Near-surface S-wave traveltime corrections and inversion: a raypath-consistent and interferometric approach

Removing near-surface effects in the processing of 3C data is key to exploiting the information provided by converted waves, particularly for the case of the PS mode where converted energy travels back to the surface as S-waves. The very low velocity of S-waves amplifies the distortions introduced by the near-surface in the PS-traveltimes. This is usually solved by computing the vertical traveltimes in the near-surface layer and removing them from the data in a surface-consistent framework. However, if the velocity change between the near-surface layer and the medium underneath is small, the vertical raypath assumption that supports the surface-consistent approach is no longer valid. This property results in a non-stationary change of the near-surface traveltimes that needs to be addressed to properly remove its effect. I show how the delays introduced by the presence of very low S-wave velocities in the near-surface can introduce raypath-dependent effects which can be larger than what can be considered a residual static. In this study, a raypath-consistent solution for removing near-surface traveltime effects is proposed. This is achieved by transforming the data, organized into receiver gathers, to the tau-p domain and performing crosscorrelation and convolution operations to capture and remove the near-surface delays from the data. The tau-differences captured during the interferometric processing of the near-surface effects are then used in an inversion algorithm to estimate the S-wave velocities in the near-surface. This processing work-flow provides not only a set of corrections but also a velocity model that is based on them. I tested this method on synthetic and field data. In both cases, removing near-surface time delays in a raypath-consistent framework improved coherency and stacking power of shallow and deep events simultaneously. Shallow events benefited most from this processing due to their wider range of reflection angles. This approach can be useful in the processing of wide-angle broadband data, where the kinematics of wave propagation are not consistent with vertical raypath approximations in the near-surface. Additionally, this method provides a near-surface S-wave velocity model that can be used for building migration velocity models or to initialize elastic full waveform inversions

Looking for Vico between zero and infinity

M.S.James Williamso

Progress on Ultra-Wideband (UWB) Multi-Antenna radar imaging for MIGA

Progress on the development of the multi-channel, ground penetrating radar imaging system is presented from hardware and software perspectives. A new exponentially tapered slot antenna, with an operating bandwidth from 100 MHz to 1.5 GHz was fabricated and tested using the eight-port vector network analyzer, designed by Rhode and Schwarz Incorporated for this imaging project. An eight element antenna array mounted on two carts with automatic motor drive, was designed for optimal common midpoint (CMP) data acquisition. Data acquisition scenarios were tested using the acoustic version of the NORSAR2D seismic ray-tracing software. This package enables the synthesis and analysis of multi-channel, multi-offset data acquisitions comprising more than a hundred thousand traces. Preliminary processing is in good agreement with published bistatic ground-penetrating radar images obtained in the tunnels of the Low-noise Underground Laboratory (LSBB) at Rustrel, France

Progress on Ultra-Wideband (UWB) Multi-Antenna radar imaging for MIGA

Progress on the development of the multi-channel, ground penetrating radar imaging system is presented from hardware and software perspectives. A new exponentially tapered slot antenna, with an operating bandwidth from 100 MHz to 1.5 GHz was fabricated and tested using the eight-port vector network analyzer, designed by Rhode and Schwarz Incorporated for this imaging project. An eight element antenna array mounted on two carts with automatic motor drive, was designed for optimal common midpoint (CMP) data acquisition. Data acquisition scenarios were tested using the acoustic version of the NORSAR2D seismic ray-tracing software. This package enables the synthesis and analysis of multi-channel, multi-offset data acquisitions comprising more than a hundred thousand traces. Preliminary processing is in good agreement with published bistatic ground-penetrating radar images obtained in the tunnels of the Low-noise Underground Laboratory (LSBB) at Rustrel, France

Progress on Ultra-Wideband (UWB) Multi-Antenna radar imaging for MIGA

Progress on the development of the multi-channel, ground penetrating radar imaging system is presented from hardware and software perspectives. A new exponentially tapered slot antenna, with an operating bandwidth from 100 MHz to 1.5 GHz was fabricated and tested using the eight-port vector network analyzer, designed by Rhode and Schwarz Incorporated for this imaging project. An eight element antenna array mounted on two carts with automatic motor drive, was designed for optimal common midpoint (CMP) data acquisition. Data acquisition scenarios were tested using the acoustic version of the NORSAR2D seismic ray-tracing software. This package enables the synthesis and analysis of multi-channel, multi-offset data acquisitions comprising more than a hundred thousand traces. Preliminary processing is in good agreement with published bistatic ground-penetrating radar images obtained in the tunnels of the Low-noise Underground Laboratory (LSBB) at Rustrel, France

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved

Reconstruction of interactions in the ProtoDUNE-SP detector with Pandora

International audienceThe Pandora Software Development Kit and algorithm libraries provide pattern-recognition logic essential to the reconstruction of particle interactions in liquid argon time projection chamber detectors. Pandora is the primary event reconstruction software used at ProtoDUNE-SP, a prototype for the Deep Underground Neutrino Experiment far detector. ProtoDUNE-SP, located at CERN, is exposed to a charged-particle test beam. This paper gives an overview of the Pandora reconstruction algorithms and how they have been tailored for use at ProtoDUNE-SP. In complex events with numerous cosmic-ray and beam background particles, the simulated reconstruction and identification efficiency for triggered test-beam particles is above 80% for the majority of particle type and beam momentum combinations. Specifically, simulated 1 GeV/$c$ charged pions and protons are correctly reconstructed and identified with efficiencies of 86.1$\pm0.6$% and 84.1$\pm0.6$%, respectively. The efficiencies measured for test-beam data are shown to be within 5% of those predicted by the simulation