Measurements of Reynolds stress in a wind-driven lagoonal estuary

Acoustic Doppler current profilers (ADCPs) have been used to measure Reynolds stresses in tidally dominated environments where wave action was minimal. In this paper, we examine observations from a microtidal estuary where the effects of wind stress and surface waves dominate the velocity variance. Reynolds stress measurements in this setting require a technique for addressing surface gravity wave contamination. We present here a method of reducing the effect of wave motion on Reynolds stresses by subtracting coincident observations along the axis of the ADCP beam. Linear wave theory is used to account for the attenuation of wave orbital velocities with depth. Using this method, Reynolds stress values are brought in line with those predicted by drag laws at the surface and bottom. The apparent Reynolds stress that is removed by the along-axis subtraction is shown to be largely due to the interaction of a slight tilt (1°) in the ADCP and the wave orbital velocity. During periods of stronger wind and waves, there is evidence of enhanced near-surface turbulence and momentum flux, presumably due to breaking waves. During these events, our calculated Reynolds stress magnitudes still appear reasonable, although the directions are suspect. We develop a diagnostic technique that clearly demarcates this region when it occurs. Coincident density profile measurements are used with the ADCP data to compute gradient Richardson numbers throughout the water column. Enhanced Reynolds stresses appear to correspond to Richardson numbers less than one. Responsible editor: Alejandro Souza     

Estimating sand concentrations using ADCP-based acoustic inversion in a large fluvial system characterized by bi-modal suspended-sediment distributions

Quantifying sediment flux within rivers is a challenge for many disciplines due, mainly, to difficulties inherent to traditional sediment sampling methods. These methods are operationally complex, high cost, and high risk. Additionally, the resulting data provide a low spatial and temporal resolution estimate of the total sediment flux, which has impeded advances in the understanding of the hydro-geomorphic characteristics of rivers. Acoustic technologies have been recognized as a leading tool for increasing the resolution of sediment data by relating their echo intensity level measurements to suspended sediment. Further effort is required to robustly test and develop these techniques across a wide range of conditions found in natural river systems. This article aims to evaluate the application of acoustic inversion techniques using commercially available, down-looking acoustic Doppler current profilers (ADCPs) in quantifying suspended sediment in a large sand bed river with varying bi-modal particle size distributions, wash load and suspended-sand ratios, and water stages. To achieve this objective, suspended sediment was physically sampled along the Paraná River, Argentina, under various hydro-sedimentological regimes. Two ADCPs emitting different sound frequencies were used to simultaneously profile echo intensity level within the water column. Using the sonar equation, calibrations were determined between suspended-sand concentrations and acoustic backscatter to solve the inverse problem. The study also analyzed the roles played by each term of the sonar equation, such as ADCP frequency, power supply, instrument constants, and particle size distributions typically found in sand bed rivers, on sediment attenuation and backscatter. Calibrations were successfully developed between corrected backscatter and suspended-sand concentrations for all sites and ADCP frequencies, resulting in mean suspended-sand concentration estimates within about 40% of the mean sampled concentrations. Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant across evaluations, suggesting that they could be applied to other sand bed rivers. © 2018 John Wiley & Sons, Ltd.     

基于ADCP反演渤海湾悬浮体浓度年变化

基于座底ADCP实测回波强度信号,结合短期实测悬浮体质量浓度,反演长时间序列悬浮体质量浓度,定量分析了渤海湾近一年悬浮体质量浓度变化特征及其影响因素。结果表明:受风浪影响,该区悬浮体质量浓度具有明显季节性变化特征,风浪作用强烈的季节其悬浮体浓度表现为相对高值。悬浮体净输运同样具明显季节性变化,秋冬强风浪作用下,悬浮体的净输运量明显增加;而在不同季节,月净输运方向具有不同的主输运方向。悬浮体质量浓度日变化受潮流控制明显,长周期变化则主要与风场的变化有关。潮流涨急过程与风致大浪过程均可引起沉积物再悬浮,导致悬浮体浓度明显增高。     

国产走航式声学海流剖面仪的应用分析

针对国产走航式声学海流剖面仪的应用性能进行评价,为用户及生产厂家提供借鉴。首先,就国产走航式声学海流剖面仪的实际数据,从不同角度和层面,全面分析和考察了其测量数据的各项性能,有针对性地绘制了各类图件,并通过数据质量、数据有效性、测流精度、测流深度等各方面的分析比对,对国产走航式声学海流剖面仪做出定性评价。其次,通过与国外同类仪器的以往应用情况进行对比分析,发现在船只转向和往复航行、加速和减速航行、高速航行时,国产走航式声学海流剖面仪表现更佳。最后,基于应用中的不足给出相关建议。     

南海北部海盆三分量磁测结果分析

1994年,中日双方合作在南海北部开展了海洋三分量磁测实验工作,采用日本东京大学地震研究所新研制的船载三分量磁力仪（Shipboard Three Component Magnetmeter,STCM）在南海北部海盆成功获得了6条共约2 500km的三分量磁测资料。本文根据前人的研究思路实现了对实测三分量磁测资料的处理分析,改进了补偿圆滑滤波算法,首次提出了比原方法更加综合直观表示测区各种磁边界状况的磁边界走向图（Magnetic boundary strike diagram, MBSD）法,并且将处理结果与南海北部海盆已识别的磁条带及其他一些典型地质现象进行了对比分析,发现本方法所揭示出的二维及三维磁边界与南海的实际地质状况有良好的吻合关系,这表明该方法可以有效处理所采集的三分量磁测资料并对研究海底磁性构造体性质有帮助。     

基于船载ADCP观测对半封闭海湾湾口断面潮流及余流的分析（英文）

基于对罗源湾可门水道的25小时连续走航ADCP观测,本文成功构建了沿走航断面共12个站位的连续海流时间序列,并对这些站位的潮流、余流以及潮通量等进行了分析。结果表明可门水道内的潮流为正规半日潮流,驻波性质明显,涨潮首先出现在水道中下层而退潮则首先发生在水道上层。水道内潮流为往复流,水道南部M2分潮流流速较大,并且其倾角自北向南逐渐增加。此外,水道两端的浅水区域内浅水分潮M4振幅较显著。可门水道内余流呈现出两层结构,20m以浅余流沿东北向流出海湾,并且出流的核心位置偏南,而20m以深的余流沿西南向流入湾内,入流的流核位于偏北的近底层区域。对潮通量的积分计算表明通过可门水道进入罗源湾的潮通量约为4.81×10^8m^3。     

用ADCP进行走航式悬沙浓度测量的初步研究

用ＤＲ３００型宽幅ＡＤＣＰ在胶洲湾口站进行了走航工断面观测。观测期间悬沙浓度小于４０ｍｇ／Ｌ,悬沙粒度分布曲线具有双峰特征,调查船航速为２￣３ｍ／ｓ。用水样过滤法率定相应的ＡＤＣＰ声学信号,获得池计算悬沙浓度的半经验公式及悬沙浓度剖面分布数据,分析结果即使在悬沙浓度较低,悬沙分选性较差,船速较高等不利于ＡＤＣＰ观测的现场条件下,测量误差与光透式浊度计的误差相当。因此,在走航状态和低悬沙浓度条件下     

Variability of Currents off the Northern Coast of New Guinea

The variability of the New Guinea Coastal Current (NGCC) and New Guinea Coastal Undercurrent (NGCUC) were examined from one year time series of current data from ADCP moorings at 2°S, 142°E and 2.5°S, 142°E. Change in the hydrographic structure induced by monsoonal wind forcing was also examined from hydrographic data along the 142°E covering consecutively two winter seasons and two summer seasons. The westward NGCUC was observed to persist year around. The annual mean depth of the current core was 220 m, the mean speed of the zonal component was 54 cm/s with a standard deviation of 15 cm/s at the 2.5°S site. Velocity fluctuations at 20–30 day period were observed year around. Seasonal reversal of the surface intensified NGCC was clearly observed. In the boreal summer characterized by the southeasterly monsoon, westward currents of over 60 cm/s were dominant in the surface layer. The warm, low-salinity layer thickened at this time and sloped down toward the New Guinea coast from the equator. This surface water accumulation may be caused by onshore Ekman drift at the New Guinea coast, combined with weak Ekman upwelling at the equator. In the boreal winter, an eastward surface current developed to 100 cm/s extending down to 100 m depth in response to the northwesterly monsoonal winds. Coastal upwelling was indicated in this season and the surface water accumulated at the equator due to Ekman convergence. Shipboard ADCP data indicated that the NGCUC intensified in boreal summer as the width and depth of the NGCUC increased.     

ADCP application for long-term monitoring of coastal water

Three kind of application of ADCP is reported for long-term monitoring in coastal sea. (1)The routine monitoring of water qualities. The water quality and ADCP echo data (600 kHz) observed in the long-term are analgzed at MT (Marine Tower) Station of Kansai International Airport in the Osaka Bay, Japan. The correlation between the turbidity and echo intensity in the surface layer is not good because air bubbles generated by breaking wave are not detected by the turbidity meter, but detected well by ADCP. When estimating the turbidity consists ofplankrton population from echo intensity, the effect of bubbles have to be eliminated. (2) Monitoring stirring up of bottom sediment. The special observation was carried out by using following two ADCP in the Osaka Bay, One ADCP was installed upward on the sea. The other ADCP was hanged downward at the gate type stand about 3 m above from the bottom. At the spring tide, high echo intensities indicating the stirring up of bottom sediment were observed. (3) The monitoring for the boundary condition of water mixing at an estuary. In summer season, the ADCP was set at the mouth of Tanabe Bay in Wakayama Prefecture, Japan. During the observation, water temperature near the bottom showed remarkable falls with interval of about 5～7d. When the bottom temperature fell, the inflow current with low echo intensity water appears at the bottom layer in the ADCP record. It is concluded that when occasional weak northeast wind makes weak coastal upwelling at the mouth of the bay, the combination ofupwelling with internal tidal flow causes remarkable water exchange and dispels the red tide.     

Conversion of Pressure to Depth for Moored Instruments Using a Reference Bottom Mounted Pressure Sensor

A new method is proposed to convert pressure measured by an instrument to water depth using an additional available bottom-moored pressure sensor. A perturbation analysis is used in this analysis, which leads to a simple formula for calculating water depth (defined as one from the mean sea surface to the instrument) from the pressure data. In field experiments, this method is easier to apply than existing methods. Based on the theoretical derivation, the error associated with the method comes from two sources when the instrument depth is known at the beginning of the measurement: temporal variation of deep water density at depths deeper than the instrument and variation in the gravitational acceleration with instrument displacement. These two sources contribute up to 4% of the error relative to the vertical displacement of the instrument, assuming the pressure sensor is accurate. With the vertical displacement of the instrument being on the order of 10?m, the absolute error is on the order of 0.4?m, which is expected and acceptable in oceanic measurements. The method is applied to data from a field experiment that took place along the Myanmar coast in December 2012.