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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
451 - 462 of 462 results
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Ionospheric plasma drift at low latitudes
Trans-equatorial F region plasma bubbles are large-scale ionospheric depleted regions that develop in the bottomside of equatorial F region due to plasma instability processes. Simultaneous all-sky imaging observations of the OI 630.0 nm and OI 777.4 nm nightglow emissions were carried out at São José dos Campos (23.21oS, 45.86oW; dip latitude 17.6oS), Brazil, during the years 2000 and 2001, a period of high solar activity. In this work we present and discuss the height-resolved nocturnal F region zonal drift velocities obtained from plasma bubbles observed in imaging observations of these two emissions for several days of 2000 and 2001. We have investigated the nighttime zonal plasma drift variations using fixed emission peak altitudes, used by earlier investigators, as well as emission peak altitudes based on simultaneous ionospheric sounding observations. The average maximum and minimum zonal plasma drift velocities inferred for both the emissions, using emission peak altitudes based on simultaneous ionospheric observations are lower and with less scatter than those using fixed emission peak altitudes. Also, the nocturnal variations of the zonal plasma drift velocities obtained for the two emissions with peak altitudes based on simultaneous ionospheric observations show better agreement than for the case with fixed emission peak altitudes.
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Forbush decreases in November 6-20, 2004 observed by the Muon Detector Network
In this paper we study the relationship between Interplanetary Coronal Mass Ejections (ICMEs) and the count rate muon decrease detected by the muon detector network in November 6-20, 2004. The Muon Detector Network is composed by the detectors installed in Nagoya (Japan), Hobart (Australian) and the prototype detector installed in the “Observatório Espacial do Sul – OES/CRSPE/INPE-MCT”, located in São Martinho da Serra, RS, Brazil. With the muons count rate observed by the Muon Detector Network, we will be able to observe, in the future,the direction in which a given ICME moves, and with that, we will be able to calculate the angle which they reach the Earth. Also, with this muon network, we will be able to send alerts of up to 12 hours before the arrival of a shock or an ICME. The Space Weather forecast method using cosmic rays will be a very important tool because it provides a forecast with good antecedence.
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Methane emissions from lakes in Pantanal – Methodology and preliminaries results
Authors Luciano Marani and Plínio C. AlvaláThe methodology and the preliminaries results of a study to evaluate the methane (CH4) emissions from lakes and floodplains in Pantanal are presented. The sample sites are chosen to represent different environmental characteristics on the region. The methane fluxes are obtained by the technique of static chamber. The work had begun in 2004 and extends for 2005, with sampling campaigns every 3-month (March, June, September and December of each year). The preliminaries results obtained during 2004 (March, June and September) shows a overall average flux of 79.3 ± 227.1 mgCH4 m-2d- 1, ranged -8.7 to 1983.1 mgCH4 m-2d-1 and also indicates that methane fluxes are influenced by the water depth and by the presence of aquatic vegetation. The fluxes
could be divided in terms of the way of methane transport through the water column in diffusive and bubble fluxes, and each one are influenced by water depth and vegetation in different ways.
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Comportamento sazonal de Bolhas de Plasma na região equatorial do Brasil observado pelo imageamento do airglow na emissão do OI 630,0 nm
Authors Igo Paulino, Amauri Fragoso de Medeiros and Ricardo Arlen BuritiThe study of the ionospheric irregularities or plasma bubbles is very important for to understand the dynamics process of the high atmosphere. The variability is a determined element in the preview of the space weather, thus the short time preview of the behavior of the bubbles is indispensable for the plain of the activities and the system of special application. In this paper we present results of two years (from September 2000 to l August 2002) of observations of the plasma bubbles through imager all sky data localized placed at São João do Cariri (7°13’S; 35°52’W). The plasma bubble showed a seasonal behavior characterized by appear between moths September and Mach of the two years observed, while in the others moths we detect few times the plasma bubble. However, we can see too that during the equinox moths the occurrence peak of the bubbles happened more early (~20:30 LT) than summer moths where the occurrence peak was around of 21:30 until 23:30 LT (Local Time). In the summer the plasma bubble occurrence was larger than equinox moths. The dynamics conditions of ionospheric plasma are dominated by electromagnetic drift ExB and depended of the conductivity across field magnetic lines in the E conjugates regions and, thus, the alignment between the magnetic meridian and the solar terminate is the responsible by bubble seasonal variation, as well as, by major occurrence this phenomenon in the summer months.
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A Statistical study of the Application of Incoherent Integration to Simulated Equatorial Electrojet Irregularities Power Spectra
The RESCO 50 MHz coherent back-scatter radar has been operated since 1998 at the INPE/MCT’s São Luís Space Observatory (2.33° S, 44.2° W, DIP: -0.5°), Brazil, on the dip equator to study the equatorial electrojet dynamics. Spectral analysis of the received echo from equatorial electrojet irregularities allow us to identify the dominant type of plasma irregularities in the electrojet bulk observed by the radar. Using curve fitting methods on the resulting power spectra it is also possible to obtain other characteristics from the echoes, such as: center of frequency distribution, spectral width and power. The usual approach in this analysis is through a Gaussian fitting based on the method of Least Square Error to parameters estimation. Before fitting the power spectra it is usual to smooth it in order to reduce the noise level and define better the center of frequency distribution. From the center of frequency distribution, we are able to deduce the Doppler shift of the irregularities in relation to the radar, which is close related to the electric fields that drives the plasma instabilities. In this work, we have simulated echoes signals from 3-meter type 1 plasma instabilities, and analyzed it in order to recover the center of frequency distribution used to simulate the data generated. As a smoothing method we have use dincoherent integration. We have applied three distinct levels of smoothing in order to evaluate the response of the fitting to this technique. The advantages and disadvantages of applying different levels of incoherent integration over power spectra of back-scatter echoes from type 1 irregularities in the parameter estimation are presented and discussed.
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AIR POLLUTION EPISODES ASSOCIATED WITH LONG RANGE TRANSPORT OF BIOMASS BURNING PRODUCTS
Authors Cláudia Boian and Volker W. J. H. KirchhoffAn experiment was performed in the north-west of the state of Paraná, at Maringá site (23.10 S; 51.10 W), from August 2001 to November 2002, to determine the impact of large scale transport, over a distant region of the biomass burning area, under the influence of the anticyclonic circulation. This is a typical local transport regime during the dry season (July-September), when intense biomass burning occurs in Central Brazil, and which gives origin to the transport of burning products from the sources to distant regions in the south of the continent. Simultaneous measurements of carbon monoxide and ozone were made in Campo Grande (20S; 54W), a moderate biomass burning region. Campo Grande is a continental site located in the Mato Grosso do Sul state, which was used as a temporary site for the present study. Vertical ozone profiles, surface carbon monoxide and ozone measurements, were compared with backward trajectories, fire pixels seen by the AVHRR satellite and meteorological conditions to determine the influence of the large scale transport at Maringá. An instrumented air-conditioned trailer was installed in a rural area (northeast of Maringá), distant some 15 km from downtown, for continuous and systematic surface ozone measurements. CO measurements were obtained from grab samples, collected weekly. The air samples were then taken to the laboratory where they were analyzed for CO by gas chromatography. Electrochemical concentration cell (ECC) ozonesondes were used to measure the vertical ozone profile. The lowest concentrations were measured in January (carbon monoxide average 110.8 ± 11.8 ppbv and ozone average 13.2 ± 4.0). These values were used as reference background values in our analysis. A clear increase in trace gas concentrations was observed in Maringá during the dry season (from August to October) when intense biomass burning occurs in Central Brazil and the transport term is more significant. An excess of four times the background value of CO was observed in Maringá during this period. Excess ozone was also observed from surface measurements and vertical ozone profiles.
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ASSOCIATION BETWEEN IONOSPHERIC PLASMA BUBBLES AND SPREAD-F
A statistical study of the association between the frequency of occurrence of the ionospheric bubbles and the range spread-F (large-scale ionospheric irregularities) is presented here. This study was based on radio frequency observations (Digisonde data) and optical observations of the airglow OI630nm by an all-sky digital imager system located at the low-latitude region – Cachoeira Paulista (22.5oS, 45oW) – and at the equatorial region – São João do Cariri (7.4oS; 36.5oW). A total of 158 nights during maximum solar cycle were analyzed being 63 nights at Cachoeira Paulista and 95 nights at São João do Cariri. The frequency of occurrence of ionospheric bubbles at Cachoeira Paulista was compared with frequency of occurrence of the range spread-F over the same site. At São João do Cariri, the frequency of occurrence of the ionospheric bubbles was compared with the frequency of occurrence of the range spread-F over São Luis (2oS; 44oW) and Fortaleza (3.5oS; 38.2oW) because unfortunately there is not a Digisonde operating at São João do Cariri. This statistical study with the local time showed that the ionospheric irregularities occur with high frequency between October and March. Also, it was observed that the occurrence of ionospheric bubbles is closely related to the occurrence of the range spread-F. The observations showed that the frequency of occurrence of ionospheric bubbles in Cachoeira Paulista is greater than the frequency of occurrence of the range spread-F. Apparently, this fact occurs because of the discrepancies between the areas of covering of each instrument utilized.
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Extension of the non-linear depth imaging capability of the inverse scattering series to multidimensional media: strategies and numerical results
Authors F. Liu, A. B. Weglein and K. A. Innanen and B. G. NitaThe inverse scattering series (ISS) has proven, and continues to prove, to be a highly effective formalism for the separate and isolated accomplishment of several key tasks of reflection seismic processing and inversion. In particular, Weglein et al. (2000), Shaw et al. (2003), and Shaw (2005) describe the development of an algorithm distilled from the ISS that concerns itself with the location of subsurface reflectors with no prior knowledge, or related intervening estimation, of the medium wavespeed. The specific non-linear data activity that accomplishes this goal has been investigated by Shaw as such for an idealized 1D pre-stack acoustic experiment; we here describe the extension of those ideas to accommodate media with lateral variation. This is a non-trivial step.
Nevertheless, beneath the added algebraic complexity, recognizable patterns and mechanisms are visible. Analysis of these terms and patterns suggests that certain portions of the 2D reflector location mechanisms of the ISS are a good starting point for the creation of algorithms for the accurate depth location of reflectors with a moderate level of lateral variability. The partial 2D imaging capability within the ISS is examined in this paper for the special case of a constant density acoustic medium and taking kh=0. We demonstrate numerical implementations of these forms and discuss ongoing work towards capturing further imaging capability residing within the ISS, especially with regards to the accommodation of larger levels of contrast and rapidity of spatial variation in medium properties.
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Common-Reflection-Surface stack – a generalized stacking velocity analysis tool
By Jürgen MannThe Common-Reflection-Surface (CRS) stack has originally been considered as an alternative stacking tool to simulate high quality zero-offset section from seismic multicoverage data. Meanwhile, this perception has significantly changed in favor of the stacking parameters employed in the CRS stack. The fully automated determination of these parameters during the CRS stack can be seen as generalization of the well established stacking velocity analysis applied in the conventional NMO/DMO/stack approach. As
the CRS stack accounts for local dip and curvature of reflectors in depth, its stacking parameters carry far more information about the subsurface than conventional stacking velocity. Consequently, applications based on such stacking parameters, e. g., velocity model determination, directly benefit from this generalization: more stable results can be achieved in a more automated manner with less rigorous constraints compared to conventional methods. I briefly review the basic concepts of the CRS stack method and illustrate them with a data example. The main message is that this method facilitates various imaging problems, e. g., inversion, depth imaging, and automated horizon picking.
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Detecting reservoir fractures and their orientation using multi azimuth walkaway VSP
More LessFour walkaway VSP lines were acquired in the Kashagan East 1 well located in the Caspian Sea. Fracture orientations in the reservoir were obtained by acquiring data from multi azimuths and offsets recorded with several 3-component geophones lowered into the carbonate zone. Orientations were detected by interpreting the polarization of the fast and slow shear waves (figure 1) observed in the horizontal geophone component data.
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Offset VSP in a deviated well to get converted shear waves
This paper presents a case history in which the main objective of the borehole seismic survey was to obtain information about converted shear waves, in order to support the evaluation of feasibility for an OBC project in a Tertiary reservoir, Offshore Brazil. The Offset VSP has shown a large degree of P to S conversion, at different layers. The well trajectory in combination with the source position allowed to get Shear velocities, and also to generate P and S images that provided an additional tool to evaluate the degree of P to S conversion.
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Seismic phase and amplitude calibration deep-water Brazil using VSP data
Authors Rafael Guerra, Carlos Rodriguez and Scott LeaneyIn this paper we review a case study where borehole seismic data acquired in a deep-water field offshore Brazil, was used to build a 1.5D-anelastic model that accurately predicts the seismic amplitude attenuation versus time and offset, due to the combined effects of geometrical spreading, transmission losses and anelastic attenuation (Q-factor). This borehole calibrated model is ray-traced to compute a seismic amplitude gain function that can be applied directly to surface seismic pre-stack gathers and the results compared to the geometrical spreading correction conventionally used. The Q(z) profile derived from the VSP data provides also very useful information for high-frequency enhancement of seismic data. Finally, we show the use of VSP data in assessing
the phase of different vintages of surface seismic data and their degree of well tie.
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