起伏地形和不均匀近地表结构,并且不需要起伏地形和近地表速度信息.为了从实际资料中消除近地表散射波,本文采用多道匹配滤波自适应减法,在砾石区见到较好效果.     

Contribution of satellite altimetry data in the geophysical investigation of the Red Sea Region, Egypt

Successful development of geodetic satellite missions has aroused new interest in determining global and regional gravity field based on satellite data. Satellite altimetry data enable direct determination of the geoid over sea regions. In Egypt, where land and marine geophysical data are inadequate because of rough topography and economic reasons, the use of satellite altimetry data is of special importance. The northern Red Sea region has been selected as a site for case study of the current research, after applying spectral analysis to reveal near-surface structure, the residual geoid of the studied region shows a good correlation with the known geologic features. Moreover, satellite-based gravity data enhance small-scale features and agrees well with land and marine gravity data. Thus, geoid undulation and satellite gravity data can be a complementary source of data to determine near-surface and deep structures.     

Atmospheric anomalies and anomalies of electricity in the near-surface atmosphere before the Kamchatka earthquake of January 30, 2016, based on the data from the Paratunka Observatory

The 15-min data of vertical ionosphere sounding and 10-min data from measurements of the vertical component (Ez) of the near-surface quasistatic atmospheric electrical field and the respective values of electrical conductance of near-surface air at the Paratunka complex geophysical observatory in the period from January 28 to January 30, 2016 have been analyzed to reveal the possible anomalies preceding the M = 7.2 earthquake that occurred on January 30, 2016, at 0325 UT. The distance between the observatory and epicenter was 117 km. These anomalies have been revealed, and the majority of them, in our opinion, may be related to the processes of earthquake preparation.     

Near-surface velocity model construction based on a Monte-Carlo scheme

In tomographic statics seismic data processing, it is crucial to determine an optimum base for a near-surface model. In this paper, we consider near-surface model base determination as a global optimum problem. Given information from uphole shooting and the first-arrival times from a surface seismic survey, we present a near-surface velocity model construction method based on a Monte-Carlo sampling scheme using a layered equivalent medium assumption. Compared with traditional least-squares first-arrival tomography, this scheme can delineate a clearer, weathering-layer base, resulting in a better implementation of datuming correction. Examples using synthetic and field data are used to demonstrate the effectiveness of the proposed scheme.     

VTI介质初至波多参数走时反演敏感核分析及反演策略

利用地震初至波走时信息建立近地表模型是地震勘探的关键步骤.由于近地表模型普遍呈现各向异性特征, 常规的各向同性近地表建模无法满足地震数据近地表校正和地下成像的需要, 因此, 发展各向异性介质的初至波走时多参数反演方法具有重要的理论意义和实际应用价值.本文基于Fomel群速(慢)度近似公式, 推导得到了声波VTI介质中16种参数化模式的走时多参数反演敏感核的解析解, 并详细分析了4种参数化模式下多参数敏感核随角度的变化特征.通过分析多参数的敏感核和多参数之间的耦合效应, 提出了在全方位和地表两种观测方式下最优的参数化方式和有效的多参数反演策略, 并通过理论分析和模型试验, 证明了所提出的反演策略的合理性和正确性.

     

Geophysical methods in drinkwater protection of near-surface reservoirs

Two case histories are presented in which near-surface water-bearing formations and their overburden are examined. This survey utilized a combination of traditional geoelectric methods (direct current resistivity and time domain induced polarization) and a special shallow-depth engineering geophysical sounding method. This latter method was developed in Hungary to investigate near-surface unconsolidated formations such as clay, silt, sand, gravel and other similarly “penetratable” formations.For a gravel terrace, in addition to the usual parameter maps (resistivity, thickness, polarizability), combined multiparametric characterization maps have been plotted. These maps illustrate the hydrogeologic value of the water-bearing formations and the protecting capacity of the overburden better than the conventional parameter maps.Surface measurement results together with filtration coefficient values show how an inexpensive geophysical survey can successfully be applied in estimating the dangerous or protected situation of near-surface reservoirs and how such a survey can be used for siting reservoirs. This work enabled the near-surface geological structure to be determined, hereby providing orientation for more expensive, highly detailed surveys.     

起伏地表采集数据的三维直接叠前时间偏移方法

提出一种可对起伏地表采集的三维地震资料直接进行偏移成像的叠前时间偏移方法和流程.它用两个等效速度描述近地表和上覆层对地震波传播的影响,可对炮、检点不在同一水平面的三维地震资料直接进行叠前时间偏移处理.该方法不对近地表地震波传播做垂直出、入射假定,因此可适应高速层出露等不存在明显低、降速带情况.描述近地表和上覆层的两个等效速度参数可依据偏移道集的同相轴是否平直来确定,避免了确定近地表速度的困难;而对已知近地表速度的情况,则可进一步修正近地表速度,获得更好的成像效果.用三维起伏地表的理论数据和中国东部某工区实际数据验证了所发展方法和处理流程的有效性和实用性.     

Near-surface layer traveltime inversion: a synthetic example1

The near-surface layer is modelled as a constant-velocity layer with varying thickness. The base of the layer is described by a B-spline curve. The optimum model is calculated by minimizing, with respect to the model parameters, the difference between traveltimes predicted by the model and those observed in the data. Once a model has been produced, corrections that are dependent on the raypath geometry through the near-surface layer can be calculated. The effect of the near-surface layer is normally considered to be consistent at each shot or geophone station for all traveltimes arriving at that location (the surface-consistent approximation). This assumption linearizes the problem, allowing timeshifts to be calculated and the traveltimes corrected to a chosen datum, representing static corrections. The single correction at each point is an averaged correction, based on an assumption that is particularly inaccurate in the presence of lateral variations of velocity or thickness of the surface layer, in the presence of large surface layer velocities or in the presence of a thick surface layer. The method presented considers the non-linear relationship between data and model explicitly, hence the correction that is dependent on the raypath. Linearization removes this dependence and reduces the problem to a surface-consistent approximation. The method is applied to synthetic data calculated from a model with surface layer variations. Comparisons are made between the corrected data resulting from the method described here and the conventional surface-consistent approach. From these results it becomes apparent that the near-surface layer inversion method presented here can reproduce accurate models and correct for near-surface layer effects in cases where conventional methods encounter difficulties. Additionally the method can be readily extended to 3D.     

Relationship between soil moisture of near surface and multiple depths of the root zone under heterogeneous land uses and varying hydroclimatic conditions

This paper presents an assessment of the relationship between near-surface soil moisture (SM) and SM at other depths in the root zone under three different land uses: irrigated corn, rainfed corn and grass. This research addresses the question whether or not near-surface SM can be used reliably to predict plant available root zone SM and SM at other depths. For this study, a realistic soil-water energy balance process model is applied to three locations in Nebraska representing an east-to-west hydroclimatic gradient in the Great Plains. The applications were completed from 1982 through to 1999 at a daily time scale. The simulated SM climatologies are developed for the root zone as a whole and for the five layers of the soil profile to a depth of 1·2 m. Over all, the relationship between near-surface SM (0–2·5 cm) and plant available root zone SM is not strong. This applies to all land uses and for all locations. For example, r estimates range from 0·02 to 0·33 for this relationship. Results for near-surface SM and SM of several depths suggest improvement in r estimates. For example, these estimates range from − 0·19 to 0·69 for all land uses and locations. It was clear that r estimates are the highest (0·49–0·69) between near-surface and the second layer (2·5–30·5 cm) of the root zone. The strength of this type of relationship rapidly declines for deeper depths. Cross-correlation estimates also suggest that at various time-lags the strength of the relationship between near-surface SM and plant available SM is not strong. The strength of the relationship between SM modulation of the near surface and second layer over various time-lags slightly improves over no lags. The results suggest that use of near-surface SM for estimating SM at 2·5–30 cm is most promising. Copyright © 2007 John Wiley & Sons, Ltd.     

A Seasonal Statistical Evaluation of COAMPS® over the Arabian Gulf Region

A statistical evaluation of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS^®) was performed over the Arabian Gulf region for the period, 1 August to 5 October, 2004. Verification skill scores of bias and root-mean-square error were estimated for surface variables and for vertical profiles to investigate any diurnal variations. The model predictions of boundary-layer heights are compared with the observations at Abu Dhabi, United Arab Emirates. The Middle East presents challenges to numerical weather prediction due to complex land-ocean-land mesoscale processes. An independent data set of surface measurements from 50 stations in the UAE was available from the Department of Water Resources Studies, Abu Dhabi for model verification. The results indicate a diurnal variation in the model errors. The errors are small considering the magnitudes of the observed variables. Errors in the coastal region can be attributed to the differences in the timing of the onset of sea and land breeze circulations in the simulations as compared to the observations. Errors are relatively smaller in the offshore locations.     

Contributions to a shallow aquifer study by reprocessed seismic sections from petroleum exploration surveys, eastern Abu Dhabi, United Arab Emirates

The US Geological Survey, in cooperation with the National Drilling Company of Abu Dhabi, is conducting a 4-year study of the fresh and slightly saline groundwater resources of the eastern Abu Dhabi Emirate. Most of this water occurs in a shallow aquifer, generally less than 150 m deep, in the Al Ain area. A critical part of the Al Ain area coincides with a former petroleum concession area where about 2780 km of vibroseis data were collected along 94 seismic lines during 1981–1983. Field methods, acquistion parameters, and section processing were originally designed to enhance reflections expected at depths ranging from 5000 to 6000 m, and subsurface features directly associated with the shallow aquifer system were deleted from the original seismic sections. The original field tapes from the vibroseis survey were reprocessed in an attempt to extract shallow subsurface information (depths less than 550 m) for investigating the shallow aquifer.A unique sequence of reproccessing parameters was established after reviewing the results from many experimental tests. Many enhancements to the resolution of shallow seismic reflections resulted from: (1) application of a 20-Hz, low-cut filter; (2) recomputation of static corrections to a datum nearer the land surface; (3) intensive velocity analyses; and (4) near-trace muting analyses. The number, resolution, and lateral continuity of shallow reflections were greatly enhanced on the reprocessed sections, as was the delineation of shallow, major faults. Reflections on a synthetic seismogram, created from a borehole drilled to a depth of 786 m on seismic line IQS-11, matcheddprecisely with shallow reflections on the reprocessed section. The 33 reprocessed sections were instrumental in preparing a map showing the major structural features that affect the shallow aquifer system. Analysis of the map provides a better understanding of the effect of these shallow features on the regional occurrence, movement, and quality of groundwater in the concession area. Results from this study demonstrate that original seismic field tapes collected for deep petroleum exploration can be reprocessed to explore for groundwater.     

Surface mercury geochemistry as a guide to volcanic vent structure and zones of high heat flow in the valley of ten thousand smokes, Katmai National Park, Alaska

A reconnaissance survey of Hg° was designed to model the 1912 Novarupta vent structure and delineate zones of near-surface high heat flow. Statistical analysis of 294 regolith samples collected at 127 sites from fossil/active fumaroles and relatively unaltered ash-flow tuff and air-fall ejecta indicates two Hg° sample populations; one associated with fumarole deposits and the other corresponding to the relatively unaltered regolith. Measured Hg° concentrations range from 12 to 6913 ppb. Sample threshold (upper limit of background Hg° concentrations; fumarole deposits: 351 ppb, unaltered regolith: 110 ppb) and contrast (sample value/threshold) determinations enable differentiation between relict and actively accumulating Hg° contents.All significant Hg° anomalies (contrast values > 1.5) occur within Novarupta Basin. High-magnitude, active Hg² enrichment was found on the Turtle, a dome-like feature northeast of the Novarupta extrusive dome. The Hg° data, coupled with available geologic and geophysical evidence, suggest a shallow intrusion beneath the Turtle. Results from two Novarupta Basin sample traverses do not support the presence of a near-surface magma feeder dike connecting the proposed intrusion beneath the Turtle with the Novarupta dome. Based on the Hg° data, the preferred vent model is one generated by collapse of supporting walls after the major eruptive phase into a cored-out explosive vent. Collapse of vent walls is initiated along a series of deep-extending faults which subsequently serve as migration pathways for Hg° to the surface. The overall vent morphology is funnel-like with subsidence concentrated in the narrow funnel center. Results of this study show that Hg° surveys can further constrain the morphology of the 1912 vent and aid in delineating zones of near-surface high heat flow in this region.     

Microbial community of cyanobacteria mats in the intertidal zone of oil-polluted coast of Saudi Arabia

Cyanobacterial mats are found at various locations along the coast of the Eastern Province of Saudi Arabia. Those mats were affected by severe oil pollution following 1991 oil spill. In this study, samples from Abu Ali Island were collected at three selected sampling sites across the intertidal zone (Lower, Middle, and Upper) in order to understand the effect of extreme environmental conditions of high salinity, temperature and desiccation on distribution of cyanobacteria along the oil polluted intertidal zone. Our investigation of composition of cyanobacteria and diatoms was carried out using light microscopy, and Denaturant Gradient Gel Electrophoresis (DGGE) technique. Light microscopy identification revealed dominant cyanobacteria to be affiliated with genera Phormidium, Microcoleus, and Schizothrix, and to a lesser extent with Oscillatoria, Halothece, and various diatom species. The analysis of DGGE of PCR-amplified 16S rRNA fragments showed that the diversity of cyanobacteria decreases as we proceed from the lower to the upper intertidal zone. Accordingly, the tidal regime, salinity, elevated ambient air temperature, and desiccation periods have a great influence on the distribution of cyanobacterial community in the oil polluted intertidal zone of Abu Ali Island.     

Investigation of topographic site effects using 3D waveform modelling: amplification,polarization and torsional motions in the case study of Arquata del Tronto (Italy)

Bulletin of Earthquake Engineering - The combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground...