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Ref. No. [UMCES] CBL 2016-011

ACT VS16-02



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 including 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.


series of nine accuracy and precision tests were conducted at three fixed salinity levels (0, 10, 35)

at each of three fixed temperatures (5, 15, 30


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


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

. 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 performance results of PME miniDOT dissolved oxygen sensor using

optical luminescence technology.

Instrument accuracy and precision for the PME miniDOT was tested under nine

combinations of temperature and salinity over a range of DO concentrations from 10% to 120% of

saturation. The means of the difference between the miniDOT and reference measurement

ranged from -0.339 to 0.126 mg/L over all nine trials. There were no consistent trends in

instrument accuracy across salinity ranges. There was a noticeable change in the direction of the

offset across temperature ranges with the average offset equal to -0.23 mg/L for the 4 and 15



trials compared to a mean offset of 0.11 mg/L for the 30


C trials. A linear regression of

instrument and reference measurements for all trials combined data (n=334; r


= 0.973; p<0.0001)

produced a slope of 0.98 and intercept of 0.020. Instrument offsets and the linear regression

omitted comparisons that were clearly impacted by contamination of bubbles of the sparging gas

that were trapped on the sensor foil due to its orientation within the tank. The absolute precision,

estimated as the standard deviation (s.d.) around the mean, ranged from 0.005 – 0.013 mg/L across

trials with an overall average of 0.008 mg/L. Relative precision, estimated as the coefficient of

variation (CV% = (s.d./mean)x100), ranged from 0.057 – 0.248 percent across trials with an

overall average of 0.098%.

Instrument accuracy was assessed under a 56 day lab stability test in a deionized water bath

cycling temperature and ambient DO saturation on a daily basis. The overall mean difference

between measurements was 0.034 (s.d. = 0.107) mg/L for 77 comparisons (out of a potential total

of 77). There was a small but statistically significant trend in accuracy over time (slope = -0.002

mg/L/d; r2 = 0.11; p=0.003) indicating very modest performance drift over the 56 days.