Data acquisition and processing at ocean bottom for a Tsunami warning system

The design and development of a Bottom Pressure Recorder for a Tsunami Early Warning System is described here. The special requirements that it should satisfy for the specific application of deployment at ocean bed and pressure monitoring of the water column above are dealt with. A high-resolution data digitization and low circuit power consumption are typical ones. The implementation details of the data sensing and acquisition part to meet these are also brought out. The data processing part typically encompasses a Tsunami detection algorithm that should detect an event of significance in the background of a variety of periodic and aperiodic noise signals. Such an algorithm and its simulation are presented. Further, the results of sea trials carried out on the system off the Chennai coast are presented. The high quality and fidelity of the data prove that the system design is robust despite its low cost and with suitable augmentations, is ready for a full-fledged deployment at ocean bed. (C) 2013 Elsevier Ltd. All rights reserved.

Ocean bottom seismic noise : applications for the crust knowledge, interaction ocean-atmosphere and instrumental behaviour

Tese de doutoramento, Ciências Geofísicas e da Geoinformação (Geofisíca), Universidade de Lisboa, Faculdade de Ciências, 2014

Composition and crystal parameters of carbonate-apatites from animal teeth and bones and from phosphate rocks of the ocean bottom

Samples of recent to Miocene fish and marine mammal bones from the bottom of the Atlantic and Pacific Oceans and Miocene Maikop deposits (Transcaspian region) are studied by X-ray diffraction technique combined with chemical and energy-dispersive analyses. Changes of lattice parameters and chemical composition of bioapatite during fossilization and diagenesis suggest that development of skeletal apatite proceeds from dahllite-type hydroxyapatite to francolite-type carbonate-fluorapatite. It is assumed that jump-type transition from dahllite to francolite during initial fossilization reflects replacement of biogeochemical reactions in living organisms, which are subject to nonlinear laws of nonequilibrium thermodynamics, by physicochemical processes according to the linear equilibrium thermodynamics.

Ocean bottom seismometer sgy-files of refraction seismic profiles from Professor Logachev cruise TTR16/3

Over the last decade pockmarks have proven to be important seabed features that provide information about fluid flow on continental margins. Their formation and dynamics are still poorly constrained due to the lack of proper three dimensional imaging of their internal structure. Numerous fluid escape features provide evidence for an active fluid-flow system on the Norwegian margin, specifically in the Nyegga region. In June-July 2006 a high-resolution seismic experiment using Ocean Bottom Seismometers (OBS) was carried out to investigate the detailed 3D structure of a pockmark named G11 in the region. An array of 14 OBS was deployed across the pockmark with 1 m location accuracy. Shots fired from surface towed mini GI guns were also recorded on a near surface hydrophone streamer. Several reflectors of high amplitude and reverse polarity are observed on the profiles indicating the presence of gas. Gas hydrates were recovered with gravity cores from less than a meter below the seafloor during the cruise. Indications of gas at shallow depths in the hydrate stability field show that methane is able to escape through the water-saturated sediments in the chimney without being entirely converted into gas hydrate. An initial 2D raytraced forward model of some of the P wave data along a line running NE-SW across the G11 pockmark shows, a gradual increase in velocity between the seafloor and a gas charged zone lying at ~300 m depth below the seabed. The traveltime fit is improved if the pockmark is underlain by velocities higher than in the surrounding layer corresponding to a pipe which ascends from the gas zone, to where it terminates in the pockmark as seen in the reflection profiles. This could be due to the presence of hydrates or carbonates within the sediments.