[Note: this is an internal working document of a USGS-SFSU collaboration. Data, analysis and results herin should not be considered as final or accurate. Final results will be presented in print.]
Miscellaneous Errors and Biases
and their Effect on the
Rating Curve and Didsharge
( references indexing )

Here some assorted experimental biases and errors are discussed:

  1. Time Error An offset in the times associated with the index data and the calibration data can lead to distorted rating curves and errors in the calculated discharge
Miscellaneous Effects
(Click on graph for blow-up.)
Uncorrected rating curve (black) and rating curve corrected for a 2.5-minute error in the UVM time (UVM times too large by 2.5 min). (p80730f.m) Comparison of daily discharge calculated from 15-minute values by simple averaging over 98 pts (24-1/2 hrs), 99 pts (24-3/4 hrs), and 100 pts (25 hours). Z (p80802a.m) Same as square to left, except with smoothing by MatLab (forward and backward filtering with a 1-pole filter, cutoff freq.=1/lunar day). Better filters may exist (see Smith 1991), but this filtering scheme, with either 99-point or 100-point averaging, seems stable enough to for our purpose, namely, to observe changes in the discharge values due to variations in the data processing. (p80803a.m)
CONCLUSIONS
  1. The slope of the rating curve is closer to 45 degrees using the centered index velocity. The slope is still not 45 degrees, presumably because the UVM does not see the slower water near the shore.
  2. The loop character of the rating curve is unaffected, as expected.
  3. The downward curvature of the curve remains. I expected this effect to decrease or go away, but it didn't.