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5th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Sep 1997 - 03 Oct 1997
- Location: São Paulo, Brazil
- Published: 07 November 1997
301 - 400 of 416 results
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Variaçăo Latitudinal do TEe e a Anomalia Equatorial
Authors M. Fedrizzi and I. Jelinek KantorO GPS (Global Positioning System) e um sistema de navegaçăo que permite determinar a posicăo e a velocidade de um objeto, fixo ou móvel, situado em qualquer ponto sobre ou próximo ŕ superfície terrestre, usando sinais de 24 satélites em órbita na Terra. Devido ao efeito da ionosfera na propagaçăo da onda eletromagnética transmitida pelos satélites do sistema GPS, em 1575,42 MHz e 1227,60 MHz, é possível obter-se o conteúdo eletrônico total, TEC, usando-se as medidas normalmente utilizadas para medidas de navegaçăo, e disponfveis pela Internet.
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Uma Metodologia para Obtençăo do TEC através do GPS
Authors I. Jelinek and M. FedrizziO GPS (Global Positioning System) e um sistema de navegaçăo que permite determinar a posicăo e a velocidade de um objeto, fixo ou móvel, situado em qualquer ponto sobre ou próximo ŕ superfície terrestre, usando sinais de 24 satélites em órbita na Terra. Devido ao efeito da ionosfera na propagaçăo da onda eletromagnética transmitida pelos satélites do sistema GPS, em 1575,42 MHz e 1227,60 MHz, é possível obter-se o conteúdo eletrônico total, TEC, usando-se as medidas normalmente utilizadas para edidas de navegaçăo, e disponfveis pela Internet.
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RED_ION - Sistemas Automatizados para Reduçăo de Ionogramas
More LessIonogramas săo registros produzidos pôr sondadores, os quais săo de grande importância nos estudos da Ionosfera sobre a propagaçăo das ondas eletrornagéeticas e nas telecomunicaçőes. Especialistas em ionosfera e técnicos que vem usando ionogramas em suas pesquisas ao longo destes anos, sabem da dificuldade que se enfrenta ao trabalhar com este dados. Para se obter as principais informaçőes dos mesmos, é preciso em primeiro lugar interpretá-los e em segundo medir seus principais parâmetros (reduzir). Só entăo, de posse destas informaçőes poderăo ser feitos cálculos de médias, levantamentos estatísticos e gráficos, para análise do comportamento da ionosfera. Para facilitar o trabalho com ionogramas foi desenvolvido o sistema Red_ion, com o qual é possível fazer a reduçăo de ionogramas de forma automatizada. O sistema năo soluciona a questăo da interpretaçăo, mas é uma ferramenta bastante eficaz no que diz respeito a mediçăo dos parâmetros ionosféricos, tomando este trabalho mais rápido, seguro epreciso.
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A Camada Ionosférica F3
Authors P.F. Barbosa Neto, I.S. Batista and M.A. AbduEste trabalho apresenta uma análise de dados da digissonda instalada nas vizinhanças de Fortaleza com o objetivo de estudar a ocorręncia de uma carnada adicional, a camada F3, na ionosfera do equador magnético. Foram analisados 2 anos de dados obtidos na estaçăo de Fortaleza (4°S, 38°W, 70S latitude magnética) no período de setembro de 1994 a outubro de 1996. Observou-se a existęncia de horários e meses preferenciais para a ocorręncia da camada adicional, os quais serăo apresentados, prelirninarmente, nesse resumo.
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Ocorręncia de Eventos Trimpi na Estaçăo Antártica Comandante Ferraz
Authors J.H. Fernandez, L. Rizzo Piazza and N. Babulal TrivediA propagaçăo de ondas de rádio em VLF (Very Low Frequency: 3-30 kHz) no guia de ondas Terra-Ionosfera pode ser perturbada por um rápido aumento local na densidade eletrônica da baixa ionosfera. Algumas dessas perturbaçőes transientes podem ser detectadas tanto na amplitude quanto na fase da onda que se propaga. Essas perturbaçőes apresentam um rapida variaçăo (da ordem de 1 s), tanto em amplitude quanta em fase, seguidas de uma recuperaçăo relativamente longa (t>20 s) e săo denominadas de EVENTOS TRIMPI.
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Estudo de Derivas Ionosféricas em Săo Luis (MA) e Cachoeira Paulista (SP), por Meio de Ionossonda Digital
Authors F.C.P. Bertoni, I.S. Batista and M.A. AbduA natureza quântica da matéria é responsável por efeitos imprescindíveis a existęncia de uma camada atmosférica ionizada - a Ionosfera. Os raios X e da faixa do extremo-ultravioleta, bem como raios cósmicos, possuem fótons com energia suficiente para arrancar elétrons de valęncia dos componentes químicos atmosféricos.
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O Perfil de Temperatura na Regiăo da Mesopausa em Săo José dos Campos Obtido com Radar de Laser
Authors M.P.P.M. Jorge, B.R. Clemesha, P.P. Batista and D.M. SimonichEste artigo trata da obtençăo do perfil de temperatura atmosférica entre 80 e 100 km de altura, regiăo da mesopausa. Ele é baseado no desenvolvimento e aprimoramento de uma técnica experimental simples que permite determinar a temperatura da atmosfera utilizando um radar de laser e as propriedades físicas do sódio mesosférico. A técnica consiste em sintonizar o radar de laser na linha D2 do sódio (5890 Ĺ) e substituir o espelho de saída do laser por urn interferômetro Fabry-Perot com "free-spectral-range" de 1,98 pm, mesmo valor da separaçăo da estrutura hiperfina da linha D2 do sódio. Inicialmente um controlador de temperatura permite variar a temperatura do Fabry-Perot e realizar uma varredura em comprimento de onda na estrutura hiperfina do sódio. Posteriormente um Fabry-Perot controlado por pressăo permite mudar o comprimento de onda do laser do máximo para o mínimo da estrutura hiperfina. A temperatura do sódio, ou da atmosfera, uma vez que estăo em equilíbrio termodinâmico, e inferida da convoluçăo entre o perfil do laser e o perfil ressonante do sódio.
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Resposta Termosférica- Ionosférica a Tempestades Magnéticas no Setor Sul-Americano
Authors X.T. Pincheira, I.S. Batista, M.A. Abdu and P.G. RichardsApresenta-se um estudo caso a caso de vários eventos de tempestade ocorridos nos anos 86 (mínimo solar) e 89 (máximo solar) para uma rede de estaçőes no setor sul-americano que cobre latitudes baixas, médias e altas: Cachoeira Paulista, CP, (23° S, 45°W,-12.6° lat.mag.) e Fortaleza, FZ, (4°S, 38°W, 4,8° lat .mag.) no Brasil e Concepción, CON, (37°S, 73°W,-25.6° lat. mag) e Ilha Rei Jorge, IRJ, (62° S, 59°W, -0.7° lat. mag.) no Chile.
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Lightning in Brazil
By O. Pinto Jr.Global and local lightning data in Brazil are revised. Brazil is the largest tropical country of the world and, in consequence, one of the main countries in terms of lightning activity. About 100 million lightning strikes occur each year in almost all parts of the country. From thunderday level and satellite data, it is well known that most of them occur in the Amazon region in association with isolated thunderstorms and tropical squall lines produced by low level convergence known as the intertropical convergence zone (lTCZ). However, no local ground lightning data are available in this region, so that the lightning characteristics can be determined. In the south and southeastern regions of the country, by tum, the lightning flashes are mainly associated with severe storms produced by cold front convection in a mountainous terrain. In this region, balloon and ground lightning data have been obtained in association with cold frontal squall lines and mesoscale convective complexes. The analysis of these data has identified new exciting aspects of the lightning research, at same time that It has encouraged its development in our country.
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Batimetria na Margem Continental Nordeste Brasileira- Comissăo Leplac - Alfa
Authors A.A.L. Alberoni and I.K. JeckA Comissăo LEPLAC-ALFA foi realizada pelo Navio Hidrográfico Sirius, da Diretoria de Hidrografia e Navegaçăo (Marinha do Brasil), nos meses de fevereiro e março de 1994. Situa-se entre as latitudes de 02°40'S e 10°40'S e entre as longitudes de 033°20'W e 037°45'W, abrangendo grande parte da Margem Continental LestelNordeste Brasileira onde se destacam platôs, terraces e montes submarinos, dentre eles o Guyot do Ceará, parte da cadeia de Fernando de Noronha, os Platós do Rio Grande do Norte e de Pernambuco, o Terraço de Natal e os Montes Submarinos do Rio Grande do Norte, Paraíba e Alagoas.
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Lightning: Measurements and Modeling
By V.A. RakovMeasurements of various characteristics of the lightning discharge will be reviewed. The use of discharges stimulated to occur (triggered) between an overhead thundercloud and a designated point on the ground for studying of the properties and the effects of lightning will be discussed. Recent findings from the experiments conducted at the Camp Blanding, Florida lightning triggering facility operated by the University of Florida will be presented. Modeling of lightning processes with the emphasis on the return stroke will be reviewed. Validation of the models using measured electric and magnetic fields due to natural and triggered lightning will be discussed.
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Development and Results of the National Lightning Detection Network in the USA
By R.E. OrvilleA review will be given of the development, installation, and use of lightning data from detection networks over the last twenty years in the United States. One path will be traced from the first successful efforts in 1979 to overlay lightning locations on radar and satellite images, to the implementation of the National Lightning Detection Network. to recent results from the "enhanced network" now operated by Global Atmospheric Inc., Tucson. Arizona. Our results show that the United States has approximately 30 million cloud-to-ground strikes per year with about 4-9 % lowering positive charge to ground. The monthly values of the percentage of positive flashes ranges from typically 3 % in the summer to 25 % in the winter. The annual maximum flash density in the United States is typically 9-11 flashes/km2 and is usually found in the state of Florida.
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The Physics of Lightning Above the Clouds
More LessWhat is our physical understanding of middle atmosphere and ionosphere perturbations caused by lightning? Electric currents and electromagnetic energy from lightning pass through the middle atmosphere and occasionally result in direct optical phenomena such as sprites, blue jets, and elves. Additionally low frequency electromagnetic energy from lightning penetrates entirely through the ionosphere, interacting with the ionospheric plasmas at all levels. These high altitude optical and electrical effects from lightning were not predicted and were thus a great surprise and continue to be exciting interest in the scientific comunity. Recent balloon, rocket and satellite experiments will form the basis for a review of the in-situ electrodynamical measurements above thunderstorms. So far no one has actually succeeded in making direct measurements in the luminous region of a red sprite, but we do not know many things about them from remote measurements. This talk will attempt to review our state of understanding of the physical phenomena in the middle atmosphere and ionosphere which is caused by lightning.
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Recent Advances in Observing the Distribution and Variability of Thunderstorms from Space
By S.J. GoodmanThe NASA optical transient detector launched in April 1995, Earth Observing System Lightning Imaging Sensor on TRMM-l scheduled for launch in late 1997, and a proposed Lightning Mapper Sensor on GOES N-P offer a new and potentially long-term, comprehensive thunderstorm observation capability. Lightning has been intermittently observed from space since the 1960s. However, these new optical sensors offer significant improvements in the direct measurement of lightning produced by individual thunderstorms and mesoscale weather systems across the earth. These data, used alone or blended with passive microwave, visible, and infrared measurements from other low earth orbiting and geostationary satellites, can be used to describe the characteristics and variability of thunderstorms from one climatic environment to another, from one season to another, and from one year to another. These observations can be used to assess the indirect methods of thunderstorm identification based on cloud top pressure, cloud top temperature, or microwave (ice) scattering index. Relationships among lightning, cloud type, cloud properties, and precipitation can also be examined on a global scale.
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Rainfall Periodicities in Amazonia
Authors E.M.C. Cutrim, D.W. Martin, E. Yulaeva, D.G. Butzow and I.M. SilvaThis study attempts to determine oscillations in the Amazonia rainfall at temporal scales between one day and one year. We examined records from a network of three stations. The network was designed to contrast rainfall in coastal Amazonia (Belem) with rainfall in central Amazonia (Manaus) and to observe the land/river influence on the rain (in central Amazonia). UFPa station is located on the Guama Campus of the Universidade Federal do Para, about 300 m from the northern margin of the Guama river; Careiro station, in a lowland varzea pasture on Careiro Island (near the confluence of the Amazon and Negro rivers); CEPLAC station, on the experimental field of the Brazilian Executive Commission for Cacao Production Planning (CEPLAC) (60 km northwest of the city of Manaus). The experimental field of cacao trees at CEPLAC is surrounded by "terra firme" rain forest. The analysis was conducted at hourly resolution for the three year period beginning in I January 1988. The results of this analysis are first presented for Careiro rainfall records and later compared with rainfall oscillations obtained at the other locations. To the extent that rainfall in eastern Amazonia originates in deep convective clouds, the results may help to understand the periodic behavior of lightning.
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Lightning Research Carried out by Companhia Energética de Minas Gerais - Brazil
Authors J. H. Diniz, A.M. Carvalho and L.C.L. CherchigliaThis paper presents an overview on the researches and studies that have been carried out by CEMIG since 1970 in its lightning research program, as well as the data obtained so far and some analysis and correlations already performed. Lightning is the major cause of non-schedule outages in CEMIG's power system (67% for the transmission system and 28% for the distribution network).
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Mesoscale Convective Systems in Brazil
More LessBrazil is a country of many contrasts, meteorology being no exception. From the vast tropical region, including the Amazon rainforest and the drought prone areas of the Northeast, through the southern tip, in a midlatitude regime with occasional winter snowstorms, Brazilian weather is quite variable. Silva Dias (1989) presented a few examples of the mesoscale systems over South America, some of which have been the subject of a considerable research effort since then.A recent work by Mohr and Zipser (1996), using the SSMII 85 GHz ice scattering signature to describe the size and intensity of Mesoscale Convective Systems - MCS - observed during 1993, shows that convective storms are well spread over South America.
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Estrutura e Evoluçăo da Nebulosidade CB atravÉs dos Dados de Relâmpagos
By A. StarostinA observaçăo dos relâmpagos em uns sistemas convectivos de mesoescala mostrou que a maior freqüęncia de relâmpagos ocorre nos estágios inicial e de maturidade (Toracinta et al. (1996)) e que as localizaçőes de freqüęncia maxima de relampagos e as areas de precipitacoes máximas săo bem coincidas no tempo e no espaço (Clodman e Chisholm (1993); Gosz at al. (1995)).
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Basic Elements and Model Comparisons in Electrodynamics: Lightning Trajectory
Authors O. Mendes Jr., O. Pinto Jr., I.R.C.A. Pinto and M. ChryssafidisLightning consists basically of a high current (-kA), transient atmospheric electric discharge with path length around several kilometers. It is due to a great amount of electric charge (-10-1 OOC) accumulated in thunderclouds (cumulonimbus) and occurs when the electric field exceeds locally the air electric insulation (> 400kV/m).There are five types of lightning discharges: intracloud, cloud-to-ground, cloud-to-cloud, from cloud to air surrounding it and from cloud top towards stratosphere. To human environment cloud-to-ground lightning is the most important although observations have shown that its occurrence is very much less than the intracloud one. The main stages of cloud-to-ground lightning are essentially the preliminary breakdown, the stepped leader, the connecting leader and the return stroke, however subsequent stages may also occur (Volland, 1984; Uman, 1987). In this paper we are interested in the development of stepped leader, which establishes the atmospheric ionized path to the complete lightning. Thus we consider basic elements of atmospheric electrodynamics, the models for simulation of lightning trajectory and their main features.
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Características dos Eventos de Raios Nuvem-Solo e sua Distribuiçăo em Área no Leste do Pará
Dentre os raios associados a nuvens cumulonimbus na troposfera, cerca de 20% săo do tipo nuvem-solo (CG). Os raios CG săo os que mais causam danos a seres vivos, edificaçőes, sistemas elétricos e de comunicaçőes terrestres.
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Ecofacies da Plataforma Continental Amazonica
Authors E. de Alencar Costa and A. FigueiredoO rio Amazonas apresenta uma vazăo que chega a atingir 350.000 m/s e fornece urn suprimento sedimentar de aproximadamente 1 bilhăo de toneladas por ano ŕ plataforma continental (MEADE et al., 1985). Com tamanha descarga sedimentar, o rio constrói urn delta submarino que estende-se até a plataforma externa (FIGUEIREDO et al., 1972). Esta regiăo sofre ainda a influęncia da corrente Norte Brasileira, que flui em direçăo NW; das grandes amplitudes de marés e fortes correntes associadas e dos ventos Alfsios de NE. A associaçăo de todos estes processos, promove uma distribuiçăo diferenciada de sedimentos e de tipos de eco ao longo da plataforma (fig. 1).
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About the Intensity of Strokes in Negative Lightning Flashes
Authors I.R.C.A. Pinto, O. Pinto Jr., J.H. Diniz and A.M. CarvalhoNegative cloud-to-ground lightning flashes were recorded by a lightning positioning and tracking system (LPATS) in the region of the Mount Agulhas Negras (altitude of 2787 m) in Brazil, during the winter and summer season of 1993. The dependence of the stroke peakcurrent on the order of the stroke, the flash multiplicity and the season was investigated. It was found that subsequent strokes tend to be less intense than first-order strokes and that first-order strokes tend to be more intense in multiple stroke flashes. It seems that the larger is the multiplicity, the higher is the intensity of the first-order stroke. The above results are more evident during the winter season. It was also found that the geometric mean of the first-order stroke peak-current increases in the winter season. The dependence of the results on the high altitude of the observation site was also investigated. Apparently, the high altitude of Mount Agulhas Negras has an effect on the lightning intensity during the summer season.
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An Evaluation of The Predicted Pulse-Type Thunderstorm Gusts Using Horizontal Divergence Field from Doppler Radar Data
Authors W.C. Maugeri Amorim, O. Massambani and I. ZawadzkiThe application of the cloud top penetrative downdraft mechanisms in combination to the Vertically Integrated Liquid water contents (VIL) and radar Echo Top heights (ET) as proposed by Stewart (1991), and in operational use as a "GUST Algorithm" at J. S. Marshall Weather Radar Observatory - Montreal, Canada, was evaluated using horizontal divergence field computed for the lowest antenna elevation (0.5 degree) from Doppler radar measurements. The study was based on a total of 25 events responsible for generating strong surface winds in the Montreal region as observed during the summers of 1994 to 1996. To compute the maximum vertical velocity (W) within the downdraft, the technique uses the estimated VIL and ET respectively related to the liquid water content and height parameters as theoreticaly proposed by Emanuel (1981). The horizontal divergence (S) was processed from differential Doppler velocity data using the "SHEAR Algorithm" also in operational use at the Radar Observatory. For all storms, Wand S were computed simultaneously in a 5 minute resolution corresponding the antenna elevation program cycle. A comparison between those two computed parameters (Wand S) resulted in an overall averaged correlation coefficient of 0.75 and an overall averaged time lag of 10 minutes. Vertical cross-sections from the Doppler radar data were used to determine that typically the level of horizontal divergences was about 1500 meters, corresponding to the height of the maximum vertical velocities. The application of a simple flux balance and mass continuity equations to the computed W for all cases, a distribution of expected heights was determined to be centered at 2000 meters level, indicating a fairly good agreement. The paper also presents a critical analysis of the assumptions built into the technique regarding the entrainment conditions at the cloud top level, as well as due to the effects of the quantitative estimation of the ET and VIL parameters from the radar reflectivity data. The results indicate that the technique can be used as a powerful nowcasting tool to potentially detect severe gust storms antecipating the presence of strong divergence field at the surface.
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Cloud-to-Ground Lightning Flash Characteritics in Meteorogical Conditions
Authors R.B.B. Gin, O. Pinto Jr., I.R.C.A. Pinto and O. Mendes Jr.About 200,000 lightning flashes recorded in the summer season of 1993 in the state of Minas Gerais, Brazil, were analysed in terms of the predominant meteorological condition in the synoptic scale. The results indicate that most lightning characteristics are independent on the synoptical conditions. However, the mean intensity of first-order strokes in both negative and positive lightning flashes were found to be lower in flashes associated with isolated thunderstorms than in flashes associated with cold front or tropical convection.
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Estimativas de Precipitaçăo Através da Freqüęncia de Raios Nuvem-Solo, em Belém
Altas freqüęncias de ocorręncias de raios e elevadas razőes de precipitaçăo, estăo principalmente associadas com as nuvens cumulonimbos, na troposfera. As relaçőes entre a eletrificaçăo dessas nuvens e a razăo de crescimento de seus hidrometeoros, bem como, a ocorręncia de uma rajada ou jorro de chuva por 4 a 6 minutos observado na superfície, após a ocorręncia de raio nas proximidades do observador, tem sido objeto de diversos relatos e estudos. Entretanto, as relaçőes de causa e efeito, nas condiçőes microfísicas que prevalecem no interior das cumulonimbos, permanecem sem explicaçăo satisfatória.
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Cloud-to Ground Lightning Flash Characteristics in Southeastern Brazil in the Winter Season
Authors R.M.L. Rocha, I.R.C.A. Pinto and O. Pinto Jr.The lightning flash characteristics in the southeastern region of Brazil were obtained in the winter season of 1993 through a lightning positioning and tracking system (LPATS). The preliminary data are presented in terms of polarity, multiplicity, and peak current of the first-order stroke. The results are compared with similar data obtained in the same region in the summer season.
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Estrutura Tridimensional da Linha de Instabilidade da Amazônia
Authors J.C. Paiva Cohen and M.A. Faus da Silva DiasAs Linhas de Instabilidade (LI) formam-se ao longo da costa norte-nordeste da América do SuI, desde a Guiana até o estado do Maranhăo, sendo que algumas destas linhas de cumulonimbus propagam-se para o interior da Bacia Arnazônica e outras dissipam-se próximo a costa atlântica. Tanto as linhas de cumulonimbus que se propagam, quanta as que năo se propagam associam-se ŕ circulaçăo de brisa marítima junto ŕ costa (Kousky, 1980). O objetivo deste trabalho é avaliar a estrutura tridimensional de uma LI através de experimentos numéricos, validando esses resultados através dos dados coletados na rede de estaçőes automáticas instaladas durante o experimento ABLE 2B (Amazon Boundary Layer).
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Severe Weather Systems for Southeast Brazil, 1989-1994
Authors J.C. Conforte, V. Brahmananda Rao and M.A.F. Silva DiasA brief climatology of severe weather systems is made for the period 1989-1994. It is found that the number of severe weather systems is highest in austral spring and lowest in winter.
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Direct Lightning Current Measurements in Southeastern Brazil I. Current Waveform
Authors M. Lacerda, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz and A.M. CarvalhoThis paper shows for the first time in the scientific literature data of 22 natural negative cloud to ground lightning discharges in South America captured by a 60 m metalic tower between 1985 and 1994. The technique for obtaining the data is briefly described. We show current waveform for several return strokes with resolution of 1 us, 0.5 us and 0.2 us.The average current waveform shows some differences when compared with data from Switzerland tower.
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Direct Lightning Current Measurements in southeastern Brazil II: Correlations
Authors M. Lacerda, O. Pinto Jr., I.J.H. Diniz, A.M. Carvalho and R.C.A. PintoThis paper shows data associated with 50 subsequent return stroke of 22 natural negative descendent Jightining discharges in Brazil captured by a 60 m metalic tower, between 1985 and 1994. It is investigated the possible correlations among the time to peak value of derivative current, time to peak current, the peak value of the electric current, and the peak value of the derivative current.We discuss some physical consequences relating to them. We suggest that there may be a non-linear correlation between the time to peak occurence and the magnitude of these parameters.
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Direct Lightning Current Measurements i
Authors M. Lacerda, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz and A.M. CarvalhoIn this paper it is analyzed 13 M-component of 11 subsequent return stroke (of order three or higer) of natural negative cloud. to ground lightning captured by a 60 m metallic tower of Cemig Research Lightning Station (CLRS) in Brazil. The CLRS .has registered Mcomponents in times less then 1.2 millisecond arter the preceding return stroke. The M-components are more. intense than those recordered in triggered lightning flashes and occur during periods of higher continuing current level The half peak Width was found to be shorter than those obtained in triggered lightning flashes.
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Basement Reactivation, Rifting and Sedimentary Basin Development on the Continental Shelf and Margin of NW Europe: Evidence from BIRPS Deep Seismic Reflection Profiling
By R. EnglandDeep seismic reflection and refraction profiling provides the most direct method of imaging basement structures and the relationship between basement structure and basin development. The technique has been successfully used to discriminate between pure and simple shear mechanisms of sedimentary basin formation, by providing the fundamental geometrical relationships between basement faults and the distribution of syn- and post-rift sedimentary sequences. It is the only technique available capable of uniquely characterising the thickness and properties of the continental basement, and therefore provides constraints for thermo-mechanical modelling of the lithosphere. Since 1984 BIRPS has acquired an extensive grid of deep seismic reflection profiles over the United Kingdom and Ireland continental shelf and continental margin. These data can now be used to synthesize the basement structure of the continental shelf of NW Europe and determine its effects on both intracontinental rifts, such as the North Sea, and on passive margin development in the NE Atlantic.
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A Intrusăo da Extensăo da Corrente das Malvinas na Costa do Rio de Janeiro, Brasil, Vista Através do Sensoriamento Remoto e Dados Biológicos in situ
Authors J.L. Stech, M.R. Stevenson, D. Dias-Brito and M. KampelAtravés de imagens do sensor Advanced Very High Resolution Radiometer (AVHRR) instalados a bordo dos satélites da série National Oceanic and Atmospheric Administration (NOAA) e possível obter mapas diários da Temperatura da Superfície do Mar (TSM) para grandes regiőes oceânicas. Stech et al. (1996) observaram, através destes mapas, importantes feiçőes oceanográficas, no Oceano Atlântico SuI. Dentre estas se destacam, o fenômeno da ressurgęncia na costa SE do Brasil e vórtices de mesoescala na Corrente do Brasil (CB). Sirnilarmente, Kampel (1993) estudou a variaçăo da confluęncia das Correntes do Brasil e Malvinas e a penetraçăo para norte, ao longo da costa brasileira, do ramo costeiro da extensăo da Corrente das Malvinas.
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Dispositivo de Proteçăo Szillard: Resultado de 55 Vistorias
Em 1989, a Comissăo Nacional de Energia Nuclear (CNEN), orgăo responsável pela orientaçăo, planejamento, supervisăo e fiscalizaçăo do comércio de materiais radioativos em território brasileiro, proibiu, através da Res. n04 de 19/4/89 (publicada no D.O. em 9/5/89), a "concessăo de autorizaçăo para utilizaçăo de material radioativo em pára-raios", por ferir o princípio da justificativa, fundamento da filosofia intemacional de radioproteçăo, que está ligada ao ganho da sociedade com essa aplicaçăo de material radioativo. "Considerando a necessidade de dar destino adequado ao material radioativo dos pára-raios desativados", foi também resolvido que "o material radioativo remanescente dos pára-raios desativados deve ser imediatamente recolhido a CNEN" (CNEN 1989), 0 que deveria se dar quando da manutencao dos mesmos.
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Lightning Characteristics Associated with Altitude and Ground Conductivity
Authors M.A.S.S. Gomes, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz, A.M. Carvalho, A.L. Padilha and I. VitorelloAbout 160,000 strokes recorded in the state of Minas Gerais in the summer season of 1993 were analysed in terms of the dependence of the peak-current stroke intensity and stroke density on altitude and ground conductivity. Preliminary results will be presented and discussed in the context of measurements made in other countries.
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Recent Trends in Stratospheric Ozone: Implications of Anthropogenic, Volcanic and Solar Cycle Perturbations
By S. ChandraSatellite instruments since early 1970 have provided an almost a continuous record of column ozone and ozone profiles on a near global basis. The quality and long term stability of these measurements are now well characterized to make realistic assessments of long term changes in stratospheric ozone associated with anthropogenic chlorine and bromine emissions, solar cycle ultraviolet flux variations and the major volcanic eruptions of El Chichon and Mt. Pinatubo. In this review I will present an overview of ozone changes derived from satellite data and their implications for future changes based on two dimensional photochemical models.
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Estimando Dimensőes Fractais de Relâmpagos
Authors A.L. Martins Jorge and M. Basílio de MatosDiversos objetos naturais apresentam características geométricas que tornam difícil a atribuiçăo de uma dimensăo inteira bem definida a eles. Um exemplo săo as linhas costeiras: definir sua extensăo e uma tarefa que exige a escolba de uma esc ala arbitrária. Quanto menor a escala mais "enseadas" e "pontas" aparecem, num processo que no limite levaria a urn comprimento infinito. Outros objetos típicos săo nuvens, árvores, rios, etc. Nesses casos podemos dizer que a melhor definiçăo de dimensăo é aquela que inclui valores fracionários, e chamamos a esses objetos de fractais.
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Observations of High Densities and Rates of Positive Flashes in Summertime Thunderstorms in Brazil
Authors R.B.B. Gin, O. Pinto Jr., I.R.C.A. Pinto and O. Mendes Jr.Observations of summertime thunderstorms in Brazil in 1993 indicate periods with the predominance of positive cloud-to-ground lightning flashes. The periods present high density (average value of 0.66/km2h.) and high hourly rate (average value of 478/h) of positive flashes. In most cases, they occurred at or near the beginning of the storm's cloud-to-ground lightning activity and had duration of about 2.Sh.
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Stratospheric Balloon Measurements of Sferics in Brazil
Authors M.M.F. Saba, O. Pinto Jr., I.R.C.A. Pinto, R.B.B. Gin and O. Mendes Jr.Measurements of sferics were obtained during two balloon flights launched from Cachoeira Paulista, Brazil, on 26 January 1994 and 23 March 1995 carrying double-probe electric field detectors. The results are discussed in terms of the polarity of the associated lightning flashes and the relationship between the sferic amplitude and the sferic decay time constant. Sferic signatures of one negative flash and two large positive flashes in the quasi-DC and VLF electric field data, obtained in 1995, are presented. From the data obtained in 1994 associated with negatives flashes, a linear relationship between the amplitude and the decay time constant of sferics was found.
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Stratospheric Electric-Field Measurements Before and After Lightning Events
Authors M.M.F. Saba, O. Pinto Jr., I.R.C.A. Pinto, R.B.B. Gin and O. Mendes Jr.Stratospheric vertical electric-field measurements associated with an isolated thunderstorm were obtained during a balloon flight launched in Cachoeira Paulista, Brazil, on 23 March 1995. The behavior of the vertical electric-field before and after large cloud-toground positive lightning flashes is discussed and attributed to the existence of static and transient shielding layers around the thunderstorm. The data just after the flashes can be explained by assuming a static shielding layer around the thunderstorm correspondent to a decrease in the conductivity inside the cloud by a factor of three or more. The data before the first lightning flash can be explained by assuming a transient shielding layer just above the top of the thunderstorm, produced by the near breakdown field inside the cloud.
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Tropospheric and Stratospheric Conductivity Measurements in Brazil
Authors M.M.F. Saba, O. Pintor Jr., I.R.C.A. Pinto and O. Mendes Jr.Conductivity measurements were carried out during a balloon flight launched from Cachoeira Paulista, Brazil (22°44' S, 44°56' W) on Jan 26, 1994. For the first time negative and positive conductivity profiles with altitude were obtained in Brazil. Along its trajectory the balloon passed over three thunderstorms, as identified by video on-board images. The data give an unique opportunity to study the stratospheric conductivity variations.
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The Solar Cycle and Cosmic Ray Particles Have Direct Influence on Stratospheric Ozone Variation?
We analyze in this work three available sets of stratospheric ozone measurements obtained by ground UV sun spectrophotometer type Dobson and low energy stratospheric cosmic rays in the period from 1957 until 1995. By the analysis of these sets of ozone data, we can see a decreasing intensity at all these latitudes (Belsk, Tbilisi and C. Paulista), given a global mean rate - 10 % during the last three solar cycles. We saw also correlations with cosmic rays measurements in the stratosphere, ozone variations and sunspot number.
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Influęncia da Radiaçăo Solar no Ser Humano
By H.A. PonzioAs radiaçőes năo ionizantes, que compreendem as ultravioleta (UV), o espectro visível (EV) e as infravermelhas (IV), săo as principais responsáveis pelos efeitos fotobiológicos provocados pelas emissőes solares nos seres vivos. As UV-B tem limitada capacidade de penetraçăo na pele e exercem seus efeitos na camada basal e acima dela; săo eritematógenas e, a longo prazo, as principais responsaveis pelo câncer de pele.
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Heat Transport Estimates in the Surface Layer of the Antarctic Polar Front Using a Satellite Tracked Drifter - First Results
Authors M. Kampel, M.R. Stevenson and A.R. AssireuThe oceans play an essential role in the dynamic climate system, via 3 distinct mechanisms: 1) they absorb and exchange carbon dioxide with the atmosphere; 2) they exchange heat, water vapor and momentum with the atmosphere. The ocean circulation redistribute heat, fresh water and dissolved chemicals around the globe; and 3) they capture heat, absorbed at the surface, in the deepest regions for periods of a thousand years or more through vertical circulation and convective mixing.
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Latitude Dependence of the QBO and QTO Characteristics of Total Ozone Measured by Toms
Authors R.P. Kane, Y. Sahai and C. CasicciaThe 12-month moving averages of TOMS total ozone data for 14 years (1979-1992) were examined for QBO and QTO (quasibiennial and quasi-triennial oscillations) and compared with stratospheric low latitude zonal wind and equatorial eastern Pacific seasurface temperature (SST). The equatorial ozone had a strong QBO of period -30 months and its maxima tallied with westerly wind maxima. At other latitudes, the ozone maxima spacings were often different from 30 months, more so in the northern hemisphere. A spectral analysis showed that both hemispheres had one peak at -20 months and another at -30 months, only up to -50° latitude. At higher latitudes, these peaks shifted to -23 months and -36 months. For 0-50°, the -30 month periodicity was symmetric in the northern and southern latitudes and showed a gradual phase shift. The northern hemisphere had an additional periodicity at -4 years, roughly matching the SST.
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Observations of Atmospheric Ozone and UV -B Radiation in Brazil
Authors Y. Sahai, V.W.J.H. Kirchhoff and N.M. Paes LemeDuring recent years atmospheric ozone has become a topic of great concern. This stems from the fact that there are serious implications of the anthropogenic sources depleting the stratospheric ozone layer. Observations of atmospheric ozone started in Brazil on a routine basis in May 1974, when Dobson spectrophotometer (n° 114) was installed at Cachoeira Paulista (23° S, 45° W), Sao Paulo.
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Alteraciones de la Columna de Ozono en Punta Arenas (Chile) y la Influencia del "Agujero de Ozono
Authors C. Casiccia and V.W.J.H. KirchhoffDesde agosto de 1992 está operando en Punta Arenas (53,2°S;70,9°W) un espectrofotómetro Brewer, modelo MK-IV (serie 068). Este es el primer instrumento instalado en Chile para observaciones sistemáticas a largo plazo, con el propósito de estudiar el comportamiento y la evolución de la capa de ozono, en la zona poblada más cerca de la Antártica, donde desde hace unos ańos, a comienzo de la primavera Austral se manifiesta el fenómeno de la formación del "Agujero de Ozono Antártico" (AOA). En este trabajo se presenta un análisis de practicamente cinco ańos de mediciones hechas con el espectrofotómetro Brewer, como también un análisis de los meses de septiembre y octubre (1992-1996), de la evolución de la capa de ozono. Se muestran las mayores disminuciones detectadas hasta este momenta sobre Punta Arenas, como por ejemplo el día 17 de octubre de 1994 cuando se midieron 145,8UD (Unidades Dobson), que es el valor más bajo medido, en cinco ańos, equivalente aproxirnado a casi el 60% abajo de la media normal. Se muestra además los resultados de los primeros sondajes de ozono realizados con sondas ECC, realizados en Punta Arenas en octubre de 1995, para analisis de la distribuici6n de ozono con la altura.
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Mapeamento Geoeletrico do Aterro da Lamenha Pequena (Curitiba - PR)
Authors A. Rigoti, V. Pinheiro Jr. and J.R. de GóisO Aterro da Lamenha Pequena é formado por duas áreas de deposiçăo de lixo, denominadas vertente suI (VS) e vertente norte (VN) localizadas na divisa dos municípios de Curitiba e Almirante Tamandaré (Fig. la). A disposiçăo dos resíduos na área se deu inicialmente na VS na decada de 1960, sendo o ate rro desativado definitivamente em 1989. Com superfície de cerca de 30.000 m2 , a VS concentra em torno de 335.000 m3 de residuos, enquanto que a VN com 70.000 m2 , aloja urn volume próximo de 475.000 m3.
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Estudio Geofísico - Geotécnico en la Ruta Nacional 150 Ischigualasto - Bermejo
Authors N.A. Ponti, A.L. Imhof, S.A. Pastore, A.E. Guell and G.O. FantonSe sintetizan tareas, resultados y conclusiones del estudio geofísico-geotécnico llevado a cabo sobre la traza de la Ruta Nacional 150, tramo Ischigualasto - Bermejo, de 36.000 metros de extensión, que une los Departamentos de Valle Fertil y Jachal, al N.E de la provincia de San Juan, Republica Argentina.- Se efectuó un relevamiento geológico, sondeos eléctricos verticales y lineas de refracción sísmica a lo largo de la traza proyectada.
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Aplicaciones Prácticas del Método de Resistividad en Arqueología - Santa Fe - Republica Argentina
More LessEl estudio de investigación geofísica fué realizado en dos solares pertenecientes a familias de conquistadores que habitaron la ciudad de Sta. Fé La Vieja, entre 1576 - 1660. Dicha ciudad está situada 80 Km al Noreste de la ciudad capital de la Provincia de Santa Fé - Rep. Argentina -. Con ese objeto aplicó el metodo de prospección geoeléctrica, el que permitió aportar datos geofísicos de gran importancia para el logro de los siguientes objetivos : - Delimitación de las ruinas (tejas de techo, partes de muros, maderas, etc.). En síntesis materiales que se emplearon en la construcción de las viviendas. - Situación y ubicación de los muros laterales y frontales de las edificaciones.
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Estudio Integrado del Area de Pato, Norte de Oficina, Cuenca Oriental de Venezuela
Authors J. Delgado, A. Ramos, E. Roa and L. HernandezEI área de estudio esta localizada en la zona de Pato, ubicada al norte del Area Mayor de Oficina, donde la Formación Oficina y la parte superior de la Formación Merecure, presentan prospectos limitados por fallas, conformando trampas estructurales similares a las encontradas en los campos tradicionales al sur de la zona de Pato y otros con características estratigráficas, como los definidos en este estudio, los cuales pertenecen a sistemas de cuńas progradantes de bajo nivel (Lowstand Wedge).
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Recent Results of UV -B Measurements in Brazil
More LessA network of UV-B meters has been organized and distributed in Brazil in association with studies of the stratospheric ozone layer and in an effort to increase public awareness of excess UV-B radiation on the human skin. In order to make UV-B measurements more accessible to the people, the UV Index has been calculated in specific cases. Three different kinds of UV-B meters are used. The most sofisticated instruments can measure very narrow spectral ranges, and they can do it almost unattended by operators. Simultaneously they measure stratospheric ozone, Sulfur dioxide and Nitrogen dioxide; these are the Brewer spectrophotometers, six of which are presently part of the network. A second class of instruments is simpler but can also make spectral measurements at different wavelengths; the network has now three GUV meters in this category. And in the third class of instruments there are the UV-Biometers, which are UV-B integrating instruments, less expensive and very convenient for different applications and interpolation purposes. There are presently 8 such instruments in operation. The whole network has recently also expanded to neighbor collaborating countries, Chile and Bolivia. Southern Chile is very interesting for observations of the Antarctic Ozone Hole, and its consequences in terms of increased UV-B; and in Bolivia, the high Andes mountains receive high doses of UV-B and UV-A, because of the altitude above sea level. We will show some of these UV results, and show differences in various regions of Brazil.
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Disturbed Days
More LessDisturbed days characterized by the geomagnetic index AA * are considered. According to the present results, the intensity of the most disturbed days will increase during the next solar cycles.
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Levantamentos Geofísicos ao Largo de 16 Praias do Litoral de 8 Estados Brasileiros
Authors M.A. Gorini, C.G. Silva, E.A. Souza, F.Z. Oliver and M.N. PrazeresEntre os meses de abril e agosto de 1995 a G.G.G. Consultoria Ltda. executou uma série de levantamentos geofísicos de alta resoluçăo em 16 praias do litoral de 8 estados brasileiros, visando a instalaçăo de urn cabo submarino de fibra ótica. Estes estudos proporcionaram urn conhecimento das características geomorfológicas do fundo submarino da plataforma continental mais interna entre os estados do Rio de Janeiro e Rio Grande do Norte.
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WIPEOUTS A Resposta Acústica da Presença de Gás nos Sedimentos do Fundo Marinho da Bacia de Campos
Authors C.Y. Murakami, D.J. Miller and W. de Almeida JúniorA Petrobras através da equipe da Geręncia de Geologia Marinha da E&P-BC com o objetivo de conhecer e elaborar modelos para auxiliar a exploraçăo de petróleo e instalaçăo de equipamentos de perfuraçăo e produçăo, tern realizado mapeamentos do fundo marinho com os dados de sonar de varredura lateral e sísmica monocanal de alta resoluçăo de 3,5kHz (SBP - subbottom profile) na Bacia de Campos.
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Interference Slow Wave in Poro-Acoustic Biot Layer and Its Potential for the Detection of Subtle Traps
Authors Pavel Krauldis and Marco A. Barsottelli BotelhoThis work proves the existence of an Interference Slow Wave (ISW) in Biot porous acoustic media. The presence of ISW is theoretically established by solving the Biot equation considering a model of one horizontal layer surrounded by two elastic half spaces. The low attenuation of ISW on lower seismic frequencies and its polarizibility in the direction of the layer makes this wave potentially useful for detecting reservoirs consisting of a saturated sandstone layer inside shale in cross-hole surveys.
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Acquisition and In-Field Processing on Bottom Cable 3-D Seismic Surveys
Authors E. Bargaud, M. Denis, J. Meunier and J.J. PostelTwo 3-D seismic surveys located off the north coast of Java between Jakarta and Cirebon, were acquired by CGG for ARCO Indonesia in conjunction with PERT AMINA.One covered 105 square kilometers in the transition zone near Cilamaya. For operational and accessibility reasons, hydrophone bottom cables were used. Geophones in marsh cases on shore and in very shallow water provided 3-D coverage beneath the shoreline from shallow marine sources. The other survey covered 189 square kilometers in a producing oil field 35 kilometers north of Pamanukan in water depths of 35 to 45 meters. The presence of many platforms, tankers, and moorings made the dual-sensor bottom cable technique ideal for this area. A patch acquisition geometry was chosen for both surveys because of its ability to provide shallow coverage and the desired data distributions under obstacles, and for its operational simplicity among the obstructions. Bottom cables were used to allow deployment near the platforms and for their low noise characteristics. Acoustic positioning provided accurate receiver positions, while minimizing surface buoys, a major source of noise. Finally, extensive QC procedures, including DGPS monitoring, positioning control, attribute mapping, and seismic processing were used to provide feedback to the crew, allowing them to optimize operations. During one survey, two field-processed, 3-D migrated data blocks were delivered to the interpreter for preliminary mapping within a week after recording the last shots on each of those blocks.
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The Challenge of Acquisition and Processing in Mountainous Thrust Areas
Authors E. Bargaud, M. Denis, J. Meunier and J.J. PostelThe issues involved in this difficult problem can be divided into 3 categories: - Adapted field parameters - Adapted logistics with lightweight equipment - Adapted processing with special techniques
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Estimativa do Fator Q em A" guas Profundas: Implicacoes nos Parametres de Aquisicao
Os dados sísmicos de superfície registrados em áreas de águas profundas na bacia sedimentar focalizada neste trabalho possuem urn 'conteúdo de freqüęncies geralmente inferior a dados equivalentes provenientes de outras áreas, inclusive áreas terrestres. Em consequęncia disto, a escolha dos parâmetres de aquisiçăo para estas áreas depende de uma avaliaçăo das propriedades dissipativas dos sedimentos sobrepostos aos reservatórios af presentes. Neste trabalho, essas propriedades da subsuperfície sao avaliadas de uma forma simples, onde o fator Q é estimado a partir da curva de drift proveniente de dados de poço. Comparaçőes nos domínios da freqüęncia e do tempo entre formas de onda geradas pela modelagem direta e suas eqüivalentes estimadas a partir de dados sísmicos de superfície propiciaram a validaçăo das estimativas obtidas. Săo, tarnbém, discutidas as implicaçőes que os efeitos dissipativos estimados tęm sobre a aquisiçăo de dados nesta área.
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Seismic Crosswell Tomography: A Gauss-Newton Type Method Based on B-splines for Velocity Field Parametrization. 2nd Part: Applications
More LessTwo applications of the Gauss-Newton type method introduced in the companion paper (Soares Filho, 1997) are presented. The first one aims to exhibit its robustness in terms of different starting points. Speciffically, the target model ("Z model") is effectively reconstructed from three very different initial models. The second application shows a straightforward consequence of small condition numbers. The stability of the method is confirmed using contaminated traveltimes with Gaussian modulated additive errors.
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Effective 2.5D True-Amplitude Kirchhoff Migration and Demigration
Authors Joăo L. Martins, Jörg Schleicher and Martin TygelKirchhoff-type migration and demigra-tion for three dimensions are exceedingly expensive processes in laterally inhomogeneous media due to the intense numerics required. For simpler types of media, however, the formulas to be im-plemented simplify considerably. For 3D in-plane wave propagation in 2D media, i.e., the 2.5D situation, 2D ray tracing is sufficient for full 3D true-amplitude migration or demigration. In ID media, both imaging operations require the solution of certain integrals of a semi-analytic character which can be implemented in an even cheaper way. For some specific velocity distributions (such as constant velocity, constant velocity gradient, constant gradient of quadratic slowness and constant gradient of logarithmic velocity) fully analytic expressions can be derived. If the velocity distribution in the true earth model can be reasonably well represented by one of the considered situations, a very fast approximate true-amplitude Kirchhoff-type migration can be performed. Moreover, simple models in which the algorithms perform fast and accurately can be of great value for (a) validating the algorithms so as to ensure correct results in the desired realistic situations and (b) gaining insight on how to interpret the results.
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The Seismic Roots of the West African Passive Margin: Northern Cameroon to Southern Gabon
By B. RosendahlTo improve our understanding of the the rift-todrift history of Atlantic passive margins, nearly 10,000 km of deep-imaging seismic data were acquired off West Africa as part of the PROBE Study. The study region extends from 4 N to 4 S and includes both the shelf areas and the adjacent oceanic crust. Acquisition parameters were specifically selected to maximize imaging of the sub-basement seismic architecture. Most of the data were shot using a 7600 cu. in. airgun array and 7100 m-Iong cable array. As much as possible, two sub-sets of crossing line orientations were used; one sub-set was shot sub-parallel to inferred flow-lines, the other sub-parallel to inferred isochrons. Ongoing data processing and reprocessing have focused on optimizing deep structure, particularly reflection Moho configuration. The geological story emerging from the PROBE Study is still incomplete, but compelling nonetheless.
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Modeling by Demigration
Authors Lúcio T. Santos, Jörg Schleicher and Martin TygelKirchhoff-type, isochrone-stack demigration is a natural asymptotic inverse to classical Kirchhoff, diffraction-stack migration. Both operations can be made true amplitude by an appropriate selection of weight functions. Isochrone-stack migration can be also used for modeling purposes. The idea is to attach to each reflector in the model a spatial wavelet with an appropriate stretch and reflection coefficient, so that the model has the form of a true-amplitude migrated section. The modeling is then realized by a true-amplitudec demigration operation. An example of a simple case is computed and the results are discussed.
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Migraçăo Pré-Empilhamento na Bacia de Campos - Urn Exemplo
Authors José Cláuver de Aguiar Júnior and Helder de AndradeA aplicaçăo da migraçăo pré-empilhamento neste caso teve como objetivo obter urn imageamento sísmico em profundidade com qualidade e confiabilidade para auxiliar a composicao do histórico geo-tectônico de uma area de exploraçăo de hidrocarbonetos, onde sao observados complexos sistemas de falhamento, possantes domos de sal e intensa atividade vulcânica intrusiva. Outra motivaçăo foi a previsăo de profundidade dos prospectos exploratórios, pelo fato desta área da bacia ainda se encontrar pouco explorada, contendo uma baixa densidade de poços, o que ificulta a utilizaçăo dos procedimentos convencionais de previsăo de profundidade por inversăo de velocidades RMS, calibradas pela correlaçăo de peços adjacentes.
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A Influęncia da Fonte em Linha na Resposta da Modelagem Sísmica
Authors Sérgio A. M. Oliveira and Irshad R. MutfiA modelagem sísmica é uma importante ferramenta que é largamente usada na interpretaçăo de dados de campo. Quando o objetivo é estimar parâmetres de subsuperfície tal como velocidade, a modelagem 2-D é uma alternativa prática e barata e que pode ser usada iterativamente. Contudo, neste caso a excitaçăo do modelo se dá por fonte em linha e esta gera urn campo de onda diferente daquele presente nos dados sísrnicos reais, já que estes últimos săo obtidos por excitaçăo por fonte pontual. Esta simplificaçăo pode levar a uma interpretaçăo errônea dos resultados. Isto é particularmente verdade no caso de estudos de resoluçăo, onde năo somente a freqüęncia central do sinal é importante, mas a forma do pulso também deve ser considerada. Este trabalho analisa o fenômeno da distorçăo da forma do pulso que ocorre no caso da fonte em linha. Aqui é apresentada uma discus săo teorica que leva em conta o problema 2-D de urn sinal transiente gerado por uma fonte em linha que se propaga em urn meio actústico. Estamos propondo urn método prático para eliminar tais distorçőes e testamos sua eficięncia em um dado sintético baseado em uma modelagem 2-D envolvendo uma estrutura em forma de cunha.
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Determinaçăo da Funçăo Característica de Hamilton: Aplicaçăo da Correçăo Dinámica.
Authors I.C. Tavares and Walter SöllnerConsidere urn sístema sfsmico consistindo de uma pilha de camadas homogęneas e isotrópicas limitadas por interfaces curvas de segunda ordem. considere a superfície da terra, onde estăo localizados fontes e receptores, como a superfície anterior e a superfície posterior aquela onde ocorrem as reflexőes. Se introduzirmos urn sistema de coordenadas xyz no sistema sísmico e assumirmos que urn raio parte da origem dessas coordenadas e chega até a superfície posterior em x'y'z', a este chamaremos de raio central.
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A unified Bom- Kirchhoff representation for acoustic media
Authors Amélia Novais, Lúcio T. Santos, Martin Tygel and Bjorn UrsinThe Born and Kirchhoff-Helmholtz integrals are the most widely used descriptions of reflected and transmitted wavefields due to smooth interfaces. Although representing basically the same phenomena, the two integrals result from quite independent formulations, and are traditionally kept as completely separate objects. Concerning the model of a single target reflector in a smooth inhomogeneous elastic anisotropic medium, it has been recently shown that the volume Born integral in the region surrounding the reflector, can be transformed into a surface scatter-ing integral on the reflector. This derived surface integral has been called Born-Kirchhoff as it relates very naturally to the Kirchhoff-Helmholtz integral, thus providing the theoretical link between the two approaches. Besides, briefly reviewing the derivation and main properties of the Born-Kirchhoff integral in the acoustic case, we use a simple synthetic example to provide a comparison between the new integral and their classical counterparts.
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Empilhamento Sismico em Meios com Variacoes Laterais de Velocidade
Authors G. Garabito C., F.W. Söllner and J.C.R. CruzO empilhamento CMP, com a correçăo NMO restrita a meios homogęneos com refletores pIanos e horizontais, quando é aplicado em meios com variaçőes laterais de velocidades apresenta dois problemas: Dispersăo dos pontos de reflexăo na presença de refletores inclinados e a possibilidade de sobreposiçăo em urn único ponto da seçăo de afastamento nulo de reflexőes provenientes de diferentes pontos com ângulos conflitantes em profundidade. Para corrigir estes problemas vários autores ( Deregowski e Rocca, 1981, Hale, 1984.) desenvolveram divers as técnicas sob o nome de correçăo DMO (dip moveout). No entanto, devido ao fato de que a correçăo DMO também foi desenvolvida com base na suposiçăo de urn meio com velocidade constante, tern sérias limitaçőes para manipular dados de meios com heterogeneidades laterais.
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SVD and Median Filters: Smoothing Seismic P-Wave Tomograms
Authors Jorge Leonardo Martins and Roseane Marchezi MisságiaSeismic ray-tracing traveltime tomography (SRTT) requires the application of some kind of smoothing procedure to the output tomograms, in order to proceed to a subsequent ray-tracing iteration. In this research, the outcomes related to the application of both SVD (Singular Value Decomposition) and median filters to smooth acoustic tomograms have been summarized. When allowing for their individual employment, median filtering has shown to present higher performance than SVD filtering in the sense that it was able to preserve structural geologic features. On the other hand, joint application of both filters has resulted to be the most efficient procedure to smooth output velocity tomograms, mainly when dealing with horizontal layering.
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Seismic Crosswell Tomography: A Gauss-Newton Type Algorithm Based on B-splines for Velocity Field Parametrization. Part I: Fundamentals
More LessA Gauss-Newton type method for seismic crosswell traveltime tomography based on B-splines products linear combinations for velocity field representation is presented. Knot points and order are estabilished through Dierckx approximation technique according to the initial guess model parameters. The Frechet derivatives are contour integrations along the rays and the regularization factor is estimated using the concepts of condition number and Backus-Gilbert spread factor for normalized resolution matrices. A numerical example demonstrates the robustness of the method.
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Traçamento de Raios a Partir de Mapas de Tempo Aplicado ŕ Sísmica Interpoços
Authors Ricardo Silva Nunes de Bragança and Wietze EckhardtA técnica de traçamento de raios possui urn papel importante no contexto dos métodos sísmicos e na tomografia sísmica em especial, visto que perrnite entre outras coisas, delinear 0 caminho percorrido pelo sinal sísmico da fonte até o receptor. O conhecimento desta informaçăo é fundamental para a realizaçăo de inversőes tomográficas, (Soares Filho, D. M., 1997) alvo de nosso estudo. Infelizmente técnicas usuais de tracamento de raios (Cerveny, V., 1987) năo săo facilmente adaptadas para utilizaçăo em meios complexos e/ou com contrastes de velocidades acentuados. Regiőes de cáusticas e áreas de sombra que surgem em tais modelos geralmente năo săo suportadas pela maioria dos algoritmos de traçamento de raios disponíveis. Com o uso de algoritmos de diferenças finitas é possível obter o campo de tempo correspondente ŕs primeiras quebras em todo o0 modelo (Vidale, J., 1988). Tal "mapa de tempo" contém toda a informaçăo necessária para a obtençăo dos caminhos dos raios desejados (Zhang, Lin., 1991).
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True-Amplitude MZO in Laterally Varying Media: Experiments on Synthetic Data
Authors Martin Tygel, Eduardo Filpo and Adelson OliveiraThe process of simulating a zero-offset (ZO) section from a given common-offset (CO) section so that primary reflections in the simulated section have the correct, (ZO) geometrical spreading, is called true-amplitude migration to zero offset (MZO). A recently proposed Kirchhoff-type, true-amplitude MZO algorithm for 2.5-dimensional models with laterally varying velocity is implemented on simple synthetic examples. The main steps of the algorithm are the construction oi"ihe stacking line and weight function for each point on the ZO section to be simulated. These include the computation of a traveltime table for construction of CO isochrones by an eikonal equation approach, as well as dynamical tracing of certain rays for each point on each isochrone. In particular, the in-plane CO isochrone curvatures are needed in the process. Comparison of the simulated ZO section with the one directly computed from the model, confirms the validity of the proposed algorithm.
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Transiçăo Crustal no Platô de Pernambuco: Urna Caracterizaçăo Geofísica a Partir de Dados do Projeto Leplac
Authors P.O. Gomes and B.S. GomesO Plato de Pernambuco é uma feiçăo fisiográfica do tipo platô marginal, que representa urn extenso patamar "embutido" no talude continental, entre as latitudes de Joăo Pessoa e Maceió, podendo ser considerado uma província geofísica da Bacia de Pernambuco-Paraíba (Fig. 1a). Dentro' da compartimentaçăo tectônica proposta para esta bacia por Mabesoone e Alheiros (1988), o Plato de Pernambuco foi informal mente destacado como uma unidade ŕ parte, situada imediatamente a leste da subbacia Cabo. Os autores chegam a inferir a presença de espessuras sedimentares de até 4.000 m sob o platô, mas năo esclarecem suas relaçőes com a referida subbacia, que, em seu esquema evolutivo, representaria o único compartimento rifteado da Bacia de Pernambuco-Paraíba.
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3-D Post-Stack Migration Velocity Analysis by Time-Slice Kirchhoff Integration
Authors Carlos Cunha and Jairo PanettaThis work presents a new algorithm for time migration, that uses the circular simetry of the tridimensional operator for zero offset data. One use of this algorithm is to prepare velocity fields for final migration. An implementation in workstations has proofed to be very efficient for tiny velocity adjustments, producing reliable and accurate sub-surface imagery. Examples of 3-D images in the North part of the field of Tubarao are presented, to show the utility of the method.
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Urn Método Eficiente para Migraçăo Pré-Empilhamento 3-D em Profundidade Reversa no Tempo pelo Método das Diferenças Finitas
Authors Paulo Eduardo Miranda Cunha and Irshad MuftiA migraçăo pré-ernpilhamento 3-D em profundidade é um dos mais importantes desafios para a indústria do petróleo. Consideráveis esforços foram consumidos na irnplementaçăo deste tipo de migraçăo sendo a maioria baseada na migraçăo de Kirchhoff. Os tempos de trânsito săo avaliados pela equaçăo da Eikonal ou princípio de Fermat que se fundamentam na teoria do raio, ou seja, ótica geométrica e săo uma aproximaçăo de alta frequęncia para os fenômenos de propagaçăo do campo. A funçăo de Green, obtida a partir da equaçăo da onda, e valida somente para meios homogenęos e as reflexőes secundárias năo săo contempladas pelo método. A soma dessas aproximaçőes pode gerar resultados incorretos.
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Migraçăo em Duas Etapas de Dados Ordenados em Afastamento Comum
Authors Reynam Pestana and Mário S. CostaO uso da equaçăo de migracao antes do empilhamento nas coordenadas de ponto medio e afastamento (Yilmaz & Claerbout, 1980) pode ser reescrita de forma a possibilitar a migraçăo de seçőes separadas de afastamento com urn. O trabalho de Popovici (1994) apresenta urn procedimento para migrar seçőes de afastamento comum, livre de artefatos de migraçăo, em meios com velocidade constante e também com variaçăo vertical.
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Migracao para Afastamento Zero por Deslocamento de Fase em Meios com Variacao de Velocidade
Authors Mário Sérgio Costa and Reynam da Cruz PestanaA migraçăo para afastamento zero (MZO) é a operaçăo que converte uma seçăo de afastamento comum em uma seçăo de afastamento zero. Para urn meio com velocidade constante a MZO é equivalente ŕ aplicaçăo do NMO ("normal move-out") seguido de DMO ("dip move-out"), mas para meios com variaçăo de velocidade a MZO é mais eficiente. Popovici (1994) apresentou uma formulaçăo integral para 0 operador de MZO derivada a partir da equaçăo DSR ("double square root") para a migraçăo antes do empilhamento.
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New Concepts in Seismic Reflection Imaging
More LessIt is widely accepted that a true-amplitude prestack migration in ultimately the most desirable reflection-imaging process. However, it makes sense to implement this process only if the macro model is sufficiently acceptable. Hence, other processes like migration-to-zerooffset, dip moveout, homeomorphic imaging and multi focusing become more and more necessary to achieve the ultimate goal. A unified theory has recently evolved for macro-model-based and non-macro-model-based reflection imaging methods. It includes Kirchhoff-type techniques, image waves and homeomorphic imaging. This paper will give a short introduction to these new fundamental reflection imaging concepts, with wich information can be obtained that goes beyond those obtained by prestack depth migration.
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A Proposal for Time-Lapse Seismic Imaging
Authors Menno Dillen, Jacob Fokkema and Kees WapenaarUp to this point the results of the 4-D experiment have been employed to produce a difference dataset from the survey at the start and the one after a certain time span. Then from this difference conclusions are drawn with respect to the medium change. In this paper a reciprocity theorem is employed to derive the volume integral representation, which shows how this difference is related to the restricted area where the changes occur. This formulation is suited for inversion. Using the boundary integral representation we arrive at an operational procedure for 4-D prestack imaging.
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Aplicaçăo da Migraçăo Pré-Empilhamento na Engenharia Submarina
Authors Helder de Andrade and Waldemar de Almeida Jr.Nos últimos anos, o incremento das atividades nas instalaçőes marítimas de equipamentos para a indústria de petróleo, tern requerido cada vez mais melhoria no imageamento do fundo e subfundo marinho, para o planejamento dos procedimentos de ancoragens de plataformas, posicionamento de dutos e também na fase inicial da perfuraçăo de poços submarinos: se jateamento ou perfuraçăo convencional. Neste sentido, a sísmica multicanal é considerada uma ferramenta fundamental para o conhecimento da seçăo sedimentar rasa, contribuindo nas avaliaçőes dos riscos geológicos ao longo do talude continental da Bacia de Campos.
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Migraçăo 3-D no Tempo Usando a Aproximaçăo Paraxial dos Raios
Authors N.P. Queiroz and W. Söllnero trabalho aqui apresentado visa a migraçăo 3-D no tempo, em amplitudes verdadeiras, de dados da seçăo afastamento nulo (zero-offset), usando a aproximaçăo de segunda ordem do tempo de trânsito de difraçăo, o espalhamento geométrico é removido através do processo de migraçăo e aplicaçăo de uma funçăo peso aos dados da seçăo afastamento nulo. O processo de migraçăo no tempo usa a funçăo difraçăo determinada através da medida de nove parâmetres da funçăo tempo de trânsito de reflexăo, e portanto sem o conhecimento do modelo de velocidades.
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Interval Velocity Determination by Time Migration Decomposition: A Synthetic Data Application
Authors Luis Montes, Walter Söllner and Peter HubralUsing the paraxial ray theory in second-order approximation of the traveltimes, we present a method to determine the interval velocities of a seismic system. The seismic system consists of a stack of isotropic and homogeneous layers separated by smooth, second-order interfaces. Measuring the traveltimes of some specially selected reflected rays, recorded on the upper border of the seismic system, the zero-offset difraction time function is determined. The interval velocities are calculated by downward continuation of the zero-offset diffraction time function applying an iterative process layer by layer. This process is controlled by using a principle of focusing.
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3-D depth migration: Various methods and how they perform on real data
By Irshad Mufti3-D depth migration is one of the most active areas of research and development and it has been approached from different angles. An accurate algorithm which work" in the space-frequency domain was introduced by Blacquiere et al. (1989). Unfortunately, it is computationally very expensive and not suitable for solving real-life 3-D migration problems. This led to the development of an alternative scheme (Hale, 1990) which sacrifices some accuracy but is much more efficient. It is commonly referred to as the Hale-McClellan method. An alternative procedure known as reverse-time migration works in the space-time domain. It ;05 based on the full wave equation and yields by far the most accurate results, but it requires extremely large computer resources. However, a series of new developments (Mufti et al., 1996) have made this algorithm a very practical tool even for migrating large exploration-scale 3-D real data. We shall provide a comparative evaluation of the results obtained by this method with the corresponding resultsfrom Hale's algorithm. This will include a detailed investigation of the impulse response as well as migration of both synthetic and real poststack 3-D seismic data. We will not present any results based on prestack migration, but we will discuss a number of serious problems with the current technology developed for prestack migration as well as some food for thought.
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Deep Seismic Reflection Profiling of the European Mosaic of Terranes: Accreation and Collapse
By R. MeissnerFor more than 100 years it has been accepted that the tectonic history of Western and Central Europe started with the Variscan orogeny in the Paleozoic. In Northern and Eastern Europe, Caledonian and older orogenies and even cratons are found, while in the South, younger tectonic features predominate. For a long time, the mechanism of the growing European mosaic, its tectonic framework, the architecture of crust and mantle, and the time sequence of collisions, accretion and collapse, remained a mystery.
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2D Imaging and Depth Tomography by Plane Wave Decomposition
Authors Dan Kosloff, Zvi Koren, Ronit Strahilevitz and Uri I. ZackhemDepth imaging and depth velocity analysis are performed in the variable angle domain. First the input is sorted into common receiver gathers. The gathers are converted into p gathers by a slant stack transformation. Migration is carried out by forming p sections and downward continuing each section separately. Velocity updating is done by grid tomography which detects nonflatness in the migrated p gathers and updates the velocity section accordingly.
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Multiple Supression in Common Offset and Stacked Sections Via Linear Radon Transform Filtering
More LessWe discuss the application of linear Radon transform (LRT) filtering for the supression of complex geometry related multiples in common offset and stacked sections. Common offset sections have to be considered for amplitude versus offset (AVO) analysis. Complex geometries give rise to events of non-hyperbolical moveouts that cannot be properly modeled by parabolic Radon transforms (PRT) and thus are not sufficiently attenuated via PRT filtering. Moreover, wave-equation based methods are still unable to deal with peg-leg multiples. On the other hand, in structurally complex areas, multiples and primaries are in general characterized by . different dips in the stack or in common offset sections allowing discrimination via LRT. For stacked sections, when more radical procedures such as internal muting are mandatory, the LRT filtering on a limited offset range, may be worthwhile.
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Deconvoluçăo de Múltiplas com Filtros Wiener-Levinson Multicanais
More LessAs múltiplas de longo período associadas ŕ reflexăo no fundo do mar chegam como eventos distintos e sua remoçăo ou atenuaçăo representam um problema importante no processamento de dados sismicos. A técnica de deconvoluçăo preditiva para s upressăo de reflexőes nniltiplas e um método estatistico que baseia-se no carater periódico destes eventos. Entretanto, a periodicidade só é preservada no caso de incidęncia vertical e seçăo de afastamento nulo, ou seja, as múltiplas năo săo periódicas para afastamentos diferentes de zero. Neste trabalho foi analisado o efeito da aplicaçăo de filtros de prediçăo multicanais no dominío t-x. Na filtragem multicanal, as características do filtro levam em conta a coeręncia lateral dos eventos refletidos presentes nos canais adjacentes. Esta propriedade dos filtros multicanais pode ser explorada de forma a permitir uma atenuaçăo mais efetiva das reflexőes múltiplas. A teoria utilizada para computaçăo dos operadores discretos multicanais conceitualmente é a mesma teoria de Wiener-Levinson empregada para obtençăo dos filtros preditivos monocanais(Barros e Porsani, 1996). Matematicamente representa a extensăo da álgebra escalar para álgebra matricial, conforme apresentamos a seguir.
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Surface-Related Multiple Removal - Applications to the Gulf of Mexico
Removal of free surface multiples from seismic reflection data is an essential pre-processing step before pre-stack migration. Any effective multiple removal method should require no a priori information about the subsurface and should leave all relevant primary events in the data unaffected.In this abstract, a surface-related multiple removal method is applied to two distinct configurations that are representative for the Gulf of Mexico: a shallow marine (subsalt) field data set and a deepwater data set. Good results demonstrate he effectiveness of surface-related multiple removal methods:only multiple energy is removed from the data whereas relatively weak primary reflections become better interpretable.
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Análise de Velocidades e Empilhamento eMP para Traços Interpolados
Authors Milton José Porsani and Reinaldo Nunes de PaivaA importância da interpolaçăo de traços sísmicos tem sido descrita por muitos autores na última década (Jakubowicz, 1994; Mannin and Spitz, 1995; Spitz, 1991, 1996; Gulunay and Chambers, 1996, Ferreira, Porsani and Ulrych, 1996, Porsani, 1997). Os problemas de aliasing espacial podem afetar a resoluçăo lateral das técnicas de filtragens e migraçăo impondo severas restriçőes no processamento sísmico. Um métoda de interpolaçăo de traços sísmicos que é eficaz mesmo na presença de eventos em aliasing foi proposto por Spitz (1991).
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AVO Processing Calibration
More LessOver the years AVO technology has been deployed in both efficient and inefficient ways in different sedimentary environments, normally functioning as a lithology indicator and sometimes as a direct hydrocarbon indicator. Several factors may be regarded as resposible for the unsuccessful applications. However, the most basic one, the properness of the processing sequence to the problem at hand, is sometimes underestimated. The ambiguity of the AVO technique and the presence of coherent noise in the data are other major factors. In this study, I developed a method to check the consistency of the AVO measurements produced by different processing sequences on a noise contaminated data. An extense reprocessing work has been employed in a marine seismic dataset, where an amplitude anomaly is related to the presence of high porosity sands saturated by light hydrocarbons. The sandstone reservoir is encased in marine shales. The anomaly is localized and is characterized by a decrease in density and Poison's ratio in the reservoir zone. The AVO signature is modeled and the corresponding normalized reflection coefficient curve is used to check the amplitude responses produced by different processing sequences. As a result of such calibration procedure the best processing sequence can be selected and it can be used for all seismic lines in the same area.
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The effects of vector attenuation on AVO of off-shore reflections
More LessIn off-shore seismic exploration, the waves transmitted at the ocean bottom have a particular characteristic. Assuming that water is lossless, their attenuation vectors are perpendicular to the ocean bottom interface. This fact affects the AVO of reflection events generated at the lower layers.
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AVO Crossplotting: Achieving New and Unbiased Hydrocarbon Indicators
More LessAVO crossplotting has been widely used in the past few years as a way of deriving improved hydrocarbon indicators from seismic data. By crossplotting the standard AVO attributes of intercept and gradient, it is possible to obtain an optimum combination of the two (the fluid factor), which is insensitive to the AVO effect of brine-saturated shales and sands. Any AVO anomaly can then be attributed to hydrocarbons or lithologic factors.However, the background shale trend observed in such crossplots is primarily due to a statistical artifact. In the presence of noise, the standard least-squares regression that is used to estimate intercept and gradient has a tendency to correlate these two attributes. This statistical trend has the same pattern as expected from background shales. Fortunately, since there is some signal in seismic data, the background trend does contain some lithologic information. This information is very limited though, and the fluid factor obtained from this mostly statistical trend is in fact very close to a far offset stack. Although far offset amplitudes are good hydrocarbon indicators, crossplotting is a very complicated way to compute a far offset stack. On the other hand, noise does not introduce a statistical correlation between stack and gradient. Since stack and gradient exhibit the same kind of trend for background shales as intercept and gradient, it is very appealing to crossplot them. Any trend observed in this crossplot would have to be related to lithology and not to a statistical artifact. Unfortunately, when doing this we find that the background trend is generally buried under background noise. However, since this new crossplot is statistically unbiased, it is possible to postulate a background trend, leading to a new definition for the fluid factor. This gives rise to unbiased hydrocarbon indicators that are not limited to far offset stacks.
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True Amplitude MZO and AVO: Application to real data
More LessWe discuss the application of true-amplitude migration to zero offset (MZO) to amplitude versus offset (AVO) studies on a real marine seismic data. The true-amplitude MZO is achieved by means of a cascaded application of standard normal moveout correction (NMO) plus a constant-velocity, true-amplitude dip moveout (DMO). This process is expected to be precise as long as we have only mild lateral velocity variations. The impact of the compensation of geometrical spreading losses from large offsets to short ones on AVO analysis is discussed. The reliable results obtained for dipping events makes this process interesting for AVO analysis in areas of relatively small structural complexity.
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Investigaçőes do Uso de Expressőes Linearizadas do Coeficiente de Reflexăo para Extraçăo de Parâmetres Elásticos
More LessA variaçăo do coeficiente de reflexăo com o ângulo de incidęncia contém informaçőes a respeito das propriedades elésticas dos meios. As fórmulas exatas para os coeficientes de reflexăo săo dadas pelas equaçőes de Zoeppritz (1919). Diversas aproximaçőes para estas expressőes podem ser encontradas na literatura, as quais tern por objetivo facilitar a compreensăo da influęncia das propriedades elásticas. Contudo, estas aproximaçőes sofrem limitaçőes em seu intervalo de validade, tais como: pequenas variaçőes nos parâmetres elásticos através da interface e/ou ângulos de incidęncia próximos da vertical. A medida que nos afastamos destas condiçőes, as aproximaçőes afastam-se da forma exata.
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Frontiers of Deep Seismic Reflection Profiling
By L.D. BrownOver the past two decades multichannel reflection profiling has grown to become the lead methodology in many national and international programs to explore the deep structure of the continental lithosphere. Deep reflection surveys by groups such as COCORP (US), LITHOPROBE (Canada), DEKORP (Germany), BIRPS (Great Britain) and ECORS (France) have made a number of major discoveries about the complexity of the lower crust and upper mantle, including delineation of crustal-scale faults, wide-spread lamination in the lower crust, magma "bright spots" in the mid-crust, systematic variations in Moho character and distinct structures in the mantle lithosphere.
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Estudo de uma Metodologia para Calibraçăo de AVO a Diferentes Litologias e Fluidos
Authors Alcides Aggio, Albano Bastos and Ariovaldo da CostaApresentamos neste artigo o resultado da análise de AVO ( Amplitude versus Offset) dos poços A e B, com produçăo em arenito, com gás e carbonato com óleo, respectivamente. Esta análise procurou basear-se nas medidas obtidas no Laboratório de Física de Rochas da PETROBRAS/CENPES, bern como nos dados de perfis de poços. Foi encontrada e implementada para a modelagem do poço B uma melhor estimativa de vs, quando comparada ŕ literatura (equaçăo de Krief, 1990), baseada em dados de carbonato fornecidos pelo laboratório. O AVO também foi calibrado através do cross-plot dos atributos PeG, Verm & Hilterman (1994), Castanha (1985), mostrando uma boa potencialidade de análise e definiçăo de topo e base do reservatório, bern como a possibilidade de rastreamento litológico nos dados sísmicos, possibilitando a estimativa da razăo vp/vs em regiőes onde năo existem poços.
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Estudo Integrado de Modelagem, Inversăo, AVO e Física de Rochas: Um Pitfall Clássico
More LessUrn procedimento combinando informaçőes de processamento sísmico, SEYEL (seçăo de velocidade), modelagem e inversao AYO (Amplitude Variation with Offset) foi aplicado em dados sísmicos 2D levantados em área sem poços de aguas profundas, para apoio no estudo preditivo de urn corpo turbidítico, identificado nas linhas sísmicas como uma anomalia de amplitude. O trabalho subdividiu-se em duas fases, antes e após a perfuraçăo. Na prime ira fase, foram descartados, por inconsistęncia com dados reais, alguns modelos litológicos possíveis de explicar a anomalia, através de modelagem sísmica. Ainda foram estimados parâmetres petrofísicos que favoreciam a ocorręncia de hidrocarbonetos. Na segunda fase, em bora prejudicada pela baixíssima qualidade do perfil de ondas S, pode-se constatar que a anomalia observada no SEYEL sendo mais devida a urn baixo de densidade do que a velocidade propriamente, como gostariamos. A referida anomalia de amplitude é um caso bern conhecido de insucesso do AYO, i.e, urn pacote espesso de areia saturada com água, com baixo conteúdo de argila e com alta porosidade, imerso em folhelhos. O insucesso, em termos de resposta para hicrocarbonetos, é parcial, pois o gás pode mostrar resposta AYO a nivel quantitativo (crossplots) maior que a água. Podemos estar ganhando urn referencial futuro para calibracao. Finalmente a irnportânicia deste trabalho é ser um convite para a integraçăo de dad os sísmicos petrofísicos, como metodologia a ser aplicada em bacias já exploradas e, neste caso, usar também a geoestatfstica para tratar os dados em linguagem de risco.
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Cancelamento de Ruído Harmônico no Traço Sísmico
More LessDuas técnicas de cancelamento de ruído harmônico no trace sísmico săo apresentadas. Cada uma delas se destina a operar sobre interferęncias harmônicas de diferentes natureza: estacionária e nao-estacionária, onde a amplitude e a fase de cada harmônica podem variar ao longo do traço. O cancelamento promovido por qualquer dos dois métodos se apresenta mais eficiente que a filtragem notch convencional, pois o ruído é estimado (amplitude e fase de cada harmônica) e subtraído do traço. Um procedimento automático para o cancelamento de ruído harmônico integrando estes dois métodos é, entăo, sugerido como uma eta+pa do préprocessamento+H62 de dados sísmicos. Resultados para dados sintéticos săo apresentados a fim de demonstrar a eficięncia do pro cedimento proposto.
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Deconvoluçăo de Dados Sísmicos com Filtros de Fase Mista
Authors Reinaldo Nunes de Paiva and Milton José PorsaniO objetivo principal da deconvoluçăo da assinatura da fonte é o aumento da resoluçăo temporal dos dados sísmicos. Uma limitaçăo da deconvoluçăo Wiener-Levinson é o fato de que o filtro, computado a partir dos coeficientes estimados da funçăo de autocorrelaçăo do pulso básico, é sempre de fase mínima (Robinson, 1980; Berkhout, 1977).
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Deconvoluçăo de Ondas Quadradas através do Filtro de Wiener
Authors Roberto J.V. Sacasa, Lourenildo W.B. Leite and André J.N. AndradeA descriçăo e aplicaçăo do filtro de Wiener representa uma técnica de grande utili dade para o tratamento de dados sísmicos no dominio do tempo. Princípios da teoria das comunicaçőes permite a formulaçăo matematica e a obtençăo da soluçăo destes filtros ótimos. O filtro de Wiener é um processo regido por uma distribuiçăo tempo invariante estacionário.
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