走航ADCP观测资料质量控制方法及应用

为完善目前走航ADCP观测资料质量控制尚未形成统一流程的问题,将走航ADCP观测资料质量控制归纳为船速获取、声速校正、偏角校正以及剖面数据处理四个主要步骤,并制定了一套较为系统的走航ADCP观测资料质量控制流程。以渤海辽东湾红沿河核电站周边海域船载走航ADCP观测为例,按照提出的流程进行走航ADCP观测资料的质量控制。通过对比原始观测数据,质量控制后的结果表明u分量流速剔除了23.56%的低可信度数据,而v分量流速剔除了25.96%的低可信度数据。10 m与15 m水深处的质量控制前后的流速-频数直方图表明,本文提出的流程能有效地降低观测随机性的影响。     

台风期间浮标和潜标上ADCP的空间变化、数据误差及校正#br#

基于南海北部浮标和潜标的声学多普勒流速剖面仪（ADCP）数据,通过一套几何算法计算了台风海鸥（1415）期间ADCP的空间变化和流速误差,并进行数据校正。浮标上,台风过后ADCP的水平位移最大可达2.61 km,水平流速误差最大可达0.27 m/s,垂向流速误差最大仅为5×10^-4 m/s;温跃层流速校正值在台风过后显著大于流速测值,这表明水平校正对于温跃层流速的质量控制很重要。潜标上,ADCP最大垂向位移增量为179 m,最大绳子倾角为35°,最大水平位移为1.5 km; ADCP水平流速误差和倾角误差都很小,在数据校正中可忽略不计,但对台风过后中层流速的垂向校正不能忽略。     

声学多普勒剖面流速仪检测方法探讨

声学多普勒剖面流速仪(Acoustic Doppler Current Profiler,简称ADCP)在国内海洋调查和水文监测行业应用越来越广泛,但是作为一种计量仪器还没有行之有效的检测方法,这对仪器的使用、数据的质量控制造成很大影响。文中对国内外ADCP现场和实验室的检测方法进行了研究探讨,提出了ADCP的检测参数以及现场和实验室检测的技术难点,并对今后ADCP的检测工作给出几点建议。     

虚拟现实技术在声学多普勒流速剖面仪保障业务中的应用初探

虚拟现实（VR）是典型的军民融合技术，在军民装备保障业务中应用广泛，可让用户熟练掌握高价值装备的操作和维修规程。为满足近年来国内海洋系统大量引进声学多普勒流速剖面仪（ADCP）装备在计量检定和维护保养等方面的迫切需求，文章从VR的技术定义和系统组成出发，总结ADCP国内计量检定和使用维护等保障工作的现状，并详细探讨利用VR技术构建ADCP仿真保障系统在ADCP保障业务中的可能应用和潜在价值，为我国ADCP保障业务的发展提供建议。     

抗差Vondrak滤波方法在内孤立波提取中的应用研究

声学多普勒流速剖面仪(ADCP)是对海洋内波监测的有效手段,但受到仪器本身和复杂的海洋环境噪声等影响,走航式ADCP记录的海流数据存在大量噪声,且混有流速异常值。为了进一步提高海洋内孤立波的提取精度与准确性,本文针对走航式ADCP海流数据特点引入IGG3方法的权函数因子,设计了一种抗差Vondrak滤波器,并与快速傅里叶变换、小波分析和滑动平均3种传统滤波方法进行对比,以验证抗差Vondrak滤波方法的有效性与优越性。研究结果表明,抗差Vondrak滤波方法不仅可以有效地滤除流速噪声,还可以自适应剔除海流观测数据中的异常值,由其提取出的内孤立波准确且各层水平流速清晰。因此,与传统滤波方法相比,抗差Vondrak滤波方法在内孤立波提取方面具有一定的优越性。     

水利系统首台进口ADCP在长江口成功开发应用对国产ADCP推广应用的启示

声学多普勒流速剖面仪(Acoustic Doppler Current Profilers,ADCP),是美国RD公司八十年代初研发生产,用于海洋海流调查的仪器,ADCP能同时采集流速、流向、水深、回波强度、航速等要素,在海洋调查中得到广泛应用。长江水利委员会水文局长江口水文实验站在1990年率先引进了美国RDI公司的窄带DR-600k ADCP,解决了长江口江面宽、风浪大、传统测验方式难以收集完整全潮潮流资料的难题。经过RD公司专家来现场安装、调试、培训等过程,历经两年在长江口徐六泾站及长江中游九江站、大通站进行专项比测试验,掌握了ADCP的操作方法,熟悉参数设置及优化,开发了ADCP数据处理软件,成功应用于长江口潮流测验。20纪90年代至今国产ADCP研制从诞生到产品不断出现,可以借鉴首台引进ADCP的成功经验。本文应与流速仪进行比测(比对),收集不同水文环境的资料样本进行分析研究,资料分析时宜与TRDI的WinRIver软件采集的船速、流速、水深等数据进行对比分析,优化国产ADCP软件的功能,提高国产ADCP软硬件的性能使用单位购买ADCP后应进行必要的外围设备配置如GNSS、外接罗经等,制定严格的操作规程、建立ADCP维护保养制度,以保证ADCP能正常收集资料。生产厂家要建立野外服务公告,对用户在使用过程中遇到的问题及处理方式方法进行公布,同时收集和分享用户的使用经验。     

底部浮泥表层推移速度分布的ADCP—GPS估测方法

ADCP对底跟踪走航观测的流速数据中包含水体底部浮泥、底沙运动信息,对比GPS定位方法算出的水体流速数据可以分离出浮泥相对于GPS定位的运动信号,从而达到对底质推移观测的目的。     

声学多普勒流速剖面仪(ADCP)国内外进展

ADCP是目前最主要的流速测量手段之一,自研发成功以后就在国内外得到了广泛的应用本文介绍了ADCP的基本原理、主要类别和国际上ADCP的发展历程,并着重介绍了近年来我国在ADCP领域的研究进展情况,以及国产ADCP在海洋观测和水文测验等领域的应用情况随着我国科研水平的提升和国产ADCP的广泛应用,我国将会在ADCP领域取得更加显著的进步。     

声相关海流剖面(ACCP)测量的流速估值方法

声相关海流剖面（ACCP）测量技术对水体回波信号进行空间相关处理来估计流速值，与声学多普勒海流剖面仪（ADCP）相比ACCP的工作频工，更适合深海测流应用，ACCP测量系统对回波信号进行时空相关处理，根据相关函数的位置来估计被测水团的流速值，ACCP从信号中提取流速值要运用参数估计技术，本文介绍了采用极大似然法和最小二乘法进行流速参数的处理方法，给出一些典型流速情形的数值计算结果。     

高含沙量下ADCP流量测验方法

我国河流汛期含沙量较大,河流中的泥沙会导致"动底"现象使ADCP底跟踪模式下施测流速和流量偏小。同时,而在高含沙量下ADCP波束能量衰减导致施测不到水深,使得垂线上各分层流速无法计算,直接影响到断面的流量施测。本文以长江、黄河高含沙量断面的ADCP流量测验为例,分析说明高含沙量情况下ADCP不同配置下流量施测的解决方法。     

Multicarrier Communication Over Underwater Acoustic Channels With Nonuniform Doppler Shifts

Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a “wideband” problem into a “narrowband” problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.      

Passive acoustic synthetic aperture processing techniques

Various parameters associated with the track of a stable CW source moving with constant velocity are estimated using synthetic aperture and Doppler processing techniques. These include the source frequency before Doppler distortion by its motion, the relative speed between the source and a constant velocity receiver, the range at closest approach to the source track, and the relative bearing to the source. Different processing techniques are suggested for a range of signal stabilities and observation times. Frequency analysis, or Doppler processing, supplements conventional synthetic aperture processing, and for relatively unstable signals a synthetic Doppler method is recommended. This method makes use of a rapid scan of signals from a succession of sensors in a horizontal line array to stimulate a higher speed motion of the array     

Channel Modeling and Threshold Signal Processing in Underwater Acoustics: An Analytical Overview

An overview of underwater acoustic channel modeling and threshold signal processing is presented, which emphasizes the inhomogeneous, random, and non-Ganssian nature of the generalized channel, combined with appropriate weak-signal detection and estimation. Principal attention is given to the formal structuring of the scattered and ambient acoustic noise fields, as well as that of the desired signal, including both fading and Doppler "smear" phenomena. The role of general receiving arrays is noted, as well as their impact on spatial and temporal signal processing and beam forming, as indicated by various performance measures in detection and estimation. The emphasis here is on limiting optimum threshold systems, with some attention to suboptimum cases. Specific first-order probability density functions (pdf's) for the non-Ganssian components of typical underwater acoustic noise environments are included along with their field covariances. Several examples incorporating these pdf's are given, to illustrate the applications and general methods involved. The fundamental role of the detector structure in determining the associated optimum estimators is noted: the estimators arc specific linear or nonlinear functionals of the original optimum detector algorithm, depending on the criterion (i.e., minimization of the chosen error or cost function) selected. Results for both coherent and incoherent modes of reception are presented, reflecting the fact that frequently signal epoch is not known initially at the receiver. To supplement the general discussion, a selected list of references is included, to provide direct access to specific detailed problems, techniques, and results, for which the present paper is only a guide.     

Spatial diversity equalization applied to underwater communications

Underwater acoustic digital communication is difficult because of the nature of the fading multipath channels. Digital signal processing, such as adaptive equalization, is known to greatly improve the communication data rate by limiting intersymbol interference (ISI). However, existing underwater acoustic equalization studies are limited to single-channel techniques, and spatial diversity processing is limited to selection or combining. In this paper, we design minimum mean-square error (MMSE) equalizers jointly among all spatial diversity channels. We call this spatial diversity equalization (SDE). Results are based on a very sparse vertical array in a midrange underwater acoustic channel. We study the effect of element number and placement, the length of the equalization filters, and linear feedforward versus nonlinear decision feedback algorithms. A suboptimum equalizer combiner (EC) is studied to alleviate the computational intensity of JCE. We first design the system for a known acoustic channel; later, some results are verified using adaptive algorithms. Results are presented both in terms of the mean-square error (MSE) and the probability of a symbol error. The latter is important as it is the ultimate interest for a digital communication system. We found that system performance improves rapidly with an increase in the number of spatial channels     

Multiple terminal acoustic communications system design

A design is presented for a system providing highly reliable command and control acoustic communications between a mother ship and a number of small fast submersibles. The small submersibles may be employed for underwater mining, exploration, bottom mapping, or military surveillance. Modulation and coding design is presented; the techniques discussed provide multiple protection against multipath and fading, high reliability, acceptable transmitted signal total time duration, simplicity, and economy. The required decision point signal-to-noise ratio (SNR) for Rayleigh fading conditions is derived for the modulation and coding design. Particular attention is paid in the receive signal processing to the Doppler (relative velocity) and Doppler variation (relative acceleration) problems inherent in a scenario with mobile endpoints. A Figure-of-Merit (FOM) calculation is provided for typical geometrical and environmental parameters. It is shown for a realistic source level that the required SNR can be achieved at long range with considerable endpoint relative motion.     

A fast algorithm for high-accuracy frequency measurement:application to ultrasonic Doppler sonar

In an attempt to investigate the technical feasibility of a CW Doppler sonar, we have examined a method of measuring low velocities with a high-velocity resolution, or frequency resolution, by use of a simple circuit configuration employing digital signal processing technique. The following discussion presents the results of the investigation. In the measuring method described, the fast Fourier transform (FFT) of undersampled data is calculated and the Doppler shift is obtained by searching for a peak frequency of the power spectrum. To achieve the intended frequency resolution of 1 Hz by FFT operation, measurement of data for a minimum measuring period of 1 s is essential. If the sampling frequency is set to 50 kHz, the number of samples obtained during the minimum measuring period of I s would amount to 50000. This is not practical in light of the time required for the FFT operation. To overcome this problem, our new measuring method employs a decimation technique for reducing the number of samples down to 1024 while maintaining a frequency resolution of about 1 Hz. This paper describes how the processing time can be drastically reduced to about 1/300th compared to the conventional technique by a combination of complex exponential functions, filtering and decimation, and thereby indicates the possibility of real-time CW Doppler data processing     

A circular passive synthetic array: an inverse problem approach

Based on the general concept of the inverse acoustic radiation problem, the temporal scanning of a stationary acoustic field along a closed contour is used to simplify the measurement approach for obtaining information on source directionality. The mathematical formulation is derived from a model of the two-dimensional acoustic field. The formulation of the inverse problem is also investigated to establish a methodology for improving the angular resolution of the array processing. The fundamental relationship between the sound sources and the circular passive synthetic array is explored, utilizing existing mathematical methods, in order to develop the processing algorithm. Other subjects of practical interest, such as directional ambiguity, effect of Doppler frequency, interference noise, and processing gain are discussed. It is concluded that the results can be used to establish guidelines for engineering design and deployment of this type of synthetic array, and to further exploit the new array signal processing technique     

Recent advances in high-speed underwater acoustic communications

In recent years, underwater acoustic (UWA) communications have received much attention as their applications have begun to shift from military toward commercial. Digital communications through UWA channels differ substantially from those in other media, such as radio channels, due to severe signal degradations caused by multipath propagation and high temporal and spatial variability of the channel conditions. The design of underwater acoustic communication systems has until recently relied on the use of noncoherent modulation techniques. However, to achieve high data rates on the severely band-limited UWA channels, bandwidth-efficient modulation techniques must be considered, together with array processing for exploitation of spatial multipath diversity. The new generation of underwater communication systems, employing phase-coherent modulation techniques, has a potential of achieving at least an order of magnitude increase in data throughput. The emerging communication scenario in which the modern underwater acoustic systems mill operate is that of an underwater network consisting of stationary and mobile nodes. Current research focuses on the development of efficient signal processing algorithms, multiuser communications in the presence of interference, and design of efficient modulation and coding schemes. This paper presents a review of recent results and research problems in high-speed underwater acoustic communications, focusing on the bandwidth-efficient phase-coherent methods. Experimental results are included to illustrate the state-of-the-art coherent detection of digital signals transmitted at 30 and 40 kb/s through a rapidly varying one-mile shallow water channel     

An integrated sensory-intelligent system for underwater acoustic signal-processing applications

A generic integrated sensory-intelligent system (ISIS) is developed for underwater acoustic signal-processing applications. ISIS constantly monitors the current acoustic channel conditions and smoothly integrates the outputs of the most appropriate signal-processing procedures or algorithms available to it for those conditions. The system is based on a generalization of a tuneable approximate piecewise linear (TAPL) model derived from the modified probabilistic neural network (MPNN). This model was designed to seamlessly integrate a set of local linear signal-processing algorithms within a given multidimensional data space. Depending on the input signal distortions, which are determined by environmental effects, ISIS automatically weighs and adds the outputs from a set of processing algorithms working in parallel. The weighting is related to the "closeness" of each algorithm to the sensed input signal characteristics or some other measured environmental state. A single tuning parameter is used to smoothly and seamlessly select appropriately among the parallel processing algorithm outputs. A very small tuning-parameter value selects the closest most appropriate algorithm output. At the other extreme, a fixed weighted average of all the algorithm outputs is produced with a very large value. Otherwise, a dynamic weighed average of all algorithm outputs is achieved with values in between. Some features and benefits of ISIS are demonstrated with an illustrative linear sweep chirp signal-detector estimation problem characterized by extremely variable Doppler conditions.     

Interrelations between matched-field processing and airborne MTIradar

In matched field processing (MFP) the spatial characteristics of a dispersive wave field are exploited to estimate certain parameters of the acoustic field, such as source location or characteristics of the acoustic channel including environmental parameters. In airborne MTI (AMTI) radar, interfering echoes (clutter) are Doppler colored due to the platform motion. Optimum clutter suppression requires space-time or space-frequency processing. Some thoughts concerning cross-fertilization between these two areas are put forward. In particular, the idea of space-time MFP is stressed. A processor for space-time power estimation is proposed