Distribution of spectral density for underwater noise in the shelf zone of the Pacific Ocean

The results of measurements for the distribution of spectral density for underwater noise in the shelf zone of the Pacific Ocean 21 km from Shikotan Island at the depth of 130 m within the frequency range 1.9–11000 Hz at the wind speed 0–40 m/s are given. Measurements were conducted within the bands of 1/3- and 1/2-octave filters over six months. In the case of a realization length of 33 min and smaller, the distribution of the instant pressure values for underwater noise can be considered normal. The distribution of deep slow variations for the intensity of underwater noise at all frequencies differed from the normal one. The values for the asymmetry parameter and the coefficient of excess are given for the variation distribution of spectral density for underwater noise.     

Correlation characteristics of variations of the ambient noise level in the shelf zone of the Pacific Ocean

Results of measuring normalized autocorrelation functions and frequency correlation functions of slow random variations in the ambient noise levels are presented. The measurements were carried out in the shelf zone of the Pacific Ocean, near Shikotan Island, at a depth of 130 m in the frequency range from 0.9 Hz to 11 kHz. The noise level’s variations were fairly synchronous in a wide frequency range. Their autocorrelation interval varied from 11 to 42 h for different frequencies, and the frequency correlation was no smaller than 0.77 within 2 decades. The integral autocorrelation interval of the wind speed’s variations was 14.1 h.     

Underwater ambient noise in shallow-water areas of the Indian Ocean within the tropical zone

Frequency spectra of underwater ambient noise were measured in the lagoon of a coral atoll, outside the reef, and on shallow-water banks in the tropical zone of the Indian Ocean. The measurements were performed in the frequency range from 0.003 to 9 kHz with the use of self-contained acoustic buoys and a small boat. In all of the regions studied, continuous underwater noise of biological origin was observed with spectral maxima at frequencies of 1–1.5 and 7–8 kHz. In the lagoon of an atoll, this noise was much more intense than regular dynamic noise in the ocean. The maximum noise levels were observed in the first half of night.     

Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean

Beginning in February 1999, an array of six autonomous hydrophones was moored near the Mid-Atlantic Ridge (35 degrees N-15 degrees N, 50 degrees W-33 degrees W). Two years of data were reviewed for whale vocalizations by visually examining spectrograms. Four distinct sounds were detected that are believed to be of biological origin: (1) a two-part low-frequency moan at roughly 18 Hz lasting 25 s which has previously been attributed to blue whales (Balaenoptera musculus); (2) series of short pulses approximately 18 s apart centered at 22 Hz, which are likely produced by fin whales (B. physalus); (3) series of short, pulsive sounds at 30 Hz and above and approximately 1 s apart that resemble sounds attributed to minke whales (B. acutorostrata); and (4) downswept, pulsive sounds above 30 Hz that are likely from baleen whales. Vocalizations were detected most often in the winter, and blue- and fin whale sounds were detected most often on the northern hydrophones. Sounds from seismic airguns were recorded frequently, particularly during summer, from locations over 3000 km from this array. Whales were detected by these hydrophones despite its location in a very remote part of the Atlantic Ocean that has traditionally been difficult to survey.     

Monitoring of anthropogenic acoustic noise in the shelf of Sakhalin Island

The method and results of many days of measurements of acoustic noise generated during installation of the oil and gas producing platform PA-B and construction of an underwater pipeline in the north-eastern shelf of Sakhalin Island are described. Acoustic measurements were carried out simultaneously with the use of five autonomous radio-hydroacoustic stations installed along the coast in a 43 km long line. The measurement objective was to control the level of anthropogenic sounds in a real time scale at the boundary of the coastal feeding area of a unique population of gray whales.     

Spatial correlation of the sound field in an ocean shelf zone

The spatial correlation of explosive signals received by hydrophones lying on the bottom of a shelf zone is studied as a function of the length of the propagation path. The correlation coefficient is found to exhibit quasi-periodic variations with increasing distance to the explosive source of sound. It is shown that the value of the correlation coefficient noticeably increases and its periodic variations practically disappear when the measurements are performed for the signals arriving by individual rays or narrow ray bundles. The low efficiency of a linear horizontal receiving array is pointed out.     

Low-frequency whale sounds recorded on hydrophones moored in the eastern tropical Pacific

An array of autonomous hydrophones moored in the eastern tropical Pacific was monitored for one year to examine the occurrence of whale calls in this region. Six hydrophones which recorded from 0-40 Hz were placed at 8 degrees N, 0 degree, and 8 degrees S along longitudes 95 degrees W and 110 degrees W. Seven types of sounds believed to be produced by large whales were detected. These sound types were categorized as either moan-type (4) or pulse-type (3) calls. Three of the moan-type calls, and probably the fourth, may be attributed to blue whales. The source(s) of the remaining calls is unknown. All of the call types studied showed seasonal and geographical variation. There appeared to be segregation between northern and southern hemispheres, such that call types were recorded primarily on the northern hydrophones in the northern winter and others recorded primarily on the southern hemisphere hydrophones in the southern winter. More calls and more call types were recorded on the eastern hydrophones than on the western hydrophones.     

Long-range sound propagation in the northwestern region of the Pacific Ocean

Results of two experiments on long-range propagation of explosion-generated signals in the northwestern Pacific are analyzed. The propagation paths used in the two experiments substantially differ in both their hydrological characteristics and the conditions of signal reception. On the first path, the omnidirectional reception of explosion-generated signals is performed on the coastal shelf. The initial part of the 850-km-long path crosses the cold Kamchatka current and the continental slope. On the second path, the signals are received near the coastline of the Simushir island with a sea depth of more than 2000 m. The path crosses the Kuril-Kamchatka trough and the frontal zone formed at the boundary between the cold Kuril-Kamchatka current and the warm Kuroshio current. The intensity characteristics of the sound fields on the paths, the time structure of the signals, and the phenomena that arise when the path crosses the continental slope and the frontal zone are considered. The results obtained from analyzing the experimental data are compared with computer calculations.     

西太平洋蒸发波导的时空统计规律研究

海洋蒸发波导自然现象对近海面电磁波的传播有重要影响,获取大面积海域蒸发波导的长时间统计分布规律,对于海上雷达、通信、制导等电磁系统的设计与应用,具有重要意义.针对现有单点局部观测方法的缺点,建立了基于美国环境预报中心再分析数据的大面积海域蒸发波导统计特性计算方法,利用太平洋气象浮标数据、北部湾海岛气象观测数据对分析方法的正确性进行了验证.利用该分析方法和最近18年的美国环境预报中心再分析数据,重点研究了西太平洋蒸发波导的统计规律,获得了蒸发波导高度在不同海域、不同月份的分布特性,建立了空间分辨率约为18 关键词： 蒸发波导 再分析数据 电磁波 统计特性     

西北太平洋副热带模态水区域声传播特性*

西北太平洋副热带模态水(STMW)是在西北太平洋夏季出现的温跃层中温度、盐度和密度具有垂向均一性的水团。由于西北太平洋副热带模态水(STMW)的存在,深海声速剖面呈现出双跃层结构,对深海远程声传播产生较大的影响。本文对比分析了西北太平洋副热带模态水(STMW)区域夏冬两季典型声速剖面环境下的声传播规律。分析结果表明,夏季声速剖面环境下,声源位于浅层声道宽度内时,声传播为浅层声道的类深海声道传播与会聚区传播的复合形式。掠射角较小的声线被限制于浅层声道中,增加了会聚区内的到达结构,并且增强了在影区的声能量,在第二影区内的传播损失比冬季声速剖面环境下最多低近60dB。本文推导了浅层声道的截止频率的近似表达式,分析结果表明,截止频率主要由浅层声道的宽度和正梯度段的声速差值决定,夏季STMW区域浅层声道截止频率主要集中在100Hz左右。     

Effect of tide on sound propagation in the shelf zone of the Sea of Japan

Experimental and numerical studies of the effect of surface and internal tides on 315-Hz sound waves propagating along fixed paths, 260 m to 23 km in lengths, oriented across the shelf of the Sea of Japan, are discussed. The measurements are performed using self-contained radio-hydroacoustic receiving stations, which are equipped with hydrophones and scalar-vector receivers, and two vertical acoustic-hydrophysical measuring systems. For the sound signals propagating along the longer paths, the intensity fluctuations are shown to loose their linear relation to the tide-caused changes in the waveguide parameters because of the refraction by the sound speed inhomogeneities induced by different hydrodynamic processes. However, it is established that the phase variations can serve as quantitative indicators of the integral changes in the waveguide parameters.     

Acoustic effects caused by high-intensity internal waves in a shelf zone

The sound field fluctuations caused by high-intensity, solitonlike, quasi-plane internal waves crossing a fixed acoustic path at different angles are numerically modeled for natural conditions of the shelf zone of the Sea of Japan. The horizontal refraction of sound is considered for the case of an acoustic path parallel to the internal wave front.     

Low frequency deep ocean ambient noise trend in the Northeast Pacific Ocean

Concern about effects of anthropogenic noise on marine life has stimulated new studies to establish present-day ocean noise levels and compare them to noise levels from previous times. This paper reports on the trend in low-frequency (10-400 Hz) ambient noise levels and presents measurements made using a calibrated multi-element volume array at deep ocean sites in the Northeast Pacific from 1978 to 1986. The experiments provided spectral noise levels as well as horizontal and vertical noise directionality. The data presented here provide evidence that the trend derived from 1960s data extended to around 1980, but has since continued at a lower rate.     

Experimental studies of low-frequency reverberation on the continental slope in the northwestern Pacific Ocean

Experimental data obtained on the continental slope near the Kamchatka peninsula for the reverberation at the frequencies 230, 600, and 850 Hz in the cases of coincident and spaced source and receiver of sound are presented. The data include the dependences of the reverberation level on time for both directional and omnidirectional receiving systems, as well as the dependences of the reverberation level on the duration of the probing pulses and on the sea depth at the source site. It is shown that, at the frequency 230 Hz, a substantial contribution to the reverberation is made by the reflection and scattering on the shelf near the coastline and in the region of the “depth drop.” At the frequencies 600 and 850 Hz, the predominant mechanism is bottom and surface scattering in the region of the continental slope.     

Generation of Underwater Noise by the Rip Zone of a Large-Amplitude Internal Wave in the Ocean

Acoustical Physics - The article discusses the results of measuring underwater noise generated by a large-amplitude solitary internal wave based on observations made near the Mascarene Ridge in the...     

Monitoring of anthropogenic noise on the shelf of Sakhalin Island during seismic survey research

The paper describes the technique and gives the results of acoustic-noise and seismoacoustic-signal-parameter measurements on a northeast shelf of Sakhalin Island, generated during seismoacoustic research at the licensed Chaivinskii site. The aim of measurements was acoustic control of the water area round an emitting vessel. Results of field measurements and 3-D simulations of seismoacoustic signal propagations on sea and land are presented.     

反向传播神经网络的太平洋海域温跃层反演*

温跃层是反映海洋温度场的重要指标,针对太平洋中东部海域复杂多变的水文情况以及传统温跃层分析模式的局限性,本文基于BOA_Argo历史网格,通过BP神经网络,建立温度剖面的经验正交系数与海面遥感数据、少量深度处海水温度之间的非线性映射关系,实现海洋垂向温度剖面的实时反演,最后利用垂向梯度法获得海洋温跃层的相关参数。实验结果表明,相比于传统方法,该方法反演得到的跃层深度与测量值更加吻合,其中上层深度平均反演误差从10.3m下降到5.7m,下层深度平均反演误差从16.8m下降到8.8m。     

Acoustic tomography of dynamic processes in a sea shelf zone with the use of complex signals

Experimental data are presented on the use of single receiving and transmitting systems in acoustic tomography of dynamic processes in a shallow sea. The experiments are based on the use of the transmission tomography and opposite-direction sounding with complex phase-manipulated signals. The original data are those obtained by the authors in 1990–2000 on the shelf of the Sea of Japan near the Gamov Peninsula, in the vicinity of the acoustical-hydrophysical experimental site of the Pacific Oceanological Institute. A possibility of using combined transmitting-receiving systems (transceivers) for monitoring the temperature and fields of currents in the ocean is demonstrated.