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Stuart N. Lane - One of the best experts on this subject based on the ideXlab platform.
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quantification of braided river Channel Change using archival digital image analysis
Earth Surface Processes and Landforms, 2010Co-Authors: Stuart N. Lane, P E Widdison, Robert E Thomas, Philip Ashworth, James L Best, Ian A Lunt, G Sambrook H Smith, Christopher J SimpsonAbstract:Historical archives of grey-scale river Channel imagery are extensive. Here, we present and test a methodology to extract detailed quantitative topographic date from such imagery of sand-bed rivers. Extracting elevation information from rivers is difficult as they are characterized by a low relative relief (less than 4 m); the area of interest may be spatially extensive (e.g. active Channel widths > 500 m in large braided rivers); the rate of Change of surface elevation is generally low except in the vicinity of individual Channel banks where the rate of Change is very high: there is the complication that comes from innundation: and there may be an added complication caused by blockage of the field of view by vegetation. Here, we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand-bed braided river dynamics, illustrated for a 500 m wide, 3 km long reach of the Spouth Sasketchewan River, Canada. Digitial photogrammetry was used to quantify dry areas and water edge elevations. A methodology was then used to calibrate the special signature of inundated areas by combining established two media digital photogrammetric methods and image matching. This allowed determination of detailed depth maps for inundated area and, when combined with dry area data, creation of depths detectable from sequential digital elevation models. The result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of rivers without needing associated calibration data, provided that imagery is of the necessary scale to capture the features of interest. We use these data to highlight several aspects of Channel Change on the South Saskatchewan River, including bar movement, bank erosion and Channel infilling.
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using sediment impact sensors to improve the morphological sediment budget approach for estimating bedload transport rates
Geomorphology, 2010Co-Authors: Emma Raven, Stuart N. Lane, R I FergusonAbstract:Constructing a sediment budget from morphological Channel Change, typically measured using repeat cross-sectional surveys, has proven a useful technique for estimating mean bedload transport rates in gravel-bed rivers. We apply and suggest improvements to the approach using new data sources from an intensely monitored 5.6 km reach of an upland gravel-bed river in northern England. Sediment impact sensors were placed in the bed to record the instantaneous passage of grains during transport events. These sensors provide valuable information for the budget including: (1) a downstream budget limit from which the rest of the budget can be calculated; (2) estimates of sediment input from tributaries; and (3) a better indication of active transport time used in the calculation of average transport rates. Further information collected from field studies include estimates of lateral inputs from the banks using field surveys and bank erosion pins and estimates of the variability of sediment porosity from bed grain size distributions. Budget calculations for different locations and time periods demonstrate large spatial and temporal variabilities in bedload transport rates over a short distance (< 3 km). Whilst some uncertainty in the new data sources remains, this work highlights some limitations of the traditional budget approach and some potential solutions; in particular the value of sediment impact sensors for sediment transport studies.
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interactions between sediment delivery Channel Change climate Change and flood risk in a temperate upland environment
Earth Surface Processes and Landforms, 2007Co-Authors: Stuart N. Lane, V Tayefi, Simon C Reid, Dapeng Yu, R J HardyAbstract:This paper uses numerical simulation of flood inundation based on a coupled one-dimensional–two-dimensional treatment to explore the impacts upon flood extent of both long-term climate Changes, predicted to the 2050s and 2080s, and short-term river Channel Changes in response to sediment delivery, for a temperate upland gravel-bed river. Results show that 16 months of measured in-Channel sedimentation in an upland gravel-bed river cause about half of the increase in inundation extent that was simulated to arise from climate Change. Consideration of the joint impacts of climate Change and sedimentation emphasized the non-linear nature of system response, and the possibly severe and synergistic effects that come from combined direct effects of climate Change and sediment delivery. Such effects are likely to be exacerbated further as a result of the impacts of climate Change upon coarse sediment delivery. In generic terms, these processes are commonly overlooked in flood risk mapping exercises and are likely to be important in any river system where there are high rates of sediment delivery and long-term transfer of sediment to floodplain storage (i.e. alluviation involving active Channel aggradation and migration). Similarly, attempts to reduce Channel migration through river bank stabilization are likely to exacerbate this process as without bank erosion, Channel capacity cannot be maintained. Finally, many flood risk mapping studies rely upon calibration based upon combining contemporary bed surveys with historical flood outlines, and this will lead to underestimation of the magnitude and frequency of floodplain inundation in an aggrading system for a flood of a given magnitude. Copyright © 2006 John Wiley & Sons, Ltd.
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interactions between sediment delivery Channel Change climate Change and flood risk in a temperate upland environment
Earth Surface Processes and Landforms, 2007Co-Authors: Stuart N. Lane, V Tayefi, Simon C Reid, R J HardyAbstract:This paper uses numerical simulation of flood inundation based on a coupled one-dimensional-two-dimensional treatment to explore the impacts upon flood extent of both long-term climate Changes, predicted to the 2050s and 2080s, and short-term river Channel Changes in response to sediment delivery, for a temperate upland gravel-bed river. Results show that 16 months of measured in-Channel sedimentation in an upland gravel-bed river cause about half of the increase in inundation extent that was simulated to arise from climate Change. Consideration of the joint impacts of climate Change and sedimentation emphasized the non-linear nature of system response, and the possibly severe and synergistic effects that come from combined direct effects of climate Change and sediment delivery. Such effects are likely to be exacerbated further as a result of the impacts of climate Change upon coarse sediment delivery. In generic terms, these processes are commonly overlooked in flood risk mapping exercises and are likely to be important in any river system where there are high rates of sediment delivery and long-term transfer of sediment to floodplain storage (i.e. alluviation involving active Channel aggradation and migration). Similarly, attempts to reduce Channel migration through river bank stabilization are likely to exacerbate this process as without bank erosion, Channel capacity cannot be maintained. Finally, many flood risk mapping studies rely upon calibration based upon combining contemporary bed surveys with historical flood outlines, and this will lead to underestimation of the magnitude and frequency of floodplain inundation in an aggrading system for a flood of a given magnitude.
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estimation of erosion and deposition volumes in a large gravel bed braided river using synoptic remote sensing
Earth Surface Processes and Landforms, 2003Co-Authors: Stuart N. Lane, Richard M Westaway, Murray D HicksAbstract:System-scale detection of erosion and deposition is crucial in order to assess the transferability of findings from scaled laboratory and small field studies to larger spatial scales. Increasingly, synoptic remote sensing has the potential to provide the necessary data. In this paper, we develop a methodology for Channel Change detection, coupled to the use of synoptic remote sensing, for erosion and deposition estimation, and apply it to a wide, braided, gravel-bed river. This is based upon construction of digital elevation models (DEMs) using digital photogrammetry, laser altimetry and image processing. DEMs of difference were constructed by subtracting DEM pairs, and a method for propagating error into the DEMs of difference was used under the assumption that each elevation in each surface contains error that is random, independent and Gaussian. Data were acquired for the braided Waimakariri River, South Island, New Zealand. The DEMs had a 1·0 m pixel resolution and covered an area of riverbed that is more than 1 km wide and 3·3 km long. Application of the method showed the need to use survey-specific estimates of point precision, as project design and manufacturer estimates of precision overestimate a priori point quality. This finding aside, the analysis showed that even after propagation of error it was possible to obtain high quality DEMs of difference for process estimation, over a spatial scale that has not previously been achieved. In particular, there was no difference in the ability to detect erosion and deposition. The estimates of volumes of Change, despite being downgraded as compared with traditional cross-section survey in terms of point precision, produced more reliable erosion and deposition estimates as a result of the large improvement in spatial density that synoptic methods provide. Copyright © 2003 John Wiley & Sons, Ltd.
Jeanyves Tourneret - One of the best experts on this subject based on the ideXlab platform.
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echo cancellation the generalized likelihood ratio test for double talk versus Channel Change
IEEE Transactions on Signal Processing, 2009Co-Authors: Jeanyves Tourneret, N J Bershad, J C M BermudezAbstract:Echo cancellers (EC) are required in both electrical (impedance mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The optimum likelihood ratio test (LRT) for this problem was studied in a recent paper. The LRT requires a priori knowledge of the background noise and double-talk power levels. Instead, this paper derives a generalized log likelihood ratio test (GLRT) that does not require this knowledge. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a Channel Change, based upon a single look. However, detection based on about 200 successive samples yields a detection probability close to unity (0.99) with a small false alarm probability (0.01) for the theoretical GLRT model. Application of a GLRT-based EC to real voice data shows comparable performance to that of the LRT-based EC given in a recent paper.
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echo cancellation a likelihood ratio test for double talk versus Channel Change
IEEE Transactions on Signal Processing, 2006Co-Authors: N J Bershad, Jeanyves TourneretAbstract:Echo cancellers (ECs) are in wide use in both electrical (four-wire to two-wire mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The control logic can be quite complicated since it is often not easy to discriminate between the echo signal and the near-end speaker. This paper derives a log-likelihood ratio test (LRT) for deciding between double-talk (freeze weights) and a Channel Change (adapt quickly) using a stationary Gaussian stochastic input signal model. The probability density function (pdf) of a sufficient statistic under each hypothesis is obtained, and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a Channel Change based upon a single look. However, postdetection integration of approximately 100 sufficient statistic samples yields a detection probability close to unity (0.99) with a small false-alarm probability (0.01)
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echo cancellation a likelihood ration test for double talk vs Channel Change
International Conference on Acoustics Speech and Signal Processing, 2006Co-Authors: N J Bershad, Jeanyves TourneretAbstract:Echo cancellers are in wide use in both electrical (four wire to two wire mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The control logic can be quite complicated (C. Breining et al., 1999) since it is often not easy to discriminate between the echo signal and the near end-speaker. This paper derives a log likelihood ratio test for deciding between double-talk (freeze weights) and a Channel Change (adapt quickly) using a stationary Gaussian stochastic input signal model. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics indicate that it is difficult to correctly decide between double-talk and a Channel Change based upon a single look. However, post-detection integration of approximately one hundred sufficient statistic samples yields a detection probability close to unity with a small false alarm probability
N J Bershad - One of the best experts on this subject based on the ideXlab platform.
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echo cancellation the generalized likelihood ratio test for double talk versus Channel Change
IEEE Transactions on Signal Processing, 2009Co-Authors: Jeanyves Tourneret, N J Bershad, J C M BermudezAbstract:Echo cancellers (EC) are required in both electrical (impedance mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The optimum likelihood ratio test (LRT) for this problem was studied in a recent paper. The LRT requires a priori knowledge of the background noise and double-talk power levels. Instead, this paper derives a generalized log likelihood ratio test (GLRT) that does not require this knowledge. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a Channel Change, based upon a single look. However, detection based on about 200 successive samples yields a detection probability close to unity (0.99) with a small false alarm probability (0.01) for the theoretical GLRT model. Application of a GLRT-based EC to real voice data shows comparable performance to that of the LRT-based EC given in a recent paper.
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echo cancellation a likelihood ratio test for double talk versus Channel Change
IEEE Transactions on Signal Processing, 2006Co-Authors: N J Bershad, Jeanyves TourneretAbstract:Echo cancellers (ECs) are in wide use in both electrical (four-wire to two-wire mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The control logic can be quite complicated since it is often not easy to discriminate between the echo signal and the near-end speaker. This paper derives a log-likelihood ratio test (LRT) for deciding between double-talk (freeze weights) and a Channel Change (adapt quickly) using a stationary Gaussian stochastic input signal model. The probability density function (pdf) of a sufficient statistic under each hypothesis is obtained, and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a Channel Change based upon a single look. However, postdetection integration of approximately 100 sufficient statistic samples yields a detection probability close to unity (0.99) with a small false-alarm probability (0.01)
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echo cancellation a likelihood ration test for double talk vs Channel Change
International Conference on Acoustics Speech and Signal Processing, 2006Co-Authors: N J Bershad, Jeanyves TourneretAbstract:Echo cancellers are in wide use in both electrical (four wire to two wire mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The control logic can be quite complicated (C. Breining et al., 1999) since it is often not easy to discriminate between the echo signal and the near end-speaker. This paper derives a log likelihood ratio test for deciding between double-talk (freeze weights) and a Channel Change (adapt quickly) using a stationary Gaussian stochastic input signal model. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics indicate that it is difficult to correctly decide between double-talk and a Channel Change based upon a single look. However, post-detection integration of approximately one hundred sufficient statistic samples yields a detection probability close to unity with a small false alarm probability
R J Hardy - One of the best experts on this subject based on the ideXlab platform.
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interactions between sediment delivery Channel Change climate Change and flood risk in a temperate upland environment
Earth Surface Processes and Landforms, 2007Co-Authors: Stuart N. Lane, V Tayefi, Simon C Reid, Dapeng Yu, R J HardyAbstract:This paper uses numerical simulation of flood inundation based on a coupled one-dimensional–two-dimensional treatment to explore the impacts upon flood extent of both long-term climate Changes, predicted to the 2050s and 2080s, and short-term river Channel Changes in response to sediment delivery, for a temperate upland gravel-bed river. Results show that 16 months of measured in-Channel sedimentation in an upland gravel-bed river cause about half of the increase in inundation extent that was simulated to arise from climate Change. Consideration of the joint impacts of climate Change and sedimentation emphasized the non-linear nature of system response, and the possibly severe and synergistic effects that come from combined direct effects of climate Change and sediment delivery. Such effects are likely to be exacerbated further as a result of the impacts of climate Change upon coarse sediment delivery. In generic terms, these processes are commonly overlooked in flood risk mapping exercises and are likely to be important in any river system where there are high rates of sediment delivery and long-term transfer of sediment to floodplain storage (i.e. alluviation involving active Channel aggradation and migration). Similarly, attempts to reduce Channel migration through river bank stabilization are likely to exacerbate this process as without bank erosion, Channel capacity cannot be maintained. Finally, many flood risk mapping studies rely upon calibration based upon combining contemporary bed surveys with historical flood outlines, and this will lead to underestimation of the magnitude and frequency of floodplain inundation in an aggrading system for a flood of a given magnitude. Copyright © 2006 John Wiley & Sons, Ltd.
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interactions between sediment delivery Channel Change climate Change and flood risk in a temperate upland environment
Earth Surface Processes and Landforms, 2007Co-Authors: Stuart N. Lane, V Tayefi, Simon C Reid, R J HardyAbstract:This paper uses numerical simulation of flood inundation based on a coupled one-dimensional-two-dimensional treatment to explore the impacts upon flood extent of both long-term climate Changes, predicted to the 2050s and 2080s, and short-term river Channel Changes in response to sediment delivery, for a temperate upland gravel-bed river. Results show that 16 months of measured in-Channel sedimentation in an upland gravel-bed river cause about half of the increase in inundation extent that was simulated to arise from climate Change. Consideration of the joint impacts of climate Change and sedimentation emphasized the non-linear nature of system response, and the possibly severe and synergistic effects that come from combined direct effects of climate Change and sediment delivery. Such effects are likely to be exacerbated further as a result of the impacts of climate Change upon coarse sediment delivery. In generic terms, these processes are commonly overlooked in flood risk mapping exercises and are likely to be important in any river system where there are high rates of sediment delivery and long-term transfer of sediment to floodplain storage (i.e. alluviation involving active Channel aggradation and migration). Similarly, attempts to reduce Channel migration through river bank stabilization are likely to exacerbate this process as without bank erosion, Channel capacity cannot be maintained. Finally, many flood risk mapping studies rely upon calibration based upon combining contemporary bed surveys with historical flood outlines, and this will lead to underestimation of the magnitude and frequency of floodplain inundation in an aggrading system for a flood of a given magnitude.
Hansulrich Schmincke - One of the best experts on this subject based on the ideXlab platform.
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boundary conditions for damming of a large river by fallout during the 12 900 bp plinian laacher see eruption germany syn eruptive rhine damming ii
Journal of Volcanology and Geothermal Research, 2020Co-Authors: Cornelia Park, Hansulrich SchminckeAbstract:Abstract The Rhine River (Germany) - the largest river in Western Europe - was dammed by pyroclastic material multiple times during the major Plinian Laacher See Eruption (12,900 BP). Dams formed both upstream and downstream of the broad tectonic Lower Neuwied Basin (LNB) which interrupts the narrow Rhine canyon. Here we document upstream damming of the Rhine River at the entrance to the LNB close to the present city of Koblenz due to overloading with tephra fall into the Rhine and its major tributaries, the Moselle and the Lahn. The dam was formed repeatedly during rapid pumiceous tephra fall events and breached during breaks in eruptive activity, causing extensive, high-energy flooding throughout the entire basin. The ephemeral Koblenz dams differed significantly from “normal” volcanically-induced dams by consisting principally of washed-together pumice clasts and some driftwood. The porous nature of pumice and its ability to absorb water were crucial factors. Thus, a large volume percentage of the tephra that had fallen into the Rhine floated submerged within the upper part of the water column or swam at the surface. Moreover, the absorption of the river water by the pumice clasts increased the sediment:water ratio of the two-phase flow considerably. We here present a model of dam formation resembling the formation of ice jams. We visualize the Koblenz dams to have been elongate, partly floating and partly grounded, permeable plugs many kilometers long and rising no higher than the flood plain. Damming was most plausibly initiated in the LNB within the area of maximum tephra loading and propagated upstream in a chain reaction comparable to the formation of traffic jams. A major dam was finally accumulated at the bottleneck entrance to the LNB, a site combining several favorable conditions: the upstream multi-Channel Rhine was confined to a single Channel, Change of flow direction by 125°, extremely low gradient (0.19‰) starting already 24 km upstream of the bottleneck, constant decrease of flow velocity over many kilometers towards the bottleneck and the Moselle River - largest tributary of the Rhine within the LNB and an important conveyor of additional tephra masses – entered the Rhine only 700 m upstream of the bottleneck. We assume that the Koblenz dams could only have formed and been stabilized by an extremely long “foot region” that extended many kilometers downstream and that was possibly connected to one or several low-rise secondary jams/dams. The backwater of Lake Brohl that was dammed by pyroclastic flows 7 km downstream of the LNB about halfway through the eruption extended further and further upstream into the LNB during the second Plinian stage of the Laacher See Eruption and was probably a major factor contributing to the formation and large size of Koblenz Dam No.4. The Koblenz dams were probably not completely sealed most of the time. This way the major pre-eruptive Rhine Channel received some water. An equilibrium condition was established that enabled the dams to remain stable as long as tephra fell into the Rhine relatively continuously.