quality control of rain gauge measurements using telecommunication microwave links
DESCRIPTION
Accurate rain rate measurements are essential for many hydrological applications. Although rain gauge remains the reference instrument for the measurement of rain rate, the strong spatial and temporal variability of rainfall makes it difficult to spot faulty rain gauges. Due to the poor spatial representativeness of the point rainfall measurements, this is particularly difficult where their density is low. Taking advantage of the high density of telecommunication microwave links in urban areas, a consistency check is proposed to identify faulty rain gauges using nearby microwave links. The methodology is tested on a data set from operational rain gauges and microwave links, in Zürich (Switzerland). The malfunctioning of rain gauges leading to errors in the occurrence of dry/rainy periods are well identified. In addition, the gross errors affecting quantitative rain gauge measurements during rainy periods, such as blocking at a constant value, random noise and systematic bias, can be detected. The proposed approach can be implemented in real time.TRANSCRIPT
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Detection of faulty rain gauges using telecommunication microwave links
Blandine Bianchi, EPFL
Alexis Berne, EPFL
Jörg Rieckermann, SWW
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Take-home message!
• Create redundant information• Use advanced data analysis techniques
We need to ensure good data quality!
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MotivationThe Hochrhein-bridge
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MotivationThe Hochrhein-bridge
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MotivationThe Hochrhein-bridge
27 cm
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MotivationThe Hochrhein-bridge
54 cm
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MotivationThe Hochrhein-bridge
54 cm
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Urban HydrologyData quality control?
• At least every two years• Dynamic calibration recommended
Stransky, D. et al. (2007) The effect of rainfall measurement uncertainties on rainfall-runoff process modelling Water Science and Technology Vol 55 No 4
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Urban Water ManagementControl charts for online sensors
-4
0
435 63 91
0
10
20
30
40
11.Jun.01 09.Jul.01 06.Aug.01
Sensor valueReference measurement = grab sample
6. aug 019. july 0111. june 01
Diff
eren
ces
Con
cent
ratio
ns
Change ofmembrane
In-control
Thomann, M. et al. (2002) An efficient monitoring concept with control charts for on-line sensors Water Science and Technology Vol 46 No 4–5 pp 107–116
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Urban HydrologyQuality control for rain gauges
-4
0
435 63 91
0
10
20
30
40
11.Jun.01 09.Jul.01 06.Aug.01
Sensor valueReference measurement = grab sample
6. aug 019. july 0111. june 01
Diff
eren
ces
Con
cent
ratio
ns
Change ofmembrane
In-control
We need• Redundant information on precipitation• Statistical quality control methods• Automated procedures
Thomann et al. (2002)
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Microwave links from telecommunication networksMWL signals are attenuated by rainfall
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Microwave links from telecommunication networksMWL signals are attenuated by rainfall
Rain gauge
MWL
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Microwave links from telecommunication networksMWL signals are attenuated by rainfall
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Microwave links from telecommunication networksMWL signals are attenuated by rainfall
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Microwave links from telecommunication networksMWL signals are attenuated by rainfall
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IdeaUsing MWL signals for quality control
#*
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ARA Glatt
ARA Neugut
Glattzentrum
Josefstrasse
ARA Werdhölzli
Wasserwerk Moos
Völkerkundemuseum
Friedhof Fluntern
Friedhof Nordheim
Friedhof Enzenbühl
Friedhof Affoltern
Friedhof Friesenberg
Friedhof Schwamendingen
0 1 2 3 4 50.5
Kilometer
TextText
Legende
!. Regenmesser ERZ und Eawag
ORANGE Richtfunkantennen
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Case study ZurichQuality control of rain gauges
Material• 14 operational links (Orange CH),
frequencies 23-58 GHz, 0.3 – 8.4 Km, • 14 rain gauges
(13 tipping-buckets and 1 weighing).
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Case study ZurichQuality control of rain gauges
Material• 14 operational links (Orange CH),
frequencies 23-58 GHz, 0.3 – 8.4 Km, • 14 rain gauges
(13 tipping-buckets and 1 weighing).
Goal and Methods
1. Detect occurrence of dry/rainy periods
=> Ratio test
2. Detect quantitative errors
=> CUSUM control charts
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Results (1) Detection of dry and rainy periods
Ratio test
1. Compute contingency table for reference periods (both sensors are in agreement)
Rain Gauge No. 8
[%]
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Results (1) Detection of dry and rainy periods
Ratio test
1. Compute contingency table for reference periods (both sensors are in agreement)
2. Define thresholds
faulty: 1%
suspicious: 5%
Rain Gauge No. 8
[%]
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Results (1) Detection of dry and rainy periods
Ratio test
1. Compute contingency table for reference periods (both sensors are in agreement)
2. Define thresholds
faulty: 1%
suspicious: 5%
3. Apply classification rule during monitoring period
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Results (1) Detection of dry and rainy periods
Ratio test
1. Compute contingency table for reference periods (both sensors are in agreement)
2. Define thresholds
faulty: 1%
suspicious: 5%
3. Apply classification rule during monitoring period
Rain Gauge No.13
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Results (2) Detection of quantitative errors
CUSUM* control chart
Suited to identify small biases/ shifts in process
1. Compute MWL rain rates and target value (reference period)
*Montgomery, D.C. (2000) Introduction to Statistical Quality Control, 4th ed. New York: John Wiley & Sons.
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Results (2) Detection of quantitative errors
CUSUM* control chart
Suited to identify small biases/ shifts in process
1. Compute MWL rain rates and target value (reference period)
2. Plotting CUSUM statistic of differences of sensors to check out-of-control
Rain Gauge No.13 vs. Link No.7
*Montgomery, D.C. (2000) Introduction to Statistical Quality Control, 4th ed. New York: John Wiley & Sons.
CU
SU
M
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Results (2) Detection of quantitative errors
CUSUM* control chart
Suited to identify small biases/ shifts in process
1. Compute MWL rain rates and target value (reference period)
2. Plotting CUSUM statistic of differences of sensors to check out-of-control
3. Apply classification rule during monitoring period
Rain Gauge No.13 vs. Link No.7
*Montgomery, D.C. (2000) Introduction to Statistical Quality Control, 4th ed. New York: John Wiley & Sons.
CU
SU
M
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Scenario analysisTesting the sensitivity of the methodology
Introducing virtual errors
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Scenario analyisTesting the sensitivity of the methodology
Introducing virtual errors
1. Blockage at 1 [mm/h]
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Scenario analyisTesting the sensitivity of the methodology
Introducing virtual errors
1. Blockage at 1 [mm/h]
2. Relative error of 170%
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Scenario analyisTesting the sensitivity of the methodology
Introducing virtual errors
1. Blockage at 1 [mm/h]
2. Relative error of 170%
3. Random error of 1-10 [mm/h]
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Conclusions
• Create redundant information• Use advanced data analysis techniques
We need to ensure good data quality!
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Conclusions
• Create redundant information• Use advanced data analysis techniques
We need to ensure good data quality!
Bianchi, B. et al., Detection of faulty rain gauges using telecommunication microwave links (submitted to Journal of Hydrology)
• We demonstrated the possibility to identify faulty rain gauges using operational telecommunication microwave links (MWL)
• The algorithms for process control are straight forward to apply, also in real-time
• MWL data are not (yet) generally available