Raw data review (QA1): Difference between revisions

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== Raw data review ==
== Raw data review ==


The objective of the raw data review is to ensure that the velocity data used for the calculation of the structure functions are of good quality before proceeding with the turbulence analysis. Bad data are typically identified from the velocity data themselves and other ancillary data (e.g. correlations). Recommendations for quality control based on each data type include:  
The objective of the raw data review is to ensure that the velocity data used for the calculation of the structure functions are of good quality before proceeding with the turbulence analysis. Bad data are typically identified from the velocity data themselves and other ancillary data (e.g. correlations). It is recommended that velocity data should be flagged if the following are observed:
 
# Data quality is poor
# Correlation
#* Low correlation values
#* flag data below a minimum threshold
#* Echo intensity anomalies
# Echo intensity  
#* Low percent good values
#* flag data where there are anomalies due to false targets (e.g “fish” detection, surface reflection, mooring line reflection)
#* Data return rate varies
# Percent good
# Unrealistic velocity values
#* flag data with low values (applies to measurement modes with in-instrument averaging across multiple pings per ensemble)
#* Evidence of phase wrapping
# Orientation (heading, pitch, roll) and depth (if sensor installed)
#* Velocities outside nominal measurement range
#* flag periods of high variability 
#* Velocities outside expected distribution
#* flag periods where instrument orientation deviates significantly from the expected behaviour of the mooring or instrument frame [(JMM) REPLACEMENT FOR 'resolve location of observations', WHICH I FOUND CONFUSING. IS THIS ANY BETTER?]
# Significant instrument motion and orientation
# Along beam velocity
#* High variability in pitch, heading and roll
#* flag values where there are variations in data return rate
#* Orientation deviates from expected values
#* flag values outside the nominal measurement range for the instrument configuration
# There is wave or periodic motion
#* flag values with evidence of phase wrapping (in pulse-pulse coherent observations)
#* Periodic motion at wave frequencies observed in velocity data
#* flag values where there is periodicity indicating waves or oscillatory motion  
# Velocity shear is too large
#* flag values that are outside of the expected distribution
#* earth velocities indicate significant horizontal shear
#* flag values where the burst variance shows evidence of spatial and temporal trends
# Stationary assumption may be violated
# Earth coordinate velocities
#* variance of velocity bursts shows spatial or temporal trends [ALTHOUGH HARD TO DETERMINE WHAT IS REAL VARIABILITY]
#* flag data where the error velocity is large (from ADCPs with at least 4 beams)
# Stratification is too large
#* flag data where the earth velocities are comparable to the ambiguity velocity to check for possible phase wrapping
#* Temperature and salinity (if available) indicate local stratification
#* flag data where the burst variance shows evidence of spatial and temporal trends  
#* flag data where there is a large horizontal shear over the observation range
#* flag data where the ADCP orientation deviates from the vertical and bin mapping may be necessary [(JMM) ALREADY INCLUDED ABOVE?]
# Temperature and salinity (if sensors installed)  
#* flag values where there is evidence of changes in local stratification and/or internal wave activity
 
If possible, it is also recommended that you compare your data between beams, between bins and over time. It can also be useful to compare data to other sensors (e.g. meteorological, wave or CTD sensors).
 
[(JMM) I STILL FIND THIS PAGE A LITTLE CONFUSING. A POSSIBLE OPTION TO REORGANIZE IS PROPOSED IN THE DISCUSSION]
 
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Return to [[ADCP structure function flow chart| ADCP Flow Chart front page]]
Return to [[ADCP structure function flow chart| ADCP Flow Chart front page]]


[[Category:Velocity profilers]]
[[Category:Velocity profilers]]

Revision as of 20:32, 12 November 2021

Raw data review

The objective of the raw data review is to ensure that the velocity data used for the calculation of the structure functions are of good quality before proceeding with the turbulence analysis. Bad data are typically identified from the velocity data themselves and other ancillary data (e.g. correlations). It is recommended that velocity data should be flagged if the following are observed:

  1. Data quality is poor
    • Low correlation values
    • Echo intensity anomalies
    • Low percent good values
    • Data return rate varies
  2. Unrealistic velocity values
    • Evidence of phase wrapping
    • Velocities outside nominal measurement range
    • Velocities outside expected distribution
  3. Significant instrument motion and orientation
    • High variability in pitch, heading and roll
    • Orientation deviates from expected values
  4. There is wave or periodic motion
    • Periodic motion at wave frequencies observed in velocity data
  5. Velocity shear is too large
    • earth velocities indicate significant horizontal shear
  6. Stationary assumption may be violated
    • variance of velocity bursts shows spatial or temporal trends [ALTHOUGH HARD TO DETERMINE WHAT IS REAL VARIABILITY]
  7. Stratification is too large
    • Temperature and salinity (if available) indicate local stratification

Return to ADCP Flow Chart front page

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