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Ref. No. [UMCES] CBL 2016-012
ACT VS16-03
4
measurement difference between the SBS HydroCAT and reference samples over the total
deployment was 0.776 ± 0.223 mg/L with a total range of 0.270 to 1.070 mg/L. There was no
measurable trend in instrument offset during the entire deployment (linear regression: r
2
=0.003;
p=0.58) as a result of either biofouling effects or calibration drift. A linear regression of the
instrument versus reference measurements over the first month (r
2
= 0.99; p<0.0001) produced a
slope of 0.947 and intercept of 1.04, indicating an initial calibration offset at the beginning of the
deployment.
At Chesapeake Biological Lab, the field test was conducted over 78 days with a mean
temperature and salinity of 25.6
o
C and 10.9. The SBS HydroCAT operated successfully
throughout the entire deployment and generated 7270 observations based on its 15 minute
sampling interval for a data completion result of 100%.
The measured DO range from our 142
discrete reference samples was 4.37 – 10.86 mg/L compared to the broader dynamic range of 2.12
to 12.81 mg/L reported by the SBS HydroCAT. The average and standard deviation of the
measurement difference between the SBS HydroCAT and reference measurements for the entire
deployment was -0.464 ±0.581 mg/L, with the total range of differences between -1.99 to 0.65
mg/L. The calculated drift rate in instrument response for the entire deployment period was -0.079
mg/L/d (r
2
= 0.49; p<0.0001).
In contrast, the drift rate for the first 35 days of the deployment was
much less, averaging only -0.016 mg/L/d (r
2
= 0.54; p<0.001). In both cases the 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<0.001) produced a
slope of 0.985 and intercept of 0.181.
No results are available for the Kaneohe Bay, HI field deployment due to a programming
error by ACT staff during the deployment set-up.
Overall, the SBS HydroCAT response showed good linearity over the two salinity ranges
tested which included fresh brackish water. The response curves were generally consistent across
the concentration range within a given test site and over the broader range of DO conditions (4 - 14
mg/L) across sites, with the noted result of a likely initial calibration offset for the freshwater test.
A linear regression of the composited data (r
2
= 0.997; p<0.0001)) had a slope of 1.043 and
intercept of -0.261.
The manufacturer declined from having the SBS HydroCAT evaluated under the profiling
application as designed in the Verification Protocols, so no results are available.
BACKGROUND AND OBJECTIVES
Instrument performance verification is necessary so that effective existing technologies can
be recognized and so that promising new technologies can be made available to support coastal
science, resource management and ocean observing systems. To this end, the NOAA-funded
Alliance for Coastal Technologies (ACT) serves as an unbiased, third party testbed for evaluating
sensors and sensor platforms for use in coastal environments. ACT also serves as a comprehensive
data and information clearinghouse on coastal technologies and a forum for capacity building
through workshops on specific technology topics (visit
www.act-us.info).
As part of our service to the coastal community, ACT conducted a performance verification
of commercially available, in situ dissolved oxygen (DO) sensors through the evaluation of
objective and quality assured data. The goal of ACT’s evaluation program is to provide technology