GNGTS 2014 - Atti del 33° Convegno Nazionale

74 GNGTS 2014 S essione 3.1 Malcolm, A. E., B. Ursin, and M. V. de Hoop, 2009, Seismic imaging and illumination with internal multiples : Geophysical Journal International, 176, 847–864. Muijs, R., Robertsson, J. O. A., Holliger, K.; 2007: Prestack depth migration of primary and surface-related multiple reflections: Part I – Imaging . Geophysics 72, S59-S69. Neut, J., A. Bakulin, S. Aramco, and D. Alexandrov, 2013, Acoustic wave eld separation using horizontal receiver arrays deployed at multiple depths on land : SEG Technical Program Expanded Abstracts 2013, 4601–4607. Ravasi, M., and A. Curtis, 2013, Nonlinear scattering based imaging in elastic media: theory, theorems and imaging conditions : GEOPHYSICS, 78. Schuster, G. T., 2010, Seismic interferometry : Cambridge University Press. Vasconcelos, I. Snieder, R., and B. Hornby, 2008, Imaging internal multiples from subsalt vsp data examples of target- oriented interferometry : GEOPHYSICS, 73. Verschuur, E., Berkhout, A.J., Wapenaar, C.P.A.; 1992: Adaptive surface-related multiple elimination . Geophysics 57, 1166-1177. Verschuur, E.; 2006: Seismic multiple removal techniques - past, present and future . EAGE publications, ISBN 90- 73781-51-5. Acquisition of geophysical data in shallow-water environments using autonomous vehicles: state of the art, perspectives and case histories L. Gasperini 1 , F. Del Bianco 2 , G. Stanghellini 1 , F. Priore 3 1 ISMAR, Istituto di Scienze Marine, U.O. Geologia Marina, CNR, Bologna, Italy 2 Consorzio Proambiente, Bologna, Italy 3 Dip. di Fisica e Scienze della Terra “Macedonio Melloni”, Università degli Studi di Parma, Italy Introduction. We present some examples of geophysical data acquisition carried out in different shallow-water environments, including a lake, a coastal lagoon an artificial channel and a river stream, by means of an Unmanned Surface Vehicle (USV) equipped with geophysical sensors that were designed and built for the purpose. First tests indicate that these technologies and methods can be employed to collect densely-spaced grids of high-resolution data, quickly, efficiently, and at a very low-cost, allowing for execution of repeated surveys even in those area not accessible through conventional systems. The intensive use of “open” technologies and software packages for data acquisition and processing has the potential of widening the application of these methods to an increasing audience of earth scientist that study geological processes in these rapidly evolving environments. A number of underwater natural or artificial environments, including harbours, coastal ar- eas, river streams, natural and artificial lakes, and coastal lagoons, are particularly affected by anthropic pressures. For this reason, they would require periodical monitoring to evaluate whether they are in a state of “equilibrium” from the geo-biological point of view. In fact, it is rather common that unbalances in environmental variables, caused by either human activity or natural process, could produce dramatic crises. To date, geo-environmental studies of shallow-water environments are not a consolidated practice, because they require a multidisciplinary knowledge and special instruments. Further- more, the high costs of such complex technologies and methods are out of the budgets of local environmental protection agencies or private consulting enterprises. As a result, such “tran- sitional” zone between the underwater environment and the “onshore” is poorly investigated through geophysical techniques, that most often represent the basis of each geo-environmental study. This lacking is due to several causes, including: 1) shallow-water environments are dif- ficultly accessed by conventional vehicles such as small boats; 2) the narrow water-column constitute an efficient waveguide for acoustic and ultrasonic signals, and limit their penetration