Using overlapping sonobuoy data from the Ross Sea to construct a 2D deep crustal velocity model     

M. M. Selvans  R. W. Clayton  J. M. Stock  R. Granot 《Marine Geophysical Researches》2012,33(1):17-32

Sonobuoys provide an alternative to using long streamers while conducting multi-channel seismic (MCS) studies, in order to provide deeper velocity control. We present analysis and modeling techniques for interpreting the sonobuoy data and illustrate the method with ten overlapping sonobuoys collected in the Ross Sea, offshore from Antarctica. We demonstrate the importance of using the MCS data to correct for ocean currents and changes in ship navigation, which is required before using standard methods for obtaining a 1D velocity profile from each sonobuoy. We verify our 1D velocity models using acoustic finite-difference (FD) modeling and by performing depth migration on the data, and demonstrate the usefulness of FD modeling for tying interval velocities to the shallow crust imaged using MCS data. Finally, we show how overlapping sonobuoys along an MCS line can be used to construct a 2D velocity model of the crust. The velocity model reveals a thin crust (5.5 ± 0.4 km) at the boundary between the Adare and Northern Basins, and implies that the crustal structure of the Northern Basin may be more similar to that of the oceanic crust in the Adare Basin than to the stretched continental crust further south in the Ross Sea.  相似文献   

Acoustic tracking of a freely drifting sonobuoy field: experimental results     

Collison  N.E.B. Dosso  S.E. 《Oceanic Engineering, IEEE Journal of》2003,28(3):544-551

This paper describes a regularized acoustic inversion algorithm for tracking individual elements of a freely drifting sonobuoy field using measured acoustic arrival times from a series of impulsive sources. The acoustic experiment involved 11 sonobuoys distributed over an 8/spl times/6-km field, with a total of six sources deployed over 72 min. The inversion solves for an independent track for each sonobuoy (parameterized by the sonobuoy positions at the time of each source transmission), as well as for the source positions and transmission instants. Although this is a strongly under-determined problem, meaningful solutions are obtained by incorporating a priori information consisting of prior estimates (with uncertainties) for the source positions and initial sonobuoy positions and a physical model for sonobuoy motion along preferentially smooth tracks. The inversion results indicate that the sonobuoys move approximately 260-700 m during the source-deployment period. Closely spaced sonobuoys move along similar tracks; however, there is considerable variability in track directions over the entire field. Positioning uncertainties in horizontal coordinates are estimated using a Monte Carlo appraisal procedure to be approximately 100 m in an absolute sense and 65 m in a relative sense. A sensitivity study indicates that the uncertainties of the a priori position estimates are the limiting factor for track accuracy, rather than data uncertainties or source configuration.  相似文献   

Travel-time curves for a simple sea floor model     

R. A. Stephen 《Marine Geophysical Researches》1982,5(3):315-326

This paper reviews a simple technique for interpreting the velocity structure of upper oceanic crust from travel-time data of sonobuoy and ocean bottom receiver refraction experiments. The technique does not involve sophisticated digital processing or synthetic seismogram analysis. Interpretations can be carried out with a pencil, paper and slide rule.Travel-time inversion procedures based on the -p transformation require the assumption of the shallowmost velocity. In some cases, however, such as oceanic crustal studies, the shallowmost velocity is one tf the critical parameters for which one wishes to invert. An inversion method for the shallowmost velocity is discussed which assumes a constant velocity gradient. The time, range and ray parameter of a point on the travel-time curve are sufficient to obtain the velocity at the top of the gradient zone and the gradient. The method can be used to interpolate the velocity-depth function into regions from which no seismic energy is returned as a first arrival. Once an estimate of the upper crustal velocity is obtained the traditional -p procedures can be applied.The model considered consists of a homogeneous layer over a layer in which velocity increases linearly with depth. For such a geometry there are three classes of behaviour of the travel-time curve based on the number of cusps: zero, one or two. The number of cusps depends on the uppermost velocity in the crust, the velocity gradient of the upper crust and the depth of the sources and receivers. It has not been previously recognized that two cusps in the travel time curve may be observed for this simple model. Since estimating the ray parameter from first arrival times is less ambiguous when there are no cusps, understanding the relations involved with the three classes aids in the design of experiments. It is reasonable to apply the model to shallow sea floor structure because of the high quality of marine refraction data which has recently been obtained.  相似文献   

Self-noise measurements using a moored sonobuoy with a suspended hydrophone     

H. -W. Kebe 《Marine Geophysical Researches》1981,5(2):207-220

Moored sonobuoys are used for refraction seismic measurements at sea, although the range of operation is limited by the self noise caused by the hydrophone suspension.In this paper the main causes of self noise are discussed and a useful deployment scheme of a moored sonobuoy with suspended hydrophone is described.Some design criteria, in particular an equation for calculation of the optimal length of the expandable rubber band-which is situated between the surface float and the damping-body-are discussed.Finally, it is shown from noise measurements during the F. S. Valdivia cruise in 1975, that self noise level in the band 2 Hz to 20 Hz is 180 mPa to 280 mPa at a fully developed windsea with a characteristic wave height of more than 4 meters and a waterstream velocity about 0.5 m s¹.During these measurements the hydrophone was attached to the cable without rubber band. It is concluded that at a normal seastate the self noise level can be reduced to the order of ocean floor noise.  相似文献   

Enhanced estimation of sonobuoy trajectories by velocity reconstruction with near-surface drifters     

Y. Chang  D. Hammond  A.C. Haza  P. Hogan  H.S. Huntley  A.D. Kirwan  B.L. Lipphardt  V. Taillandier  A. Griffa  T.M. Özgökmen 《Ocean Modelling》2011,36(3-4):179-197

An investigation to improve trajectory prediction using Lagrangian data is presented. The velocity field of a data assimilating model, EAS-16, is corrected using drifter observations taken during an experiment off Taiwan. The results are tested using another independent Lagrangian data set provided by sonobuoys launched in the same area. The latter have instrument chains that extend well into the water column. Consequently the corrected model velocities were projected into the water column in order to calculate sonobuoy trajectories. The drifter and sonobuoy trajectories both show two distinct regimes in the considered area of approximately 1/2° square. One regime is dominated by shelf dynamics, the other by meandering of the Kuroshio, with a sharp boundary dividing the two. These two regimes are not reproduced by the trajectories of the EAS-16 model. When the drifter data are blended with the model velocities, synthetic sonobuoy trajectories track the observed ones much better, and the two regimes are clearly depicted. Two different methods for the velocity reconstruction are tested. One is based on a variational approach and the other on a normal mode decomposition. Both methods show qualitatively similar improvements in the prediction of sonobuoys trajectories, with a quantitative improvement in the total rms error of approximately 50% and 25%, respectively.  相似文献   

渤海模型冰运动特征的现场观测研究     

颜钰  顾卫  许映军  李倩 《海洋学报(英文版)》2019,38(3):17-25

Sea ice drift is mainly controlled by ocean currents, local wind, and internal ice stress. Information on sea ice motion, especially in situ synchronous observation of an ice velocity, a current velocity, and a wind speed, is of great significance to identify ice drift characteristics. A sea ice substitute, the so-called "modelled ice", which is made by polypropylene material with a density similar to Bohai Sea ice, is used to complete a free drift experiment in the open sea. The trajectories of isolated modelled ice, currents and wind in the Bohai Sea during non-frozen and frozen periods are obtained. The results show that the currents play a major role while the wind plays a minor role in the free drift of isolated modelled ice when the wind is mild in the Bohai Sea. The modelled ice drift is significantly affected by the ocean current and wind based on the ice–current–wind relationship established by a multiple linear regression. The modelled ice velocity calculated by the multiple linear regression is close to that of the in situ observation, the magnitude of the error between the calculated and observed ice velocities is less than12.05%, and the velocity direction error is less than 6.21°. Thus, the ice velocity can be estimated based on the observed current velocity and wind speed when the in situ observed ice velocity is missing. And the modelled ice of same thickness with a smaller density is more sensitive to the current velocity and the wind speed changes. In addition, the modelled ice drift characteristics are shown to be close to those of the real sea ice, which indicates that the modelled ice can be used as a good substitute of real ice for in situ observation of the free ice drift in the open sea, which helps solve time availability, safety and logistics problems related to in situ observation on real ice.  相似文献   

Simulating ocean acoustic tomography measurements with Hamiltonian ray tracing     

Georges  T. Jones  R. Riley  J. 《Oceanic Engineering, IEEE Journal of》1986,11(1):58-71

Tomographers map mesoscale ocean structure by inverting acoustic travel-time measurements through networks of underwater paths. To know where to deploy sensors and how to interpret their measurements, one must first understand the "forward problem," that is, how the sound channel and mesoscale features refract sound in three dimensions, and how such refraction alters the pulse-arrival sequence. We use a Hamiltonian ray-tracing program called HARPO to compute the refraction by continuous three-dimensional ocean models and to display the results in ways that add insight about refractive effects. We first simulate propagation in a simple range-independent sound channel, showing how pulse-arrival sequence depends on channel parameters and sensor placement. Next, we add linear range dependence and show that it is hard to extract range information from pulse measurements at one range. Finally, we add a simple model of a mesoscale eddy including its currents and show that deflection and splitting of the sound channel significantly alter the pulse-arrival sequence. Two diagrams that have not been widely used before are useful ways to display the arrival-time and ray-focusing perturbations caused by changes in ocean structure: they are plots of range versus launch angle and range versus travel time. Examples of azimuthal deflection, three-dimensional eigenrays, and reciprocal propagation through eddy currents are shown, and simplified methods for estimating the travel time of three-dimensional eigenrays are evaluated.  相似文献   

通用型海洋水色遥感精确瑞利散射查找表   总被引：2，自引：1，他引：2  

何贤强  潘德炉  白雁  龚芳 《海洋学报》2006,28(1):47-55

当前对海洋水色遥感精确瑞利散射的计算均采用查找表方式进行,但由于这些查找表是针对特定遥感器生成的,无法直接应用于新的水色遥感器,给实际应用带来一定程度的麻烦,为此提出了一种通用的海洋水色遥感精确瑞利散射查找表.首先,详细地推导了加倍法解大气矢量辐射传输方程的基本关系式和实际的计算原理.通过与MODIS精确瑞利散射查找表计算结果比较,证明利用加倍法计算瑞利散射的精度优于0.25%,完全能够满足当前海洋水色遥感大气校正对瑞利散射计算精度的要求,并可以用来生成精确瑞利散射查找表.其次,利用加倍法解大气矢量辐射传输方程,生成了一个通用的海洋水色遥感精确瑞利散射查找表,验证结果表明该查找表可用于所有水色遥感器的精确瑞利散射计算,且计算精度优于0.5%.  相似文献   

Kirchhoff向下延拓法在海洋合成多道地震走时反演中的应用*     

张茂传  徐敏  赵旭  张佳政  查财财  VithanaM.V.P.  狄会哲  曾信 《热带海洋学报》2020,39(4):80-90

海洋多道地震数据建模和成像是获取洋壳速度和构造信息的重要手段。海水层的存在使得多道地震拖缆接收到的折射波走时信息仅仅存在于较远的炮检距, 近炮检距被强振幅海底反射波覆盖, 制约了走时数据拾取和反演效果。本文基于波动方程的Kirchhoff积分法, 成功实现了多道地震数据向下延拓, 获取到了更大炮检距区间的初至折射波走时拾取, 并将其应用于洋中脊新生洋壳2A/2B层的合成多道地震数据走时反演。比较向下延拓前后的走时拾取范围及走时反演结果表明, 向下延拓法能够保持地震波场的运动学和动力学特征不变, 在共炮集数据的更大炮检距范围内进行初至折射走时拾取, 从而增加反演的数据选择和浅层射线覆盖, 反演结果能更加准确地分辨出洋壳2A/2B层界面, 并得到更高的分辨率和更准确的速度结构剖面。  相似文献   

A general purpose exact Rayleigh scattering look-up table for ocean color remote sensing     

HE Xianqiang  PAN Delu  BAI Yan  GONG Fang 《海洋学报(英文版)》2006,25(1):48-56

1 Introduction In the total radiance received by an ocean color remote sensor, over 80% radiance is the contribution being scattered by air molecule and aerosol, and a wa- ter-leaving radiance carrying the ocean color informa- tion is only a small part. T…  相似文献   

Application of leeway drift data to predict the drift of panga skiffs: Case study of maritime search and rescue in the tropical pacific     

《Applied Ocean Research》2017

The use of Search and Rescue (SAR) drift forecasting in an operational capacity is demonstrated through two SAR case studies, each predicting the drift of a panga skiff for 120 h (Case 1) and 72 h (Case 2). The leeway characteristics of panga skiffs were previously unknown, until a leeway field study was undertaken in mid-2012 to empirically determine the influence of wind and waves on their drift. As part of the two case studies described herein, four ocean models were used as environmental forcing for a stochastic particle trajectory model, to forecast the drift and resulting search areas for the panga skiffs. Each of the four ocean models were tested individually, and then combined into a consensus forecast to ascertain which ocean model was the most accurate in terms of distance error of modelled positions compared to actual panga skiff locations. Additionally, a hit analysis was undertaken to determine whether the panga skiff was located within the forecast search areas for each ocean model, and for consensus search areas. Finally, an assessment of the search area sizes was carried out to assess the single ocean model forecast search area sizes, and how they compared with the consensus search area size. In both of the case studies, all four ocean model forecast search areas contained the panga skiff at the time intervals tested, indicating a 100% hit rate and general consensus between the ocean models. The consensus search area, where all four ocean models overlapped, was approximately one third the size of the average single model search area. This demonstrates that the consensus search areas provide a more efficient search area compared to individual ocean model search area forecasts.  相似文献   

Refraction of Sound in a Horizontally Inhomogeneous, Time-Dependent Ocean     

《Oceanic Engineering, IEEE Journal of》2006,31(2):384-401

Measurements of the three-dimensional (3-D) structure of a sound-speed field in the ocean with the spatial and temporal resolution required for prediction of acoustic fields are extremely demanding in terms of experimental assets, and they are rarely available in practice. In this study, a simple analytic technique is developed within the ray approximation to quantify the uncertainty in acoustic travel time and propagation direction that results from an incomplete knowledge or purely statistical characterization of sound-speed variability in the horizontal plane. Variation of frequency of an acoustic wave emitted by a narrowband source due to a temporal variation of environmental parameters is considered for deterministic and random media. In a random medium with locally statistically homogeneous, time-dependent 3-D fluctuations of the sound speed, calculation of the signal frequency and bearing angle variances as well as the travel-time bias due to horizontal refraction is approximately reduced to integration of respective statistical parameters of the environmental fluctuations along a ray in a background, range-dependent, deterministic medium. The technique is applied to acoustic transmissions in a coastal ocean, where tidally generated nonlinear internal waves are the prevailing source of sound-speed fluctuations, and in a deep ocean, where the fluctuations are primarily due to spatially diffuse internal waves with the Garrett–Munk spectrum. The significance of 3-D and four-dimensional (4-D) acoustic effects in deep and shallow water is discussed.  相似文献   

Multiple-source localization using GPS technology and receivedarrival time structure analysis in an air-deployed system     

Stotts  S.A. Martin  J.L. Bedford  N.R. 《Oceanic Engineering, IEEE Journal of》1997,22(3):576-582

An efficient and robust method has been developed to locate multiple impulsive sources in an ocean environment. Global position system (GPS) receivers were installed on sonobuoys to obtain their locations within a few meters of accuracy. A sonobuoy field was deployed in a ring-type pattern. Charges were then set off at arbitrary locations within the ring, High-resolution plots were used to obtain direct path and/or first bottom bounce arrivals on each buoy. A model grid of arrival times was constructed, corresponding to the dimensions of the buoy field. A ray model previously developed here at the Applied Research Laboratories at the University of Texas at Austin (ARL:UT) was used to obtain model travel times. The minimum value of the least-square-type error between the real arrival times and the modeled travel times resulted in an unambiguous location of the source, within the limits of the grid spacing chosen. This value was calculated by picking one receiver as the reference and then summing the timing errors of the remaining receivers relative to the reference. Successive iterations with finer grid spacings result in source localization within the accuracy of the buoy locations. The localization routine was extended by allowing permutations of the pulse arrivals on each buoy to account for multiple sources closely separated in time and/or space. An automated correlation technique is presented as an alternative to the leading edge-detection method used here for obtaining relative arrival times. Two proof-of-concept experiments were performed and some results of data obtained at Lake Travis and the Gulf of Mexico are presented  相似文献   

An analysis on the error structure and mechanism of soil moisture and ocean salinity remotely sensed sea surface salinity products   总被引：1，自引：0，他引：1  

CHEN Jian  ZHANG Ren  WANG Huizan  AN Yuzhu  WANG Luhu  WANG Gongjie 《海洋学报(英文版)》2014,33(1):48-55

For the application of soil moisture and ocean salinity（SMOS） remotely sensed sea surface salinity（SSS） products,SMOS SSS global maps and error characteristics have been investigated based on quality control information.The results show that the errors of SMOS SSS products are distributed zonally,i.e.,relatively small in the tropical oceans,but much greater in the southern oceans in the Southern Hemisphere（negative bias） and along the southern,northern and some other oceanic margins（positive or negative bias）.The physical elements responsible for these errors include wind,temperature,and coastal terrain and so on.Errors in the southern oceans are due to the bias in an SSS retrieval algorithm caused by the coexisting high wind speed and low temperature; errors along the oceanic margins are due to the bias in a brightness temperature（TB） reconstruction caused by the high contrast between L-band emissivities from ice or land and from ocean; in addition,some other systematic errors are due to the bias in TB observation caused by a radio frequency interference and a radiometer receivers drift,etc.The findings will contribute to the scientific correction and appropriate application of the SMOS SSS products.  相似文献   

Combination of Least Square and Monte Carlo Methods for OBS Relocation in 3D Seismic Survey Near Bashi Channel     

Feng Du  Fudong Yang  Minghui Zhao  Qiang Wang  Xuelin Qiu 《Marine Geodesy》2013,36(5):494-515

Abstract

The relocation of ocean bottom seismometers (OBSs) is a key step in analyzing the three-dimensional seismic tomographic structure of crust and mantle. In order to get the accurate location of OBSs on the seafloor, we analyze the travel times of direct water waves emitted by air-guns. The Monte Carlo and least square methods have been adopted to calculate the true OBS location. The secondary time correction is necessary if the arrivals of direct water waves show overall time drift during relocation which maybe originates from remnant of linear clock drift correction and average errors of travel time picking, mean water velocity assumption, and experiment geometry. We have improved the original OBS relocation procedure which we used previously for other experiments by deliberateness of a secondary time correction and automatically approaching the really mean water velocity. A series of synthetic tests are carried out firstly to document the feasibility of our procedure and then it is applied on a real experiment. In here, we relocate 28 OBSs in total were relocated in 3D seismic survey near Bashi Channel. Relocation results show that the drifting distances for the 28 OBSs range from 65 to 1136 m between the deployed and relocated locations deduced by relocation results. The Pearson correlation coefficient between OBS drifting direction and sea current direction is 0.79, indicating that the two sets of data are highly linearly related and further manifest the sea current as the most possible driving force for OBS drifting during landing on the seafloor but its detailed influence mechanism is unclear by now. This research is necessary and critical for velocity structure modeling, and the optimal relocation program provides valuable experiences for 3D seismic survey in other area.  相似文献   

SEDIS IV型短周期自浮式海底地震仪数据校正方法   总被引：6，自引：0，他引：6  

薛彬  阮爱国  李湘云  吴振利 《海洋学研究》2008,26(2)

利用15台SEDISIV型短周期自浮式海底地震仪在南海中、北部地壳深部结构调查中所获得的资料,探讨了海底地震仪数据校正的方法和校正后的效果,结果表明:使用该地震仪所获得的原始资料经过放炮时间、炮点坐标数据局部化、海底地震仪位置误差以及记录时间漂移4方面的校正后,数据更趋合理,误差显著降低。放炮时间的校正消除了时钟漂移和时间延迟的误差;炮点坐标数据局部化处理消除了炮点位置整体趋势性偏移的现象;试错法进行位置误差和记录时间的精细校正时,时间漂移的校正量值约为几个到十几个毫秒,位置校正的量值仅在几米到数百米之间,实测数据所绘曲线的形态和位置都与理论曲线十分吻合,可见校正后误差显著降低。  相似文献   

多方向不规则波传播变形数值模拟   总被引：2，自引：1，他引：1  

潘军宁左其华  王红川 《海洋工程》2004,22(3):14-19,29

在推广的缓坡方程数学模型基础上建立了多方向不规则波数学模型,综合考虑了波浪折射、绕射、反射、底摩擦和风能输入等因素。基于线性波浪理论,将波浪方向谱在频率和方向上按等能量分割法离散后,分别计算各组成波的传播变形,再计算合成波要素。缓坡方程数学模型采用改进的ADI法求解,计算效率高,稳定性好。采用椭圆形浅滩不规则波模型试验结果和单突堤不规则波绕射理论解对数学模型进行了验证,数值模拟结果和试验值及理论解符合良好。利用该模型进行了某港港内波浪折射、绕射和反射的联合数值模拟,给出了合理的港内波高分布。  相似文献   

Development of the POLCOMS–WAM current–wave model     

R. Bolaños  P. Osuna  J. Wolf  J. Monbaliu  A. Sanchez-Arcilla 《Ocean Modelling》2011,36(1-2):102-115

The continuous research and improvement of ocean modelling helps to provide a more sustainable development of coastal and offshore regions. This paper focuses on ocean modelling at the NW Mediterranean using the POLCOMS–WAM model with new developments. The Stokes’ drift effect on currents has been included and the distribution of surface stress between waves and currents has also been considered. The system is evaluated in the NW Mediterranean and an evaluation of different forcing terms is performed. The temperature and salinity distributions control the main patterns of the Mediterranean circulation. Currents are typically small and therefore the modification of waves due to the effect of currents is minimal. However, the wave induced currents, mainly caused by a modified wind drag due to waves, produce changes that become an important source of mass transport. POLCOMS was able to reproduce the main Mediterranean features, its coupling with WAM can be a very useful tool for ocean and wave modelling in the Mediterranean and other shelf seas.  相似文献   

KMAH index and separation of PSP-waves from streamer data     

Georgy Mitrofanov  Viatcheslav Priimenko 《Marine Geophysical Researches》2018,39(3):349-362

The presence of triplications (caustics) can be a serious problem in seismic data processing and analysis. The travel-time curve becomes multi-valued and the geometrical spreading correction factor tends to zero due to energy focusing. To select the regions of possible triplications (caustics) of travel-times, which can arise during the propagation of reflected seismic waves, we use the Keller–Maslov–Arnol’d-Hörmander (KMAH) index. The identification of such regions improves the selection of signals associated with target reflecting horizons and their use in solving various inverse dynamic problems, including amplitude-versus-offset (AVO) and full-waveform inversions. The importance of the KMAH index increases in 4D surveys when the structure of the model is already known, and it is necessary to conduct a detailed analysis of the shapes of seismic signals with increasing accuracy when solving inverse seismic problems. In addition, this index can be valuable when solving various marine seismic problems associated with single and converted waves, in particular with PSP-waves. The present work is dedicated to the separation of signals associated with this type of wave using surface marine seismic data. However, the proposed algorithm has a wider application. It is based on: (i) a priori information on the medium under study; (ii) ray tracing method. The ray tracing method enables the identification of the corresponding signals and the determination of the time and space intervals, in which such signals are most accurately traced. These intervals are used in the selection of target signals, particularly signals related to PSP-waves. In order to select optimal areas of observation with higher amplitudes of target signals, we use the \(\tau -p\) transform. To improve the stability of the signal separation, KMAH index is used. This approach allows the elimination of possible triplications (caustics) in the travel-time curve from the selected intervals.  相似文献   

Hindcasting wave spectra in finite‐depth waters     

A. K. Laing 《新西兰海洋与淡水研究杂志》2013,47(4):541-553

A model is described for hindcasting or forecasting waves in finite‐depth waters. The model is particularly applicable to coastal sites where the water is depth‐limited. The wave energy density spectrum is modelled in the frequency‐directional domain. For each spectral component a ray is defined along which wave energy propagates to reach the site. For sites exposed to the open ocean a background spectral wave model is required to provide input to the ray endpoints. Further growth and dissipation is then effected along the rays according to the local wind and water depth. The model was used to hindcast wave spectra over a period of 9 months for a site in the Canterbury Bight, New Zealand. The results were compared with measurements from a Waveridcr buoy at the site. The model succeeds in explaining about 40% of the variance in measured significant wave heights. However, the present application is handicapped by errors inherent in the background spectral model and in specifying the local wind.  相似文献