Technical Report No. 210 036040-6-T PRELIMINARY REPORT ON THE COOLEY-BIFI EXPERIMENT by Richard M. Heitmeyer Peter W.Wood Approved by; __________ _. Theodore G,. Birdsall COOLEY ELECTRONICS LABORATORY Department of Electrical and Computer Engineering The University of Michigan Ann Arbor, Michigan for Contract No. N00014-67-A-0181-0032 Office of Naval Research Department of the Navy Arlington, Virginia 22217 October 1971 Approved for public release; distribution unlimited.

ABSTRACT An underwater acoustic propagation experiment was jointly conducted by NUSC at New London, Connecticut and a team from Cooley Electronics Laboratory at The University of Michigan. A special pseudo- random waveform, complement phase modulating a carrier was transmitted continuously for 58.5 hours. The power and angle of the carrier, the power in the sidebands, and the noise power in the signal bandwidth were recorded continuously during this time. In addition, the total power and the power spectrum in a narrow band about the carrier were recorded as a measure of the forward scattering reverberation. Also, the cross-correlation of the received signal with a stored reference was continuously computed in order to examine the multipath structure and its stability. This report presents a brief description of the experiment and the on-line analysis of the results. 111

ACKNOWLEDGEMENTS The work described in this report is the result of cooperative research conducted jointly by The University of Michigan and the U. S. Navy. Signal processing was performed by the Stochastic Signal Processing Group of Cooley Electronics Laboratory (CEL), University of Michigan under the direction of Dr. T. G. Birdsall. Activities of this group are sponsored by Code 468 of the Office of Naval Research. The BIFI range is operated by Code 2211, Ocean Sciences Division of the New London Laboratory, Naval Underwater Systems Center (NUSC/NLL) under the direction of Mr. W. R. Schumacher. The data were taken as a part of the continuing shallow water research program being conducted by NUSC/NLL supported by NAVSHIPS OOV1L Exploratory Development program. The authors wish to acknowledge the work of many individuals in both groups whose enthusiastic support made successful completion of this test possible. The most significant single task encountered in preparing for the test was the writing, testing and documentation of the real-time computer program used for data acquisition and analysis. The overall chore fell to Kurt Metzger of CEL with several major program segments being provided by Dr. Birdsall. iv

The signal processing scheme employed requires highstability reference oscillators at the transmitting and receiving locations. The oscillators and associated synthesizers were provided by NUSC and were adjusted and tested over an extensive period by Mr. Hans Arens of E-71, Federal German Republic, an exchange engineer presently working at NUSC/NLL. His skill and care resulted in frequency stability which was a full order of magnitude better than had been anticipated. The coordinator of the joint test for NUSC was Mr. Bernard Sussman. His untiring efforts and knowledge of the facilities were crucial factors in successfully dealing with problems as they arose. Many others played an important part in preparations for, and conduct of, the test. Among these are Brian Barton of CEL who prepared materials for the test, Mrs. Ann Fulmer who assisted in documentation of programs and who has typed this report and Messrs. Carl Milner and Pete Trask of NUSC who monitored the transmitting equipment at Block Island. Messrs. Hector Bernier and Hans Arens of NUSC cooperated in the data taking phase. v

TABLE OF CONTENTS Page ABSTRACT iii ACKNOWLEDGEMENTS iv LIST OF ILLUSTRATIONS vii LIST OF SYMBOLS ix CHAPTER I: THE COOLEY-BIFI EXPERIMENT1 I. 1 The BIFI Range1 I. 2 The Transmitted Signals 7 I. 3 The Equipment Configuration 10 I. 4 Quantities Measured 12 I. 4. 1 Power and Angle Measurements 12 I. 4. 2 Surface Reverberation Measurements 16 I. 4. 3 Multipath Arrival Measurements 17 CHAPTER II: THE RESULTS OF THE ON-LINE ANALYSIS 18 II. 1 Power and Angle Measurements 18 II. 2 The Surface Reverberation Measurements 50 II. 3 Multipath Arrival Measurements 50 REFERENCES 57 DISTRIBUTION LIST 58 vi

LIST OF ILLUSTRATIONS Figure Title Page 1 The BIFI range 3 2 Bottom profile 5 3 Sound velocity contours 6 4 A complement-phase modulated signal 7 5 The RMS spectrum of a complement-phase modulated signal for L = 15, D = 8 9 6 The Cooley-BIFI experiment equipment configuration 11 7 The frequency response of the digital processing filters 14 8 Sideband signal-to-noise plot for the 400 Hz 19signal 23 9 Sideband signal-to-noise plot for the 127 Hz signal 24 10 Unity gain plot for the 400 Hz signal 2731 11 Unity gain plot for the 127 Hz signal 32 12 Constant gain plot for the 400 Hz signal 3438 13 Constant gain plot for the 127 Hz signal 39 14 Angle plot for 400 Hz signal 4146 15 Angle plot for 127 Hz signal 47 vii

LIST OF ILLUSTRATIONS (Cont.) Figure Title Page 16 Sideband signal-to-noise summary plot 48 17 Unity-gain summary plot 49 18 Successive multipath pictures taken 100 seconds apart between 2249 and 2318 on 10 Sept 70 using the 400 Hz signal transmission 51 19 Successive multipath pictures taken 100 seconds apart between 0653 and 0721 on 10 Sept 70 using the 400 Hz signal transmission 52 20 Successive multipath pictures taken 100 seconds apart between 1044 and 1112 on 11 Sept 70 using the 127 Hz signal transmission 53 21 Multipath stability plot 56 viii

LIST OF SYMBOLS C carrier power measurement S sideband power measurement N noise power measurement S actual received sideband power A N the noise power passed through the sideband processing filter (S/N) the sideband signal-to-noise ratio f carrier frequency D number of cycles of carrier per digit of the modulating sequence d duration of the modulating sequence digit L number of digits in the modulating sequence T period of the transmitted signal zAf the frequency separation between the lines in the spectrum of the transmitted signal B frequency spread under the main lobe of the power spectrum of the transmitted signal B the tooth bandwidth in the digital processing filters m B the bandwidth of the reverberation processing filter r ix

CHAPTER I THE COOLEY BIFI EXPERIMENT An underwater acoustic propagation experiment was jointly conducted by NUSC at New London and a team from the Cooley Electronics Lab at The University of Michigan at Ann Arbor. This experiment is an extension of project MIMI propagation and signal processing research. During the week of 7 September 1970 approximately 58. 5 hours of reception were taken and analyzed on-line at the BIFI range of NUSC. The analysis was performed by Mr. Peter Wood and Dr. Richard Heitmeyer using the Cooley Measurement Package in the MIMI Field-8 data acquisition and signal processing equipment. In addition to the on-line analysis, about 1. 5 million digital words of reception at intermediate stages of processing were recorded for later processing at CEL. This report presents a brief description of the BIFI range, the experiment, and some of the on-line analysis. A more complete report is planned. I.1 The BIFI Range The material in this section is taken from Ref. 1. A more complete discussion on the BIFI range can be found there.

-2Location and Facilities The BIFI range, illustrated in Fig. 1, is part of the New London Laboratory of the Naval Underwater System Center located at New London, Connecticut. It extends from Block Island (BI), Rhode Island to Fisher Island (FI), New York, a distance of 18.6 nautical miles, and to Watch Hill Point, Rhode Island, a distance of 12 nautical miles. The Cooley-BIFI experiment used only the BI to FI portion of the range. The transmitting site for the BIFI range is located on Block Island. Bottom mounted, omnidirectional projectors are located at point S (Fig. 1) and connected to BI by cable. The projectors used were a 400 Hz Minneapolis-Honeywell source with a bandwidth of 70 Hz and a source level of 89 dB/1 pLbar/l yard, and a 127 Hz Minneapolis-Honeywell source with a bandwidth of 25 Hz and a source level of 106 dB/1 pbar/1 yard. The receiving site used for the experiment is located at Fisher Island. A bottom- mounted DT- 5S hydrophone located at point H1 in Fig. 1, and connected to FI by submarine cable, was used for the experiment. This phone was approximately three feet off the bottom at a depth of 1 50 feet. Both the transmitting site and the receiving site are connected to the BIFI laboratory at NUSC by telephone lines. A telephone line to the transmitter site at BI was used in the experiment to provide

72 50' 40''NEW LONDON F!'&:s 10'_ECP ____,_ __C;<'l' IBLOCKISLAND Y<> |u - ACOUSTIC RANGE Fig. 1. BI range. o 0 Nauticl Miles 7 50o' l' —--- --- Source: USL Tech Memo 2211-281-68 Fig. 1. BIFI range

-4voice communications between BI and the BIFI lab at NUSC. To transmit the received signal from the hydrophones at FI back to the BIFI lab for processing, a 15 kHz B.W. telephone line was used. Oceanographic and Acoustical Characteristics The BIFI range is a shallow water range. From BI, the water depth drops to 110 feet in about one mile. It stays at that depth for approximately 10 miles and then becomes irregular over the remaining distance to FI. The composition of the bottom is soft mud and sand from BI, becoming progressively more rocky as FI is approached. The bottom profile is shown in Fig. 2. The general character of the velocity gradient for the BIFI range depends on the season. In summer, the velocity gradient is negative resulting in mostly bottom reflecting paths. In winter the velocity gradient is slightly positive and the paths become mostly surface reflecting. Iso-velocity contours for both summer and winter are shown in Fig. 3. Summer conditions were presumed to hold for this experiment. Previous work by NUSC predicted the propagation loss in September at the frequencies of interest would be approximately 90 dB at 127 Hz and 110 dB at 400 Hz.

-5or SOURCE 50 l loo. y 150-HYDROPHONEs,.. 200 x. 250 -.2 I I I 20 15 10 5 0 DISTANCE FROM SOURCE, MILES Source: USL Tech Memo 2211-281-68 Fig. 2. Bottom profile, Block Island to Fishers Island

uj ~ —FISHERS ISLAND — ^^^^^^^^^ BLOCK ISLAND-. WINTER I ------ I ___ I ____ I ______ I I I 27 2421181512963 30~~~~~~ LU ^-FISHERS ISLAND SM MER BLOCK ISLAND_-.30 24 21 18 15 12 9 6 3 0 DISTANCE (KILOMETERS) 5B Source: USL Tech Memo 2211-281-68 Fig. 3. Sound velocity contours (M/S) block island sound 10 1506~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~................................. Z520~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~............. \~ ~ ~ ~ ~ ~~~~~~~~~~~~~~........................ ~~~~~~~~~~~~~~~ so ~ ~ ~ ~ ~ ~ ~ ~ ~............................ O ~ ~ ~ ~~ ~~~~.~~~~~~~i~~~~~~-:i~~~~~~~~~~~~i~~~~~~ri~~~~~~~~~iliii ~.................................................................................... SUMMER BLOCK ISIAND~~~~~........................................................................................................................... 8................... k slan d soun

-7I.2 The Transmitted Signals Two different signals were used for the Cooley-BIFI experiment. Each of these signals consisted of a linear-maximal binary sequence, complement-phase modulating a carrier. The phase of the carrier is either +45~ or -45~ depending on the value of the binary digit in the modulating sequence. A portion of such a waveform is shown in Fig. 4 where: f carrier frequency d duration of the sequence digit D number of cycles of carrier per sequence digit. +1 d=D/f C -I (a) 1 I1/fC (b) Fig. 4. A complement-phase modulated signal (a) a portion of the modulating waveform (b) the resulting transmission

-8Both of the signals used in the experiment had an integral number of cycles per digit D. The signals are periodic with period T given by T = L d = LD/f where L is the number of digits in one period of the modulating sequence. For the two signals of interest in this experiment f = 400 Hz c D =8 d = 0.02 sec L = 31 T = 0.62 and f = 127 Hz c D =8 d = 0.063 sec L = 15 T = 0.945 The bandwidth, B, (frequency spread under the main lobe) and the spectral line spacing, Af, for the two signals are (see Fig. 5).

-9f + l llll,.ll 111 I.. Il I Fig. 5. The RMS spectrum of a complement-phase modulated signal for L = 15, D = 8

-10for the 400 Hz signal B = 100 Hz Af = 1.61 Hz and for the 127 Hz signal B = 32 Hz Af = 1.06 Hz The number of spectral lines between the first two zeros is 2L-1, and the fraction of the total power in the carrier is 2 21 I. 3 The Equipment Configuration The configuration of the equipment used in the Cooley-BIFI experiment is shown in Fig. 6. The signal generating equipment at the transmitting site, and the signal processing equipment at the receiving site were provided by Cooley; the source, hydrophones and frequency references were supplied by NUSC. Stability of the frequency reference was investigated by H. J. Arens and reported in Ref. 2. Both references are more stable than I part in 109. The different components in Fig. 6 function as follows. The output of the frequency synthesizer at the transmitting site is a sine wave at a frequency equal to 4 x f. This signal is converted to a square wave reference, at the same frequency, by the phase-locked function generator. The resulting square wave is then used as a clock

BLOCK ISLAND Reference * Oscillator Reference * GR 1161* Oscillator Synthesizer I Frequency* C ounter Hickock Mod I CRO 5000 FLD oGR 1161 * 4x carrierDisplay Cmpur Clock Synthesizer frequecn Scope I o_______ 0^ Input (A DEC model\ Phase-Locked PDP8/L with 4 x carrier frequency Functio expanded ca- I Generator pabilities) | Int Input G Teletype (used as 1/3 octave filter I Igt l _______3_____0 _____0 j Digital o Modulator (LMSG) |I-~ -- -- -- -| ~~~~B.P. [ * NUSC system components FISHER ISLAND Filter 15 kHz data line* (passive) o System components being furnished by Cooley Laboratory Amplifier * Amplifier * System r Hydrophone Transducer System Fig. 6. The Cooley-BIFI experiment equipment configuration

-12to the digital modulator whose output, after filtering, is the signal described in the preceding section. This signal is amplified and then transmitted down the BIFI range. It is received at Fisher Island and sent over phone lines to the NUSC lab. At the lab it is first filtered with a 1/3 octave filter and then processed by the FIELD-8 computer. 1.4 Quantities Measured The measurements made in the Cooley-BIFI experiment fall into one of three categories: (1) power and angle measurements of the received signal, (2) measurements of the surface reverberation effect, and (3) measurements of the multipath arrivals. Each set of measurements is computed and recorded every 100 seconds. For the 400 Hz signal, each set of measurements is computed on the basis of approximately 80 seconds of data and for the 127 Hz signal each set of measurements is computed on the basis of approximately 60 seconds of data. I.4.1 Power and Angle Measurements. C Power. The C power measurement is a measure of the power present in the carrier of the received signal transmission. It is determined as that power passed through a digital processing filter with a frequency response as illustrated in Fig. 7a. The bandwidth of this filter, B, depends on the signal transmitted. In particular

-13B =0. 013 Hz for the 400 Hz transmission m and B =0.016 Hz for the 127 Hz transmission. N Power. The N power measurement is a measure of the noise power contained within the main lobe of the received signal spectrum: f - B/2 < If l < f + B/2. It is determined as that power passed c - - c through the digital processing filter with a frequency response as illustrated in Fig. 7c. Such a filter is often referred to as a comb filter. It is to be noted that each tooth in the comb filter of Fig. 7c is centered midway between the spectral lines in the signal spectrum. Moreover, the bandwidth of each tooth is B, the same B as used for the carrier power measurement. S Power. The S power measurement is a measure of the signal power within the main lobe of the received signal power spectrum, excluding the carrier power. It is determined as that power passed through the digital processing filter of Fig. 7b. This filter is recognized-as a comb filter with a tooth missing at the carrier frequency. The remaining teeth are aligned with the line frequencies of the transmitted signal. The bandwidth of each tooth is also B m Sideband Signal-to-Noise Ratio S/N. The sideband signal-to-noise ratio is a measure of the signal-to-noise ratio of the output of the

-II-B' f1 m f f c (a) A ^B m (b) Ld f f (b) -~I I Bn, -~) l-Ld Af f Af C 2 c 2 (c) Fig. 7. The frequency response of the digital processing filters (a) carrier power filter, (b) sideband power filter, (c) noise power filter

-15sideband processing filter of Fig. 7b. This quantity is not measured directly, although it can be related to the measurements as follows. Denote the actual sideband power at the output of the sideband processing filter by S watts and denote the actual noise power at the output of the sideband processing filter by N watts. Let the noise power out of the noise processing filter be denoted by N. Then S = 10 log10(S+N) (1) and N = 101og10 (N) (2) so that S-N = 10 log (S + Except for statistical fluctuations and the effect of one missing tooth in the sideband processing filter, N and N are equal. Therefore S- N 10 log10 ) (3) The output sideband signal-to-noise ratio, S/N, is inferred from S- N using (3) whenever S > N. The input sideband signal-tonoise ratio is 20.8 dB below this for the 400 Hz signal and 18.1 dB below for the 127 Hz signal.

-16Carrier Angle (A). The carrier angle is a measure of the relative difference between the phase of the output of the carrier processing filter (Fig. 7a) and the phase of the local reference oscillator (Fig. 6). 1.4.2 Surface Reverberation Measurements. The effect of surface reverberation is to scatter some of the power of a transmitted frequency into sidebands on either side of that frequency. It is felt that this scattered power should lie between 0.1 Hz and 0.4 Hz on either side of the transmitted frequency, depending upon the spectrum of the surface waves. For the signals used in the Cooley-BIFI experiment, the spacing between the lines in the power spectrum is large enough so that the sideband line frequencies do not interfere with the power scattered from the carrier frequency. Thus, the surface reverberation effect can be measured by computing the power spectrum of the received signal in a bandwidth B centered about the carrier line. The bandwidth B is chosen large enough to include the power scattered by surface reverberation but small enough to exclude the power in the sideband line frequencies. In particular, B was taken as 0.8 Hz for the 400 Hz signal and 1.06 Hz for the 127 Hz signal. In addition to calculating the reverb power spectra, the total power in the bandwidth B minus the carrier power was calculated for each data set.

-171.4.3 Multipath Arrival Measurements. The crosscorrelation function between the demodulated received signal and a pulse- compression reference was used to measure the multipath structure of the channel. In the absence of noise, this function has a triangular peak of width, 2d, centered at the arrival time of each signal path (mod T) with an amplitude proportional to the amplitude of the signal transmitted over that path. This is the same as if a single large one-digit pulse had been transmitted once every T seconds and received through a matched filter. As a measure of the time stability of the channel multipath structure, the zero-delay cross- correlation coefficient between the demodulated received signal and the replica was calculated for each data set. When this coefficient fell below a set value, indicating a marked change in the multipath structure, the current signal became the replica and the new multipath picture displayed. Otherwise, the previous replica and display were held. The changing magnitude of the correlation coefficient is an indicator of how fast the multipath structure is changing.

CHAPTER II THE RESULTS OF THE ON-LINE ANALYSIS In this chapter the results of the on-line analysis of the 58.5 hours of the Cooley-BIFI data are presented. Of the total data, 56. 5 hours of data were taken using the 400 Hz signal transmission and 2 hours of data were taken using the 127 Hz transmission. During the 400 Hz signal transmission, the experiment was interrupted twice, with the result that the largest portion of uninterrupted 400 Hz measurements was 41.75 hours. II.1 Power and Angle Measurements This section contains plots of S- N, the three powers S, C and N and the carrier angle as continuous functions of time. (The continuity is obtained by a linear interpolation between successive data points.) The different powers appearing in these plots are expressed in decibels above an arbitrary reference and the carrier angle is expressed in terms of the number of cycles relative to the phase of the reference oscillator. A plot of S- N and N power for the 400 Hz signal appears in Figs. 8a - 8e and the corresponding quantities for the 127 Hz signal are illustrated in Fig. 9. Both of these plots include two additional vertical scales, one for the output sideband signal-to-noise -18

B/F/ S-IV PLO 1?MCE EDTI Fig. 8. Sideband signal-to-noise plot for the 400 Hz signal (a) BIFI S-N plot 1 (a) BIFI S-N plot 1

S-AS-seA ^~~~~~~~~~~~~~~~~~a V IA Am WV r^ iAA sA I 9- -z~0St~-gb B/Fl S-/v PLOT Z 9 SCPT 70 400 /Z CMP MODE Z "~~~~~~~~~~ F /100 ILCO /300 %*00 A5M 1600 17000 *00 (90 tZ YM1E ~?DT Fig. 8(b). BIFIS-Nplot 2

s s \ \ \' t I, iA I,i -P APU A r ~i^ f I I _ - -- I —- - -- - — I — 1 1 4 /tl~ t) 1 1 B/F/ S-A/ PLOT 3 i I too woo0 oooo o0o o i0 0wo wojo o 00 Qoow6 00 0700 aeoo 9oo ja TIME EDT Fig. 8(c). BIFB S-N plot 3 Fig. 8(c). BIFI S-N plot 3

TIfiE ED T |o Fig, BII S-N plot 4!!...,' ywt A. I'S'' i ~, i. / 3 ar..-' - oo 21X Fig. 8(d)BnI I'H- pLo 44 JO SEPT 70 4o0 HZ CwP MO!~ A A' 9 /W,' 1300 Ii.0 t. HOO SO0 I00. IlO0 180 0t f~00f'-':-" Fig. 8(d). BIFI S-N plot 4

I" NOISE- 70 Da J B/ / S-/ PLOT /0 SEPT 1/ SEPT 70 400h#f c *o41002 2400 Z300 000 W O 0o00 oo0 o 040o 050 7 00 0800 900 o "T/fE E DT Fig. 8(e). BIFI S-N plot 5

1! ~T 7'90-0 no NO zoo' 0, I V! ),.._8 I/ SEP 70 /Z ZCIP10, 4:0 0~.1000 1100 /ZOO.o00 T/ME E D7 Fig. 9. Sideband signal-to-noise plot for the 127 Hz signal

-25ratio S/N and one for the input sideband signal-to-noise ratio. The relation between these quantities and S- N is discussed in Section 1.4. 3. It is noted that key correspondences are S - N = 0 dB — > S/N = -c dB S - N = 3 dB -- S/N = 0 dB and for large S/N S - N S/N When the S- N measurement drops below zero, the scale relating S/N to the sideband signal-to-noise ratio S/N is not valid. The most important feature to be noted from Figs. 9 and 10 is that S- N only occasionally takes on values large enough to indicate a significant sideband signal component in the reception. Part of the signal degradation is due to the very large bursts of N power that occur frequently during the course of the experiment. (Most, if not all, of these bursts of N power can be attributed to the local shipping noise.) The remaining signal degradation is the result of the relatively large amount of propagation loss on the BIFI range.

-26Figures 10a - 10e plot S power, C power and N power for the 400 Hz signal transmission and Fig. 11 plots the same quantities for the 127 Hz transmission. These plots are referred to as the unity-gain plots since the vertical scaling is determined as if the processing filters in Figs. 7a - 7c all have gain equal to one at the peak of each tooth. In Figs. 10 and 11 it is noted that, in general S (sideband power) is greater than or equal to N (noise power) even during the bursts of shipping noise. This is a consequence of the fact that the S measurement consists of not only the true sideband power S, but also the component of noise N where N 10 log10 N A second feature to be noted in Figs. 10 and 11 is that, unlike the S (sideband power) measurement, C (carrier power) is only slightly affected by the bursts of shipping noise. This is reasonable since the noise passed through the single tooth C power processing filter (Fig. 7a) is only a fraction of the noise passed through the S multi-tooth comb filter (Fig. 7b).

~ICv F'o,4 14 ocru VEz r,,y. 8 SEPT 9 SEPr 700 Z400 CfP MOODE 2 2z z00 O 300ao oreo o Soo o 00 00000 0- OOO: oo o00o o T/IE iDT Fig. 10. Unity gain plot for the 400 Hz signal (a) BIFI unity gain plot 1

SIDEBAMD NO/SE /m/OT: NtOSE AND SIDeBAND COOEC7TO FOR 1/3 OCTAVE F uLT.R B/IF U/NITY GAIN PLOT L 9SEPT 7400 WZ CMP MAfO~E 2 O0 //00 A1,0 /00 14WO 1500 1600 /700 1/00 1900 ZOOO o00 — D i.. I i i Fig. 10(b). BIFI unity gain plot 2

SIDE*ANO CR l 8a 11 1 t~ QE. NA||~ nHovE: N/Se. NDSiDE& AMP CORAECMD0 FM I/3 O CAVE ril. req B/ /N IN7Y GAIN PLOT 3 9 SEPT 10 SEPT 70 400 HZ CMP'OwE2!oj0 zso 000 ooo ooo ao5o oto s'o a0o0o 0700 cow OM9 7rAME rLT Fig. 10(c). BIFI unitygainplot3

QQ /1 kI 1 Abm MW AN SIKMA.0'CORECM (iynF WPi 1\A II I ij OFir 1 I I I -I' I I I i 4 Io SE~~r 70 400 hIIZ c~~fP MOM Z. NO/SC~ ~ ~ ~ ~ i 000 j/4 I tD /it""' 14,0fmn^ Mo i6 10 8 O 20 O ^v-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/ -CARR(R? 0,bre: Ksf AD S/icep CORRECTD FOR 1/3 OCT4VIE utino 58/FI UM7Y GA// RPOT 4 1 OS(Pt 70 400 6Z ClIP MOOA. Z oo (100 Ioo 3o 3o1400 IctX) 16')3 /C /8w) o 190oo LIoo zWao';77M~ Eifr Fig. 10(d). BIFI unity gain plot 4

CARRIER O7 KO1Sf( AWS OCAVEAb CORRICtLD 60- FOR:/s oNos V~ /nx nt~fI BI/Fl UNITY GA / PLOT S. 10 SCPT II SEPT 70 400 xZ CMP MOD( 2.......! *I_ -i- I...i IJ!J —,,,-,,,. -.~L 2z00 z300 0000 /oo o0t 0o 030 4o. 0QSOO o0600 Of00 00 0900 tOO TF/ME EDT Fig. 10(e). BIFI unity gain plot 5

AO.~~~~~~~~~~~~~~~ A.A P 3C I ISIDES $~~~~~L / i Sl 90- hA NO/St r3 I~~~~~~~~~~~~~~~~~~~~~~I B/F/ /A'7Y GAIN PLOT I/ SEPT 70 /Zi7 #Z CWP MODE 4 _____________ t ______ I ______m_____ —--— _______ —---- 2 ------ I ------------ I -— I - 0900 1000 oo00 /200 1300 TIME EDT Fig. 11. Unity gain plot for the 127 Hz signal

-33Figures 12a - 12e and Fig. 13 again plot S power, C power and N power for the 400 Hz and 127 Hz transmission respectively. The vertical scaling on these plots, however, is determined as if the product of the power gain and the bandwidth of the processing filters of Fig. 7 is constant. This scaling is equivalent to adding a constant gain to the C power plot for both signal transmissions. This additive gain is 20. 9 dB for the 400 Hz and 17.8 dB for the 127 Hz signal transmissions. The resulting plots are referred to as "constant gain-bandwidth" plots. The constant gain-bandwidth plots are best suited for illustrating the behavior of the C power measurement. In Figs. 12 and 13 the large amount of variation in C power relative to the variation in S power is apparent. This behavior can be modeled by viewing the ocean as a time varying narrow notched filter. The C power fades occur when the notch passes through the carrier frequency line. The S power, however, remains relatively unaffected by the motion of the notch if the notch bandwidth is modeled to be only a small fraction of the total signal bandwidth.

CARRIRv I - 9SESPT la9 4~f' 70 ~00 AIZ CMP CfODE 2 cEM' ~ ~ ~ ~ ~ TME Z \I Fig. 12l Cosplot for the 400 Hz signal. () BI onstant gn pot 00gain-bandwidth (a) BIFI constant gain-bandwidth 1

70A91f CO#ST GTAW-BA HDDTH 2 9 SCPr 70 400 HZ * CMP #AOA Z /O~d~ LIP6 AW OM Jew MOYI O too* /74W A900 19W 1 zl 21o o O aw iwo~~~~fe> Two iiw~~~~~w ~^ /roi~~~~twsaw ciiw~o PT 70400P Fig. 12(b). BIFI const. gain-bandwidth 2

IAV - CARRIER ~~s r S I P~~~a~~n/DN'cnSIA M A I~~~~~~~~~~~~~A 70OB/Fl CO/AvS GA/I- BAANDW/DrYIh 3.9 SEPT 10 5rPr'70 400 HZ crP MM0 Z0 zzWo 1 200S V" OO OO' -am 00 0X 0 90 090 0O Fig. T2(c). BIFI const. gain-bandwidth 3 Fig. 12(c). BIFI const. gain-bandwidth 3

AOl _ I I BI/F COW5Tr GA// BA WIYTH 4 0/ SEPT 70 400 HIZ CA/P MOE Z /0000 1/0 Oo 500 0 O /600 0 900 zo o zo h/0o TIME E.DT Fig. 12(d). BIFI const. gain-bandwidth 4

w-~~~~~~~~~~~9'IAO WI~ ~ A~ ^ &3-~~~~~~~~~~~~~~~~~~1 78/P CONVST GAIN BAIVNDWIDTH 5S 10 /OSEPT / SEPT 70 400 /i CMP MODE Z 200 z2300 0000 M0/00 OLO 0300' 0o400 0500 000 0700 OO 0900 77TIME EDT Fig. 12(e). BIFI const. gain-bandwidth 5

41\~ tf^'"\CARRIER K~~~~~~~~~~~~~~ 14 ~~-SIS/DT8AND 9i 0 70; B/F/ CO/S7: GAIN-BANDW/0ID7 / SEPT 70 17 /(Z C$P MfVoDE C900 1000 1/00 Arc00 TIME EDT Fig. 13. Constant gain plot for the 127 Hz signal

- 40The last quantity measured in this group of measurements is the carrier phase angle. The carrier phase is plotted in cycles (relative to the phase of the reference oscillator) against time for the 400 Hz transmission in Figs. 14a - 14e and the 127 Hz transmissions in Fig. 15. The feature that is most important in these plots is the stability of the carrier phase. A "rapid" change of the order of one cycle per hour at 400 Hz (such as 0330 - 0530 on 9 September 1970) indicates a stability of 1 part in 1. 44 x 106, or a frequency shift of.00028 Hz. Thus for signal processing of CW the BIFI area is very similar to the Straits of Florida. The excellent stability lends great credulity to the very small fluctuations that do occur. Both the major maxima and major minima are separated by approximately 12 hours, indicating a probable tidal cause. This cyclic behavior is more apparent in Fig. 14f in which carrier angle is plotted against a compressed time scale. The significant parts of the sideband power measurements for the Cooley-BIFI experiment are summarized in Figs. 16 and 17. Figure 16 consists of an S- N plot of those portions of the data for which S- N exceeded 6 dB for extended periods of time. Figure 17 consists of the unity-gain plot of the same data.

9 3 -6b B/if A/CLE PLOT 1 _, - 8 SEPT7 95EPT 70 40 vz CMP foo0f z L -- ----- ~ ----— ______ L _____ t ______ I ____.... I!.a... I1. I.... -I 2WO 2300 00000 0 0'0 0300 4 30 OO S0 OOO 0700 060 0900 MWi T/M~E LO7 Fig. 14. Angle plot for 400 Hz signal (a) BIFI angle plot 1

96 -, (0 B/Ft ANGLE PLOT r? ^. SOOT 70 s400 fZ CtlP MODEC F I1 _ II_____IJ.__ I _ L - - -- - - /000 f00 /Moo /3o0 1400 MO /600 /0 0900 00 0 0 w20n 77M ELOT Fig. 14(b). BIFI angle plot 2

963 _ XI B/F/ A/VCLE P LOT J 9 9 SEPT I /O SEPT 70 400 oZ C P MOD 2 tOO O230 0000 0/00 tozoo ao0 0400 0QO00 0600 0700 0800 C09 TI/ME ei7 Fig. 14(c) BIFI angle plot 3

94NB/Fl AA/GLF PLOT 4 d00o AZ CMFP MODt Z jo S 7Pr 70 100 1100 /Z00 000 /400 WO /600 /700 *00 1800 2OOO a100 zo2 TIAE tOT Fig. 14(d). BIFI angle plot 4

9, 3 -3 a8ir/ ANGLE PLOT S -9 10 SEPT 11 SEPT 70 4V00 H COlO 2oor Z I- - -I. —-..- l -i —,.. —-i4 liZ C AIf Z i_ 2200 z3.W0 o000 ooo oMo o300 04o00 osoo o 00 0700 o000 0900 oo 7-TIME DT Fig. 14(e). BIF angle plot 5

Cycles 9 6 3 -6 -9'-9 I I I I I I I 1 I I I I I I I I I I I I I I I I I I 1 i I I I I 1 1I I I I I I I 1 I I I I I I 1 I I I.. 2400 1200 2400 1200 2400 9 Sept 70 10 Sept 70 TIME Fig. 14(f). Angle summary plot, 400 Hz

(n, PI 81-Ff A/VCLE PLOT./1SEPT 70 /A 7 HZ CM MODE.4 0900- 1000 1100 j700o 1300 TINE EAP Fig. 15. Angle plot for 127 Hz signal

I~~~~~~~~~~~~~~~~~~~~~~~~~~~ -.. ~....... ~~~~~~~~~~~ ~.:.............'"' CD~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~7 0~~~~~~~~~~~~ ~:t* —t-i:f: -ft... 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CD~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~7 ----- ----- ----— ~ ~ ~ ~ ~ ~i-li-:-L_~.,.;2',-+~ -~' ~~~~~~~~~~~~~~~~~~~~~~~..............................................-.:.-'."-':-:-..~I-1:;- — I -........... — -9*2~ ~~~~~~~~~~~~~I 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -8 —1 —------ ------ - -- -- --- ~ ~ ~ ~ ~ ~ ~ ~ l~-~t ~ CL~~~~~~~~~~~~~~~r'~;-~~~+=~~ -- ------- al~~~~- -C~ r r...............~r i -i-'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-49-.-..:.:..-'..................-.:_........?.: _ _.'.:;:.... -::_-_- -, I;.:.:::::;::::::::::: ~~~~~~~~~~~~~......!:: -- -:..._:::-~::::.:: 7.77 T —., ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~-;~ ff i i i i~ ~ ~~~~~~~~~~~ ~~~~~~~~~~.-.~::.~,:~.:.'.T?':.;:.::_:......:'. -,_..: L"'~::::::::::::::::: _.,, ___':'::............ ~.... -:::'........ 7 -— j-._:_I -71:-~~~~~~~~~~~~~~~~~~~~~~~~~~~t -1~ +'i --- 7t...... ~ +............t'-7 7777777777~~~~~~~~~~~ —-~~,i: --; 7: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~' 7 —( 1 k4r............,: 77r - 7~ —t —..~............ I...... H i l -_l!...t --; - — T T 4-~~~~~~~~~~~~~~~~~~~c — ~ — -4. ~~-:7~~~~~~~~~~~~~~ +FF 441 —F -~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~~~ ~H~H~H~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ — L -iLt ~~

-50A final note: during the 127 Hz transmission, the level of the received signal was decreased approximately 20 dB at about 1058 on 11 September. This attenuation has been compensated for on all of the power plots by adding in a 20 dB gain after 1058 of 11 September. II. 2 The Surface Reverberation Measurements The on-line analysis does not indicate a significant surface reverberation effect. The reverb power measurements appear to consist only of the normal amount of noise in the reverb bandwidth as do the reverb spectra displays. It should be mentioned that the lack of significant reverberation effect measurement might be attributed to the exceptionally calm sea that prevailed during the course of the experiment. II. 3 Multipath Arrival Measurements The multipath measurement consists of the multipath pictures and the correlation coefficient. Figures 18, 19 and 20 illustrate three sequences of multipath pictures taken at different times during the course of the experiment. Each picture is the envelope of the pulse compression filter output (the magnitude of the cross-correlation between the demodulated received signal and the pulse- compression reference, see Section I. 4.3). Successive pictures in each sequence were taken 100 seconds apart. The time axis for each picture is indicated by tick marks. These tick marks are separated by a time equal

UOTSSTIusujt I-e1Ut.S ZH 00nf aq:ulsn 0L61 aqualdas OT uo 8Tgg puB 6g ua^aq aedev spuooas OO Ua3Oe saJnloTd q4edTlnIu aATssaooanS 8T i spuooos O'O *" - - SPUODas 0 -0 - spuooas goO - - *_bsM.1..:;,;~":':';......... \:,: _._. * * - \-;.v0<,tBb vS. \ ^^ ^.. *... *.L - b.. * -....,.'*: ~;'^ * -. ~. ~ ~ ~ ~ ~ ~ o ~~~.* —:, —............... ~ * -,-:..:.-.,,%....... - -. *; * * 6~7t,72,7;; - ^^_. r.::^4% ~..-'...4::';.,~.a.,~..o o o e o o o o o

uoTSSTUusUrjTl IU&S ZH 00} ~qtI Su1sg 0L61 J/aqualdag 0oi uo 1ZL0 Put C90 uaaAcq l:a.td spuooas 001 uawp sanj:i:d ql'dlijntu aATssaOOnS 6T'6It spuoOas gO'0 spuooas go *0.;..."............ LO....'' -'......*....'...........'.... -.L0 P...................."'.. *....... */* ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ *~ 81TL 0 1%........'............' ~ ~.. *...*.. *.. ~%< ee ~ ~ *. TI,' *~~~~~~~~~~~~~~~~~~~~''"'"' ~.. ~ *'~.* %: ~.~~~~~~~ ~.~....~.: k'0^^ ^^^ /'.'^.*~-,'^-^>^^''........,*d*~'....''' J........... do-~~~~~~~~ *" s\'... 90 ^;^.^\^f/^^ -. ^ -*^. —^*^ ~S 90~~~~''^'^^ ^ ^'.\' *^^^ ~ o * ~ e j~~~~~~~~aa~~~~~~ ~ a -gs-~~~~~~~~~~~~~~e

-53EDT EDT: **..*0 *..0....................... * 0* ~. -.....'.... 1.044 *. "- - *... *.-. *.* 0. 063 seconds 0~~~~~~~~~~~~~~~ * 0. 063 seconds Fig. 20. Successive multipath pictures taken 100 seconds apart between 1044 and 1112 on 11 September 1970 using the 127 Hz signal transmission

- 54to the digit duration in the modulating waveform. Figures 18 and 19 were taken during the 400 Hz transmission so that the time between tick marks is 0. 02 seconds. Figure 20 was taken during the 127 Hz transmission so that tick marks are separated by 0. 063 seconds. The vertical scaling in the multipath pictures is not the same for each picture but may differ by a factor of a power of two from picture to picture. Thus, it is not necessarily true that an arrival peak in one multipath picture is greater than the corresponding arrival peak in another picture. The multipath pictures in Fig. 18 were taken between 2249 and 2318 on 10 September 1970. As can be seen from Figs. 8e and 12e, both the sideband signal-to-noise ratio and the C power were large and relatively stable during this period. The multipath pictures in Fig. 19 were taken twelve hours earlier between 0653 and 0721 on 10 September 1970. By referring to Figs. 8c and 12c, it is seen that again both the sideband signal-to-noise ratio and C power are relatively large. In this case, however, the C power suffers a deep fade between 0711 and 0718 with the lowest value of C power occurring at 0715. It appears from Fig. 17 that the correspondence of this deep carrier fade on the multipath pictures is, at most, a slight instability. Detailed investigation of the multipath phase structure is called for. The multipath pictures in Fig. 20 were taken between 1044

-55and 1112 on 11 September 1970 during the 127 Hz signal transmission. The temporal spacing between the tick marks is about three times as great as for the 400 Hz transmission, that is the resolution for the 127 Hz transmission is about one-third that for the 400 Hz transmission. At the 127 Hz frequency, at least two and sometimes three strong arrival paths appear, each arrival being separated by about.09 seconds. The multipath correlation coefficient for delay T = 100 sec is plotted in decibels against time in Fig. 21 between 2300 and 0500 on the 10th and 11th of September. The poor signal-to-noise ratio at the processor output during most of this period precluded any attempt to study multipath behavior vs. time.

It t <,, —- o txo,. (co^0 ttr/o, co.) t.ou\^-~yo tMA (OWrw POWt //mmse pow_ fyI\ f K AY B/Fi MULIT/PATH STABILITY PLOT 10 JS~PT 1 SEPT 70 4oo00...... _.... I I - * I I I L I X _ Z300 0000 0/00 WO 00 OJ300 0400 TIME EDT Fig. 21. BIFI multipath stability plot

REFERENCES 1. R. W. Hasse and W. R. Schumacher, BIFI Shallow Water Program, USL Tech. Memo No. 2211-281- 68, December 4, 1968. 2. Frequency Stability of External Frequency Standards to be used in BIFI Experiments by University of Michigan in Sept. 1970, Memo from Hans J. Arens, to Code 2211, dated 21 September 1970. -57

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Security Classification DOCUMENT CONTROL DATA - R & D Stecurity classification of title, body of abstract and indexing annotation must be entered when the overall report is classified). ORIG (INAT! NG ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION Cooley Electronics Laboratory Unclassified University of Michigan 2b. GROUP Ann Arbor, Michigan 48105 3 REPORT TITLE PRELIMINARY REPORT ON THE COOLEY-BIFI EXPERIMENT 4. DESCRIPTIVF NOTES (Type of report and.inclusive dates) Technical Report No. 210 -- 036040-6-T AU THOR($S (First name, middle initial, last name) Richard M. Heitmeyer and Peter W. Wood 6 REPORT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS October 1971 76 2 8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR*S REPORT NUMBER(S) N00014-67-A-0181-0032 036040-6-T b. PROJIECT NO c. 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned this report) d. __________________________ TR210 10. DISTRIBUTION STATEMENT, Approved for public release; distribution unlimited. 1. SUJPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Office of Naval Research Department of the Navy l _____________________________________ Arlington, Virginia 22217 13. ABSTRACT An underwater acoustic propagation experiment was jointly conducted by NUSC at New London, Connecticut and a team from Cooley Electronics Laboratory at The University of Michigan. A special pseudo-random waveform, complement phase modulating a carrier was transmitted continuously for 58. 5 hours. The power and angle of the carrier, the power in the sidebands, and the noise power in the signal bandwidth were recorded continuously during this time. In addition, the total power and the power spectrum in a narrow band about the carrier were recorded as a measure of the forward scattering reverberation. Also, the crosscorrelation of the received signal with a stored reference was continuously computed in order to examine the multipath structure and its stability. This report presents a brief description of the experiment and the on-line analysis of the results. DD FOR 1473 (PAGE ) S/N 01 01-807-681 1 Security Classification A-314

Security Classification 14. LINK A LINK S LINK C KEY WORDS I ROLE WT ROLE WT ROLE WT Signal processing Acoustic propagation Underwater sound propagation IS DD IFNORMve1473 (BACK) S/N 0101-807-6821 Security Classification A- 31409

UNIVERSITY OF MICHIGAN 3 9015 03026781111 111 IIeI 03026 7812e nd