bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarimetric passive remote sensing of ocean wind vectors
Authors: Yueh S. H. , Kwok R. , Li F. K. , Nghiem S. V. , Wilson W. J. , Kong J. A.
Published: February 2004

This paper investigates the theory of polarimetric passive remote sensing of wind‐generated sea surfaces and the potential application of polarimetric radiometry to ocean wind remote sensing. Theoretical polarimetric emission coefficients of small‐scale sea surfaces are evaluated using the small perturbation method (SPM). The SPM is derived to second order and applied to the Stokes vectors of thermal emission from random rough dielectric surfaces described by anisotropic directional spectra. To verify the accuracy of the SPM, a Monte Carlo simulation is performed to calculate the Stokes vectors of the emission from the simulated one‐dimensional random rough surfaces with a power law spectrum for various observation angles and surface parameters. The theoretical results of the SPM for all four Stokes parameters are in excellent agreement with the numerical results obtained from the Monte Carlo simulation. Moreover, the second‐order coherent fields are indispensable in the theoretical evaluation of the third and fourth Stokes parameters. Otherwise, the reflectivities of random rough surfaces would be significantly overestimated, and the signs of the third and fourth Stokes parameters would be incorrect. The SPM is then applied to small‐scale sea surfaces described by an empirical sea surface spectrum. It is found that the azimuthal signatures of Stokes parameters agree qualitatively well with aircraft Ku‐band radiometer data. Theoretical model functions of the Stokes parameters are illustrated. Advantages of wind direction retrieval using polarimetric Q and U measurements are discussed, and it is expected that a spaceborne polarimetric radiometer has a potential of providing wind vector measurements with uniform accuracy across all parts of swath.
Calculation of the electromagnetic fields induced in the head of an operator of a cordless telephone
Authors: Martens L. , De Moerloose J. , De Zutter D. , De Poorter J. , De Wagter C.
Published: February 2004

This paper shows the capability of the finite difference time domain (FDTD) method to predict the interaction between the human body and the electromagnetic field generated by a cordless telephone. Both the influence of the human head on the performance of the cordless telephone and the energy deposited in the human head have been determined. The interaction has been evaluated for a simple dipole model and for an accurate “box” model of the telephone. The FDTD method is a versatile method for refining the antenna model. The results show that the use of the accurate box model in combination with a realistic model of the head derived from a nuclear magnetic resonance image is a prerequisite for accurate determination of the near fields induced in the head. The total amount of power absorbed in the head has been compared to the radiated power. From our calculations we found that about 15% of the antenna input power at 900 MHz is absorbed in the head.
Spectral approach to solving three‐dimensional Maxwell's diffusion equations in the time and frequency domains
Authors: Druskin Vladimir , Knizhnerman Leonid
Published: February 2004

We describe a new explicit three‐dimensional solver for the diffusion of electromagnetic fields in arbitrarily heterogeneous conductive media. The proposed method is based on a global Krylov subspace (Lanczos) approximation of the solution in the time and frequency domains. We derive solutions stable to spurious curl‐free modes and provide estimates of the computer complexity involved in the calculations. Such estimates together with numerical experiments attest to a computationally efficient method suitable for large‐scale problems. Also included are modeling examples drawn from practical geophysical applications.
Transverse electric mode scattering from rectangular grooves in parallel plate
Authors: Lee Jung H. , Eom Hyo J. , Lee Jae W. , Yoshitomi Kuniaki
Published: February 2004

An analytic solution for transverse electric mode scattering from a parallelplate waveguide with periodic grooves is obtained. The Fourier transform is used to express the scattered field in the spectral domain as superposition of the parallel‐plate waveguide modes. The simultaneous equations are solved to represent the transmitted field in series form which is very efficient for numerical computation. When we use the residue calculus, the reflection and transmission coefficients are obtained, and their bandstop filter characteristics are studied in terms of frequency and groove sizes.
Utilization of wavelet concepts in finite elements for an efficient solution of Maxwell's equations
Authors: Sarkar Tapan K. , Adve Raviraj S. , García‐Castillo Luis Emilio , Salazar‐Palma Magdalena
Published: February 2004

The principles of dilation and shift are two important properties that are attributed to wavelets. It is shown that inclusion of such properties in the choice of a basis in Galerkin's method can lead to a slow growth of the condition number of the system matrix obtained from the discretization of the differential form of Maxwell's equations. It is shown that for one‐dimensional problems the system matrix can be diagonalized. For two‐dimensional problems, however, the system matrix can be made mostly diagonal. This paper illustrates the application of the new type of “dilated” basis for a Galerkin's method (or equivalent, for example, finite element method) for the efficient solution of waveguide problems. Typical numerical results are presented to illustrate the concepts.
Plane wave scattering by dielectric elliptic cylinder coated with nonconfocal dielectric
Authors: Sebak A. , Ragheb H. A. , Shafai L.
Published: February 2004

The scattering cross section of a dielectric elliptic cylinder coated with nonconfocal dielectric is investigated. An exact dual series solution based on the boundary value method and employing the addition theorem of Mathieu functions is derived. Both transverse magnetic and transverse electric cases are considered. The infinite series' of the solution are truncated after a finite number of terms to generate numerical data. A convergence check is built into the computer program, and the geometrical dimensions considered are within the low‐frequency range. It is shown that this solution is much more general than all other solutions given before because it can handle a variety of scattering geometries.
Copolarized and cross‐polarized enhanced backscattering from two‐dimensional very rough surfaces at millimeter wave frequencies
Authors: Phu Phillip , Ishimaru Akira , Kuga Yasuo
Published: February 2004

Wideband millimeter wave experiments from 75–100 GHz on the scattering from two‐dimensional very rough conducting surfaces are presented. The two‐dimensional very rough surfaces are manufactured using a computer‐numerical‐controlled milling machine so that the surface statistics are precisely controlled. The surfaces have both Gaussian roughness statistics and Gaussian surface correlation functions. Bistatic scattering experiments on surfaces with either isotropic or anisotropic correlation functions are performed. Copolarized and cross‐polarized bistatic scattering cross sections are measured for both transverse electric and transverse magnetic incidence at 20°. For isotropic surfaces, backscattering enhancement exists for both copolarized and cross‐polarized returns and is found to be a function of the surface rms slope. In addition, a strong frequency dependence is observed across the 25‐GHz bandwidth in the cross‐polarized returns. To investigate the effect of surface correlation anisotropy, scattering experiments on anisotropic rough surfaces are also performed. It is found that the bistatic scattering cross section for an anisotropic surface is a function of the effective correlation length projected along the plane of scattering. Results on the bistatic scattering experiments presented here serve as a motivation to further pursue more elaborate and complete scattering experiments in order to advance research on scattering from very rough surfaces.
Application of beam simulation to scattering at low grazing angles: 2. Oceanlike surfaces
Authors: Rino Charles L. , Ngo Hoc D.
Published: February 2004

The beam simulation method developed by Maystre and Saillard is applied to one‐dimensional power law surfaces with the same dielectric properties and average spatial wave number content as wind‐driven ocean waves. In the beam simulation method the scattering from overlapping surface subsegments is first computed and then coherently combined to obtain the scattered field. The beam simulation method is generally more efficient than the method of moments, but it is not an exact numerical method. Thus we have developed a measure of the minimum subbeam size that can be used for improved efficiency. This measure can be interpreted as the maximum distance on the surface over which local structures interact. We find that the maximum interaction distance at 80° incidence can be as large as 200λ, and it increases with increasing incidence angle. As large‐scale surface waves begin to dominate the surface structure, significant departures from the behavior predicted by first‐order perturbation theory are observed within the accurate computation range of low grazing angle backscatter. The results are discussed in light of ocean scattering data that evidently cannot be explained by existing theories.
On the synthesis of fractal radiation patterns
Authors: Werner D. H. , Werner P. L.
Published: February 2004

The fundamental relationship between self‐similar, that is, fractal, arrays and their ability to generate radiation patterns which possess fractal features is examined in this paper. The theoretical foundation and design procedures are developed for using fractal arrays to synthesize fractal radiation patterns having certain desired characteristics. A family of functions, known as generalized Weierstrass functions, are shown to play a pivotal role in the theory of fractal radiation pattern synthesis. These functions are everywhere continuous but nowhere differentiable and exhibit fractal behavior at all scales. It will be demonstrated that the array factor for a nonuniformly but symmetrically spaced linear array can be expressed in terms of a Weierstrass partial sum (band‐limited Weierstrass function) for an appropriate choice of array element spacings and excitations. The resulting fractal radiation patterns from these arrays possess structure over a finite range of scales. This range of scales can be controlled by the number of elements in the array. For a fixed array geometry, the fractal dimension of the radiation pattern may be varied by changing the array current distribution. A general and highly flexible synthesis technique is introduced which is based on the theory of Fourier‐Weierstrass expansions. One of the appealing attributes of this synthesis technique is that it provides the freedom to select an appropriate generating function, in addition to the dimension, for a desired fractal radiation pattern. It is shown that this synthesis procedure results in fractal arrays which are composed of a sequence of self‐similar uniformly spaced linear subarrays. Finally, a synthesis technique for application to continuous line sources is presented which also makes use of Fourier‐Weierstrass expansions.
The embedding method and differential run equations for the inverse scattering problem in a layered medium
Authors: Klyatskin V. I. , Koshel K. V. , Shevtsov B. M.
Published: February 2004

The one‐dimensional transient problem of a wave incidence on a layer of inhomogeneous medium is considered. It is shown that a measurement of the internal fields allows one to reconstruct the permittivity profile in certain parts of the slab. Combining the embedding and differential run equations, we obtain the closed equations for the internal fields and construct the solution procedure for the inverse scattering problem. The generalization of the analytical solution of the inverse problem, for the case in which the time dependence of scattering field is exponential, is presented.
An improved model of equatorial scintillation
Authors: Secan J. A. , Bussey R. M. , Fremouw E. J. , Basu Sa.
Published: February 2004

One of the main limitations of the modeling work that went into the equatorial section of the Wideband ionospheric scintillation model (WBMOD) was that the data set used in the modeling was limited to two stations near the dip equator (Ancon, Peru, and Kwajalein Island, in the North Pacific Ocean) at two fixed local times (nominally 1000 and 2200). Over the past year this section of the WBMOD model has been replaced by a model developed using data from three additional stations (Ascension Island, in the South Atlantic Ocean, Huancayo, Peru, and Manila, Phillipines; data collected under the auspices of the USAF Phillips Laboratory Geophysics Directorate) which provide a greater diversity in both latitude and longitude, as well as cover the entire day. The new model includes variations with latitude, local time, longitude, season, solar epoch, and geomagnetic activity levels. The way in which the irregularity strength parameter CkL is modeled has also been changed. The new model provides the variation of the full probability distribution function (PDF) of log (CkL) rather than simply the average of log (CkL). This permits the user to specify a threshold on scintillation level, and the model will calculate the percent of the time that scintillation will exceed that level in the user‐specified scenario. It will also permit calculation of scintillation levels at a user‐specified percentile. A final improvement to the WBMOD model is the implementation of a new theory for calculating S4 on a two‐way channel.
A discrepancy in the International Radio Consultative Committee report 322‐3 radio noise model: The probable cause
Authors: Sailors David B.
Published: February 2004

The cause of a discrepancy in the CCIR Report 322‐3 (International Radio Consultative Committee (CCIR), 1988) radio noise model is reported. The basis for this discrepancy results from the procedure used to prepare the measured noise data for the determination of a global numerical representation of the 1‐MHz data. In the development of the model, correction factors to an older CCIR model were determined for each measurement site. These corrections were interpolated for each time block and season to a grid of 100 latitude points by 84 longitude points. The correction factors at each grid point were then added to corresponding values for the older CCIR model, and finally, the resulting data for each time block and season were numerically mapped. Nineteen locations were used in the final model. Four sites used in the original CCIR model were not used. As either no correction factors were obtained for these locations or a correction factor of zero was used to maintain the status quo, the interpolation algorithm produced erroneous values near these four sites in determining the 100‐by‐84 grid of correction factors. For Bill, Wyoming, the result is not too serious; but for the other three sites at some seasons and time of day, the error is serious. For Thule, Greenland; for Ibadan, Nigeria; and for Byrd Station, Antarctica; the maximum and minimum errors were 10.1 and −10.8 dB; 12.5 and −1.5 dB; and 12.0 and 3.0 dB, respectively. Examination of the geographical extent of these errors reveals that the error is not confined to the measurement location but in fact can be very large. This geographical enhancement of the error is most serious during June, July, and August and least serious during December, January, and February. The error as a function of frequency was found to be diurnally dependent, being more serious during the daytime hours. The absence of the data locations as nodes in the interpolation affected the accuracy of the interpolation itself. The CCIR Report 322‐3 atmospheric noise model should be used with caution, especially for locations in the northern and southern high latitudes, the Arabian Peninsula, northern Africa, and the Mid‐Atlantic Ocean areas.
Evolutionary approach in transient electrodynamics problems
Authors: Nerukh A. G.
Published: February 2004

The approach for handling transient electrodynamics problems based on their description by an integral Volterra equation is presented. The expression for a resolvent of this three‐dimensional space‐time vector equation for the case of a time‐varying dielectric restricted by a plane boundary is derived. Using this approach it is demonstrated that an oblique incidence of a plane monochromatic wave on a boundary of a dielectric whose permittivity changes abruptly in time leads to a formation of a continuous wave spectrum. In the case of a point source of electromagnetic radiation, the presence of a plane boundary leads to a replacement of a convergence point of secondary spherical waves to the mirror symmetrical point. The field in this point has a bounded value, as differentiated from the case of an unbounded medium.
Rotation of the Chortís block causes dextral slip on the Guayape fault
Authors: Gordon Mark B. , Muehlberger William R.
Published: February 2004

The Chortís block is undergoing deformation as a direct result of large‐magnitude sinistral strike‐slip faulting on the North America‐Caribbean plate boundary. We have studied the Chortís block using geologic mapping, remote imagery, and earthquake seismology to evaluate the effect that large‐magnitude strike‐slip faulting has on an adjacent microcontinental block. In the eastern part of the Chortís block, recent geologic mapping has shown that the northeast striking Guayape fault is dextral instead of sinistral as previously assumed. Because this is a major fault that cuts most of the Central America isthmus, the new evidence for dextral slip necessitates a reinterpretation of the active tectonics of the Chortís block. The presence of several north trending rifts in the western part of the Chortís block has led previous workers to propose that the Chortís block is divided into smaller, independently rotating blocks. We use earthquake seismology and remote imagery data to extend this interpretation to the central portion of the Chortís block. However, we have modified their model to account for dextral slip on the Guayape fault. We believe that rotation of the Chortís block causes dextral slip on the Guayape fault even though Central America is undergoing large sinistral displacement with respect to North America.
Middle Ordovician high PT metamorphic rocks in eastern Australia: Evidence from K‐Ar ages
Authors: Fukui Shiro , Watanabe Teruo , Itaya Tetsumaru , Leitch Evan C.
Published: February 2004

Phengite, separated from a metagabbro, three blueschist, and one metabasite that occur as blocks in serpentinite melange in the New England Fold Belt, eastern Australia, has yielded K‐Ar ages of 465 – 480 Ma, significantly older than the age of most components of the belt. The schists and metabasite contain either glaucophane and/or crossite intergrown with the phengite, providing the first conclusive evidence for early Paleozoic subduction accretion associated with the east Gondwana margin. The tectonic affinity of the blocks is uncertain. They and other small early Paleozoic convergent margin elements in the New England Fold Belt may be allochthonous remnants of an arc system accreted in the Devonian or Carboniferous, or they may be related to early Paleozoic convergent margin components found farther inboard in the Paleozoic fold belts of eastern Australia.
Late Silurian‐Early Devonian transpressional rift origin of the Quebec Reentrant, northern Appalachians: Constraints from geochemistry of volcanic rocks
Authors: Keppie J. Duncan , Dostal J.
Published: February 2004

Silurian‐Devonian rocks in the northwestern mainland Appalachians form part of an overstep sequence deposited across the vestiges of Iapetus after the collision of Laurentia and Gondwana. They occur in three synclinoria (Gaspé‐Connecticut Valley, Merrimack‐Aroostook, and Fredericton synclinoria), separated by two anticlinoria (Munsungun‐Pennington‐Boundary Mountain‐Bronson Hill and Miramichi). Silurian rocks in Gaspé‐Connecticut Valley and Merrimack‐Aroostook synclinoria consist of shelf and trough sediments derived mainly from Laurentia to the northwest, with some local contributions from an ephemeral landmass (Appalachia) and from the Miramichi Highlands, hi contrast, Early Devonian rocks in all three synclinoria are mainly flysch derived from the southeast in Avalonia. Interbedded volcanic rocks are predominantly Late Silurian‐Early Devonian in age. They are generally bimodal with the mafic rocks exhibiting a change from transitional alkalic‐tholeiitic to tholeiitic around the Siluro‐Devonian boundary, broadly coincident with the Salinic disturbance in the Gaspe Peninsula. The geochemical characteristics of the basalts indicate that they were erupted in a continental intraplate environment with melting migrating upward through time across the garnet to spinel phase boundary as stretching increased. Thermal uplift during rifting is inferred to have led to erosion associated with the Salinic disturbance. The start of the volcanism appears to coincide with a switch from sinistral to dextral transpression along the orogen that may be related to the change from clockwise to anticlockwise rotation of Laurentia relative to Gondwana. The effects of dextral transpression vary with the trend of the orogen; intense deformation and metamorphism occurred in the Central Mobile belt opposite the New York and St. Lawrence promontories, whereas rifting developed in the Quebec Reentrant, leading to thinning of the crust, up‐welling of the asthenosphere, melting, and magmatism.
Decompression and anatexis of Himalayan metapelites
Authors: Harris Nigel , Massey John
Published: February 2004

The Miocene leucogranites of the High Himalayas have been emplaced within a metasedimentary wedge, defined by the Main Central Thrust (MCT) and the South Tibetan Detachment System (STDS), a low‐angle detachment fault. Isotopic and tectonic constraints indicate that orogenic collapse along the South Tibetan Detachment System occurred at ∼20 Ma, synchronous with anatexis and emplacement of the leucogranites, thus suggesting that exhumation and anatexis were related. The isotope geochemistry of the Himalayan leucogranites indicates that their source lies within the metapelites of the metasedimentary wedge. Pelitic assemblages exhibit an inverted metamorphic geotherm consistent with wedge corner flow which stacked sillimanite‐grade thrust sheets onto kyanite‐grade rocks. However, the leucogranite protolith is not the sillimanite migmatites into which the melts have been emplaced but may be correlated with kyanite schists from near the base of the wedge. In the Langtang section of northern Nepal, leucogranite melts, formed from vapor absent incongruent melting of muscovite, were extracted from their source and migrated over distances >10 km before emplacement close to the STDS. A consequence of fractional melting in the hanging wall of the MCT is instability of the metasedimentary wedge. Decompression melting from depths >40 km can generate a melt fraction of ∼7%, depending on the initial temperature and muscovite content of the protolith. Enhancement of the available melt fraction during exhumation may have been critical in allowing the melt to migrate from its source under an extensional régime.
Thermal evolution of the Gangdese batholith, southern Tibet: A history of episodic unroofing
Authors: Copeland Peter , Harrison T. Mark , Pan Yun , Kidd W. S. F. , Roden Mary , Zhang Yuquan
Published: February 2004

The Gangdese batholith, southern Tibet, was part of an Andean‐type arc at the southern margin of Asia prior to the collision of India and Asia at approximately 50 to 40 Ma. Fission‐track and 40Ar/39Ar analyses of 28 rocks from 10 Gangdese granitoid plutons along an ∼250 km length of the batholith in the Lhasa region provide a detailed understanding of the age and the postcrystallization erosional and tectonic history of these rocks. These data suggest a range of ages for these plutons of 94 to 42 Ma, with the majority being of Tertiary age. The postcrystallization cooling histories of all of these plutons are characterized by marked discontinuities. We conclude that most of these discontinuities, and all of them after 40 Ma, reflect tectonic changes that produced brief pulses of rapid erosion which were distributed in both space and time. In addition to the initial cooling of hot magma against cold country rock, all of the rocks we studied showed evidence for at least one subsequent episode of rapid cooling, dropping many tens of degrees in a few million years. Conversely, these plutons all experienced intervals during which they cooled very slowly or not at all; these slow‐cooling intervals lasted from 5 to 50 million years. Our data indicate that since the collision between India and Asia began, response to continued convergence has been quite variable in even this relatively small area. The data reported here are consistent with a recently proposed model of Oligo‐Miocene crustal shortening along the Gangdese Thrust system in this area.
Remagnetizations and postfolding oroclinal rotations in the Cantabrian/Asturian arc, northern Spain
Authors: Parés Josep M. , Van der Voo Rob , Stamatakos John , Pérez‐Estaún Andres
Published: February 2004

Devonian carbonates in the Cantabrian Arc reveal characteristic magnetizations with coherent, shallow, upward inclinations. The magnetizations appear to be carried by magnetite. Within‐site directions are very well grouped, but site‐mean declinations range from easterly to south–southwesterly in in situ as well as tilt‐corrected coordinates, as has also been observed in previous studies of other formations in the arc. The widely varying declinations of all studies roughly correlate with the overall structural trends of the arc and suggest that the sites underwent rotations in a process that involved folding about vertical axes and tightening of arc. Upon tilt correction the inclinations of our study, on the other hand, become scattered, and it is concluded that the magnetizations were acquired after Late Carboniferous folding about horizontal axes. The oroclinal rotations therefore also must have occurred after the Late Carboniferous folding phase. The previous paleomagnetic results had been interpreted mostly as primary magnetizations residing in hematite. However, inclination only fold‐tilt tests applied to these results suggest that many, if not all, of the directions were acquired during the earlier stages of the Late Carboniferous folding. Thus all paleomagnetic results from the Cantabrian Arc appear to be remagnetizations, but the ages of the remagnetizations vary from pre‐to synfolding for the mostly hematitic formations to postfolding for the Devonian carbonates. The reversed‐polarity inclinations of the hematite‐bearing formations have mean values ranging from +25° to +5°, whereas the carbonates have a mean inclination of −8°. On the basis of inclinations predicted for the area from results from stable Europe, the Pyrenees, and the Iberian Meseta, the ages of these remagnetizations can be inferred to range from about 320 Ma to 260 Ma. Because all the remagnetizations reveal rotated declination patterns, the oroclinal rotations occurred well after the main phase of Hercynian deformation (320–280 Ma). While the timing of the rotations is unconstrained at the younger end, they must have occurred during or after the Permian (best estimate is less than 260 Ma), which is much later than anticipated from other geological considerations.
Origin of gneisses in the aureole of the San Gabriel anorthosite complex and implications for the Proterozoic crustal evolution of southern California
Authors: Barth Andrew P. , Wooden J. L. , Tosda R. M. , Morrison Jean , Dawson D. L. , Hernly B. M.
Published: February 2004

Granulite facies gneisses along the southwestern margin of the San Gabriel anorthosite complex include compositionally banded, locally migmatitic felsic gneisses and mafic granulites, with rare interlayered augen gneiss and garnet+hypersthene+spinel aluminous gneiss. Previous workers accepted a 1.4 Ga age for these granulites and a 1.2 Ga age for the adjacent anorthosite complex and hence that this Proterozoic basement is allochthonous with respect to the southwestern United States part of the North American craton. Solvus geothermometry in felsic and mafic granulites yields minimum metamorphic temperatures of 900–950°C, and new U‐Pb zircon data yield a minimum metamorphic age of 1186 Ma, coincident with that of the adjacent anorthosite. We reinterpret these rocks as a 1190 Ma anorthosite complex and its granulite‐grade thermal aureole. Geochemical data suggest that the anorthosite complex intruded Early Proterozoic rocks correlative with the Mojave crustal province, representing the North American craton exposed to the northeast. We conclude that these Proterozoic basement rocks represent the southwestern margin of the North American craton and not an exotic terrane accreted in Mesozoic or Tertiary time.
Extensional tectonics in the vicinity of a transform fault in north Iceland
Authors: Långbacka Bo Olof , Gudmundsson Agust
Published: February 2004

At the junction between an oceanic transform fault and the adjacent ridge segments, there is normally a curved fabric. The Tröllaskagi peninsula is located just south of the junction between the Kolbeinsey ridge and the Tjörnes fracture zone and offers a rare opportunity for studying the three‐dimensional tectonics of the associated curved fabric. For the purpose of elucidating its infrastructure, we measured the attitudes of tens of lava flows and several hundred dykes, faults, and mineral veins in 28 profiles in the northern half of the Tröllaskagi peninsula. At sea level the general dip of the lava pile is 6°–14°, but in the northernmost part of the peninsula the dip is 10°–36°, with an average of 22°. Most dykes are basaltic and strike north or NNE. They are exceptional as regards thickness, frequency of multiple dykes and crustal dilation. The average thickness, 5.9 m, and a crustal dilation of 28% in a 4.5‐km‐long profile are the highest figures reported from regional dyke swarms in Iceland. Most faults are normal faults. The curved fabric is limited to the northernmost part of the Tröllaskagi peninsula and consists of two main sets of fractures. One set includes north and NNE striking faults, mineral veins, and dykes. The other set consists of NW striking (oblique) faults, mineral veins, and tilted lava flows. A boundary element model indicates that the abnormal lava dip and the NW striking (oblique) extensional structures in the northernmost part of the peninsula are attributable to the stress field associated with the junction between the Kolbeinsey ridge and the Tjornes fracture zone.
The transition from a volcanic to a nonvolcanic rifted margin off eastern Canada
Authors: Keen C. E. , Potter D. P.
Published: February 2004

Three multichannel seismic reflection profiles were collected on the rifted continental margin southeast of Nova Scotia, eastern Canada. The profiles cross the East Coast Magnetic Anomaly (ECMA), which parallels much of the margin of eastern North America south of the Grand Banks and which is usually associated with the transition from continental to oceanic crust. Studies to the south of the work reported here suggest that the ECMA may be related to the emplacement of large thicknesses of late rift stage or early drift stage igneous material which is characterized by seaward dipping reflections in basement and a high‐velocity lower crustal layer. The seismic data show that seaward dipping reflections (SDR) continue northward into the study area and support the correlation between the SDR unit and the presence of a well‐developed ECMA. Magnetic modeling confirms this association, although it does not rule out an additional contribution to the magnetic anomaly from an edge effect or suture. Just north of the study area the ECMA diminishes and is no longer well developed. The SDR unit also terminates and it is not observed over most of the Nova Scotian margin. If our understanding of the origin of these features is correct then their disappearance marks a transition from a volcanic margin in the south to a nonvolcanic margin in the north. The association of the transition with significant changes in the prerift fabric of the adjacent continental crust, in the trend of synrift extensional structures, and in the width of the zone of thinned continental crust below the margins must be clues to the deeper processes controlling the amount of volcanism produced. We suggest that these clues are consistent with small‐scale convection as a mechanism for delivering large melt volumes to crustal depths during rifting.
Closed‐form solution for finger width in sandy soils at different water contents
Authors: Liu Yaping , Steenhuis Tammo S. , Parlange J.‐Yves
Published: February 2004

Wetting front instability and gravity‐driven fingers can occur during infiltration in sandy soil. These soils overlay many major aquifers. Finger width and velocity are important parameters in predicting the risk of groundwater pollution in these soils. In previous studies, closed‐form solutions were developed for air dry soil. In uniformly wet soils, where the fingers are much wider, predictive finger width equations have failed so far. In this paper we simplify further the Parlange‐Hill closed‐form solution for dry soil and show that, by taking hysteresis into account, it applies to fingers emanating from a point source in a sandy test soil at two widely different moisture contents.
A higher‐order approximation to effective conductivity in media of anisotropic random structure
Authors: Indelman P. , Abramovich B.
Published: February 2004

Properties of the effective conductivity tensor Keff are studied by deriving the second‐order terms in its expansion in the variance σ2 of normally distributed log conductivity. It is shown that for media of anisotropic structure, the components of the effective conductivity tensor are expressed by a functional of the log conductivity covariance; that is, it depends on the shape of the correlation function and not only on anisotropy ratios, variance σ2, and space dimensions. However, the trace of Keff is independent of the log conductivity autocovariance, and for a given mean conductivity depends only on σ2. The dependence of the effective conductivity on the correlation structure is illustrated for Gaussian and exponential autocovariances of log conductivity and for two‐ and three‐dimensional flows.
Transport modeling in heterogeneous aquifers: 1. Statistical description and numerical generation of gravel deposits
Authors: Jussel Peter , Stauffer Fritz , Dracos Themistocles
Published: February 2004

Transport of solutes in groundwater is decisively influenced by the heterogeneity of the aquifer. The goal of the present work is the numerical generation of synthetic heterogeneous aquifer models based on a statistical description of heterogeneities in gravel aquifers. Large unweathered outcrops in several gravel pits in northeastern Switzerland were investigated in this context. On the basis of sedimentological observations it was possible to specify distinct sedimentary structures appearing as lenses or layers. All structures have been identified in each of the investigated outcrops. By inspecting and analyzing photographs of the outcrops, it was possible to estimate the probability density functions (pdf) of the geometrical attributes of the sedimentary structures. Disturbed and undisturbed samples were taken from these structures to estimate the pdf of their hydraulic properties, that is, the hydraulic conductivity and the porosity. The information obtained is used to generate distinct numerical realizations by unconditional stochastic simulation of synthetic aquifers having the same statistical properties with respect to hydraulic conductivity and porosity as the investigated deposits.
Water transfer and major environmental provisions of the Central Valley Project Improvement Act: A preliminary economic evaluation
Authors: Loomis John B.
Published: February 2004

Increasing block water pricing, water transfer, and wildlife refuge water supply provisions of the Central Valley Project (CVP) Improvement Act are analyzed in terms of likely farmer response and economic efficiency of these provisions. Based on a simplified partial equilibrium analysis, we estimate small, but significant water conservation savings due to pricing reform, the potential for substantial water transfers to non‐CVP customers in severe drought years when the water price exceeds $110 per acre foot (1 acre foot equals 1.234 × 103 m3) and positive net benefits for implementation of the wildlife refuge water supply provisions. The high threshold water price is partly a result of requiring farmers to pay full cost on transferred water plus a surcharge of $25 per acre foot if the water is transferred to a non‐CVP user. The act also sets an important precedent for water pricing reform, water transfer provisions, and environmental surcharges on water users that may find their way to other Bureau of Reclamation projects.
Marginal bed load transport in a gravel bed stream, Sagehen Creek, California
Authors: Andrews E. D.
Published: February 2004

Marginal bed load transport describes the condition when relatively few bed particles are moving at any time. Bed particles resting in the shallowest bed pockets will move when the dimensionless shear stress т* exceeds a value of about 0.020. As т* increases, the number of bed particles moving increases. Significant motion of bed particles, i.e., when a substantial fraction of the bed particles are moving, occurs when т* exceeds a value of about 0.060. Thus marginal bed load transport occurs over the domain 0.020 < т* < 0.060. Marginal bed load transport rates and associated hydraulic characteristics of Sagehen Creek, a small mountain gravel bed stream, were measured on 55 days at discharges ranging from slightly less than one half of the bank‐full discharge to more than 4 times the bank‐full discharge. Dimensionless shear stress varied from 0.032 to 0.042, and bed particles as large as the 80th percentile of the bed surface were transported. The relation between reference dimensionless shear stress and relative particle protrusion for Sagehen Creek was determined by varying т*ri to obtain the best fit of the Parker bed load function to the measured transport rates. During the period of record (water years 1954–1991), the mean annual quantity of bed load transported past the Sagehen Creek gage was 24.7 tons. Forty‐seven percent of all bed load transported during the 38 years of record occurred in just 6 years. During 10 of the 38 years of record, essentially no bed load was transported. The median diameter of bed load was 26 mm, compared to 58 mm in the surface bed material.
Numerical simulation of downstream fining by selective transport in gravel bed rivers: Model development and illustration
Authors: Hoey Trevor B. , Ferguson Rob
Published: February 2004

A numerical model has been developed for the routing of gravel‐sized sediment along a river channel which is free to adjust both its long profile and surface texture. Hydraulic calculations use a step‐backwater approach, and sediment transport is predicted with the method of Parker (1990a), which uses a low degree of size selectivity. Exchange of sediment between the surface and subsurface is described using the modified Exner equation of Parker and Sutherland (1990). The model is applied to an idealized channel based on the highly concave Allt Dubhaig, Scotland, in which fining by particle wear is minor. The rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to <102 years under the present flow regime of the river. The evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described. It is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective. This run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions, which are summarized here and will be described in a subsequent paper.
Comparison of transfer function and deterministic modeling of area‐averaged solute transport in a heterogeneous field
Authors: Tseng Peng‐Hsiang , Jury William A.
Published: February 2004

The predictions of two one‐dimensional solute transport models describing area‐averaged mean field concentrations under steady state water flow conditions were tested through numerical experiments. The two models are based on different solute dispersion process hypotheses, namely, the stochastic‐convective process of the convective lognormal transfer function model and the advective‐dispersive process of the advection‐dispersion equation model. Two hypothetical random fields having different correlation structures for their hydraulic and retention properties were generated through a random scaling factor δ. The numerical experiments were conducted by running solute transport simulations in these hypothetical fields, and the simulation results were used to calibrate the two process models. The simulation results demonstrated that even under steady state, one‐dimensional water flow in the medium having a short correlation length scale, considerable local variations in solute concentration were still present in the simulation results. The observed dispersion in the mean field data was intermediate between the representations in the two extreme process hypotheses of the two models tested, and neither model was accurate over the entire range of testing. Predictions of the asymptotic dispersivity based on the analysis used in saturated flow were not valid under unsaturated conditions. Complete knowledge of the velocity field was required in the latter case to predict the asymptotic dispersivity.
A framework for quantitative analysis of surface water‐groundwater interaction: Flow geometry in a vertical section
Authors: Nield Simon P. , Townley Lloyd R. , Barr Anthony D.
Published: February 2004

A numerical model is used to examine groundwater flow in vertical section near surface water bodies, such as lakes, wetlands, ponds, rivers, canals, and drainage and irrigation channels. Solutions are generated partly by superposition to achieve computational efficiency. A large number of flow regimes are identified, with their characteristics controlled by regional water table gradients, recharge to the aquifer, water body length, aquifer anisotropy, and the hydraulic resistance of the bottom sediments. Different flow regimes are distinguished by the presence and nature of groundwater mounds or depressions near the edges of a surface water body and by corresponding stagnation points. Ranges of values for dimensionless flow parameters over which particular regimes occur are determined for six representative geometries and presented in the form of transition diagrams. Increasing anisotropy or sediment resistance and decreasing the length of a water body relative to aquifer thickness are shown to have similar effects on flow geometry, the main effect being an increasing tendency for stagnation points to form in the interior of the aquifer. Flow‐through behavior becomes more prevalent with decreasing anisotropy and sediment resistance and increasing water body length.
Evaporation of intercepted snow: Analysis of governing factors
Authors: Lundberg A. , Halldin S.
Published: February 2004

Insufficient understanding of winter hydrology conditions still hampers progress in predicting springtime discharge. The least known term in the winter water balance is evaporation, particularly of intercepted snow. Recent studies have shown that the evaporation from intercepted snow can be important. This paper elaborates factors governing evaporation of intercepted snow. Measurements with a cut tree‐weighing device combined with a method to measure throughfall and drip gave a maximum evaporation rate of 0.3 ± 0.06 mm/h or 3.3 ± 0.06 mm/24 hours from a 6‐m‐high spruce. Calculations of evaporation with a combination equation and different ways to calculate the aerodynamic resistance and the evaporation from a snow‐intercepted canopy during melt and sleet events showed that the most important factors for calculating the evaporation were the relative humidity, the aerodynamic resistance, the wind speed, and the intercepted mass. Less important factors were the energy to melt the intercepted snow, the method for calculating reduction in evaporation caused by a partly snow‐covered canopy, accuracy in measurement of wind speed, air temperature, and net radiation.
Comparison of the Eagleson statistical‐dynamical water balance model with numerical simulations
Authors: Salvucci Guido Daniel , Entekhabi Dara
Published: February 2004

With minor modification an existing analytic model employing a simple statistical description of soil moisture dynamics is found to give accurate estimates of the mean water balance partitioning; comparisons are made to a Monte Carlo numerical simulation of unsaturated moisture flow in a soil column. In the statistical‐dynamical model the complex temporal and spatial characteristics of the soil moisture profile are approximated by a single effective soil moisture: the equilibrium soil moisture (S0) for which the modeled long‐term mean fluxes are in balance. The relation between this equilibrium soil moisture and the equivalent steady state moisture profile (the steady profile which transmits the long‐term mean flow) is discussed. The test numerical integrations of the flow and conservation equations are designed to represent a deep one‐dimensional soil column. Soil surface boundary conditions are defined by the interaction of the surface soil moisture with a stochastic event‐based atmospheric forcing model, allowing for state dependent switching from flux boundary conditions (rainfall intensity and potential evaporation) to concentration conditions (ponded and dry surface), thus simulating infiltration‐excess runoff production and soil‐limited evaporation. The ability of the equilibrium model to estimate the mean water balance under a large range of soil textures (from clay to sand loam) and climate forcings (humid to arid) implies that the soil moisture profile may, for purposes of climate water balance, be represented in a simple fashion.
The topography of optimal drainage basins
Authors: Sun T. , Meakin P. , Jøssang T.
Published: February 2004

A model for drainage networks and their associated landscapes has been developed. This model is based on the minimum energy dissipation principle and an empirical relationship s ∼ Qα between the slope s of each link in a channel network and the mean annual discharge Q that flows through it. The model was studied using six different values for the exponent α. The surfaces of these minimum energy dissipation drainage networks appear to be more complex than simple self‐affine fractals. The drainage basins in these optimal drainage networks have power law size (area) distributions with a universal exponent, which is independent of the value of α. For the minimum energy dissipation drainage networks obtained using a particular value for α, the basin shapes are similar to each other. An empirical relationship has also been found to relate the basins' “length‐width” ratio to the value of α.