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Long range shock waves from a large explosion underwater: experiment and data 7. The data This chapter describes the data which has been acquired, with particular emphasis on that from the instrumentation at sea. A list of sites at which the larger of the two explosions is known to have been recorded is given in Appendix E and illustrated on the map in Fig. 7.1. The list includes the sites at sea, and BGS temporary and permanent sites covering the UK and Eire. In addition to the permanent land stations of the various BGS networks and University arrays, a number of temporary stations were deployed for the event by other organisations including The Dublin Institute of Advanced Studies (72 stations), University of Hull (5 stations) and Glasgow University (2 stations). This report concentrates on the data from the sea bed instrumentation along the great circle path from the shot point to Tentsmuir A (Fig. 2.2). These comprise the PUSSes and the BGS Sea Bottom Package and the land station at Tentsmuir. These files were subjected to pre-treatment in order that the maximum amount of data could be recovered, and that the final data set files should all be in the same format. 7.1 DATA FORMAT The format selected for the data files consists of a four line header block containing information on: ( 1) The fi lename (2) The source explosion (3) The station, channel and instrument (4) The data, e.g. sampling rate, units etc. followed by the data values for a single channel in double precision fixed format in order that the full number of significant figures could be preserved for data from all sources. An example is given in Table 7.1. The header was designed to contain all the information required by standard time series analysis programs. 38
Long range shock waves from a large explosion underwater: experiment and data The processing of the data required to put the data into the required format is outlined below. The data set is now available on magnetic tape in ASCII format both "as digitised" and after processing. The currently available files are given in Appendix G. 7.2 DISPLAY OF THE DATA The data obtained from the PUSSes, the BGS instrumentation at sea and some preliminary results from the land station at Tentsmuir are displayed in Appendix F. In each case, the whole of the data in each data file is displayed graphically in Appendix Fl, with the regions of the trace (2 sees) containing the acoustic arrivals in Appendix F2 and those containing the seismic arrivals in Appendix F3. 7.3 PREPROCESSING OF THE DATA FILES. The preliminary processing to which the data has been subjected is described in the following paragraphs. 7. 3. I De s p; k; ng Close examination of the data files revealed some channels on which spikes were present which were artifacts of the digitisation process. These were removed where one could be confident that they were not part of the data stream. In cases of doubt, they were left in. The criterion for use with the continuously recorded instruments was that the spike should not be present on the jet pen playout of the data. Vith the digitally recorded PUSS instruments, the spikes were usually unambiguous. Two of the PUSS files were found to have a very low amplitude signal which was partly masked by spikes with a very uniform spacing and size, which were not readily susceptible to filtering (Zl4Gl.DAT, Zl4G2.DAT). In order to render this data accessible, a program was written allowing one to zoom in on a spike and remove it. In files other than the two named above, the vast majority were single point 39
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Appendix A: Proposed schedule for L
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16:47:00 16:47:20 16:47:30 16:47:34
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08:12:45 08:12:50 08:13:00 08: 13:2
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PUSS 3 (INSTRUMENT 11) REDEPLOYED 2
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PUSS 6 (INSTRUMENT 14) REDEPLOYED 2
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Appendix C: Locations of sites at s
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(2) PUSS LOCATIONS SITE 1 (PUSS 2)
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Fix: 56°42.810N aN = .001N +1 m 01
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Appendix D: MODELS FOR COMPUTER SIM
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(c) Permanent land stations with a
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5 14 Hydr. Z X y Hydr. z X y First
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F.3.9 PUSS 10 at 9.982 km, 9001b sh
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Fig. F.2.16 BGS Sea Vertical Hydrop
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I-' -oJ w Fig. F.3.6 BGS Sea Bottom
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I-' ()) 0 Fig. F.3.13 BGS Sea Botto
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.... (J) 0 Fig. F.3.13 BGS Sea Bott
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Start of record = 11:52:05.0 Filena
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Start of record = 15:22:05.0 Filena
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BGS VHS Start of record = 11:53:13.
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Plate 16 Plate 17 Plate 18 Plate 19
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Plate 4 Plate 5 Plate 6
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Plata 10 Plate 1 1 Plate 12
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Plate 16 Plate 17 Plate 18
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Plate 22 Plate 23
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Plate 28 Plate 26
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