1. Marian Muste1 Juan Gonzalez-Castro2 Dongsu Kim1 Kwonkyu Yu1
Uncertainty Analysis for Flow Measurements and Techniques using Standardized Methodology
Marian Muste1
Juan Gonzalez-Castro2
Dongsu Kim1
Kwonkyu Yu1
Thank you for inviting me to present a part of my work.
As I am close to my stay in Karlsruhe, I would like to thank to the people of the Institute for rewarding me with a memorable experience.
Thank Prof. Jirka and Rodi for inviting me and as well to Volker, Tobias, Thorsten, Connie, Elleta, Charlotte, Gregor, Andreas, Gerd for interacting closer during my stay here. Above all, thank you for the wonderful coffee breaks, that I found essential for the progress in research.
Back at IIHR I work well, but here I work well and with pleasure.
I hope to become a frequent back-commer here in Karlsruhe, as some of my predecessors are these days.
1 IIHR- Hydroscience & Engineering, The University of Iowa
2 South-Florida Water Management District, West Palm Beach

2. Overview Background Uncertainty Analysis (UA) Frameworks
AIAA (1995)
UA Implementation Example
Methodology
Assessment of Elemental Uncertainties
Customized GUI for UA Implementation
Conclusions
Outlook

3. regarding uncertainty analysis originated from a Hydrologic Service
Background
SAMPLE REQUEST
regarding uncertainty analysis originated from a Hydrologic Service
…. Has anybody out there had to defend the validity of an ADCP flow measurement against a legal challenge from a third party?
……When current meters were used to undertake these measurements we could claim that the flow measurement was undertaken in conformance with British and International standards for current meter gauging and that the current meter had a valid calibration certificate…
In the case where flow measurements are now taken using ADCPs we feel more vulnerable to legal challenges. This is for two reasons:
1. There is no ISO document in place. The Agency has to rely on its own internal document on gauging procedures which is based on the draft ISO document.
2. ADCPs do not have "certificates of calibration" . The only checks on the performance that can be made are against other ADCPs or other types of flow monitoring equipment.
(posted on the USGS’ Hydro-Acoustics Work Group webpage by
R. Iredale, The Environment Agency of England and Wales, 2005)

4. Guide to the Expression of Uncertainty Measurement (ISO, 1993)
UA Frameworks
Over the last 50 years, considerable efforts have been made by professional societies to develop and implement uncertainty analysis (UA).
One of the rigorous UA methodology (based on sound statistical and engineering concepts):
Guide to the Expression of Uncertainty Measurement (ISO, 1993)
- adopted widely by various scientific & research communities, e.g., NIST (1994), NF ENV (1999)
- the guide recognizes the need for further adaptation for specific areas
Specific adaptations for engineering:
- Assessment of Wind Tunnel Data Uncertainty (AIAA, 1995)
- Test Uncertainty (ASME, 1998)
Key assumptions/concepts for ISO (1993)-based standards
- Gaussian pdf-s for the error sources
- 2 sample standard deviations for 95% confidence level
- for large samples (N ≥ 10), special procedures for handling small samples
- RSS used for combining uncertainties
- Taylor-series expansion for propagation of uncertainties
- total uncertainties expressed using confidence intervals

5. UA Frameworks
Terminology for ISO (1993) - based standards
The 3 standards provide the same total measurement uncertainty

6. Engineering approach, simple, clear, widely applied
AIAA (1995)
Engineering approach, simple, clear, widely applied
Bias error (b): fixed, systematic
Bias limit (B): estimate of b
Precision error (e): random
Precision limit (P): estimate of e
Total error: d = b + e

7. Implementation Sequence
AIAA (1995)
Implementation Sequence
Key feature: data-reduction equation
r = r(X1, X2, X3,…, Xj)

8. Implementation Aspects
AIAA (1995)
Implementation Aspects
Measurement systems for each individual variable Xi : instrument, data acquisition and reduction procedures, operational environment (laboratory, in situ), the flow and its interaction with the instrument and the environment
Estimates of errors are meaningful only when considered in the context of the process leading to the value of the quantity under consideration
Uncertainties estimated following the signal propagation from sensor to the final result
Uncertainties estimated with a pre-established confidence level (95% for most engineering areas)
UA differently conducted dependent on the type of experiment:
Single test (for complex or expensive experiments): one set of measurements (X1, X2, …, Xj) for r
Multiple tests (ideal situations): many sets of measurements (X1, X2, …, Xj) for r at a fixed test condition with the same measurement system

9. MULTIPLE TESTS (recommended)
AIAA (1995)
MULTIPLE TESTS (recommended)
Given a data reduction equation for a measurement
The result and its uncertainty is
with
The uncertainty in the final result
where the bias limit of the result is
and the precision limit of the result is

10. AIAA (1995)
SINGLE TEST
Given a data reduction equation for a measurement
The result and its uncertainty is
The uncertainty in the final result
where the bias limit of the result is
and the precision limit of the result is
 Based on prior information

11. Implementation Aspects
AIAA (1995)
Implementation Aspects
sound engineering judgment to optimize the output with minimum costs, e.g.:
use of end-to-end uncertainty estimation approach
uncertainty sources < 1/4 or 1/5 of the largest sources are usually considered negligible
specific procedures for single and multiple measurements
specific procedures for dealing with small statistical samples
methodology for assessment of calibration uncertainties
methodology for data validation

12. Implementation Aspects
AIAA (1995)
Implementation Aspects
Integration of UA in all phases of the measurement

13. IMPLEMENTATION EXAMPLE
AIAA (1995)
IMPLEMENTATION EXAMPLE
Extensively used in laboratory measurements and field conditions, from simple (Pitot tube) to complex (LDV) instruments
Widely applied for teaching and research purposes
Successful implementation to discharge measurements:
conventional instruments (Muste et al. 2007)
contemporary, nonintrusive techniques:
Large-Scale Particle Image Velocimetry (Y-S. Kim et al, 2007)
Acoustic-Doppler Current Profilers (Gonzalez-Castro & Muste, 2007)

14. ADCP UA: Implementation
Currently, ADCPs are the most efficient instrument for riverine environment characterization (monitoring and research needs)
If properly operated, the instrument can accurately document discharges, mean velocities, and selected turbulence characteristics
Despite their extensive use, there are aspects regarding their capabilities, operation, and uncertainty analysis not documented yet

15. ADCP Uncertainty Analysis (UA) status
ADCP UA: Implementation
ADCP Uncertainty Analysis (UA) status
Past efforts (non-standardized methodologies)
Discharge: Simpson & Oltman (1992), Gordon (1993), Lipscomb (1995), Morlock (1996), Simpson (2001), Gartner (2002), Muller (2002), Yorke & Oberg (2002), USGS-RDI (2005)
Turbulence measurements: Droz (1998), Stacey (1999), Nystrom (2002), Schemper & Admiraal (2002)
On-going efforts (standardized methodology)
UA formulated within the framework of authoritative engineering standards

16. ADCP UA: Implementation
Discharge Measurement with ADCP mounted on a boat
where

17. ADCP UA: Elemental Uncertainty Assessment
Error identification

18. ADCP UA: Implementation
Data Reduction Equations (Teledyne/RDI’s ADCP)

19. ADCP UA: Implementation
Exact approach – discharge in the direct measured area
Using BT

20. ADCP UA: Implementation
Exact approach: in-bin discharge
Using BT
If , the discharge is a functional relationship of the form:

21. ADCP UA: Implementation
Exact approach – top and bottom discharges (extrapolation)

22. ADCP UA: Implementation
Uncertainty Propagation to Final Result: Bias Limit

23. ADCP UA: Implementation
Uncertainty Propagation to Final Result: Precision Limit
Uncertainty Propagation to Final Result: Total Uncertainty

24. ADCP UA: Implementation
Practical approach
(pitch and roll neglected in DRE; errors accounted through end-to-end calibrations)
velocity (instrument coordinates neglecting the pitch and roll angle)
= beam angle,
= angle of the flow to instrument
β = angle of the boat velocity
= in beam water velocities
= boat velocity
where
total discharge

25. ADCP UA Software - architecture
Developing tools - Borland C++ Builder (v.6) & Microsoft Access
Software Configuration

26. ADCP UA Software - GUIs Archive database
- Elemental uncertainties are archived in categories based on river characteristics.
- Users with limited level of preparedness can estimate uncertainties
using default values obtained in similar environment and operating conditions.
- The stored information is updated as soon as new measurements are processed.
- User can also create new archives using new classification categories

27. ADCP UA Software - GUIs
Information for archiving

28. ADCP UA Software - GUIs
Assessment of bias limit

29. ADCP UA Software - GUIs
Assessment of precision limit

30. ADCP UA Software & GUIs
Assessment of total uncertainty

31. Conclusions
Feasibility of UA engineering standards for implementation to ADCP measurements
The methodology is comprehensive, simple to implement
Easily upgradeable as new info occur
UA allows tracing of the measurement accuracy to primary standards  withstand legal and strict QA/QC requirements
Finalization of UA – an extensive and expensive effort Collaboration between manufacturers and users in a coordinated effort = key to complete UA for the variety of measurement situations and operating conditions encountered in monitoring practice
The framework was adopted by ASCE’s HME Task Committee and the UNESCO group on Data Requirements for Integrated Urban Water Management (Fletcher et al., 2007)
Currently evaluated by the ISO committee (Herschy)
- The capabilities and limitations are presented throughout the lectures in connection with the issues discussions
Assumption made herein is that the basic operating parameters selected during data collection (e.g., bin size, mode, bottom track, water pings per ensemble, blanking distance) adequately match physical conditions such that we have mainly to deal with inherent errors and flow characteristics 8

32. Conclusions
The UA customized software for ADCP velocity and discharge measurements requires minimum user preparation
Autoarchiving uncertainties for specific environments and operating conditions can provide information about dominant sources of uncertainties at various sites.
By continuously increasing the sample size through archiving, the UA output is progressively enhanced.

33. Outlook
Work closely with manufacturers and users to assess elemental error sources (manufacturer, operator, environment, or combinations) and integrate them in the AIAA (1995) uncertainty assessment framework for rigorous documenting velocity and discharge measurement accuracy
Conduct sensitivity analysis and field tests for compiling uncertainty minimizations guidelines
Develop operational guidelines for conducting accurate measurements in various flow regimes

34. Outlook
Need for coordination and extensive collaboration among ADCP manufacturer, operators, data users, and third-party evaluators
Need for evaluation of the status of current developments and to strategize for integrative efforts to assess methodologies for operation and accuracy assessment of the ADCP as well as other flow measurement techniques over an extend the range of flow conditions (present WMO effort)
IIHR is willing to be actively involved in the WMO initiative

35. Thank you!
Questions?