Moving-boat Acoustic Doppler Current Profiler Research Articles

Improvements to estimate ADCP uncertainty sources for discharge measurements

The use of moving boat ADCPs (Acoustic Doppler Current Profilers) for discharge measurements requires identification of the sources and magnitude of uncertainty to ensure accurate measurements. Recently, a tool known as QUant was developed to estimate the contribution to the uncertainty estimates for each transect of moving-boat ADCP discharge measurements, by varying different sampling configurations parameters through the use of Monte Carlo simulations. QUant is not only useful for estimating ADCP discharge measurement uncertainty, but also for identifying contributions of the various sources of uncertainty.However, the software requires long computational times, and the method to estimate the uncertainty of multiple-transect measurements does not consider the correlation of the variables between transects. Therefore, improvements in QUant are needed to optimize its application for practical purposes by hydrographers immediately after discharge measurements.This work presents four approaches for optimizing the performance of QUant to estimate the contribution to the uncertainty of different selected variables on ADCP discharge measurements and describes a new method of estimating multi-transect uncertainty with the QUant model that considers the correlation of errors in selected variables between transects. The approaches for optimization and the new multi-transect uncertainty method are evaluated using a dataset of 38 field measurements from a variety of riverine settings.

Estimating the Calibration Error–Caused Bias Limit of Moving-Boat ADCP Streamflow Measurements

AbstractThe bias error in moving-boat acoustic Doppler current profiler (ADCP) streamflow measurements can be separated into two classes: calibration and application. Accordingly, the total bias li...

Estimating Bias Limit of Moving-Boat ADCP Streamflow Measurements

AbstractThis paper presents a methodology for estimating the bias limit of moving-boat acoustic Doppler current profiler (ADCP) streamflow measurements based on the classical error analysis techniq...

Estimating uncertainty of streamflow measurements with moving-boat acoustic Doppler current profilers

ABSTRACTA theoretical and a semi-empirical model are presented for estimating the uncertainty of streamflow measurements made with an acoustic Doppler current profiler (ADCP) mounted on a moving platform. Both models are based on the statistical analysis of ADCP ensemble discharge time series collected during a transect; therefore, they account for all random error sources associated with the measurement at a site. The theoretical model is developed based on the law of propagation of variance; it explores the theoretical relationship between the variables involved in the problem. The semi-empirical model is developed based on the theory of dimensional analysis; it explores the empirical relationship between the variables. The semi-empirical model is calibrated using 205 transect datasets and verified with an additional 382 transect datasets. It provides a useful tool for the uncertainty analysis and uncertainty-based measurement quality control of moving-boat ADCP streamflow measurements.

Estimating random uncertainty of depth-averaged velocities measured by moving-boat acoustic Doppler current profilers

This paper presents a mathematical model for estimating the standard uncertainty of depth-averaged velocities measured by moving-boat acoustic Doppler current profilers. A general form of the presented uncertainty model was developed based on the law of propagation of variances and dimensional analysis. It was then calibrated using 30 datasets of stationary ADCP measurements, in which standard uncertainties were available from statistical analysis of the data. Because the model utilizes velocity data collected at a site, it accounts for all random error sources including ADCP system noise and ambient turbulence encountered at the site; it also accounts for the cross-correlation of ADCP depth cells in velocity measurements. The presented uncertainty model can be used in field surveys or data post-processing. It provides a useful tool for assessing the quality of ADCP measured depth-averaged velocities. A moving-boat ADCP measurement on the Mississippi River is presented as an application example. This paper also explores some insights on ADCP velocity profile and time series data.

Monte Carlo Approach for Uncertainty Analysis of Acoustic Doppler Current Profiler Discharge Measurement by Moving Boat

AbstractThis paper presents a method using Monte Carlo simulations for assessing uncertainty of moving-boat acoustic Doppler current profiler (ADCP) discharge measurements using a software tool known as QUant, which was developed for this purpose. Analysis was performed on 10 data sets from four Water Survey of Canada gauging stations in order to evaluate the relative contribution of a range of error sources to the total estimated uncertainty. The factors that differed among data sets included the fraction of unmeasured discharge relative to the total discharge, flow nonuniformity, and operator decisions about instrument programming and measurement cross section. As anticipated, it was found that the estimated uncertainty is dominated by uncertainty of the discharge in the unmeasured areas, highlighting the importance of appropriate selection of the site, the instrument, and the user inputs required to estimate the unmeasured discharge. The main contributor to uncertainty was invalid data, but spatial inh...

Application of shallow-water acoustic tomography to measure flow direction and river discharge

High-frequency Fluvial Acoustic Tomography System (FATS) was initially used to measure flow velocity and river discharge in a mountainous river. The results showed the high-frequency FATS, not only improves the velocity resolution, but also reduces the minimum operational range from 76m to 43m in compare with the previous type of FATS. The analysis of sound wave propagation (Ray tracing) showed the bottom topography can be the reason of multi-ray paths of sound wave in the shallow freshwater rivers. A new formula based on the continuity equation introduced to estimate the variations of the angle between the flow direction and the FATS transmission line. The flow direction was measured using two crossed FATS transmission lines of 53kHz and 30kHz. The results compared to the up-looking ADCP (Acoustic Doppler Current Profiler) deployed near the intersection of the two lines which measured the changes in flow direction. The results affirmed the efficiency of the proposed method. Finally, the river discharge was estimated by both FAT systems and compared to the Rating Curve method and moving-boat ADCP estimates. The relative error of the FATS discharge measurements was less than 10%.

Statistical quality control of streamflow measurements with moving-boat acoustic Doppler current profilers

ABSTRACTThis technical note presents a new methodology for the statistical quality control of streamflow measurements with moving-boat acoustic Doppler current profilers. The methodology consists of two alternative acceptance criteria: uncertainty-based and residual-based. The former uses the uncertainty and the latter uses the maximum residual as a measurement quality indicator. Application examples are given to compare the proposed criteria with the existing criteria. The proposed criteria provide a unified quality control and may help determine the optimal number of transacts, avoiding potentially overdone or insufficient measurements.

Improved flow velocity estimates from moving-boat ADCP measurements

Acoustic Doppler current profilers (ADCPs) are the current standard for flow measurements in large-scale open water systems. Existing techniques to process vessel-mounted ADCP data assume homogeneous or linearly changing flow between the acoustic beams. This assumption is likely to fail but is nevertheless widely applied. We introduce a new methodology that abandons the standard assumption of uniform flow in the area between the beams and evaluate the drawbacks of the standard approach. The proposed method strongly reduces the extent over which homogeneity is assumed. The method is applied to two field sites: a mildly curved bend near a junction featuring a typical bend flow and a sharply curved bend that features a more complex sheared flow. In both cases, differences are found between the proposed method and the conventional method. The proposed technique yields different results for secondary flow patterns compared with the conventional method. The velocity components estimated with the conventional method can differ over 0.2 m/s in regions of strong shear. We investigate the number of repeat transects necessary to isolate the mean flow velocity vector from the raw ADCP signal, discarding the influences of noise, positioning and projection errors, and turbulence. Results show that several repeat transects are necessary. The minimum number of repeat measurements needed for robust mean velocity estimates is reduced when applying the proposed method.

Continuous monitoring of a dam flush in a shallow river using two crossing ultrasonic transmission lines

Continuous measurements of streamflow and water temperature were carried out in a shallow gravel-bed river during dam flushing operations using a new shallow acoustic system with two crossing transmission lines. The fluvial acoustic system (FAS) was equipped with four 25 kHz broadband omnidirectional transducers. The reciprocal sound transmissions were performed between the two pairs of acoustic stations, located on both sides of the river. The four-station FAS enabled the measurement of the stream direction in addition to the depth- and range-averaged sound speed, and therefore water velocity. Discharge values computed from FAS reports were compared to those estimated by the moving-boat acoustic Doppler current profiler (ADCP) and rating curve (RC) methods. FAS estimates were in good agreement with ADCP and RC estimates over a range of 50 to 180 m3 s−1. The temperature gradients induced strong sound scattering for the 25 kHz FAS. The fine suspended sediment particles also induced a gradual decrease in the signal-to-noise ratio of the FAS. Nevertheless, the FAS has been proved to be a reliable and accurate technique for the continuous measurement of cross-sectional average velocity/water temperature.

Extrap: Software to assist the selection of extrapolation methods for moving-boat ADCP streamflow measurements

Selection of the appropriate extrapolation methods for computing the discharge in the unmeasured top and bottom parts of a moving-boat acoustic Doppler current profiler (ADCP) streamflow measurement is critical to the total discharge computation. The software tool, extrap, combines normalized velocity profiles from the entire cross section and multiple transects to determine a mean profile for the measurement. The use of an exponent derived from normalized data from the entire cross section is shown to be valid for application of the power velocity distribution law in the computation of the unmeasured discharge in a cross section. Selected statistics are combined with empirically derived criteria to automatically select the appropriate extrapolation methods. A graphical user interface (GUI) provides the user tools to visually evaluate the automatically selected extrapolation methods and manually change them, as necessary. The sensitivity of the total discharge to available extrapolation methods is presented in the GUI. Use of extrap by field hydrographers has demonstrated that extrap is a more accurate and efficient method of determining the appropriate extrapolation methods compared with tools currently (2012) provided in the ADCP manufacturers' software.

Practical aspects of ADCP data use for quantification of mean river flow characteristics; Part II: fixed-vessel measurements

Acoustic Doppler Current Profilers (ADCP) are increasingly used for velocity and discharge measurements in riverine environment capitalizing on operation efficiency and rugged configuration. Part I of the paper investigated the potential of the moving-boat ADCP measurements to appropriately describe mean velocity field in river cross sections. It was concluded that the ADCP data collected during transects for estimation of discharges is not readily usable for estimation of the mean velocity distribution over the depth. Given the increased demand of the latter data for studies such as sediment transport, ecohabitat restoration, and for supporting numerical simulations, measurements with ADCP at fixed locations are evaluated from the same perspective. The paper reviews first general instrument requirements to accurately measure mean and time-resolved characteristics of turbulent river flows and subsequently formulates practical guidelines for conducting measurements of this kind. Next, the paper analyzes a set of ADCP data collected at fixed river locations using long sampling times. The effect of sampling time length on the accuracy of the mean velocities and turbulence intensities profiles is investigated using several statistical criteria. Time-resolved turbulence characteristics, such as autocorrelation and power spectrum, are also analyzed to verify ADCP capabilities to capture finer details of the turbulence in riverine environment. Additionally, the paper reviews the potential of ADCP fixed-location measurements to measure depth and to quantify near-bed layer velocities.