Verification of mean volume backscattering strength obtained from acoustic Doppler current profiler by using sound scattering layer

ABSTRACT:   Acoustic Doppler current profilers (ADCPs) have recently been used to estimate the dynamic characteristics and biomass of sound scattering layers (SSLs) or swimming speed of fish schools and to analyze SSL spatial distribution or various behavior patterns. This paper shows that it is necessary to verify mean volume backscattering strength (MVBS, dB) values acquired from each beam for quantitative analysis of the spatial distribution or the biomass estimates of such specific targets as SSL or a fish school when using an ADCP. In this study, the SSL was selected to be a homogeneous density layer over a large area and two methods were used to verify the MVBS values from each beam of the ADCP. First, a mutual comparison among four beams was conducted after calculating MVBS from the measured echo intensity. Second, the MVBS values were verified using comparison between the calculated MVBS from the 153.6 kHz ADCP and MVBS from three frequencies of a well-calibrated scientific echosounder. Moreover, the dominant scatterers (euphausiids) were collected by a framed midwater trawl. From these samples, biological data were used to identify the different frequency characteristics between two systems, using a distorted-wave Born approximation (DWBA) theoretical backscattering model in order to assess the averaged target strength and target strength TS differences for the three frequencies.     

Variability in the spawning habitat of Pacific sardine (Sardinops sagax) off southern and central California

The spatial pattern of sardine spawning as revealed by the presence of sardine eggs is examined in relation to sea surface temperature (SST) and mean volume backscatter strength (MVBS) measured by a 150 kHz acoustic Doppler current profiler (ADCP) during four spring surveys off central and southern California in 1996–99. Studies in other regions have shown that MVBS provides an excellent measure of zooplankton distribution and density. Zooplankton biomass as measured by survey net tows correlates well with concurrently measured MVBS. The high along‐track resolution of egg counts provided by the Continuous Underway Fish Egg Sampler (CUFES) is a good match to the ADCP‐based data. Large interannual differences in the pattern and density of sardine eggs are clearly related to the concurrently observed patterns of surface temperature and MVBS. The strong spatial relationship between sardine eggs and MVBS is particularly evident because of the large contrast in zooplankton biomass between the 1998 El Niño and 1999 La Niña. The inshore distribution of sardine spawning appears to be limited by the low temperatures of freshly upwelled waters, although the value of the limiting temperature varies between years. Often there is an abrupt offshore decrease in MVBS that is coincident with the offshore boundary of sardine eggs. Possible reasons for this association of sardine eggs and high zooplankton biomass include an evolved strategy that promotes improved opportunity of an adequate food supply for subsequent larval development, and/or adult nutrient requirements for serial spawning. Hence, the distribution of these parameters can be used as an aid for delineating the boundaries of sardine spawning habitat.     

Using an ADCP to determine canal seepage loss in an irrigation district

Seepage from earthen irrigation canals represents substantial water loss in irrigation districts. Historically, the determination of canal seepage was accomplished using the inflow-outflow method with propeller and electromagnetic type flow meters. This method was difficult, time consuming, and limited by measurement device accuracy. In recent years, advances in technology have lead to the widespread use of Acoustic Doppler Current Profilers (ADCP) for discharge measurements in streams and rivers. Even though ADCP use has become widespread for stream discharges, studies to determine canal seepage using this new technology are limited. Using an ADCP, extensive field measurements were conducted in the Middle Rio Grande Conservancy District. This paper describes the ADCP measurement protocol used to measure irrigation canal seepage and presents predictive equations for determining canal seepage based on flow rate and canal geometry.     

Observation of three‐dimensional flow structures and effluent transport around fish cages using a towed ADCP and free‐fall multi‐parameter profiler

A field campaign was conducted around salmon cages, using a combination of a towed ADCP and a free‐fall multi‐parameter profiler, in order to investigate flow structures and the possible distribution of effluent materials. Two transect observations showed that hydrographic conditions changed dramatically within 5 days, from highly stratified open water conditions to weak stratification. Three‐dimensional observation revealed that flow was blocked behind the cages and that the blockage was reduced as the distance from the cages increased. The flow speed was positively correlated with the intensity of the backscattering signal. The R² value was high immediately behind the cages and decreased with distance from the cages. The flow time series behind the cages exhibited a k^–2 power law spectrum that was consistent with a typical internal wave spectrum. This suggests that eddies shed from the cages were highly influenced by stratification. We estimated the rate of kinetic energy dissipation, , from YODA Profiler data based on the Thorpe scale approach. We also estimated the eddy diffusivity coefficient, . Both and followed a lognormal probability density function. The mean was consistent with a one‐dimensional diffusion model assessed from the R² values of flow speed and backscatter intensity.     

Modelling the dispersal of larval Japanese sardine, Sardinops melanostictus, by the Kuroshio Current in 1993 and 1994

Acoustic Doppler current profiler (ADCP) data collected during routine monitoring surveys of the distribution and abundance of Japanese sardine larvae ( Sardinops melanostictus ) off the Pacific coast of Japan in February 1993 and 1994 were used to construct stationary average flowfields for three levels in the upper 100 m in each year. No large-scale meanders in the path of the Kuroshio Current were present in either year, but the axis of the current was closer to the coast in 1993 than in 1994. The flowfields were used to drive a particle-tracking model representing the dispersal of sardine eggs and larvae. Particles were released in accordance with the observed distribution of eggs, and their positions tracked for up to 40 days. In 1993, the model indicated that ≈ 50% of the egg production was carried north-eastwards out of the survey area into the area of the NW Pacific referred to as the Kuroshio Extension Zone. In contrast, only 5% of the egg production was exported to the Extension Zone in 1994, the remainder being retained in Japanese coastal waters. The consequences of the different dispersal patterns are discussed in relation to subsequent recruitment to the sardine stock. Based on commercial catch data, survival of the 1993 year class was 15% of that for the 1994 class. Hence, the results indicate that export of larvae to the Kuroshio Extension cannot in itself lead to successful recruitment.     

ADP应用于黄河水文测验的探讨

Acoustic Doppler Current Profilers(ADCP)是利用声学多普勒原理进行研制的，是目前世界上最为先进的河流流速流量实时测量设备.介绍了这种设备的性能,设备装置及应用方法.在当前治黄工作对水文测验提出的高频,在线,实时的水文现代化要求下,ADCP在黄河水文测验中有着明显的应用优势,同时,支持ADCP在我国推广应用的相关技术规范需尽早出台.     

基于计算机的信息数据处理方法研究

针对目前数据质量控制和处理方法的问题,采用拉依达准则剔除异常数据,卡尔曼滤波处理同一水层的数据,平滑滤波处理剖面上的数据,Akima插值计算缺测层的数据。通过实验检验,非常有效。     

走航式多普勒流速剖面仪在水文测验中的应用

多普勒流速剖面仪(Doppler Current Profiler)是世界先进和快速有效的测流仪器.本文通过分析声学多普勒流速剖面仪的测流原理,与传统测流方法对比声学多普勒流速剖面仪.通过大创项目,结合山东滨海地区河流的实际测流,主要探讨了声学多普勒流速剖面仪(Acoustic Doppler Current Profiler,ADCP)的突出优点.ADCP的合理使用可以为未来河道开发治理、水资源管理和防洪减灾提供科学依据.     

Horizontal current field, ADCP backscatter, and plankton distribution in Sagami Bay, Japan

The dry mass of zooplankton and backscatter from an acoustic Doppler current profiler (ADCP) used in Sagami Bay, Japan, from 9 to 13 April 2005 were well correlated (correlation coefficient = 0.72, root mean square dry weight = 2.5 mg m⁻³). The horizontal current field and zooplankton distribution were estimated from shipboard ADCP data. Although sea surface temperature and chlorophyll a concentration observed by satellite were consistent with the current field, a counterclockwise circulation associated with the Kuroshio meander, zooplankton were mainly distributed downstream of the phytoplankton population by horizontal current advection.     

宽带声学多普勒技术用于灌区量水

在美国加利福尼亚州Imperial灌区进行了便携式微型ADCP现场试验，并采用河流型ADCP同步比测。微型ADCP六次实测流量相对标准差仅为1.22 %。在该灌渠试验条件下，微型ADCP单次流量测验随机不确定度仅为1.75%，达到国家规范一类精度水文站高水位级允许总随机不确定度指标。试验和分析结果表明，微型ADCP精度高、使用方便，比河流型ADCP更适合灌区量水，可以取代传统流速仪作为率定或校核其它灌区量水方法的标准仪器。