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1.
Low-frequency ambient-noise measurements in the South Fiji basin 总被引：1，自引：0，他引：1
The effect of wind speed on ambient noise has been measured in an experiment carried out in the South Fiji basin. The noise data in the band 15-250 Hz are well correlated with the variations in the local wind speed. The relationship between noise level N and wind speed ν is expressed by N =B +20n log ν. The constants B and n have been estimated by fitting the data using this model. The analysis indicates that there are two types of behavior: for ν>15 kn, a value of n =1.5 is obtained for the entire band, whereas for ν<15 kn, there is no correlation with wind speed observed in the data. The results suggest that there is a delay of 40-120 min for the effect of wind on the hydrophone noise level 相似文献
2.
The authors study the scattering of monochromatic plane acoustic waves incident at 90° angles relative to the axis of symmetry (i.e. broadside or beam aspect) on solid elastic spheroids. In this analysis, the aspect ratios of the spheroids vary in the range 2⩽L / D ⩽5 in steps of one. The nondimensional frequency kL /2 is kept within the band 2⩽kL /2⩽24. A numerical solution based on a modification of the T -matrix method is generated. The authors generate predictions for the backscattered echoes and graphically display their frequency dependence in order to study the resonance features present within them. In this three-dimensional study, the authors identify the (leaky) Rayleigh-type resonances consistent with those present in infinite cylinders 相似文献
3.
4.
Wimbush M. Chiswell S.M. Lukas R. Donohue K.A. 《Oceanic Engineering, IEEE Journal of》1990,15(4):380-383
A four-year record from an inverted echo sounder deployed near Palmyra Island at 6°N in the central Pacific Ocean is compared with a simultaneous record of subsurface pressure from this island lagoon. A factor m , converting round-trip acoustic travel time to surface dynamic height relative to a deep pressure level, was estimated from the ratio of the spectra of the two records in the energetic synoptic oscillation band. Year-to-year variation in m was not statistically significant. For the overall record, m was found to be -70±8 dynamic m/s, where the error bounds represent a 90% confidence interval. This is consistent with first-baroclinic-mode excitation 相似文献
5.
Sereno T.J. Farrell W.E. Orcutt J.A. Adair R.G. 《Oceanic Engineering, IEEE Journal of》1988,13(4):254-262
The propagation loss from a shallow underwater explosion to a buried vertically polarized seismometer over the frequency band between 3 and 15 Hz was measured during the 1983 Ngendei Experiment. The data was recorded in 5.5-km-deep water in the southwest Pacific with a triaxial borehole seismograph emplaced 50 m within the basaltic basement. It is found that the average power decays as r -3 (r is slant range) beyond 30 km and that the propagation loss is minimal between 6-9 Hz. At shorter ranges, the propagation loss is more complicated and exhibits a stronger frequency dependence. Power in the first water wave is estimated for both buried and ocean-bottom sensors. The ocean-bottom power is approximately 7 dB higher than that recorded by the buried sensor, and both exhibit similar decay rates 相似文献
6.
An acoustic wave scattering model is formulated and solved for three homogeneous layers consisting of a thin solid sediment layer sandwiched by semi-infinite water and solid basalt media. The model is applied to two cases to analyze both the physical parameters affecting reflection loss and the effects of interface roughness scattering. It is shown that effects of attenuation in the sediment layer, especially of S -waves, combine with conversion and scattering processes of the basalt interface to constitute the dominant mechanism of reflection loss, especially in the small grazing angle directions. The scattering process is found not only to produce the well-known acoustic energy loss from specular to nonspecular directions, but also to alter the conversion efficiency between P and S waves with a resulting loss or gain 相似文献
7.
It is possible to localize a nonmaneuvering moving source radiating a constant frequency tone from measurements of the Doppler-shifted frequency at several sensors. Due to the nonlinear nature of the problem, it is necessary to find the solution by grid searches. However, if measurements of the rates of frequency changes are available, the search is only in three dimensions instead of the normal five in source frequency, its x -y positions, and speeds. The validity of combining frequency and frequency-rate measurements is confirmed with simulation studies. The overall system includes a least-squares track-sort algorithm to differentiate the true track from the extraneous track, and a Kalman tracker for the prediction of future source positions, thereby reducing the grid search size. An error analysis relating localization accuracy to uncertainties in frequency measurements and sensor positions is also given 相似文献
8.
北部湾东北部表层沉积物主微量元素空间分布特征 总被引：1，自引：0，他引：1
A multi-index analysis including grain size, major and trace elements is performed on the surface sediments from the northeastern Beibu Gulf to trace the sources of the sediments and to understand the controlling factors for elements distribution. The mean grain size exhibits a wide variation ranging from 0.09Φ to 8.05Φ with an average value of 5.33Φ. The average contents of major elements descend in an order of c(SiO_2)c(Al_2O_3)c(Fe_2O_3)c(CaO)c(MgO)c(K_2O)c(Na_2O)c(TiO_2)c(P_2O_5)c(MnO), while those of trace elements exhibit a descending order of c(Sr)c(Rb)c(V)c(Zn)c(Cr)c(Pb)c(Ni)c(Cu)c(As). On the basis of elementary distribution characteristics and statistical analyses, the study area is divided into the four zones: Zone I is located in the northeastern coastal area of the gulf, which receives large amount of fluvial materials from local rivers in Guangxi and Guangdong, China, and the Qiongzhou Strait; Zone Ⅱ is located in the center of the study area, where surface sediments exhibits a multiple source; Zone Ⅲ is located in the Qiongzhou Strait, where surface sediments are dominated by materials from the Zhujiang River and Hainan; Zone IV is located in the southwest of the study area, where surface sediments are mainly originated from the Red River and Hainan. The statistical analyses of sediment geochemical characteristics reveal that the grain size, which is mainly influenced by hydrodynamics and mineral composition of terrigenous materials, is the leading factor controlling the elementary distribution.Meanwhile, impacts from anthropogenic activities and marine biogenic process will also be taken into consideration. 相似文献
9.
The nature and accuracy of ice-characterization measurements needed to test two microwave backscattering models are clarified by examining the sensitivities of these models to variations in the geophysical parameters they require as input. First, the Bragg, or small perturbation, model for rough surface scattering, which appears appropriate for backscattering from new ice types at L -band, is considered. The sensitivities of this model to variations in the dielectric constant of the ice and to the power spectrum of surface roughness are examined. The dense-medium radiation-transfer model at X -band is considered for backscattering from air bubbles embedded in multilayer ice. The sensitivities of this model to air-bubble size, air-volume fraction, and dielectric loss in the ice are examined. Based on these sensitivities, quantitative characterization guidelines for model testing are discussed 相似文献
10.
《Oceanic Engineering, IEEE Journal of》1989,14(1):17-75
The problem of underwater acoustic scattering from truly composite wind-wave surfaces under zero-gradient conditions (Δc =0) is examined. Here the dominant small-scale component is postulated to be a soliton surface ensemble, produced by the nonlinear wind-wave interactions and associated with the wind-drift surface layer riding on the underlying, mostly large-scale gravity-capillary component of the composite surface. A general bistatic analysis, based on the Kirchhoff approximation, is presented, which includes arbitrary geometries, beam patterns, and general signals. Both low-frequency O(0.2-1 kHz) and high-frequency O(≳3 kHz) signals are considered, and far-field (Fraunhofer) geometries are assumed. Surface Doppler, including Doppler spread and the modulation effects of the large-scale component, are examined. Both forward-scatter and backscatter regimes are considered in the determination of the scattered field and received wave intensities, scattering cross-sections, and coherency measures of surface scatter. Particular attention is given to the high-frequency cases, with small grazing angles, moderate-to-strong mean surface winds, and essentially bubble-free regimes. Recent empirical data appropriate to these conditions are included, which support the soliton conjecture and illustrate the general results. Both coherent and incoherent scattering are examined, along with relevant surface Doppler data 相似文献
11.
河流入海水体悬沙浓度的变化直接反映该流域人类活动和自然应力的影响。基于密西西比河塔伯特兰丁站长期水文资料,本文采用百分位法、Mann-Kendall法等统计方法对近40年密西西比河入海水体悬沙浓度进行分析,探究密西西比河通过“鸟足状”三角洲进入墨西哥湾的水体悬沙浓度变化过程及其可能影响因素。结果表明:（1）在1976?2015年期间,密西西比河入海水体悬沙浓度展现阶段性下降趋势,其中第一时期即1976?1987年期间,入海水体悬沙浓度相对较高,平均值为0.33 kg/m3;第二时期即1988?2015年期间,悬沙浓度较低且平均值为0.25 kg/m3。（2）密西西比河日径流量与悬沙浓度之间的关系符合高斯分布。与1976?1987年相比,1988?2015年期间水沙关系曲线较为扁平,日均超过0.60 kg/m3的高悬沙浓度事件明显减少。在低流量及起动流量阶段,悬沙浓度随着流量的增加而增加,在流量接近20 000 m3/s时,悬沙浓度达到最大值,流量高于20 000 m3/s后,悬沙浓度反而随着流量增加而减小。同时,密西西比河月均水沙关系在1976?1987年期间呈双绳套样,1988?2015年期间则呈现“先沙后水”的顺时针单一型绳套样。（3）分洪工程建设及土壤保持措施是影响密西西比河入海水体悬沙浓度的主要原因。其中,工程建设减少了河道沿程沉积物物源,土壤保持措施使土地侵蚀减少,从而使得悬沙浓度保持较低水平。此外,极端水文事件对密西西比河入海悬沙浓度的影响较小。 相似文献
12.
A microwave technique for the measurement of ocean wave spectra has been compared with wave gauge output during extensive field testing. The method is based on the dual-frequency technique for detecting long ocean waves by matching the modulation of short waves with the beat wavelength between two transmitted microwave frequencies. The new method, however, utilizes three microwave frequencies in order to reduce mean backscatter not related to short-wave modulation. Two prototype scatterometers have been built using three frequencies at L -band and at K u-band. Wave spectra have been measured by both radar systems which, when properly normalized, agree well with simultaneous in situ measurements taken by conventional wave gauges at the pier site. Thirteen sets of spectra have been computed, five of which correspond to a situation in which a local wind sea was generated and then decayed. The present experiment does not demonstrate the directionality of this new technique 相似文献
13.
Chapman N.R. Stinson K. Levy S. Cabrera J. Oldenburg D.W. 《Oceanic Engineering, IEEE Journal of》1988,13(4):215-221
A method has been presented for estimating the elastic properties of sea-floor sediment by inverting the amplitude-range information of precritical reflection data. The method was tested using synthetic data for reflection from a half-space sediment model and the estimates values for the P - and S -wave speeds and the density were in good agreement with the geoacoustic model parameters. The synthetic data were also used to determine the sensitivity of the method to interference from reflections from subbottom layers. In most practical cases the interference is not likely to be a problem for precritical reflection data. The method was then applied to measurements of seafloor reflection obtained in an experiment carried out off the west coast of Canada. The estimated values of the elastic properties of the topmost sediment layer were consistent with values available from the literature, and with estimates from other experiments carried out in the same region 相似文献
14.
曼氏无针乌贼(Sepiella maindroni)繁殖习性及其产卵场修复的研究 总被引：8，自引：5，他引：3
采用对比分析方法,观察了曼氏无针乌贼的繁殖习性,比较了不同产卵附着物的附卵效果,选择典型产卵场(中街山列岛海区)进行附着物的调查。结果表明,曼氏无针乌贼有较高等复杂的性行为,有显著的求偶、争偶及雌雄搏斗现象,乌贼交配对其它乌贼交配有诱导作用;乌贼对附卵基有严格选择,没有充足适宜的附卵基,不仅使乌贼产卵时间延迟、数量减少,而且易被水流冲散、沉入底部致受精卵大量死亡,是影响乌贼繁衍的重要因素;附卵基附卵效果依次为聚乙烯(PE)绳、聚丙烯(PP)绳、钢筋、竹子、木头,颜色依次为黑色、蓝色、红色、黄色,形状依次为圆柱体、正三棱柱体、正长方体、扁长方体,粗度以直径0.25—0.50cm为宜,此外附卵基间应有适当空隙;目前,中街山列岛海区柳珊瑚(Plexaauraa sp.)生物量为0.15—0.64棵/m2,平均生物量为0.32棵/m2,资源数量趋于恢复,但远不能适应乌贼资源修复需要。增殖放流试验表明,修复乌贼资源的可能性很大,但在加大增殖放流工作的同时,必须尽快开展产卵场生态环境修复尤其是产卵附着物修复工作。 相似文献
15.
The distribution of dissolved oxygen in the western Taiwan Strait was discussed by using the method of harmonic analysis. The periodic variation of dissolved oxygen in seawatcr can be expressed by the Fourier series:whereto is annual average value; Am andφm are amplitude and phase of constituent, respectively. The distribution of A0 and the annual and semiannual constants (Am, φm) of dissolved oxygen in the surface, bottom and vertical section of the western Taiwan Strait were described. The effect of the various currents on the distribution of dissolved oxygen was also discussed. 相似文献
16.
-Six cruises were carried out off the south bank of Fujian - Taiwan during the period of December 21, 1987 to November 15, 1988 to estimate the contribution of bacterial biomass carbon (BBC) to the totai particulate organic pools using epifluorescent microscopic technique. The results show that the standing crop of bacteria fluctuated from 0. 95 to 66. 60 mg /m3 (dry weight). Upwelling phenomena appeared in the region around Nanpeng Island in summer while in the region of Waixie in all seasons. The average value of BBC was 27. 60(±6. 08)mg/m3and 21. 32 (±2. 34) mg/m3 respectively. The seasonal and spatial distribution is discussed in relation to environmental factors as well as upwelling phenomena. The role of bacteria in the flow of material and energy in the upwelling ecosystem is emphasized. 相似文献
17.
马氏珠母贝(Pinctada martensii)2个地理群体杂交子代的杂种优势和遗传变异 总被引：1，自引：0，他引：1
采用马氏珠母贝的印度群体(II0)和三亚群体(SS0)的2×2双列式杂交获得了4组子代,II1(II0♀×II0♂)、IS1(II0♀×SS0♂)、SI1(SS0♀×II0♂)和SS1(SS0♀×SS0♂);分析表明,杂交组子代IS1和SI1在壳高、壳长、绞合线长、壳宽、壳重上都表现出杂种优势;IS1在壳宽指数上表现出杂种优势,而在总重和壳重指数上未表现杂种优势;SI1在总重和壳宽指数上表现出杂种优势,而在壳重指数上未表现杂种优势;SI1在壳高、壳长、绞合线长和壳重上的杂种优势较IS1高,差异极显著(P0.01),而IS1在壳宽上的杂种优势较SI1高,差异极显著(P0.01)。应用6个微卫星位点分析4个组合子代的平均FST值为0.357,表明4个组合子代间有较大的遗传差异和较高的分化水平;平均等位基因数依次为SI1(6.17)IS1(6.00)II1(5.00)SS1(4.67),等位基因丰度依次为SI1(5.34)IS1(5.04)II1(4.47)SS1(4.55),期望杂合度(He)依次为IS1(0.55)SI1(0.54)SS1(0.44)II1(0.42),观察杂合度(Ho)依次为SI1(0.52)IS1(0.46)SS1(0.35)II1(0.29),杂交子代的杂合度和遗传多样性高于自繁子代,杂交增加了杂交子代的杂合度和遗传多样性,杂种优势与杂合度和遗传多样性增加直接相关;综合考虑杂种优势与遗传变异的结果,确定三亚野生群体♀×印度养殖群体♂杂交组合作为"珍珠贝育种规划POBs"的主要育种方式。 相似文献
18.
Abundance, variability, and potential grazing impact of planktonic ciliates in the open subaratic Pacific Ocean 总被引：1，自引：0，他引：1
The abundance and variability of planktonic ciliates in the open subarctic Pacific were determined during four month-long cruises in 1987 and 1988. The ciliate community, numerically dominated by relatively small aloricate choreotrichs, was comparable in abundance to communities in a range of oceanic and neritic environments, including waters with much higher average chlorophyll concentrations. Integrated (0–80m) ciliate biomass was typically 100–200mgC m−2, although 3- to 4-fold higher levels were observed on two occasions in spring. Ciliate community biomass, in general, was dominated by large (>20μm width) individuals, although in August 1988 the biomass of smaller cells was as great or greater. The estimated grazing impact of the ciliate community averaged 20% of the primary production. On one instance in May 1988, however, a large biomass of ciliates led to an estimated grazing impact equivalent to 55% of phytoplankton production. While ciliates may be major phytoplankton grazers during sporadic ciliate “blooms”, dino- and other heterotrophic flagellates, which make up the bulk of microheterotroph biomass, must normally be of equal or greater importance as herbivores in this ocean region. 相似文献
19.
Wen Shengchang 《海洋学报(英文版)》1988,7(3):325-343
The method developed by Wen et al. (1988 a) for deriving theoretical wind wave frequency spectrum in deep water is extended to the case of water of finite depth, in which a parameter η=H/d is introduced, where H and d represent the average wave height and water depth respectively. The derived spectra reduce to those in deep water when η=0. The case of η=1/2 corresponds to waves impending to break because of the effect of the bottom. Simplified forms of spectra are given. The theoretical results agree with the observed spectra well. 相似文献
20.
In this paper, a comparison among the seven large meanders of the Kuroshio is made in order to probe into their similarity and differences. The major results are described as follows.1. Although the three phases for the seven large meanders such as their formations, maturity, as well as decline are very similar to one another, each meander has its own trivial difference in detail.2.The paths of the first six large meanders in the mature phase may be classified into ten types: U1, V1, U2, V2, U1', V1', U2', V2',φ and W.3.The seven large meanders may be grouped into two patterns, i. e. , pattern Ⅰ and pattern Ⅱ. Pattern Ⅰ includes the first and the fourth large meanders, and pattern Ⅱ includes the rest of the above meanders.4. Four standards for identifying the large meanders of the Kuroshio are put forward. 相似文献