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…

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

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)

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

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)

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

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

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...

Metrology : Sensor inter calibration SSC from optical sensors

Metrology : Sensor inter calibration SSC from optical sensors

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

Optical sensor calibration in g/l In situ Vs Lab

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?

Calibration – In situ

Calibration – In situ SSC from optical sensors 0.0021 / 0.0019 / 0.0021 / 0.0022 / 0.0022 / 0.0025 Individual uncertainty : from 10% to 100%....on average between 10% to 30%

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=0.0006 NTU OBS (NTU) Neap Neap/Spring Spring SSC (g/l) SSC (g/l) SSC (g/l) OBS (NTU) OBS (NTU) OBS (NTU)

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=0.0006 NTU

Acoustic sensor calibration in g/l

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...

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

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

SSC : Acoustic sensors SSC from acoustic sensors

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

SSC : Acoustic sensors SSC from acoustic sensors

SSC : Acoustic sensors SSC from acoustic sensors Within the TMZ

SSC : Acoustic sensors SSC from acoustic sensors Within the TMZ

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...)

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, …