1. Quantifying SPM in estuaries and coastal seas
Ifremer et al…
Marion Chapalain, Romaric Verney, Matthias Jacquet, David le Berre, Aurelien Gangloff, Ivane Pairaud, Xavier André, Michel Répécaud, Christophe Ravel, François Bourrin, Gael Many, Flavie Druine, Julien Deloffre, Robert Lafite, David Doxaran, Sabine Charmasson, Jean Philippe Lemoine, Frederic Jourdin…

2. Measuring where and what?
[Cohesive] Sediment fluxes from land to open ocean

3. Measuring where and what?
[Cohesive] Sediment fluxes from land to open ocean
From estuaries to coastal seas
From O(1g/l) to O(0.001g/l)

4. Measuring where and what?
[Cohesive] Sediment fluxes from land to open ocean
Water sampling
Optical sensors (transmission / backscattering)
Acoustic sensors (backscattering)

5. Platforms [Cohesive] Sediment fluxes from land to open ocean
Monitoring station Estuary Banks
Buoys / Moorings
Gliders / Autonomous profilers
Optical systems (OBS-like) and Acoustic profilers (ADCP)
From O(0. 001) to O(0.1)g/l
Optical systems (OBS-like) and Acoustic profilers (ADCP)
From O(0. 001) to O(0.1)g/l
Optical systems (OBS-like)
From O(0. 01) to O(1)g/l
Long term (>1y)
Long term (>1y)
Mid term (~1month)

6. Platforms [Cohesive] Sediment fluxes from land to open ocean
Necessary complement of the autonomous platforms for validation / representativeness : ship-based measurements
Investigating vertical/horizontal gradients, measuring additional parameters (PSD, density, OM content…) and collecting samples

7. Quantyfing SSC & uncertainty
Strategy for quantyfing SSC
Calibration in g/l
Sample the SSC gradient for reliable calibration?
Grab bed sediment samples + lab calibration
Influence of
SPM variability?
Solution?
Yes No
Quantyfing SSC & uncertainty
But sensors provide indirect measurements : NTU / dB…
Expectation on uncertainty…
In between….
Tend to
be critical
<20%
VERY GOOD
<50%
Accept.
>100%
BAD
Pre-operation
1NTU = 1NTU?
Metrology
Sensor Accuracy
Optical / Acoustics

8. Metrology : Sensor inter calibration
Until recently…no real and systematic metrology strategy
(because we considered that the calibrated signal was our target...not the NTU signal)
But this assumption is no more true when we operate monitoring networks...

9. Metrology : Sensor inter calibration
SSC from optical sensors

10. Metrology : Sensor inter calibration
SSC from optical sensors

11. Metrology : Sensor inter calibration
SSC from optical sensors
Not an issue as far as you recalibrate the sensor in g/l…but an issue when changing sensors by others...if metrology fails to reach good standards

12. Optical sensor calibration in g/l
In situ Vs Lab

13. Can we rely on NTU->g/l relationship from lab calibration?
Calibration – In lab
SSC from optical sensors
Can we rely on NTU->g/l relationship from lab calibration?

14. Calibration – In situ

15. Calibration – In situ SSC from optical sensors
/ / / / /
Individual uncertainty : from 10% to 100%....on average between 10% to 30%

16. Calibration – In situ SSC (g/l) SSC (g/l) SSC (g/l)
SSC from optical sensors
In the TMZ
Spring
Spring
Neap
SSC (g/l)
SSC (g/l)
SSC (g/l)
OBS (NTU)
OBS (NTU)
SSC= NTU
OBS (NTU)
Neap
Neap/Spring
Spring
SSC (g/l)
SSC (g/l)
SSC (g/l)
OBS (NTU)
OBS (NTU)
OBS (NTU)

17. Calibration – In situ SSC from optical sensors SSC=0.00175 NTU
In estuaries and TMZ…flocculation processes are very intense and variable...and can drastically impact the quality of SSC time series
SSC= NTU

18. Acoustic sensor calibration in g/l

19. NR = NE - 20log(R2) +10log(V) - 2R(w+ s) + IV
SSC : Acoustic sensors
NR = NE - 20log(R2) +10log(V) - 2R(w+ s) + IV
Depends on SSC, particle features (size/density/composition)
Below 100mg/l : only water attenuation
Methodology : calibrating ADCP Vs Optical sensor
Above 100mg/l…more complex...but not impossible...

20. SSC : Acoustic sensors SSC from acoustic sensors Current speed BI (dB)
Converting dB in g/l ?
BI (dB)

21. SSC : Acoustic sensors SSC from acoustic sensors OBS (g/l) ADCP (g/l)
Optimal floc size (um)

22. SSC : Acoustic sensors
SSC from acoustic sensors

23. SSC : Acoustic sensors SSC from acoustic sensors
Constant diameter (40um)
OBS (g/l)
ADCP (g/l)

24. SSC : Acoustic sensors
SSC from acoustic sensors

25. SSC : Acoustic sensors
SSC from acoustic sensors
Within the TMZ

26. SSC : Acoustic sensors
SSC from acoustic sensors
Within the TMZ

27. Recommended last sheet of the presentation
Main critical points:
Pre- operation : sensor metrology & filter preparation
Operation : sampling & filtration procedure Vs instruments & Environment
Post-operation : Calibration & decomposing uncertainy
Uncertainty estimations
bias, random errors of different steps : not evaluated yet
overall error : from RMSE
representativity / „scale of confidence“ : only starting – demonstrated significant variabilities
Recommendations for good practice (3 max.):
Metrology of sensors
Enough calibration sample to capture the SPM variability (what about storm events?)
Take care about the sample collection technique (compared to the vertical gradients...)

28. Correction procedures
General workflow
Pre-Measurement
Measurement
Post-Measurement
required precision & accuracy
needed parameters/sensors
Sensor failures
Electronic Sensor drift
optics degradation
bio-fouling …
Changes in particle chararacteristics
optical / acoustical backscatter & absorption coefficients
natural processes (periodical, singular)
human activities (dredging, dumping)
Correction procedures
sensor failures
changes in particle characteristics
sensor arrangement (to avoid disturbances)
Error determination
calibration
operational
representativeness
operation resources
e.g. ships, divers, …
regular, emergency
Ongoing monitoring of sensor quality
 (near) real time data processing
optimal filter to detect sensor problems
optimal data representations ….
Delayed mode data processing
Maintenance
manually
automated
sensor exchange
Lab calibration against standard (formacine, …
In-situ calibration with water samples
ship surveys
special parameters
representat.
Lab calibration against standard (formacine, …