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1.
The water gun is a relatively new marine seismic sound source that produces an acoustic signal by an implosive rather than explosive mechanism. A comparison of the source characteristics of two different-sized water guns with those of conventional air guns shows the the water gun signature is cleaner and much shorter than that of a comparable-sized air gun: about 60–100 milliseconds (ms) for an 80-in3. (1.31-liter (I)) water gun compared with several hundred ms for an 80-in3. (1.31–1) air gun. The source spectra of water guns are richer in high frequencies (>200 Hz) than are those of air guns, but they also have less energy than those of air guns at low frequencies. A comparison between water gun and air gun reflection profiles in both shallow (Long Island Sound)-and deep (western Bermuda Rise)-water settings suggests that the water gun offers a good compromise between very high resolution, limited penetration systems (e.g. 3.5-kHz profilers and sparkers) and the large volume air guns and tuned air gun arrays generally used where significant penetration is required. 相似文献
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V. A. Lazarev A. I. Malekhanov L. R. Merklin V. I. Romanova V. I. Talanov A. I. Khil’ko 《Oceanology》2013,53(6):755-761
Experimental results of the seismic profiling with bottom penetration up to 1000 m based on broadband signals and conducted in the Caspian Sea sites are presented. Use has been made of synchronized sequences of probing pulses with linear frequency modulation at a frequency deviation of 50 to100 Hz. The pulses were emitted by a towed sound source of an original design (acoustic power up to 300 W, frequency ranged from 100 to 1000 Hz) and received by a standard digital seismic streamer. The processing of the signals involved the matched filtering of the individual pulses and the trajectory accumulation of a long sequence of pulses lengthwise the horizontal-homogeneous reflecting layers of the bottom structure. The adaptive stacking procedure taking into account the linear inclinations of the individual layers allowed us to enlarge the stacking interval by up to 100 pulses and to increase the effective depth and the spatial resolution of the seismic profiling, which gave us a total increase of more than 30 dB in the S/N ratio. In our view, the seismic profiling using low-power (about 100 W) and broadband (up to several hundred Hz) coherent sound sources represents a promising technology for decreasing the hazardous impact on aquatic ecosystems. The approach developed is an alternative to the conventional technology of marine seismic prospecting based on powerful pulse sources of the shock type (air guns, sparkers) in the low frequency range (less than ～200 Hz). 相似文献
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针对水声信号所处环境复杂、背景噪声源多的特点,提出了一种基于JFET的超低噪音放大电路,该电路选用两片低噪音的场效应管2SK170作为第一级放大器件,经过CR高通滤波连接到同相放大电路,整体电路增益可达70dB;为进一步提升接收信号信噪比,结合双T滤波器特点优化设计出一种高Q值选频电路;通过Multisim14仿真表明,设计的电路在1 Hz处的电压噪声密度仅为2.4 nV/Hz0.5,滤波器Q值可达25.6,结合实际电路测试结果表明,设计的电路能够满足水声测量要求。 相似文献
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A. A. Mishenin S. I. Kosyakov S. N. Kulichkov 《Izvestiya Atmospheric and Oceanic Physics》2016,52(6):606-614
The possibility of estimating the parameters of surface pulsed sources from data on acoustic waves recorded in the atmosphere is studied. Experimental values are given for peak pressure P + of recorded acoustic signals, wave-profile area S + in their positive phase, and length t + of this phase, and the approximations of these parameters are obtained within wide ranges of source energy 10–3 < E < 1010 kg TNT and scaled distances 1 < R/E 1/3 < 4 × 104 m/kg1/3. Conventional methods of estimating the acoustic energy E according to data obtained from acoustic measurements in the atmosphere are analyzed, and ways to improve their accuracy are proposed. The influence of the type of explosions on the parameters P +, S +, and t + of acoustic signals at long distances R/E 1/3 > 500 m/kg1/3 from explosions is shown. 相似文献
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Mjelde Rolf Fjellanger Jan Petter Digranes Per Kodaira Shuichi Shimamura Hideki Shiobara Hajime 《Marine Geophysical Researches》1997,19(1):81-96
A 140 km long wide-angle seismic profile has been acquired by use of 6 Ocean Bottom Seismographs across the Jan Mayen Ridge, North Atlantic. The profile was acquired twice; once with a traditionally tuned standard source and secondly with a somewhat smaller source tuned on the first bubble pulse. Analysis of the frequency content of the data reveals that the single-bubble source within the 10-15 Hz frequency range generates a signal with a level about 5 db above that of the standard source. These differences can partly be related to differences in airgun depth. The higher output level for these frequencies enables the single-bubble source to resolve intra-crustal structures with a higher degree of certainty, when compared to the data acquired by use of the standard source array. The standard source seems to generate slightly more energy for frequencies around 6 Hz, probably due to the use of a large 1200 in/sup3 gun in this array. These low frequencies a re of importance for mapping of lower crustal and upper mantle structures, and it is recommended that this is taken into account when seismic sources for mapping of deep crustal and upper mantle structures are designed. 相似文献
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Results obtained from simulating the propagation of infrasonic waves from the Chelyabinsk meteoroid explosion observed on February 15, 2013, are given. The pseudodifferential parabolic equation (PDPE) method has been used for calculations. Data on infrasonic waves recorded at the IS31 station (Aktyubinsk, Kazakhstan), located 542.7 km from the likely location of the explosion, have been analyzed. Six infrasonic arrivals (isolated clearly defined pulse signals) were recorded. It is shown that the first “fast” arrival (F) corresponds to the propagation of infrasound in a surface acoustic waveguide. The rest of the arrivals (T1–T5) are thermospheric. The agreement between the results of calculations based on the PDPE method and experimental data is satisfactory. The energy E of the explosion has been estimated using two methods. One of these methods is based on the law of conservation of the acoustic pulse I, which is a product of the wave profile area S/2 of the signal under analysis and the distance to its source E I [kt] = 1.38 × 10–10 (I [kg/s])1.482. The other method is based on the relation between the energy of explosion and the dominant period T of recorded signal E T [kt] = 1.02 × (T [s]2/σ)3/2, where σ is the dimensionless distance determining the degree of nonlinear effects during the propagation of sound along ray trajectories. According to the data, the explosion energy E I,T ranges from 1.87 to 32 kt TNT. 相似文献
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Development of a System for 3D High-resolution Seismic Reflection Profiling on Lakes 总被引：2，自引：0，他引：2
A high-resolution three-dimensional (3D) seismic reflection system for small-scale targets in lacustrine settings has been
developed. Its main characteristics include navigation and shot-triggering software that fires the seismic source at regular
distance intervals (max. error of 0.25 m) with real-time control on navigation using differential GPS (Global Positioning
System). Receiver positions are accurately calculated (error<0.20 m) with the aid of GPS antennas attached to the end of each
of three 24-channel streamers. Two telescopic booms hold the streamers at a distance of 7.5 m from each other. With a receiver
spacing of 2.5 m, the bin dimension is 1.25 m in inline and 3.75 m in crossline direction. To test the system, we conducted
a 3D survey of about 1 km2 in Lake Geneva, Switzerland, over a complex fault zone. A 5-m shot spacing resulted in a nominal fold of 6. A double-chamber
bubble-cancelling 15/15 in3 air gun (40–650 Hz) operated at 80 bars and 1 m depth gave a signal penetration of 300 m below water bottom and a best vertical
resolution of 1.1 m. Processing followed a conventional scheme, but had to be adapted to the high sampling rates, and our
unconventional navigation data needed conversion to industry standards. The high-quality data enabled us to construct maps
of seismic horizons and fault surfaces in three dimensions. The system proves to be well adapted to investigate complex structures
by providing non-aliased images of reflectors with dips up to 30°. 相似文献
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An unexplained result of broad-band transmission experiments made more than ten years ago by DeFerrari in the Straits of Florida (center frequency ~500 Hz, bandwidth ~100 Hz, water depth ~200-m, range ~20 km) is that the measured pulse response functions failed to show the expected multipath replicas of the transmitted pulse and instead were smeared into a single broad cluster (duration ~50-~350 ms) in which the unresolved multipaths fluctuated rapidly in geophysical time (coherence time ≪12 min) leaving only a relatively stable envelope that is useful for oceanographic inversion. It is demonstrated here that the effects of internal waves on sound pulse propagation in the Straits of Florida can explain these observed results, and it is suggested that similar instabilities of acoustic multipaths due to internal waves are to be expected in other shallow-water propagation conditions. The demonstration is based on numerical simulations with the broad-band UMPE acoustic model that includes multiple forward scattering from volume inhomogeneities induced by internal wave fluctuations that are described by a broad spectrum of excitation. The simulated temporal variability, stability, and coherence of acoustic pulse arrivals are displayed on geophysical time scales from seconds to many hours and are qualitatively in agreement with the measured data in the Straits of Florida 相似文献
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《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(9):1548-1563
The seasonal variability of the carbon dioxide (CO2) system in the Southern Ocean, south of 50°S, is analysed from observations obtained in January and August 2000 during OISO cruises conducted in the Indian Antarctic sector. In the seasonal ice zone, SIZ (south of 58°S), surface ocean CO2 concentrations are well below equilibrium during austral summer. During this season, when sea-ice is not obstructing gas exchange at the air–sea interface, the oceanic CO2 sink ranges from −2 to −4 mmol/m2/d in the SIZ. In the permanent open ocean zone, POOZ (50–58°S), surface oceanic fugacity fCO2 increases from summer to winter. The seasonal fCO2 variations (from 10 to 30 μatm) are relatively low compared to seasonal amplitudes observed in the subtropics or the subantarctic zones. However, these variations in the POOZ are large enough to cross the atmospheric level from summer to winter. Therefore, this region is neither a permanent CO2 sink nor a permanent CO2 source. In the POOZ, air–sea CO2 fluxes calculated from observations are about −1.1 mmol/m2/d in January (a small sink) and 2.5 mmol/m2/d in August (a source). These estimates obtained for only two periods of the year need to be extrapolated on a monthly scale in order to calculate an integrated air–sea CO2 flux on an annual basis. For doing this, we use a biogeochemical model that creates annual cycles for nitrate, inorganic carbon, total alkalinity and fCO2. The changing pattern of ocean CO2 summer sink and winter source is well reproduced by the model. It is controlled mainly by the balance between summer primary production and winter deep vertical mixing. In the POOZ, the annual air–sea CO2 flux is about −0.5 mol/m2/yr, which is small compared to previous estimates based on oceanic observations but comparable to the small CO2 sink deduced from atmospheric inverse methods. For reducing the uncertainties attached to the global ocean CO2 sink south of the Polar Front the regional results presented here should be synthetized with historical and new observations, especially during winter, in other sectors of the Southern Ocean. 相似文献
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I. I. Pipko S. P. Pugach I. A. Repina O. V. Dudarev A. N. Charkin I. P. Semiletov 《Izvestiya Atmospheric and Oceanic Physics》2015,51(9):1088-1102
This article presents the results of long-term studies of the dynamics of carbonate parameters and air–sea carbon dioxide fluxes on the Chukchi Sea shelf during the summer. As a result of the interaction of physical and biological factors, the surface waters on the west of Chukchi Sea were undersaturated with carbon dioxide when compared with atmospheric air; the partial pressure of CO2 varied in the range from 134 to 359 μatm. The average value of CO2 flux in the Chukchi Sea per unit area varied in the range from–2.4 to–22.0 mmol /(m2 day), which is significantly higher than the average value of CO2 flux in the World Ocean. It has been estimated that the minimal mass of C absorbed by the surface of Chukchi Sea from the atmosphere during ice-free season is 13 × 1012 g; a great part of this carbon is transported to the deeper layers of sea and isolated from the atmosphere for a long period of time. The studies of the carbonate system of the Chukchi Sea, especially of its western part, will provide some new data on the fluxes of carbon dioxide in the Arctic Ocean and their changes. Our analysis can be used for an interpretation of the satellite assessment of CO2 fluxes and dissolved CO2 distribution in the upper layers of the ocean. 相似文献
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利用15 N示踪法实测南海水体反硝化速率的研究发现,培养水样在长时间密闭放置过程中也会受到外界空气的污染,且其29N2/28N2比值恒定为0.007 35。根据空气背景中29N2/28N2比值恒定的特征,提出基于质量平衡关系校正空气N2污染的方法,通过将样品实测29N2浓度扣除由外界空气贡献的29N2浓度,可获得由生物反硝化作用所产生的29N2准确浓度,进而可计算出准确的反硝化速率。经空气29N2背景校正后,29N2浓度的偏差明显小于未经校正的结果,且29N2浓度与培养时间之间的线性相关性显著加强,凸显出空气29N2背景校正是获取准确反硝化速率的关键。鉴于15 N示踪法已被广泛应用于海洋水体与沉积物反硝化速率的测定中,所提出的空气29N2背景校正方法具有重要的意义。 相似文献
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Mollusk shells contain many isotopic clues about calcification physiology and environmental conditions at the time of shell formation. In this review, we use both published and unpublished data to discuss carbon isotopes in both bivalve and gastropod shell carbonates. Land snails construct their shells mainly from respired CO2, and shell δ13C reflects the local mix of C3 and C4 plants consumed. Shell δ13C is typically >10‰ heavier than diet, probably because respiratory gas exchange discards CO2, and retains the isotopically heavier HCO3 ?. Respired CO2 contributes less to the shells of aquatic mollusks, because CO2/O2 ratios are usually higher in water than in air, leading to more replacement of respired CO2 by environmental CO2. Fluid exchange with the environment also brings additional dissolved inorganic carbon (DIC) into the calcification site. Shell δ13C is typically a few ‰ lower than ambient DIC, and often decreases with age. Shell δ13C retains clues about processes such as ecosystem metabolism and estuarine mixing. Ca2+ ATPase-based models of calcification physiology developed for corals and algae likely apply to mollusks, too, but lower pH and carbonic anhydrase at the calcification site probably suppress kinetic isotope effects. Carbon isotopes in biogenic carbonates are clearly complex, but cautious interpretation can provide a wealth of information, especially after vital effects are better understood. 相似文献
17.
Yutaka W. Watanabe Yoshiyuki Takahashi Takashi Kitao Koh Harada 《Journal of Oceanography》1996,52(3):301-312
Concentrations of total carbonate, alkalinity and dissolved oxygen were obtained near the 1973 GEOSECS stations in the North Pacific subpolar region north of 40°N along 175°E between 1993 and 1994. A difference of excess CO2 content between the GEOSECS and our expeditions was estimated. The maximum difference in water column inventory of excess CO2 has increased by about 280 gC m–2 above 2000 m depth which apparently means an uptake of excess CO2 taken from air to sea during the last two decades. An averaged value of the annual flux of excess CO2 at 75–1000 m depth was 8.63±2.01 gC m–2yr–1 in the North Pacific subpolar region. By introducing the annual flux of excess CO2 into a two-box model for the North Pacific subpolar region, a penetration factor of excess CO2 from air to sea was obtained to be 1.08×10–2 gC m–3ppm–1 in the North Pacific subpolar region. Based on this factor, the surface concentration of excess CO2 in the North Pacific subpolar region was estimated to be 68 mole I–1, suggesting that the North Pacific subpolar region absorbed atmospheric excess CO2 more than the saturated concentration of excess CO2. Total amount of excess CO2 taken from the North Pacific subpolar region by 1993 was estimated to be 36.2×1015 gC, which was equal to about one tenth of that released by human activities after the preindustrial era. 相似文献
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浅地层剖面是基于声学信号(频率在几百至几千赫兹)在沉积物中的传播得到可反映沉积地层结构的数据,海底反射系数与沉积物物理性质密切相关。Biot-Stoll声波传播理论模型可以预测海底沉积物的物理性质,构建反射系数等声学参数与物理参数之间的关系,但在不同的海域采用不同的参数所获得的效果不同。为此,本文基于南海北部陆坡海底表层沉积物的实测物理参数,利用Biot-Stoll模型建立研究区海底反射系数和沉积物物理性质之间的关系,结果表明模型计算值与样品实测值吻合度总体较好,偏差在0.1%～4.9%之间,并建立了频率3.5 kHz时海底反射系数与沉积物孔隙度、密度、平均粒径之间的关系方程,且方程拟合度较高,可决系数R2均大于0.99。在对典型Chirp剖面数据计算其海底反射系数的基础上,反演了海底表层沉积物的孔隙度、密度、颗粒平均粒径等物理性质,其中反演孔隙度、密度、平均粒径与实测孔隙度、密度、平均粒径相对误差均小于5%,结果与实测值基本相符,表明该反演方法在南海北部陆坡区的应用是可行的。 相似文献
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小尺度湍流过程对河口物质输运与能量交换至关重要。受传统观测方法的限制, 河口浅水区域的剖面观测资料至今较为匮乏, 进而限制了湍流过程的研究。为此, 采用新型5波束声学多普勒流速剖面仪(Nortek Signature 1 000 kHz AD2CP)在长江口开展湍流剖面观测, 获取高频、低噪的高质量湍流剖面数据, 并与声学多普勒点式流速仪(acoustic doppler velocimeters, ADV)同步观测的数据进行对比。结果表明, 通过AD2CP与ADV获得的近底部边界层摩阻流速u*、拖曳系数Cd、雷诺应力SR等特征参数基本一致, 底摩擦与波浪能量为河口区域湍动能的主要输入源。湍流垂向结构存在显著的非局地平衡, 即温盐等斜压作用引起的浮力通量、对流项以及强波浪作用影响的脉动压力做功、黏性输运等因素可能为长江口湍流非局地平衡的主因。 相似文献
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A three-component pop-up ocean-bottom seismograph was built at the Institute of Oceanographic Sciences in 1978. It is constructed around a buoyant 71 cm diam aluminium alloy forged sphere which contains three 4.5 Hz orthogonal geophones and an external hydrophone. The instrument will record continuously in analogue mode for over eight days using a modified reel-to-reel tape-recorder running at 1.5 mm s-1. The geophones have a bandwidth of 2–25 Hz and the hydrophone bandwidth is 5–40 Hz. Ballast release is by pre-set clock or by acoustic command.Fifty-four deployments have been carried out in five cruises for the loss of only one instrument. Good recordings of dropped weights, airguns, explosions and earthquakes have been obtained. 相似文献