Accession Number : ADA190253

Title :   Analysis of Central Arctic Noise Events.

Descriptive Note : Master's thesis,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING

Personal Author(s) : Townsend-Manning, Mary

PDF Url : ADA190253

Report Date : Jun 1987

Pagination or Media Count : 186

Abstract : Digital ambient noise data from the FRAM IV experiment of April 1982 were searched for ambient noise transients using a detection program. The time series of the resulting detections were examined visually to categorize each detection as a transient, artifact or false alarm. The transient events were located in space using time delays between signal arrival at different hydrophones. The cross shape of the FRAM IV horizontal array permitted location in both bearing and range. The source strength of each event was calculated using a simple dipole source model. Refraction and scattering of the acoustic path in the Arctic Ocean was taken into account. The overall number of events detected, and hence their interarrival times and spatial density, were all affected by the background ambient noise level. The detection program used the same threshold signal-to-noise level for all data tapes, so when ambient noise level were low more detections occurred. The mean interarrival time between events was 100 seconds. The interarrival time fit a J shaped gamma probability distribution. The number of events detected per area decreased with range from the array center. Half of the events occurred within 3000 meters of the array. In this area there were 0.3 events per square kilometer per hour. The event population showed no predominant angular dependence. The strengths calculated using the simple dipole model had a mean of 430 kN overall and 260 kN during quiet times. Stronger events occurred during times with high ambient noise levels.

Descriptors :   *AMBIENT NOISE, *BACKGROUND NOISE, *TRANSIENTS, *COMPUTER PROGRAMS, ACOUSTIC DATA, ANGLES, ARCTIC OCEAN, ACOUSTIC ARRAYS, ARRIVAL, DATA BASES, DATA PROCESSING, DELAY, DENSITY, DETECTION, DIGITAL SYSTEMS, DIPOLES, FALSE ALARMS, HIGH RATE, HORIZONTAL ORIENTATION, HYDROPHONES, LEVEL(QUANTITY), MAGNETIC TAPE, QUIET, ACOUSTIC REFRACTION, ACOUSTIC SCATTERING, SIGNAL TO NOISE RATIO, ACOUSTIC SIGNALS, SOUND TRANSMISSION, SOURCES, SPATIAL DISTRIBUTION, STRENGTH(GENERAL), THRESHOLD EFFECTS, TIME INTERVALS, TIME SERIES ANALYSIS, ALGORITHMS, LEAST SQUARES METHOD, LINEAR ARRAYS, BEARING(DIRECTION), LOW FREQUENCY, MULTICHANNEL, PEAK VALUES, PACK ICE, UNDERICE, PROBABILITY DISTRIBUTION FUNCTIONS, LOW PRESSURE, SPRING SEASON, THESES

Subject Categories : Acoustics
      Computer Programming and Software

Distribution Statement : APPROVED FOR PUBLIC RELEASE