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Ref. No. [UMCES] CBL 2016-011
ACT VS16-02
4
A functional response time test was conducted by examining instrument response when
rapidly transitioning between adjacent high (9.6 mg/L) and low (2.0 mg/L) DO water baths,
maintained commonly at 15
o
C.
The calculated τ
90
was 90 s during high to low transitions and 63 s
for low to high transitions covering the 8 mg/L DO range.
At Houghton, MI a field deployment test was conducted under the ice over 104 days with a
mean temperature and salinity of 0.7
o
C and 0.01. The PME miniDOT operated successfully
throughout the entire 15week deployment and generated 9859 observations based on its 15 minute
sampling interval for a data completion result of 100%. It should be noted that for this deployment
a wiping system was not yet available, so some caution should be used in comparisons against the
other field test results. The average and standard deviation of the measurement difference over the
total deployment was 0.029 ± 0.072 mg/L with a total range of -0.307 to 0.205mg/L. The drift rate
of instrument offset, estimated by linear regression (r
2
=0.373; p<0.0001), was 0.001 mg/L/d. This
rate would include any biofouling effects as well as any electronic or calibration drift. A linear
regression of the instrument versus reference measurements over the first month (r
2
= 0.97;
p<0.0001) produced a slope of 0.92 and intercept of 1.03.
At Chesapeake Biological Lab, a field deployment test was conducted over 78 days with a
mean temperature and salinity of 25.6
o
C and 10.9. The PME miniDOT generated 21,810
observations over the 11 week deployment based on its 5 minute sampling interval; however, only
18,173 of the measurements were considered acceptable based on values that were less than 2
mg/L from any minimum reference sample over a similar timeframe and less than 2 mg/L from
continuously monitored DO from a nearby independent data sonde. The accepted data resulted in a
data completion rate for this deployment of 83%. The average and standard deviation of the
difference between instrument and reference measurements for the deployment was -0.40 ±0.702
mg/L, with the total range of differences between -1.90 to 0.86 mg/L. The calculated drift rate in
instrument response for the entire deployment period (using the accepted data) was -0.026 mg/L/d
(r
2
= 0.83; p<0.001). If we consider only the first 35 days of the deployment before any indication
of a malfunction, the drift rate was only -0.009 mg/L/d (r
2
= 0.34; p<0.001). A linear regression of
the instrument versus reference measurements for the first month (r
2
= 0.98; p<0.001) produced a
slope of 0.968 and intercept of 0.306.
At Kaneohe Bay, HI a field deployment test was conducted over 121 days with a mean
temperature and salinity of 25.8
and 33.4
o
C. The PME miniDOT reported 16,957 observations
based on its 10 minute sampling interval over the 17 week deployment. Only two instrument value
fell outside of an acceptable data range based on ± 2mg/L from any min-max reference sample for
essentially a 100% data completion result. The average and standard deviation of the differences
between instrument and reference readings (limited to ± 2.0 mg/L DO; n=128 of 129 potential
observations) were 0.201 ± .426 mg/L, with a total range in the differences of -1.7021 to 1.441
mg/L.
There was a small, but statistically significant, drift in instrument offset (slope = 0.003
mg/L/d; r
2
= 0.05; p=0.009) throughout the deployment period. A linear regression of the
instrument versus reference measurements for the first month (r
2
= 0.97; p<0.001) had a slope of
1.052 and intercept of -0.258.
Overall, the response of the PME miniDOT response showed good linearity overall all
three salinity ranges including freshwater, brackish water, and oceanic water; but with slightly
higher variability for the oceanic test in Kaneohe Bay. Good agreement between instrument and
reference measurements was observed over a wide range of DO conditions varying between 4 to