Acoustic recording locations near Northstar Island, Beaufort Sea, Alaska, 30 August, 1, and 17 September 2000; 10 and 12 August 2001; 5, 6, and 12 September 2002; and 11 August 2003. Northstar Island is shown as a white square, the CIDS caisson as a gray diamond, the NE DASAR as a black triangle, and the recording stations as filled circles. The station numbers indicated refer to Table I .
Sealift barge 400 carrying two process modules, upon its arrival at Northstar Island’s southern dock on 10 August 2001. The Ocean-class tug Navigator can be seen alongside the barge on one side.
(a) Broadband levels of underwater sound for 14 types of island-related vessel (mainly tugs and crew boat) activities, as a function of distance from sound source. Data are split into three broad categories. (I) Sounds during arrival at Northstar of three sealift barges (August 2001, blue circles), specifically (1) arrival of barges 420 and 411 with three accompanying tugs; (2) barge 411 and tug, bow aspect; (3) barge 400 and tug, stern aspect. (II) Sounds during tug activities, consisting mainly of holding and maneuvering barges at the Northstar dock during various operations (August 2001, red triangles, and August 2003, black crosses): (4) River-class (RC) tug pushing on barge while ocean-class (OC) tug is standing by. (5) Two tugs idling (one RC and one OC). (6) OC tug pushing on barge while RC tug is standing by. (7) RC and OC tug maneuvering a barge and (8) holding it in place during offloading of equipment. Two other tugs were present but were standing by, idling. (9) Tugs holding barge 420 immediately preceding the offloading of a compressor module and (10) during the offloading. Four tugs (one OC and three RC) were present but usually only two were working at any point in time. (11) Point-class (PC) and RC tugs holding a gravel barge during reconstruction of the island’s gravel berm. (III) Crew vessel sounds (September 2002, squares), specifically (12) crew boat arriving (bow aspect); (13) crew boat leaving (stern aspect); and (14) hovercraft (from Blackwell and Greene, 2005 ). The logarithmic regression model shown was fitted to recording (3) only (R is in meters, see text). (b) Broadband levels of underwater sound as a function of distance from Northstar, while vessels were present or absent at the island. Line colors indicate the vessel types involved: sealift tugs (red), fuel transfer vessels and a self-propelled (SP) barge (black), a self-propelled barge alone (blue), or no vessels present (green). Data collected on 30 August, 1 and 17 September 2000; 10 and 12 August 2001; 5 and 6 September 2002. For comparison, levels for the island-related vessel activities [Fig. 3(a) ] are also shown in gray shading.
Variability in broadband levels of underwater sound at fixed locations as recorded continuously by the near-island CH [(a), (b)] and the NE DASAR [(c), (d)] during periods in September 2001 and 2002. In (c) and (d), black diamonds indicate sound spikes created when the acoustics crew’s vessel approached the DASAR instrumentation for servicing.
Broadband levels as recorded by a cabled hydrophone, located north of Northstar, for two days in September during each of 2001 and 2002. Light-gray shading shows periods corresponding to the scheduled daily crew boat trips (14 in 2001, 8 in 2002, see text). In 2001, five pairs of crew boat runs (i.e., a total of 10) were close enough in time that their periods overlap. Dark-gray shading with diamond symbols shows periods corresponding to the arrival and departure of the daily barge and associated tug.
Propagation loss as calculated using boat-based recordings from 2000 and 2002. The logarithmic spreading loss model [Eq. (1) ] was fitted to broadband levels of underwater sound. Filled and empty symbols indicate measurements made with and without boats present at Northstar, respectively. See text for rationale for excluding some data points.
Underwater sound-pressure density spectra near Northstar, with diesel versus gas turbine generators, and away from the island. The black and dark gray lines show spectra for the quietest periods in 2001 and 2002, respectively, as recorded by the cabled hydrophone (CH) near the island (frequency range ). The island’s primary power was provided by a diesel-powered generator in 2001 versus a series of Solar gas-turbine generators (of which two were generally running) in 2002. The light gray line shows spectra for a representative sample obtained from Northstar on a quiet day (6 September 2002), during boat-based (BB) recordings (frequency range ).
Underwater sound-pressure density spectra during production, with and without drilling, 5 September 2002 (range ). Received spectrum levels for the black and gray plots are to be read on the left and right axes, respectively. Broadband levels shown are for the frequency range .
Percentile sound spectral densities of underwater island sound versus frequency , as recorded by CH in (a) 2001 at range and (b) 2002 at range . Six days of data were used each year. Spikes of boat sound (see Fig. 5 ) were removed from the analysis. The statistical spectra in each graph are based on the number of measurements shown in the lower left corner. See text for details.
Underwater narrow-band spectra of vessel sounds near Northstar. (a) Sound-pressure density spectra of an Ocean-class tug (at ) and a crew boat (at ). (b) Percentile sound spectral densities of underwater sound from vessels versus frequency, as recorded by a cabled hydrophone in 2002. Data in (b) consist of the boat-affected segments (215 samples) excluded from the analysis in Fig. 9(b) ; otherwise, they were analyzed and plotted as in Fig. 9 .
Broadband A-weighted levels of in-air sound as a function of distance from Northstar and presence of boats. Filled and empty symbols indicate measurements made, respectively, with and without boats present at Northstar. All recordings were made north of Northstar except for a transect east (E) of the island on 12 August 2001.
Airborne sound-pressure density spectra of island sounds, as recorded from a near and distant station on 6 September 2002. Broadband levels shown are for the frequency range , unweighted.
Sampling date and direction from Northstar , station ID, distance from , water depth, sea state, and mean wind speed for all acoustic recording locations, open water seasons 2000–2003.
Broadband (10–500 and ) percentile levels of underwater sound and from Northstar Island in 2001, 2002, and 2003, in dB re: . The near-island sound levels were obtained using a cabled hydrophone (CH) located from Northstar or a DASAR (NS) located from Northstar. The distant sound recordings were obtained using a DASAR (NE) located about northeast of Northstar.
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