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Ref. No. [UMCES] CBL 2016-010
ACT VS16-01
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EXECUTIVE SUMMARY
The Alliance for Coastal Technology (ACT) conducted a sensor verification study of in situ
dissolved oxygen sensors during 2015-2016 to characterize performance measures of accuracy and
reliability in a series of controlled laboratory studies and field mooring tests in diverse coastal
environments. The verification included several months of Laboratory testing along with three field
deployments covering freshwater, estuarine, and oceanic environments.
Laboratory tests of accuracy,
precision, response time, and stability were conducted at Moss Landing Marine Lab.
A series of nine
accuracy and precision tests were conducted at three fixed salinity levels (0, 10, 35) at each of three
fixed temperatures (4, 15, 30
o
C). A laboratory based stability test was conducted over 56 days using
deionized water to examine performance consistency without active biofouling. A response test was
conducted to examine equilibration times across an oxygen gradient of 8mg/L at a constant
temperature of 15
o
C. Three field-mooring tests were conducted to examine the ability of test
instruments to consistently track natural changes in dissolved oxygen over extended deployments of
12-16 weeks. Deployments were conducted at: (1) Lake Superior, Houghton, MI from 9Jan – 22Apr,
(2) Chesapeake Bay, Solomons, MD from 20May – 5Aug, and (3) Kaneohe Bay, Kaneohe, HI from
24Sep – 21Jan. Instrument performance was evaluated against reference samples collected and
analyzed on site by ACT staff using Winkler titrations following the methods of Carignan et al. 1998.
A total of 725 reference samples were collected during the laboratory tests and between 118 – 142
reference samples were collected for each mooring test. This document presents the results of two
different models of the JFE Advantech RINKO optical dissolved oxygen sensors (AroUSB and AroW-
USB). Both models were tested in all Laboratory trials and the fast-response AroUSB was used in the
field profiling application, while the wiper based AroW-USB was used in the extended field mooring
applications.
Instrument accuracy and precision for the AroUSB and AroW-USB sensors were tested under
nine combinations of temperature and salinity over a range of DO concentrations from 10% to 120% of
saturation. The laboratory testing set-up did result in bubbles from the sparging gases used to change
DO levels occasionally becoming trapped on the sensor foil and those data where noted were excluded
from any comparisons to reference samples. The means of the difference between the AroUSB and
reference measurement for the nine trials ranged from -0.277 to 0.265 mg/L. A linear regression of the
accepted data (n=377; r
2
= 0.965; p<0.0001) produced a slope of 1.015 and intercept of 0.098. For the
AroUSB, the absolute precision, estimated as the standard deviation (s.d.) around the mean, ranged
from 0.002 – 0.014 mg/L across trials with an overall average of 0.004 mg/L. Relative precision,
estimated as the coefficient of variation (CV% = (s.d./mean)x100), ranged from 0.013 – 0.278 percent
across trials with an overall average of 0.058%. The means of the difference between the AroW-USB
and reference measurements ranged from -0.277 to 0.134 mg/L across all trials. A linear regression of
the accepted data (n=257; r
2
= 0.976; p<0.0001) produced a slope of 0.969 and intercept of 0.114. The
absolute precision for the AroW-USB were ranged from 0.001 – 0.012 across trials, with an overall
average of 0.004 and the relative precision ranged from 0.017 – 0.247 percent across trials with an
overall average of 0.051%.
For the 56 day lab stability test, the overall mean of the differences between AroUSB and
reference measurements was 0.001 (± 0.326) mg/L. There was no significant trend in accuracy over
time (slope = -0.0007 mg/L/d) that would indicate any type of performance drift over the duration.
The overall mean of the differences between AroW-USB and reference measurements was -0.154 (±
0.319) mg/L. There was a minor drift in instrument accuracy over the deployment (slope = -0.006
mg/L/d; r
2
=0.17) but the goodness of fit was low due to several outliers.