UNCLASSI FIED AD ARMED SERVICES TECHNICAL INFORMI AlIMGTON HALL STATION RLIN 12, VIRGINIA AGENCY UNCLASSIFIED

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1 UNCLASSI FIED AD ARMED SERVICES TECHNICAL INFORMI AlIMGTON HALL STATION RLIN 12, VIRGINIA AGENCY UNCLASSIFIED

2 NOTICE: Ihen govermment or other dawings, specifications or other data are used for any purpose other than in connection with a definitely related gover nt procurement opation, the U. S. Government thereby incurs no responsibility, nor any obligation whatsoever; and the fact that the Govezn ment may have formulated, furnished, or i any way supplied the said drawdngs, specifications, or other data is not to be regarded by implication or otherwise as in any manner licensing the holder or any other person or corporation, or conveying any rights or permission to manufacture, use or sell any patented invention that ma a any way be related thereto.

3 ONARRA9SANSETT MARINE LABDORA TORY * A"IDUATE SCHOOL OF O'CEANOGRAPHY UVERSITY OF RHODE ISLAND leference No ACOUSTICS PROJECT The Relation~ship Between Wind Speed And Shallow Water Ambient Noise by F, T, Dietz, J, S, Kahn and Wo 0, Birch LI A KINGSTON, RHODE ISLAND NO OTS

4 GRADUATE SCIHiOL OF OCEANOGRAPHY NARRAGASTT MRINES LAMMATAORY University of Rhode Wsan Kingston, Rhode Islanid I Reproduction of the, material contained in tisi report in whole or in paa't la permitted for any plzrpose of the United States G6ornment., RefeenceNo. 8- ACOUSTICS PROJECT The Relationship Between Wind Speed And Shallow Water Ambient Noie by Frank T, Dietz, J, Steven Kahn and William B. Birch Technical Report No. 8 Approved for Distribution -jb A. Knauuu, Deoan Off ice of Naval Research Contract Nonr-300( 04) NR Januaary, 1963

5 K45 FOURTH ONNTRNATIONAL!CONARES ft ACOUSTIC$ COPE NIHAGEIN AUGUST 1962 THE RELATiONSH i BETWEEN WIND SPE-ED AND SHALLOW WATER AMBIENT NOISE Frahk T. Diettj J. Steven Kahn, and Wi fiab ai. *ifch universi ty of Rhode isl. i nd, Kingston,.I. Duering the Jierlod from Odetobei 1958 through September I'95-9; the University of Rhode Istand supported by the Office Of Naval Research, made a systematic series Of, afibi-ent noise Spectrum deteurml ations in the o wer West Passage of Narragansett Bay, Rhode Island. This body of water extends h a northmsouth directi.dk and, in the viciflity of th6 hydrophohe linstal lation, 1s approxilmately one mile In width. It is bounded on the west by the mailand and on the east by in Island. The mid-channel depth is 40 a 50 feet. The purposes of the measurement progrm were to study the characteristics of the ambient noise and to deteiiiine possilible correilations between the noise and certain envionmentat factors, such as: wind speed, wind! direction, wave height, rainfall :, and tldal currents. In order to acco plish this a sampling Scheduie was devised which called for a total of 864 spectrum deterfiinatirons over the course of a year. Readings were made each month durling two weeks chosen at random wi th-in the month. During each of the two weeks, two days of the five weekdays and one of the two weekend days were se+ ]ected at random. Further, each of the three sampl ing days was divided inito six equally spaced hour groups, and two spectrum determinations 4ere made Writhin each of the hour groups at times chosen at random. Thus, the acoustic spectrum was measured twelve times per day, three days per week, two weeks per month. This resulted in seventy-two spectra per month. The receiving system consisted of a Brush Type AX-58C hydrophone, with preample- 'let, supported one foot above a silty-sand bottom In forty feet of water approxinately 900 feet from the west shore of the bay. The signals from the hydrophone were amplified and frequency analysed by a Bruel and Kjaer Spectrum Analyser on a onemthlrd 3ctave basis and recorded :by a B & K Graphic Level Recorder. The recorder was opersted at a paper speed of I mm/sec and approximately 1.9 min. were required to scan the spectrum between 40 cps and cps. Calibration was accomplished by injecting a random noise signal Lnto the hydrophone preamplifier and recording it, after it passed through the complete system, on the same paper tape as the sound slpctrum, This procedure allowed the determination of the average spectrum levels associated with nineteen selected frequencies, distributed over the frequency band, to be made in under ten minutes. Acoustic and environmental information were entered in IBM punch cards and procassed with the aid of the CoMputation Centers at Brown University and the University of Rhode Island. Significant correlations between ambient noise and the environmental variables were found for wind speed, rainfall, and tidal currents. The effect of wind on the sea surface in our locality is a coip iex nel and no attempt has been made to present any correlations between ambient noise and sea state. Tidal currents influence the noise spectrum below 100 cps and are likewise omitted from this presentation. This paper is concerned with some of the relationships between wind speed and ambient noise. Wind speed and direction measurements were obtained from a Bendix- Friez record-ing anemometer mounted fifteen feet above the water surface and approximately 900 feet from the hydrophone. The results to be presented are based on a tot al of 651 spectrum determinations. Of the original 864 spectra, 213 were excluded frm the a-ayses be--as -of the presence of rainfall or the presence of ship nd bioiogical noise.

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