Case Study of Precision of GPS Differential Correction Strategies: Influence on aDcp Velocity and Discharge Estimates

Rennie, C. D.; Rainville, F.

doi:10.1061/(asce)0733-9429(2006)132:3(225)

Cited by 41 publications

(17 citation statements)

References 9 publications

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“…This can be explained by the fact that near the surface Method A is more sensitive to errors caused by positioning, while near the bed, hence with distance from the sounder, as the beam spread increases, the improvement obtained using Method A is more pronounced (Figure 11a). These values can reach ±0.03 m s -1 and confirms the earlier finding of Rennie and Rainville (2006) which showed that GPS corrections can have average errors of about ±0.03 m s -1 (Figures 12a and 12c). As Figure 12 shows, the magnitude of errors related to dGPS accuracy are higher than those related to tilt sensor accuracy, for both confluences.…”

Section: Number Of Repeat Transectssupporting

confidence: 90%

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Evaluation of aDcp processing options for secondary flow identification at river junctions

Moradi

Vermeulen

Rennie

et al. 2019

Earth Surf Processes Landf

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Secondary circulation in river confluences results in a spatial and temporal variation of fluid motion and a relatively high level of morphodynamic change. Acoustic Doppler current profiler (aDcp) vessel‐mounted flow measurements are now commonly used to quantify such circulation in shallow water fluvial environments. It is well established that such quantification using vessel‐mounted aDcps requires repeated survey of the same cross‐section. However, less attention has been given to how to process these data. Most aDcp data processing techniques make the assumption of homogeneity between the measured radial components of velocity. As acoustic beams diverge with distance from the aDcp probe, the volume of the flow that must be assumed to be homogeneous between the beams increases. In the presence of secondary circulation cells, and where there are strong rates of shear in the flow, the homogeneity assumption may not apply, especially deeper in the water column and close to the bed. To reduce dependence on this assumption, we apply a newly‐established method to aDcp data obtained for two medium‐sized (~60–80 m wide) gravel‐bed river confluences and compare the results with those from more conventional data processing approaches. The comparison confirms that in the presence of strong shear our method produces different results to more conventional approaches. In the absence of a third set of fully independent data, we cannot demonstrate conclusively which method is best, but our method involves less averaging and so in the presence of strong shear is likely to be more reliable. We conclude that it is wise to apply both our method and more conventional methods to identify where data analysis might be impacted upon by strong shear and where inferences of secondary circulation may need to be made more cautiously. © 2019 John Wiley & Sons, Ltd.

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Section: Number Of Repeat Transectssupporting

confidence: 90%

“…Czuba et al, 2011) and gravity currents (e.g. Such processing must take into account positioning (Rennie and Rainville, 2006) and orientation (Zhao et al, 2014) errors, and the treatment of repeat section measurements (e.g. Research has also shown the need to make repeat section measurements (e.g.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of aDcp processing options for secondary flow identification at river junctions

Moradi

Vermeulen

Rennie

et al. 2019

Earth Surf Processes Landf

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“…The compass error for the calibrated RiverSurveyor compass was assumed to be 2° [ Marsden , ], and the resulting error in bottom‐track velocity was calculated for every ensemble using equation (A7) of Rennie and Church []. The error in RTK‐GPS‐derived velocity was assumed to be 0.031 m s −1 [ Rennie and Rainville , ]. Finally, the total uncertainty due to both bed load temporal variability and measurement errors was calculated using the root sum of squares [ Rennie and Church , , equation (A6)].…”

Section: Methodsmentioning

confidence: 99%

“…The error in RTK-GPS-derived velocity was assumed to be 0.031 m s À1 [Rennie and Rainville, 2006]. Finally, the total uncertainty due to both bed load temporal variability and measurement errors was calculated using the root sum of squares [Rennie and Church, 2010, equation (A6)].…”

Section: Adcp Surveymentioning

confidence: 99%

Linking the spatial distribution of bed load transport to morphological change during high‐flow events in a shallow braided river

et al. 2015

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This paper provides novel observations linking the connections between spatially distributed bed load transport pathways, hydraulic patterns, and morphological change in a shallow, gravel bed braided river. These observations shed light on the mechanics of braiding processes and illustrate the potential to quantify coupled material fluxes using remotely sensed methods. The paper focuses upon a 300 m long segment of the Rees River, New Zealand, and utilizes spatially dense observations from a mobile acoustic Doppler current profiler (aDcp) to map depth, velocity, and channel topography through a sequence of high-flow events. Apparent bed load velocity is estimated from the bias in aDcp bottom tracking and mapped to indicate bed load transport pathways. Terrestrial laser scanning (TLS) of exposed bar surfaces is fused with the aDcp surveys to generate spatially continuous digital elevation models, which quantify morphological change through the sequence of events. Results map spatially distributed bed load pathways that were likely to link zones of erosion and deposition. The coherence between the channel thalweg, zone of maximum hydraulic forcing, and maximum apparent bed load pathways varied. This suggests that, in places, local sediment supply sources exerted a strong control on the distribution of bed load, distinct from hydraulic forcing. The principal braiding mechanisms observed were channel choking, leading to subsequent bifurcation. Results show the connection between sediment sources, pathways, and sinks and their influence on channel morphology and flow path directions. The methodology of coupling spatially dense aDcp surveys with TLS has considerable potential to understand connections between processes and morphological change in dynamic fluvial settings.

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“…Non-periodic and low frequency vertical motions, such as due to tides, squat, long-period heave, and other dynamic draft effects, can only be effectively measured by post-processing kinematic (PPK) or RTK GPS (Bisnath et al 2004b;Beaulieu et al 2009). Providing real-time measurements in the field, RTK GPS have been used to resolve water velocities measured with an ADCP into earth coordinates when bottom tracking is not possible (Rennie and Rainville 2006), to measure water levels from buoys (Rocken et al 1990;Kelecy et al 1994;Bisnath et al 2003), water surface profiles from river shores (Kessler and Lorenz 2010) or from a moving boat (Hess 2003;Zhao et al 2004;Bauer et al 2007;Sime et al 2007), wave heights (Bender et al 2010), in support to hydrographic surveys (Bisnath et al 2004a;Moegling et al 2009), and to verify and calibrate hydrodynamic models (Church et al 2008;Capra et al 2010).…”

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confidence: 99%

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2014

Limnology & Ocean Methods

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Direct measurement of water levels and velocities can provide fundamental insight into the hydrodynamics of tidal rivers and estuaries. They represent a reliable source of data for the verification and calibration of numerical models. Such knowledge is also crucial for navigation, environmental assessments, and coastal protection and development. To reach a high level of description, measured data must cover a wide range of spatial and temporal variability. Long-term monitoring stations provide high-frequency records, but they are usually limited in number, thereby limiting their ability to represent spatial features of the flow. Conversely, satellitebased measurements provide synoptic snapshots of a region, but they are limited in their temporal resolution and interpretation of the velocity field. Boat surveys remain the best compromise between fixed measurements and remote sensing observations for the characterization of nonstationary hydrodynamic fields. They can ensure both spatial and temporal coverage, provided that the sampling strategy and resolution is adapted to the size and rate of evolution of the structures measured (e.g., Rixen et al. 2001).In the field, meeting these requirements is often a challenge, as both the instrumentation and survey strategy must meet the criteria and constraints set by the users (e.g., sampling requirements, finite measurement time, and resources) and by the environment (e.g., presence of tides, size of the river). This has been facilitated in part by the development of new technologies over the last decades, including acoustic Doppler current profilers (ADCP) for water velocity meaQuantifying lateral and intratidal variability in water level and velocity in a tide-dominated river using combined RTK GPS and ADCP measurements AbstractCross-sectional gradients in water levels and velocities play a determining role in the circulation dynamics of tidal rivers and estuaries. Documenting and analyzing their variability throughout a tidal cycle require observations with high spatial and temporal resolution. A survey strategy and a data analysis procedure have been designed to obtain continuous and synoptic water level and velocity fields over a tidal cycle, along 13 cross-sections of the St. Lawrence fluvial estuary dominated by large tidal ranges. The method combines both RTK GPS and ADCP technologies for the simultaneous measurement of water levels and velocities along repeated boat transects, allowing fast data acquisition over wide river sections and under rapidly changing conditions. The reconstruction of continuous and synoptic fields is made by interpolation. Simplifying assumptions about data stationarity and/or homogeneity are avoided by adapting the interpolation procedures to the shape and distribution of the underlying data in a space-time reference frame, thus minimizing distortion in the reconstructed quantities. The capabilities and limitations of the method are assessed through error computations and comparisons with alternate data analysis methods and complement...

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Case Study of Precision of GPS Differential Correction Strategies: Influence on aDcp Velocity and Discharge Estimates

Cited by 41 publications

References 9 publications

Evaluation of aDcp processing options for secondary flow identification at river junctions

Evaluation of aDcp processing options for secondary flow identification at river junctions

Linking the spatial distribution of bed load transport to morphological change during high‐flow events in a shallow braided river

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