A summary of commercial acoustic sediment profiling using the AQUAscat acoustic backscatter instrument

1. © 2017 Aquatec Group
AQUAscat Technology
Commercial Acoustic Sediment Profiling
Andy Smerdon
Managing Director
HYDRALAB+ Workshop Foresight WP6
Environmental Hydraulics Institute IH Cantabria
Universidad de Cantabria
Thursday 18 May 2017

2. © 2017 Aquatec Group
Overview
AQUAscat TECHNOLOGY – COMMERCIAL ACOUSTIC SEDIMENT PROFILING
• Introduction to Aquatec
• AQUAscat Instrument
• Operational Limits
• Calibration
• Examples of Use

3. © 2017 Aquatec Group
Aquatec Group Ltd
• Founded in 1990
• Headquartered in Basingstoke,
UK
• Design and manufacture all
products and engineered
solutions
• Products sold worldwide
• ISO9001 - ISO14001
BS OHSAS 18001
• Design, manufacture and
supply of subsea instrumentation,
communications, and cathodic
protection systems
• Specialise in acoustics, optics, suspended sediment
• Instrumentation & solutions for ocean science
and offshore energy

4. © 2017 Aquatec Group
Sediment? Solved
SOLUTIONS FOR SEDIMENT MONITORING
Observing Suspended Sediment
• NEW AQUAlogger 310TY
Advanced turbidity logger
• AQUAscat 1000 range of
acoustics suspended sediment
profilers
• Secchi disc
Collecting Suspended Sediment
• Sediment traps, water samplers,
Niskin bottles and rosettes
Collecting Deposited Sediment
• Grabs and corers

5. © 2017 Aquatec Group
AQUAlogger 310TY
SIMPLY ADVANCED
Observing sediment
• Turbidity to 10,000FTU
(typical)
• Suspended sediment
concentration (with SSC
Converter)
User-friendly features
• Quick start
• Shake to show
• Off-the-shelf batteries
• Tablet compatible
Flexible sampling
• Delayed start
• Continuous or burst sampling
• Sample averaging
• Variable sample rates for each sensor
• Advanced logging settings
Visualise &
communicate with
swappable modules

6. © 2017 Aquatec Group
AQUAscat 1000
ACOUSTIC SUSPENDED SEDIMENT PROFILER

7. © 2017 Aquatec Group
Acoustic Backscatter Principle
• Each transducer transmits short pulses of
ultrasound between 0.3 and 5 MHz
• Sediment in water scatters sound, which is picked
up by the same transducer
More sediment = Higher scattering intensity
• Different size sediment scatters sound more or
less, depending on the frequency of sound
• The time of arrival of scattered sound is used to
construct a spatial profile of suspended scatterers

8. © 2017 Aquatec Group
Frequencies
Single frequency
• Measured signal varies with particle size
• Requires physical samples to be taken
Signal
Particle Size
Measured signal vs Particle size: Fixed
concentration (1MHz)
Measured signal vs Particle Size: Fixed
concentration (0.5 - 4MHz)
Multiple frequency
• Use the size dependent response to
different frequencies to determine
particle size.
• Calculate concentration using particle
size information
Signal
Particle Size

9. © 2017 Aquatec Group
AQUAscat 1000
MAIN FEATURES
• Multiple Frequency Acoustic Backscatter System
• Variable bin size from 2.5 mm to 4 cm
• 256 profile bins with ensemble averaging (up to 10m)
• 4 Channels
• Frequency range from 300 kHz to 5 MHz
• Cabled or built-in transducers
• Pressure and temperature sensors
• Flexible deployment programming
• Large storage capacity
• Internal battery, optional external
• USB data download

10. © 2017 Aquatec Group
AQUAtalk
CONFIGURATION & DOWNLOAD SOFTWARE

11. © 2017 Aquatec Group
AQUAtalk

12. © 2017 Aquatec Group
AQUAscat Toolkit
USED FOR POST-PROCESSING DATA
• Basic Functions for:
– Loading & inspecting files
– Reading instrument details
– Applying CTD corrections for speed of sound
– Correcting for range
– Detecting the bed
– Saving as Matlab .MAT structure files or text files
– Spatial & Temporal Averaging
• Calibration Functions
• Modelling Functions
• Data Inversion Functions
– Explicit Acoustic Back Scatter (ABS) to Suspended Sediment
Concentration (SSC) inversion
– Implicit Inversion
– Direct Calibration

13. © 2017 Aquatec Group
Operational Limits
SEDIMENT SIZE AND RANGE

14. © 2017 Aquatec Group
Modelling
THE LIMITS OF ACOUSTIC BACKSCATTER
• System has linear data acquisition for precise
backscatter measurement
• Extra gain available for long range applications
• Minimum detectable signal limited by resolution of data
converter
• System rarely saturates
• Backscatter reduces with particle size
• Backscatter is attenuated by high concentrations
• Low concentrations present low backscatter

15. © 2017 Aquatec Group
Modelling
THE LIMITS OF ACOUSTIC BACKSCATTER

16. © 2017 Aquatec Group

17. © 2017 Aquatec Group

18. © 2017 Aquatec Group
Calibration
AQUATEC’S APPROACH USING THE SYSTEM CONSTANT kt

19. © 2017 Aquatec Group
Calibration
EQUATION FOR MEASURED BACKSCATTER SIGNAL V
• ks Sediment Constant
• kt System Constant
• M Mass Concentration
• r Range from transducer
•  Range modifier
•  Attenuation (water + sed)
- Equations from Thorne & Hardcastle, 1998


rts
e
r
Mkk
V 2

Measure
Calculate
Derive


r
s
t
eMk
Vr
k 2


20. © 2017 Aquatec Group
Calibration
AQUATEC CALIBRATION TANK
• Tank Ø0.4 m by 2.1 m
• Water and sediment re-circulated
• Homogenous mixture of glass beads
• Uniform ¼ phi size distribution
• Pump sampled data at 60 cm
• Average 3600 profiles at 1 Hz
– Minimise reverberation
– Minimise signal noise

21. © 2017 Aquatec Group
Calibration
AQUAscat TOOLKIT CALIBRATION PROCESS

22. © 2017 Aquatec Group
Examples of Use
FLUMES, FIELD, AND EXPERIMENTAL

23. © 2017 Aquatec Group
Example 1
FZK Große Wellen Kanal (GWK), Hanover, Germany

24. © 2017 Aquatec Group
Example 1
RANGE CORRECTED BACKSCATTER
200 400 600 800 1000 1200
0.2
0.4
0.6
0.8
1 -80
-60
-40
-20
200 400 600 800 1000 1200
0.2
0.4
0.6
0.8
1
-80
-60
-40
-20
200 400 600 800 1000 1200
0.2
0.4
0.6
0.8
1 -80
-60
-40
-20

25. © 2017 Aquatec Group
Example 1
IMPLICIT INVERSION

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Example 1
PROCESSED DATA
Time (s)
Range(m)
Sediment Concentration (g/l)
0 200 400 600 800 1000 1200
0.2
0.4
0.6
0.8
1
0
0.1
0.2
0.3
0.4
0.5
Time(s)
Range(m)
Mean Sediment D50 (mm)
0 200 400 600 800 1000 1200
0.2
0.4
0.6
0.8
1
0
0.1
0.2
0.3
0.4
0.5

27. © 2017 Aquatec Group
Example 2
Sea Palling, Norfolk, UK
• Aim: to evaluate
effects of shore
parallel breakwaters
in tidal
environments on
coastal morphology
• Explicit inversion
using sediment trap
size data
• Processed data
looks at mean
concentration at one
elevation

28. © 2017 Aquatec Group
Example 2
PROCESSED DATA
• Above: Concentration - 0.075 m
above bed
• Right: Altimetry - bed range
from each transducer

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Example 3
HR Wallingford, UK Fast Flow Facility: Sediment Turbulence Experiment
• Above: Concentration at 0.075m above bed
• Right: Bed range from each transducer

30. © 2017 Aquatec Group
Example 3
HR Wallingford, UK Fast Flow Facility: Sediment Turbulence Experiment

31. © 2017 Aquatec Group
Example 3
HR Wallingford, UK Fast Flow Facility: Sediment Turbulence Experiment

32. © 2017 Aquatec Group
Example 4
Analysis of Flow within a Flow
• Detection of Pulsed Leak from Water Pipe in Water
510mm
Transducer Depth
Leak
Transducer
Water Surface
Pipe
Horizontal Range
Angle
+
-

33. © 2017 Aquatec Group
Example 4
Analysis of Flow within a Flow
Reflection from
the nozzle
Induced horizontal currents
drawn in by the vertical flow
from the nozzle can be seen
from the backscatter data
2 seconds
7 seconds
Large return from
impedance boundary of
different
temperature/aeration in
liquid
Time
Range(fromTransducer(cm)
20cm
52cm
32cm

34. © 2017 Aquatec Group
Example 4
Analysis of Flow within a Flow
Range from transducer
Phaseshiftbetweenprofiles(deg)
Current reversal

35. © 2017 Aquatec Group
Future Work
• Detailed analysis of attenuation for wash load
• Interpretation of floc behaviour
• Analysis of bimodal distributions
• Evaluation of bubble influence
• Validation of high concentration performance
• Needs lab and field data from users!
• Interested in collaboration for lab & field experiments

36. © 2017 Aquatec Group
Thank you
Any questions?