Contribution of the relative velocity between source and receivers to electromagnetic fields in the sea     

E. E. S. Sampaio 《Studia Geophysica et Geodaetica》2006,50(1):89-104

The analysis of the primary electromagnetic fields caused by steady state or transient electric current flowing along a current loop moving with a constant velocity below the sea surface has several applications. It supports the analysis of submarine physical data and it is useful for protecting ships from the threat of sea mines. The usual approach to the solution for the primary field starts from a hertz vector potential in the frequency domain due to a magnetic dipole. Subsequently it employs Fourier, Laplace, and Hankel transforms to describe the time variation of the primary electromagnetic induced field due to a loop. The result is applicable to both shallow and deep sea water environments. Because of the difference in velocity between source and receiver, a careful application of the convolution integral is necessary in order to adapt the source pulse solution to any type of transmitting current waveform. Furthermore, since the scattered field represents a fraction of the primary field, even minor differences in it caused by the differential velocity renders inadequate interpretation of EMI data.  相似文献   

Waveshapes of continuing currents and properties of M-components in natural negative cloud-to-ground lightning from high-speed video observations   总被引：2，自引：1，他引：2  

Leandro Z.S. Campos  Marcelo M.F. Saba  Osmar Pinto  Jr.  Maurício G. Ballarotti   《Atmospheric Research》2007,84(4):302-310

Continuing current is a continuous mode of charge transfer to ground in a lightning flash. The extent to which the continuing current contributes to the total negative charge lowered to earth is large. In order to study the waveshape of the continuing currents of natural flashes, we developed a computational algorithm that analyzes the pixels of the images obtained by a high-speed camera and plots luminosity-versus-time. Tower measurements have shown that during the continuing current phase of the flash the luminosity of the channel is directly proportional to the current that flows through it. Using this information it was possible to infer the continuing current waveshape for 63 natural discharges and classify them into six different types. Statistics on some characteristics of 345 M-components (that occurred during the same 63 events) are also presented. As far as we know, this is the first study on waveshapes of continuing currents for natural lightning.  相似文献   

Revisited Formulation and Applications of FFT Moving Average     

de Figueiredo  Leandro Passos  Grana  Dario  Le Ravalec  Mickaele 《Mathematical Geosciences》2020,52(6):801-816

Mathematical Geosciences - The fast Fourier transform-moving average (FFT-MA) is an efficient method for the generation of geostatistical simulations. The method relies on the calculation of a...  相似文献   

Effect of coupling noise on the interpretation of results of electromagnetic horizontal sounding and modeling     

Leonardo S. R. Mocitaiba  Edson E. S. Sampaio  Olivar A. L. de Lima 《Studia Geophysica et Geodaetica》2017,61(4):801-825

The time variation of a source of alternating current produces an electromagnetic coupling between the transmitting and receiving systems in induced electrical polarization and resistivity surveys that employ horizontal electrical sounding. The coupling alters, sometimes significantly, the resistivity and chargeability values and, consequently, compromises the interpretation of the data. This work develops the analysis of this coupling on the time domain for both a homogeneous Earth and an Earth constituted of several homogeneous horizontal layers. Based on the results, it evaluates the theoretical variation of the voltage and compares it to observed data of an induced electrical polarization and resistivity survey with horizontal electrical sounding. The comparative study of the voltage decay curves assesses the contribution of the electromagnetic coupling to the values of the chargeability and apparent resistivity as a function of the bipole length and the period of the source current. Besides that, the respective pseudosections have delineated the horizontal and vertical variations of those two electrical properties, providing the interpretation of the geoelectrical section. This research is important for the oil industry because it may furnish information that help to: (i) define the structure of the sedimentary strata; (ii) estimate the clay content of the sandstones; and (iii) detect the possible presence of metallic sulphide halos at fractured zones of the sediments above the oil reservoir. It may be adapted to analysis of EM coupling in both resistive and induced electric well logs.  相似文献   

Mid Campanian‐Lower Maastrichtian magnetostratigraphy of the James Ross Basin,Antarctica: Chronostratigraphical implications     

Florencia N. Milanese  Eduardo B. Olivero  María E. Raffi  Pablo R. Franceschinis  Leandro C. Gallo  Steven M. Skinner  Ross N. Mitchell  Joseph L. Kirschvink  Augusto E. Rapalini 《Basin Research》2019,31(3):562-583

The James Ross Basin, in the northern Antarctic Peninsula, exposes which is probably the world thickest and most complete Late Cretaceous sedimentary succession of southern high latitudes. Despite its very good exposures and varied and abundant fossil fauna, precise chronological determination of its infill is still lacking. We report results from a magnetostratigraphic study on shelfal sedimentary rocks of the Marambio Group, southeastern James Ross Basin, Antarctica. The succession studied covers a ~1,200 m‐thick stratigraphic interval within the Hamilton Point, Sanctuary Cliffs and Karlsen Cliffs Members of the Snow Hill Island Formation, the Haslum Crag Formation, and the lower López de Bertodano Formation. The basic chronological reference framework is given by ammonite assemblages, which indicate a Late Campanian – Early Maastrichtian age for the studied units. Magnetostratigraphic samples were obtained from five partial sections located on James Ross and Snow Hill islands, the results from which agree partially with this previous biostratigraphical framework. Seven geomagnetic polarity reversals are identified in this work, allowing to identify the Chron C32/C33 boundary in Ammonite Assemblage 8‐1, confirming the Late Campanian age of the Hamilton Point Member. However, the identification of the Chron C32/C31 boundary in Ammonite Assemblage 8‐2 assigns the base of the Sanctuary Cliffs Member to the early Maastrichtian, which differs from the Late Campanian age previously assigned by ammonite biostratigraphy. This magnetostratigraphy spans ~14 Ma of sedimentary succession and together with previous partial magnetostratigraphies on Early‐Mid Campanian and Middle Maastrichtian to Danian columns permits a complete and continuous record of the Late Cretaceous distal deposits of the James Ross Basin. This provides the required chronological resolution to solve the intra‐basin and global correlation problems of the Late Cretaceous in the Southern Hemisphere in general and in the Weddellian province in particular, given by endemism and diachronic extinctions on invertebrate fossils, including ammonites. The new chronostratigraphic scheme allowed us to calculate sediment accumulation rates for almost the entire Late Cretaceous infill of the distal James Ross Basin (the Marambio Group), showing a monotonous accumulation for more than 8 Myr during the upper Campanian and a dramatic increase during the early Maastrichtian, controlled by tectonic and/or eustatic causes.  相似文献   

Understanding how environmental heterogeneity and elevation drives the distribution of woody communities across vegetation types within the campo rupestre in South America     

Marcelo Leandro BUENO  Vanessa Leite REZENDE  Luiza Fonseca A.DE PAULA  Joo Augusto Alves MEIRA-NETO  José Roberto Rodrigues PINTO  Andreza Viana NERI  Vanessa PONTARA 《山地科学学报》2021,(5):1192-1207

The campo rupestre sensu lato is a vegetation type that occurs in South American mountains, supports a distinctive flora characterized by high rates of endemism, high herbaceous species richness and often-neglected but also species-rich of the arboreal stratum. We aimed to investigate how environmental factors and elevation are associated with the distribution and diversity of woody species in different rupestrian vegetation types across South America. Using a database of 2,049 woody species from 185 sites across four vegetation types within the campo rupestre, we assessed how the vegetation types were grouped according to their floristic composition and number of shared indicator species, as well as by using different beta diversity indices. The most important variables from a set of 27 variables(e.g. altitude, geo-edaphic and climatic) explaining species distribution were identified using redundancy analysis(RDA) and variation partitioning methods. The distribution of vegetation types was related to both environmental and spatial fractions, with a set of 17 variables retained(e.g. rockiness, grass cover and temperature seasonality as the most important variables). There was an association between the floristic composition of each vegetation type and the elevation range. Although the identified vegetation types are floristically related, they are distinguished by exclusive and habitat-specialist woody species. This uniqueness of vegetation types should be considered in terms of complementarity for the conservation of campos rupestres.  相似文献   

Seasonal and inter-annual variability of water quality in the Uruguay River,Argentina     

Juan C. Colombo  Carlos N. Skorupka  Claudio Bilos  Leandro Tatone  Natalia Cappelletti  M. Carolina Migoya 《水文科学杂志》2013,58(6):1155-1163

Abstract

Water quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month^-1), discharge (7000–28 000 m³ s^-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m^-2 d^-1; total solid load: <1000 to 100 000 t d^-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus.  相似文献   

Potential of the LASH model for water resources management in data-scarce basins: a case study of the Fragata River basin,southern Brazil     

Samuel Beskow  Luis Carlos Timm  Vitor Emanuel Quevedo Tavares  Tamara Leitzke Caldeira  Leandro Sanzi Aquino 《水文科学杂志》2013,58(14):2567-2578

ABSTRACT

The objective of this study was to evaluate, based on a data-scarce basin in southern Brazil, the potential of the Lavras Simulation of Hydrology (LASH) model for estimating daily streamflows, annual streamflow indicators and the flow–duration curve. It was also used to simulate the different runoff components and their consistency with the basin physiographical characteristics. The statistical measures indicated that LASH can be considered suitable according to widely used classifications and when compared with other studies involving hydrological models. LASH also showed satisfactory results for annual indicators, especially for maximum and average annual streamflows, as well as for the flow–duration curve. It was found that the model was consistent with the basin characteristics when simulating runoff components. The results obtained in this study allowed us to conclude that the LASH model has the potential to aid practitioners in water resources management of basins with scarce data and similar soil and land-use conditions.