This paper presents the general features of parameter sensitivity maps and illustrates their practical use. We define parameter sensitivity maps as geoelectric responses in the measuring plane (at the surface) due to an elementary cube within the subsurface at three different depths. Responses of the three component as well as the total response of electrical dipoles formed on opposite cube surfaces are shown. In this paper we present such maps for 14 various linear electrode arrays. This paper is followed by an accompanying one about nonlinear and focussed arrays. Parameter sensitivity maps in these two papers provide a compact characterization of all known geoelectric arrays. We give several examples how to use them in planning and interpretation of field measurements.
In this paper we present, at first time in a geophysical journal, parameter sensitivity maps of nonlinear and focussed electrode arrays. We present them as anomalies due to electric dipoles forming on opposing surfaces of an elementary cube within the subsurface at three different depths, and not only the total effect of the dipole, but also of its components are shown. Parameter sensitivity maps of non-linear arrays, compared to those of linear arrays, have in general 1. more equal sensitivity values in x and y directions, 2. more chances for antisymmetry axes, 3. smoother lateral distribution of sensitivity values. We recommend a systematic use of parameter sensitivity maps in geoelectric prospecting, both in planning and interpretation of field measurements.
This paper investigates the effect of electrode positioning errors on the inverted pseudosection. Instead of random spacing errors (as usually assumed in geoelectrics) we exactly measured this effect among field conditions. In the field, in spite of the greatest possible care, the electrode positions contain some inaccuracy: either in case of dense undergrowth, or varied topography, or very rocky field. In all these cases, it is not possible to put the electrodes in their theoretical position. As a consequence, the position data will contain some error. The inaccuracies were exactly determined by using a laser distance meter. The geometrical data from real field conditions and by using Wenner-
, pole-dipole and pole-pole arrays were then considered over homogeneous half space.As we have found, the positioning errors can be regarded as insignificant, even in case of relatively uncomfortable field conditions. However, in case of very rocky surface the distortions are more significant, but it is still possible to make some corrections: either by neglecting a few electrode positions with the greatest positioning error, or to minimize the inline errors, even on the price that offline deviations are high.
Authors:S. Szalai, M. Abd Alla, S. Ahmed, and et al.
In this paper we provide a field example for the determination of the location and direction of fissures in narrow, elongated measuring areas. The test measurements were carried out on the Mokattam plateau at Cairo (Egypt). Direction, length of the layout and the profile length all were very limited, since the measurements had to be carried out within a narrow (2-10 m wide) stripe, between a built-in area and a cleft rim. Interpretation of field measurements was supported by (1) analogue model experiments, and (2) parameter sensitivity maps. As it was found from laboratory experiments, fissures are indicated by potential-difference maximums along profiles measured by using three-electrode array (if the reference point is between the potential electrodes). The mean distance between two neighbouring maximums throughout the whole profile was found to be about 3-4 m, corresponding to the distance between the most visible fissures on the cleft wall. The Schlumberger null-array has been found to be an appropriate tool in determination of the direction of fissures. Its resolution is higher than that of the classical Schlumberger array. Its only disadvantage is that on the azimutal diagram it gives two times more minimum pairs than the number of fissures. Among such constrained circumstances the best method to get useful information about location and direction of fissures in the subsurface limestone is to use jointly corresponding traditional and null-arrays. While the location is given best by traditional three-electrode array measurement, the direction of the fissures is given from the joint interpretation of the Schlumberger null-array and the traditional Schlumberger array. In this way it is to separate several fissure directions.
Authors:S. Szalai, M. Varga, A. Novák, and L. Szarka
In frames of a Hungarian Scientific Research Fund (OTKA) project (No. K49604), we systematically investigated all published surface geoelectric arrays, since a part of them are out of use, even completely forgotten. Even in case of these latter ones we were optimistic in their potential renaissance, due to the rapid advance in geophysical knowledge and technical development. Therefore at first we collected all surface geophysical arrays, ever used in geophysical exploration. We presented all of them in a standard way, and we classified them. This collection proved to be the basis of still on-going inter-comparisons. We revealed the original motivation of their design, as well. Then we produced parameter sensitivity maps for all possible arrays, by using a new analytical approach. Parameter sensitivity maps for non-linear and focussed arrays had never been presented before. Through examples (mainly for null-arrays, one of the focal points of our project) we presented, how these maps can be applied. Then another characterizing parameter, the depth of investigation was studied. The so-called depth of investigation characteristics (DIC) was computed for all the 30 arrays, where it exists, both in terms of Roy and Apparao (1971) and Edwards (1977). We carried out various comparisons, and revealed a complex relation among vertical resolution, depth of investigation and noise. We showed how the depth of investigation is constrained by the noise level. Therefore the maximal (theoretical) depths of investigation for 6 arrays were studied at various noise levels. Besides some further theoretical studies, our further work will concentrate on measurements. The general characterization of so many geoelectric arrays provides a better knowledge about them, and it will be hopefully useful also for other teams to select always the optimal arrays in their field problem. It should be mentioned, that this paper does not contain mathematical details. If the reader would like to reproduce the results demonstrated on the figures, the referred previous publications of the authors should be studied.
Short-term fluctuations of indoor radon may occur due to weather conditions, seismic activity etc. These average out during the year. According to our measurements, in the very same room the yearly average of radon concentration may also change by 25–50% from year to year. This observation may make the comparison of indoor radon levels of houses measured in different years unjustified; large scale radon maps based upon such data are less reliable. Possible causes of such year-by-year changes are discussed empirically. The conclusions may be helpful to foresee long-term tendencies, implied by changes of living habits and by climatic shifts.
Authors:S. Szalai, M. Varga, A. Novák, and L. Szarka
In this paper we provide a comprehensive summary about the practical results of the OTKA project K49604. 1. We calculated the consequences of incorrect positioning of the electrodes for various multielectrode systems. In practice these effects were found to be negligible. The only exception is the case of rocky surface, where it is impossible to put the electrodes in the desired positions. The errors can however be kept within an acceptable range, if the electrodes of the linear arrays are put off-set, at right angles from the measuring line. A five-six times larger off-set has less effect than a certain mis-position along the line, connecting the electrodes. 2. We carried out tensorial geoelectric measurements around the Cistercian Monastery at Pilisszentkereszt. Areal measurements provide much more detailed and unambiguous anomalies than 2D profile measurements, and the tensor invariant representation of apparent resistivity anomalies provides a realistic picture about the lateral variation of the subsurface resistivity, even in field circumstances. 3. We tested the applicability of 3D electrical resistivity tomography (ERT) technique to detect landmines in different soil conditions and at various depths. Metallic and non-metallic landmines buried in wet and dry soils had been synthetically modeled. According to the inverted resistivity data using the dipole axial array in wet environment, it was possible to locate the metallic and non-metallic landmines as long as the noise level was about 5%. 4. We elaborated moreover a geoelectrical procedure which is able to map multidirectional fissure systems by combining geoelectrical profiling and geoelectrical azimuthal measurements. Results received by using both the so-called null-, and traditional arrays were jointly interpreted. The humidity of the fissures affects the measured results significantly, and in a meaningful way. 5. We presented the socalled standardized pricking probe (PP) surveying technique and demonstrated its usefulness in an archaeological study. The PP images proved to be definitely more close to the realistic shape of the buried chapel than the geoelectric and magnetic measurements, and they also revealed more details about the subsurface than the georadar. The optimum PP parameters: horizontal interval, pricking depth, observable quantity and its way of presentation were optimized through field experiments. For more details see the cited publications. The figures ever published in Hungarian journals are not reproduced here.
Authors:M. Szalai, J. Kőszegi, S. Toepfer, and J. Kiss
The larvae of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) are largely restricted to the roots of maize as food source, and their feeding damage can cause yield losses. The adults are active flyers in search for pollen sources or for new maize fields to colonise. The D. v. virgifera colonisation of first-year maize fields from adjacent continuous maize fields was studied in a 20 km2 intensive agricultural area in South-Western Hungary between 2008 and 2010. Using non-baited yellow sticky traps the infestation levels of adult D. v. virgifera were compared between six first-year maize fields and seven to 12 adjacent continuous maize fields during a seven week period in July and August in each year. The infestation in the continuous maize fields accounted for more than 60% of the variation in the adult D. v. virgifera captures in the adjacent first-year maize fields indicating that adjacent maize fields are the major source of dispersal into first-year maize and not, or to a lesser extent, the area-wide infestation levels. Therefore, estimating the risks of D. v. virgifera infestations in fields of a maize-rotating farmer can be supported by assessing the infestation levels in neighbouring continuous maize fields.
Authors:S. Szalai, I. Kósa, T. Nagy, and L. Szarka
Water and pollution transport takes places in fissures, and fissures may also reduce the stability of the rock body. Therefore, fissures in rock are an important issue, especially in case of multi-directional fissure systems, where the situation is more complicated.The so-called azimuthal technique, by using the Schlumberger array is a routinely applied method in geoelectric fissure detections. As we demonstrate it by using analogue model measurements, this method has several shortages. In absence of
information, the fissure directions could be obtained only in 60% of the total cases with a precision of ±10%. We have also demonstrated that the effectivity of the method becomes even worse, when the covering sediment layer is thicker. At the same time, when we simply rejected the anisotropy paradox, it was found, that the effectivity of the method is increasing with increasing sediment thickness. The original azimuthal technique is based on the generally accepted hypothesis of the so-called geoelectric anisotropy paradox. The analogue modelling results have made clear that the critical point of the method is the application of the anisotropy paradox. The fissure directions can only be determined, if the conditions of the anisotropy paradox are clearly defined. However, having more than one fissure directions, statistically these fissure directions can be correctly determined.
Authors:M. Dobos-Kovács, E. Horváth, A. Farsang, Edith Nagy, Andrea Kovács, F. Szalai, and S. Bernáth
Haemorrhagic nephritis and enteritis of geese as a new disease was first described in Hungary in 1969. The authors identified the causative agent of the outbreaks occurring in 1969 as a polyomavirus by PCR in 2001. In order to study the pathogenesis of the virus, one-day-old goslings were infected with tissue homogenate that tested positive for polyomavirus by PCR. Morphological, light and transmission electron microscopic (TEM) examinations have revealed that goose haemorrhagic polyomavirus replicates in the endothelial cells of the blood vessels and capillaries of diseased birds. Infection causes damage and necrosis of the endothelial cells. The virus was not observed in the parenchymal cells. Oedema and haemorrhages found throughout the body may be due to the dysfunction or functional deficiency of endothelial cells damaged by the virus.