bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous oblique sounding with Doppler analysis and low‐probability‐of‐intercept communications using digital ionosondes
Authors: Haines D. Mark , Reinisch Bodo W. , Cheney George P.
Published: February 2004

This paper describes a waveform, modulator, and demodulator for which a U.S. patent has recently been granted. Using a programmable ionospheric sounder (the Digisonde portable sounder, or DPS), the composite spread‐spectrum radio signal has been generated, and preliminary on‐the‐air tests have been made to verify its efficacy. The new radio signal uses an eight‐dimensional (8‐D) set of digital message symbols, each defined by a unique position in an 8‐D orthogonal signal space, providing a symbol set of over 250 million symbols. Four dimensions are spanned by modulating time delay, amplitude, frequency, and spreading code, while a second subcarrier in phase quadrature to the first nearly doubles the capacity by providing four more orthogonal dimensions: time delay, amplitude, code, and phase modulation. This large symbol set allows the signal to carry 10 s of data bits simultaneously in the same radio bandwidth that conventional direct sequence (DS) spread‐spectrum signals use to convey only 1 bit of information while, like conventional DS, providing in excess of 30 dB of signal processing gain. The benefits provided by this new waveform are (1) higher data rates without channel equalization; (2) lower interference to other users of the radio spectrum; and (3) low power or extended range operation.
Scattering by grooves of arbitrary profile on cylindrical surfaces
Authors: Kiang Jean‐Fu
Published: February 2004

A generalized mode‐matching method is developed to study the scattering properties of conducting cylinders with periodic grooves of arbitrary cross section. Reflection matrices are derived to reduce the number of unknowns. This method is illustrated by studying three types of periodic grooves with dielectric filling on a cylindrical surface. Radar cross sections by an incident TE wave are obtained, and the effects of frequency, groove profile, groove depth, and filling permittivity are analyzed.
Imaging coherent backscatter radar observations of topside equatorial spreadF
Authors: Hysell D. L. , Woodman R. F.
Published: February 2004

Multiple baseline interferometric imaging of a large‐scale topside spreadFdepletion has been performed at the Jicamarca Radio Observatory near Lima, Perú. A new imaging technique makes it possible to examine the detailed structure of the scatter from field‐aligned irregularities in and around the depletion, A new antenna at Jicamarca, physically separated from the main antenna array, provided very long interferometry baselines up to ∼94 λ long for the observations. High‐resolution images of coherent backscatter from the radar plume were computed from the interferometry data using the maximum entropy method. These images show that scattering regions with small Doppler velocities lay mainly along the boundary of the depleted region. Meanwhile, regions with high Doppler velocities were located within the depletion itself and could be seen convecting upward through the depleted channel.
Electromagnetic inverse scattering: Retrievable information and measurement strategies
Authors: Bucci O. M. , Isernia T.
Published: February 2004

With reference to inverse scattering from an unknown object of limited extension embedded in a homogeneous background at a fixed frequency, we show that only a finite‐dimensional representation of the unknown contrast can be hopefully retrieved. Exploiting the quasi‐band‐limitedness property of scattered fields, an accurate upper bound to the dimension of such a space is evaluated in both the single incidence and multiview cases. Moreover, effective schemes are given to collect all the information available from the scattering experiments in a nonredundant manner. As a by‐product, an optimal (minimally redundant) sampling strategy for the monostatic radar cross section is also provided. Finally, we briefly discuss how the requirement for a globally effective and reliable solution scheme can lead to a reduction of the actually retrievable information.
New permittivity measurements of seawater
Authors: Ellison W. , Balana A. , Delbos G. , Lamkaouchi K. , Eymard L. , Guillou C. , Prigent C.
Published: February 2004

We have measured the permittivity of representative samples of natural seawater, synthetic seawater, and aqueous NaCl solutions over the frequency range 3–20 GHz, in 0.1‐GHz steps and over the temperature range −2°–30°C in 1° steps. Additional measurements have been made at spot frequencies (23.8, 36.5, and 89 GHz) and at selected temperatures between −2° and 3O°C. The data from these measurements have allowed us to deduce an interpolation function for ε(υ t, S) in the ranges 2 ≤ υ ≤ 20 GHz, −2° ≤ t ≤ 30°C, and 20‰ ≤ S ≤ 40‰ with a precision of 1%. If the frequency range is extended up to 40 GHz, the precision of the interpolation function is about 3%.The data have also allowed us to compare the permittivities of natural seawater, synthetic seawater, and aqueous NaCl solution with the same salinities. Natural and synthetic seawater have the same permittivities within a 1% experimental error estimate. An aqueous NaCl solution has a significantly different permittivity (up to about 6% difference, depending upon the frequency and temperature).
Comparisons of TOPEX and Global Positioning System total electron content measurements at equatorial anomaly latitudes
Authors: Vladimer J. A. , Lee M. C. , Doherty P. H. , Decker D. T. , Anderson D. N.
Published: February 2004

Discrepancies exist between vertically measured ionospheric total electron content (TEC) and slant measurements of TEC that are converted to vertical with the use of a mapping function. Vertical measurements of TEC that are determined by the TOPEX altimeter are compared with equivalent vertical TEC values that are derived from the Global Positioning System (GPS) constellation at latitudes −40° to +40° and longitudes 180° to 360° during periods in 1993, 1994, and 1995. Also, comparisons are made with the Phillips Laboratory parameterized ionospheric model (PIM) predictions of vertical and equivalent vertical TEC from the same observation points. A trend of disagreement in maximum and minimum TEC values is observed between TOPEX and GPS passes that involve measurements within 20° to the south and to the north of the geomagnetic equator. PIM model predictions, although not exact in value, are consistent in configuration with these observations of overestimation as well as underestimation of TEC. It is shown that the errors are dependent on not only elevation angle but also azimuth of the line‐of‐sight direction. The elevation mapping function that relates the line‐of‐sight TEC to vertical TEC and other assumptions that are made in the application of the ionospheric shell model may be contributing factors to the slant‐to‐vertical conversionerrors.
The Manastash Ridge radar: A passive bistatic radar for upper atmospheric radio science
Authors: Sahr John D. , Lind Frank D.
Published: February 2004

We describe a novel method for radar remote sensing of the upper atmosphere which relies upon commercial FM broadcasts near 100 MHz. These broadcasts have high average power and excellent radar ambiguity function. With proper processing we can study the spatial and temporal distribution and Doppler spectrum with excellent and completely unambiguous resolution. Since this passive system has no transmitter, there are enormous benefits in safety, expense, shielding, antenna and receiver design, and licensing issues. Some new problems are introduced, but these are solved with relatively little expense. After presenting the technical basis for such a radar, we describe an instrument that we are building at the University of Washington to study high‐latitude plasma irregularities in the E region.
Observations of coherent emissions from soils
Authors: Schmugge T. J. , Jackson T. J. , O'Neill P. E. , Parlange M. B.
Published: February 2004

Observations of the microwave emissions at 1.413 GHz (L band) and 2.65 GHz (S band) from a silt loam soil exhibited an oscillatory behavior in time as the soil was being irrigated. The oscillations are attributed to interference between reflections from the air‐soil interface and the wet soil‐dry soil interface as the latter moved down in the soil. The magnitude of the first oscillation at L band was 56 K, and at S band it was 40 K, with oscillation damping out after about three cycles to the brightness temperature expected for the wet soil. The emission was modeled using a coherent model, and the results show qualitative and quantitative agreement with the observations.
Impact of new permittivity measurements on sea surface emissivity modeling in microwaves
Authors: Guillou C. , Ellison W. , Eymard L. , Lamkaouchi K. , Prigent C. , Delbos G. , Balana G. , Boukabara S. A.
Published: February 2004

As part of a measuring program dedicated to the analysis of the dielectric properties of seawater in the frequency range 3–89 GHz, a new dielectric permittivity model based on the standard Debye theory has been developed for remote sensing applications over the ocean below 40 GHz, together with polynomial interpolations at the millimeter frequencies 85.5 and 89 GHz. The aim of this paper is to test the relevance of these new dielectric measurements through statistical comparisons of radiative transfer predictions with satellite and airborne radiometric data between 18 and 89 GHz. A radiometric sensitivity analysis to the permittivity measurement errors is proposed, which yields a sea surface brightness temperature accuracy of at least 0.5 K below 20 GHz, 1 K at 24 GHz, and 1.5 K at 37 and 89 GHz. At frequencies less than 40 GHz, superiority of the revised Debye model is pointed out over the most commonly used model ofKlein and Swift[1977]. At millimeter frequencies the new permittivity expressions deviate significantly from the standard Debye predictions, especially at low temperature, suggesting the influence of a second “high‐frequency” Debye relaxation. Our comparisons with radiometric data at 89 GHz and in the channel 85.5V of the special sensor microwave imager tend to support this hypothesis. The results emphasize the importance of an adequate modeling of the complex permittivity of seawater as input to the surface emissivity models, at any frequency of the microwave spectrum, and augur interesting outputs in both in‐flight calibration and interpretation of satellite data.
Mode of extensional tectonics in the southeastern Betics (SE Spain): Implications for the tectonic evolution of the peri‐Alborán orogenic system
Authors: Martínez‐Martínez J. M. , Azañón J. M.
Published: February 2004

The Gibraltar arc, which closes the westernmost part of the Mediterranean basin, is a Miocene A‐type subduction arc formed by the continental collision of various pre‐Miocene terranes in the major zone of collision between the Iberian and African cratons. The hanging‐wall block, known as the Alborán domain, has undergone more than 300 km migration from a more easterly position, where it was the continuation of the Alpine Cretaceous‐Paleogene orogen. Contemporaneous with thin‐skinned thrusting in the footwall, the Alborán domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a NNW‐SSE system, orthogonal to the belt axis, in the late Burdigalian‐Langhian to a WSW directed orogen‐parallel one in the Serravallian. The superposition of these two systems resulted in a chocolate tablet megastructure. This extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc. Orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust; nevertheless, orogen‐parallel extension is more difficult to explain in this context. We advocate that the WSW directed low‐angle normal faults formed during large‐scale extension in connection with important westward arc migration. The driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model. Constraints on both the timing and the kinematics of extension, as presented in this paper, seem to support the contribution of both mechanisms. Convective removal may have started the process, but continued N‐S convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination.
Origin of the high plateau in the central Andes, Bolivia, South America
Authors: Lamb Simon , Hoke Leonore
Published: February 2004

The Bolivian Altiplano, in the Central Andes of South America, is part of the second largest high plateau on Earth. It is an elongate region of subdued relief, ∼1.2 × 105 km2 and ∼4 km above sea level, bounded by the Eastern Cordillera and volcanic arc (Western Cordillera). Here the crust is up to ∼75 km thick. We describe the Cenozoic geological evolution of this region, using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure. Crustal shortening and magmatic addition and, locally, sedimentation are the main mechanisms of Cenozoic crustal thickening, leading to nearly 4 km of surface uplift since the Paleocene. Addition of mafic melts appears to be a first‐order mechanism of Cenozoic crustal growth, contributing ∼40% of the crustal thickening beneath the volcanic arc. Removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind‐arc mafic volcanism, at ∼23 Ma and 0 – ∼5 Ma, contributing to the surface uplift. The Altiplano originated as a sedimentary basin, several hundred kilometers wide, between the proto‐Western Cordillera and a narrow zone of uplift (proto‐Eastern Cordillera) farther east. The latter zone formed by inversion of the center of a wide lacustrine or marine Cretaceous ‐ Paleocene basin close to sea‐level at ∼45 Ma. A thickness of 2–4 km of Paleogene continental elastics accumulated in the proto‐Altiplano basin. Subsequently, in the Oligocene, we estimate that this region and the western margin of the Eastern Cordillera were technically shortened ∼22% (∼65 km), resulting in ∼9 km of average crustal thickening. The Altiplano basin was rejuvenated at ∼25 Ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting Eastern and Western Cordilleras. Between ∼25 and 5 Ma, folding and thrusting in the western margin of the Eastern Cordillera migrated westward into the center of the Altiplano basin, essentially terminating deposition, except in local subbasins, and accommodating ∼13% (∼30 km) of shortening and an estimated ∼7 km of average crustal thickening. Subsequently, there has been strike‐slip deformation and limited local thrusting (< 5 km of shortening). Geomorphological and geochronological evidence for 1.5–2 km of surface uplift of this region since the Late Miocene suggests ∼14 km of lower crustal thickening beneath an essentially rigid “lid”, and can be explained by ∼100–150 km of underthrusting of the Brazilian shield and adjacent regions beneath the eastern margin of the Central Andes. The present subdued relief in the Altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin.
Tertiary tectonic evolution of the external South Carpathians and the adjacent Moesian platform (Romania)
Authors: Maţenco L. , Bertotti G. , Dinu C. , Cloetingh S.
Published: February 2004

Depth‐interpreted seismic sections of the Getic Depression foredeep, paleostress indicator data and analysis of outcrop‐ to regional‐scale structures are integrated to derive the tectonic evolution of the South Carpathians ‐ Moesian platform area. Following Late Cretaceous and older orogenic phases, the South Carpathians ‐ Moesian platform area underwent strike‐slip deformation with NE‐SW oriented compression and NW‐SE tension. In Paleogene to Early Burdigalian times, tensional deformation is recorded which led to the opening of WSW‐ENE to E‐W trending extensional basins. In the Late Burdigalian, NE‐SW oriented contraction took over causing the oblique inversion of preexisting extensional structures. During Sarmatian times, NW‐SE and slightly younger N‐S trending compression caused the activation of mainly NW‐SE dextral strike‐slip faults and, in the frontal areas, south directed thrusting. The NW‐SE direction of extension determined for Paleogene to Early Burdigalian times is hardly compatible with presently accepted models of substantially continuous dextral wrenching between the Intra‐Carpathians units to the north of the South Carpathians and the Moesian platform to the south. In contrast, we have demonstrated dextral transpressive to transtensional movements within an E‐W trending corridor from the Late Burdigalian to Late Sarmatian which are compatible with available models.
Present‐day dynamics of the Aegean region: A model analysis of the horizontal pattern of stress and deformation
Authors: Meijer P. Th. , Wortel M. J. R.
Published: February 2004

In order to gain quantitative insight into the forces that control the present‐day stress field and pattern of horizontal motions in the Aegean region, we adopt a forward model approach. Mechanisms that have been proposed to explain the present‐day tectonics are represented, to first approximation, in terms of the expected force distributions. On the basis of a thin elastic shell representation of the Aegean lithosphere we then calculate the stress field and displacements associated with these force sets and compare the results with observations of the state of stress based on geological studies of fault kinematics, strain as expressed by earthquake focal mechanisms, and horizontal motions measured by means of satellite geodesy. The two most commonly cited mechanisms suggested to control the Aegean tectonics, (1) the push exerted by the westward moving Anatolian block and (2) forces associated with the Hellenic subduction zone, are first analyzed separately. It is found that the westward Anatolian push alone does not explain the observed prevalence of tensional stress. This is also expressed in a mismatch between the displacements computed to result from the westward push and the observed horizontal velocities. Regarding the forces on the Aegean overriding margin, we find that a model with outward pulling forces of uniform magnitude, acting normal to the arc from the SW Peloponnese to Rhodes, yields a stress field that matches the observed pattern of tension to a large extent. This distribution of forces is consistent with the notion of gravitational spreading of the Aegean lithosphere. The pattern of seismic strain of the overriding margin may evidence the occurrence of a small additional resistive force. Although the prevalence of tension thus appears due mainly to the subduction‐related forces, other aspects of the stress field and also the pattern of horizontal motions indicate that these forces act in combination with westward push. Our model results allow us to address the relation between the forces experienced by the upper plate and the kinematics of subduction, not just in terms of a vertical cross section but also by taking into account the along‐arc dimension.
Tectonic evolution of the Montagne Noire and a possible orogenic model for syncollisional exhumation of deep rocks, Variscan belt, France
Authors: Aerden Domingo G. A. M.
Published: February 2004

Structural analysis in the Montagne Noire, including a study of inclusion trail patterns in andalusite, garnet, and staurolite porphyroblasts, reveals a succession of five foliations in alternately steep and flat‐lying orientations. This is inferred to reflect multiple gravitational collapse phases that intervened during continuous plate convergence. Initial crustal thickening by foliation development and folding (D1) was responsible for eclogite‐facies metamorphism in the gneissic basement. Subsequent thrusting and recumbent folding (D2) generated a subhorizontal crenulation cleavage during Namuro‐Westphalian times, while previous steep structures became rotated. Petrological and microstructural evidence indicate that thrust nappes were emplaced by a gravitational spreading mechanism, while undergoing internal thinning. An important amount of basement exhumation took place synchronously. These observations form the basis for a new orogenic model in which thermal reequilibration of a previously thickened orogen induces gravitational instability in the upper crust. Collapse of the upper crust causes it to spreadout horizontally over continuously converging relatively cool plates thereby creating low‐angle thrust nappes. The upper crustal thinning facilitates simultaneous extrusion of lower crust in vertical root zones at the orogen center, which on reaching the higher part of the orogen can be incorporated in the nappes and displaced horizontally. Following such a mechanism of nappe tectonics, renewed horizontal shortening (D3) produced the Montagne Noire gneissic dome by upright folding of nappe‐related foliations with orogen‐parallel stretching. Previous crustal thinning had led to an increased heat flux between basement and cover so that during D3, cover sequences were still rising in temerature, while basement rocks had already commenced their retrograde path during D2. Peak‐metamorphic conditions in the cover triggered a second gravitational collapse during Namurian times (D4) producing a 2 km wide subhorizontal shear zone in which orogen‐parallel stretching continued. At the surface, deformation was accommodated by decollements, normal faulting, and basin formation. Gneissic rocks below the shear zone were not affected by the collapse because a stronger rheology and horizontal shortening was probably continuous here. Retrograde cooling of the cover restored gravitational equilibrium and caused its renewed upright folding during late‐Variscan times (D5). Permian postorogenic extension (D6) oriented at a high angle to the previous orogen‐parallel stretching completed exhumation of the gneiss dome. The dome structure of the Montagne Noire metamorphic core complex was acquired during compressional tectonics and later modified (flattened) by synorogenic and postorogenic extensional events. A similiar polyphase origin appears not to be excluded for other metamorphic core complexes with poorly constrained preextension histories.
Yadong cross structure and South Tibetan Detachment in the east central Himalaya (89°–90°E)
Authors: Wu Changde , Nelson K. D. , Wortman Greg , Samson Scott D. , Yue Yongjun , Li Jixiang , Kidd W. S. F. , Edwards M. A.
Published: February 2004

The Yadong cross structure (YCS), occurring at ∼89°30′ east longitude in the Himalaya, is the largest across‐strike discontinuity in the geologic structure and topography of the High Himalaya between the Himalayan syntaxes. It is manifest by a plan view left offset of the topographic crest of the range and a coincident, apparent, left strike offset of the South Tibetan Detachment System (STDS) of about 70 km. New field mapping indicates that the STDS intersects the west side of the YCS at Zherger La and further suggests that the YCS is the surface expression of a large north‐northeast striking west facing lateral ramp in the Himalayan thrust system. The Greater Himalayan allochthon is apparently draped across this lateral ramp, resulting in a north‐northeast striking monoclinal flexure of the allochthon manifest in the Chomolhari range. Superimposed steep west‐northwest directed normal shear appears to have obliterated earlier northerly directed STDS shear fabric along along the YCS segment of the Tethyan belt/Greater Himalayan belt contact. Recent seismicity suggests that the Greater Himalayan allochthon is still moving southward along the lateral ramp. U‐Pb monazite dates on leucogranites in the footwall of the STDS on opposite sides of the YCS are suggestive of a south‐to‐north decrease in the crystallization age of these granites. The age pattern is consistent with southward “extrusion” of the Greater Himalayan allochthon and suggests the possibility of determining an average slip rate for the STDS by dating granites in the immediate footwall of the STDS that are substantially separated in north‐south section. An average slip rate of about 7 mm/yr between 23 and 12 Ma is suggested by the data presented here.
Analogue modeling of faulting pattern, ductile deformation, and vertical motion in strike‐slip fault zones
Authors: Dauteuil O. , Mart Y.
Published: February 2004

The relationship between faulting, ductile deformation, and vertical displacement in provinces of strike‐slip faults were analyzed using analogue modeling. The described experiment considered a two‐layer, small‐scale model for the lithosphere, set on a low‐viscosity fluid that allowed free isostatic compensation. The development of the faults and their orientation follow generally Riedel's model, but fault spacing depends on the thickness of the brittle layer, and lateral displacement of the brittle layer was associated with series of deep, elongated depressions that developed along the trace of the principal strike‐slip fault. The depressions correspond to local thinning of the brittle layer, and the amount of thinning is more than 60% in places. The underlying ductile layer displayed two types of superimposed deformation, namely a series of tight, parallel folds, occurring on top of elongated domes. The folds are attributed to the compressive component of the strike‐slip displacement, and the updoming to the extensional component. The elongated domes are located beneath the superficial depressions, and the deeper troughs underlie shallow uplifted structures in the deformed band. Significant vertical motion was observed along faults that are considered as perfectly strike‐slip faults, according to the classical Riedel model. The thinning of the brittle layer, and the deep deformation of the ductile layer, are in good agreement with actual examples of pull‐apart basins and elongated swells in large strike‐slip zones. A new structural pattern developed during strike‐slip shear is proposed, relating the geometrical relationships between faults, folds, and elongated domes to the stress axes.
Contour mapping of relic structures in the Precambrian basement of the Reelfoot rift, North American midcontinent
Authors: Dart Richard L. , Swolfs Henri S.
Published: February 2004

A new contour map of the basement of the Reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features. The major features are two asymmetric intrarift basins, bounded by three structural highs, and the rift margins. The basins are oriented normal to the northeast trend of the rift. Two of the highs appear to be ridges of undetermined width that extend across the rift. The third high is an isolated dome or platform located between the basins. The minor features are three linear structures of low relief oriented subparallel to the trend of the rift. Two of these, located within the rift basins, may divide the rift basins into paired subbasins. These mapped features may be the remnants of initial extensional rifting, half graben faulting, and basement subsidence. The rift basins are interpreted as having formed as opposing half graben, and the structural highs are interpreted as having formed as associated accommodation zones. Some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime. A detailed knowledge of the geometries of the Reelfoot rift's basement features, therefore, is essential when evaluating their seismic risk potential.
Snow surface energy exchanges and snowmelt at a continental, midlatitude Alpine site
Authors: Cline Donald W.
Published: February 2004

The objectives of this study were to measure and evaluate the energy balance of a continental, midlatitude alpine snowpack during spring snowmelt conditions, to relate variations in the energy budget and snowmelt to synoptic weather patterns, and to evaluate the performance of a point energy and mass balance model of a snow cover (SNTHERM) in alpine conditions. The investigation was conducted during the 1994 snowmelt season at Niwot Ridge (3517 m above sea level (asl); 40°03′N, 105°35′W) in the Colorado Front Range. Net radiative fluxes and net turbulent fluxes respectively provided 75% and 25% of the total energy available for snowmelt during the season. Sublimation losses were limited to only 4% of the initial snow water equivalence at the site. The largest energy available for snowmelt was associated with a ridge in the upper airflow over the central and southern Rocky Mountains that permitted warmer air into the region. Using measured data from the study site, the SNTHERM model estimated the disappearance of the snowpack just 3 days earlier than the observed 42‐day ablation period.
Fractionally differenced ARIMA models applied to hydrologic time series: Identification, estimation, and simulation
Authors: Montanari Alberto , Rosso Renzo , Taqqu Murad S.
Published: February 2004

SinceHurst[1951] detected the presence of long‐term persistence in hydrologic data, new estimation methods and long‐memory models have been developed. The lack of flexibility in representing the combined effect of short and long memory has been the major limitation of stochastic models used to analyze hydrologic time series. In the present paper a fractionally differenced autoregressive integrated moving average (FARIMA) model is considered. In contrast to using traditional ARIMA models, this approach allows the modeling of both short‐ and long‐term persistence in a time series. A framework for identification and estimation is presented. The data do not have to be Gaussian. The resulting model, which replicates the sample probability density of the data, can be used for the generation of long synthetic series. An application to the monthly and daily inflows of Lake Maggiore, Italy, is presented.
Experimental determination of colloid deposition rates and collision efficiencies in natural porous media
Authors: Kretzschmar Ruben , Barmettler Kurt , Grolimund Daniel , Yan Yao‐de , Borkovec Michal , Sticher Hans
Published: February 2004

Mobile colloids in groundwater aquifers and soils can serve as carriers for strongly sorbing contaminants and thereby facilitate contaminant transport. Therefore mobile colloids may have to be considered in modeling the fate of strongly sorbing contaminants in subsurface environments. In this study we present a Chromatographic short‐pulse technique for measuring colloid deposition rate coefficients and experimental collision efficiencies in natural porous media. The method was evaluated using four different experimental systems of increasing complexity. Short pulses (equivalent to 0.002 to 0.03 pore volumes) of latex or humic‐coated hematite suspensions were injected under saturated flow conditions into laboratory columns packed with glass beads, soil, or aquifer materials. Colloid breakthrough curves were measured on‐line using fluorescence and UVVIS spectrophotometers. Deposition rate coefficients determined with the short‐pulse method were in excellent agreement with results from step‐input experiments. Experiments with different flow rates and column dimensions showed that colloid deposition generally followed a first‐order kinetic rate law. On the basis of experimental fast deposition rates, collision efficiencies for colloid deposition can be calculated. The results demonstrate that the short‐pulse method can be used very efficiently for studying the effects of solution chemistry and flow velocity on the kinetics of colloid deposition in natural porous media. The short‐pulse method has several advantages over the more traditionally used step‐input experiment and allows running several experiments on a single column without significant blocking or filter ripening effects.
On weather normalizing customer‐level billing data
Authors: Bamezai Anil
Published: February 2004

This paper develops a conceptual framework for estimating both nonlinear and time‐varying weather impacts from customer‐level billing histories. The framework is flexible insofar as multiple model specifications can be derived from it for real‐world application. Next, through statistical tests the paper evaluates the performance of 10 progressively complex weather specifications applied to a sample of billing data. These tests reject many of the simple and commonly used weather specifications, demonstrating the importance of accurate weather modeling.
Drainage basin responses to climate change
Authors: Tucker Gregory E. , Slingerland Rudy
Published: February 2004

Recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion. The sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution. The GOLEM model simulates basin evolution under the action of weathering processes, hillslope transport, and fluvial bedrock erosion and sediment transport. Results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change. An increase in runoff intensity (or a decrease in vegetation cover) will lead to a rapid expansion of the channel network, with the resulting increase in sediment supply initially generating aggradation along the main network, followed by downcutting as the sediment supply tapers off. By contrast, a decrease in runoff intensity (or an increase in the erosion threshold) will lead to a retraction of the active channel network and a much more gradual geomorphic response. Cyclic changes in runoff intensity are shown to produce aggradational‐degradational cycles that resemble those observed in the field. Cyclic variations in runoff also lead to highly punctuated denudation rates, with denudation concentrated during periods of increasing runoff intensity and/or decreasing vegetation cover. The sediment yield from threshold‐dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes, a finding which underscores the need for caution in interpreting modern sediment‐yield data.
A numerical analysis of the effects of coatings and gaps upon relative dielectric permittivity measurement with time domain reflectometry
Authors: Knight J. H. , Ferré P. A. , Rudolph D. L. , Kachanoski R. G.
Published: February 2004

Fluid‐filled gaps or dielectric coatings around parallel‐wire transmission lines affect the ability of time domain reflectometry (TDR) to measure the water content of soils and other porous materials. We use a steady state, two‐dimensional, finite element numerical solution of Laplace's equation to analyze these effects. We prove that the numerically determined electrostatic potential distribution and boundary fluxes can be used to calculate the equivalent relative dielectric permittivity measured by TDR by comparing the results of the numerical model with those obtained using existing analytical solutions for special cases. We then analyze the effects of fluid‐filled concentric gaps that completely or partially surround TDR rods. The results show that an analytical solution due to Annan [1977b] for nonconcentric gaps can be used as a good approximation to predict the effect of concentric gaps or coatings that completely surround the rods. Coatings or gaps filled with low relative dielectric permittivity materials have a greater impact on the measured relative dielectric permittivity than those filled with high dielectric media. An increase in the thickness of the gap or coating for given rod diameters and separations increases the impact of the coating. To a lesser degree, the impact of a coating of a given thickness decreases with an increase in the ratio of the rod diameter to the rod separation. A gap or coating of a given thickness and relative dielectric permittivity will have a greater impact on the response of a three‐rod probe than on that of a two‐rod probe with the same rod diameter and separation of the outermost rods. Partial air gaps surrounding less than 30° of the rod circumference are not likely to affect the probe response significantly.
A two‐dimensional analytical solution of groundwater response to tidal loading in an estuary
Authors: Sun Hongbing
Published: February 2004

A two‐dimensional transient groundwater flow equation for a confined nonleaky aquifer is solved analytically with an estuary tidal‐loading boundary condition. The amplitude and phase of the tide varies with position and time, respectively. These variations, called the “damping coefficient,” for amplitude, and “separation constant,” for phase along the coastline, are considered in the analysis. The solution presented is more advanced than the traditional one‐dimensional analytical solution with a one‐dimensional tidal‐loading boundary condition. The damping coefficient and separation constant in the application study are obtained from the harmonic analysis of the observed tidal level in Apalachicola Bay, Florida. The analytical solution is compared to a two‐dimensional finite difference solution. A numerical simulation illustrates the response of piezometric head to tidal loading. The piezometric head and phase from both solutions match closely. The analytical and numerical solutions show that a piezometric head along both sides of the estuary can be predicted given a tidal elevation at the entry of an estuary. The fluctuation of piezometric head in response to tidal loading diminishes rapidly inland and diminishes slowly along the coastline of an estuary. There are also obvious phase shifts associated with spatial variations as the wave propagates.
Hillslope evolution by diffusive processes: The timescale for equilibrium adjustments
Authors: Fernandes Nelson F. , Dietrich William E.
Published: February 2004

Diffusive processes such as creep, rain splash, and biogenic transport play a major role in controlling the development of convex hilltops on soil‐mantled landscapes. Although many diffusion‐based models have been proposed, little attention has been given to the effects of changing transport rates and boundary conditions. We use numerical and analytical solutions of the one‐dimensional diffusion equation to explore whether hilltop convexities can be in equilibrium with contemporary climate and local channel incision rates. The results show that the timescale of such morphological adjustments varies substantially depending on whether the hillslope is tending to increase or decrease its convexity through time. By comparing the relaxation times estimated here with the frequency of the climatic oscillations observed in the last few million years, we argue that most of the convex hilltops observed in the field today are likely to be far from time‐independent morphological features.
Effects of column conditions on the first‐order rate modeling of nonequilibrium solute breakthrough: Cylindrical macropores versus spherical media
Authors: Young Dirk F. , Ball William P.
Published: February 2004

When first‐order mass transfer models are used to interpret diffusion‐based nonequilibrium transport through soil columns, significant misinterpretations may result if experimental impacts on the model fits are not well understood. For the specific case of slow diffusion in spherical sorbent particles, we have previously demonstrated the manner in which estimated rate constants vary with a dimensionless “exposure time” of solute to sorbent. In the current work we extend our quantitative analysis of these concerns to the case of cylindrical macropore flow, where the geometry of the diffusion matrix is that of an annular region surrounding a central flow‐permeable cylinder. Our results show that similar to the spherical sorbent case, variations in the first‐order coefficient fitted to macropore column data are not necessarily related to variation in underlying diffusion rates and that the variations are similarly dependent upon the column run conditions. However, for the macropore case the proposed nondimensional timescale is even more successful at characterizing the variation in the fitted first‐order mass transfer parameter. On the basis of these results we are able to further generalize our conclusions with regard to the effects of experimental conditions such as solute retardation factor (sorption affinity) and solute input conditions (pulse duration). For short exposure times to solute (relative to the characteristic time for diffusion) the ratio of the fitted first‐order rate coefficient to the underlying diffusion rate (K) varies with dimensionless contact time (т) in a consistent manner (K ∼ т−0.4) irrespective of geometry. Only at long exposure time does the fitted K approach a value that we can independently derive on the basis of equivalent second moments.
Documentation and significance of the perirheic zone on inundated floodplains
Authors: Mertes Leal A. K.
Published: February 2004

The transfer of water, sediment, and other materials to floodplains is a function of the hydrology of inundation. Inundation of floodplains by regional water, that is, overbank flow from the main river channel, and local water, that is, groundwater, hyporheic water, local tributary water, and direct precipitation onto the floodplain, is such that some rivers inundate dry floodplains, while other rivers inundate fully saturated floodplains. Remote sensing and field data from the large rivers Missouri, Mississippi, Amazon, Ob'‐Irtysh, Taquari, and Altamaha show a variety of water types on inundated floodplains, including areas of mixing of river and local water defined as the “perirheic zone.” For the rivers examined here, only the Missouri River flooded its entire valley with sediment‐rich river water. Therefore the floodplains of these large rivers from the Arctic to the Amazon are only partially inundated with river water during floods and the corresponding perirheic zones may encompass a significant floodplain ecotone.
A hybrid model for point rainfall modeling
Authors: Gyasi‐Agyei Yeboah , Willgoose Garry R.
Published: February 2004

A hybrid point rainfall model, a product of two random processes, is presented. The model uses a jitter model, a general technique for improving the fit of any point process based model. We use the nonrandomized Bartlett‐Lewis rectangular pulse and an autoregressive model as a jitter. First, the five parameters of the Bartlett‐Lewis model are estimated by the method of moments using the mean of one aggregation level and the dry probabilities of all aggregation levels considered. Second, the parameters of the autoregressive model are derived from the moments of the historical data and those given by the Bartlett‐Lewis model, without additional cost in terms of parameter calibration. Using 15‐min point rainfall data of Capella, central Queensland, Australia, as a test case, the results of the hybrid model were better than the best results given by the randomized Bartlett‐Lewis model. On its own the nonrandomized Bartlett‐Lewis model produced very poor results.
Infiltration from a surface point source and drip irrigation: 2. An approximate time‐dependent solution for wet‐front position
Authors: Revol P. , Clothier B. E. , Mailhol J.‐C. , Vachaud G. , Vauclin M.
Published: February 2004

Raats' [1971] steady state theory is here extended to provide an approximate analysis of the transient pattern of wetting around a point source. The assumption that a steady state regime prevails behind the wet front and the use of the Clothier [1984] and Philip [1984] theories on water movement along the streamlines allows an approximate transient solution for surface point source infiltration to be developed. This procedure was previously tested against absorption theory and laboratory experiments [Revol et al., 1995], but now this new analysis is evaluated via a field test. The vertical elongating influence of gravity is found to be well predicted. Application of this analysis to design purposes is also mentioned. The role of the macroscopic characteristic capillary length of unsaturated flow, λc, is highlighted by this approximate solution. Finally, we propose a method that allows estimation of λc from a point‐source infiltration experiment.
An algorithm for computing moments‐based flood quantile estimates when historical flood information is available
Authors: Cohn T. A. , Lane W. L. , Baier W. G.
Published: February 2004

This paper presents the expected moments algorithm (EMA), a simple and efficient method for incorporating historical and paleoflood information into flood frequency studies. EMA can utilize three types of at‐site flood information: systematic stream gage record; information about the magnitude of historical floods; and knowledge of the number of years in the historical period when no large flood occurred. EMA employs an iterative procedure to compute method‐of‐moments parameter estimates. Initial parameter estimates are calculated from systematic stream gage data. These moments are then updated by including the measured historical peaks and the expected moments, given the previously estimated parameters, of the below‐threshold floods from the historical period. The updated moments result in new parameter estimates, and the last two steps are repeated until the algorithm converges. Monte Carlo simulations compare EMA,Bulletin 17B's [United States Water Resources Council, 1982] historically weighted moments adjustment, and maximum likelihood estimators when fitting the three parameters of the log‐Pearson type III distribution. These simulations demonstrate that EMA is more efficient than theBulletin 17Bmethod, and that it is nearly as efficient as maximum likelihood estimation (MLE). The experiments also suggest that EMA has two advantages over MLE when dealing with the log‐Pearson type III distribution: It appears that EMA estimates always exist and that they are unique, although neither result has been proven. EMA can be used with binomial or interval‐censored data and with any distributional family amenable to method‐of‐moments estimation.
Removal of pooled dense, nonaqueous phase liquid from saturated porous media using upward gradient alcohol floods
Authors: Lunn Stuart R. D. , Kueper Bernard H.
Published: February 2004

Laboratory experiments employing 90% by volume alcohol solutions are used to compare the abilities of ethanol and 1‐propanol to remove pooled tetrachloroethene (PCE) from saturated porous media using low upward hydraulic gradients. Equilibrium ternary phase diagrams measured for the systems water/PCE/ethanol and water/PCE/1‐propanol indicate that for alcohol concentrations below the miscibility envelope, 1‐propanol will partition predominantly into the dense, nonaqueous phase liquid (DNAPL) phase while ethanol remains in the aqueous phase. Interfacial tension and phase density measurements show that while both systems demonstrate a reduction in interfacial tension with increasing alcohol content, the density difference between the aqueous and DNAPL phases is only reduced for the 1‐propanol system. Two‐dimensional experiments in saturated porous media using alcohol floods ranging in size from 0.125 pore volumes (PV) to 1.0 PV recovered between 5.7% and 98.7% of the PCE mass. The removal mechanisms for the ethanol floods included enhanced dissolution followed by miscible displacement, while the 1‐propanol floods removed PCE by DNAPL swelling and interfacial tension reduction leading to immiscible displacement followed by miscible displacement. Recovery results and effluent composition histories indicate that hydrodynamic instabilities and dispersion cause significant alcohol slug deterioration and confirm the necessity of using an appropriate size alcohol slug of sufficient concentration for efficient PCE mass recovery.