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Harbour Sea-floor Clearance: “HD” High Definition Magnetic Survey Performance
Author(s)
Type
Conference paper
Language
English
Obiettivo Specifico
1.6. Osservazioni di geomagnetismo
2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini
3.4. Geomagnetismo
Status
Published
Conference Name
Issued date
October 21, 2009
Conference Location
Stockolm, Sweden
Subjects
Abstract
Seafloor clearance methods based on acoustic,
direct-inspection, and single-sensor magnetic approaches suffer from limitations in controlling the target-sensor distance, and may prove ineffective when the small size or the dangerous nature of targets requires high accuracy in localization.
Moreover, random magnetic variations over time bring about spatial decorrelation phenomena, and hinder the application of
double-sensor methods in noisy harbour environments.
The new High Definition (HD) magnetic survey protocol tackles the measurement-distance problem in two ways: first, by varying the sensor depth dynamically, and secondly by backprojecting the measured field according to seafloor data and vertical incremental factors associated with the bandwidth
characteristics of targets. The method to make up for timeinduced loss in spatial localization ability exploits the local
behaviour of a coherence function, which correlates local observations to a set of spatially-stabilized reference stations. The
consequent normalization of measured magnetic signals allows one to assign the monitored areas with a specific level of
confidence in the detection results, ranging from 100% (certainty) to 0% (random events).
The principles of HD detection have been fully applied in the seafloor clearance of the firing test site located south of Cape
Teulada (Sardinia, Italy), where very weak signal sources such as cartridge cases, mines, and small objects down to 1 Kg mass
values (lobster pots) have been successfully localized, even when covered by extensive colonies of Posidonia.
direct-inspection, and single-sensor magnetic approaches suffer from limitations in controlling the target-sensor distance, and may prove ineffective when the small size or the dangerous nature of targets requires high accuracy in localization.
Moreover, random magnetic variations over time bring about spatial decorrelation phenomena, and hinder the application of
double-sensor methods in noisy harbour environments.
The new High Definition (HD) magnetic survey protocol tackles the measurement-distance problem in two ways: first, by varying the sensor depth dynamically, and secondly by backprojecting the measured field according to seafloor data and vertical incremental factors associated with the bandwidth
characteristics of targets. The method to make up for timeinduced loss in spatial localization ability exploits the local
behaviour of a coherence function, which correlates local observations to a set of spatially-stabilized reference stations. The
consequent normalization of measured magnetic signals allows one to assign the monitored areas with a specific level of
confidence in the detection results, ranging from 100% (certainty) to 0% (random events).
The principles of HD detection have been fully applied in the seafloor clearance of the firing test site located south of Cape
Teulada (Sardinia, Italy), where very weak signal sources such as cartridge cases, mines, and small objects down to 1 Kg mass
values (lobster pots) have been successfully localized, even when covered by extensive colonies of Posidonia.
References
[1] Hill M.N., Mason C.S., 1962, “Diurnal variations of the earth’s magnetic
field al sea”, Nature, Vol. 195, 365-366.
[2] Faggioni O., Caratori Tontini F., 2002, “Quantitative evaluation of the
time-line reduction performance in high definition marine magnetic
survey”, Mar. Geoph. Res., Vol. 33, pp. 353-365.
[3] Faggioni O., Beverini N., Carmisciano C., 1997, “Geomagnetic time
variations and high definition study of space magnetic effects induced
by artificial submerged sources”, Boll. Geof. Teor. Appl., Vol XXXVIII,
N 3-4, pp. 211-228.
[4] E. Di Gennaro, E. Bovio, F. Baralli, O. Faggioni and M. Soldani, 2008,
“Clearance operation of Teulada Site (Italy): a novel approach for short
term MCM missions in seafloor hard conditions”, CD-ROM Proceedings
of UDT Europe 2008 Conference, June 11-13, Glasgow, UK.
field al sea”, Nature, Vol. 195, 365-366.
[2] Faggioni O., Caratori Tontini F., 2002, “Quantitative evaluation of the
time-line reduction performance in high definition marine magnetic
survey”, Mar. Geoph. Res., Vol. 33, pp. 353-365.
[3] Faggioni O., Beverini N., Carmisciano C., 1997, “Geomagnetic time
variations and high definition study of space magnetic effects induced
by artificial submerged sources”, Boll. Geof. Teor. Appl., Vol XXXVIII,
N 3-4, pp. 211-228.
[4] E. Di Gennaro, E. Bovio, F. Baralli, O. Faggioni and M. Soldani, 2008,
“Clearance operation of Teulada Site (Italy): a novel approach for short
term MCM missions in seafloor hard conditions”, CD-ROM Proceedings
of UDT Europe 2008 Conference, June 11-13, Glasgow, UK.
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