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This paper presents initial analysis results of ambient noise measurements from an active ice pressure ridge over a 3‐day period in April 1979. The site was a research ice camp 180 miles from the pole in the Eurasian Basin of the Arctic Ocean. The ridge was instrumented with calibrated hydrophones paired in both the horizontal and vertical directions. Their distance from the ridge was about 100 m and their outputs were tape recorded. Dimensional surveys of the active portions of the ridge were made at the surface. Source level linear density is deduced from ambient noise measurements near the pressure ridge by assuming the ridge to be a line source of spatially incoherent point sources. Measured Arctic transmission loss data are used to deduce an active pressure ridge average separation compatable with previously measured omnidirectional ambient noise data statistics for the month of April. The effects of surface/image interference are present in the data and allow a preliminary estimate of acoustic sourc...

Experimental results of acoustic‐propagation measurements made in the Beaufort Deep of the Arctic Ocean in April 1963 are given. Explosive source stations were made by light aircraft at distances of 3, 6, 9.5, 13.5, 26.5, 46, and 115 nm (nautical miles) from a manned camp where the signals from hydrophones in the water and seismometers mounted in the ice were recorded. From these measurements, and from ray calculations based on measurements of water temperature made during the experiment, the following were derived and are presented: transmission loss as a function of frequency, range, the relative energy content of signals from surface‐ and bottom‐reflected rays; the relative effectiveness of hydrophones and ice‐mounted vertical seismometers in detecting underwater sound energy; transmission loss in excess of predicted divergence loss.

While conducting propagation experiments in a shallow water area using the MK61 SUS (Sound, Underwater Signal) at 60‐ft detonation depth and at ranges of 5 to 20 nautical miles, it was noted that the shock wave and the first and second bubble pulses arrived as separate and distinct arrivals in the signal. The limited multipaths in this particular area allowed separate energy analyses of each of the pulses. These energy analyses are compared with Weston's theoretical predictions of source energy flux density. The first bubble pulse energy relative to the shock wave was less, and the second bubble pulse energy was greater, than that predicted by Weston. Sixty feet is considerably above his “critical depth” for a 2‐lb TNT charge and, therefore, in a zone where bubble migration effects reduce the energy of the bubble pulses. Weston cautions that his source level predictions at such shallow depth are inaccurate. A “best estimate” of MK61 SUS at 60‐ft energy source level was derived from a summation of Weston's shock wave energy, which should be independent of depth, and relative measurements of first and second bubble pulse energies.

Water flow around hydrophones and their cables can induce turbulence, flutter, and bounce noises that interfere with measurements of ambient noise at frequencies of 10 Hz or less. Assuming these noises to be uncorrelated at independently suspended hydrophones and with the ocean ambient noise of interest, it is possible to remove their influence from the result of the ambient noise measurement. Two hydrophones can be suspended independently but closely compared to the wavelength of interest, thereby assuring that the ambient noise is highly correlated. The desired ambient noise level will then be given by the covariance of the two hydrophone signals.

Directional, spectral, and statistical properties of the under‐ice noise in the arctic are presented. The measurements were made during a 15‐day period on an ice floe in the Beaufort Basin in April 1963.

Ice pressure ridge activity occurred over a three‐day period in the immediate vicinity of a research ice camp 180 miles from the pole in the Eurasian Basin of the Arctic Ocean in 1979. The ridge was instrumented with both horizontal and vertical calibrated hydrophone pairs at a distance of about 100 m and the acoustic output tape recorded. Dimensional surveys were made atop the ice of the active portions of the ridge. Correlation and spectral analyses were performed which allowed quantitative assessments of source level in the hand 3–1000 Hz. These data, along with previously measured arctic transmission loss, were used to derive a model of pressure ridge area distribution and density by matching previously gathered statistical ambient noise data. The observed ice ridge noise was abundant in fairly long‐lasting tunais as low as 8 Hz attributed to a “slipping clutch” effect. These were the first known quantitative acoustical measurements of a nearby pressure ridge.

A 1983 paper, “Arctic data collection the easy way—Data buoys” [J. Acoust. Soc. Am. Suppl. 1 74, S2 (1983)], presented data buoys as a partial solution to the problems and limitations inherent to manned operations in the Arctic. The present paper describes the successes and failures of these devices, as applied to Arctic underwater acoustics, in the intervening years and what has been done with the large quantities of data that they have generated. This will include wide‐area, synoptic collection of ambient noise level data, as well as first‐ever measurement of low‐frequency propagation during the summertime in the Central Arctic using autonomous cw projector and receiving data buoys. Plans for even more sophisticated devices to be installed in 1988 are discussed. [Work supported by U.S. Navy.]

This paper presents a review of developmental and operational use of Arctic data buoys. There are many problems involved with aircraft and icebreaker logistics for scientific support in the Arctic. Manned research stations on sea ice are expensive, self‐contaminating in terms of acoustic and electromagnetic noise, and generally limited to a 40‐ to 50‐day period in the springtime. Autonomous data buoys, on the other hand, do not suffer those limitations. These devices can be installed by paradrop, aircraft ice‐landing, submarine, or ice‐breaker in almost any geographic area of the Arctic Ocean, peripheral seas, and marginal sea ice zones to collect and report data over all seasons. There are restrictions, of course, as to what can be accomplished automatically within a small buoy hull, and almost all Arctic buoys, so far, have been mechanically passive. Recent advances in low‐power microprocessors and memories enable considerable increases in the extensive in‐buoy processing needed for data compression to accomodate the limited capacities of polar orbiting scientific satellites. [Work supported by U.S. Navy and NOAA.]

Correlations exceeding 50% have been measured between wind speed and under‐ice ambient noise levels in one‐third octave bands. Using barometric data, meteorologists derive geostrophic wind from the atmospheric pressure gradient. The present research involved measuring correlations between the magnitude of the atmospheric pressure gradient and under‐ice noise levels in one‐third octave bands to determine if noise‐prediction models could be developed. Then, one could use meteorological data to generate “isonoise” contour maps for the Arctic Ocean similar to isobaric maps. Barometric and ambient noise data were available from a trio of buoys drifting in the Beaufort Sea for over a year. For one‐third octave bands centered at 3.2, 10, and 32 Hz, correlations with the air pressure gradient magnitude were normally 50% or better. At 1000 Hz the correlation was nominally 25%, a result attributed to higher propagation loss at that frequency and the need for knowledge of pressure gradient on a smaller scale. Predictive models were derived for each frequency for each of the four annual sessions. [Work supported by ONR.]