Data Quality
The quality of the data obtained at the four stations was verified by plotting
pressure and velocity data of the individual bursts using the SonTek ViewHydra
software. Header files (*.HDR) produced by the SonTek ADV software during
initial raw data processing contain burst statistics for evaluating: mean heading,
pitch and roll angles, mean temperature, and mean pressure. Recorded heading
and pitch and roll angles were inspected to determine if there were significant
changes in pod orientation and tilt.
ADV data were screened using SonTek ViewHYDRA software. All stations
encountered periods when the signal quality was below acceptable levels or when
velocities exceeded the velocity range settings. That conclusion was made from
observing the ADV receiver correlations while employing filter options. Sensor
movement, or intermittent or continuous emergence of the sensor near low tide is
inferred to cause poor data quality. In post-processing usable velocity data,
velocity ambiguities including spikes greater than 2 m/sec were removed by
iterative linear interpolation between adjacent good data points.
Following recovery it was noted that the Druck pressure sensor for sta OS 3
was drained of silicone fluid and partially filled with sand. This probably caused
an air bubble in the outer pressure sensor area that biased the readings at this
location.
ADP transect data were viewed, pre-processed, and filtered using SonTek
ViewADP software. The quality of the ADP data is good, with some obvious
inconsistencies in current speed over short periods. These inconsistencies in
current velocity are indicative of the dynamic environment and the motion of the
ADP instrument during data collection. The instances of visually incongruent
data correlate with high standard deviations in the velocity data, which are likely
the result of vessel motion that are not compensated for by the instrument,
external sensors, and software. The use of the smoothing tools in the post-
processing software is helpful in overcoming the occasional poor quality
recorded data. A signal-to-noise ratio filter (>15-20 dB) was also used to remove
data with poor acoustic quality. The few instances where this filter did remove
data were in slightly deeper water (10-15m), farther from the shoreline where
there may be less particulate matter to reflect the acoustic signal back to the
instrument. Very little of the ADP transect data was discarded because of poor
quality.
References
Earle, M. D., McGehee, D., Tubman, M. (1995). "Field wave gaging program,
wave data analysis standard," Instruction Report CERC-91-1, U.S. Army
Engineer Waterways Experiment Station.
Folonoff, N. P., and Millard, R. C., Jr. (1983). "Algorithms for computation of
fundamental properties of seawater," UNESCO Technical Papers in Marine
Science 44, Division of Marine Sciences, UNESCO, Paris, France.
Hericks, D., and Simpson, D. (2000). "Grays Harbor estuary physical dynamic
study," Final Data Report: September 11, 1999 - November 17, 1999.
D19
Appendix D Field Data Collection
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