43 research outputs found
Wave-equation based seismic multiple attenuation
Reflection seismology is widely used to map the subsurface geological structure of
the Earth. Seismic multiples can contaminate seismic data and are therefore due to be
removed. For seismic multiple attenuation, wave-equation based methods are proved
to be effective in most cases, which involve two aspects: multiple prediction and
multiple subtraction. Targets of both aspects are to develop and apply a fully datadriven
algorithm for multiple prediction, and a robust technique for multiple
subtraction. Based on many schemes developed by others regarding to the targets, this
thesis addresses and tackles the problems of wave-equation based seismic multiple
attenuation by several approaches.
First, the issue of multiple attenuation in land seismic data is discussed. Multiple
Prediction through Inversion (MPTI) method is expanded to be applied in the poststack
domain and in the CMP domain to handle the land data with low S/N ratio,
irregular geometry and missing traces. A running smooth filter and an adaptive
threshold K-NN (nearest neighbours) filter are proposed to help to employ MPTI on
land data in the shot domain.
Secondly, the result of multiple attenuation depends much upon the effectiveness
of the adaptive subtraction. The expanded multi-channel matching (EMCM) filter is
proved to be effective. In this thesis, several strategies are discussed to improve the
result of EMCM. Among them, to model and subtract the multiples according to their
orders is proved to be practical in enhancing the effect of EMCM, and a masking filter
is adopted to preserve the energy of primaries. Moreover, an iterative application of
EMCM is proposed to give the optimized result.
Thirdly, with the limitation of current 3D seismic acquisition geometries, the
sampling in the crossline direction is sparse. This seriously affects the application of
the 3D multiple attenuation. To tackle the problem, a new approach which applies a
trajectory stacking Radon transform along with the energy spectrum is proposed in
this thesis. It can replace the time-consuming time-domain sparse inversion with
similar effectiveness and much higher efficiency.
Parallel computing is discussed in the thesis so as to enhance the efficiency of
the strategies. The Message-Passing Interface (MPI) environment is implemented in
most of the algorithms mentioned above and greatly improves the efficiency
High-resolution imaging beneath the Santorini volcano
Volcanoes are surface expressions of much deeper magmatic systems, inaccessible to direct observation. Constraining the geometry and physical properties of these systems, in particular detecting high melt fraction (magma) reservoirs, is key to managing a volcanic hazard and understanding fundamental processes that lead to the formation of continents. Unfortunately, unambiguous evidence of magma reservoirs has not yet been provided due to the limited resolving power of the geophysical methods used so far.
Here, a high-resolution imaging technique called full-waveform inversion was applied to study the magmatic system beneath the Santorini volcanic field, one of the most volcanically and seismically active regions of Europe. Quality-controlled inversion of 3d wide-angle, multi-azimuth ocean-bottom seismic data revealed a previously undetected high melt fraction reservoir 3 km beneath the Kolumbo volcano, a centre of microseismic and hydrothermal activity of the field.
To enable the above method to handle land data, two major algorithmic improvements were added to the high-performance inversion code. First, to simulate instrument response of land seismometers, a pressure-velocity conversion has been implemented in a way that ensures reciprocity of the discretised 2nd-order acoustic wave equation. Second, the immersed-boundary method, originally developed for computational fluid dynamics, was implemented to simulate the wave-scattering off the irregular topography of the Santorini caldera. These advancements can be readily used to provide a higher-resolution image of the melt reservoir beneath the Santorini caldera already detected by means of travel-time tomography.Open Acces
Proceedings of the International Workshop on Medical Ultrasound Tomography: 1.- 3. Nov. 2017, Speyer, Germany
Ultrasound Tomography is an emerging technology for medical imaging that is quickly approaching its clinical utility. Research groups around the globe are engaged in research spanning from theory to practical applications. The International Workshop on Medical Ultrasound Tomography (1.-3. November 2017, Speyer, Germany) brought together scientists to exchange their knowledge and discuss new ideas and results in order to boost the research in Ultrasound Tomography
Uncertainties in the Estimation of the Shear-Wave Velocity and the Small-Strain Damping Ratio from Surface Wave Analysis
L'abstract è presente nell'allegato / the abstract is in the attachmen
Earth resources. A continuing bibliography with indexes, issue 23
This bibliography lists 226 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1979 and September 30, 1979. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis