Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration
Abstract
:1. Introduction
2. Methodology
2.1. Experimental Set-Ups
2.1.1. NTNU Flume: Monostatic Acoustic System
2.1.2. UniBo Flume: Bistatic Acoustic System
2.2. Acoustic Theory
2.2.1. Basic Principles
2.2.2. Monostatic Sonars
2.2.3. Bistatic Sonars
2.2.4. Echo Intensity (EI)
2.3. Data Postprocessing
2.3.1. ADCP Data Postprocessing
2.3.2. Detection of the Immobile Bed and the Cells Containing Bedload Velocities (Ubertone Instruments)
2.3.3. UVP Data Postprocessing
2.3.4. ADVP Data Postprocessing
2.3.5. Imaging Data Postprocessing
3. Results
3.1. Apparent Bedload Velocities—UniBo Experiments (ADVP vs. ADCP)
3.2. Apparent Bedload Velocities—NTNU Experiments (UVP vs. ADCP)
3.3. Deviation in the Bedload Velocity Estimation: UniBo Experiments (ADVP vs. ADCP)
3.4. Deviation in the Bedload Velocity Estimation—NTNU Experiments (UVP vs. ADCP)
3.5. Echo Intensity: UniBo Experiments
3.6. Echo Intensity: NTNU Experiments
4. Discussion
4.1. Apparent Bedload Velocity
4.2. Echo Intensity
5. Conclusions
- A finer cell resolution and the possibility of profiling the bedload velocities.
- The possibility of detecting the thickness of the active bedload layer.
- Easier characterization of the backscattering sources, e.g., the influence of the immobile surface irregularity, isolating the surface from volume scattering.
- More focused beams, i.e., a smaller beam opening angle, φ, should lead to a more superficial sampling of the bedload. This implied that for a given frequency, a larger transducer should return more realistic data in the absence of water bias.
- A lower frequency (e.g., 0.5 MHz) should be avoided in laboratory conditions because the measured velocities severely underestimated the real bedload velocity. An exception could be considered in cases of high suspended sediments in a water column or a very deep environment where stronger penetration and longer ranges are required [22].
- The finer the resolution, the better the results. This implies shorter pulses for PC but not for the BB, in which the pulse and cell sizes are partially independent [39]. However, in field applications, it is impossible to have a cell size in the range of the bedload active layer. Thus, more attention should be paid to more efficient acoustic sampling.
- The higher grazing angle, θ, results in a higher underestimation of the bedload velocity and less sensitivity in the echo intensity when the bedload transport conditions change. However, it should not be larger than the critical angle of reflection [38].
- The echo intensity might be used as an indicator for the bedload concentration if the cell resolution and source intensity are known a priori.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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EXP | Q | H | U | D50 | Rep | ucr* | u* | |
---|---|---|---|---|---|---|---|---|
L/s | m | m s−1 | mm | \ | m s−1 | m s−1 | ||
NTNU | sandEXP1 | 80.00 | 0.40 | 0.3 | 0.35 | 20.00 | 0.014 | 0.015 |
sandEXP2 | 100.00 | 0.40 | 0.39 | 0.35 | 20.00 | 0.014 | 0.019 | |
sandEXP22 | 120.00 | 0.40 | 0.43 | 0.35 | 20.00 | 0.014 | 0.021 | |
UniBo | EXP1 POS1 | 111.68 | 0.31 | 0.45 | 1.00 | 97.00 | 0.021 | 0.023 |
EXP1 POS2 | 111.48 | 0.31 | 0.41 | 1.00 | 97.00 | 0.021 | 0.025 | |
EXP2 POS1 | 111.26 | 0.27 | 0.58 | 1.00 | 97.00 | 0.021 | 0.034 | |
EXP2 POS2 | 110.97 | 0.27 | 0.59 | 1.00 | 97.00 | 0.021 | 0.038 |
Type | f | Dt | λ | φ | Near Field | θ | Ds | PRF | vmax/Rmax | PL | Cell Size |
---|---|---|---|---|---|---|---|---|---|---|---|
MHz | mm | mm | ° | m | ° | mm | m s−1/m | mm | mm | ||
UVP | 3.0 | 7.0 | 0.5 | 2.0 | 24.8 | 25 | 39 | 1200 | 0.30/0.29 | 4 | 4.4 |
UVP | 1.5 | 20.0 | 1.0 | 1.4 | 101.4 | 25 | 44 | 1000 | 0.49/0.35 | 4 | 4.4 |
UVP | 0.5 | 15.0 | 3.0 | 5.7 | 19.0 | 25 | 104 | 900 | 1.33/0.38 | 10.4 | 10.4 |
UVP | 3.0 | 7.0 | 0.5 | 2.0 | 24.8 | 90 | 7 | 1200 | 0.30/0.29 | 4 | 4.4 |
UVP | 1.5 | 20.0 | 1.0 | 1.4 | 101.4 | 90 | 20 | 1000 | 0.49/0.35 | 4 | 4.4 |
UVP | 0.5 | 15.0 | 3.0 | 5.7 | 19.0 | 90 | 15 | 900 | 1.33/0.38 | 10.4 | 10.4 |
ADVP | 1.0 | 25.0 | 1.5 | 0.0 | / | n.a. | 25 | 500 | 1/0.4 | 1.4 | 1.4 |
ADCP SPro | 2.0 | 15.0 | 0.7 | 1.3 | 76.0 | 20 | 36 | / | 2/5 | 0.7 | / |
EXP | SPro | Camera | ADVP | ||||
---|---|---|---|---|---|---|---|
Qsm | va | EI | vc | K | va | EI | |
35 cm to BED | g s−1 | m s−1 | dB | m s−1 | / | m s−1 | µV × 10−3 |
EXP1 POS1 | 2.46 | 0.006 | 62.2 | 0.07 | 0.35 | 0.035 | 0.18 |
EXP1 POS2 | 0.005 | 62.2 | 0.040 | 0.17 | |||
EXP2 POS1 | 12.63 | 0.014 | 62.5 | 0.11 | 0.55 | 0.055 | 0.41 |
EXP2 POS2 | 0.014 | 62.3 | 0.058 | 0.45 |
EXP | SPro | Camera | 0.5 MHz | 3 MHz | 1.5 MHz | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Qsm | va | EI | vc | K | dt | va | EI | va | EI | va | EI | |
35 cm to BED | g s−1 | m s−1 | dB | m s−1 | / | mm | m s−1 | µV × 10−3 | m s−1 | µV × 10−3 | m s−1 | µV × 10−3 |
sandEXP1 | 0.00 | 0.002 | 57.9 | 0.02 | 0.06 | 0.53 | 0.002 | 0.45 | 0.005 | 0.11 | 0.01 | 0.39 |
sandEXP2 | / | / | / | 0.05 | 0.12 | / | 0.010 | 0.65 | 0.022 | 0.93 | 0.035 | 0.91 |
sandEXP22 | 0.49 | 0.007 | 57.5 | 0.08 | 0.20 | 2.26 | / | / | / | / | / | / |
ADVP | SPro | |||||||
---|---|---|---|---|---|---|---|---|
EXP | va | STDva | repSTDva | va | beforeSTDva | STDva | repSTDva | FD |
m/s | m/s | m/s | m/s | m/s | m/s | m/s | % | |
EXP1 POS1 | 0.035 | 0.0400 | 0.0030 | 0.007 | 0.006 | 0.003 | 0.0023 | 49% |
EXP1 POS2 | 0.04 | 0.0510 | 0.0050 | 0.006 | 0.005 | 0.003 | 0.0025 | 59% |
EXP2 POS1 | 0.0545 | 0.0480 | 0.0040 | 0.014 | 0.012 | 0.009 | 0.0020 | 43% |
EXP2 POS2 | 0.058 | 0.0510 | 0.0040 | 0.014 | 0.011 | 0.007 | 0.0031 | 40% |
EXP | 0.5 MHz | 1.5 MHz | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
va | before STDva | STDva | repSTDva | FD | va | before STDva | STDva | repSTDva | FD | ||
m s−1 | m s−1 | m s−1 | m s−1 | % | m s−1 | m s−1 | m s−1 | m s−1 | % | ||
sandEXP1 | 0.002 | 0.0065 | 0.0054 | 0.0015 | 17% | 0.01 | 0.0514 | 0.0077 | 0.0016 | 9% | |
sandEXP2 | 0.01 | 0.0306 | 0.0119 | 0.00025 | 21% | 0.035 | 0.0711 | 0.0345 | 0.0124 | 30% | |
sandEXP22 | / | / | / | / | / | / | / | / | / | / | |
SPro (2MJHz) | 3 MHz | ||||||||||
va | before STDva | STDva | repSTDva | FD | va | before STDva | STDva | repSTDva | FD | ||
m s−1 | m s−1 | m s−1 | m s−1 | % | m s−1 | m s−1 | m s−1 | m s−1 | % | ||
sandEXP1 | 0.002 | 0.001 | 0.0004 | 0.0001 | 80% | 0.005 | 0.0409 | 0.0067 | 0.0014 | 19% | |
sandEXP2 | / | / | / | / | / | 0.022 | 0.054 | 0.011 | 0.0042 | 28% | |
sandEXP22 | 0.007 | 0.005 | 0.0040 | 0.0010 | 43% | / | / | / | / | / |
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Conevski, S.; Aleixo, R.; Guerrero, M.; Ruther, N. Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration. Water 2020, 12, 3318. https://doi.org/10.3390/w12123318
Conevski S, Aleixo R, Guerrero M, Ruther N. Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration. Water. 2020; 12(12):3318. https://doi.org/10.3390/w12123318
Chicago/Turabian StyleConevski, Slaven, Rui Aleixo, Massimo Guerrero, and Nils Ruther. 2020. "Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration" Water 12, no. 12: 3318. https://doi.org/10.3390/w12123318
APA StyleConevski, S., Aleixo, R., Guerrero, M., & Ruther, N. (2020). Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration. Water, 12(12), 3318. https://doi.org/10.3390/w12123318