ALBERT

Notes: Classification of soil based on structure is useful for conveying information about physical properties and soil processes. The distance transform is an image analysis technique suitable for quantifying soil structure. An analysis of distance transform data, in the form of cumulative area distribution curves for previously published images of soil structures of various types, is presented. The images were used to derive a quantitative classification of structure using maximum distance of solid from a macropore (Dmax, measured), the distance from macropore space containing 50% of the solid area (k, derived by fitting a sigmoidal function to the cumulative area distribution curve), the total interface length between pore and solid per area of sample (IA, measured), the porosity or the proportion of pores per area of sample (PA, measured) and the pore distribution characteristic (n, derived by fitting a sigmoidal function to the cumulative area distribution curve) which is related to the number, continuity and distribution of pores. The influence of image resolution was investigated, and within limits found to be fairly small. The final classification of soil structure was based on the hypothesized relations between the descriptors and structure-forming processes.

Notes: To investigate the effect of soil physical conditions and land use on emissions of nitrous oxide (N2O) to the atmosphere, soil cores of an imperfectly drained gleysol were taken from adjacent fields under perennial ryegrass and winter wheat. The cores were fertilized with ammonium nitrate and incubated at three different temperatures and water-filled pore space (WFPS) values, and N2O emissions were measured by gas chromatography. Emissions showed a very large response to temperature. Apparent values of Q10 (emission rate at (T + 10)°C/emission rate at T°C) for the arable soil were about 50 for the 5–12°C interval and 8.9 for 12–18°C; the corresponding Q10s for the grassland soil were 3.7 and 2.3. Emissions from the grassland soil were always greater than those from the arable soil, although the ratio narrowed with increasing temperature. Changes in soil WFPS also had a profound effect on emissions. Those from the arable soil increased about 30-fold as the WFPS increased from 60 to 80%, while that from the grassland soil increased 12-fold. This latter response was similar to earlier field measurements. The N2O emissions were considered to be produced primarily by denitrification. We concluded that the impacts of temperature and WFPS on emissions could both be explained on the basis of existing models relating increasing respiration or decreased oxygen diffusivity, or both, to the development of anaerobic zones within the soil.

Notes: The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC.The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P 〈 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water-soluble P than either the Olsen or Morgan tests for P in soil.

Notes: This study tested the hypothesis that, like dissolved organic nitrogen (N), dissolved organic phosphorus (P) and sulphur (S) are more mobile in soil than is organic carbon (C). To do so, I compared the sorption of organic P and S to subsoil materials with that of organic C. Soil samples were equilibrated with water-soluble organic matter from the forest floor at pH 4 and in the equilibrium solutions organic C, P, and S, and their distributions between the hydrophilic and hydrophobic fraction were determined. Sorption of C within the organic matter did not differ from that of P and S. However, the hydrophilic fraction contained the vast majority of P and S and sorbed far less than the hydrophobic fraction. So the overall retention of organic P and S was smaller than that of organic C. This result suggested that dissolved organic matter is more important in the loss of plant nutrients than in the release of C from soil.

Notes: Despite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non-steady-state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple-component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine-textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non-steady-state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non-linear increase in its concentration in the headspace of a non-steady-state chamber.

Notes: The structural condition of swelling soils can be assessed from their shrinkage curves. We re-evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ϑ. The points on the e–ϑ curve were fitted with a constitutive shrinkage equation using an unbiased least-squares, curve-fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(ϑ), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(ϑ), from which the maximum curvature at the wet end was used to separate the structural shrinkage, Sc, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, Sc and the volumetric air content, θac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential.

Notes: It is essential that important field processes are taken into account to model water flow and chemical transport accurately in agricultural fields. Recent field studies indicate that transport through macropores can play a major role in the export of solutes and particulates from drained agricultural land into surface water. Non-ideal drain behaviour may further modify the flow and transport. We extended an existing two-dimensional flow and transport model for variably saturated soils (SWMS_2D) by adding a macropore domain and an additional Hooghoudt drain boundary condition. The Hooghoudt boundary condition accounts for an entrance head needed to initiate flow into the drains. This paper presents the application of the new model (M-2D) to an agricultural field in Switzerland. To understand interactions between macropore flow and drains better we simulated water flow and bromide transport for four different field scenarios. We considered both collector drains only with an ideal drain boundary condition (with and without macropores) and collectors and laterals with a Hooghoudt boundary condition (also with and without macropores). For each scenario, inverse modelling was used to identify model parameters using 150 days of data on observed cumulative discharge, water table depth, and tracer concentration. The models were subsequently tested against a 390-day validation data set. We found that the two additional components (macropore flow, drain entrance head) of the M-2D model were essential to describe adequately the flow regime and the tracer transport data in the field.

Notes: The processes controlling the solid–solution partitioning of organic matter in soils are central to understanding carbon cycling in terrestrial ecosystems, yet are poorly understood at present. We studied the partitioning of soil organic matter between solid and solution in batch titrations of 12 soil samples from three European forests in a range of climates. We also examined the release of soil organic matter on repeated leaching. The partitioning was simulated using a model that pictures the pool of potentially mobile organic matter to consist of fractions of differing solubilities. Desorption of organic matter was then effected by an increase in the electrical charge of the organic molecules due to their chemical reactions with other soil components.The model could simulate the partitioning of organic matter in all the soils using two parameters describing the amounts of soil organic matter in each fraction. The release of organic matter on repeated leaching was reasonably well described. The model predicted that dissolved organic matter should have become more hydrophilic with depth in the soil, due to the retention of more hydrophobic components in the upper horizons. This accorded with observed compositions of the soil organic matter. The model also showed that at the ambient pH of the soils, only a small proportion of the potentially mobile organic matter (comprising fulvic acids and hydrophilic moieties) was involved in partitioning to the solution.

Notes: Organic acidity and its degree of neutralization in the forest floor can have large consequences for base cation leaching under different tree species. We investigated the effect of organic acids on base cation leaching from the forest floor under six common North American tree species. Forest floor samples were analysed for exchangeable cations and forest floor solutions for cations, anions, simple organic acids and acidic properties. Citric and lactic acid were the most common of the acids under all species. Malonic acid was found mainly under Tsuga canadensis (hemlock) and Fagus grandifolia (beech). The organic acids were positively correlated with dissolved organic carbon and contributed significantly to the organic acidity of the solution (up to 26%). Forest floor solutions under Tsuga canadensis contained the most dissolved C and the most weak acidity among the six tree species. Under Tsuga canadensis we also found significant amounts of strong acidity caused by deposition of sulphuric acid from the atmosphere and by strong organic acids. Base cation exchange was the most important mechanism by which acidity was neutralized. Organic acids in solution from Tsuga canadensis, Fagus grandifolia, Acer rubrum (red maple) and Quercus rubra (red oak) were hardly neutralized while much more organic acidity was neutralized for Acer saccharum (sugar maple) and Fraxinus americana (white ash). We conclude that quantity, nature and degree of neutralization of organic acids differ among the different tree species. While the potential for base cation leaching with organic acids from the forest floor is greatest under Tsuga canadensis, actual leaching with organic anions is greatest under Acer saccharum and Fraxinus americana under which the forest floor contains more exchangeable cations than does the strongly acidified forest floor under Tsuga canadensis.

Notes: Physical fractionation is used increasingly to study the turnover of organic matter in soil. This essay links the methods of fractionation to concepts of turnover by defining levels of structural and functional complexity that refer to experimentally verifiable pools of organic matter in the soil.Physical fractionation according to size and density of soil particles emphasizes the importance of interactions between organic and inorganic soil components in the turnover of organic matter. It allows the separation of free and occluded uncomplexed organic matter and of primary and secondary organomineral complexes. This methodological approach recognizes that the overall regulation of decomposer activity is through the structure of soil, which determines gas exchange, the availability of substrates and water, and the transport of solutes.Results from physical fractionations suggest three levels of structural and functional complexity in the turnover of organic matter in soil. Primary organomineral complexes isolated from fully dispersed soil account for the primary level of complexity. The clay-, silt- and sand-sized complexes are seen as the basic units in soil, surface reactions between substrates, organisms and minerals being the main regulatory mechanisms. Secondary complexes reflect the degree of aggregation of primary organomineral complexes and refer to the second level of complexity. Physical protection of uncomplexed organic matter and soil organisms and the creation of gas and moisture gradients are emergent features regulating the turnover at this level of complexity. The structurally intact soil (the soil in situ) constitutes the third level of complexity. This integrates the effects of primary and secondary complexes. Emergent structural features associated with this level are resource islands, macropores, roots, mesofauna, tillage and soil compaction, the corresponding functional features being related to the transport and exchange of solutes and gases, and the spatial distribution and comminution of litter and uncomplexed organic matter. Thus, a thorough understanding of the turnover and storage of organic matter in soil can be acquired only by considering all levels of complexity in the decomposition subsystem.

Notes: The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride-extractable Al and the base-extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above-ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)3. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)3 occurs but is the exception.

Notes: A major concern with the safe re-use of biosolids on land is the potential for release of metals from organic matter in the biosolids, due to decomposition proceeding as biosolids age. To quantify the effects of biosolid aging on Cd and Zn bioavailability, two sewage sludges (Lagoon sludge and Filtered sludge) and a garden compost were incubated at 25°C and 35°C for 100 days. Changes in availability of Cd and Zn were determined using isotope dilution principles, with the materials being labelled with carrier-free 109Cd and 65Zn. We determined isotopically exchangeable metal pools (E values) and plant available metal pools (L values) by measuring specific activities of Cd and Zn in soil extracts and in wheat plants, respectively. Changes in carbon content over time were determined using 13C-NMR spectroscopy and chemical extraction methods, and related to changes in availability of metal pools as determined by isotopic procedures.Hot-water-extractable carbon content, assumed to represent easily decomposable organic matter, decreased during the 100 days by 80–190 mg kg−1. The Compost and Lagoon sludge showed no change in L values for Cd or Zn with time, but in the Filtered sludge the L values for Cd and Zn increased significantly, by 43% and 56%, respectively. The isotopically exchangeable pools of Cd and Zn did not change with incubation treatment of the biosolids.These data indicate that the potential for metal release from biosolids as organic matter decomposes depends to a large extent on the biosolid composition.

Notes: The podzolization process is examined in the light of measurements of the solubility characteristics of aluminium fulvate, the extent of dissolution of a proto-imogolite sol by fulvic acid, the adsorption capacity of proto-imogolite for fulvic acid and aluminium fulvate, and published evidence. Fulvic acid at 500 mg l−1 acting on a proto-imogolite (PI) preparation containing 0.95 mmol l−1 Al as PI did not bring enough Al into solution at pH 4.5–5.0 over 4–15 months to cause significant precipitation of the fulvic acid. As allophanic Bs horizons of podzols typically have pH ≥ 4.8, fulvic acids entering them in drainage water cannot be quantitatively precipitated by dissolution of Al from the allophane. They are, however, strongly absorbed on the allophane, and this must be the mechanism that removes most of the fulvic acid at the top of the Bs horizon, and which contributes, along with colloidal humus and root decomposition, to the formation of a Bh horizon.We conclude that fulvic acid plays no active role in podzolization, but only recycles Al and Fe, that have been transferred by biological processes to the O horizon, back to the Bh horizon. The podzolization process, which leads to the formation of an allophanic Bs horizon underlying a progressively deepening E horizon, requires the dissolution of Al-humate and allophanic precipitates at the Bh–Bs interface as well as progressive attack on the more readily weatherable minerals. Inorganic acids, particularly episodic fluxes of nitric acid, could play a major role in this, as well as attack by readily metabolized complexing acids such as oxalic and citric acids released by roots and fungi.In addition to throwing light on the podzolization process, the experimental results provide an explanation of the lower limit to C:Al ratios reported in natural waters, and a check on the applicability of the WHAM chemical equilibrium model to Al–fulvate–proto-imogolite equilibria. In Ca-containing fulvate solutions, Al-fulvate begins to precipitate when C:Al falls below 50, which is also the limiting ratio observed in natural waters. WHAM calculations overestimate by 70–85% the amount of Al-fulvate formed over 4 months at pH 4.5–5.0 in Ca-containing fulvate–imogolite systems.

Notes: Much soil research needs statistics to support and confirm impressions and interpretations of investigations in field and laboratory. Many soil scientists have not been trained in statistical method and as a result apply quite elementary techniques out of context and without understanding.This article concentrates on the most common abuses and misunderstandings and points authors to proper use. It distinguishes variance and standard deviation for measuring dispersion from standard error to indicate confidence in estimates of means. It describes the strictly limited context in which to use the coefficient of variation. It stresses the importance of quoting means and differences between them in contrast to statistical significance, which is at best of secondary interest. It guides readers to inspect and explore their data before deciding to transform them for analysis and illustrates what can be achieved by taking logarithms of single variates and by principal component analysis of multivariate data.

Notes: Changes in farming practices over long times can affect the sorption behaviour of MCPA ((4-chloro-2-methylphenoxy)acetic acid). We studied the adsorption–desorption mechanisms of MCPA on soil with varied amounts and origins of soil organic matter obtained from a long-term field experiment with various organic amendments. The origin of the soil organic matter seems to be crucial for the sorption behaviour of MCPA. Samples of soil amended with sewage sludge sorbed MCPA more strongly than the soil under any other treatment. Peat-amended soil was second followed by soil receiving animal manure, green manure, mineral fertilizer without N and the fallowed soil. Both the carbon content and the origin of the organic matter are important for the sorption. A decrease of carbon content of a soil does not necessarily imply a reduction of sorption capacity for polar organic acids such as MCPA. Nevertheless, our adsorption–desorption experiments suggest that with decreasing carbon content the role of mineral sorption mechanisms could become more pronounced. Our results showed that interactions of soil organic matter and soil minerals distinctly influence adsorption properties for MCPA.

Notes: Replacement of native deep-rooted grasses by shallow-rooted ones has resulted in greater losses of water and nitrogen by drainage. To counter this effect we have tested the hypothesis that liming, and the conversion of annual grass pastures to perennial grass pastures, could improve the sustainability of grazing systems in the high rainfall zone (〉 600 mm per annum) in southeastern Australia, through better use of water and nitrogen. A field experiment consisting of sixteen 0.135 ha (30 m × 45 m) grazed paddocks representing four pasture combinations (annual pasture (mainly Lolium rigidum) without lime (AP–); annual pasture with lime (AP+); perennial pasture (mainly Phalaris aquatica) without lime (PP–), and perennial pasture with lime (PP+)) was carried out from 1994 to 1997 on an acid Sodosol (Aquic Hapludalf) in southern New South Wales, Australia. Measurements were made of surface runoff, subsurface flow (on top of the B horizon) and soil water content. The results showed that perennial grass pastures, especially PP+, extracted approximately 40 mm more soil water each year than the annual grass pastures. As a result, surface runoff, subsurface flow and deep drainage were at least 40 mm less from the perennial pastures. These measurements were further supported by a simulation of soil water deficit and deep drainage for AP– and PP+ paddocks, using 10 years' past meteorological records. Overall, the results suggested that well-grown, phalaris-based pastures could reduce recharge to groundwater and make pastoral systems more sustainable in the high rainfall zone.

Notes: Considerable attention has been paid recently to the influence of surface rock fragments on hydrological and erosional processes, although much of this research has been done on disturbed soils under laboratory conditions. I have studied the effects of rock fragments on soil infiltration, runoff and erosion under field conditions using simulated rainfall on bare areas of natural soils within typical Mediterranean scrubland characterized by patchily distributed vegetation. Sample areas were chosen where rock fragments cover more than half the surface within unvegetated patches. Twenty experiments were carried out by applying rain at an intensity of 55 mm h−1 for 60 minutes. This approach shows that rock fragments (i) retard ponding and surface runoff, and (ii) give greater steady-state infiltration rates and smaller interrill runoff discharges, sediment concentrations and interrill erosion rates. A second set of six experiments was carried out by applying rainfall at an intensity of 55 mm h−1 for two runs of 60 minutes. The second run was initiated 10 minutes after the first. During this interval, surface rock fragments were removed in order to measure their effects on infiltration, interrill runoff and erosion rates. In this way, I showed that water and soil losses are reduced by the rock fragments. After the removal of rock fragments the steady-state infiltration rate diminished from 44.5 to 27.5 mm h−1 and the runoff coefficient, sediment concentration and erosion rates were, respectively, 3, 33 and 39 times greater than they were before the rock fragments were removed.

Notes: Upward infiltration experiments under tension were used to demonstrate the presence of non-equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non-aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single-porosity Richards equation, as well as a variably saturated, dual-porosity model and a dual-permeability model for characterizing non-equilibrium water flow. The laboratory experiments were carried out on 0.10-m-long soil cores having an internal diameter of 0.10 m. Constant pressure heads of −0.10 and −0.01 m were used as the lower boundary condition. Each infiltration was followed by a single-rate evaporation experiment to re-establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus-1D software) with a Marquardt–Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non-equilibrium flow. This behaviour could be well characterized using a model of physical non-equilibrium that divides the medium into inter- and intra-aggregate pores with first-order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis.

Notes: Dipolar dephasing was investigated as a means for quantitatively differentiating protonated and non-protonated and molecularly mobile and rigid components in soil organic matter. We experimented on cellulose, hemicelluloses, lignin, a protein, chitin, charcoal, palmitic acid and two waxes which served as model systems for components of soil organic matter. Dipolar dephasing decay curves showed significant deviation from the expected exponential decay (for non-protonated and methyl carbons) and Gaussian decay (for non-methyl protonated carbons), partly due to rotational and dipolar modulation. No signal is observed for most protonated carbon (excluding methyl carbon) for a dipolar dephasing delay of 45 μs, and so we generated three subspectra, representing non-protonated, non-methyl protonated and methyl carbon classes, requiring the acquisition of just the 0- and 45-μs dipolar dephased spectra. This methodology was applied to eight samples of soil organic matter, allowing the determination of relative contributions of overlapping resonances such as C-substituted and H-substituted aromatics (110–145 p.p.m.), carbohydrate anomeric and tannin (90–110 p.p.m.), and amino acid and methoxyl (45–65 p.p.m.). The waxes behaved aberrantly, probably because some of their components are highly mobile. We determined accurately the exponential dipolar dephasing decay rates of non-protonated carbon resonances, free from the interference of rotational and dipolar modulations.

Notes: Classical double-layer theory is adapted to consider drainage under gravity, air-drying, rewetting with distilled water or with solution, and cation exchange when the double-layer is under a very small retaining pressure or matric potential. In this study, the solid system retains its geometry and the double-layers are either bounded by an air–water interface or are restricted by the solid geometry. The model as presented is suitable for PCs but is restricted to mono- and divalent cations in the presence of a monovalent anion. Representative results for three surface charge densities, three ionic strengths and three ratios of mono- to divalent cations are presented. During drainage, the proportion of monovalent cations increases slightly, the ambient anion concentration decreases, whereas the ionic ratio is relatively constant. During drying by evaporation, the proportion of monovalent cations decreases markedly, whereas the anion concentration and the ionic ratio both increase in the ambient solution. These patterns affect the behaviour of roots and organisms in the soil.The Gapon Exchange constant is found to vary with the initial composition of the double-layer and with the composition of the added solution, but for each combination it tends to an equilibrium value as the volume of the added solution increases. The value of the constant is sensitive to the charge density of the clay surface; the greater the charge density the smaller is the Gapon Exchange constant, suggesting that it should be referred to as the Gapon parameter rather than the Gapon constant. The limitations of the classical theory are discussed in relation to the results obtained.

Notes: Little is known about solubility and soil solution concentrations of most elements occurring in the solid phase of soils. This study reports changes in solution concentrations of 60 mineral elements following CaCO3 addition to a moderately acid semi-natural soil, and possible mechanisms accounting for the differing solubility patterns as related to soil acidity are discussed. Soil solutions were obtained by high-speed centrifuging and ultrafiltration (0.2 μm) of samples at 60% water-holding capacity of the A horizon of a Cambisol developed from a shale–gneiss moraine and supplied with CaCO3 at 20 rates to yield a soil solution pH range of 5.2–7.8. Concentrations of elements were determined in the solutions by ICP-AES or (for most elements) ICP-MS. Several distinct patterns of soil solution concentrations as a function of soil solution pH were demonstrated. Positively related to pH and CaCO3 supply were soil solution concentrations of As, Br, Mo, S, Sb, Se, U, and W, and to a lesser degree, Co, Cr, Hg, Mg, and Sr. Inversely related to pH were concentrations of Al, B, Ba, Bi, Cs, Ce, Eu, Ga, Ge, Fe, Li, K, Rb, Na, Th, and Ti; less distinctly inversely rated were Dy, Er, Gd, Hf, La, Lu, Mn, Nd, Pr, Sm, Sc, Si, Tl, Tm, and Yb. ‘U-shaped’ relationships to pH were demonstrated for the concentrations of Ag, Cd, Nb, Ni, P, V, and Zr. There were no or irregular relations between pH and concentrations of Be, Cu, Ho, Pb, Ta, and Tb. Differences between elements in their soil solution concentrations as related to total (HNO3-digestible) concentrations and the solubility of organic C were also treated. Increasing the pH of a soil by adding CaCO3 changes the solubility of most mineral elements substantially, the several distinct patterns observed being governed by, for example, ionic properties and charge, affinity for organic compounds, and pH-dependent formation and solubility of complexes.

Notes: Error in models and their inputs can be propagated to outputs. This is important for modelling soil processes because soil properties used as parameters commonly contain error in the statistical sense, that is, variation. Model error can be assessed by validation procedures, but tests are needed for the propagation of (statistical) error from input to output. Input error interacts with non-linearity in the model such that it contributes to the mean of the output as well as its error. This can lead to seriously incorrect results if input error is ignored when a non-linear model is used, as is demonstrated for the Arrhenius equation. Tests for non-linearity and error propagation are suggested. The simplest test for non-linearity is a graph of the output against the input. This can be supplemented if necessary by testing whether the mean of the output changes as the standard deviation of the input increases. The tests for error propagation examine whether error is suppressed or exaggerated as it is propagated through the model and whether changes in the error in one input influence the propagation of another. Applying these tests to a leaching model with rate and capacity parameters showed differences between the parameters, which emphasized that statements about non-linearity must be for specific inputs and outputs. In particular, simulations of mean annual concentrations of solute in drainage and concentrations on individual days differed greatly in the amount of non-linearity revealed and in the way error was propagated. This result is interpreted in terms of decoherence.

Notes: Iron-cyanide complexes are present in soils on sites of former gas plants and coke ovens. We have studied the sorption of the complexes ferricyanide, [Fe(CN)6]3–, and ferrocyanide, [Fe(CN)6]4–, on goethite in batch experiments, including the effects of concentration, time, ionic strength, pH, and the extent of reversibility. The sorption of ferricyanide showed features of both outer-sphere and inner-sphere complexation: its extent decreased with increasing pH; it depended on ionic strength; it was quickly and completely reversible; and it induced a change in surface electric potential. In contrast, sorption of ferrocyanide depended on pH to a lesser extent and was not affected by ionic strength at different pHs. The desorption was slower and incomplete. For ferrocyanide we conclude that sorption involves inner-sphere complexation and precipitation of a Berlin-Blue-like phase on the goethite surface.

Notes: Stratigraphic, reservoir and fluid interpretation demands a thorough understanding of the seismic-to-well tie. Data phase, polarity and tuning effects significantly influence this tie and are often poorly understood. By relating seismic character to known subsurface geology, the interpreter should gain better understanding and be able to calibrate himself to his data. This is an important preliminary stage in any seismic interpretation beyond structure.

Notes: Parallels are drawn between phenomena observed in optics and typical characteristics in exploration seismology. Considerations are also made in the context of major physical theories throughout the centuries. It is concluded that the one key similarity between optics and seismics is the transmission volume, which has ‘fuzzy’ characteristics. Distribution of energy in this volume determines the achievable resolution and might give an insight into spatial inhomogeneities in the subsurface.

Notes: Uplift and the accompanying reduction in overburden result in anomalously high velocity in the uplifted rock unit relative to its current depth. The present work utilizes the non-uniqueness of the parameters of instantaneous velocity versus depth functions as an effective tool for uplift studies. The linear function with its two parameters, V0 and k, is a very simple function and is used as the illustrative vehicle. In the parameter space, i.e. in a plot where one axis represents V0 and the other axis represents k, non-uniqueness can be represented by contours of equal goodness-of-fit values between the observed data and the fitted function. The contour delimiting a region of equivalent solutions in the parameter space is called a ‘solution trough’. Uplift corresponds to a rotation of the solution trough in the parameter space. It is shown that, in terms of relative depth changes, there are five possible configurations (five cases) of uplift in a given area (the mobile location) relative to another area (the reference location). The cases depend on whether the uplifted location had attained a (pre-uplift) maximum depth of burial that was greater than, similar to, or smaller than the maximum depth of burial at the reference location. Interpretation of the relationships between the solution troughs corresponding to the different locations makes it possible to establish which of the five cases applies to the uplifted location and to estimate the amount of uplift that the unit had undergone at that location. The difficulty in determining the reduction in velocity due to decompaction resulting from uplift is a main source of uncertainty in the estimate of the amount of uplift. This is a common problem with all velocity-based methods of uplift estimation. To help around this difficulty, the present work proposes a first-order approximation method for estimating the effect of decompaction on velocity in an uplifted area.

Notes: Ideally, traditional vibroseis processing produces a band-limited zero-phase Klauder wavelet through cross-correlation of the sweep with the recorded signal. An alternative wavelet processing method involves deconvolving the sweep from the recorded vibroseis trace. This deconvolution can be achieved through frequency-domain division. We compare and contrast the advantages and disadvantages of sweep deconvolution versus cross-correlation on synthetic and real data.

Notes: The seminal 1954 paper by J.G. Hagedoorn introduced a heuristic for seismic reflector imaging. That heuristic was a construction technique – a ‘string construction’ or ‘ruler and compass’ method – for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace. Later, Kirchhoff migration was developed. This method is based on an integral representation of the solution of the wave equation. For decades Kirchhoff migration has been one of the most popular methods for imaging seismic data. Parallel with the development of Kirchhoff wave-equation migration has been that of Kirchhoff inversion, which has as its objectives both structural imaging and the recovery of angle-dependent reflection coefficients. The relationship between Kirchhoff migration/inversion and Hagedoorn's constructive technique has only recently been explored. This paper addresses this relationship, presenting the mathematical structure that the Kirchhoff approach adds to Hagedoorn's constructive method and showing the relationship between the two.

Notes: We provide a data-driven macro-model-independent stacking technique that migrates 2D prestack multicoverage data into a common-offset (CO) section. We call this new process the CO common-reflection-surface (CRS) stack. It can be viewed as the generalization of the zero-offset (ZO) CRS stack, by which 2D multicoverage data are stacked into a well-simulated ZO section. The CO CRS stack formula can be tailored to stack P-P, S-S reflections as well as P-S or S-P converted reflections. We point out some potential applications of the five kinematic data-derived attributes obtained by the CO CRS stack for each stack value. These include (i) the determination of the geometrical spreading factor for reflections, which plays an important role in the construction of the true-amplitude CO section, and (ii) the separation of the diffractions from reflection events. As a by-product of formulating the CO CRS stack formula, we have also derived a formula to perform a data-driven prestack time migration.

Notes: There is general agreement between different theories giving expressions for the overall properties of materials with dry, aligned cracks if the number density of cracks is small. There is also very fair agreement for fluid-filled isolated cracks. However, there are considerable differences between two separate theories for fluid-filled cracks with equant porosity. Comparison with recently published experimental data on synthetic sandstones gives a good fit with theory for dry samples. However, although the crack number density in the laboratory sample is such that first-order theory is unlikely to apply, expressions correct to second order (in the number density) provide a worse fit. It also appears that the ratio of wavelength to crack size is not sufficiently great for any detailed comparison with effective-medium theories, which are valid only when this ratio is large. The data show dispersion effects for dry cracks and scattering, neither of which will occur at sufficiently long wavelengths. Data from the water-saturated samples indicate that the effect of equant porosity is significant, although the two theories differ strongly as to just how significant. Once again, and in spite of the reservations mentioned above, a reasonable fit between theory and observation can be shown.

Notes: We investigate the seismic detectability of an overpressured reservoir in the North Sea by computing synthetic seismograms for different pore-pressure conditions. The modelling procedure requires the construction of a geological model from seismic, well and laboratory data. Seismic inversion and AVO techniques are used to obtain the P-wave velocity with higher reliability than conventional velocity analysis. From laboratory experiments, we obtain the wave velocities of the reservoir units versus confining and pore pressures. Laboratory experiments yield an estimate of the relationship between wave velocities and effective pressure under in situ conditions. These measurements provide the basis for calibrating the pressure model. Overpressures are caused by different mechanisms. We do not consider processes such as gas generation and diagenesis, which imply changes in phase composition, but focus on the effects of pure pore-pressure variations. The results indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep North Sea reservoirs.

Notes: In order to plan surveys for seismic time-lapse studies, seismograms are usually simulated for a set of earth models corresponding to different stages of the oil production process. This can be expensive because, for reasons of accuracy, finite-difference (FD) modelling is very often applied.We present the Born repeat-modelling technique (BRM), which is a combination of FD modelling and perturbation theory. Production effects are considered as small perturbations of the earth model, and the Born approximation is used to compute the change in the wavefield due to production-induced modifications to the reservoir properties. This is very efficient in the situation described above.We give a detailed description of the proposed modelling scheme and discuss its applicability. The theoretical foundations of BRM are presented for onshore seismic experiments, and an extension to the case of marine (pressure) seismograms is derived. In addition, the performance of BRM is demonstrated with several numerical examples.

Notes: During 1999, horizontal-loop electromagnetic (HLEM) measurements were made over a buried dike in the Al Quweira area, southwest Jordan, using the APEX MAX MIN III instrument, as part of a mineral exploration project. The objectives of the study were (i) to evaluate the resolution of the HLEM technique in field work in detecting and locating anomalies caused by vein-like bodies, and (ii) to assess the capability of HLEM surveys for detecting targets in other locations throughout our geophysical survey programme. In-phase and quadrature anomalies were recorded with 50 m and 100 m coil separations and multiple frequencies across the strike of the buried dike. Data recorded at 43 locations, spaced 10 m apart along the survey line, were interpreted quantitatively. For a 50 m separation, corresponding to shallow depths of investigation, the results do not show any recognizable response from the buried dike. The HLEM data were modelled using a three-layer structure in order to estimate the thickness of the weathering layer along the survey line. Conversely, data obtained with a 100 m separation, corresponding to moderate depths of investigation, reveal significant anomalies from the buried dike at high frequencies. A phasor or vector diagram was used to calculate the response parameter, depth and dip of the buried dike.

Notes: Electrical resistivity tomography was used in Beauce (France) to assess the water extraction by corn plants (evapotranspiration). The acquired pseudosections show conductive anomalies under the plants. A 2D inversion of measurements led us to identify clear resistive features associated with the water losses under the corn-plant rows. New models have been calculated with two different 3D algorithms (finite-difference and moment-method) to take into account 3D structure of the ground and to confirm that periodic resistive features may generate shifted apparent-resistivity anomalies.

Notes: We present a numerical method of simulating seismic wave propagation on unstructured 2D grids. The algorithm is based on the velocity–stress formulation of the elastic wave equation and therefore uses a staggered grid approach. Unlike finite-element or spectral-element methods, which can also handle flexible unstructured grids, we use explicit differential operators for the calculation of spatial derivatives in each time step. As shown in previous work, three types of these operators are used, and their particular performance is analysed and compared with standard explicit finite-difference operators on regular quadratic and hexagonal grids. Our investigations are especially focused on the influence of grid irregularity, sampling rate (i.e. gridpoints per wavelength) and numerical anisotropy on the accuracy of numerical seismograms. The results obtained from the various methods are therefore compared with analytical solutions. The algorithm is then applied to a number of models that are difficult to handle using (quasi-)regular grid methods. Such alternative techniques may be useful in modelling the full wavefield of bodies with complex geometries (e.g. cylindrical bore-hole samples, 2D earth models) and, because of their local character, they are well suited for parallelization.

Notes: An accurate finite-difference solution is developed for the paraxial wave equation in 3D seismic migration. The conventional alternating-direction-implicit (ADI) scheme used in migration causes errors, because the variables in the migration problem are complex-valued, not real-valued, and the imaginary part of the higher-order spatial derivatives cannot be ignored. The accuracy of the 3D paraxial extrapolator is preserved by (i) retaining these higher-order terms so that it does not produce the apparent azimuthal anisotropy in conventional migration, and (ii) filtering the non-physical evanescent waves during the downward extrapolation. The implementation of the accurate solution consists of two steps: firstly, the application of ADI to solve two tridiagonal systems sequentially, and secondly, an interpolation between the extrapolated wavefields of successive extrapolation levels. The method is computationally efficient as it uses the ADI scheme and, in addition, couples the correction for azimuthal anisotropy and the suppression of evanescent waves into a single operation, the interpolation step.

Notes: A prestack reverse time-migration image is not properly scaled with increasing depth. The main reason for the image being unscaled is the geometric spreading of the wavefield arising during the back-propagation of the measured data and the generation of the forward-modelled wavefields. This unscaled image can be enhanced by multiplying the inverse of the approximate Hessian appearing in the Gauss–Newton optimization technique. However, since the approximate Hessian is usually too expensive to compute for the general geological model, it can be used only for the simple background velocity model.We show that the pseudo-Hessian matrix can be used as a substitute for the approximate Hessian to enhance the faint images appearing at a later time in the 2D prestack reverse time-migration sections. We can construct the pseudo-Hessian matrix using the forward-modelled wavefields (which are used as virtual sources in the reverse time migration), by exploiting the uncorrelated structure of the forward-modelled wavefields and the impulse response function for the estimated diagonal of the approximate Hessian. Although it is also impossible to calculate directly the inverse of the pseudo-Hessian, when using the reciprocal of the pseudo-Hessian we can easily obtain the inverse of the pseudo-Hessian. As examples supporting our assertion, we present the results obtained by applying our method to 2D synthetic and real data collected on the Korean continental shelf.

Notes: Consideration is given to some special features of normalized apparent-resistivity (NAR) curves, resulting from the deployment of Wenner electrode arrays on the surface above dipping earth structures. Limiting values of the potential are derived when a direct-current source is located at points on the surface above a simple two-region dipping-bed earth model and their influence on corresponding NAR curve characteristics is investigated. Particular attention is given to the exploitation of such features to provide a new and direct approach to model parameter estimation, either as an alternative to traditional curve-matching techniques or as a source of supporting information when other earth model characterization methods have been employed. Throughout, the emphasis is on the single-dipping-bed model, but application to more complex structures is discussed, including examples of two dipping beds, dipping dikes and more general tilted unconformities.

Notes: Shallow SH-wave reflections are far from routine, although their study can provide insights into important properties of near-surface materials that cannot be inferred from P-wave data alone. Difficulties in separating SH-wave reflections from Love waves are generally considered the major obstacle to progress in shallow SH-wave seismic reflection. This may be the case in surveys undertaken at great depths, but it is not necessarily true for reflection data gathered at shallow and ultra-shallow depths. This paper shows that when SH-wave data possess wavelengths greater than the thickness of the superficial layer, Love waves are not greatly dispersed. In this case, misinterpretation between parts of reflection hyperbolae and waveguide arrivals is sufficiently limited. In a one-layer model earth, which well approximates typical situations of the near-surface underground, the most energetic modes (the lowermost modes) of the dispersed surface waves have a dominant frequency band that falls below the wavelet spectrum of the shallow reflections; therefore, they can be filtered out in the frequency domain. Higher modes, although their spectral content overlaps that of the reflections, exhibit small amplitudes on seismograms and leave strong reflections unaffected.We present field examples from three different sites where we were able to obtain ultra-shallow reflections (〈 3 m) in unconsolidated sediments. The high level of resolution (vertical resolution up to 15 cm) suggests that SH-wave reflection imaging has the potential to complement other high-resolution techniques, such as P-wave reflection and ground-penetrating radar (GPR) imaging, allowing a better and more complete characterization of the near-surface environments.

Notes: Many DC resistivity inversion schemes use a combination of standard iterative least-squares and truncated singular value decomposition (SVD) to optimize the solution to the inverse problem. However, until quite recently, the truncation was done arbitrarily or by a trial-and-error procedure, due to the lack of workable guidance criteria for discarding small singular values. In this paper we present an inversion scheme which adopts a truncation criterion based on the optimization of the total model variance. This consists of two terms: (i) the term associated with the variance of statistically significant principal components, i.e. the standard model estimate variance, and (ii) the term associated with statistically insignificant principal components of the solution, i.e. the variance of the bias term. As an initial model for the start of iterations, we use a multilayered homogeneous half-space whose layer thicknesses increase logarithmically with depth to take into account the decrease of the resolution of the DC resistivity technique with depth. The present inversion scheme has been tested on synthetic and field data. The results of the tests show that the procedure works well and the convergence process is stable even in the most complicated cases. The fact that the truncation level in the SVD is determined intrinsically in the course of inversion proves to be a major advantage over other inversion schemes where it is set by the user.

Notes: A method to estimate interval velocities and thickness in a horizontal isotropic layered medium from wide-angle reflection traveltime curves is presented. The method is based on a relationship between the squared reflection traveltime differences and the squared offset differences relative to two adjacent reflectors. The envelope of the squared-time versus offset-difference curves, for rays with the same ray parameter, is a straight line, whose slope is the inverse of the square of the interval velocity and whose intercept is the square of the interval time. The method yields velocity and thickness estimates without any knowledge of the overlying stratification. It can be applied to wide-angle reflection data when either information on the upper crust and/or refraction control on the velocity is not available. Application to synthetic and real data shows that the method, used together with other methods, allows us to define a reliable 1D starting model for estimating a depth profile using either ray tracing or another technique.

Notes: The inversion of geoelectrical resistivity data is a difficult task due to its non-linear nature. In this work, the neural network (NN) approach is studied to solve both 1D and 2D resistivity inverse problems. The efficiency of a widespread, supervised training network, the back-propagation technique and its applicability to the resistivity problem, is investigated. Several NN paradigms have been tried on a basis of trial-and-error for two types of data set. In the 1D problem, the batch back-propagation paradigm was efficient while another paradigm, called resilient propagation, was used in the 2D problem. The network was trained with synthetic examples and tested on another set of synthetic data as well as on the field data. The neural network gave a result highly correlated with that of conventional serial algorithms. It proved to be a fast, accurate and objective method for depth and resistivity estimation of both 1D and 2D DC resistivity data. The main advantage of using NN for resistivity inversion is that once the network has been trained it can perform the inversion of any vertical electrical sounding data set very rapidly.

Notes: We have developed a three-dimensional inverse scheme for carrying out DC resistivity surveys, incorporating complicated topography as well as arbitrary electrode arrays. The algorithm is based on the finite-element approximation to the forward problem, so that the effect of topographic variation on the resistivity data is effectively evaluated and incorporated in the inversion. Furthermore, we have enhanced the resolving power of the inversion using the active constraint balancing method. Numerical verifications show that a correct earth image can be derived even when complicated topographic variation exists. By inverting the real field data acquired at a site for an underground sewage disposal plant, we obtained a reasonable image of the subsurface structures, which correlates well with the surface geology and drill log data.

Notes: New formulations of boundary conditions at an arbitrary two-dimensional (2D) free-surface topography are derived. The top of a curved grid represents the free-surface topography while the grid's interior represents the physical medium. The velocity–stress version of the viscoelastic wave equations is assumed to be valid in this grid. However, the rectangular grid version attained by grid transformation is used to model wave propagation in this work in order to achieve the numerical discretization. We show the detailed solution of the particle velocities at the free surface resulting from discretizing the boundary conditions by second-order finite-differences (FDs). The resulting system of equations is spatially unconditionally stable. The FD order is gradually increased with depth up to eighth order inside the medium. Staggered grids are used in both space and time, and the second-order leap-frog and Crank–Nicholson methods are used for time-stepping. We simulate point sources at the surface of a homogeneous medium with a plane free surface containing a hill and a trench. Applying parameters representing exploration surveys, we present examples with a randomly realized surface topography generated by a 1D von Kármán function of order 1. Viscoelastic simulations are presented using this surface with a homogeneous medium and with a layered, randomized medium realization, all generating significant scattering.

Notes: In the process of removing the primary field from fixed-wing time-domain airborne EM data, the response is decomposed into two parts, which are referred to here as the time-domain ‘in-phase’ and ‘quadrature’ components. The time-domain in-phase component is dominated by the primary field, which varies significantly as the transmitter–receiver separation changes. The time-domain quadrature component comes solely from the secondary response associated with currents induced in the ground and this is the component that has traditionally been used in the interpretation of data from fixed-wing towed-bird time-domain EM systems. In the off-time, the quadrature response is very similar to the total secondary response. However, there are large differences in the on-time and even some small differences in the off-time.One consequence of these differences is that when airborne EM data are to be interpreted using a synthetic mathematical model, the synthetic data calculated should also be the quadrature component. A second consequence relates to the time-domain in-phase component which is sometimes used to estimate the receiver-sensor (bird) position. The bird-position estimation process assumes there is no secondary field in the in-phase component. If the ground is resistive, the secondary contained in the in-phase component is small, so the bird-position estimate is accurate to about 30 cm, but in highly conductive areas the secondary contribution can be large and the position estimate can be out by as much as 5 m. A third consequence arises for highly conductive bodies, the response of which is predominantly in-phase. This means that any response from these types of body is lost in the component that has been removed in the primary-field extraction procedure. However, if the bird position is measured very accurately, the actual free-space primary field can be estimated. If this is then subtracted from the estimated primary (actually free-space primary plus secondary in-phase response), then the residual is the secondary in-phase response of the ground. Using this methodology, very conductive ore bodies could be detected. However, a sensitivity analysis shows that detection of a large vertically dipping very conductive body at 150 m depth would require that the bird position be measured to an accuracy of about 1.4 cm and the aircraft attitude to within about 0.01°. Such tolerances are very stringent and not easily attainable with current technology.

Notes: A method using simple inversion of refraction traveltimes for the determination of 2D velocity and interface structure is presented. The method is applicable to data obtained from engineering seismics and from deep seismic investigations. The advantage of simple inversion, as opposed to ray-tracing methods, is that it enables direct calculation of a 2D velocity distribution, including information about interfaces, thus eliminating the calculation of seismic rays at every step of the iteration process. The inversion method is based on a local approximation of the real velocity cross-section by homogeneous functions of two coordinates. Homogeneous functions are very useful for the approximation of real geological media. Homogeneous velocity functions can include straight-line seismic boundaries. The contour lines of homogeneous functions are arbitrary curves that are similar to one another. The traveltime curves recorded at the surface of media with homogeneous velocity functions are also similar to one another. This is true for both refraction and reflection traveltime curves. For two reverse traveltime curves, non-linear transformations exist which continuously convert the direct traveltime curve to the reverse one and vice versa. This fact has enabled us to develop an automatic procedure for the identification of waves refracted at different seismic boundaries using reverse traveltime curves. Homogeneous functions of two coordinates can describe media where the velocity depends significantly on two coordinates. However, the rays and the traveltime fields corresponding to these velocity functions can be transformed to those for media where the velocity depends on one coordinate. The 2D inverse kinematic problem, i.e. the computation of an approximate homogeneous velocity function using the data from two reverse traveltime curves of the refracted first arrival, is thus resolved. Since the solution algorithm is stable, in the case of complex shooting geometry, the common-velocity cross-section can be constructed by applying a local approximation. This method enables the reconstruction of practically any arbitrary velocity function of two coordinates. The computer program, known as godograf, which is based on this theory, is a universal program for the interpretation of any system of refraction traveltime curves for any refraction method for both shallow and deep seismic studies of crust and mantle. Examples using synthetic data demonstrate the accuracy of the algorithm and its sensitivity to realistic noise levels. Inversions of the refraction traveltimes from the Salair ore deposit, the Moscow region and the Kamchatka volcano seismic profiles illustrate the methodology, practical considerations and capability of seismic imaging with the inversion method.

Notes: Estimations of porosity and permeability from well logs are important yet difficult tasks encountered in geophysical formation evaluation and reservoir engineering. Motivated by recent results of artificial neural network (ANN) modelling offshore eastern Canada, we have developed neural nets for converting well logs in the North Sea to porosity and permeability. We use two separate back-propagation ANNs (BP-ANNs) to model porosity and permeability. The porosity ANN is a simple three-layer network using sonic, density and resistivity logs for input. The permeability ANN is slightly more complex with four inputs (density, gamma ray, neutron porosity and sonic) and more neurons in the hidden layer to account for the increased complexity in the relationships. The networks, initially developed for basin-scale problems, perform sufficiently accurately to meet normal requirements in reservoir engineering when applied to Jurassic reservoirs in the Viking Graben area. The mean difference between the predicted porosity and helium porosity from core plugs is less than 0.01 fractional units. For the permeability network a mean difference of approximately 400 mD is mainly due to minor core-log depth mismatch in the heterogeneous parts of the reservoir and lack of adequate overburden corrections to the core permeability. A major advantage is that no a priori knowledge of the rock material and pore fluids is required. Real-time conversion based on measurements while drilling (MWD) is thus an obvious application.

Notes: The quantities measured in transient electromagnetic (TEM) surveys are usually either magnetic field components or their time derivatives. Alternatively it might be advantageous to measure the spatial derivatives of these quantities. Such gradiometer measurements are expected to have lower noise levels due to the negative interference of ambient noise recorded by the two receiver coils. Error propagation models are used to compare quantitatively the noise sensitivities of conventional and gradiometer TEM data. To achieve this, eigenvalue decomposition is applied on synthetic data to derive the parameter uncertainties of layered-earth models. The results indicate that near-surface gradient measurements give a superior definition of the shallow conductivity structure, provided noise levels are 20–40 times smaller than those recorded by conventional EM instruments. For a fixed-wing towed-bird gradiometer system to be feasible, a noise reduction factor of at least 50–100 is required. One field test showed that noise reduction factors in excess of 60 are achievable with gradiometer measurements. However, other collected data indicate that the effectiveness of noise reduction can be hampered by the spatial variability of noise such as that encountered in built-up areas. Synthetic data calculated for a vertical plate model confirm the limited depth of detection of vertical gradient data but also indicate some spatial derivatives which offer better lateral resolution than conventional EM data. This high sensitivity to the near-surface conductivity structure suggests the application of EM gradiometers in areas such as environmental and archaeological mapping.

Notes: A space–frequency domain 2D depth-migration scheme is generalized for imaging in the presence of anisotropy. The anisotropy model used is that of a transversely isotropic (TI) medium with a symmetry axis that can be either vertical or tilted. In the proposed scheme the anisotropy is described in terms of Thomsen parameters; however, the scheme can accommodate a wide range of anisotropy rather than only weak anisotropy. Short spatial convolution operators are used to extrapolate the wavefields recursively in the space–frequency domain for both qP- and qSV-waves. The weighted least-squares method for designing isotropic optimum operators is extended to asymmetric optimum explicit extrapolation operators in the presence of TI media with a tilted symmetry axis. Additionally, an efficient weighted quadratic-programming design method is developed. The short spatial length of the derived operators makes it possible for the proposed scheme to handle lateral inhomogeneities. The performance of the operators, designed by combining the weighted least-squares and weighted quadratic-programming methods, is demonstrated by migration impulse responses of qP and qSV propagation modes for the weak and strong TI models with both vertical and tilted symmetry axes. Finally, a table-driven shot-record depth-migration scheme is proposed, which is illustrated for finite-difference modelled shot records in TI media.

Notes: Perturbation methods are common tools for describing wave propagation in weakly anisotropic media. The anisotropic medium is replaced by an average isotropic medium where wave propagation can be treated analytically and the correction for the effect of anisotropy is computed by perturbation techniques. This works well for anisotropies of up to 10%. Some materials (e.g. shales), however, can exhibit a much stronger anisotropy. In this case a background is required which still can be treated analytically but is applicable to stronger P-wave anisotropy. We present an averaging technique to compute a best-fitting ellipsoidal medium to an arbitrary anisotropic medium. Ellipsoidal media are sufficiently simple for analytical expressions to be available for many applications and allow consideration of strong P-wave anisotropy. The averaging of the arbitrary anisotropic medium can be carried out globally (i.e. for the whole sphere) or sectorially (e.g. for seismic waves propagating predominantly in the vertical direction). We derive linear relationships for the coefficients of the ellipsoid which depend on the elastic coefficients of the anisotropic medium. We also provide specifications for best-fitting elliptical and best-fitting isotropic media. Numerical examples for different rocks demonstrate the improved approximation of the anisotropic model obtained using the formulae derived, compared with the conventionally used average isotropic medium.

Notes: There is significant evidence that the anelastic loss of seismic energy is linked to petrophysical properties such as porosity, permeability and clay content. Thus, reliable estimation of anelastic attenuation from seismic data can lead to improved methods for the prediction of petrophysical properties. This paper is concerned with methods for the estimation of attenuation at sonic frequencies (5–30 KHz) from in situ data. Two independent methods have been developed and tested for estimating compressional-wave attenuation from full-waveform sonic data. A well-established technique, the logarithm spectral ratio (LSR) method, is compared with a new technique, the instantaneous frequency (IF) method. The LSR method uses the whole spectrum of the seismic pulse whilst the IF method uses a carefully estimated value of instantaneous frequency which is representative of the centre frequency of the pulse. In the former case, attenuation estimation is based on the relative variation of amplitudes at different frequencies, whilst in the latter case it is based on the shift of the centre frequency of the pulse to lower values during anelastic wave propagation. The IF method does not assume frequency independence of Q which is a necessary assumption for the LSR method, and it provides a stable frequency log, the peak instantaneous frequency (PIF) log, which may be used as an indicator for attenuation under certain limitations. The development and implementation of the two methods is aimed at minimizing the effect of secondary arrivals, such as leaky modes, and involved a series of parameter tests. Testing of the two methods using full-waveform sonic data of variable quality, obtained from a gas-bearing sandstone reservoir, showed that the IF method is in general more stable and suitable for full-waveform sonic data compared with the LSR method. This was evident especially in data sets with high background noise levels and wave-interference effects. For good quality data, the two methods gave results that showed good agreement, whilst comparison with other log types further increased confidence in the results obtained. A significant decrease (approximately 5 KHz) in the PIF values was observed in the transition from an evaporite/shale sequence to the gas-bearing sandstone. Average Q values of 54 and 51 were obtained using good quality data from a test region within the gas-saturated sandstone reservoir, using the LSR and IF methods, respectively.

Notes: The spiking deconvolution of a field seismic trace requires that the seismic wavelet on the trace be minimum phase. On a dynamite trace, the component wavelets due to the effects of recording instruments, coupling, attenuation, ghosts, reverberations and other types of multiple reflection are minimum phase. The seismic wavelet is the convolution of the component wavelets. As a result, the seismic wavelet on a dynamite trace is minimum phase and thus can be removed by spiking deconvolution. However, on a correlated vibroseis trace, the seismic wavelet is the convolution of the zero-phase Klauder wavelet with the component minimum-phase wavelets. Thus the seismic wavelet occurring on a correlated vibroseis trace does not meet the minimum-phase requirement necessary for spiking deconvolution, and the final result of deconvolution is less than optimal. Over the years, this problem has been investigated and various methods of correction have been introduced. In essence, the existing methods of vibroseis deconvolution make use of a correction that converts (on the correlated trace) the Klauder wavelet into its minimum-phase counterpart. The seismic wavelet, which is the convolution of the minimum-phase counterpart with the component minimum-phase wavelets, is then removed by spiking deconvolution. This means that spiking deconvolution removes both the constructed minimum-phase Klauder counterpart and the component minimum-phase wavelets. Here, a new method is proposed: instead of being converted to minimum phase, the Klauder wavelet is removed directly. The spiking deconvolution can then proceed unimpeded as in the case of a dynamite record. These results also hold for gap predictive deconvolution because gap deconvolution is a special case of spiking deconvolution in which the deconvolved trace is smoothed by the front part of the minimum-phase wavelet that was removed.

Notes: In adapting the prestack migration technique used in seismic imaging to the inversion of ground-penetrating radar (GPR) from time- to depth-sections, we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems, albeit with three assumptions. The first two assumptions concern the electromagnetic characteristics of the medium, primarily that the medium must be perfectly resistive and non-dispersive, and the third concerns the antennae radiation pattern, which is taken to be 2D. The application of this adaptation of the inversion method is confirmed by migrating actual GPR measurements acquired on the test site of the Laboratoire Central des Ponts et Chaussées. The results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures. The field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non-dispersive medium. The assumption of a 2D antennae radiation pattern, however, produces artefacts that could be significant for laterally heterogeneous media. Nevertheless, where the medium is not highly laterally heterogeneous, the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium; the scatterers are well focused from diffraction hyperbolae and well localized. Spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass. Objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high, as in the case of iron or water in gneiss gravels. Furthermore, the suitability of multi-offset protocols to estimate the electromagnetic propagating velocity and to decrease the non-coherent noise level of measurements is confirmed. Our velocity estimation is based on the semblance calculation of multi-offset migrated images, and we confirmed the relevance of this quantification method using numerical data. The signal-to-noise ratio is improved by summing multi-offset results after the addition of random noise on measurements. Thus the adaptation of prestack migration to multi-offset radar measurements significantly improves the resolution of the scattering potential of the medium. Limitations associated with the methods used here suggest that 3D algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium.

Notes: Artificial neural networks can be used effectively to identify and classify multiple events in a seismic data set. We use a specialized neural network, a self-organizing map (SOM), that tries to establish rules for the characterization of the physical problem. Selected seismic data attributes from CMP gathers are used as input patterns, such that the SOM arranges the data to form clusters in an abstract space. We show with synthetic and real data how the SOM can identify and classify primaries and multiples, and how it can classify the various types of multiple corresponding to a certain generating mechanism in the subsurface.

Notes: GPR reflection energy varies with antenna orientation relative to the strike and dip of the reflector. This directional dependence of GPR responses was investigated through numerical experiments and was used to estimate the azimuth of fractures and joints. Three antenna configurations were considered in this study: perpendicular-broadside (YY mode), parallel-broadside (XX mode) and cross-polarization (YX mode). The reflection energy in the cross-polarization mode shows a shape characteristic similar to the strike, regardless of the dip angle. Those in the other two modes show quite different amplitudes from the strike, depending on the dip angle. We have developed a strike-direction-finding scheme using data obtained from the three different modes for the same survey line. The azimuth angle of each reflector was displayed in colour on the GPR profile. This scheme was applied to a field survey at a granite quarry in southern Korea. The GPR profiles showed different images of the reflectors depending on the antenna configuration. The estimated azimuths of reflectors obtained using our scheme matched fairly well with those of known fractures and joints.

Notes: Spherical coordinates are a natural orthogonal system for describing wavefronts emanating from a point source. A regular grid distribution in the Cartesian-coordinate system tends to undersample the wavefront description near the source (at the highest wavefront curvature) and oversample it away from the source. Spherical coordinates, in general, provide a more balanced grid distribution for characterizing point-source wavefronts. Our numerical implementation confirms that the recently introduced fast marching algorithm is both a highly efficient and an unconditionally stable eikonal solver. However, its first-order approximation of traveltime derivatives can induce relatively large traveltime errors for waves propagating in a diagonal direction with respect to the coordinate system. Examples, including the IFP Marmousi and the SEG/EAGE 3D salt-dome models, show that a spherical-coordinate implementation of the method results in far fewer errors in traveltime calculation than the conventional Cartesian-coordinate implementation, and with practically no loss in computational advantages.

Notes: The root cause of the instability problem of the least-squares (LS) solution of the resistivity inverse problem is the ill-conditioning of the sensitivity matrix. To circumvent this problem a new LS approach has been investigated in this paper. At each iteration, the sensitivity matrix is weighted in multiple ways generating a set of systems of linear equations. By solving each system, several candidate models are obtained. As a consequence, the space of models is explored in a more extensive and effective way resulting in a more robust and stable LS approach to solving the resistivity inverse problem. This new approach is called the multiple reweighted LS method (MRLS). The problems encountered when using the L1- or L2-norm are discussed and the advantages of working with the MRLS method are highlighted. A five-layer earth model which generates an ill-conditioned matrix due to equivalence is used to generate a synthetic data set for the Schlumberger configuration. The data are randomly corrupted by noise and then inverted by using L2, L1 and the MRLS algorithm. The stabilized solutions, even though blurred, could only be obtained by using a heavy ridge regression parameter in L2- and L1-norms. On the other hand, the MRLS solution is stable without regression factors and is superior and clearer. For a better appraisal the same initial model was used in all cases. The MRLS algorithm is also demonstrated for a field data set: a stable solution is obtained.

Notes: Amplitude-variation-with-offset (AVO) analysis is based on the Zoeppritz equations, which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence. High-frequency (up to 700 Hz) AVO studies, presented here, have been used to determine the physical properties of sediments in a shallow marine environment (20 m water depth). The properties that can be constrained are P- and S-wave velocities, bulk density and acoustic attenuation. The use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections. In the past, marine sediments have been modelled as elastic materials. However, viscoelastic models which include absorption are more realistic. At angles of incidence greater than 40°, AVO functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence. The influence of S-wave velocity on the reflection coefficient is small (especially for low S-wave velocities encountered at the sea-floor). Thus, it is difficult to extract the S-wave parameter from AVO trends. On the other hand, P-wave velocity and density show a considerably stronger effect. Attenuation (described by the quality factor Q) influences the reflection coefficient but could not be determined uniquely from the AVO functions. In order to measure the reflection coefficient in a seismogram, the amplitudes of the direct wave and the sea-floor reflection in a common-midpoint (CMP) gather are determined and corrected for spherical divergence as well as source and streamer directivity. At CMP locations showing the different AVO characteristics of a mud and a boulder clay, the sediment physical properties are determined by using a sequential-quadratic-programming (SQP) inversion technique. The inverted sediment physical properties for the mud are: P-wave velocity α=1450±25 m/s, S-wave velocity β=90±35 m/s, density ρ=1220±45 kg/m3, quality factor for P-wave QP=15±200, quality factor for S-wave QS=10±30. The inverted sediment physical properties for the boulder clay are: α=1620±45 m/s,β=360±200 m/s,ρ=1380±85 kg/m3,QP=790±660,QS=25±10.

Notes: The most difficult part of multicomponent processing is the estimation of the shear-wave velocity map for migration. We used refracted shear waves and a simple iterative method called wavefield continuation (WFC) to evaluate the shallow shear-wave velocity profile on a real data example. The WFC was developed in 1981 by Clayton and McMechan to determine compressional-wave velocity profiles from refracted compressional waves. The application to refracted shear waves is straightforward. The real data example shows that shear structure can be easily determined independently of the compressional structure.

Notes: A model-independent Hamiltonian formulation of paraxial and diffracted ray-tracing equations is presented. It is applied to asymptotic Green's function computations. The medium can have an arbitrary number of interfaces, possibly intersecting at diffracting edges and vertices. Continuously varying model parameters and anisotropy are allowed. The algorithm for elastic waves, involving accuracy control and amplitude computation, is implemented in a platform-independent object-orientated C++ package. Numerical tests and modelling examples are presented.

Notes: This paper describes the results of using geophysical techniques to investigate three columns of the Pronaos of the Antonino and Faustina temple (AD 141) in Rome, Italy; the columns are of cipollino marble which shows alternate sequences of mica and calcite beds. We applied seismic refraction using traditional interpretation, and seismic transmission tomography. The comparison between the results of the refraction study and the 2D and 3D isotropic tomographic analyses suggested anisotropic characteristics for the marble, and this prompted us to perform a further tomographic experiment, taking into account these characteristics of the material. Assuming an elliptical model, the main directions of anisotropy were detected. Two velocity fields corresponding to the main directions of the anisotropy were measured and anomalies such as cracks and fractures were noted. The conjugate-gradient algorithm was used to invert the data. The results of the isotropic and anisotropic models were compared. The correlation between the methods highlighted the characteristics of the marble, i.e. anisotropy, depth of the weathering, fractures and small cracks. The results show that the material of the columns is in reasonable condition, with the exception of a surface area 6 cm to 15 cm deep that we estimate has been weathered for 2000 years, and that has been particularly affected by pollution in the last century.

Notes: This is the final paper in a series on the 3D multicomponent seismic experiment in Oman. In this experiment a 3D data set was acquired using three-component geophones and with three source orientations. The data set will subsequently be referred to as the Natih 9C3D data set. We present, for the first time, evidence demonstrating that shear waves are sensitive to fluid type in fractured media. Two observations are examined from the Natih 9C3D data where regions of gas are characterized by slow shear-wave velocities. One is that the shear-wave splitting map of the Natih reservoir exhibits much larger splitting values over the gas cap on the reservoir. This increase in splitting results from a decrease in the slow shear-wave velocity which senses both the fractures and the fracture-filling fluid. Using a new effective-medium model, it was possible to generate a splitting map for the reservoir that is corrected for this fluid effect. Secondly, an anomaly was encountered on the shear-wave data directly above the reservoir. The thick Fiqa shale overburden exhibits a low shear-wave velocity anomaly that is accompanied by higher shear reflectivity and lower frequency content. No such effects are evident in the conventional P-wave data. This feature is interpreted as a gas chimney above the reservoir, a conclusion supported by both effective-medium modelling and the geology.With this new effective-medium model, we show that introduction of gas into vertically fractured rock appears to decrease the velocity of shear waves (S2), polarized perpendicular to the fracture orientation, whilst leaving the vertical compressional-wave velocity largely unaffected. This conclusion has direct implications for seismic methods in exploration, appraisal and development of fractured reservoirs and suggests that here we should be utilizing S-wave data, as well as the conventional P-wave data, as a direct hydrocarbon indicator.

Notes: A three-dimensional (3D) inversion program is developed to interpret gravity data using a selection of constraints. This selection includes minimum distance, flatness, smoothness and compactness constraints, which can be combined using a Lagrangian formulation. A multigrid technique is also implemented to resolve separately large and short gravity wavelengths. The subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters, i.e. the densities of each block. Weights are given to each block depending on depth, a priori information on density and the density range allowed for the region under investigation. The present computer code is tested on modelled data for a dipping dike and multiple bodies. Results combining different constraints and a weight depending on depth are shown for the dipping dike. The advantages and behaviour of each method are compared in the 3D reconstruction. Recovery of geometry (depth, size) and density distribution of the original model is dependent on the set of constraints used. From experimentation, the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies. The inversion method is tested on real gravity data from the Rouyn-Noranda (Quebec) mining camp. The 3D inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface; it enables the determination of the geometry of plutons and intrusive rocks at depth.

Notes: We present a new automatic time-picking method based on third-order statistics, namely bicoherence correlation. Contrary to conventional methods, which are based on second-order statistics (i.e. cross-correlation or neural-network trainings), our method is less sensitive to coloured noise as well as the bandwidth of the signal. Bicoherence correlation can also be used for autotracking events in seismic data for an interpretation.

Notes: Electrical and electromagnetic profiling methods are used extensively in environmental geophysical investigations for many different purposes. The pulled array continuous electrical sounding (PACES) method, where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations, has been used extensively for mapping the vulnerability of aquifers in Denmark. Measurements are taken every 1 m, and 10–15 km of profile can be achieved in one day.This paper presents a theoretical study of the resolution capabilities of PACES measurements as they are now performed, and an experimental design study for including an inductive source in the measuring equipment. The joint interpretation of the galvanic data set of ordinary PACES measurements with inductive data from a horizontal magnetic dipole source will enhance the resolution capabilities of the data set significantly. The study is carried out as an analysis of the uncertainty of the model parameters of one-dimensional three-layer models using the estimation error variances of the inversion problem.The results indicate that the addition of only two frequency data from a magnetic dipole source will substantially improve the resolution of the subsurface resistivity structure. The improvement is model dependent, but reduction in the relative error of model parameters by an order of magnitude is observed.

Notes: Self-potential anomalies with unexplained high values have been observed in various places. Such anomalies were reported in Peru more than 30 years ago. An explanation is proposed based on the electrokinetic effect obtained when a topographic high occurs above a rock layer through which water filtrates and which itself lies over a highly resistive layer. In such a case a fairly high self-potential may occur. Conversely, when one of these conditions is not met, the self-potential anomaly at the earth's surface resulting from the electrokinetic effect is strongly attenuated.

Notes: The shape and location of clay within sandstones have a large impact on the P-wave and S-wave velocities of the rock. They also have a large effect on reservoir properties and the interpretation of those properties from seismic data and well logs. Numerical models of different distributions of clay – structural, laminar and dispersed clay – can lead to an understanding of these effects. Clay which is located between quartz grains, structural clay, will reduce the P-wave and S-wave velocities of the rock. If the clay particles become aligned or form layers, the velocities perpendicular to the alignment will be reduced further. S-wave velocities decrease more rapidly than P-wave velocities with increasing clay content, and therefore Poisson's ratios will increase as the velocities decrease. These effects are more pronounced for compacted sandstones. Small amounts of clay that are located in the pore space will have little effect on the P-wave velocity due to the competing influence of the density effect and pore-fluid stiffening. The S-wave velocity will decrease due to the density effect and thus the Poisson's ratio will increase. When there is sufficient clay to bridge the gaps between the quartz grains, P-wave and S-wave velocities rise rapidly and the Poisson's ratios decrease. These effects are more pronounced for under-compacted sandstones. These general results are only slightly modified when the intrinsic anisotropy of the clay material is taken into account. Numerical models indicate that there is a strong, nearly linear relationship between P-wave and S-wave velocity which is almost independent of clay distribution. S-wave velocities can be predicted reasonably accurately from P-wave velocities based on empirical relationships. However, this does not provide any connection between the elastic and petrophysical properties of the rocks. Numerical modelling offers this connection but requires the inclusion of clay distribution and anisotropy to provide a model that is consistent with both the elastic and petrophysical properties. If clay distribution is ignored, predicting porosities from P-wave or S-wave data, for example, can result in large errors. Estimation of the clay distribution from P-wave and S-wave velocities requires good estimates of the porosity and clay volume and verification from petrographic analyses of core or cuttings. For a real data example, numerical models of the elastic properties suggest the predominance of dispersed clay in a fluvial sand from matching P-wave and S-wave velocity well log data using log-based estimates of the clay volume and porosity. This is consistent with an interpretation of other log data.

Notes: The detecting capabilities of some electrical arrays for the estimation of position, size and depth of small-scale targets were examined in view of the results obtained from 2D inversions of apparent-resistivity data. The two-sided three-electrode apparent-resistivity data are obtained by the application of left- and right-hand pole–dipole arrays that also permit the computation of four-electrode and dipole–dipole apparent-resistivity values without actually measuring them. Synthetic apparent-resistivity data sets of the dipole–dipole, four-electrode and two-sided three-electrode arrays are calculated for models that simulate buried tombs. The results of two-dimensional inversions are compared with regard to the resolution in detecting the exact location, size and depth of the target, showing some advantage for the two-sided three-electrode array. A field application was carried out in the archaeological site known as Alaca Hoyuk, a religious temple area of the Hittite period. The two-dimensional inversion of the two-sided three-electrode apparent-resistivity data has led to locating a part of the city wall and a buried small room. The validity of the interpretation has been checked against the results of subsequent archaeological excavations.

Notes: Following the probability tomography principles previously introduced to image the sources of electric and electromagnetic anomalies, we demonstrate that a similar approach can be used to analyse gravity data. First, we give a coherent derivation of the Bouguer anomaly concept as a Newtonian-type integral for an arbitrary mass distribution buried below a non-flat topography. A discretized solution of this integral is then derived as a sum of elementary contributions, which are cross-correlated with the gravity data function in the expression for the total power associated with the Bouguer anomaly. To image the mass distribution underground we introduce a mass contrast occurrence probability function using the cross-correlation product of the observed Bouguer anomaly and the synthetic field due to an elementary mass contrast source. The tomographic procedure consists of scanning the subsurface with the elementary source and calculating the occurrence probability function at the nodes of a regular grid. The complete set of grid values is used to highlight the zones of highest probability of mass contrast concentrations. Some synthetic and field examples demonstrate the reliability and resolution of the new gravity tomographic approach.

Notes: A high-resolution method to image the horizontal boundaries of gravity and magnetic sources is presented (the enhanced horizontal derivative (EHD) method). The EHD is formed by taking the horizontal derivative of a sum of vertical derivatives of increasing order. The location of EHD maxima is used to outline the source boundaries. While for gravity anomalies the method can be applied immediately, magnetic anomalies should be previously reduced to the pole. We found that working on reduced-to-the-pole magnetic anomalies leads to better results than those obtainable by working on magnetic anomalies in dipolar form, even when the magnetization direction parameters are not well estimated. This is confirmed also for other popular methods used to estimate the horizontal location of potential fields source boundaries.The EHD method is highly flexible, and different conditions of signal-to-noise ratios and depths-to-source can be treated by an appropriate selection of the terms of the summation. A strategy to perform high-order vertical derivatives is also suggested. This involves both frequency- and space-domain transformations and gives more stable results than the usual Fourier method.The high resolution of the EHD method is demonstrated on a number of synthetic gravity and magnetic fields due to isolated as well as to interfering deep-seated prismatic sources. The resolving power of this method was tested also by comparing the results with those obtained by another high-resolution method based on the analytic signal. The success of the EHD method in the definition of the source boundary is due to the fact that it conveys efficiently all the different boundary information contained in any single term of the sum.Application to a magnetic data set of a volcanic area in southern Italy helped to define the probable boundaries of a calderic collapse, marked by a number of magmatic intrusions. Previous interpretations of gravity and magnetic fields suggested a subcircular shape for this caldera, the boundaries of which are imaged with better detail using the EHD method.

Notes: Azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock. The symmetry of a rock with horizontal bedding that contains two or more non-orthogonal sets of vertical fractures may be approximated as monoclinic with a horizontal plane of mirror symmetry. For offsets that are small compared with the depth of the reflector, the azimuthal variation in P-wave AVO gradient for such a medium varies with azimuth as 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR236:GPR_236_mu1" location="equation/GPR_236_mu1.gif"/〉 where φ is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave. φ2 depends on both the normal compliance BN and the shear compliance BT of the fractures and may differ from zero if BNBT varies significantly between fracture sets. If BNBT is the same for all fractures, 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR236:GPR_236_mu2" location="equation/GPR_236_mu2.gif"/〉 and the principal axes of the azimuthal variation in P-wave AVO for fixed offset are determined by the polarization directions of a vertically propagating shear wave. At larger offsets, terms in 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR236:GPR_236_mu3" location="equation/GPR_236_mu3.gif"/〉 and 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR236:GPR_236_mu4" location="equation/GPR_236_mu4.gif"/〉 are required to describe the azimuthal variation in AVO accurately. φ4 and φ6 also depend on BNBT. For gas-filled open fractures 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR236:GPR_236_mu5" location="equation/GPR_236_mu5.gif"/〉 but a lower value of BNBT may result from the presence of a fluid with non-zero bulk modulus.

Notes: A method of compensating for the presence of discrete overburden velocity anomalies during depth conversion of time horizons interpreted on conventional, post-stack time-migrated seismic data is presented. Positive and negative time delays are estimated either from the push-down or pull-up of reflectors directly beneath the anomalies or from interpreted time thickness of the anomalous body and interval velocities estimated from well data. The critical steps are pre-stack simulation of seismic acquisition across the velocity anomalies, incorporating the effects of a Fresnel volume which changes its width as a function of depth, and simulation of common-midpoint (CMP) stacking using a linear regression of time delay, Δt, versus offset-squared, X2. The time-correction method predicts the time distortion for any target horizon and the distortion is removed as a correction in time. Depth conversion is then performed using a background velocity function. The final average velocity map is calculated from the resulting depth structure and the raw times at the target horizon. The method is implemented by manipulating time grids within an industry-standard mapping package. The final average velocity map shows steep lateral velocity gradients which are constrained by the interpreted boundaries of the velocity anomalies.

Notes: Routine amplitude-versus-offset or amplitude-versus-angle (AVA) analysis is founded on the predicted reflectivity of a planar boundary between isotropic homogeneous half-spaces, yet many real boundaries of interest to hydrocarbon exploration may violate these assumptions. Here, we evaluate consequences of boundary roughness, i.e. small-scale, sub-resolution topography, on the reflecting boundary, to find whether sub-resolution topography can deceive routine AVA analysis and produce misleading hydrocarbon indicators. We use noise-free synthetic CMP and stacked-section seismograms, generated with a Kirchhoff-integral method, for offsets up to 4000 m. The reflecting boundary was at 2000 m depth below a single overburden layer, and comprised isolated mounds or channels (sinusoidal cross-section, 5–40 m high and 100–750 m wide), and more complex roughness (simulated with seven 1.5–2 km long bathymetric profiles across modern-day river-beds, with dune and bar features up to approximately 20 m or 20 ms TWT vertical relief, and 10–100 m or more lateral extent). Flat-boundary responses were taken as the ‘reference’ against which to compare waveforms and amplitudes through semblance analysis, AVA intercept A and slope B cross-plots, and inferred Poisson's ratios. Physical properties of the media were based on shales and brine- or oil-sands from an offshore UK oilfield.For the CMP centred on the topographic feature, isolated mounds and channels produced correlated excursions of A and B from the flat-boundary response (by approximately 35–200%), simulating the familiar ‘background trend’ but sometimes oblique to it. Inferred Poisson's ratios were around 0.3, but for some channels often fell as low as 0.2, potentially interpretable as gas sand. For complex boundary topographies on a shale/brine-sand model, AVA parameters were extracted for 29 CMPs, 100 m apart along each of seven profiles. On a cross-plot, they spanned the flat-boundary response on a linear trend B = (0.01 ± 0.02) – (1.72 ± 0.09)A, similar to reported real data and a realistic ‘mudrock trend’ but with outliers both above and below it that could be interpreted as ‘real’ weak anomalies. Poisson's ratios were 0.30 ± 0.01, between the expected values for brine- and oil-sand. This suggests that boundary roughness may contribute to observed trends on cross-plots and possibly small, but potentially laterally extensive, false AVA anomalies may also be induced.

Notes: A cross-plot of the shape factors and the structural indices, determined from gravity anomalies over various idealized sources, namely horizontal/vertical lines and vertical ribbons with various strike lengths and depth extents, forms a closed loop. Different segments of this loop, termed the source geometry identification loop (SGIL), correspond to different source geometries. Combined use of the structural index and the shape factor determined from an isolated gravity anomaly reduces the ambiguity in characterizing the source geometry. A simulated example and three field examples, namely a Cuban chromite anomaly, an Indian example over manganese ore and a sulphide ore from Quebec, have been analysed by the proposed method in order to identify their respective source geometries.

Notes: Field and ‘noisy’ synthetic measurements of electric-field components have been inverted into 3D resistivities by smoothness-constrained inversion. Values of electrical field can incorporate changes in polarity of the measured potential differences seen when 2D electrode arrays are used with heterogeneous ‘geology’, without utilizing negative apparent resistivities or singular geometrical factors. Using both the X- and Y-components of the electric field as measurements resulted in faster convergence of the smoothness-constrained inversion compared with using one component alone. Geological structure and resistivity were reconstructed as well as, or better than, comparable published examples based on traditional measurement types. A 2D electrode grid (20 × 10), incorporating 12 current-source electrodes, was used for both the practical and numerical experiments; this resulted in 366 measurements being made for each current-electrode configuration. Consequently, when using this array for practical field surveys, 366 measurements could be acquired simultaneously, making the upper limit on the speed of acquisition an order of magnitude faster than a comparable conventional pole–dipole survey. Other practical advantages accrue from the closely spaced potential dipoles being insensitive to common-mode noise (e.g. telluric) and only 7% of the electrodes (i.e. those used as current sources) being susceptible to recently reported electrode charge-up effects.

Notes: A number of laboratory tests (uniaxial, triaxial and hydrostatic) have been conducted on a dry porous limestone. A conceptual model is proposed to correlate deformation and damage fields (including acoustic emission activity) with the variation of ultrasonic velocities, quality factors and energies as measures of attenuation. This correlation is presented in a stress deviator versus confining pressure diagram. In this way, the successive steps occurring in the damage process of this rock are well described. In particular, the quality factor of S-waves distinguishes clearly the onset of the initially stable cracking, while the velocity of S-waves and strain measurements are sensitive to dilatancy which appears later in the damage process of the limestone studied.

Notes: When a vertical fault or dike scatters a normally incident TE-mode plane wave, the horizontal components of the electric and the magnetic fields vary along the direction perpendicular to the strike. This scattering is also responsible for the formation of a vertical component of the magnetic field, which also varies along the direction perpendicular to the strike. Analysis of the lateral variations of the field components permits the identification of the type of geological structure, either fault or dike, as well as an estimate of the position of the geological contacts and the electrical conductivity of each medium. Previous exact analytical solutions have shown that two Fourier cosine integrals can express each field component. A series of functions specified for each model represent the kernel of each integral. From the field components obtained from the first non-zero term of each series, we calculated the following functions: the dip angle and the ellipticity of the vertical polarization ellipse in a plane perpendicular to the strike of the structure, and the azimuth and the ellipticity of the horizontal ellipse. We established master-curves of these functions for the interpretation of vertical faults and dikes for the polarization ellipsoid, for instance VLF or audio-frequency methods. This representation has as variable the induction number 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR240:GPR_240_mu1" location="equation/GPR_240_mu1.gif"/〉, and as parameters σ2/σ1 and 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR240:GPR_240_mu2" location="equation/GPR_240_mu2.gif"/〉, where a denotes the half-thickness of the dike. The interpretation procedure using curve fitting is possible because the induction number is represented on a logarithmic scale. This procedure represents an important step before automatic interpretation is carried out. Two case histories using field data illustrate the effectiveness of the procedure and the type of quantitative interpretation obtained from it.

Notes: The attenuation of compressional and shear waves (Qp and Qs) has been studied by several authors but most of these investigations were performed on deep buried reservoir sandstones in order to distinguish between gas and condensate reservoirs and water-saturated sandstones. We present a preliminary investigation into the use of seismic wave attenuation as a measure of the geotechnical parameters of the near-surface marine sediments, a little-studied geological setting. A 6.9 m-long gravity core was taken from the continental slope of the Barents Sea at a water depth of 2227 m. The core was primarily composed of brown to olive-grey clayey mud, having a high content of foraminifers and being locally bioturbated. The values of Qp and Qs were determined using the rise-time method at 19 and 18 different points of the core, respectively, and they were correlated with geotechnical parameters such as wet bulk density, porosity, water content, shear strength and C/P ratio (the ratio of shear strength to overburden pressure). The calculated correlation coefficients for all correlations ranged from −0.39 to 0.41, suggesting that the attenuation characteristics of seismic waves could not be used to derive geotechnical parameters of marine sediments. However, with such a small data set it is difficult to determine clearly whether attenuation is primarily a frequency-dependent parameter and consequently not related to sediment properties, or whether the limited number of data points is the main factor responsible for the low correlation coefficients observed. Moreover, several different methods are available for the computation of the quality factor Q, and the rise-time method may not be the most appropriate means of determining the attenuation on near-surface marine sediments.

Notes: Trichomes decrease water loss in some plant species, but their influence on water loss from alfalfa (Medicago sativa L.) forage is unknown. A study was conducted which measured the water loss from field-grown, harvested forage of three erect, glandular-haired alfalfa germplasms, KS161, KS210 and KS224, the eglandular ‘Arc’ cultivar and the ‘Kenland’ cultivar of red clover (Trifolium pratense L.). Harvests were taken once in 1995 and 1997, and four times in 1996. Plant height, phenological stage, upper and lower stem diameters, leaf:stem ratio and apical stem densities of simple, procumbent glandular and erect glandular trichomes were determined. The drying rate constants of the forage were calculated by a combination of parametric and non-parametric modelling techniques. The harvest × germplasm interaction was significant for all parameters measured. The density of erect glandular hairs varied among entries for all harvests, while the drying rate of harvested forage differed among entries for three of the six harvests. Correlations between densities of erect glandular hairs and drying rate constants were generally low and non-significant, except for one harvest. Erect glandular hairs, at the densities measured in this study, generally did not influence drying rates of alfalfa forage. However, density of total trichomes was significantly and negatively correlated with drying rate for all alfalfa entries. The diameter of the stem had the greatest negative impact on drying rate.

Notes: Two factorial design experiments were carried out in the spring of 1994 and 1995, each of 6 weeks, to quantify the effects of sward height (SH), concentrate level (CL) and initial milk yield (IMY) on milk production and grazing behaviour of continuously stocked dairy cows. In Experiment 1, forty-five Holstein Friesian cows were in five groups with initial milk yields of 16·9, 21·1, 28·0, 31·5 and 35·5 kg d–1, grazed sward heights were 3–5, 5–7 and 7–9 cm (LSH, MSH and HSH respectively), and concentrates were fed at rates of 0, 3 and 6 kg d–1. In Experiment 2, 48 cows were in two groups with IMY of 21·3 and 35·5 kg d–1, grazed sward heights were 3–5 and 7–9 cm (LSH and HSH), and concentrates were fed at 0 and 6 kg d–1 and ad libitum. Multiple regression models were used to quantify the effects of the three variables on milk yield persistency (MYP), estimated herbage dry-matter (DM) intake (HDMI), grazing time (GT) and rate of DM intake (RI). The partial regression coefficients showed that increased SH led to increased MYP (Experiment 1 P 〈 0·001, Experiment 2 P 〈 0·05), increased HDMI (P 〈 0·01, P 〈 0·01), increased GT (P 〈 0·001, P 〈 0·05) and increased RI (P 〈 0·001, P 〈 0·05). Increasing CL led to increased MYP (NS, P 〈 0·001), decreased HDMI (P 〈 0·001, P 〈 0·001), decreased GT (NS, P 〈 0·001) and decreased RI (P 〈 0·001, P 〈 0·001). Higher IMY level of cows decreased MYP (P 〈 0·001, P 〈 0·001), increased HDMI (P 〈 0·001, P 〈 0·001), increased GT (P 〈 0·001, P 〈 0·05) and increased RI (P 〈 0·05, P 〈 0·01). The models were highly significant (P 〈 0·001), and accounted for 0·48–0·87 of the total variance. The partial regression coefficients quantified the extent to which GT and RI by cows respond positively to higher IMY, and negatively to increased CL, but respond differently (GT declines in response to a higher RI) with increasing SH.

Notes: The microbial matter fraction was determined in perennial ryegrass silages of different dry-matter (DM) contents, ensiled with or without Lactobacillus plantarum. 15N-Leucine and the bacterial cell wall constituent diaminopimelic acid (DAPA) were used as markers for microbial-N. Perennial ryegrass crops with DM contents of 202, 280 or 366 g kg−1 fresh weight were ensiled in laboratory-scale silos and stored for 3 to 4 months. At different times after ensiling, silages were analysed and microbial fractions were isolated. Microbial-N concentration determined with 15N-leucine reached a maximum during the first week of ensilage. It remained unchanged thereafter, except in silage with a DM content of 280 g kg−1 in which it decreased (P 〈 0·01) by 32% during storage. After 3 to 4 months ensilage, microbial-N concentration varied from ≈0·3 to ≈1·7 g kg−1 DM. A negative relationship was observed between microbial-N concentration and silage DM content. Inoculation resulted in an approximately twofold increase (P 〈 0·001) in microbial-N concentration. Microbial-N concentrations determined with DAPA were 1·14–2·07 times higher than those determined with 15N-leucine. However, 19–35% of the DAPA in silage occurred in a soluble form, indicating that this fraction of DAPA was not associated with intact bacteria.

Notes: As a consequence of heterogeneous transport in soils, only a small part of the soil might be responsible for sorbing incoming elements. After staining preferential flow paths in forested Dystric Cambisol with a colour dye, we sampled soil material from the flow paths and from the soil matrix. We measured chemical properties and sorption isotherms of these two flow regions and estimated the significance of preferential flow paths for the transport of solutes leached from wood ash applied at the surface. In the A horizon (0–9 cm depth), the cation exchange capacity of the flow paths was 83.8 mmolc kg−1, while that of the soil matrix was only 74.6 mmolc kg−1. The base saturation was 42% and soil organic matter content was 41% larger in flow paths than in the soil matrix. The sorption capacity for Cu was also larger than in the matrix, whereas the sorption capacity for Sr was similar in both flow regions. The impact of the addition of 8 t wood ash ha−1 on soil chemical properties was restricted mainly to the flow paths in the uppermost 20 cm of the soil; it was negligible in the matrix and at greater depths. Concentrations of exchangeable Ca in the flow paths increased nearly 10-fold during the 6 months following the addition of the wood ash, and those of organically bound Pb by 50%. The opposite effect was found for exchangeable Al. Our results show that only part of the whole soil volume, approximately 50% of 0–20 cm in our study, is involved in transporting and sorbing the elements applied with the wood ash or as tracers. Such differences must be considered when calculating the maximal impact of any addition of fertilizer, wood ash, or liming agent.

Notes: Simulation models are useful tools to understand the interaction between the transformation and the transport of nitrogen in the field. This study was done to calibrate, test and analyse a mechanistic, one-dimensional model that describes the transport and transformations of nitrogen in the soil. The physical module describes transport of water, heat and solute, and the biological module simulates transformations of C and N with a restricted number of measurable organic pools. The calibration was based mainly on laboratory experiments independent of those used to evaluate the model. The evaluation procedure used field data collected on a bare loamy soil. The profiles of water content, water potential, temperature, chloride and nitrate (15N-labelled and unlabelled) concentrations were measured from 0 to 150 cm continuously for 1 year. Simulated results were in good agreement with experimental data. However, some discrepancies were noticeable for chloride and nitrate concentrations in the deep layers. These differences were probably due to an underestimation of mass transport in the deep layers. A sensitivity analysis was carried out to determine the response to changes in some parameters in terms of mineralization, leaching and model efficiency. Mineralization is more sensitive to biological factors whereas nitrate leaching is more sensitive to initial and boundary conditions and hydraulic parameters. The experiment ran for only 1 year, which was too short a time to test biological factors.

Notes: Laser-optical measurements and fibre optics are potentially attractive tools for applications in soil science because of their great sensitivity and selectivity and their capabilities for on-line and in situ analysis. We have investigated laser-induced breakdown spectroscopy (LIBS) for the quantitative detection of metal ions on the surface of natural soil samples from two sites (Hohenschulen and Oderbruch, Germany). The LIBS technique allows the spatially resolved investigation of adsorption and desorption effects of ions in soil. A frequency doubled (532 nm) and Q-switched Nd:YAG laser with a pulse duration of 8 ns is focused on the soil surface and induces a plasma. Typical power densities are 150 mJ mm−2. The plasma emission is recorded in time and spectrally resolved by a gateable optical multichannel analyser (OMA). A delay time of about 500 ns between laser pulse and OMA gate was used to resolve single atomic and ionic spectral lines from the intense and spectrally broad light that is emitted by the plasma itself. The dependency of the LIBS signal of a single spectral line on the amount of water in the sample is investigated in detail. The results indicate that quenching of water in the plasma plume reduces the line intensities, while the interaction with aquatic colloids increases the intensity. The two processes compete with each other, and a non-linear correlation between measured line intensities and the amount of water in the sample is obtained. This is verified by a simple computer simulation and has to be taken into account for the quantitative interpretation of LIBS signals, e.g. when absolute concentrations are estimated. In the present investigation natural calcium concentrations 〈 2 μg kg−1 were measured with the LIBS technique in the samples for the two test sites. In addition, measurements were made with dry and water-saturated BaCl2 mixed soil samples, and no significant difference in the detection limit for barium was obtained.

Notes: A new sampling technique for measuring the concentrations of trace gases (CH4, CO2 and N2O) in the soil atmosphere from well-defined depths is described. Probes are constructed from silicone tubing closed with silicone septa on both ends, thereby dividing an inner air space from the outer soil atmosphere without a direct contact. The gas exchanges between the inner and outer atmosphere only by diffusion through the walls of the silicone tube. Tests revealed that the gases N2O, CO2 and CH4 in the enclosed space reached 95% equilibrium with the surrounding atmosphere at 20°C within 7 h or faster. The probe measurements are reproducible: the standard deviation of samples taken from 26 probes stored in the laboratory atmosphere equalled that of a standard gas. The probes can easily be constructed and installed at specified depths in the soil.The method has the following advantages compared with other methods that use spaces with holes in them for gas exchange: (i) the silicone probe enables trace gases to be sampled in wet soils, including ones that are waterlogged or temporarily saturated; (ii) the sampling itself does not create low pressure and hence does not create mass flow in the soil matrix from undefined depths; and (iii) the probe can be made to take samples of gas of any required size. The silicone probes did not show ageing effects during 18 months of use in the field in a mineral soil under grass. The probes yielded comparable results: three probes inserted at 5 cm depth in a uniformly treated 100-m2 plot provided nearly identical average trace gas concentrations within the measurement period.

Notes: Rare earths are applied widely in Chinese agriculture to improve crop nutrition and incidentally in fertilizers, yet little is known of their effect on the biological functioning of the soil. We have studied the effects of lanthanum and of mixtures of rare earths on the potential ammonium oxidation and nitrogen mineralization in soil by incubation experiments in the laboratory. The no-observed-effect and median effective concentrations of the rare earths on these two processes are reported, and their corresponding mechanisms are discussed. For mixtures, the no-observed-effect concentrations relating to potential ammonium oxidation and N mineralization were at 393 and 373 mg rare earths kg−1 soil, respectively, and their median effective concentrations were at 1576 and 1108 mg kg−1 soil, respectively. When lanthanum was applied alone, the no-observed-effect concentrations relating to potential ammonium oxidation and N mineralization were at 432 and 443 mg La kg−1 soil, respectively, and their median effective concentrations were at 18 212 and 1237 mg kg−1 soil, respectively. Therefore, the influence of mixtures of rare earths on potential ammonium oxidation or on N mineralization was slightly stronger in comparison with that of lanthanum. Mineralization of nitrogen is apparently more sensitive to the stress caused by rare earths than ammonium oxidation. We conclude that the influence of individual rare earths in the mixtures on the above two processes can be additive and that the present dosage of mixed rare earths (〈 230 g ha−1 year−1 or 0.15 mg kg−1 soil year−1) currently applied in China can hardly affect the potential ammonium oxidation and N mineralization in the soil even over a long period.

Notes: Estimation of the phosphate adsorption capacity in highly weathered acid soils is crucial for adopting appropriate phosphate fertilization practices. In this work, the salt sorption effect was used to develop a method for estimating phosphate adsorption capacity from the decrease in electrical conductivity of a potassium dihydrogen phosphate solution brought in contact with acidic soil samples from surface and subsurface horizons of Acrisols. The method is fast and simple and requires only the use of a conductimeter.

Notes: Tillage and traffic modify soil porosity and pore size distribution, leading to changes in the unsaturated hydraulic properties of the tilled layer. These changes are still difficult to characterize. We have investigated the effect of compaction on the change in the soil porosity and its consequences for water retention and hydraulic conductivity. A freshly tilled layer and a soil layer compacted by wheel tracks were created in a silty soil to obtain contrasting bulk densities (1.17 and 1.63 g cm−3, respectively). Soil porosity was analysed by mercury porosimetry, and scanning electron microscopy was used to distinguish between the textural pore space and the structural pore space. The laboratory method of Wind (direct evaporation) was used to measure the hydraulic properties in the tensiometric range. For water potentials 〈 −20 kPa, the compacted layer retained more water than did the uncompacted layer, but the relation between the hydraulic conductivity and the water ratio (the volume of water per unit volume of solid phase) was not affected by the change in bulk density. Compaction did not affect the textural porosity (i.e. matrix porosity), but it created relict structural pores accessible only through the micropores of the matrix. These relict structural pores could be the reason for the change in the hydraulic properties due to compaction. They can be used as an indicator of the consequences of compaction on unsaturated hydraulic properties. The modification of the pore geometry during compaction results not only from a decrease in the volume of structural pores but also from a change in the relation between the textural pores and the remaining structural pores.