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Salt Dilution Uncertainty and Proposed Metadata Requirements

Salt Dilution Uncertainty and Proposed Metadata Requirements. CWRA Conference Vancouver Gabe Sentlinger Mar 7, 2013. Use standard error propagation relation In most cases δ M is small (0.1 %) can be in the range of 1-10 %

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Salt Dilution Uncertainty and Proposed Metadata Requirements

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  1. Salt Dilution Uncertainty and Proposed Metadata Requirements CWRA Conference Vancouver Gabe Sentlinger Mar 7, 2013

  2. Use standard error propagation relation In most cases δM is small (0.1 %) can be in the range of 1-10 % δCF.T is based on calibration procedure and site specific regression if no calibration was done (2-7 %) Don’t torpedo your measurement! -We all have different methods for SD, we want to identify sources of error/uncertainty and control for them. -Ensure calibration, repeatability, linearity of method Quantifying Uncertainty (Content AZ, Photo GS)

  3. So maybe we have an Error Budget that we need to work within for a given RISC Class. Where do we want to spend that budget, where is the low-hanging fruit? Possible RISC Standards: Error Budget

  4. Left Bank Q = 0.245 cms Thalweg Q = 0.297 cms Right Bank Q = 0.345 cms Average Q = 0.304 cms Swoffer Q = 0.297 cms • Currently unquantified. Multiple probes, or injections, can help determine appropriate mixing reach for given Q • This is a single pulse measured on left and right bank, and thalweg. Standard Deviation ±21%. Lowest Fruit: Mixing Error

  5. How much error is introduced by assuming a CF.T for automated measurements? • Is CF.T a function of EC.T? It shouldn’t be. • Is CF.T a function of Instrument? It shouldn’t be. • Is Background EC.T constant over measurement? Impetus for Study: Automated Gauging

  6. This histogram shows that 95% of CF.T values are within 5% of the median value. So if you just used the median CF.T value, only 5% error introduced into Q measurement. • Recent improvements to methods may eliminate the site specificity. Constant CF.T or Site Specific?

  7. Reduce the amount of salt required for a given flow/ reduce uncertainty associated with salt dilution measurement. • Establish SOP to ensure data quality and traceability, quantify uncertainty, and protect sensitive habitat. Need for fast, accurate, reproducible method

  8. What is the limit of the instrument? • This is a Unidata 6536B with resolution of 0.01 uS/cm but accuracy of 0.5% of the reading. We found quanta of 0.3uS/cm. Instrument Accuracy/Resolution

  9. Oakton Con110 has better accuracy and resolution at lower ranges, higher SNR, therefore less uncertainty in Q. Instrument Accuracy/Resolution

  10. -Salter kitchen scale 5000±1 g ml: $35. -MyWeigh BCS-80 scale 80±0.02kg: $171. -JScale HP-50x 50±.01g: $29. Calibration Party!

  11. -10 ml graduated plastic syringe stated error ±0.01 ml, free(!) at pharmacy. -102 ml ± 0.069 ml, which is 1.4%. - I use 5.02 ± 0.048 ml, or 1.0%. -No significant temperature effect over range of interest (0-25ºC) Calibration Party!

  12. -1000 μl pipettor Diamond Pro : 275$ -measured 997 ± 5ul (0.5%) -did not measure temperature dependence Calibration Party!

  13. -5 ml glass pipette stated error ±0.01 ml, with bulb 15$. -41 measurements, average volume 4.99 +/-0.035 ml (0.7%).  Calibration Party!

  14. -1000 ml plastic graduated cylinder stated error ±10ml at 20ºC: 64$ -20 measurements, average volume 500.5 +/-2.1 ml (0.4%).  -temperature dependence of 0.1 ml/ºC, 1ml in range from 0-10ºC, less than measurement error. Calibration Party!

  15. -500 ml glass volumetric flask ±0.2ml at 20ºC: 35$ -not calibrated, assumed to be within specs. -Total cost of calibration party, 22$, reduction of total error by approximate 5%. Calibration Party!

  16. Uncertainty should be a trade off between effort/cost and accuracy. • For example, lab glassware is more accurate, but more expensive, fragile, and difficult to use in the field. • Plasticware is less expensive, more rugged, but less accurate and subject to temperature effects. But to what degree, should we worry about it? • Our tests show that there is a temperature effect of 0.1 ml/oC. Need for fast, accurate, reproducible method

  17. We’ve (AZ) identified a problem with a pre-mixed standard solution of salt and distilled water. The distilled water in the standard dilutes the total solution; like running in sand you move forward each time, but your reference point moves farther back. • I worked out the equations for 5ml injections of 3 std concentrations in 500ml of stream sample. This can be a significant source of error for this method of CF.T derivation, especially at higher background EC.T values. Calibration Factor Error (in progress)

  18. A more accurate representation of the mass for each standard injection (i is initial in sample, s is std injection; will change subscripts in V2.0) Assuming the increase in mass for each injection is only the mass from the added NaCl • The bias is positive, CF.T is overestimated; Q is proportional to 1/CF.T so it produces estimates of Q that are lower than true. • The correction to the error I’ve worked out (for distilled water solute) to be: Calibration Factor Correction (in progress)

  19. Metadata required to assess quality (uncertainty) of measurement • Useful to have to determine sources of error, better understand the measurement Draft Metadata (1/2)

  20. If uncertainty cannot be assessed, a nominal uncertainty is assumed, ±15-30%. Draft Metadata (2/2)

  21. It’s unlikely that all errors would align. It’s good to do repeat measurements, and repeat CF.T measurements, for a given stage to determine the repeatability of the measurement. Estimate of Uncertainty

  22. Questions? (Ask Andre, I need a nap) ~Fini

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