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: abb@arctic.mit.edu

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: kvdh@polar.whoi.edu

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: eks@polar.whoi.edu

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.