SonTek, a Xylem brand
142 RiverSurveyor S5/M9 System Manual (February 2013)
G-8.1 Discharge Uncertainty Calculation
The Discharge Measurement Report includes the estimated uncertainty of every discharge
measurement. This calculation is done two different ways: Statistical or ISO.
• The Statistical (abbreviated Stats) uncertainty calculation uses a method developed by re-
searchers at the U.S. Geological Survey. In general this provides the most reliable indicator of
measurement quality.
• The ISO method is based on the international standard and provides the results of a pub-
lished, standard technique. In some cases it may not provide as reliable an indicator of data
quality, as it makes limited use of data from the site.
The uncertainty calculations are based on several different parameters. In addition to overall
uncertainty, the calculation looks at the contribution of each parameter.
• Accuracy: the accuracy of RiverSurveyor velocity.
• Depth
o In the Statistical calculation, this term includes both uncertainty in the depth
measurement and the effect of changes in depth between stations.
o In the ISO calculation, this term includes only the uncertainty in depth measure-
ments.
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