New Publications are available for Seismology
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New Publications are available now online for this publication.
Please follow the links to view the publication.Chirp sub-bottom profiler for TOBI, a deep ocean survey vehicle
http://dl-live.theiet.org/content/conferences/10.1049/cp_19970670
The implementation of chirp sonar represents a recent upgrade step in the profiler system of SOC's deep ocean survey vehicle TOBI (Towed Ocean Bottom Instrument), a multi-sensor platform used for deep ocean scientific and commercial research and mapping. The existing profiler system consists of a seven transducer array of 110 mm diameter free-flooded rings for operation to full ocean depths. In addition novel slow waveguides on each transducer are employed to modify the acoustic directivity pattern of the individual elements. It transmits a single frequency (7.5 kHz), 500 W pulse 0.26 ms long, giving a range of up to 70 m penetration over soft sediment. Although this gives a theoretical vertical resolution of 0.2 m, ringing significantly degrades this performance. The use of a long chirp pulse reduces the effect of ringing whilst, with the use of a suitable matched filter, preserving the original resolution. Previous implementations of chirp sub-bottom profilers have relied on ship-board signal processing. This is not ideal in the TOBI case as the electrical characteristics of the 10 km tow cable can detrimentally modify any raw signals. Hence, all signal processing electronics, pulse profiles and matched filtering in this new design are located within the TOBI vehicle putting tight constraints on the size, power requirements and cable bandwidth available to the system. The use of quadrature sampling and a hardware matched filter make for a small, low cost, low power design which uniquely combines the processing performance of a ship-based system with the lower acoustic noise and smaller acoustic footprint of a deep-towed system.Multiscale-combined seismic waveform inversion using orthogonal wavelet transform
http://dl-live.theiet.org/content/journals/10.1049/el_20010131
A method of multiscale-combined inversion (MCI) using the orthogonal wavelet transform is applied to an inverse seismic waveform based on the convolutional model. MCI is a promising method because of its low dependence on the initial model, convergence efficiency and robustness. Numerical results show the effectiveness and potential of the method.Comparison of the seismic and ground probing radar methods in geological surveying
http://dl-live.theiet.org/content/journals/10.1049/ip-f-1.1988.0045
The use of ground probing radar has increased significantly over the past few years in the civil engineering field. As a geophysical technique it has much in common with the seismic reflection method. The information derived from both methods is displayed as a time/distance cross-section, which is very similar in appearance to a geological cross-section. However, the time section can only be converted to a depth section when the velocity of propagation of the seismic or electromagnetic pulse within each of the resolved layers is known. The use of these two methods in shallow geological surveys at the site investigation stage of a civil engineering construction is reviewed and illustrated by case histories. It is shown that the development of high-frequency sources has improved the resolution obtainable from the seismic reflection method while the gradual improvement in instrumentation has resulted in greater penetration being achieved with the radar method. A consideration of the penetration shows that with both methods it is largely controlled by the moisture content of the superficial deposits, which has a very strong influence on the attenuation of both seismic and electromagnetic energy. The effect is, in fact, complementary since a dry material will transmit electromagnetic energy better than a saturated one, while the converse is true for seismic energy.