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Keith vonder Heydt Woods Hole Oceanographic Institution Woods Hole, MA 02543 Arthur M. Baggeroer Massachusetts Institute of Technology Cambridge, MA 01239 1. Introduction The focus of work proposed for the CEAREX Acoustics Camp (A-Camp) was a better understanding of the environmental dependencies of the acoustic character of the Arctic. In addition to direct acoustic measurements at A-Camp using a large horizontal hydrophone array, multiple vertical hydrophone arrays and geophone arrays, regular CTD and meteorology measurements were made. Acoustic data were recorded by a multichannel digital acquisition system, capable of >120 dB dynamic range, developed at WHOI and described in "High continuous bandwidth multi-channel acquisition system" (von der Heydt, 1991). The MIT/WHOI digital data set consisted of 40 channels devoted to hydrophone sensors of the horizontal array and 12 channels from four 3-axis geophones. Channels were selectively recorded for periods of days on a 14-channel FM tape recorder. All data included on the CD-ROM "CEAREX-1" were acquired on the digital system. In support of coherent processing techniques for the low frequency data (1 to 250 Hz) recorded from the hydrophone arrays, an independent system, operating in the 10 kHz region, was used to continuously measure time delays between six tone burst sources and the array sensors, all at a common depth. These travel times were later used to estimate relative locations of sensors. Nominal estimates of these locations are tabulated as supporting data on the CD-ROM. 2. Rationale The following interests highlight the motivation for acoustic work conducted at the CEAREX A-Camp: 2.1. Previous work has shown that 3-axis geophones can provide superior data compared to hydrophones for understanding acoustic energy loss mechanisms related to ice scattering and mode conversion. For this purpose "Plate Wave" signals were generated at many sites about the camp by detonating small explosive charges deployed through holes in the ice at depths ranging from 4 to 64 feet. These signals were recorded on both hydrophones and geophones. 2.2. Earlier Arctic work has shown both high spatial and temporal coherence. While high temporal coherence is not surprising given the lack of surface roughness due to the ice cover, the high spatial coherence was unexpected. An objective of the CEAREX effort was to continue these investigations using a horizontal hydrophone array with a 20 km aperture. A 300 cubic inch airgun was used as the signal source from the Oceanography Camp (O-Camp) at a range of 200 km. 2.3. Two further objectives were a continuation of Arctic ambient noise work for the purpose of compiling event statistics, and the acquisition of long time series receptions from the Greenland Sea tomography array. The report "CEAREX "A"-Camp: Navigation, Bathymetry, CTD, Meteorology, and LORFAR Data Report (von der Heydt, et al., 1991) is a digest of navigation, bathymetry, CTD, meteorology and one type of ambient noise acoustic data acquired during the CEAREX experiment at the Acoustic ("A") Camp site over the period 23 March through 20 April 1989. Other pertinent information is included in this report that would be useful to anyone interested in the acoustic data either as presented in the "sampler" data set on the CD-ROM "CEAREX-1" or from our complete data set from the A-Camp experiment. Papers and reports resulting from analysis of the data set include Fricke (1991), Gerstoft and Schmidt (1991), Miller and Schmidt (1991), Peal (1990), Schmidt and LePage (1991, work in progress), Schmidt and Kim (1991, in preparation), and Seong (1991.) 3. Data Format Description Each file begins with an ASCII header of 512 bytes with information concerning the experiment, the number of sensors, and the number of data values in the file. A stream of all the data for the first sensor follows this header. The end of the data for the sensor is indicated by a newline character. The data for the second sensor follows in the same way, with the sequence repeated for all sensors. The last record in the file may be padded to 512 characters with blanks. All data were sampled at 1 KHz. A listing of sensor locations relative to the nominal origin at sensor 9 is given in the description of file 3. The Fortran data format is E8.6; the C language format is 13.6e. 4. Data Files Files are in the sub-directory \NOISE\ACOUSTIC on this CD-ROM. 4.1. File CRX22.DAT - AMBIENT NOISE This file contains 700416 data values (700.416 seconds) from each of four sensors. These data were acquired as an ambient noise experiment during a particularly windy day in the field. The initial start time of the data is 4/11/89/1534Z. The wind speed on this day exceeded twenty knots. The sensors recorded on the file are (in order): NE320, NW7000, G4Y, and G4Z. The first two are hydrophones with a sensitivity of -160 db re: 1 volt per micropascal. The first hydrophone was hardwired to the acquisition equipment at base camp. The second hydrophone, NW7000, communicated with base camp via a radio link with 10db of gain. A gain normalization was applied to the data from this sensor to make the hydrophone gains consistent. The last two sensors, G4Y and G4Z, include the horizontal and the vertical component, respectively, of geophone G4. Total file size is 39223813 bytes, consisting of a 512-character header, 4 groups of 700416 values each (14 characters per value), a newline (0D hexadecimal) following each group and an additional newline at the end of the file. For the CD-ROM, the files were converted into 512-character records. For cross-referencing with original data held by the investigators, this file contains data copied from WHOI optical disk CRX22.dat. 72 records starting at record 157 are included, for channels 24, 36, 50, and 51. Channel 36 is scaled by 0.31623 to normalize for preamp gain, as described above. 4.2. File CRX52.DAT - PLATE WAVE EXPERIMENT This file contains 450001 values (450.001 seconds) from each of six sensors: NW20, APEX, NE40, G1X, G1Y, and G1Z. The data were acquired during a `Plate Wave Experiment' in which primer cord and SUS explosives were set off near the A-Camp. The data were collected at 1631Z 16 April 1989. Three shot events are recorded in this file: a primer cord shot at 32 feet depth; a second one at 64 feet depth; and finally a SUS shot at 800 feet. The first three sensors in the file are ordinary hardwired hydrophones with sensitivity of -160 db re 1V/uPa. The latter three include both horizontal components and the vertical component of geophone G1. Total file size is 37800603 bytes. This consists of a 512-character header, 4 groups of 450001 values each (14 characters per value), a newline following each group and an additional newline at the end of the file. For cross-referencing with original data held by the investigators, this file contains data copied from WHOI optical disk CRX52.dat. Fifty-four records starting at record 556 are included for channels 5, 9, 11, 40, 41 and 42. 4.3. File CRX58.DAT - REMOTE AIR GUNS / AMBIENT NOISE This file contains 55001 data values from 50 sensors, collected at 0848Z 17 April 1989. Only 55 seconds of data are included because of the large number of sensors. During this interval, an air gun was shooting at a 48 second period from the O-Camp, approximately 300 km to the northeast. With signal processing, it is possible to detect these signals. Otherwise, the data can also serve as a sample of ambient noise on a fairly quiet day in the Arctic. The first 38 channels are hydrophones with a sensitivity of -160 dB re: 1 volt per micropascal. The last twelve channels are geophones. The last eight hydrophones on the file were radio-linked phones with an extra 10 db of gain, for which no normalization is made. The following is a list of "X-Y" sensor position estimates in meters realtive to a Y-axis baseline between the apex sensor, Ch9, and Ch7. The position listing is in the order of the channels in the data file (note that Ch16 has been deleted.) Channels 2, 4, 6, 8, 10 and 12 were "source" sensors used for the acousting tracking system, from which these positions were derived. GX and GY denote the horizontal components of a geophone, GZ denotes the vertical component. ch0: 5755.07 2583.25 S8 ch 1: 14.0834 17.537 NE20 ch 2: 1338.32 -1742.18 S9 ch 3: 51.0266 62.375 NE80 ch 4: -5563.56 -3346.58 S10 ch 5: -34.8596 30.741 NW40 ch 6: -2443.09 4484.51 S11 ch 7: 23.3318 -9.845 SE20 ch 8: -2.7237 288.45 ch 9: 0 0 APEX ch 10: -2.7237 -401.526 S13 ch 11: 28.6041 30.965 NE40 ch 12: -21.6686 12.825 NW20 ch 13: -10.28 -13.397 SW20 ch 14: -27.8904 -34.931 SW40 ch 15: 37.2584 -29.693 SE40 ch 16: 64.7682 -50.206 SE80 (deleted from file) ch 17: 129.213 -99.734 SE160 ch 18: -59.3577 55.013 NW80 ch 19: -49.2728 -62.052 SW80 ch 20: 103.035 121.974 NE160 ch 21: -96.0213 -122.533 SW160 ch 22: -117.35 99.552 NW160 ch 23: -272.318 222.216 NW320 ch 24: 170.479 197.15 NE320 ch 25: -187.487 -289.897 SW320 ch 26: 263.392 -211.6 SE320 ch 27: 547.593 -432.586 SE640 ch 28: -372.394 -568.349 SW640 ch 29: -499.854 415.074 NW640 ch 30: 402.652 489.644 NE640 ch 31: -1570.55 1156.8 NW2400 ch 32: -3054.26 2043.8 NW4800 ch 33: 1075.34 -766.27 SE1200 ch 34: 2118.93 -1530.41 SE2400 ch 35: 3880.64 -1319.69 SE4800 ch 36: -6252.05 3747.81 NW7000 ch 37: 8007.07 -141.98 SE9000 ch 38: -9458.89 6173.48 NW11000 Geophones: ch 40: -31.38 45.66 G1X ch 41: G1Y ch 42: G1Z ch 43: -27 -12 G2X ch 44: G2Y ch 45: G2Z ch 46: 28.76 -5.07 G3X ch 47: G3Y ch 48: G3Z ch 49: 22.95 49.21 G4X ch 50: G4Y ch 51: G4Z Total file size is 38501263 bytes. This consists of a 512-character header, 50 groups of 55001 values each (14 characters per value), a newline following each group and an additional newline at the end of the file. For cross-referencing with original data held by the investigators, this file contains data copied from WHOI optical disk CRX58.dat. Six records starting at record 26 are included. Channel 16 was deleted due to excessive noise. 5. References Fricke, R. (1991) Finite Difference Solution For Acoustic Scattering From Ice Keels and Rough Ice. MIT-WHOI Joint Program, Ph.D. thesis, May 1991. In preparation for Journal of the Acoustical Society of America. Gerstoft, P., and Schmidt, H. (1991) Boundary element approach to ocean seismo-acoustic facet reverberation, Journal of the Acoustical Society of America, 89(4), pp. 1629-1642. Miller, B., and Schmidt, H. (1991) Observation and inversion of seismo-acoustic waves in a complex Arctic ice environment, Journal of the Acoustical Society of America, 89(4), pp. 1668-1685. Peal, K.R. (1990) Arctic remote autonomous measurement platform - post CEAREX engineering report. Woods Hole Oceanographic Institution. Technical Report no. 90-46. Schmidt, H. and LePage, K. (1991) Three-dimensional diffuse scattering by a rough ice cover. Journal of the Acoustical Society of America, work in progress. Schmidt, H., and Kim, J. (1991) Numerical modeling of acoustic emission from propagating cracks. Journal of the Acoustical Society of America, in preparation. Seong, W. (1991) Hybrid Galerkin Boundary Element Wavenumber Integration Method for Acoustic Propagation in Laterally Inhomogenous Media. Massachusetts Institute of Technology, Department of Oceanographic Engineering, Ph.D. thesis. von der Heydt, K.(1991) High Continuous Bandwidth Multichannel Acquisition System. Woods Hole Oceanographic Institution. Technical Report no. 91-14. von der Heydt, K., Galbraith, N.R., Baggeroer, A.B., Meunch, R., Guest, P.S., Davidson, K.L. (1991) CEAREX "A" - Camp: Navigation, Bathymetry, CTD, Meteorology, and LOFAR Data Report. Woods Hole Oceanographic Institution. Technical Memorandum no. WHOI-1-91, 152 pp. + appendix. Includes 14 color plates. 6. Contact Information Dr. Arthur B. Baggeroer (MIT PI, acoustics) Massachusetts Institute of Technology Building 5-204 77 Massachusetts Avenue Cambridge, MA 01239 Phone: 617-253-4336 Telemail: A.BAGGEROER/Omnet Internet: firstname.lastname@example.org Keith von der Heydt, (WHOI PI, data acquisition systems) Woods Hole Oceanographic Institution Woods Hole, MA 02543 Phone: 508-457-2000 Telemail: K.VONDERHEYDT/Omnet Internet: email@example.com Dr. Ira Dyer (acoustics) Massachusetts Institute of Technology Building 5-212 77 Massachusetts Avenue Cambridge, MA 01239 Phone: 617-253-6824 Telemail: I.DYER/Omnet Dr. Henrik Schmidt (acoustics) Massachusetts Institute of Technology Building 5-204 77 Massachusetts Avenue Cambridge, MA 01239 Phone: 617-253-5727 Telemail: H.SCHMIDT.MIT/Omnet Dr. Robin Muench (oceanography) Science Applications International Corporation 13400B Northrup Way Suite 36 Bellevue, WA 98005 Phone: 206-747-7152 Telemail: R.MUENCH/Omnet Dr. Ken Davidson (meteorology) Naval Postgraduate School Department of Meteorology, Code MR/Gs Monterey, CA 93943-5000 USA Phone: 408-646-2451 Telemail: K.DAVIDSON/Omnet Edward K. Scheer (acoustics processing) Woods Hole Oceanograhic Institution Woods Hole, MA 02543 Phone: 508-457-2000 Internet: firstname.lastname@example.org T.C. Yang (acoustics, vertical arrays) Naval Research Laboratory 4555 Overlook Avenue SW Washington DC 20375-5000 Telemail: T.YANG/Omnet Peter Weibe (biology) Woods Hole Oceanographic Institution Woods Hole, MA 02543 Phone: 508-457-2000 Charles Greene (biology) Cornell University Ecology and Systematics Ithaca, NY Telemail: C.GREEN/Omnet 7. Acknowledgments We would like to acknowledge the following people, some as participants at the CEAREX A-Camp, and some for work in preparation for and analysis following the field effort. In some cases these people have made independent submissions of data to the CD-ROM "CEAREX-1". Jay Ardai, LDGO; Tom Bordley, NRL (during CEAREX); John Borge, Luftransport; Tom Curtin, ONR; Edgar Depowski, Luftransport; Greg Duckworth, BBN; Ira Dyer, MIT; Rob Fricke, MIT; Nan Galbraith, WHOI; Allan Gill, AE; Chuck Green, Cornell; Peter Guest, NPS; Rob Handy, WHOI; Pat Kelly, NRL (during CEAREX); Neil McPhee, WHOI; Robin Muench, SAIC; Bob Obrochta, ONR; Ken Peal, WHOI; Ken Prada, WHOI; Henrik Schmidt, MIT; Don Spiel, NPS; Dean Stuart, PSC; Matt Valley, JCSAC; Pete Weibe, WHOI.