Inversion of Lloyd Mirror Field for Determining a Source's Track

This paper describes a simple approach for inferring the depth and track of a sound source at short ranges by inversion of acoustic field data at a set of sea bottom hydrophones. At short ranges, the acoustic field consists of a dominant Lloyd mirror (LM) signal from the direct and surface-reflected ray paths and a series of bottom-reflected paths that modulate the LM signal. A computationally efficient propagation model based on the method of images is developed to calculate replica fields for the inversion. The matched field inversion method for inferring the source depth and track is demonstrated using data from an experiment carried out in shallow water off the east coast of Canada. The estimated values were in very good agreement with independent measurements taken during the experiment.     

Experimental matched-field localization results using a short vertical array and mid-frequency signals in shallow water

Traditionally, matched-field processing (MFP) has been used to localize low-frequency sources (e.g., <300 Hz) from their acoustic signals received on long vertical arrays. However, some sources emit acoustic signals of much higher frequency. Applying MFP to signals in the mid-frequency range (e.g., 1-4 kHz) is a very challenging problem because MFP's sensitivity to environmental parameter mismatch becomes more severe with increasing frequency. Robust MFP techniques are required to process signals in the mid-frequency range. As a practical issue, short vertical arrays are more convenient to work with than are long vertical arrays; they are easier to deploy and are less prone to large amounts of deformation. However, short vertical arrays undersample the water column, which can result in severely degraded MFP performance. In this paper, we present experimental data results for this nonconventional paradigm. Using the environmentally robust broad-band L/sub /spl infin//-norm estimator, MFP results are given using shallow-water experimental data. This data consisted of broad-band signals in the 3-4-kHz band collected on an eight-element 2.13-m vertical array. These results serve to demonstrate that good localization performance can be attained for this difficult problem. Guidelines on the appropriate use of ray and normal-mode propagation models are also presented.     

基于北斗短报文的海洋观测实时通信系统的设计与研发

北斗一代和北斗二代短报文每次通信数据长度只有78个字节，每次通信后间隔60秒或者300秒才能进行下一次通信，远远满足不了海洋观测实时通信的需求。设计了一套基于北斗短报文的海洋观测实时通信系统，北斗多卡机作为数据发送端，采用哈夫曼压缩算法将观测数据压缩后分成多个数据包，通过多个北斗卡分别发送，岸站接收系统接收到分包的数据后，将接收的数据包解压缩并整合成完整的观测数据。哈夫曼压缩算法将观测数据压缩50%左右，将1组观测数据压缩后发送3次，通过岸上3个月和海上1个月的测试，观测数据接收成功率达到了96%以上，验证了基于北斗短报文的海洋观测实时通信系统的可行性和实用性。     

Experimental study on the cyclic behavior of loose calcareous sand under linear stress paths

Abstract

Hollow cylinder torsional shear tests on loose isotropically and anisotropically consolidated calcareous sand were conducted to investigate the cyclic behavior under three different linear stress paths, including horizontal line, oblique line, and vertical line stress paths, in a coordinate system of the normal stress difference and the horizontal shear stress. The dominant strain components of the isotropically consolidated specimens are affected by the stress paths. With increasing consolidation stress ratio, axial strain gradually becomes the dominant strain component under the three different stress paths. The cyclic strength of the isotropically consolidated specimens under the three different stress paths are almost the same, while for the anisotropically consolidated specimens, the cyclic strengths are strongly affected by the stress paths. These results indicate that conventional cyclic triaxial tests may overestimate cyclic strength in some cases. Irrespective of the stress paths and cyclic stress ratios, the terminal residual excess pore pressure ratio decreases with increasing consolidation stress ratio. Moreover, an empirical equation is proposed to describe the relationship between the normalized shear work and the normalized residual excess pore pressure ratio. The comparative study reveals that the relationship proposed for silica sand is not suitable for the dynamic analyses of calcareous sand.     

Study on the Kuroshio and the Tsushima Current

I summarize the variations of the path of the Kuroshio and of the Tsushima Current mainly based on the results of my studies. The Tsushima Current forms three branches just after it enters the Japan Sea through the Tsushima Strait. The first and third branch currents flow along the Japanese and Korean coasts, respectively, and the second branch current flows from the western channel of the Tsushima Strait to the west of the Oki Islands only in summer from June to August. Properties of the topographic waves which are thought to work on the formation of the second branch are described mainly in terms of the dispersion relations. The Kuroshio has three typical paths,i.e., the nearshore and offshore non-large-meander paths and the typical large-meander path. The Kuroshio alternately takes the nearshore and offshore paths in the non-large-meander period, occasionally changes from the nearshore nonlarge-meander path to the large-meander path and, after having taken the large-meander path for several years, changes to the offshore non-large-meander path. Sea levels south of Japan are clearly different between the non-large-meander and large-meander periods, while they are not different between the periods of the nearshore and offshore non-large-meander paths. But, sea level and water properties in the coastal region show remarkable features during short periods of transitions between the typical non-large-meander paths. Future problems and subjects of studies on these currents are indicated. Especially, importance of velocity monitoring of the Kuroshio is emphasized, and a design of the observation across the Tokara Strait is proposed.     

OSCR wave measurements-some preliminary results

OSCR is an HF radar system that has been developed for high spatial resolution coastal surface current measurement. This paper describes preliminary results that demonstrate that wave measurement can be successfully obtained from suitably processed OSCR data. Comparisons with data from a WAVEC directional buoy are presented and show encouraging agreement. Some of the limitations to the measurement process are discussed and indicate a maximum range of about 20 km. Surface current variability on short time scales presents the most serious obstacle to wave measurement. This appears to be more of a problem when the mean currents are large, in that in these circumstances the data fail initial quality control criteria. However, in lower mean currents, the effect is often still present and leads to errors in long wave measurement     

Acoustic Theory Application in Ultra Short Baseline System for Tracking AUV

The effective tracking area of ultra short baseline (USBL) systems strongly relates to the safety of autonomous underwater vehicles (AUVs). This problem has not been studied previously. A method for determining the effective tracking area using acoustic theory is proposed. Ray acoustic equations are used to draw rays, which ascertain the effective space. The sonar equation is established in order to discover the available range of the USBL system and the background noise level using sonar characteristics. The available range defines a hemisphere like enclosure. The overlap of the effective space with the hemisphere is the effective area for USBL systems tracking AUVs. Lake and sea trials show the proposed method's validity.     

Regional seismic observations of the Ontong Java plateau and East Mariana Basin

P-waves recorded on Ponape Island at the northern end of the Ontong Java plateau have been investigated. Different modes of propagation in the distance range 12° to 17° Δ between paths from Melanesian earthquakes across the Ontong Java plateau and paths from Mariana earthquakes across the eastern Mariana basin suggest that the mantle underlying the regions is not homogeneous. Travel-times of P-waves beneath the Ontong Java plateau are slower than for paths beneath the east Mariana basin. The frequency content of the first-arriving P-waves is lower for paths across the Ontong Java plateau than for the east Mariana basin. The disparate crustal thicknesses of the Ontong Java plateau and east Mariana basin may influence the relative amplitude of oceanic Pn, with smaller amplitudes corresponding to a thicker crust. Pn-P differential times for the Ontong Java plateau show a general decrease with the depth of earthquake focus but no comparable trend is seen in the Mariana data, possibly because of the scatter. The observation of high-frequency oceanic Pn propagation across the Ontong Java Plateau is suggestive that the plateau is not of continental origin.     

High-frequency radars: physical limitations and recent developments

High-frequency (HF) radars based on ground-wave propagation are used for remotely sensing ocean surface currents and gravity waves. For some 20 years a number of systems have been developed taking advantage of improved electronics and computer techniques. However, the performance of these systems are limited by physical constraints, which are due to HF wave propagation and scattering as well as to the technical design of the measuring system. Attenuation of the HF ground-wave is strongly dependent on the radio frequency and sea-water conductivity. Experimental data confirm the predicted decrease of propagation range with decreasing conductivity. HF radar systems use different methods of spatial resolution both in range and azimuth. Range resolution by means of short pulses and frequency-modulated chirps is compared, as well as azimuthal resolution by means of beam forming and direction finding (phase comparison). The emphasis is placed on recent developments.     

一种新型多功能海洋浮标

介绍一种多功能海洋考察与观测用浮标的结构、性能。浮标带有短波无线电遥控和数据传输功能、可外挂多种传感器;该浮标采用小水线结构,在较高海况下,具有较好的安定性。浮标配置了差分型全球定位（DGPS）接收机和短波电台,可对浮标的位置和工作状况实施实时监测,对浮标的工作程式实时遥控并进行必要的数据传输。浮标电子舱内具有大容量多通道数据采集记录系统,DGPS的lpps（1 pulse per second）信号被用于多浮标数据采集的精确同步。浮标可用于海洋监测、考察;也可用于水下目标高精度大地坐标测量等海洋工程。     

Using the adaptive simulated annealing algorithm to estimate ocean-bottom geoacoustic properties from measured and synthetic transmission loss data

This paper presents the results obtained using the adaptive simulated annealing (ASA) algorithm to invert the test cases from the Geoacoustic Inversion Techniques Workshop held in May 2001. The ASA algorithm was chosen for use in our inversion software for its speed and robustness when searching the geoacoustic parameter solution space to minimize the difference between the observed and the modeled transmission loss (TL). Earlier work has shown that the ASA algorithm is approximately 15 times faster than a modified Boltzmann annealing algorithm, used in prior versions of our TL inversion software, with comparable fits to the measured data. Results are shown for the synthetic test cases, 0 through 3, and for the measured data cases, 4 and 5. The inversion results from the synthetic test cases showed that subtle differences between range-dependent acoustic model version 1.5, used to generate the test cases, and parabolic equation (PE) 5.0, used as the propagation loss model for the inversion, were significant enough to result in the inversion algorithm finding a geoacoustic environment that produced a better match to the synthetic data than the true environment. The measured data cases resulted in better fits using ASTRAL automated signal excess prediction system TL 5.0 than using the more sophisticated PE 5.0 as a result of the inherent range averaging present in the ASTRAL 5.0 predictions.     

全站仪内供电系统的保养

全站仪是由电子经纬仪与光电测距仪组合的仪器,是集自动测距、测角、计算、数据存储及数据传输于一体的自动化、数字化及智能化的三维坐标测量与定位系统,是一种当今广泛应用于大地测量、工程测量、数字化测图的电子测量仪器,是现代测绘行业最主要、最普通的测绘仪器,仪器的维护和供电系统的保养,已经成为测绘生产单位的一项工作。     

Ocean current estimation using a Multi-Model Ensemble Kalman Filter during the Grand Lagrangian Deployment experiment (GLAD)

In the summer and fall of 2012, during the GLAD experiment in the Gulf of Mexico, the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) used several ocean models to assist the deployment of more than 300 surface drifters. The Navy Coastal Ocean Model (NCOM) at 1 km and 3 km resolutions, the US Navy operational NCOM at 3 km resolution (AMSEAS), and two versions of the Hybrid Coordinates Ocean Model (HYCOM) set at 4 km were running daily and delivering 72-h range forecasts. They all assimilated remote sensing and local profile data but they were not assimilating the drifter’s observations. This work presents a non-intrusive methodology named Multi-Model Ensemble Kalman Filter that allows assimilating the local drifter data into such a set of models, to produce improved ocean currents forecasts. The filter is to be used when several modeling systems or ensembles are available and/or observations are not entirely handled by the operational data assimilation process. It allows using generic in situ measurements over short time windows to improve the predictability of local ocean dynamics and associated high-resolution parameters of interest for which a forward model exists (e.g. oil spill plumes). Results can be used for operational applications or to derive enhanced background fields for other data assimilation systems, thus providing an expedite method to non-intrusively assimilate local observations of variables with complex operators. Results for the GLAD experiment show the method can improve water velocity predictions along the observed drifter trajectories, hence enhancing the skills of the models to predict individual trajectories.     

Simulation of an Inertial Acoustic Navigation System With Range Aiding for an Autonomous Underwater Vehicle

This paper presents an integrated navigation system for underwater vehicles to improve the performance of a conventional inertial acoustic navigation system by introducing range measurement. The integrated navigation system is based on a strapdown inertial navigation system (SDINS) accompanying range sensor, Doppler velocity log (DVL), magnetic compass, and depth sensor. Two measurement models of the range sensor are derived and augmented to the inertial acoustic navigation system, respectively. A multirate extended Kalman filter (EKF) is adopted to propagate the error covariance with the inertial sensors, where the filter updates the measurement errors and the error covariance and corrects the system states when the external measurements are available. This paper demonstrates the improvement on the robustness and convergence of the integrated navigation system with range aiding (RA). This paper used experimental data obtained from a rotating arm test with a fish model to simulate the navigational performance. Strong points of the navigation system are the elimination of initial position errors and the robustness on the dropout of acoustic signals. The convergence speed and conditions of the initial error removal are examined with Monte Carlo simulation. In addition, numerical simulations are conducted with the six-degrees-of-freedom (6-DOF) equations of motion of an autonomous underwater vehicle (AUV) in a boustrophedon survey mode to illustrate the effectiveness of the integrated navigation system.     

Acoustic Detection and Localization of a Turboprop Aircraft by an Array of Hydrophones Towed Below the Sea Surface

The acoustic spectrum of a propeller-driven aircraft is dominated by a series of spectral lines that are harmonically related to the blade rate (which is equal to the product of the propeller rotation rate and the number of blades on the propeller). We show that an array of acoustic sensors towed below the sea surface can be used for the passive detection and localization of such an aircraft. The acoustic energy from an aircraft is found to reach the subsurface sensors via two propagation paths: a bottom reflection path that enables the aircraft to be detected at long ranges, and a direct path that is present only when the aircraft passes overhead. For each of these paths, the observed variation with horizontal range of the Doppler shift in the blade rate closely matches the variation predicted by the simple model presented in this paper. Good agreement between theory and experiment is also obtained for the variation with horizontal range of the aircraft's apparent bearing. Thus, by using the observed Doppler shift and apparent bearing information, we were able to estimate the aircraft's horizontal range, speed, direction, and altitude.      

SAMI: a low-frequency prototype for mapping and imaging of theseabed by means of synthetic aperture

The objective of the Synthetic Aperture Mapping and Imaging (SAMI) project was to develop and to test at sea a wide-band synthetic aperture sonar prototype, capable of providing high-resolution seafloor images together with bathymetry maps. This system used the motion of a physically small array in order to synthesize a longer array, providing images with an across-track resolution independent of both range and transmit frequency. Such systems are clearly very relevant to the high-precision long-range (low-frequency) imaging of the sea bottom. The project has led to the construction of a prototype tested at sea on several well-known areas for comparison with existing images and maps. These areas included several types of sea bottom, depths, and geological structures. The results obtained in real time, on-board ship, have shown the relevance of the proposed wide-band techniques. The many profiles produced have provided high-resolution images and maps of various seafloors. Interpretation by geologists showed that the system was capable of providing the same or finer detail than a deep-sea short-range, high-frequency system and maintained a higher resolution over a wider swath. The sea data processed have shown that the system provided maps with a cubic meter voxel. The resolution cell is constant over the whole range (50 to 2500 m) thanks to the dynamic focusing of the synthetic aperture. Postprocessing of a part of the data stored during the experiments has been carried out in the laboratory. This work has shown that techniques such as autofocusing can give an increase in resolution (i.e., gain in contrast and resolution of about 3 dB). The results displayed in the paper show the relevance of the techniques developed to the provision of a complete high-performance imaging tool for the oceanographic community     

The coupled oceanographic–tomographic analysis and prediction system: A practical means for utilizing high frequency tomography in the world's oceans

Details are presented of a methodology that utilizes acoustic travel time information in an ocean circulation model. Recent developments of this model-oriented tomography are discussed, representing some significant improvements over earlier formulations. More accurate means of determining the arrival times of specific ray paths are detailed, along with a means of estimating possible errors in the calculated travel times. The assimilation of the observed arrival time information into an ocean model is achieved using a Kalman gain, and more advanced expressions for calculating the Kalman gain are presented. A formulation to account for errors in the stated positions of a source and receiver is also presented. It is shown that the methodology performs fairly well in reproducing observed travel time anomalies. However, the model-predicted anomalies along a specific ray path may not always track the observed anomalies for that path when assimilating multiple ray path data. Results indicate that additional work is required to determine a means of handling observed arrival time data without having prior knowledge of the magnitude of errors in the observations. Results from simulation experiments provide estimates of: (1) potential errors when the travel times for ray paths are only sampled at discreet intervals as opposed to continuously and (2) to what degree acoustic data can be expected to “correct” model-predicted fields.     

A Marine Environment Early Warning Algorithm Based on Marine Data Sampled by Multiple Underwater Gliders

This study analyzes and summarizes seven main characteristics of the marine data sampled by multiple underwater gliders. These characteristics such as the big data volume and data sparseness make it extremely difficult to do some meaningful applications like early warning of marine environment. In order to make full use of the sea trial data, this paper gives the definition of two types of marine data cube which can integrate the big marine data sampled by multiple underwater gliders along saw-tooth paths, and proposes a data fitting algorithm based on time extraction and space compression(DFTS) to construct the temperature and conductivity data cubes. This research also presents an early warning algorithm based on data cube(EWDC) to realize the early warning of a new sampled data file.Experiments results show that the proposed methods are reasonable and effective. Our work is the first study to do some realistic applications on the data sampled by multiple underwater vehicles, and it provides a research framework for processing and analyzing the big marine data oriented to the applications of underwater gliders.     

Modal evolution and inversion for seabed geoacoustic properties inweakly range-dependent shallow-water waveguides

In a shallow-water ocean environment, the range dependent variation of the geoacoustic properties of the seabed is one of the crucial factors affecting sound propagation. Since the local modes of propagation depend on the spatial changes in the bottom sediments, the local eigenvalues of these modes are useful as tools for examining the range dependence of the sediment properties. In order to extract the local eigenvalues from measurements of the pressure field in a laterally inhomogeneous waveguide, the zeroth-order asymptotic Hankel transform with a short sliding window is utilized. The local peak positions in the output spectra differ from the local eigenvalues due to both the range variation of the local modes and the interference of adjacent modes. The departure due to the former factor is evaluated analytically by using the stationary phase method. In order to reduce the error induced by the latter factor, mode filtering is utilized by incorporating data from a fixed vertical array of receivers. The methods developed are applied to simulated pressure field data as well as experimental field data, and it is shown that the range evolution of the local modes can be successfully estimated. In addition, field measurements are used to demonstrate that the modal trajectories in range can be used to infer the range-dependent geoacoustic properties of the seabed     

A steady model of typical non-large-meander paths of the Kuroshio Current

Conditions south of Cape Shiono-misaki for the nearshore and offshore non-large-meander (NLM) paths of the Kuroshio Current are studied using a two-layer reduced gravity model. A steady and non-diffusive state is assumed, and the conservation laws of Bernoulli's function and potential vorticity along the current axis are used. Spatial changes of velocity and depth of the current are imposed as boundary conditions south of Cape Shiono-misaki. These conditions are based on the facts that are ohserved south of the cape: abrupt acceleration of the Kuroshio and the spatial change of sea levels. The current paths east of the cape are computed.This model reproduces well the actual nearshore NLM paths. It also produces offshore NLM paths west of and over the Izu Ridge, but not east of the Izu Ridge. Diffusion of vorticity may be important for the eastern part of the offshore NLM path.An increase of velocity south of the cape is necessary for producing realistic NLM paths. The velocity increase accompanies a decrease of current depth owing to Bernoulli's conservation, and the depth decrease in turn diminishes the absolute vorticity owing to the potential vorticity conservation. The velocity increase, on the other hand, strengthens the negative velocity shear and diminishes the relative vorticity. If the decreases of the relative and absolute vorticities compensate each other, the path goes excessively southward owing to the negative curvature south of the cape. Dominance of the relative vorticity change over the absolute vorticity change prevents, the path from shifting southward and causes the realistic NLM paths.The NLM paths need different amplitudes of the changes south of the cape depending on the velocity and transport of the current, but in any case, the nearshore NLM path needs larger changes than the offshore NLM path. This property and the amplitude of the changes are consistent with observations.