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6th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 1999 - 19 Aug 1999
- Location: Rio de Janeiro, Brazil
- Published: 15 August 1999
21 - 40 of 399 results
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Atividade Solar Nos Anéis De Crescimento De Árvores Em Canela
Authors Nivaor Rodolfo Rigozo and Daniel Jean Roger NordemannTree ring studies are usually used to determine or verify climatic factors which prevail at a given place or region
and may cause tree ring width variations. Few studies are dedicated to the geophysical phenomena which may
underlie these tree ring width variations. Furthermore, it is known that some trrestrial phenomena suffer
influence from short and long time scale solar variability. So, a study on solar activity records in tree rings at
short time scales was developed. In order to determine a tree growth ring width mean chronology, an optical
and computational method was set up and applied to tree samples (araucaria and pine trees) from Canela-RS,
Brasil. Spectral analysis by maximum entropy method and iterative regression was applied to the search of
periodicities related to solar activity phenomena. The results obtained have shown periodicities related to 11 yr
and 22 yr solar cycle influence on tree growth rings.
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Diurnal Variation Of Summertime Cloud-To-Ground Lightinig Activityactivityin The Southeastern Brazil
This paper reports the results of an analysis of 300,000 cloud-to-ground flashes recorded in the southeastern
Brazil in the summer season of 1993 in terms of the local time dependence of their characteristics. Whereas the
lightning activity of negative and positive cloud-to-ground flashes exhibit a diurnal cycle with a well-defined
time of maximum frequency in the afternoon, the flash multiplicity and peak current intensity do not exhibit such
a local time variation. The local time dependence and geographic distribution of the lightning activity are in
agreement with what is expected from isolated thunderstorms. In turn, the peak current intensity and the flash
multiplicity did not show any dependence on local time. The results are compared with similar data obtained in
the western and eastern U.S. in the period 1995-97.
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Uma Análise Do Modelo De Madden&Marshall Para Descrever A Polarização Elétrica Observada Em Rochas Contendo Argila Disseminada
Authors Alexandre Nunes Barreto and Carlos Alberto DiasThe impedance function associated to the Madden & Marshall model proposed to describe membrane polarization,
was rewriten using five new parameters with clear petrophysicalmeaning. The behavior of this function was
analyzed together with its new parameters when varying the electrochemical parameters of the originalmodel and
some limitations were shown.
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Long Term Variation Of The Lightning Flash Characteristics In The Southeastern Brazil:1988-1995
The long-term variation of the cloud-to-ground lightning flash density in terms of its geographical, monthly and
diurnal distribution is presented, based on the longest lightning data set ever obtained in the tropics. The
results are based on 12.8 millions cloud-to-ground lightning flashes recorded in the southeastern Brazil from
1988 to 1995 with a lightning network consisting of four LPATS sensors located in Minas Gerais. They should be
considered as reference for future studies in this region.
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Estudo Geofísico Preliminar Com Os Métodos Tem/Fem Na Planície Costeira Norte Fluminense
More LessIn 1998, ON/CNPq and LENEP/UENF undertook a geophysical pilot study in the Northern Coastal Plain of Rio de Janeiro State, near Rio das Ostras town. The region is characterised by both the scarcity of drinking water for human consumption and the existence of saline intrusions; this last caused mainly by the presence of a complex quaternary geology and the excessive exploitation of the aquifers. The research was performed by employing the time (TEM) and frequency (FEM) domains electromagnetic methods to evaluate the effectiveness of both methods in these geological conditions in order to be able to formulate a more comprehensive hidrogeological research in the region in near future. The FEM profiles and the uni-dimensional interpretation of the TEM were able to depict the different geological formations, to locate the main aquifers and to reveal the salty water- fresh water contact. Our results evince a promising future for using eletromagnetic geophysical methods in the region as well as it confirmed that a regional survey is essential in the indication of most suitable places to locate productive fresh-water wells.
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Mesospheric Reduction Of The Chemical Heating Rates By Nightglow Emissions At 23Os And 4Os
Authors P.R. Fagundes, D. Gobbi, H. Takahashi and Y. SahaiSimultaneous observations of several nightglow emissions have been carried out at Fortaleza (40S, 380W) and
Cachoeira Paulista (23oS, 45o W), Brazil, since 1987. Using the OH Meinel (9,4) and O2 atmospheric b(0,1) bands
observed at these two stations during the period from 1987 to 1994, we present and discuss the night-time
reduction in chemical heating rates by these mesospheric airglow emissions. The total emission rates of the OH
Meinel bands and O2 atmospheric b(0,0) and O2 infrared atmospheric (1Δg) bands were calculated using the
reported data for the relative band intensities I(ν/,ν//)/I(9,4), I(O2b(0,0))/I(O2 b(0,1)) and I(O2 (1Δg))/ I(O2b(0,1)). This
study showed that the reduction in chemical heating rates (RCH) by the OH Meinel bands, at both the locations,
has seasonal variations with monthly mean values varying from 0.4 K/day* to 0.9 K/day* (where day* means
averaged over the night). However, the RCH rates due to the radiation in the Meinel bands at Cachoeira Paulista
presented a weak ter-annual variations, whereas at Fortaleza semi-annual variations were observed. Also, the
RCH rates by O2* showed semi-annual variations at both locations, presenting values from 0.05 K/day* to 0.25
K/day*.
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Comparison Between The Mesopause Temperature+D57 Profiles Measured With A Sodium Temperature Lidar And The Oh (6,2) And 02A (0,1) Rotational Temperatures 23Os
Authors P.P. Batista, B.R. Clemesha, D. Gobbi, M.P.P.M. Jorge, D.M. Simonich, H. Takahashi and I. VaselovskiiThe mesopause temperature profile has been measured at São José dos Campos (23.2o S, 45.9o W) for a total of 15
nights from July to October 1998. The technique used is the measurement of the Doppler temperature of the sodium
atoms present in the atmospheric sodium layer with a Lidar. During 7 of the 15 days of Lidar temperature data,
simultaneous measurements of the rotational temperature of the OH(6,2) band at 843.0 nm and the O2 (0,1)
Atmospheric band at 864.5 nm were obtained at a nearby station, Cachoeira Paulista (22.7o S , 45.2o W), with a tilting
filter photometer. There is a fair agreement between the OH temperature and the Gaussian weighted temperature
calculated using the Lidar temperatures centered on 84.7 km and with a half-width of 4.5 km, consistent with rocket
measurements for the OH emission profile, for most of the days. But no consistent combination of height and half-width
can reproduce the absolute value and variation of the O2 (0,1) temperature for most of the days, suggesting that the
transition probabilities used for determining the latter may need to be revised.
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Study Of The Space Variations Of The Energetic He Ions At Low Altitudes In Brazilian And South Atlantic Magnetic Anomaly Region
Authors G. Pugacheva, A. Gusev, T. Kohno, I. Martin and W. SpjeldvikThe L distribution of 1 - 9 MeV/nuc helium ion flux observed with the low altitude Japanese OHZORA satellite
has a multipeak structure, different from one flux maximum of proton radiation belt and two flux maxima of
electron radiation belt. The peak fluxes of 1 - 3 MeV/nuc He ions are located at L=1.35-1.6, L ~ 1.8 - 2.3 (only in
1984), and L = 2.8 - 3.2. Recently, two low altitude satellite SAMPEX (1992 – up to now) and MIDORI (1996-97)
missions reported new observations of energetic He flux peaked at L ~ 2 and show the existence of stable (at
least with lifetime of several years) flux there at higher energies above 10 MeV/nuc in contrast to the lower
energies. To analyze the nature of the multipeak structure and the origin of the L=2 helium flux we studied
magnetic local time dependence of the peak helium fluxes observed by OHZORA. The 1 - 3 MeV/nuc helium ion
flux exhibits strong local-time variation at L ~ 3 having several times greater flux at the evening side at MLT =
17-21 hours than at the other MLT sides. The one of possible explanation of the flux variation with MLT is that ~
1 MeV/nuc helium ions do not drift around the Earth and are located at L about 3 due to the ion interactions
with the Earth's electric morning-evening field.
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A 2D Simulation Of The Proton Radiaton Belt With Pellpack Code
Authors A. Gusev, I. Martin, G. Pugacheva, A. Christy and W. SpjeldvikThe numerical solution of diffusion equation for geomagnetically trapped protons taking into account
deceleration of protons by Coulomb interactions with free and bounded electrons, the charge exchange
process, the cosmic ray albedo neutron decay (CRAND) source and electric and magnetic radial diffusion was
obtained using the PELLPACK code based on the finite element method. The advantage of the method in
comparison with the traditional finite differences method is a several order greater speed of computation at the
same precision. When boundary conditions at L=7 are given with the distribution function extracted from
proton spectrum obtained on board of ATS 6 satellite, the PELLPACK code produces 2D unidirectional proton
flux at the top of geomagnetic lines from L=1 up to L=7 that satisfactory agrees with the AP8 model proton flux
for all proton energies more than ~ 300 - 500 keV. For less proton energies AP8 model predicts the trapped
proton fluxes on several orders of magnitude greater than PELLPACK code at L < 4 that possibly could be
explained by uncertainty of very low energy proton flux data at L=7. The detailed fitness of observational model
proton fluxes by numerical theoretical solution of transport equation is still not attained.
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Fast 3-D Modeling And Inversion Of Surface Em Data
More LessThis work presents an algorithm for three-dimensional modeling and inversion of electromagnetic field data. In recent
years, there has been an increase in use of electromagnetic techniques for mineral, oil and geothermal exploration.
Since most of the targets are of three-dimensional nature, it is important to consider the full dimensionality of the problem
in the interpretation. The forward code is based on a finite difference approximation while the sensitivities needed in the
inversion are obtained from the forward problem based on the reciprocity principle. A parametric functional is constructed
using the data misfit and a model misfit to an a priori earth model, weighted by a regularization parameter. This functional
is then minimized using the conjugate gradient method. The most time consuming parts of an inversion algorithm are the
forward problem and calculation of the sensitivities. Also, in the 3-D problem, storage becomes another important issue.
First results will be presented, along with methods that will help improve both speed and storage on the way to make the
3-D problem tractable.
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Sound Velocity Of Drilling Mud Saturated With Reservoir Gas
Authors José M. Carcione and Flávio PolettoDrillings muds are used to balance subsurface pressures, lubricate the drillstring, clean the
bottom of the hole, remove cuttings and aid formation evaluation. During drilling, the mud
is pumped down the drill pipe and returns via the annulus between the drill string and the
formations. If the pore-fluid formation pressure exceeds that of the mud column, reservoir gas
can enter the wellbore? creating a kick and causing severe damage. Knowledge of the in-situ
sound velocity of drilhng mud can be useful for evaluating the presence and amount of gas
invasion in the drilling fluid. Technologies such as mud pulse acoustic telemetry require this
information. In the following sections, we propose a model for calculating the in-situ density
and sound velocity of water-based and oil-based drilling muds containing formation gas.
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A Study About The Occurrence Of Days With High Activity Of Cloud-To-Ground Lightning Flashes In The Southeastern Brazil In The Years 1992 To 1994
Authors Heloisa H. Faria, Osmar Pinto Junior, André M. Carvalho and Armando C. FilhoThe occurrence of days with high activity of cloud-to-ground lightning flashes in the southeastern Brazil in the
years 1992 to 1994 was investigated. The high activity days were arbitrarily defined as those with more than
20,000 cloud-to-ground flashes. The meteorological conditions and flash characteristics during these days were
determined. The lightning data were obtained through a lightning location system (LPATS), and the flash
characteristic studied were the polarity, the peak current intensity and the diurnal distribution.
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Signal To Noise Ratio Enhancement By Adaptive Filtering
Authors Enrique D. Mercerat and Alberto H. CominguezAn adaptive filtering techniquewas implemented in order to remove random noise from seismic data. The operator
was calculated in the frequency-offset domain (FX), and it could enhance the lateral coherence of seismic events.
For each frequency an optimum Wiener filter was designed following the classical approach using the complete
seismic section. After that, an adaptive algorithm was implemented to actualize the filter coefficients in order to
reduce the output error. This automatic actualization avoided us the use of predetermined design windows. The
adaptive filter was based on a generalized expression of the least-mean square (LMS) filter dealing with complex
frequency input signal. The performance was evaluated on synthetic seismic data contaminated with additive
gaussian noise.
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Seismic Imaging Of The Crust In The Aconquija And Adjacent Regions; Catamarca, Tucuman And Santiago Del Estero, Argentina
More LessDeep Seismic Study, in eastern and western foothills of Sierra de Aconquija, northwestern Sierras Pampeanas, Argentina, shows the deep structure of the range and the deep geometry of the Andean foreland basin. "Self-truncating" extended correlation algorithm was applied to compute cross-correlation between the sweep and the records of Vibroseis lines. Special procedures, such as finite difference migration, FX deconvolution, FMED processing and complex demodulation, were applied in order to improve the interpretation. On the eastern side of Sierra de Aconquija, the structure is characterized by reverse faulting with eastward vergence, with the Guasayán and El Rosario faults exhibiting the most deformation. To the south, the Guasayán fault produces the uplift of the Guasayán basement range over tertiary deposits, and can be identified in the seismic reflection record down to 40 km depth. On the western side of Sierra de Aconquija, the deep structure of Campo del Arenal is characterized by westward vergent structures controlled by the anisotropy of the Sierra de Aconquija basement. Further to the west, the deformation style changes to eastward vergence. Conspicuous sub-horizontal acoustic-reflectors at about 18, 30, 40 and 50 km depth, are interpreted as present or past brittle-ductile transitions.
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Log-Derived Rock Strength Evaluation
Authors José Agnelo Soares and Lucia Duarte DillonSeveral oil industry operations, like borehole stability, pore collapse analysis and hydraulic fracturing, demand
rock mechanical knowledge that sometimes is unavailable or is only poorly known. Statistical relationships
defined through dynamic and static rock properties, simultaneously determined in lab tests, yield a novel
approach to continuously evaluate rock strength over whole depth well intervals.
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Métodos Geoelétricos Aplicados No Estudo Do Lençol Freático Em Área De Disposição De Resíduos Industriais
Ensaios geofísicos pelo método da eletrorresistividade, utilizando as técnicas de campo da sondagem elétrica vertical –
SEV (arranjo Schlumberger) e caminhamento elétrico - CE (arranjo dipolo-dipolo), foram executados em áreas de
disposição de resíduos industriais no município de Iracemápolis-SP. Os estudos geofísicos visaram obter um
diagnóstico prévio dos materiais em subsuperfície frente à possível contaminação por resíduos industriais. Foram
executadas três SEV´s, as quais caracterizaram a litologia dos materiais em subsuperfície em solo superficial seco
(resistividade variando de 13 a 14.353 ohm.m), solo de alteração de diabásio (resistividade variando de 25 a 83 ohm.m)
e diabásio (resistividade de 617 ohm.m). A profundidade do nível d´água obtido apresentou uma variação de 9,3 (SEV-
01) a 13,5 (SEV-03) metros. Para o CE, foram levantadas cinco linhas, a partir das quais, pode-se delimitar a área de
disposição de resíduos, avaliar as condições da pluma de contaminação e determinar as direções preferenciais do fluxo
d´água subterrâneo. Mapas referentes a três níveis de investigação (profundidades teóricas de 10, 20 e 30 metros)
evidenciam que a pluma tende a diminuir sua faixa de contaminação em função da profundidade, restringindo-se a
locais isolados. Duas direções preferenciais do fluxo subterrâneo d´água foram identificadas, acompanhando, de um
modo geral, a topografia do local estudado.
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Estudos Morfológicos Das Depleções Do Plasma Ionosférico Por Imagens Digitalizadas
Authors Daniela Cristina Santana, J.H.A. Sobral and H. TakahashiA ionosfera, ambiente natural de propagação dos sinais de comunicação, foi descoberta inicialmente devido a
observação de variações periódicas nas medições do campo geomagnético que combinadas com a alta condutividade
elétrica da ionosfera, podem alterar a trajetória desses sinais de comunicação. É uma região rica em fenômenos
naturais de importância direta para o homem e o para meio ambiente. É justamente um desses fenômenos, denominado
de depleções do plasma ionosférico, exclusivo das regiões equatoriais, que queremos enfatizar. Para o seu estudo, há
várias técnicas desenvolvidas, das quais podemos citar a luminescência atmosférica, ou o airglow. O acompanhamento
constante do airglow noturno permite realizar um estudo morfológico e dinâmico da ionosfera noturna. As imagens
digitalizadas do airglow noturno são obtidas pelo imageador all-sky 180º que é um equipamento recém desenvolvido
pelo grupo de pesquisa Luminescência Atmosférica - LUME, da área de Ciências Espaciais e Atmosféricas - CEA, do
Instituto Nacional de Pesquisas Espaciais – INPE e encontra-se em operação desde outubro de 1997 no laboratório do
LUME em Cachoeira Paulista(22.7ºS, 45.0ºW) – SP. O airglow noturno existe em vários comprimentos de onda sendo
que para o registro das depleções do plasma ionosférico é necessário a emissão do OI 6300 Å (λ = 630 nm), uma luz
vermelha de muita baixa intensidade, que está presente na termosfera. As depleções do plasma ionosférico variam a
intensidade da emissão do OI 630 nm de acordo com o cotidiano e a estação do ano. Os nossos estudos focalizam as
depleções do plasma ionosférico que ocorrem sobre a região de Cachoeira Paulista(22.7ºS, 45.0ºW) – SP,
principalmente as fortíssimas ocorrências nas noites de 30/01/1998 e 26/08/1998. As imagens digitalizadas das
depleções do plasma ionosférico via OI 630 nm obtidas pelo imageador all-sky 180º são analisadas e processadas por
aplicativos computacionais em desenvolvimento na linguagem computacional Interactive Data Language – IDL,
seguindo os padrões básicos para o desenvolvimento de um aplicativo computacional. Esses aplicativos computacionais
introduzem uma nova técnica fotométrica para o estudo das depleções do plasma ionosférico.
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About The Seasonal Distribution Of Geomagnetic Activity
The annual distribution of geomagnetic activity is studied through the geomagnetic indices aa, Dst and AE,
according to different levels of intensity for each of the indices. For thresholds that correspond to moderate to
fairly intense storms, the distribution follows the well-known pattern of a seasonal variation, with maxima
around the equinoxes and minima near the solstices. However, the observed pattern deviates from this behavior
as the distribution refers to levels associated to the occurrence of more intense storms. For the latter type of
storms, the geomagnetic index aa shows the occurrence of a peak in July (but not in January, as a seasonal
symmetry would suggest). The contribution of very intense storms to the July peak seems to be evenly
distributed along the 11 solar cycles covered by this index. Furthermore, although the records for the indices
Dst and AE are restricted to shorter time intervals as compared to aa, they also show the possible existence of
this peak for July.
The present analysis gives also some indications for the existence of a peak in November in the distribution of
very intense storms. This peak shows up particularly for the indices Dst and AE, whose records go back only to
1957. Therefore, its real existence is more questionable than that of the peak for July.
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Phase Relationship Between F-Region Electron Density And Electric Field Fluctuations-Some New Observations
Authors P. Muralikrishna, M.G.S. Aquino, S.M. Soares and M.C. De FariaIn-situ measurements of the height variation of the ionospheric electric field and electron density variations were made
with a rocket-borne electric field double probe and two different types of electron density probes. A Brazilian made
SONDA III rocket carrying these experiments in addition to other airglow experiments was launched on 18-th December,
1995 at 2117 hrs (LT) from the equatorial rocket launching station, Alcantara. The rocket reached an apogee altitude of
557km and covered a horizontal range of 589km. Several ground equipments were operated during the launch campaign
with the specific objective of knowing the ionospheric conditions at the time of launch and thereby to launch the rocket
into an F-region prone to the presence of large plasma bubbles. The rocket in fact passed through several medium scale
plasma bubbles and the electric field double probe and the electron density probes detected the presence of a wide
spectrum of electric field and electron density irregularities. In the base of the F-region the electric field double probe
measurements clearly indicated the presence of large amplitude fluctuations, closely associated with large amplitude
electron density irregularities But in the height region close to the rocket apogee though the electron density profile
showed the presence of large scale spatial structures, the electric field measurements did not show fluctuations of similar
amplitude. Being a nighttime launch one would expect the electron density irregularities, if generated by the well-known
cross-field instability mechanism, in height regions where the electron density gradient is downward, i.e in the same
direction as the ambient Hall electric field. An FFT algorithm was then used to estimate the spectral distribution of the
electric field and electron density fluctuations, thus estimating the height variation of the spectral variation. Some new
results on the phase relationship between the electric field and electron density fluctuations are presented here.
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Ionospheric Experiments On Board The Brazilian Scientific Applications Satellites Saci-1 And Saci-2
Authors P. Muralikrishna, M.A. Abdu, S. Domingos, J.A.C.F. Neri and L.P. VieiraA set of three plasma diagnostic experiments, known as PLASMEX, are developed for launch on board the
Brazilian Scientific Applications Satellites SACI-1 and SACI-2. The main objective of the experiments is to
investigate the phenomenon of ionospheric plasma bubbles, known to exist in the ionospheric region over a
wide range of latitudes. It is intended to make measurements of the density, temperature and spectral
distribution of the irregularities in the ionospheric plasma using (1) a High Frequency Capacitance Probe for
measuring the plasma density, (2) a fixed-bias Langmuir Probe for measuring the electron density profile and
the spectral distribution of plasma irregularities, and (3) an Electron Temperature Probe for measuring the
kinetic temperature of the ionospheric electrons. While the satellite SACI-1, is to be launched this year from
China on board a LONG MARCH rocket SACI-2 is also expected to be launched this year on board a Brazilian
satellite launch vehicle VLS from Alcantara-MA. In the High Frequency Capacitance Probe a metallic sensor in
the form of a sphere of about 60mm diameter is used as a capacitance element in the tank circuit of a "Clapp"
type oscillator. In the fixed bias Langmuir Probe a metallic sensor, similar to that used in the HFC experiment, is
used to collect the elctron or ion currents from the ambient plasma. The sensor potential is selected using
telecommands, from four predetermined values namely -1V, 0V, +1V and +2V. In the Electron Temperature Probe
two semicircular metallic sensors in the form of a circular disc, is used to determine the kinetic temperature of
the ionospheric electrons. On board SACI-1 the HFC, LP and ETP sensors are mounted at the extremities of
three of the four solar panels, while on board SACI-2 they are mounted at the extremities of three deployable
booms about 1m long. The PLASMEX experiments will be operated by commands from an onboard Microcontroller.
While SACI-1 has a near polar sun synchronous orbit, SACI-2 has a low inclination orbit. Thus SACI-1
can give a complete global coverage for the measurement of plasma parameters, while SACI-2 can give detailed
information on the behaviour of these parameters in the low latitude and equatorial regions. A brief summary of
the experiments PLASMEX along with details of the data acquisition system, on board processing of the LP ac
data etc. is presented here.
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