A generalized framework for high‐frequency optimum target detection in a shallow water, random wave scattering environment

Slowly varying motions and drift forces of a large moored ship in random waves at 35m water depth are investigated by an experimental wave basin study in scale 1:50. A simple horizontal mooring set-up is used. A second-order wave correction is applied to minimize “parasitic” long waves. The effect on the ship motion from the correction is clearly seen, although less in random wave spectra than in pure bi-chromatic waves. Empirical quadratic transfer functions (QTFs) of the surge drift force are found by use of cross-bi-spectral analysis, in two different spectra have been obtained. The QTF levels increase significantly with lower wave frequencies (except at the diagonal), which is special for finite and shallow water. Furthermore, the QTF levels frequencies at low frequencies increase significantly out from the QTF diagonal. Thus Newman’s approximation should preferrably not be used in these cases. Using the LF waves as a direct excitation in a “linear” ship force analysis gives random records that compare reasonably well with those from the cross-bi-spectral analysis. This confirms the idea that the drift forces in shallow water are closely correlated to the second-order potential, and thereby by the second-order LF waves.

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Polychaete palaeoecology in an early Late Ordovician marine astrobleme of Sweden

Geological Magazine ◽

10.1017/s0016756810000579 ◽

2010 ◽

Vol 148 (2) ◽

pp. 269-287 ◽

Cited By ~ 7

Author(s):

MATS E. ERIKSSON ◽

ÅSA M. FRISK

Keyword(s):

Shallow Water ◽

High Frequency ◽

Relative Frequency ◽

Late Ordovician ◽

Crater Floor ◽

Drill Core ◽

Upper Ordovician ◽

Composition Characteristic ◽

Post Impact ◽

Early Late

AbstractThe post-impact Dalby Limestone (Kukruse; Upper Ordovician) of the Tvären crater, southeastern Sweden, has been analysed with regards to polychaetes, as represented by scolecodonts. A palaeoecological succession is observed in the Tvären-2 drill core sequence, as the vacant ecospace was successively filled by a range of benthonic, nektonic and planktonic organisms. Scolecodonts belong to the first non-planktonic groups to appear and constitute one of the most abundant fossil elements. The polychaete assemblage recorded has an overall composition characteristic of that of the Upper Ordovician of Baltoscandia. Oenonites, Vistulella, Mochtyella and the enigmatic ‘Xanioprion’ represent the most common genera, whereas Pteropelta, Protarabellites?, Atraktoprion and Xanioprion are considerably more rare. The assemblage differs from coeval ones particularly in its poorly represented ramphoprionid fauna and the relatively high frequency of ‘Xanioprion’. A taxonomic succession and changes in abundance and relative frequency of different taxa is observed from the deepest part of the crater and upwards towards more shallow water environments. The initial post-impact assemblage does not, however, necessarily represent a benthonic colonization of the crater floor. Instead it seems to be a taphocoenosis, as indicated by its taxonomic correspondence to the rim facies fauna recovered from Dalby Limestone erratics of the Ringsön island. The Tvären succession has yielded considerably richer scolecodont assemblages than hitherto recorded from the approximately coeval Lockne crater, possibly as a consequence of shallower water settings in the former area.

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Limitations of target detection in horizontal acoustic surveys of extremely shallow water bodies

Fisheries Research ◽

10.1016/j.fishres.2019.05.005 ◽

2019 ◽

Vol 218 ◽

pp. 94-104

Author(s):

Ievgen Koliada ◽

Helge Balk ◽

Michal Tušer ◽

Ladislav Ptáček ◽

Jan Kubečka

Keyword(s):

Shallow Water ◽

Target Detection ◽

Water Bodies ◽

Acoustic Surveys

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Paleoenvironments and high-frequency cyclicity from Cenozoic South-East Asian shallow-water carbonates: a case study from the Oligo-Miocene buildups of Malampaya (Offshore Palawan, Philippines)

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2003.11.012 ◽

2004 ◽

Vol 21 (1) ◽

pp. 1-21 ◽

Cited By ~ 40

Author(s):

F. Fournier ◽

L. Montaggioni ◽

J. Borgomano

Keyword(s):

Shallow Water ◽

High Frequency ◽

East Asian

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